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  • Articles  (43,332)
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  • 101
    Electronic Resource
    Electronic Resource
    The value of laser in the treatment of malignant disease of the larynx (1991)
    Springer
    Lasers in medical science 6 (1991), S. 451-455 
    Details
    ISSN: 1435-604X
    Keywords: Larynx ; Endoscopic microlaryngeal surgery ; CO2 laser
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract The value of functional and reconstructive surgery to the larynx in the treatment of malignant tumours to preserve residual function as far as possible has been clearly demonstrated. A further step in the development of ‘functional surgery’ is classical microsurgery of the larynx which facilitates diagnosis and endoscopic microsurgical treatment of benign tumours. However, recently following the introduction of the carbon dioxide (CO2) laser it has been shown that it is possible to treat also malignant tumours of the larynx by endoscopic microsurgery. An incision made by the photo-thermal CO2 laser scalpel is characterized by the relative absence of bleeding, lack of post-operative oedema, rapid epithelialization without associated infection or cicatrization and this results in optimal post-operative laryngeal function. This paper presents the results of treatment of selected cases of T1 and T2 carcinoma of the glottis treated by CO2 laser excision under microlaryngoscopic control. In this series healing was rapid with minimal hospitalization and without a tracheostomy. Excellent functional results were achieved and the patient was able to return rapidly to his original occupation. It is our opinion that at present this treatment modality represents the optimal treatment for T1 and T2 carcinoma of the glottis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02042469
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  • 102
    Electronic Resource
    Electronic Resource
    Announcements (1990)
    Springer
    Research in engineering design 2 (1990), S. 61-62 
    Details
    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02029822
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  • 103
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    Announcements (1991)
    Springer
    Research in engineering design 2 (1991), S. 116-116 
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    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01579256
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  • 104
    Electronic Resource
    Electronic Resource
    Grammatical approaches to engineering design, part I: An introduction and commentary (1991)
    Springer
    Research in engineering design 2 (1991), S. 121-135 
    Details
    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract A grammar is a definition of a language written in a transformational form. To the extent that design requirements and designed artifacts can be represented by some language, and to the extent that design is a transformation from function to form, grammars might facilitate the development of theories and methods for design. The syntax, lexicon, and semantics of a formal language are analogous to the configuration, components, and behavior of an engineering design. Furthermore, the computational complexity of various grammatical formalisms might provide a foundation upon which to base complexity measures in design. We discuss grammatical formalisms and give examples of how grammars might facilitate design automation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01578994
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  • 105
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    Editorial: Improving Engineering Design (1991)
    Springer
    Research in engineering design 2 (1991), S. 183-183 
    Details
    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01579216
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  • 106
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    Design synthetic reasoning: A methodology for mechanical design (1991)
    Springer
    Research in engineering design 2 (1991), S. 221-238 
    Details
    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Design synthetic reasoning is a methodology to support the process of design synthesis and includes within its scope support for associated processes of design verification, behavior derivation, and function justification. The design synthesis of machines is viewed as the development of a specification of required behavior, and transformation of the specification into the description of a structure (or assembly) of machine components. In this paper, the process of design synthesis is modeled as a sequence of applications of transformation rules. These rules either respecify, elaborate, reduce, or reformulate the expression of required behavior, and ultimately allow matching and selection of structurally compatible machine components and relationships from a design library. The specification of required behavior for a simple rotary actuator is developed and progressively transformed to synthesize the structures of two different patented rotary actuating devices. The ability of both devices to produce the required behavior is verified, and the property of self-locking for both the devices is derived from the structure descriptions. The functions (purposes) of components and relationships in each device are extracted from the trace of transformation rules applied during the verification and derivation process for each device.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01579219
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  • 107
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    Announcements (1991)
    Springer
    Research in engineering design 3 (1991), S. 57-59 
    Details
    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01580068
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  • 108
    Electronic Resource
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    Dimensional Variable Expansion—A formal approach to innovative design (1991)
    Springer
    Research in engineering design 3 (1991), S. 75-85 
    Details
    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract A methodology called Dimensional Variable Expansion (DVE) is presented to formalize the process of design space expansion and design innovation. Unlike parametric design, where the structure of the design is specified and only the parameters are allowed to vary, DVE creates new structures, including new variables, constraints, and a reformulation of the objective function. Via DVE, a body is expanded into multiple regions by dividing along a dimensional variable, and then each region is permitted independent properties. Optimality conditions are used to determine which variables to expand and which regions should be subject to property modifications. With DVE the degrees-of-freedom of a design can be expanded and designs with unique features can be derived.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01581341
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  • 109
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    An application of axiomatic design (1992)
    Springer
    Research in engineering design 3 (1992), S. 149-162 
    Details
    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract For the field of design to become a discipline, it must have the prerequisites of a discipline: principles and a process of solving problems using these principles. This paper presents a case study for axiomatic design, illustrating the process of using the design axioms (i.e., the Independence Axiom and the Information Axiom) in designing an artificial skin. The axioms are used to guide the analysis of a process design for an artificial skin graft. The analysis indicates that the current design does not meet the requirements specified by the axioms and should be redesigned to overcome the difficulties it has experienced in the field. Alternative solutions are generated following a systematic analysis of the design problem, and the best alternative is identified.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01580517
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  • 110
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    Book review (1992)
    Springer
    Research in engineering design 3 (1992), S. 243-246 
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    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01580846
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  • 111
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    Editorial: Research in Engineering Design (1992)
    Springer
    Research in engineering design 3 (1992), S. 193-193 
    Details
    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01580841
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  • 112
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    A taxonomy for mechanical design (1992)
    Springer
    Research in engineering design 3 (1992), S. 179-189 
    Details
    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract This paper presents a taxonomy that provides a basis for characterizing mechanical design methods and theories. The taxonomy has three primary divisions: the environment, the problem, and the process. Each of these factors is further subdivided into its important characteristics. For example, the process is divided into plan, processing action, effect, and failure action. This paper discusses the options for each characteristic. An overview of the proposed taxonomy is given in section 2 of this paper. Section 3 describes details of the design environment; section 4 gives details on the description of the design problem itself; and section 5 provides details on the design process. In section 6, the taxonomy is applied in two ways: it is first used to clarify the meaning of differing, commonly used design terms, such as selection design, configurational design, parametric design, and redesign; and, second, the taxonomy is used to classify a representative sample of design process research efforts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01580519
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  • 113
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    Integrating the user into research on engineering design systems (1992)
    Springer
    Research in engineering design 3 (1992), S. 211-221 
    Details
    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Engineering design research has historically been evaluated in terms of its computational performance. However, in many cases this research implies hypotheses about human behavior which are ignored. In this paper, we argue that the systems emerging from design research will benefit from investigating how people use them to accomplish work, and from the incorporation of principles of Participatory Design (Floyed et al., 1989) at the earliest stages of the development process. Using a case study, we present the evolution of a CAD system that supports complex mathematical modeling. This design effort is examined according to principles outlined in another well-documented effort in Participatory Design. Finally, despite the common misconception that such considerations impede basic research, we argue that continuous user involvement can guide research by validating experimental hypotheses and pointing to areas for future inquiry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01580843
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  • 114
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    A data representation for collaborative mechanical design (1992)
    Springer
    Research in engineering design 3 (1992), S. 233-242 
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    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Collaborative design projects place additional burdens on design documentation practices. The literature on group design has repeatedly documented the existence of problems in design decision-making due to the unavailability of design information. This paper describes a data representation developed for collaborative mechanical design information. The data representation is used to record the history of the design as a sequence of design decisions. The resulting data base records the final specifications, the alternatives which were considered during the design process, and the designers' rationale for choosing the final design parameters. It is currently implemented in a computerized data base system under development at Oregon State University (OSU).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01580845
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  • 115
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    Design principles for cognitive artifacts (1992)
    Springer
    Research in engineering design 4 (1992), S. 43-50 
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    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Modern designs are more than ever before required to be understandable and usable by their intended audience. As machines get ever more complex, it becomes essential for designers to provide a user-centered design that focuses upon the needs and abilities of the user. This paper presents an analysis of cognitive artifacts—devices designed to maintain, display, or operate upon information in order to serve a representational function. An important design consideration is the human action cycle which means that artificial devices must support both execution and evaluation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02032391
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  • 116
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    Simulation of human error in reinforced concrete design (1992)
    Springer
    Research in engineering design 4 (1992), S. 51-60 
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    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Available statistical data suggest that human error in design causes a significant proportion of performance failures; namely, structural failure, cost overruns, and delays. A Human Reliability Analysis (HRA) model has been developed to simulate the effect of human error on the design computations of a reinforced concrete beam. The proposed HRA model incorporates the effect of “self-corrections”; this is a process where tasks are re-evaluated if the result appears to be not within “reasonable” expectations. Calculation, table look-up, chart look-up, and table ranking microtasks were incorporated into the proposed HRA model; human perormance data are described for each of these microtasks. It was found that human error, particularly multiple errors, lead to a significant loss of structural safety.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02032392
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  • 117
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    Evolutionary design theory using dynamic variation and thermodynamic selection (1991)
    Springer
    Research in engineering design 3 (1991), S. 39-55 
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    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract A general evolutionary design theory is presented which incorporates variation processes and selection processes to design fluid/thermal/chemical devices. A biologically consistent view of evolution splits the process into variation and selection. The variation process is quantitatively modeled using dynamic equations that govern structural changes. Steady-state and stability of design variation is related to growth and decay factors and environmental control parameters. The selection process is quantitatively modeled using nonequilibrium thermodynamics to indicate performance. Both structure and environment contribute to entropy production. This requires computational modeling of fluid dynamics, heat transfer, chemical diffusion, and reactions. Special cases of engineering design evolution are shown theoretically and with a numerical example. The theory could rectify the impact of engineered structures on the natural environment and provide a basis for designing machines with coupled physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01580067
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  • 118
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    Paconius and the pedestal for Apollo: A case study of error in conceptual design (1991)
    Springer
    Research in engineering design 3 (1991), S. 123-128 
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    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract A classic case history of an engineering failure related by Vitruvius is presented as a paradigm of human error in the design process. It is argued that a familiarity among designers with such case studies could be instrumental in reducing conceptual errors in the design process generally.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01581344
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  • 119
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    Announcements (1992)
    Springer
    Research in engineering design 3 (1992), S. 191-191 
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    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01580520
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  • 120
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    Knowledge-based interpretation of architectural drawings (1992)
    Springer
    Research in engineering design 3 (1992), S. 195-210 
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    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract A method for machine interpretation of architectural (or other) schematic drawings is presented. The central problem is to build an efficient drawing parser (i.e., a program that identifies the semantic entities, characteristics, and relationships that are represented in the drawing). The parser is built from specifications of the drawing grammar and an underlying spatial model. The grammar describes what to look for, and the spatial model enables the parser to find it quickly. Coupled with existing optical recognition technology, this technique enables the use of drawings directly as: (1) a database to drive various Architecture-Engineering-Construction (AEC) applications; (2) a communication protocol to integrate CAD systems; (3) a traditional user interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01580842
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  • 121
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    Preface (1992)
    Springer
    Research in engineering design 4 (1992), S. 1-1 
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    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02032387
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  • 122
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    Announcements (1992)
    Springer
    Research in engineering design 3 (1992), S. 247-248 
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    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01580847
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  • 123
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    Shared memory in design: A unifying theme for research and practice (1992)
    Springer
    Research in engineering design 4 (1992), S. 23-42 
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    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract This paper presents a new unifying theme for design theory by emphasizing the importance of context. We arrive at our conclusions by examining and then criticizing the legitimacy of universal methods in design upon which the critical importance of context emerges. The collaborative aspects of design focuses attention on the conception of shared meaning. We introduce and elaborate the concept of shared memory as the embodiment both of context and of shared meaning. Using the concept of shared memory in vertical and horizontal forms, within and between disciplines, respectively, we both account for past observations of design in practice and recommend actions to improve design in the future. We examine several practical implications of the growing importance of shared memory in industrial firms and for design teams. We then consider and recommend specific research programs which will help designers capture and make better use of this critical resource.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02032390
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  • 124
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    Encoding mechanical design features for recognition via neural nets (1992)
    Springer
    Research in engineering design 4 (1992), S. 67-74 
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    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Within mechanical computer-aided design (CAD), pattern-recognition techniques are fundamental to feature recognition. The use of neural net software as the pattern-recognition element depends upon encoding schemes which extract critical information from candidate geometric subsets. The trained memory can then determine if a particular candidate geometric subset corresponds to a feature of interest. Successful experiments with particular encoding schemes over a restricted class of features will be presented. Neural nets were chosen with the long-term view toward a feature-recognition architecture where the end-user could customize the domain of features that can be recognized. The training of the neural net memory would be achieved through a graceful graphics interface. Extensive programming and knowledge bases would be avoided. This envisioned architecture will be presented to provide a context for the encoding schemes.
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    URL: http://dx.doi.org/10.1007/BF01580145
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  • 125
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    Topological properties that model feature-based representation conversions within concurrent engineering (1992)
    Springer
    Research in engineering design 4 (1992), S. 147-158 
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    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract One of the fundamental axioms of concurrent engineering is that undertaking functional design without foreseeing the manufacturing process leads to production delays and increased costs. This widely accepted concurrent engineering principle is given a formal basis by development of a mathematical model for the conversion of a feature-based design representation to a manufacturing representation. Within the domain of thin-walled components, it is shown that the conversion to tooling cost representations can result in a discontinuous function when the sets of design and manufacturing representations have been formulated as topological spaces. This discontinuity formally reflects the folklore that a small design change can significantly increase product cost. The mathematical sophistication required within this model is suggestive of why manufacturability evaluations can be quite difficult.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01607943
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  • 126
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    Announcements (1992)
    Springer
    Research in engineering design 4 (1992), S. 191-194 
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    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01607947
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  • 127
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    A taxonomy of the product realization process environment (1992)
    Springer
    Research in engineering design 4 (1992), S. 203-213 
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    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The realization of concepts into products is an extremely complex and poorly understood process. Companies and researchers are developing software aids and tools in a somewhat ad hoc manner. Differing claims are made for such tools, without there being much underlying understanding about what they are supposed to do. As part of a project to develop a strategy for applying computer-based tools to the process of realizing products, this paper proposes a taxonomy which encompasses most of the factors involved and defines the environments in which computer-based tools operate. Several other uses for this taxonomy are suggested, including identifying how the different types of computer-based tools support or replace various human activities or tasks; outlining a strategy for automating the process, as part of a strategy for applying the right tool for the task; and identifying where new tools might be developed.
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    URL: http://dx.doi.org/10.1007/BF02032464
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  • 128
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    Structural synthesis under manufacturability constraints: A CAD system for the design of injection-molded product housings (1993)
    Springer
    Research in engineering design 5 (1993), S. 185-201 
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    ISSN: 1435-6066
    Keywords: Computer-aided design ; Design for manufacture ; Injection molding ; Structural synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract We describe a computer-aided design system that automatically constructs the internal functional surface shapes of plastic injection molded product housings. Fundamental manufacturability constraints related to the geometry of injection mold parting and the solidification of molten plastic are identified. These constraints are embodied in structural synthesis operators that create the internal shapes given a set of functional requirements. An implementation, which is integrated with a system that automatically designs the external visible surface of the housing, is discussed. Algorithms for the structural synthesis operators are provided along with sample output demonstrating their operation.
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    URL: http://dx.doi.org/10.1007/BF01608362
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  • 129
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    A meta-model for mechanical products based upon the mechanical design process (1993)
    Springer
    Research in engineering design 5 (1993), S. 140-160 
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    ISSN: 1435-6066
    Keywords: Design documentation ; Features ; Functional modeling ; Product modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract This paper describes preliminary work toward the develoment of a framework and a system for modeling the “meta-physical” information of mechanical products. Meta-physical information is that information which describes the nature or reason for existence of objects in the physical product model. Such information includes product and feature functionality, design intent, relations, constraints and viewpoint-dependent definitions. This effort has resulted in an initial model structure and a prototype system. The product model consists of a meta-physical product model with attached physical product models containing, among other information, geometry, dimensions, tolerances, and features. The content and structure of the product model correspond directly to the information used and produced during the mechanical design process. The prototype system integrates a solid modeler, a feature modeler, a dimension and tolerance modeler, and a meta-physical modeler. This paper provides an overview of the meta-model structure, usage and potential.
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    URL: http://dx.doi.org/10.1007/BF01608360
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    Announcements (1993)
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    Research in engineering design 5 (1993), S. 238-238 
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    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01608365
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    Constraint-based design using an operational approach (1993)
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    Research in engineering design 5 (1993), S. 202-217 
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    ISSN: 1435-6066
    Keywords: Constraint-based design ; Feature modeling ; Geometric reasoning ; Graph grammar ; Knowledge-based inference
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Constraint-based design, which explicitly represents and operates upon constraints, has been recognized as a promising tool for achieving intelligent support of design, particularly the design of mechanical parts or assemblies. It is essential for a constraint-based system to realize the constraint-solving capability. This paper presents an operational approach to constraint solving using incremental feature operations. The approach is based on an operational interpretation of constraints, i.e. the constraint satisfaction is carried out in terms of operations incrementally. A grammatic formalism is used for operational modeling of constraints. Each graph production within a graph grammar corresponds to an operation or a sequence of operations designated for constraint satisfaction that is related to a rule or a procedure. Therefore, a constraint satisfaction process can be represented by a graph grammar parsing process. The operation sequence is planned by graph grammar parsing and invocation of the related rules or procedures. Constraints are then evaluated by invoking the sequenced operations. Features are introduced as higher-level abstractions into the geometric constraints network. This enables reasoning about design validation from topological and manufacturing views.
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    URL: http://dx.doi.org/10.1007/BF01608363
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    Research in engineering design 5 (1993), S. 240-240 
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    ISSN: 1435-6066
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
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    URL: http://dx.doi.org/10.1007/BF01608367
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    Robust optimal design using a second-order tolerance model (1994)
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    Research in engineering design 6 (1994), S. 25-37 
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    ISSN: 1435-6066
    Keywords: Optimization ; Robust design ; Tolerances ; Variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract In this paper we present a general, quantitative method for developing designs that are robust to variation in design variables and parameters. Variation is defined in terms of tolerances which bracket the expected deviation of uncertain quantities about nominal values. We specifically address the case where input variations are assumed to be random variables that are normally distributed. The method incorporates a second-order tolerance model as part of a nonlinear optimization process. The second-order tolerance model makes it possible to estimate the skewness of function distributions, which are modeled with a three-parameter gamma distribution. We apply the method to determine robust designs for 11 test cases that span a variety of problems; robustness is verified with Monte Carlo simulation. The method enables a designer to understand and account for the effects of tolerances, making it possible to build robustness into an engineering design.
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    URL: http://dx.doi.org/10.1007/BF01588089
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    A model-based method for organizing tasks in product development (1994)
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    Research in engineering design 6 (1994), S. 1-13 
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    ISSN: 1435-6066
    Keywords: Concurrent engineering ; Design management ; Design process improvement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract This research is aimed at structuring complex design projects in order to develop better products more quickly. We use a matrix representation to capture both the sequence of and the technical relationships among the many design tasks to be performed. These relationships define the “technical structure” of a project, which is then analyzed in order to find alternative sequences and/or definitions of the tasks. Such improved design procedures offer opportunities to speed development progress by streamlining the inter-task coordination. After using this technique to model design processes in several organizations, we have developed a design management strategy which focuses attention on the essential information transfer requirements of a technical project.
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    URL: http://dx.doi.org/10.1007/BF01588087
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    Testing the hypothesis law of design: The case of the Britannia Bridge (1994)
    Springer
    Research in engineering design 6 (1994), S. 38-57 
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    ISSN: 1435-6066
    Keywords: Britannia Bridge ; Design laws ; Design process ; Design reasoning ; Hypotheses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract In a recent paper, Dasgupta[6] has claimed to have identified two universal, qualitativelaws of design. Of these, one is called thehypothesis law, which states that: “A design process that reaches termination does so through one or more cycles of hypothesis creation, testing and (if necessary) modification.” This law was arrived at from arguments based on a model of the design process at the “knowledge level”[9] and on the concept of “bounded rationality”[15]. In the present article we describe an extensiveempirical test of the hypothesis law using an important historical case study. The case in question is the design, conducted between 1844 and 1847, of the Britannia Bridge which spanned the Menai Straits in Wales. Using published records of the project as the basis for our evidence, we shall show that the design process followed in this project strongly corroborates the hypothesis law.
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    URL: http://dx.doi.org/10.1007/BF01588090
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    Qualitative reasoning and the representation of fundamental principles in structural engineering (1994)
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    Research in engineering design 6 (1994), S. 61-72 
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    ISSN: 1435-6066
    Keywords: Inference strategy ; Qualitative reasoning ; Structural engineering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Qualitative reasoning is a methodology for deriving the behavior of a device from a declarative representation of relevant fundamental principles and a high-level description of the device. This article and its companion present a qualitative reasoning framework, named the space-centered framework, for reasoning about the behavior of structural systems subjected to loads. The framework includes a representation of the topology and geometry of a structure, and the fundamental principles of equilibrium, compatibility and force-deformation relationships. A parameter, such as a displacement or an internal force, is represented qualitatively by its algebraic sign and its relationship in magnitude with other parameters in the model. Component qualitative states incorporate the fundamental principles for a class of components, such as frame members or supports. The conjugate analogy between the equilibrium and compatibility laws is recognized in the representation. Processes acting between components represent fundamental principles of equilibrium and compatibility at the connections. A companion paper presents the inference strategy for the space-centered framework and its application to qualitative analysis of conceptual designs of structures.
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    URL: http://dx.doi.org/10.1007/BF01579984
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    A referential scheme for modeling and identifying spatial attributes of entities in constructed facilities (1994)
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    Research in engineering design 6 (1994), S. 142-168 
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    ISSN: 1435-6066
    Keywords: Geometric modeling ; AEC ; CAD/CAE ; Facility
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract This paper presents a referential scheme for representing and identifying the spatial extent of physical entities of constructed facilities, such as buildings and offshore structures. Using the basic operations of a non-manifold geometric modeler, a set of high-level algebraic operations is defined. The scheme and its algebra are used for modeling the spatial attributes of a facility entity at two levels: primary and secondary. The primary representation uniquely captures an entity's spatial attributes at the “skeletal” level and is used mainly for identifying discipline-independent topological relationships of that entity with others. Secondary representations, on the other hand, are used to provide an entity's discipline-specific geometric attributes. The topological relationships and geometric attributes of facility entities thus need not be explicitly stored, but can be computed on demand by the underlying non-manifold modeler.
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    URL: http://dx.doi.org/10.1007/BF01607276
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    Automatically deriving behavior constraints for performance variables in mechanical design (1994)
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    Research in engineering design 6 (1994), S. 85-102 
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    ISSN: 1435-6066
    Keywords: Analysis ; Behavior derivation ; Constraints
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Generation of the behavioral constraint equations needed for analysis in the mechanical design synthesis-analysis iteration loop is currently based on approaches that model the behavior of an entire system or subsystem of the design. This paper presents a general approach to constraint derivation that is localized around design performance variables. The approach consists of an amenable design configuration representation, a standard format for representing behavior knowledge, and an algorithm that builds a constraint network that can be used to solve for the performance variables by applying behavioral knowledge to the configuration. The algorithm works outward from the initial performance variables, creating new performance variables as required, and processing only those behavior laws and components of the design needed to obtain a solution. It can take design variables (known conditions or variable parameters) into account, takes advantage of the part-subpart hierarchy in the configuration, can exploit previous solutions, and can detect indeterminacy that is sometimes caused by simplifying assumptions.
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    URL: http://dx.doi.org/10.1007/BF01579986
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    Conceptual robustness in simultaneous engineering: An extension of Taguchi's parameter design (1994)
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    Research in engineering design 6 (1994), S. 211-222 
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    ISSN: 1435-6066
    Keywords: Engineering design ; Simultaneous engineering ; Concurrent engineering ; Robust design ; Distributed optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Simultaneous engineering processes involve multifunctional teams; team members simultaneously make decisions about many parts of the product-production system and aspects of the product life cycle. This paper argues that such simultaneous distributed decisions should be based on communications about sets of possibilities rather than single solutions. By extending Taguchi's parameter design concepts, we develop a robust and distributed decision-making procedure based on such communications. The procedure shows how a member of a design team can make appropriate decisions based on incomplete information from the other members of the team. More specifically, it (1) treats variations among the designs considered by other members of the design team asconceptual noise; (2) shows how to incorporate such noises into decisions that are robust against these variations; (3) describes a method for using the same data to provide preference information back to the other team members; and (4) provides a procedure for determining whether to release theconceptually robust design or to wait for further decisions by others. The method is demonstrated by part of a distributed design process for a rotary CNC milling machine. While Taguchi's approach is used as a starting point because it is widely known, these results can be generalized to use other robust decision techniques.
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    Flow through anisotropic networks (1990)
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    Stochastic environmental research and risk assessment 4 (1990), S. 175-191 
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    ISSN: 1436-3259
    Keywords: Flow through porous media ; random network ; macro-permeability ; micro-geometry ; statistical mechanics ; anisotropy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract This paper presents an analysis of Hagen-Poiseulle flow through plane random anisotropic networks of interconnected channels. Macroscopic permeability tensor of the network is expressed in terms of statistico-geometrical characteristics like the degree of anisotropy in channel orientations, average co-ordination number of the network and first two moments of channel length distribution. Analytical results are illustrated and verified using numerical analysis of flow in a simulated random network. The emphasis of the paper is on the effects of anisotropy on distributions of flow rates in channels. It is shown that, due to anisotropy the maximum flow rate generally occurs in channels that are not aligned along the direction of the macroscopic pressure gradient.
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    URL: http://dx.doi.org/10.1007/BF01543082
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    Editorial (1990)
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    Stochastic environmental research and risk assessment 4 (1990), S. 253-254 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01544079
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    Predicting cumulative sediment depostition in large reservoirs (1990)
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    Stochastic environmental research and risk assessment 4 (1990), S. 241-251 
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    ISSN: 1436-3259
    Keywords: Sedimentation ; Large Reservoirs ; Markov Chains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Sediment deposition and its accumulation in a large resorvoir depends on the inflow and reservoir storage content, respectively. Because of this fact it is possible to model the cumulative deposition of sediment as an additive process defined on a bivariate Markov chain. Using the bivariate Markov chain model the mean and variance of the cumulative deposition of John Martin Reservoir, Colorado, U.S.A. are estimated and compared with observed sedimentation data.
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    On the optimal risk based design of highway drainage structures (1990)
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    Stochastic environmental research and risk assessment 4 (1990), S. 295-308 
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    ISSN: 1436-3259
    Keywords: Risk-based design ; uncertainty analysis ; hydraulic design ; bridge ; culvert
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract For a proposed highway bridge or culvert, the total cost to the public during its expected service life includes capital investment on the structures, regular operation and maintenance costs, and various flood related costs. The flood related damage costs include items such as replacement and repair costs of the highway bridge or culvert, flood plain property damage costs, users costs from traffic interruptions and detours, and others. As the design discharge increases, the required capital investment increases but the corresponding flood related damage costs decrease. Hydraulic design of a bridge or culvert using a riskbased approach is to choose among the alternatives the one associated with the least total expected cost. In this paper, the risk-based design procedure is applied to pipe culvert design. The effect of the hydrologic uncertainties such as sample size and type of flood distribution model on the optimal culvert design parameters including design return period and total expected cost are examined in this paper.
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    Rainfall estimation using raingages and radar — A Bayesian approach: 2. An application (1991)
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    Stochastic environmental research and risk assessment 5 (1991), S. 31-44 
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    ISSN: 1436-3259
    Keywords: Radar rainfall ; gage rainfall ; parameter uncertainty ; Bayesian estimation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract In Seo and Smith (this issue), a set of estimators was built in a Bayesian framework to estimate rainfall depth at an ungaged location using raingage measurements and radar rainfall data. The estimators are equivalent to lognormal co-kriging (simple co-kriging in the Gaussian domain) with uncertain mean and variance of gage rainfall. In this paper, the estimators are evaluated via cross-validation using hourly radar rainfall data and simulated hourly raingage data. Generation of raingage data is based on sample statistics of actual raingage measurements and radar rainfall data. The estimators are compared with lognormal co-kriging and nonparametric estimators. The Bayesian estimators are shown to provide some improvement over lognormal co-kriging under the criteria of mean error, root mean square error, and standardized mean square error. It is shown that, if the prior could be assessed more accurately, the margin of improvement in predicting estimation variance could be larger. In updating the uncertain mean and variance of gage rainfall, inclusion of radar rainfall data is seen to provide little improvement over using raingage data only.
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    URL: http://dx.doi.org/10.1007/BF01544176
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    A Monte Carlo study of rainfall forecasting with a stochastic model (1992)
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    Stochastic environmental research and risk assessment 6 (1992), S. 27-45 
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    ISSN: 1436-3259
    Keywords: Rainfall ; Precipitation ; Forecasting ; Real-time ; Modeling ; Simulation ; Stochastic ; Prediction ; Sampling ; Measurement ; Updating ; Filtering ; Estimation ; Short-term
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities.
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    Boundary element method for analyzing flow through a random semiconfined aquifer (1992)
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    Stochastic environmental research and risk assessment 6 (1992), S. 81-88 
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    ISSN: 1436-3259
    Keywords: Helmholtz equation ; random parameter ; semiconfined aquifer ; groundwater flow ; boundary element method ; perturbation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract With the aid of perturbation technique a boundary element procedure is developed for solution of two-dimensional Helmholtz equation with a random parameter of small variability. The perturbation boundary element method does not require specification of probability density function of the parameter but only its mean and standard deviation. The method is used to analyze steady-state groundwater flows in a horizontal shallow semiconfined aquifer (homogeneous and isotropic) of probabilistic properties. To illustrate the applicability of the method, a simple numerical example is presented. As the nature of perturbation method suggests, the developed method is valid only when the perturbed value of the parameter is of a small order.
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    Drought description (1991)
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    Stochastic environmental research and risk assessment 5 (1991), S. 255-260 
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    ISSN: 1436-3259
    Keywords: Drought ; probability ; stochastic process ; water management
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract What constitutes a comprehensive description of drought, a description forming a basis for answering why a drought occurred is outlined. The description entails two aspects that are “naturally” coupled, named physical and economic, and treats the set of hydrologic measures of droughts in terms of their multivariate distribution, rather than in terms of a collection of the marginal distributions.
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    Farlie-Gumbel-Morgenstern bivariate densities: Are they applicable in hydrology? (1992)
    Springer
    Stochastic environmental research and risk assessment 6 (1992), S. 47-54 
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    ISSN: 1436-3259
    Keywords: Bivariate density ; dependence structure ; correlation coefficient ; Farlie-Gumbel-Morgenstern density ; Farlie polynomial density
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Certain bivariate densities constructed from marginals have recently been suggested as models of hydrologic variates such as rainfall intensity and depth. It is pointed out that (i) these densities belong to the families of the Farlie-Gumbel-Morgenstern densities and the Farlie polynomial densities, which have been extensively studied in the statistical literature, and that (ii) these densities have a limited potential applicability in hydrology since they can model only weakly associated variates, whose product-moment correlationR is within the range |R|≤1/3, under the first family of densities, and |R|≤1/2 under the second family.
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    Statistical validation of GCM-simulated climates for the U.S. Great Lakes and the C.I.S. Emba and Ural River basins (1992)
    Springer
    Stochastic environmental research and risk assessment 6 (1992), S. 69-80 
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    ISSN: 1436-3259
    Keywords: Hydrology ; global circulation models ; statistics ; climate change
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Many researchers use outputs from large-scale global circulation models of the atmosphere to assess hydrological and other impacts associated with climate change. However, these models cannot capture all climate variations since the physical processes are imperfectly understood and are poorly represented at smaller regional scales. This paper statistically compares model outputs from the global circulation model of the Geophysical Fluid Dynamics Laboratory to historical data for the United States' Laurentian Great Lakes and for the Emba and Ural River basins in the Commonwealth of Independent States (C.I.S.). We use maximum entropy spectral analysis to compare model and data time series, allowing us to both assess statistical predictabilities and to describe the time series in both time and frequency domains. This comparison initiates assessments of the model's representation of the real world and suggests areas of model improvement.
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    Comparison of non-Gaussian multicomponent and periodic autoregressive models for river flow (1992)
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    Stochastic environmental research and risk assessment 6 (1992), S. 223-238 
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    ISSN: 1436-3259
    Keywords: River Flow Model ; Time Series ; Autoregressive
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The Non-Gaussian Multicomponent model for river flow (NGM) of Vandewiele and Dom is modified in order to facilitate maximum likelihood estimation. It is also generalized so that a wider variety of river flows at a diversity of time steps can be modeled. This model is applied to two basins in Belgium and France with very different areas, both at monthly and weekly time scale. Results on the quality of forecasting and simulation (especially simulation of low and high flow volumes) are compared with those of classical Periodic Autoregressive models (PAR). Results with NGM are always better, in most cases considerably better. This is due to the fact that NGM models explicitly take into consideration the presence of so called flow components, like baseflow and direct flow recession, which are phenomena well known to hydrologists.
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    On the lengths of crossing exursions: the case of a discrete normal process with underlying exponential autocovariance (1992)
    Springer
    Stochastic environmental research and risk assessment 6 (1992), S. 167-182 
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    ISSN: 1436-3259
    Keywords: Crossing theory ; exponential autocovariance model ; discrete time series ; Weibull distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract An expression is derived for the probability distribution of excursion lengths above a fixed level, for the specific case of a discrete random process sampled from an underlying, continuous normal process with exponential autocovariance function. The expression can be integrated numerically for small excursion lengths, and used with time-series simulations to qualitatively reveal the form of the distribution. Such computations indicate that excursions lengths are well approximated by a Weibull distribution to at least the 0.95 probability value. The fit improves with increasing fixed level, and with decreasing time constant of the process. In addition, an expression is given for the expected number of crossings of a fixed level, analogous to well known formulae used in estimating expected values for the cases of a continuous process and a discrete stepped process.
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    A multivariate gamma distribution arising from a Markov model (1992)
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    Stochastic environmental research and risk assessment 6 (1992), S. 183-190 
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    ISSN: 1436-3259
    Keywords: Markov chains ; seasonality ; multivariate gamma distributions ; weighted sums of gammas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A Markov chain{X t }, which has been useful for modelling in hydrology, can be specified by the Laplace transform (LT) of the conditional p.d.f. ofX t+1 givenX t =x t , which is assumed to be of the ‘exponential’ formH(θ)exp{-G(θ)x t }. For appropriate choice ofH andG the marginal distribution ofX t is the (univariate) gamma distribution. In this case, the joint p.d.f. ofX t +1,...,X t+n and its LT, are obtained, and this is extended to a seasonal version of the chain. A simple method of generating observations from these multivariate gamma distributions is noted, and the joint LT is applied to the problem of determining moments of weighted sums of such variables.
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    The use of geometric and gamma-related distributions for frequency analysis of water deficit (1992)
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    Stochastic environmental research and risk assessment 6 (1992), S. 239-254 
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    ISSN: 1436-3259
    Keywords: Water deficit ; Geometric distribution ; Exponential distribution ; Deficit duration ; Deficit severity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract This paper presents an approach to perform statistical frequency analysis of water deficit duration and severity using respectively the geometric and exponential distributions. Monthly mean water discharges are compared to a given threshold and classified in two mutually exclusive ways. This leads to a two state random variable such that: a success represents the absence of a water deficit event (mean monthly discharge exceeds threshold), and a failure, a water deficit event (mean monthly discharge is below threshold). If we suppose that this random variable gives rise to a Markov process of order 1, then the duration of a water deficit event X (consecutive months in deficit) will have a geometric distribution. In turn, the summation of discharges in deficit will give the severity of a water deficit event which can be represented by a one-parameter exponential distribution. The threshold or base level is taken as a percentile of the observed mean discharges of a given month. This base level, which varies from month to month, can be viewed as the limit of an acceptable deficit (or energetic failure) associated to a given empirical probability of being in deficit. The second step of the approach is to estimate the value of the parameter for each distribution using the maximum likelihood method. Expressions for the estimator of a given percentile, $$\hat x_q $$ , as well as its variance are deduced. Finally, the presented models are applied to observed data.
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    Development of unbiased plotting position formula for General Extreme Value distributions (1993)
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    Stochastic environmental research and risk assessment 7 (1993), S. 1-13 
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    ISSN: 1436-3259
    Keywords: Unbiased plotting position ; General Extreme Value distribution ; order statistics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Expressions for the expected values of GEV order statistics have been derived in simple summation form and in terms of probability weighted moments. Using exact plotting positions from GEV order statistics a new unbiased plotting position formula has been developed for the General Extreme Value distribution. The formula can, explicitly, take into account the coefficient of skewness, γ (or the shape parameter, k), of the underlying distribution. The developed formula better approximates the exact plotting positions as compared to other existing formulae and is quite easy to use.
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    The development of stochastic space transformation and diagrammatic perturbation techniques in subsurface hydrology (1993)
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    Stochastic environmental research and risk assessment 7 (1993), S. 14-32 
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    ISSN: 1436-3259
    Keywords: Stochastic hydrology ; random fields ; space transformation ; perturbation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract This paper develops concepts and methods to study stochastic hydrologic models. Problems regarding the application of the existing stochastic approaches in the study of groundwater flow are acknowledged, and an attempt is made to develop efficient means for their solution. These problems include: the spatial multi-dimensionality of the differential equation models governing transport-type phenomena; physically unrealistic assumptions and approximations and the inadequacy of the ordinary perturbation techniques. Multi-dimensionality creates serious mathematical and technical difficulties in the stochastic analysis of groundwater flow, due to the need for large mesh sizes and the poorly conditioned matrices arising from numerical approximations. An alternative to the purely computational approach is to simplify the complex partial differential equations analytically. This can be achieved efficiently by means of a space transformation approach, which transforms the original multi-dimensional problem to a much simpler unidimensional space. The space transformation method is applied to stochastic partial differential equations whose coefficients are random functions of space and/or time. Such equations constitute an integral part of groundwater flow and solute transport. Ordinary perturbation methods for studying stochastic flow equations are in many cases physically inadequate and may lead to questionable approximations of the actual flow. To address these problems, a perturbation analysis based on Feynman-diagram expansions is proposed in this paper. This approach incorporates important information on spatial variability and fulfills essential physical requirements, both important advantages over ordinary hydrologic perturbation techniques. Moreover, the diagram-expansion approach reduces the original stochastic flow problem to a closed set of equations for the mean and the covariance function.
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    Two kinds of moment ratio diagrams and their applications in hydrology (1993)
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    Stochastic environmental research and risk assessment 7 (1993), S. 41-65 
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    ISSN: 1436-3259
    Keywords: Moment ratio diagrams ; Log-Pearson Type III ; Generalized Gamma ; geometric mean ; harmonic mean
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract We refocus attention on moment ratio diagrams and their uses in hydrology with four major objectives: (1) to summarize the information available in the literature about possible uses of the traditional moment ratio diagram introduced by Karl Pearson, which uses the coefficient of skewness and of kurtosis to compare the shapes of various distributions commonly used in hydrology; (2) to complete this traditional MRD by integrating into it the regions occupied by the log-Pearson Type III and generalized gamma distributions which are more and more used in hydrology; (3) to present another MRD which uses ratios of moments of orders −1 (harmonic mean), quasi zero (geometric mean) and 1 (arithmetic mean); (4) to stress the need to consider the different MRD's (along with the more recently introduced L-moment ratio diagrams) as complementary tools for choosing between distributions fitted to hydrologic data. Finally, using Monte Carlo simulation we compare the two types of diagrams as tools to identify and discriminate between different distributions.
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    Parameter identification in particle models (1993)
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    Stochastic environmental research and risk assessment 7 (1993), S. 109-130 
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    ISSN: 1436-3259
    Keywords: Particle models ; transport equations ; parameter identification ; adjoint modelling ; cost function ; gradient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract For the simulation of the transport of dissolved matter particle models can be used. In this paper a technique is developed for the identification of uncertain parameters in these models. This model calibration is formulated as an optimization problem and is solved with a gradient based algorithm. Here adjoint particle tracks are used for the calculation of the gradient of the cost function. The performance of the calibration method is illustrated by simulations and an application to a river Rhine water quality calamity in November 1986.
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    Empirical Orthogonal Function (EOF) analysis of spatial random fields: Theory, accuracy of the numerical approximations and sampling effects (1993)
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    Stochastic environmental research and risk assessment 7 (1993), S. 146-160 
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    ISSN: 1436-3259
    Keywords: EOF analysis ; numerical approximations ; sampling effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Empirical Orthogonal Function (EOF) analysis of spatial random fields involves calculation of the eigenfunctions of the covariance kernel of the field. For real-world applications, a numerical approximation is necessary because the process is spatially discretized. An approximation for two-dimensional fields is proposed and then, analytical solutions of the integral problem are derived and used to study the accuracy of the numerical approximations. Sampling effects are also considered.
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    Solution of stochastic groundwater flow by infinite series, and convergence of the one-dimensional expansion (1994)
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    Stochastic environmental research and risk assessment 8 (1994), S. 139-155 
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    ISSN: 1436-3259
    Keywords: Porous media ; random media ; random fields ; groundwater flow ; stochastic hydrology ; stochastic partial differential equations ; perturbation methods ; Taylor expansions ; hierarchical systems ; Green's functions ; effective conductivity ; homogenization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract This paper investigates analytical solutions of stochastic Darcy flow in randomly heterogeneous porous media. We focus on infinite series solutions of the steady-state equations in the case of continuous porous media whose saturated log-conductivity (lnK) is a gaussian random field. The standard deviation of lnK is denoted ‘σ’. The solution method is based on a Taylor series expansion in terms of parameter σ, around the value σ=0, of the hydraulic head (H) and gradient (J). The head solution H is expressed, for any spatial dimension, as an infinite hierarchy of Green's function integrals, and the hydraulic gradient J is given by a linear first-order recursion involving a stochastic integral operator. The convergence of the ‘σ-expansion’ solution is not guaranteed a priori. In one dimension, however, we prove convergence by solving explicitly the hierarchical sequence of equations to all orders. An ‘infinite-order stochastic solution is obtained in the form of a σ-power series that converges for any finite value of σ. It is pointed out that other expansion methods based on K rather than lnK yield divergent series. The infinite-order solution depends on the integration method and the boundary conditions imposed on individual order equations. The most flexible and general method is that based on Laplacian Green's functions and boundary integrals. Imposing zero head conditions for all orders greater than one yields meaningful far-field gradient conditions. The whole approach can serve as a basis for treatment of higher-dimensional problems.
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    URL: http://dx.doi.org/10.1007/BF01589894
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    A probability-weighted moment test to assess simple scaling (1994)
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    Stochastic environmental research and risk assessment 8 (1994), S. 173-183 
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    ISSN: 1436-3259
    Keywords: Probability weighted moment ; scaling in rainfall ; stable distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract We present a statistically robust approach based on probability weighted moments to assess the presence of simple scaling in geophysical processes. The proposed approach is different from current approaches which rely on estimation of high order moments. High order moments of simple scaling processes (distributions) may not have theoretically defined values and consequently, their empirical estimates are highly variable and do not converge with increasing sample size. They are, therefore, not an appropriate tool for inference. On the other hand we show that the probability weighted moments of such processes (distributions) do exist and, hence, their empirical estimates are more robust. These moments, therefore, provide an appropriate tool for inferring the presence of scaling. We illustrate this using simulated Levystable processes and then draw inference on the nature of scaling in fluctuations of a spatial rainfall process.
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    A model for the generation of simultaneous daily discharges of two rivers at their point of confluence (1990)
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    Stochastic environmental research and risk assessment 4 (1990), S. 255-276 
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    ISSN: 1436-3259
    Keywords: Stochastic hydrologic process ; daily discharges ; correlated generation ; simulation
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    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A geomorphological study at the confluence of the Danube and the Isar in Bavaria required long series of daily discharges in both rivers. A model that generates simultaneous correlated streamflows in both rivers was developed and tested. The model is a modified shot noise model, first developed by Treiber (1975) for a single river, that was adapted to two rivers. It generates correlated pulses of events that produce flow for each river, and these pulses are then convoluted with a river specific systems function. The model, after being calibrated for the two rivers on the basis of 85 years of records, yields artificial series of discharges, in which the statistical properties of the historical records are reproduced. The performance of the model was tested with 20 generated series each 100 years long.
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    Errata toBuishand, T. A. andDemarée, G. R.: Estimation of the annual maximum distribution from samples of maxima in separate seasons. Stochastic Hydrol. Hydraul.4 (1900) 89–103 (1990)
    Springer
    Stochastic environmental research and risk assessment 4 (1990), S. 321-321 
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    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
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    Rainfall estimation using raingages and radar — A Bayesian approach: 1. Derivation of estimators (1991)
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    Stochastic environmental research and risk assessment 5 (1991), S. 17-29 
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    ISSN: 1436-3259
    Keywords: Co-kriging ; parameter uncertainty ; Bayesian estimation ; radar rainfall ; gage rainfall
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Procedures for estimating rainfall from radar and raingage observations are constructed in a Bayesian framework. Given that the number of raingage measurements is typically very small, mean and variance of gage rainfall are treated as uncertain parameters. Under the assumption that log gage rainfall and log radar rainfall are jointly multivariate normal, the estimation problem is equivalent to lognormal co-kriging with uncertain mean and variance of the gage rainfall field. The posterior distribution is obtained under the assumption that the prior for the mean and inverse of the variance of log gage rainfall is normal-gamma 2. Estimate and estimation variance do not have closed-form expressions, but can be easily evaluated by numerically integrating two single integrals. To reduce computational burden associated with evaluating sufficient statistics for the likelihood function, an approximate form of parameter updating is given. Also, as a further approximation, the parameters are updated using raingage measurements only, yielding closed-form expressions for estimate and estimation variance in the Gaussian domain. With a reduction in the number of radar rainfall data in constructing covariance matrices, computational requirements for the estimation procedures are not significantly greater than those for simple co-kriging. Given their generality, the estimation procedures constructed in this work are considered to be applicable in various estimation problems involving an undersampled main variable and a densely sampled auxiliary variable.
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    Numerical methods for stochastic differential equations (1991)
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    Stochastic environmental research and risk assessment 5 (1991), S. 172-172 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The numerical analysis of stochastic differential equations differs significantly from that of ordinary differential equations due to the peculiarities of stochastic calculus. This book provides an introduction to stochastic calculus and stochastic differential equations, both theory and applications. The main emphasise is placed on the numerical methods needed to solve such equations. It assumes an undergraduate background in mathematical methods typical of engineers and physicists, through many chapters begin with a descriptive summary which may be accessible to others who only require numerical recipes. To help the reader develop an intuitive understanding of the underlying mathematicals and hand-on numerical skills exercises and over 100 PC Exercises (PC-personal computer) are included. The stochastic Taylor expansion provides the key tool for the systematic derivation and investigation of discrete time numerical methods for stochastic differential equations. The book presents many new results on higher order methods for strong sample path approximations and for weak functional approximations, including implicit, predictor-corrector, extrapolation and variance-reduction methods. Besides serving as a basic text on such methods. the book offers the reader ready access to a large number of potential research problems in a field that is just beginning to expand rapidly and is widely applicable.
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    A Neumann expansion approach to flow through heterogeneous formations (1991)
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    Stochastic environmental research and risk assessment 5 (1991), S. 207-226 
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    ISSN: 1436-3259
    Keywords: Stochastic groundwater flow ; Neumann expansion ; stochastic partial differential equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A stochastic approach is used for the study of flow through highly heterogeneous aquifers. The mathematical model is represented by a random partial differential equation in which the permeability and the porosity are considered to be random functions of position, defined by the average value, constant standard deviation and autocorrelation function characterized by the integral scale. The Laplace transform of the solution of the random partial differential equation is first written as a solution of a stochastic integral equation. This integral equation is solved using a Neumann series expansion. Conditions of convergence of this series are investigated and compared with the convergence of the perturbation series. For mean square convergence, the Neumann expansion method may converge for a larger range of variability in permeability and porosity than the classic perturbation method. Formal expressions for the average and for the correlation moments of the pressure are obtained. The influence of the variability of the permeability and porosity on pressure is analyzed for radial flow. The solutions presented for the pressure at the well, as function of the permeability coefficient of variation, may be of practical interest for evaluating the efficiency of well stimulation operations, such as hydraulic fracturing or acidizing methods, aimed at increasing the permeability around the well.
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    Drought forecasting: Methodological topics from a systems perspective (1991)
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    Stochastic environmental research and risk assessment 5 (1991), S. 267-279 
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    ISSN: 1436-3259
    Keywords: Drought forecasts ; forecast lead time ; forecast skill ; forecast value ; limits of predictability ; propagation of uncertainty ; hydrometeorologic coupling ; drought management decisions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A systemic framework is presented for organizing knowledge about drought forecasting. It includes these topics: couplings among a descriptive drought model, monitoring system, and forecasting system; propagation of uncertainties; types of forecasts and attributes of performance such as the lead time and skill; sufficient measures of skill and economic value of forecasts; theoretical and operational limits of predictability; and the interface between forecasts and drought management decisions. Reviews of operational forecasts of the seasonal snowmelt runoff volumes and forecasts of the seasonal cyclone frequencies. temperature, and precipitation in the United States illustrate the methodological topics, outline the present limits of drought predictability, and suggest promising research paths. Among them are modeling of forecast uncertainties and their propagation from states of atmospheric circulation to states of a hydrologic regime, and exploring novel forms of the hydro-meteorologic coupling that would extend the lead time and/or increase the skill of long-range drought forecasts.
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    Bayesian analyses of seasonal runoff forecasts (1991)
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    Stochastic environmental research and risk assessment 5 (1991), S. 295-322 
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    ISSN: 1436-3259
    Keywords: Runoff forecasts ; forecast uncertainty ; forecast skill ; forecast message ; Bayesian processor of forecasts ; sufficiency characteristic ; Bayesian correlation score ; stochastic disaggregation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Forecasts of seasonal snowmelt runoff volume provide indispensable information for rational decision making by water project operators, irrigation district managers, and farmers in the western United States. Bayesian statistical models and communication frames have been researched in order to enhance the forecast information disseminated to the users, and to characterize forecast skill from the decision maker's point of view. Four products are presented: (i) a Bayesian Processor of Forecasts, which provides a statistical filter for calibrating the forecasts, and a procedure for estimating the posterior probability distribution of the seasonal runoff; (ii) the Bayesian Correlation Score, a new measure of forecast skill, which is related monotonically to theex ante economic value of forecasts for decision making; (iii) a statistical predictor of monthly cumulative runoffs within the snowmelt season, conditional on the total seasonal runoff forecast; and (iv) a framing of the forecast message that conveys the uncertainty associated with the forecast estimates to the users. All analyses are illustrated with numerical examples of forecasts for six gauging stations from the period 1971–1988.
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    Announcements (1992)
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    Stochastic environmental research and risk assessment 6 (1992), S. 3-4 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
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    Multiscale adaptive estimation of the conductivity field from head and tracer data (1993)
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    Stochastic environmental research and risk assessment 7 (1993), S. 66-82 
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    Keywords: Parameter identification ; multiscale ; transport ; adaptive
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Large scale fluctuations in the conductivity field are regionalized and estimated via a maximum likelihood, adjoint-state methodology. Small-scale fluctuations within each region are estimated adaptively via a Kalman-like stochastic filter. The variance and integral scale within each region are assumed to control the small-scale fluctuations. A Monte Carlo technique is used to examine the distribution of large-scale conductivity estimates.
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    Announcements (1994)
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    Stochastic environmental research and risk assessment 8 (1994), S. 156-156 
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    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
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    Accuracy assessment of optimum interpolation in multichannel precipitation analysis (1990)
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    Stochastic environmental research and risk assessment 4 (1990), S. 43-53 
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    ISSN: 1436-3259
    Keywords: Missing data ; Interpolation in hydrology ; Multichannel precipitation time series ; Spectral analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The accuracy of an optimum interpolation technique in filling missing values in multichannel (or multisite) hydrologic series containing time-coincident data gaps is examined. The applied methodology is based on the maximum entropy method (MEM) of spectral estimation or multivariate autoregressive modeling and heavily depends upon the properties of multichannel prediction error filter (PEF). Six precipitation time series spatially located within a hydrologic basin are used and time-coincident artificial gaps are created in all six series. The performance of the technique is assessed by comparing the filled-in series to the observed and by employing spectral analysis. The results reveal the usefulness of the method in multichannel hydrologic analysis.
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    Technical comments (1990)
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    Stochastic environmental research and risk assessment 4 (1990), S. 83-88 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
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    Gaussianity and linearity tests of hydrologic time series (1990)
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    Stochastic environmental research and risk assessment 4 (1990), S. 121-134 
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    ISSN: 1436-3259
    Keywords: Hydrologic time series ; Linearity ; Gaussianity ; Hinich's test
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Although the non-Gaussian nature of many hydrologic time series is well recognized and their nonlinearity is suspected, neither property is well tested. This situation has existed partly because of a lack of appropriate tests. Recently Hinich (1982) has developed a test to test the linearity of time series which is based on the bispectral characteristics of the series. This test is used in this study to investigate the linearity and non-Gaussian characteristics of annual and daily rainfall and runoff series. The annual series may be modeled by linear models with Gaussian inputs. The daily data, on the other hand, often demonstrate nonlinear characteristics and are non-Gaussian as well.
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    Stochastic modelling of dispersion in shallow water (1990)
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    Stochastic environmental research and risk assessment 4 (1990), S. 161-174 
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    Keywords: advection-diffusion equation ; random walk model ; random flight model ; stochastic differential equation ; Fokker-Planck equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A random walk model to describe the dispersion of pollutants in shallow water is developed. By deriving the Fokker-Planck equation, the model is shown to be consistent with the two-dimensional advection-diffusion equation with space-varying dispersion coefficient and water depth. To improve the behaviour of the model shortly after the deployment of the pollutant, a random flight model is developed too. It is shown that over long simulation periods, this model is again consistent with the advection-diffusion equation. The various numerical aspects of the implementation of the stochastic models are discussed and finally a realistic application to predict the dispersion of a pollutant in the Eastern Scheldt estuary is described.
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    The first and the second e of the extreme value distribution, EV1 (1991)
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    Stochastic environmental research and risk assessment 5 (1991), S. 69-76 
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    ISSN: 1436-3259
    Keywords: Peaks over threshold ; Binomial distribution ; Poisson distribution ; Generalised Pareto distribution ; Extreme-Value distribution, type I ; Generalised Extreme-Value distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract In the peak over threshold model resulting in the Extreme-value distribution, type I, (EV1) the firste of the distribution function is based on the Poisson number of exceedances, and the seconde arises from the Exponentially distributed magnitudes. This paper, on the one hand, generalises the Poisson model to the (positive and negative) Binomial distribution, and, on the other hand, the Exponential distribution is generalised to the Generalised Pareto distribution. Lack of fit with respect to the Poisson and Exponential distribution is measured by statistics derived from those which would be locally most powerful if the estimates of the location and scale parameter were equal to the true parameter values. Ways of combining both statistics are discussed.
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    URL: http://dx.doi.org/10.1007/BF01544179
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    Stochastic overland flows (1991)
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    Stochastic environmental research and risk assessment 5 (1991), S. 105-124 
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    ISSN: 1436-3259
    Keywords: Stochastic differential equations ; overland flows ; Monte-Carlo simulations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The theory developed in Part I of this paper is now applied to study the probabilistic behavior of the depth at the outlet of an impermeable overland flow section under the diffusion and kinematic wave approximations. This process is excited by stochastic rainfields which are conceptualized from radar observations. The depth at the outflow section is of prime importance and the solution methodology concentrates on obtaining the evolutionary probability distribution function for this physical quantity. This theoretical distribution is then compared with the empirical distribution function obtained from a thousand Monte-Carlo simulations. The simplified theory leading to the Fokker-Planck equation is also investigated. It is observed that the ‘time window’ used for simulation purposes can affect the results. The theoretical methodology performs satisfactorily when compared to simulation results. Some of the notable features of the proposed methodology are presented and further suggestions for improvement and extension of this work are discussed.
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    URL: http://dx.doi.org/10.1007/BF01543053
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    Observed advantage for negative binomial over Poisson distribution in partial duration series (1991)
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    Stochastic environmental research and risk assessment 5 (1991), S. 135-146 
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    ISSN: 1436-3259
    Keywords: Hydrology ; runoff ; partial duration series ; negative binomial distribution ; Poisson distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The goodness of fit of the negative binomial and the Poisson distributions to partial duration series of runoff events is tested. The data have been recorded by eight hydrometric stations located on ephemeral rivers in Isreal. For each station, a number of threshold discharges are considered, by that series of nested subsamples are formed. Owing to size limitations, a Chi-square test is conducted on samples associated with low to moderate threshold discharges. Positive results, at a 5% significance level, are obtained in 30 out of the 53 tests of the Poisson distribution, and in 22 out of the 28 tests of the negative binomial distribution. The fit of the Poisson distribution to samples of conventionally recommended sizes (of 2 to 3 events per year) is found positive for five rivers and negative for the three other rivers The fit of the negative binomial distribution to these samples is found positive for six rivers, inconclusive for one river and short of data for the eighth river. Mixed results are obtained as the threshold level is raised. Therefore, no direct extrapolation is possible to samples associated with high thresholds. An indirect extrapolation is drawn through a comparison of the actual properties of the samples with those expected under a perfect fit of the distribution functions. Ranges of such properties are defined with respect to the properties of the tested samples and to the test results. The actual properties of nine of the eleven samples associated with high thresholds (i.e. mean number of events 〈-0.1year −1) are found within these ranges. This provides a hint for a probable good fit of either distribution, and particularly the negative binomial, to the occurrence frequency of high events.
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    URL: http://dx.doi.org/10.1007/BF01543055
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    A univariate model for long-term streamflow forecasting (1991)
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    Stochastic environmental research and risk assessment 5 (1991), S. 189-205 
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    ISSN: 1436-3259
    Keywords: ARIMA model ; entropy ; Lagrange multipliers ; streamflow forecasting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract This paper, the second in the series, verifies the entropy-based univariate model developed in the first paper for long-term streamflow forecasting on five rivers from different regions of the world. The results of the model are compared with the corresponding results of ARIMA and state-space model. The Lagrange multipliers of the univariate model are found similar to autocorrelation coefficients of the ARIMA model. Forecasts by ARIMA and univariate models were comparable for periodic streamflow, but for forecasting of highly variable streamflows the univariate model was superior.
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    URL: http://dx.doi.org/10.1007/BF01544057
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    Editorial (1991)
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    Stochastic environmental research and risk assessment 5 (1991), S. 253-254 
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    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01543132
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    The GF algorithm for reservoir storage, yield and spillage distributions for non-seasonal and seasonal independent inflow processes (1992)
    Springer
    Stochastic environmental research and risk assessment 6 (1992), S. 135-149 
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    ISSN: 1436-3259
    Keywords: Generating function ; finite stochastic reservoir ; seasonal inflow ; Markov chain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract a well-known generating function formula for the equilibrium storage distribution in a finite Moran reservoir having IID inflows and unit release is extended to apply to a class of nondecreasing staircase-like release policies withm unit increments,m〉1, and to seasonal inflows. The analysis is conducted in terms of an alternative to the Moran inflow-outflow sequencing scheme, with the release during a working interval controlled by the water level at the beginning of that interval. In addition to the storage, the equilibrium distributions of yield and spillage are obtained. Illustrative examples are provided.
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    An extreme value analysis of the flow of Burbage Brook (1992)
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    Stochastic environmental research and risk assessment 6 (1992), S. 151-165 
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    ISSN: 1436-3259
    Keywords: Extreme values ; Generalized Pareto Distribution ; maximum likelihood ; peaks over threshold ; return levels ; river flows
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract An extreme value analysis of the flow of Burbage Brook is carried out by modelling peaks over a high threshold. The aims are to illustrate recently developed statistical techniques and to report on interesting features of the flow of the brook over a 58-year period. Peak flows are found to show marked seasonal variation and a downward trend. Then-year return level is estimated for various values ofn, and the reliability of the estimates is assessed.
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    URL: http://dx.doi.org/10.1007/BF01581447
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    Spatial variability and interpolation of daily precipitation amount (1992)
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    Stochastic environmental research and risk assessment 6 (1992), S. 209-221 
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    ISSN: 1436-3259
    Keywords: geostatistics ; precipitation ; water balance models ; semivariogram ; kriging ; spatial variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Daily precipitation amounts show spatial variation over sub-continential regions. Point measurements, representative for regions of land, have to be interpolated towards unobserved locations. In this study four days in 1984 were selected to investigate the spatial variability of daily precipitation amount in North-western Europe in relation to the meteorological conditions. Data were interpolated using Kriging. Crossvalidation was used to compare interpolated values with measured values. Large differences in the spatial structure of daily precipitation amount are obsered as a result of different meterological conditions. Stratification of the study area into a coastal, a mountainous and an interior stratum proved to be successful, reducing the Mean Squared Error of Prediction with up to 55%.
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    URL: http://dx.doi.org/10.1007/BF01581451
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    Optimal operation model of a single reservoir with drought duration explicitly concerned (1992)
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    Stochastic environmental research and risk assessment 6 (1992), S. 123-134 
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    ISSN: 1436-3259
    Keywords: Reliability analysis ; Drought duration ; Reservoir operation ; Markov decision process
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract In this paper, a new model for a single reservoir operation optimization is proposed. The proposed model can design the optimal operation policy of a reservoir with explicit consideration of drought duration. The authors model this problem by formulating a single-stage loss function as a function of both the reservoir release and drought duration. Thereby the expected loss per period which is calculated based on the above extended single-stage loss function is minimized in infinite time horizon on the basis of Markov decision process (MDP) theory. The reliability indices are estimated as expected loss per period for specified extended loss functions. Finally, the features of the proposed model are illustrated through numerical analysis.
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    URL: http://dx.doi.org/10.1007/BF01591334
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    Spatial variability and interpolation of daily precipitation amount (1992)
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    Stochastic environmental research and risk assessment 6 (1992), S. 304-320 
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    ISSN: 1436-3259
    Keywords: geostatistics ; precipitation ; water balance models ; semivariogram ; kriging ; spatial variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Daily precipitation amounts show spatial variation over sub-continential regions. Point measurements, represntative for regions of land, have to be interpolated towards unobserved locations. In this study four days in 1984 were selected to investigate the spatial variability of daily precipitation amount in north-western Europe in relation to the meteorological conditions. Data were interpolated using kriging. Crossvalidation was used to compare interpolated values with measured values. Large differences in the spatial structure of daily precipitation amount are observed as a result of different meteorological conditions. Stratification of the study area into a coast, a mountain and an interior stratum proved to be successful, reducing the Mean Squared Error of Prediction with up to 55%.
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    Announcements (1993)
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    Stochastic environmental research and risk assessment 7 (1993), S. 83-83 
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    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
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    URL: http://dx.doi.org/10.1007/BF01581568
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    A scale-invariant approach to flood-frequency analysis (1993)
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    Stochastic environmental research and risk assessment 7 (1993), S. 33-40 
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    ISSN: 1436-3259
    Keywords: Fractal ; flood-frequency ; scale-invariant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract In order to study historical flood-frequency records we plot the log of the number of floods on a river per unit time in which the peak discharge exceeds a specified value against the log of that value. For ten benchmark stations we find good correlations with scale-invariant (fractal) statistics. We suggest that the underlying physical processes associated with the generation of floods are sufficiently scale invariant over time scales from one to one hundred years that they provide a rational basis for the application of scale-invariant statistics. Our results fall within the range of flood-frequency estimates made by other statistical techniques. We propose that the ratio of the ten-year peak discharge to the one-year peak discharge β is a quantitative measure of flood potential. With scale invariance β is also the ratio of the one-hundred year flood to the ten-year flood. We find that the values of β for ten stations on rivers throughout the country range from 2.04 to 8.11 and find strong regional variations that can be correlated in terms of climate. Our results are consistent with the observed fractal statistics in sedimentary sections. We have also carried out R/S analyses for the ten stations and have obtained values of the Hurst exponent. We find that the Hurst exponent cannot be used for flood-frequency forecasting.
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    Evaluation of safety of hydraulic structures affected by migrating pits (1993)
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    Stochastic environmental research and risk assessment 7 (1993), S. 131-145 
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    ISSN: 1436-3259
    Keywords: Safety ; reliability analysis ; uncertainty analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Because it can be carried by flowing water, a sand/gravel pit on the river bed could migrate downstream. Consequently, the presence of pits on river beds could pose a safety threat to in-stream hydraulic structures such as bridge piers. A pit migration model can be used to predict progressive changes of pit geometry as it migrates downstream. However, due to the existence of many uncertainties, the maximum pit depth cannot be predicted with certainty. This paper adopted a simple pit migration model and evaluated the uncertainty associated with the calculated maximum pit depth. Such information is essential for evaluating the probability that a migrating pit could pose a safety threat to a downstream hydraulic structure. Three reliability analysis techniques were applied and their performances were compared.
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    URL: http://dx.doi.org/10.1007/BF01581421
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    Evaluating the effect of land development on sediment transport using a probability density function (1993)
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    Stochastic environmental research and risk assessment 7 (1993), S. 102-108 
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    ISSN: 1436-3259
    Keywords: Sedimentation ; probability density function ; synthetic study ; development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract An important problem in sedimentation analysis is the development of a channel section that preserves, as best as possible, the current sedimentation regime even though the flood frequency tendencies have been altered due to land development within the catchment. In order to accomplish this task, a methodology is needed that estimates sediment transport capacity for various channel configurations. Such a procedure is described which allows the computation of the total sediment transport capacity for each of several T-year return frequency runoff hydrographs. This information is used to obtain an approximate probability distribution for the total sediment transport capacity, and the mean and standard deviation of this distribution are computed. Comparing the results for the catchment in its present state with a future developed state, using a selection of new channel parameters, indicates how to improve the channel to control changes in sedimentation due to development. The analysis procedure provides a basis for estimating a new channel configuration such that the new flow conditions retain, as best as possible, the existing condition sedimentation effects, and hence retain the natural sediment supply and transport trends even though runoff flow rates have changed due to land development within the catchment. The results of Wilson Creek are typical of the several sites examined, see Table 3 below. The T=2, T=5, T=25, and T=100 year values for total sediment transport capacity, in kilotons, are 6.9, 39.4, 61.3, and 96.7 with a mean of 17.1 and standard deviation of 19.3. After development with no change in the channel the respective values increase to: 17.9, 84.6, 128.1, and 258.0 with a mean of 39.1 and standard deviation of 44.3. A new channel can be constructed which will reduce these sediment transport capacity values, after development, to 5.2, 41.0, 62.0, and 124.8 with a mean of 17.4 and standard deviation of 22.0.
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    Parameter estimation for 3-parameter log-logistic distribution (LLD3) by Pome (1993)
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    Stochastic environmental research and risk assessment 7 (1993), S. 163-177 
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    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The principle of maximum entropy (POME) was employed to derive a new method of parameter estimation for the 3-parameter log-logistic distribution (LLD3). Monte Carlo simulated data were used to evaluate this method and compare it with the methods of moments (MOM), probability weighted moments (PWM), and maximum likelihood estimation (MLE). Simulation results showed that POME's performance was superior in predicting quantiles of large recurrence intervals when population skew was greater than or equal to 2.0. In all other cases, POME's performance was comparable to other methods.
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    On the validity of empirical power laws (1993)
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    Stochastic environmental research and risk assessment 7 (1993), S. 179-194 
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    ISSN: 1436-3259
    Keywords: Hydrological processes ; power laws ; spurious self-correlation ; lake hydrology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Empirical power laws are frequently used to relate parameters in complex hydrological and hydrometeorological processes. The validity of power laws relating two parameters with a common variable may be compromised by spurious influences of the common variable. Theoretical results are presented that allow both the spurious self-correlation coefficient and the slope of a spurious self-correlation to be determineda priori. Raising a common variable to a higher power in either parameter amplifies the spurious effects. Power law regression equations are not single-valued analytical functions and must not be treated as such. Because of the strong influence of a common variable on the correlation coefficient, the transfer of a common variable from one side of a power-law regression equation to another (by cross-multiplying) may severely distort the results. Examples from lake hydrology are presented.
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    A master equation for reactive solute transport in porous media (1993)
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    Stochastic environmental research and risk assessment 7 (1993), S. 255-268 
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    ISSN: 1436-3259
    Keywords: Groundwater hydrology ; solute transport ; master equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The mean value of a density of a “cloud of points” described by a generalized Liouville equation associated with a convection dispersion equation governing adsorbing solute transport yields a joint concentration probability density. The general technique can be applied for either linear or nonlinear adsorption; here the application is restricted to linear adsorption in one-dimensional transport. The equation generated for the joint concentration probability density is in the general form of a Fokker-Planck equation, but with a suitable coordinate transformation, it is possible to represent it as a diffusion equation with variable coefficients.
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    Comparisons of Weibull- and exponential-based partial duration stochastic flood models (1993)
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    Stochastic environmental research and risk assessment 7 (1993), S. 283-297 
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    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A stochastic flood model with a Weibull distribution for flood exceedances is examined and compared to the traditional exponential-based model in terms of predictive and descriptive properties. The model is based upon the traditional representation of the flood mechanism as a Poisson counting process. It is expected that the more flexible Weibull distribution will be capable of modeling flood series which exhibit a wider range of variability than the exponential model. The Weibull-based model is shown to possess predictive properties which are superior to the exponential model when samples exhibit coefficients of variation less than 1.5 and sample sizes are on the order of 2 events per year. These characteristics are shown to exist in many observed flood series in the Gulf Coast of the United States.
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    Probabilistic assessment of travel times in groundwater modeling (1994)
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    Stochastic environmental research and risk assessment 8 (1994), S. 19-55 
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    ISSN: 1436-3259
    Keywords: Indicator kriging ; stochastic simulation ; soft data ; Walker Lake ; sequential simulation ; scaling-up
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A Monte Carlo approach is described for the quantification of uncertainty on travel time estimates. A real (non synthetic) and exhaustive data set of natural genesis is used for reference. Using an approach based on binary indicators, constraint interval data are easily accommodated in the modeling process. It is shown how the incorporation of imprecise data can reduce drastically the uncertainty in the estimates. It is also shown that unrealistic results are obtained when a deterministic modeling is carried out using a kriging estimate of the transmissivity field. Problems related with using sequential indicator simulation for the generation of fields incorporating constraint interval data are discussed. The final results consists of 95% probability intervals of arrival times at selected control planes reflecting the original uncertainty on the transmissivity maps.
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    Joint conditional simulations and the spectral approach for flow modeling (1994)
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    Stochastic environmental research and risk assessment 8 (1994), S. 79-108 
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    ISSN: 1436-3259
    Keywords: Stochastic flow equations ; conditional simulation ; spectral representations ; joint conditioning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The use of data to condition single random fields has a well-established history. However, the joint use of data from several cross-correlated random fields is not as well developed. For example, the use of both transmissivity and head data in a steady state 2-d stochastic flow problem is essentially an inverse problem that is very important for both flow and transport predictions. This problem is addressed here by using a combination of numerical simulation and analytical methods and its application illustrated. The type of information conveyed by the different data categories is explored. The results presented are especially interesting in that head and transmissivity each give different information: Head values would appear to constrain the geometry of the paths while transmissivity data yields information about travel times. The linearized model is expanded to an iterative procedure and the “true” conditional distribution at several locations is compared with the iterative solution. The problem mentioned above is one with a special transfer function specified by the flow equation. In the second part of the paper a Fast Fourier Transform method for generation and conditioning of two or more random fields is introduced. This procedure is simple to implement, fast and very flexible.
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    Interpolation of runoff applying objective methods (1993)
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    Stochastic environmental research and risk assessment 7 (1993), S. 269-281 
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    ISSN: 1436-3259
    Keywords: Runoff ; stochastic interpolation ; objective analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The paper treats the problem of interpolating annual runoff from regular streamflow measurements in a regional scale applying objective methods. These methods are adapted to point processes like temperature and precipitation. Modifications are needed to account for the fact that streamflow is an integrated process following the hierarchical structure of river systems. The most straightforward method is therefore to relate the interpolation to the existing river network. For theoretical reasons it is preferable to interpolate the lateral inflow rather than the flow in the river itself. Procedures for the interpolation with the different approaches are developed and discussed. Special attention is put on the question how the equation of continuity can be satisfied. The Laagen drainage basin in southern Norway is used as a test area. The data consist of annual observations of streamflow and digital map information on river networks and drainage basin boundaries.
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    Effective hydraulic conductivity of nonstationary aquifers (1994)
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    Stochastic environmental research and risk assessment 8 (1994), S. 1-17 
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    ISSN: 1436-3259
    Keywords: Stochastic diffusion equations ; effective hydraulic conductivity ; correlation scale ; heterogeneous aquifers ; spectral representation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Assuming that the ln hydraulic conductivity in an aquifer is mathematically approximated by a spatial deterministic “surface”, or trend, plus a stationary random noise, we treat the problem of finding what the effective hydraulic conductivity of that aquifer is. This problem is tackled by spectral methods applied to a type of diffusion equation of groundwater flow, together with suitable coordinate transformations. Analytical (exact) solutions in terms of elementary functions are presented for one- and three-dimensional finite and infinite domains. Stability criteria are obtained for the solutions, in terms of a critical parameter, that turns out to involve the product of correlation scale and trend gradient. For the case of finite and symmetrical domains, additional provisions to insure the stability of numerical calculations of effective hydraulic conductivity are provided. Effective hydraulic conductivity is an important property, with potential applications in the calibrations of groundwater and transport numerical models.
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    MMO: An improved estimator for log-Pearson type-3 distribution (1994)
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    Stochastic environmental research and risk assessment 8 (1994), S. 219-231 
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    ISSN: 1436-3259
    Keywords: Parameter estimation ; flood frequency analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A mixed method combining the method of moments and the method of optimization (MMO) was developed for estimating the parameters of the log-Pearson type 3 (LP3) distribution. The MMO estimates the parameters of mean and standard deviation by the method of indirect moments (MIM) and estimates the coefficient of skewness by minimizing both the relative root average square error (RRASE) and the relative average bias (RAB). Both the predictive capability and descriptive capability of six popular estimation methods were evaluated using 90 sets of observed flood data and six selected LP3 populations with 1000 samples for each selected sample size. The performance of the MMO was compared with those of five other selected estimation methods. A weighted ranking index (WRI) procedure was developed to help select the best combination of distribution and method for the Louisiana flood data. The WRI takes both the predictive capability and the descriptive capability into account in the evaluation. The combination of LP3/MMO was found to be the best combination for Louisiana flood data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01587236
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  • 198
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    Electronic Resource
    Unsaturated flows in soils with self-similar hydraulic conductivity distribution (1994)
    Springer
    Stochastic environmental research and risk assessment 8 (1994), S. 281-300 
    Details
    ISSN: 1436-3259
    Keywords: Stochastic analysis ; unsaturated flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract In this article, we are concerned with the statistics of steady unsaturated flow in soils with a fractal hydraulic conductivity distribution. It is assumed that the spatial distribution of log hydraulic conductivity can be described as an isotropic stochastic fractal process. The impact of the fractal dimension of this process, the soil pore-size distribution parameter, and the characteristic length scale on the variances of tension head and the effective conductivity is investigated. Results are obtained for one-dimensional and three-dimensional flows. Our results indicate that the tension head variance is scale-dependent for fractal distribution of hydraulic conductivity. Both tension head variance and effective hydraulic conductivity depend strongly on the fractal dimension. The soil pore-size distribution parameter is important in reducing the variability of the unsaturated hydraulic conductivity and of the fluxes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01588758
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  • 199
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    Entropy principles in the prediction of water quality values at discontinued monitoring stations (1994)
    Springer
    Stochastic environmental research and risk assessment 8 (1994), S. 301-317 
    Details
    ISSN: 1436-3259
    Keywords: Change ; discontinued stations ; entropy ; networks ; optimization ; prediction ; unbiased ; water quality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A new methodology for predicting water quality values at discontinued water quality monitoring stations is proposed. The method is based upon the Principle of Maximum Entropy (POME) and provides unbiased predictions of water quality levels at upstream tributaries and on the mainstem of a river given observed changes in the distribution of the same water quality parameter at a downstream location. Changes in the values of water quality parameters which are known a priori to have occurred upstream, but which are not sufficiently large to account for all the observed change in the same water quality parameter at the downstream location are able to be incorporated in the method through the introduction of a new term in the basic entropy expression. Application of the procedure to water quality monitoring on the Mackenzie River in Queensland, Australia indicates the method has considerable potential for prediction of water quality at discontinued stations. The method also has potential for identifying the location of causes of observed changes in water quality at a downstream station.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01588759
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  • 200
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    Sampling variance of a T-year flood estimated by curve-fitting (1994)
    Springer
    Stochastic environmental research and risk assessment 8 (1994), S. 233-258 
    Details
    ISSN: 1436-3259
    Keywords: Flood ; China ; river ; sampling variance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The sampling variance of a T-year flood when estimated using a curve-fitting method results from the errors in hydrologic observations, plotting positions, and model-fitting. This paper develops a method to quantify the contribution of plotting positions to the sampling variance of the T-year flood magnitude. Application of the method to 150 flood-flow data sets of 41 rivers in the People's Republic of China show that the errors due to plotting positions contribute more to the sampling variance than others.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01587237
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