ALBERT

Description: In this paper, we present an algorithm for partitioning any given 2D domain into regions suitable for quadrilateral meshing. It is able to preserve the symmetry of the domain if any, and can deal with inner boundaries and multidomain geometries. Moreover, this method keeps the number of singularities at the junctions of the regions to a minimum. Although each part of the domain, being four-sided, can be easily meshed using a structured method, we provide a meshing process that guarantees near perfect quality for most quadrilaterals of the resulting mesh. The partitioning stage is achieved by solving a PDE-constrained equation based on the geometric properties of the domain boundaries. An analysis of the generated mesh quality is provided at the end, showcasing that the meshes obtained through our algorithm are especially suitable for finite element methods.

Description: Biodiesel production from non-edible feedstocks is currently drawing much attention due to legitimate concerns about the effects of using edible oil for fuel. Pangium edule Reinw is a non-edible feedstock. Pangium is a tall tree native to the Micronesia, Melanesia and the mangrove swamps of South-East Asia. In this study, biodiesel production and characterization from P. edule oil was reported. The seeds were obtained from Bogor, Indonesia. The oil was found to have an acid value of 19.62 mg KOH/g oil. Therefore, a two-step acid–base-catalysed transesterification was used to produce biodiesel. This was followed by evaluating the physical and chemical properties of biodiesel and its blends with diesel. It has been found that the determined properties of P. edule methyl ester indicate that the oil can be considered as a future biodiesel source. The most remarkable feature of P. edule is its cloud, pour and cold filter plugging points. This biodiesel yielded cloud, pour and cold filter plugging points of –6, –4 and –8 °C, respectively. This indicates the viability of using this biodiesel in cold countries. Therefore, it is suggested that more research should be conducted on P. edule for future biodiesel production.

Description: The paper presents a new Kernel-based monitoring algorithm compared with statistical process control methods, such as DISSIM and MS-PCA and some others methods widely used in process control applications. The proposed algorithm is a modified version of the well known support vector domain description (SVDD). The last one is commonly used for one-classification problems, named also novelty detection. In this paper, we have used a modified SVDD endowed with useful tools to manage multi-classification problems. The proposed classifier is also able to deal with stationary as well as non-stationary data. The principle is based on the dynamic update of the training set through a recursive deletion/insertion procedure according to adequate rules. In order to reduce the computational complexity and improve the rapidity of convergence, the algorithm considers in each run a limited frame of samples for the training process. To prove its effectiveness, the approach is assessed at first on artificially generated data. Then, we have performed a case study applied on chemical process.

Description: A series of nonionic surfactants were synthesized from gallic acid and polyethylene glycols with different molecular weights. Chemical structures of the surfactants were confirmed using elemental analysis, infrared and nuclear magnetic resonance ( 1 H-NMR) spectroscopy. Surface activities of the surfactants in their solutions were determined by surface tension measurements. Increasing the polyethylene glycol chain length increased the surface activity of the surfactants in solutions. Measurements of interfacial tension between surfactants solutions and substrates with different polarity showed that the type of substrates plays functioning role on the interfacial properties. Thermodynamic properties of adsorption and micellization processes showed their tendency towards adsorption at solution interface and micellization in their solutions. Results showed reasonable surface activities compared to conventional nonionic surfactants.

Description: Compressed sensing for multiple input multiple output (MIMO) radar can potentially enhance spatial resolution and improve jamming noise suppression capability by making use of information about the sparse “scene.” In this paper, an efficient method for anti-jamming in MIMO chaotic radar direction finding of point-like targets is proposed. The novelty of this paper is that it capitalizes on chaotic coded waveform to construct measurement operator, which shows a low correlation with jamming noise; therefore, the proposed approach can take advantage of the sparse optimization method to suppress jamming noise of the received signals. A directional optimization algorithm based on gradient pursuit is implemented in reconstruction of the sparse “scene.” The performances of the proposed approach are evaluated via computer simulation studies and shown to outperform conventional methods.

Description: This paper presents the implications of the adjustable fountain wave soldering process during pin through hole (PTH) component assembly process. The PTH vertical fill was carried out experimentally by using a newly developed adjustable fountain wave soldering machine ( \({0^{\circ}}\) conveyor angle). A similar printed circuit board and components were assembled by using a conventional wave soldering machine ( \({6^{\circ}}\) conveyor angle). This paper focuses on vertical filling by using both wave soldering methods. A non-destructive X-ray computed tomography scanning machine was employed to inspect the vertical fill of each PTH. The percentage of the vertical fill for two different wave soldering machines was analyzed. The PTH filling phenomenon during wave soldering was also discussed. FLUENT software was utilized to simulate the PTH vertical filling of adjustable fountain wave soldering. The volume of fluid model tracked the flow front of the molten solder. The simulation and experimental results showed a nearly identical solder filling profile. The void of the PTH vertical filling was also visualized under an X-ray CT scanning machine.

Description: Mechanical alloying was employed to synthesize Al–Zn–Mg–Cu alloys with nickel additives from elemental powders via high-energy ball milling. The milled powders were cold compacted and sintered thereafter. The sintered compacts underwent homogenization treatments at various temperature conditions and aged at 120 °C for 24 h (T6). Subsequently, the compacts were retrogressed at 180 °C for 30 min and re-aged at 120 °C for 24 h (RRA). The milled powders and heat-treated products were characterized via X-ray diffraction (XRD), scanning electron microscopy, and energy-dispersive spectroscopy. The crystallite sizes and micro-strains of the alloy powder were estimated with the broadening of XRD peaks by using the Williamson–Hall equation. The results show that Zn, Mg, and Cu atoms are soluble in the Al matrix after milling for 5 h. The Vickers hardness of Al alloys was enhanced following retrogression and re-aging treatments. The addition of nickel influenced the hardness of the compacted powders.

Description: Many fiber types are used in fiber-reinforced concrete (FRC) pavements. The maximum undamaged defect size ( d max ) concept has been applied to predict notch-based fracture in different types of concrete. The present paper applies this concept to different types of FRC pavement, namely, glass fiber-reinforced concrete pavement and steel fiber-reinforced concrete pavement. Due to the quasi-brittle manner of concrete, various fracture models have been developed to study the crack propagation in the pavement structures. The fracture energy was determined based on the recommendation of the RILEM Committee 50-FMC. An experimental study was carried out to investigate the effect of adding short fiber, steel or glass, in controlling the fracture energy of concrete. The analysis was invoked for constant fiber length of 25mm. The flexure test of single-edge notched and unnotched specimens was performed using three-point bending configuration. Four different values of crack-depth ratios were considered, mainly, 0.00, 0.10, 0.25, and 0.40. Experimental results showed that the calculated d max based on RILEM Committee 50-FMC is greater than the maximum aggregate size (MAZ). This means that there is no compatibility between the flexural strength of FRC and its fracture energy calculated based on RILEM Committee 50-FMC. Therefore, a modified calculation of the area of load-deflection curve was suggested to improve the reliability of fracture energy measured based on RILEM Committee 50-FMC. It is found based on this modification that d max is less than 0.7 MAZ.

Description: Advances in research and development of geopolymer concrete have made it a feasible alternative material for civil and infrastructural applications. However, currently, there is a gap in design methodology due to lack of knowledge on geopolymer concrete, which has been a significant barrier for engineers and designers. The current research addresses this gap, modeling an equivalent stress block of fly-ash-based geopolymer concrete, to enable the design of sections. It was found that the design parameters based on the standard codes are not well suited for the fly-ash-based geopolymer concrete structures. In addition, the elastic modulus model obtained from Ordinary Portland Cement concrete is inappropriate for fly-ash-based geopolymer. Therefore, in this study, the stress–strain relation, an elastic modulus model and equivalent stress block design parameters were obtained from experimental results, also using prior published data, for flexural strength predictions of fly-ash-based geopolymer concrete members. A simplified stress–strain relationship based on Thorenfeldt’s model, as well as the stress block design equations, was fit to test data. The results showed that the simplified stress–strain model is reasonably accurate. The prediction of flexural moment capacity based on the proposed design parameters correlated well with experimental test data. It was found that the nominal moment capacity using standard code design parameters was about 1.43 times higher than with the proposed design parameters.

Description: Radio frequency spectrum is too crowded and expensive to install new broadband channels. Free space optical (FSO) communication is a viable technology, which offers enormous bandwidth, license-free spectrum and non-interfering nature. But the FSO link deteriorates significantly due to the atmospheric turbulence and sever weather conditions (fog, cloud and snow). Hybrid FSO/RF communication system with independent coding scheme has been suggested in the literature. But such systems are expensive and have synchronization issue. We propose a hybrid FSO/RF communication system with joint coding scheme. A novel puncturing optimization algorithm is developed, which adaptively tackle fading effects of the individual communication link. The proposed puncturing algorithm gives more than 3 dB power gain over the fixed system.

Description: The nature of microbial communities and their relation to enzyme activities in the Taptapani hot spring Odisha, India, is a neglected area of investigation. To address this, the microbial diversity, enzyme activities and the physicochemical factors of the hot spring water were studied. Organisms were identified using the 16S rDNA, 28S rDNA and 18S region of rDNA for bacteria, fungi and algae, respectively, after amplification by the polymerase chain reaction. Phylogenetic analysis of the sequenced gel electrophoresis bands revealed a great diversity of microorganisms. Based on morphology, nine groups of bacteria, three groups of fungi and four groups of algae were dominant during all seasons. The growth behavior of the selected isolates was studied at different elevated temperatures which revealed that all ten isolates (six bacteria, three fungi and one alga) were able to grow in the temperature range of 50–80°C and at pH 4–9. Maximum temperature and pH for the amylase activity were found to be 80 and 9°C, respectively, while an optimum amylase activity was observed at 60°C and pH 9. Considerable activity was observed at both acidic and alkaline pH (4.0–10.0), suggesting wide technical applications for these enzymes and indicating that these enzymes are novel.

Description: This paper introduces a methodology for creating geometrically consistent subsurface simulation models, and subsequently tetrahedral finite element (FE) meshes, from geometric entities generated in gOcad software. Subsurface simulation models have an intrinsic heterogeneous characteristic due to the different geomechanics properties of each geological layer. This type of modeling should represent geometry of natural objects, such as geological horizons and faults, which have faceted representations. In addition, in subsurface simulation modeling, lower-dimension degenerated parts, such as dangling surfaces, should be represented. These requirements pose complex modeling problems, which, in general, are not treated by a generic geometric modeler. Therefore, this paper describes four important modeling capabilities that are implemented in a subsurface simulation modeler: surface re-triangulation, surface intersection, automatic volume recognition, and tetrahedral mesh generation. Surface re-triangulation is used for regenerating the underlying geometric support of surfaces imported from gOcad and of surface patches resulting from intersection. The same re-triangulation algorithm is used for generating FE surface meshes. The proposed modeling methodology combines, with some adaptation, meshing algorithms previously published by the authors. Two novel techniques are presented, the first for surface intersection and the second for automatic volume recognition. The main contribution of the present work is the integration of such techniques through a methodology for the solution of mesh generation problems in subsurface simulation modeling. An example illustrates the capabilities of the proposed methodology. Shape quality of generated triangular surface and tetrahedral meshes, as well as the efficiency of the 3D mesh generator, is demonstrated by means of this example.

Description: An automated approach to quadrilateral mesh generation with complex internal geometric feature constraints is presented in this paper. It can deal with all kinds of feature constraints such as internal holes, constraint lines, constraint points, density lines and density points, etc., and satisfy special requirements of mesh generation for numerical analysis. The quadrilateral mesh is generated based on the looping algorithm. As the core of the algorithm, the new splitting criteria are put forward to improve the quality and efficiency of mesh generation. The method of dealing with feature constraints is proposed by considering constraint lines and points, density lines and density points as internal holes with zero area. The method for generating boundary elements is also introduced to improve the element quality around the boundary and feature constraints. For the situation in which feature constraints subdivide the domain into sub-domains, an automatic determination method of sub-domain boundaries is presented. An improved looping algorithm is presented for 3D surface meshing with feature constraints. The determination of proper splitting plane and the handling of feature constraints are put forward. The program of quadrilateral mesh generation has been developed based on the method presented in this paper and successfully applied to mesh generation in several engineering fields.

Description: This paper aims to introduce a unified code for fluid flow modeling in complex channels reconstructed from imagery. Given a binary image of a cross-section or projection of planar connected channels with circular cross-sections, we wish to: (1) reconstruct a three-dimensional model of the boundary of the geometry, (2) establish boundary condition of the flow field, and (3) compute a fluid simulation based on a Cartesian grid. Our solution has the following advantages. First, we use the same mathematical tools throughout the process i.e. a level set function and a skeleton to describe the geometry. The skeleton of the geometry is essential in the imagery part to transform the 2D geometry into a 3D geometry but is also essential in the fluid flow part to construct a velocity field of reference for boundary conditions in the mechanical fluid flow model. Then, the integration of the geometry into the fluid mechanic code is simplified thanks to a Cartesian grid taking into account the geometry through the level set function. Finally, this work leads to a stand-alone code capable of simulating 3D flows in geometry reconstructed 2D images. We show its usefulness in applications to medical imagery (namely angiography) and bifluid flows in microchannels.

Description: This paper presents simulation methodology that combines a local nonmatching grid with a discrete fracture model. Designed for 2D and 3D multiphase flow simulations in standard simulators, the method handles matrix–matrix, fracture–fracture, and matrix–fracture connections in the context of an unstructured, local nonmatching grid. The grid is generated at the fracture intersections, enabling accurate modeling of small control volumes between connecting fractures. Grids are obtained simply by redistributing the volume of small control volumes surrounding the small control volumes, making the method computationally efficient. A unified method to calculate the interblock transmissibility is used for both matching and nonmatching mesh. An unstructured finite-volume graph-based reservoir simulator with a two-point flux approximation reads the new grid by making a simple modification to the graph of connections between the control volumes. The method requires no special treatment of fracture–fracture or matrix–fracture transmissibility calculations and has the flexibility to simulate any flow problem efficiently. Several 2D and 3D numerical examples demonstrate the method’s performance and accuracy. Both simple and complex fracture configurations are presented with various levels of geologic and fluid complexity. The numerical results are in good agreement with those of a reference solution obtained on a finely structured grid.

Description: Remeshing is an important problem in variety of applications, such as finite element methods and geometry processing. Surface remeshing poses some unique challenges, as it must deliver not only good mesh quality but also good geometric accuracy. For applications such as finite elements with high-order elements (quadratic or cubic elements), the geometry must be preserved to high-order (third-order or higher) accuracy, since low-order accuracy may undermine the convergence of numerical computations. The problem is particularly challenging if the CAD model is not available for the underlying geometry, and is even more so if the surface meshes contain some inverted elements. We describe remeshing strategies that can simultaneously produce high-quality triangular meshes, untangling mildly folded triangles and preserve the geometry to high-order of accuracy. Our approach extends our earlier works on high-order surface reconstruction and mesh optimization by enhancing its robustness with a geometric limiter for under-resolved geometries. We also integrate high-order surface reconstruction with surface mesh adaptation techniques, which alter the number of triangles and nodes. We demonstrate the utilization of our method to meshes for high-order finite elements, biomedical image-based surface meshes, and complex interface meshes in fluid simulations.

Description: This paper presents an anisotropic adaptive strategy for CFD that combines a nearly body-fitted mesh strategy with an iterative anisotropic adaptation to the flow solution. The nearly body-fitted mesh method consists in modelling embedded interfaces by a level-set representation in combination with local anisotropic mesh refinement and mesh adaptation (Quan et al. in Comput Methods Appl Mech Eng 268:65–81, 2014 ). The generated nearly body-fitted meshes are used to perform CFD simulations. Besides, anisotropic mesh adaptation based on the Hessian of the flow solution is used to improve the accuracy of the solution. We show that the method is beneficial in challenging CFD simulations involving complex geometries and time dependent flow, as it suppresses the need for the tedious process of body-fitted mesh generation, without altering the finite element formulation nor the prescription of boundary conditions. The methodology yields accurate flow solutions for a reasonable computational cost, despite very limited user interaction.

Description: In this paper, two PDE-based mapping operators for the generation of unstructured meshes are compared. While the Winslow operator allows the construction of valid meshes for most configurations, the functional-based operators based on area, length, orthogonality and their combinations provide a finer control on the resulting meshes. Two distinct discretization methods of the operators are also compared. An original approach using a finite difference scheme on unstructured meshes is implemented and compared to a finite volume formulation. While more complex to implement and control, mainly because of the cross-derivative terms which must be carefully discretized, the finite volume method yields a more robust and stable formulation that allows dealing with sharp curvature variations of the boundaries. Finally, a criterion for the mesh smoothness which has a global definition is presented in order to compare the smoothness of the resulting mesh obtained by different operators.

Description: Development and application of metal matrix composite materials and increased application of calculations, simulations and modeling in the area of semi-solid solidification ask for the knowledge of compocasting for these materials. In this study, a self-organizing hierarchical particle swarm optimizer is implemented for computational modeling and optimization of the compocast high strength and highly uniform Al matrix composites. The matrix of the composite was a 6061 Al alloy and the reinforcement was alumina particle (Al 2 O 3 p). Experimental results were obtained for hardness, tensile and fatigue properties of the Al alloys with different vol.% of micro-particles. The tensile strength of the composites increased considerably by increasing the reduction ratio in the cold rolling process. It is observed that the presence of reinforcement in the Al alloy degrades the low-cycle fatigue property when the Al matrix composites are subject to strain-controlled cyclic loading. The method combines position update rules, the standard velocity and the strengths of particle swarm optimization with the ideas of selection, crossover and mutation from GA.

Description: In this paper, we present formulae for evaluating differential quantities at vertices of triangular meshes that may approximate potential piecewise smooth surfaces with discontinuous normals or discontinuous curvatures at the joint lines. We also define the C 1 and C 2 discontinuity measures for surface meshes using changing rates of one-sided curvatures or changing rates of curvatures across mesh edges. The curvatures are computed discretely as of local interpolating surfaces that lie within a tolerance to the mesh. Together with proper estimation of local shape parameters, the obtained discontinuity measures own properties like sensitivity to salient joint lines and being scale invariant. A simple algorithm is finally developed for detection of C 1 or C 2 discontinuity joint lines on triangular meshes with even highly non-uniform triangulations. Several examples are provided to demonstrate the effectiveness of the proposed method.

Description: We propose simple and efficient optimization-based untangling strategies for 2D polygonal and 3D polyhedral meshes. The first approach uses a size-based mesh metric, which eliminates inverted elements by averaging element size over the entire mesh. The second method uses a hybrid quality metric, which untangles inverted elements by simultaneously averaging element size and improving element shape. The last method using a variant of the hybrid quality metric gives a high penalty for inverted elements and employs an adaptive sigmoid function for handling various mesh sizes. Numerical experiments are presented to show the effectiveness of the proposed untangling strategies for various 2D polygonal and 3D polyhedral meshes.

Description: In this paper, we present a Delaunay refinement algorithm for 4-dimensional ( \(\hbox {3D}+t\) ) segmented images. The output mesh is proved to consist of sliver-free simplices. Assuming that the hyper-surface is a closed smooth manifold, we also guarantee faithful geometric and topological approximation. We implement and demonstrate the effectiveness of our method on publicly available segmented cardiac images. Finally, we devise a tightly coupled parallelization technique to boost the performance of our 4-dimensional mesher, thereby taking advantage of the multi-core and many-core platforms already available in the market.

Description: Shape idealization transformations are very common operations when adapting a CAD component to FEA requirements. Here, an idealization approach is proposed that is based on generative shape processes used to decompose an initial B-Rep solid, i.e., extrusion processes with material addition are used to segment a solid. The corresponding extrusion primitives form the basis of candidate sub-domains for idealization and their connections conveyed through the generative processes they belong to, bringing robustness to set up the appropriate connections between idealized sub-domains. This is made possible because the connections between extrusion primitives have an explicit geometric representation and can be used to bound the connections between idealized sub-domains. Taking advantage of an existing construction tree as available in a CAD software does not help much because it may be complicated to use it for idealization processes because this tree structure is not unique. Using generative processes attached to an object that is no longer reduced to a single construction tree but to a graph containing all non-trivial construction trees, is more useful for the engineer to evaluate variants of idealization. From this automated decomposition, each primitive is subjected to a morphological analysis to define whether it can idealized or not. Subsequently, geometric interfaces between primitives form also a graph that can be used to process the connections between the idealized sub-domains generated from the primitives. These interfaces are taken into account to determine more precisely the idealizable sub-domains and their contours when primitives are incrementally merged to come back to produce the global morphological analysis of the initial object. A user-defined threshold is used to tune the morphological analysis with respect to further user parameters. Finally, the idealizable sub-domains and their connections are processed to locate the mid-surfaces and connect them using generic criteria that the user can tune locally using complementary criteria.

Description: Automotive companies continuously strive to design better products faster and more cheaply using simulation models to evaluate every possible aspect of the product. Multidisciplinary design optimization (MDO) can be used to find the best possible design taking into account several disciplines simultaneously, but it is not yet fully integrated within automotive product development. The challenge is to find methods that fit company organizations and that can be effectively integrated into the product development process. Based on the characteristics of typical automotive structural MDO problems, a metamodel-based MDO process intended for large-scale applications with computationally expensive simulation models is presented and demonstrated in an example. The process is flexible and can easily fit into existing organizations and product development processes where different groups work in parallel. The method is proven to be efficient for the discussed example and improved designs can also be obtained for more complex industrial cases with comparable characteristics.

Description: A new indirect quadrangular mesh generation algorithm which relies on sequential decision-making techniques to search for optimal triangle recombinations is presented. In contrast to the state-of-art Blossom-quad algorithm, this new algorithm is a good candidate for addressing the 3D problem of recombining tetrahedra into hexahedra.

Description: Haptic feedback usually involves two types of stimulation forces: forces that address the touch sense and forces that address the kinesthetic perception. Touch forces have a low intensity and a complex structure since they reflect contact phenomena where friction plays an important role. Therefore, they are quite difficult to simulate. Virtual prototyping with haptic feedback should ideally involve both types of forces, but the integration of the touch feeling makes the simulator very complex. In this paper, we present a novel concept for virtual prototyping in which the touch interaction is separated from the kinesthetic force feedback. This is possible using a prototype that has a real part undertaking the touch interaction and a virtual part that simulate feedback for the kinesthetic forces. In this way, a full haptic interaction with the virtual prototype is established by means of a device that provides a realistic simulation of the product. In order to illustrate the concept, several experiments have been carried out for the case of specific subsystems of a car, which are particularly involved in the driver–car interaction: steering system, clutch pedal and the gearshift. A user test is described in the last part as well as the conclusions of the research.

Description: A new closed advancing-layer method for generating high-aspect-ratio elements in the boundary-layer (BL) region is presented. This approach utilizes a recent connectivity optimization-based moving mesh strategy for deforming the volume mesh as the BL is inflated. It handles very efficiently BL front collision and produces a natural smooth anisotropic blending between colliding layers. Moreover, it provides a robust strategy to couple unstructured anisotropic mesh adaptation and high-aspect-ratio elements pseudo-structured BL meshes. The proposed method is directly compared to a well-established open advancing-layer method. Results for typical aerospace configurations are presented that provide a clear comparison between both methods as well as the effectiveness of the connectivity optimization-based moving mesh strategy. They show that the closed method yields similar results in terms of mesh quality and efficiency, and that the considered moving mesh strategy is an efficient and effective method for deforming the unstructured volume mesh.

Description: The effect of partial heating and cooling on laminar natural convective heat transfer in right-angle triangular cavity filled with water has been investigated numerically. The triangular cavity is presented in nine different configurations namely Left-Bottom, Left-Middle, Left-Top, Middle-Bottom, Middle-Middle, Middle-Top, Right-Bottom, Right-Middle and Right-Top and the length of the thermally active wall is b  =  L /3. The base wall is considered as partially hot while the side wall as partially cold. Two-dimensional steady-state continuity, Navier–Stokes and energy equations along with the Boussinesq approximation are solved using the finite volume method. The Rayleigh number is varied from 10 5 to 10 7 . Results revealed that the heat transfer rate is high for LB walls whereas low for RT location. Also, the heat transfer rate enhancement is observed for all values of Rayleigh number.

Description: Hot compression tests were carried out to study the deformation behaviors of a lead-free machinable brass using Gleeble-1500 thermal simulator in the temperature range of 823–973K and the strain rate range of 0.01–10 s −1 . The results show that the flow behavior of the lead-free machinable brass is strongly influenced by strain rate and temperature, and the flow stress increases with increasing strain rate and decreasing temperature. The constitutive equations incorporating the effects of strain rate and temperature have been established to model the hot deformation behavior of this alloy. The reliability of the developed constitutive model was demonstrated by the mean percentage error of 10.82 % and the correlation coefficient of 0.98. Moreover, the flow stability/instability of the lead-free machinable brass was carefully investigated on the basis of dynamic material modeling approach. It was found that plastic deformation was stable for processing conditions in which the strain rate range was 1–10 s −1 within the temperature range of 823–923 K.

Description: Active control can expand operation range of compression systems. However, most of existing active controllers depend on known system characteristics and thus have limited engineering application. Robust control methods are used to alleviate the negative effects of uncertainties, but, with conservative results. In order to overcome the weakness of existing active controllers, a second-order MG surge model was presented using a close-coupled valve as actuator. Then, one active surge controller was designed based on backstepping control, in which, fuzzy system was used to model unknown system characteristics. Simulation results showed that the designed controller stabilized compression system outside the surge line, enlarge compressor’s working range and additionally showed strong robustness against uncertainties such as unmodelled dynamics, flow and pressure disturbances.

Description: In this paper, the effects of the use of metakaolin instead of cement on the mechanical properties of mortars, high temperature, alkali–silica reaction, resistance to sulfate, absorption capacity and permeability were studied. In the study, 0, 5, 10, 15 and 20 % cement was replaced by metakaolin by weight to design five different types of mortar. 1-, 3-, 7-, 28-, 56-, 90- and 180-day compressive and flexural strengths and 28-day absorption capacity were determined. Similarly, compressive strength loss in mortar exposed to 200, 500 and \({700\,^\circ{\rm C}}\) for 3 h was determined. The resistance of mortars containing metakaolin to sulfate and alkali silica reaction was determined in accordance with ASTM C 1012 and ASTM C 1260 standards, respectively. It was found that the use of metakaolin had a positive effect on the mechanical properties of the mortars positively and that it reduced the absorption capacity and degrees of expansion caused by ASR and sulfate attack.

Description: In order to verify the microstructure of saline soil in Qarhan Salt Lake area and its behaviors of mechanics and compressive strength, nine-group saline soil samples with different salt content were collected from the Qarhan Salt Lake and the microstructure of samples was scanned by electron microscope. Direct shear test and compression test were made accordingly. The behaviors of mechanics and compressive strength of saline soil were analyzed from the microstructure. The paper puts forward the skeleton connecting forms between particles of saline soil and took its results in comparison with the studies of Xinjiang plate-like saline soil. The study results show that: (1) The link of soil particles have three forms: ① point contact; ② stacked contact; ③ salt crystals cementation. (2) Saline soil with different salt content has different microstructure. The more dense the microstructure is, the stronger the salt crystals cement, and saline soils show higher mechanical and strength characteristics. Salt crystals cementation is the significant factor which affects the saline soil mechanics and strength characteristics. (3) Unconfined compressive strength significantly changes when salinity reaches and exceeds 45.74 %. (4) Compared with Xinjiang plate-like saline soil, as the difference of grain grade, with the increase in salt content, the microstructure and strength changes are different between the saline soils in Qinghai Qarhan Salt lake and Xinjiang province.

Description: In this study, a series of cast polyamide-based composite materials were produced by injection molding process. In the production of composite materials, cast polyamide and short glass fiber were used as matrix and reinforcement materials, respectively. The specimens obtained from composite materials having different fiber content were tested to determine tensile and impact strength, modulus of elasticity, tensile elongation and density of composites. In addition, scanning electron microscopic studies were carried out on the fracture surfaces of impact test specimens. It was observed that mechanical properties of composites such as tensile strength and modulus of elasticity increased when the fiber volume content is increased up to 35%. However, these properties decreased at the fiber content higher than that of 35%. Moreover, tensile elongation and impact energy values were decreased when the fiber content was increased. In addition, the fiber efficiency factor increased with the increasing fiber content up to 35%, and after this point, it decreased with the increasing fiber content. On the other hand, it was observed that the fiber efficiency factor for modulus of elasticity was higher than that of the tensile strength. Consequently, it was observed that adding short glass fiber up to 35% was an effective method to improve mechanical properties of cast polyamide-based composites.

Description: An alternative numerical method is developed to find stable and unstable periodic orbits of nonlinear dynamical systems. The method exploits the high efficiency of the Levenberg–Marquardt algorithm for medium-sized problems and has the additional advantage of being relatively simple to implement. It is also applicable to both autonomous and non-autonomous systems. As an example of its use, it is employed to find periodic orbits in the Rössler system, a coupled Rössler system, as well as an eight-dimensional model of a flexible rotor-bearing; problems which have been treated previously via two related methods. The results agree with the previous methods and are seen to be more accurate in some cases. A simple implementation of the method, written in the Python programming language, is provided as an Appendix.

Description: The structural health evaluation is performed by comparing the responses between the undamaged and damaged states. Because it is impractical to collect the response data at the intact state, it is important to establish the baseline data to be compared at measurement. The measured frequency response functions (FRFs) in the neighborhood of the first resonance frequency are transformed to the proper orthogonal mode (POM) corresponding to the first proper orthogonal value (POV). The POM data set at the first measurement on the damage-expected structure is taken as the baseline datum, and it is compared with another set extracted from the structure to attach a small mass on an element. The POM difference between two states is utilized as an index to detect damage. The FRF variation before and after a small mass attachment for the purpose of detecting the damage is investigated. The validity of the proposed method based on POM variation is illustrated in the damage detection of a two-dimensional frame structure model. It is shown that the damage region in the frame structure can be inferred by gradually narrowing from the global structure to the damage-expected element.

Description: Formation of the vortex at the dams creates the air entrainment to the intakes and reduces the dewatering capacity of the system (in case of insufficient submergence of the intake). One of the common methods to preventing the air entrance and reducing the power of the vortex is the using of the meshed plates. Because of the researches on the using of vertical meshed plates on the vertical intakes are insufficient, in this research, the effect of the dimensions of the meshed plates on the critical submergence in an experimental model has been studied. The results showed that using the vertical meshed plates can increase the critical submergence for same discharge rates to 51 %.

Description: The N th-best user selection scheme is efficient in outdated channel information conditions where the user that was the best at the selection time instant could not be the best at the transmission time instant. Also, this scheme is useful when the scheduling unit fails in error in selecting the best user among all the available users. Furthermore, the N th-best user selection scheme is efficient in situations where, while the best user is waiting to be scheduled by a certain base station or a scheduling unit, it gets scheduled by other unit. In the proposed scheme, the secondary user with the N th-best end-to-end signal-to-noise ratio (SNR) is scheduled the system resources. In our paper, closed-form expressions are derived for the outage probability, average symbol error probability, and ergodic channel capacity assuming imperfect estimation of channel state information and Rayleigh fading channels. Furthermore, to further analyze the system performance, the system is studied at the high SNR regime. The derived analytical and asymptotic expressions are verified by Monte-Carlo simulations. Main results illustrate that the diversity order of the studied multiuser cognitive N th-best user selection network is the same as its non-cognitive counterpart. Also, findings show that with perfect channel estimation of secondary users, the diversity order of the system linearly increases with decreasing the order of the scheduled user, and vice versa, whereas a zero diversity gain is achieved by the system and a noise floor appears in the results when the channels of secondary users are imperfectly estimated assuming constant estimation error variance. Finally, results illustrate that the imperfect estimation of the secondary cell-primary cell channel affects only the coding gain of the system without affecting the diversity order.

Description: Alkali–aggregate reaction (AAR) is a chemical reaction with known injuries to the old concrete structures. A concrete dam situated in a humid and hot region is commonly susceptible to the occurrence of the reaction. It is a main challenge for the engineers and owners of such structures to make the required rehabilitation measurements. As the primary step, they should estimate future performances of the AAR-affected dams by suitable computer programs. The present study deals with simulation of AAR injuries to the performances of a concrete arch dam. A FE-based computer code, NSAD-DRI, is developed to simulate AAR using a robust mathematical model. On the other side, a nonlinear algorithm has been already implemented in NSAD-DRI for identifying initiation and propagation of crack profiles during the analyses. AMIR-KABIR dam is selected as case study and is modeled by the developed program. The results indicate that AAR may alter various responses of the dam and cause new crack profiles within the dam body. Meanwhile, the current results are in good agreement with those extracted from a similar linear analysis.

Description: Demand for higher accuracy and control systems is growing rapidly and becoming more important in high-tech industries. However, precise position control of a pneumatic cylinder is very difficult to achieve due to the compressibility of air, nonlinear behavior of the air flow rate through the valves and the friction force between the cylinder and the piston of the system. The purpose of this paper was to present a model and a novel linear process control strategy to design a position controller for a real-time pneumatic system. This paper mainly analyzes the horizontal and vertical precision positioning control under loading effect for pneumatic system in real-time experiment. System identification approach is selected to obtain the plant model. Predictive Functional Control with observer (PFC-O) design is proposed as control strategy to improve tracking performance of the pneumatic system. Performance assessment of the controller was performed in MATLAB. The effectiveness of the proposed control strategy is verified through real-time experiment with the plant. The simulation and the experimental results confirm that the proposed PFC-O controller shows good control performance with various load configurations.

Description: The Neoproterozic-related structures have provided important insights into the tectonic history of the Egyptian Eastern Desert as well as the Arabian–Nubian Shield (ANS). The Gabal Abu Houdeid (GAH) area is in the extreme northern portion of the Hamisana shear zone (HSZ), one of the major high-strain zones in the ANS. The Neoproterozoic rocks exposed around GAH include ophiolitic ultramafic–mafic rocks, island-arc metasediments, metavolcanic rocks, intrusive syn-tectonic granodiorites, post-tectonic gabbros, and granites. The analysis of large-scale structures and fault kinematic data in terms of ductile and brittle deformation indicates that the sequence of folding and faulting events was constrained by available litho-tectonic units. Four deformational events are distinguished in the Neoproterozic rocks. Event D1 a pure compression stress regime with σ1 stress axis trending NNW–SSE to N–S represents an early shortening event associated with the Pan-African thrusting, during which intra-oceanic arcs and plateaus were accreted. Event D2 characterized by structures developed under ENE–WSW compressional regime (shortening event) and considered as the early stage of the second episode of collision within the Pan-African orogeny. Event D3 transpressional deformation associated with E–W contraction and N–S extension. It is the main event that controlled the deformation along the HSZ during the late stages of the collision between the East and West Gondwana in terms of escape tectonics. The D4 event is interpreted as a post-orogenic extensional event manifested by E–W dextral strike-slip and dip-slip normal faults striking NNW–SSE to N–S and E–W, which began to occur after the emplacement of post-tectonic granites.

Description: Anaerobic digestion of limed fleshing solid waste from leather-processing industry and effluent treatment liquid waste was studied in a two-phase digester. The hydrolysis and acidification stages resulted in the formation of volatile fatty acid (VFA), where the maximum concentration of total VFA observed in the acidogenic reactor was 18,225mg/L and the average VFA concentration was 10,574mg/L for hydraulic retention time (HRT) of 10days. The hydrolyzed predigested material was tested in a methanogenesis reactor for biogas generation at HRT of 20 days. The two-phase process of the digestion system has been modeled using adaptive neuro-fuzzy inference system (ANFIS) with HRT, pH and organic loading rate (OLR) as input parameters and cumulative gas production as output parameter. The average CH 4 production rate over the entire study period was 0.31m 3 CH 4 /kg VS destroyed and 0.15m 3 CH 4 /kg VS fed at an overall average OLR of 1.05 ± 0.05kg VS/m 3 day. Modeling with ANFIS using HRT, OLR and pH as inputs and cumulative production of gas as output produced a mean-square error of only 0.00049 which is relatively more accurate with reference to available literature.

Description: Project success is a fundamental issue for any planning, design and construction development. Thus, it effects the stakeholders which involve government, developer, constructor and communities as the end users. Critical success factors (CSFs) have been key aspects of a construction project which are considered to be a means to improve the effectiveness of project. CSF literature has been widely addressed, and many researchers evaluated the gaps in CSFs for construction projects’ success. However, this paper highlights the importance levels of interdependency among the CSFs which has rarely been explored in the prior studies. In this study, most influential factors in successfully completing construction projects are used to develop a new integrated model, multi-criteria construction projects CSF model. A novel hybrid multi-criteria decision-making (MCDM) model is used to address the dependence relationships of factors with the aid of grey relational analysis, analytical network process (ANP) and Decision-Making Trial and Evaluation Laboratory (DEMATEL). The initial model of the study is designed by considering five main criteria with 43 sub-criteria. DEMATEL is applied to construct interrelations among criteria and sub-criteria in the integrated model. By using this approach, the interdependencies strength among the criteria and sub-criteria is tested. The ANP method is then adopted in order to determine the relative importance of the CSFs, and used to identify how the CSFs are weighted and prioritized by the construction professionals, who are all working in different areas of the construction industry. The development of this MCDM model helps project parties in Malaysia in identifying the key elements and factors that need to be thoroughly considered and managed for construction project success. The results of this study can also be a guide for the construction organizations to allocate their resources such as financial and time for the construction projects according to the importance level of construction project success factors.

Description: Laboratory tests were done to study the load-settlement behaviour. These tests evaluated rigid square footing on sandy soil and a layered system, stabilised with different dimensions and different cement contents. Nineteen plate load tests were done to make evaluations. The soil type used in tests was poorly graded sand in a box container with the following dimensions; cross section 130 cm × 130 cm and depth 100 cm. The soil was compacted in layers 10-cm thick. Cement was added in percentages of 2.5, 5 and 7.5 % by dry weight of soil. Samples were cured for 28 days, after which they were tested. Experimental data demonstrated effectiveness in terms of increasing bearing capacity and reducing settlement of the stabilised soil–cement layers. Results also showed difference in terms of crack propagation mechanism between samples with different cement contents as evaluations of number and direction. The load-time curves determined from test data showed that the required time to make constant the load variation versus time was more in those samples with 7.5 % cement content compared to those with cement contents of 2.5 and 5 %.

Description: The stilling basin has been accepted to be the most powerful hydraulic structure for the dissipation of the flow energy. The size and geometry of the stilling basin affect the formation of flow patterns, which can be influential for hydraulic performance of the whole system. The Nazloo Dam in Iran was selected as the study area. The USBR II stilling basin was conducted for four convergence angles ( \({5^{{\circ}}, 7.5^{{\circ}}, 10^{{\circ}},}\) and \({12.5^{{\circ}}}\) ). The convergence walls cause the jump to stabilize inside the basin and cause the energy loss to increase in the stilling basin. To simulate the hydraulic jump in the convergence stilling basin conditions in this region, a free surface computational fluid dynamics (CFD) numerical model has been applied. The commercially known software, FLOW-3D \({^\circledR}\) , was applied to numerically solve the Navier–Stokes equations for solution domains, namely the shout, the stilling basin and the downstream of dam, and to estimate the turbulence flow, the standard k- \({\varepsilon}\) and RNG models was used. These models are based on the volume-of-fluid method, and they are capable of simulating the hydraulic jump. The calculated results such as the pressure, the velocities, the flow rate, the surface height air entranced, the kinetics energy, the kinetics energy dissipated, and the Froude number were compared with the scale model data where available. This allowed a comparison for the use of CFD as a cost-effective alternative to physical models. The physical model and CFD model results showed good correlations.

Description: The specific inflow distribution along the horizontal wellbore is significantly uneven in highly heterogeneous reservoirs. Such uneven influx is recognized as the cause of early water breakthrough, poor oil sweep efficiency and low ultimate recovery. Interval control valves (ICVs) are practical completion hardwares that can actively equalize the contributions from all controlled zones. However, the wellhead penetration limitation impedes ICVs’ application in highly heterogeneous reservoirs, which require many control intervals. This paper proposes a new completion methodology that combines ICVs and variable-density perforations (ICVs + VDP) to eliminate the limitation of ICVs applied in highly heterogeneous reservoirs. The ICVs + VDP completion can achieve more subtle controls because VDP is capable of reducing the inflow difference in each subzone. A steady-state modeling approach and a transient-state modeling approach are used to evaluate the effect of the ICVs + VDP completion on inflow equalization and well performance optimization. The observations from case study show that horizontal wells with the ICVs + VDP completion can considerably delay water breakthrough, improve oil recovery, and reduce water production in highly heterogeneous reservoirs.

Description: This paper proposes a new development of kinematic path-tracking control algorithm for differential wheeled mobile robot system, using back-stepping technique based online auto-tuning slice genetic algorithm (SGA). The aim of the proposed robust feedback nonlinear kinematic controller is to find the optimal velocity control action for the real National Instrument mobile robot model in following a pre-defined continuous path precisely and quickly. The SGA guided by Lyapunov stability criterion is implemented as a stable and robust online auto-tune algorithm to find the optimal parameters for the proposed controller. The robustness and effectiveness of the proposed tuning control algorithm are validated by MATLAB simulation results and LabVIEW experimental work; this is demonstrated by overcoming the unmodeled kinematic disturbances, minimizing the tracking error and obtaining the smooth and optimal velocity control signals, with the minimum number of fitness evaluation.

Description: Finite element modeling has been performed using finite element code CASTEM to predict the flexural response of rectangular RC beams strengthened with externally bonded fiber reinforced polymer (FRP) materials by various techniques. Damage model for plain concrete, elastic perfectly plastic behavior for steel bars, elastic–plastic isotropic behavior for steel–concrete interface, linear elastic behavior for FRP materials and perfect bond for FRP-concrete interface were adopted for finite element modeling. In order to validate the finite element modeling approach, a comprehensive experimental program was designed and carried out to compare the experimental and the model results. RC beams were strengthened using CFRP and GRFP materials with various techniques and then tested in three point bending. Comparison of modeling and experimental results was carried out in terms of load–deflection response. The results of numerical simulation showed close agreement with the experimental observations. The ability of the finite element modeling technique adopted in this study to predict damage and cracking pattern is also highlighted in this paper.

Description: Buckling mode interaction of elastic systems in the presence of initial imperfections is well known to have a detrimental effect on the response of a wide range of structural systems. This has been demonstrated mostly analytically for simple models, assuming small displacements, thus obtaining results with questionable validity in the post-buckling range. In order to acquire additional insight into this issue, in the first part of the present paper, two different versions of the well-known 2-DOF Augusti model, whose independent buckling modes are both stable, are studied analytically without any simplifying assumptions with respect to the magnitude of deformation, in order to accurately demonstrate the coupling phenomena in the presence of imperfections in the pre- and post-buckling range. Depending on the nature of the structure’s rotational springs, its post-buckling equilibrium path may be either stable or unstable. Afterward, the elastic response of two examples of laced built-up columns is illustrated numerically, one characterized by interaction between in-plane global and local buckling and the other by in- and out-of-plane global buckling, featuring similar response to that of the two 2-DOF models, respectively, thus demonstrating occurrence of such behavior in actual structural systems.

Description: External confinement of columns of existing reinforced concrete buildings using fiber-reinforced polymer (FRP) composites can significantly increase the ductility and compressive strength of structural members against seismic actions. Therefore, knowledge on the behavior of FRP confined concrete/reinforced concrete members under cyclic stresses is vitally important for realistic prediction of seismic performance of retrofitted structures. In this study, available experimental data on the cyclic stress–strain behavior of FRP confined concrete/reinforced concrete members are evaluated in a comparative manner, and accuracy of several stress–strain models proposed for FRP confined concrete is discussed in terms of prediction of the skeleton curves, as well as the unloading–reloading branches of the cyclic stress–strain relationships of the tested samples. Furthermore, a new model is proposed for the prediction of unloading and reloading branches based on the cyclic tests carried out specifically for this purpose. The predictions of the proposed model and two other available models proposed for cyclic loading are compared with experimental data, and a satisfactory agreement is observed between the predictions and experimental data.

Description: In this study, ten Indiana basins were selected to investigate their geomorphologic characteristics. The drainage area of these basins covers a wide range. Stream networks of these basins are classified according to both Strahler’s and Shreve’s ordering systems. Based on these ordering systems, more than twenty primary and secondary geomorphologic parameters were determined for each study basin. Horton’s laws of stream numbers, stream length and stream area were checked and found valid for these Indiana basins. Values of cumulative drainage area were used to investigate the exceedance probability distribution of mean annual discharge and energy fluxes in the study watersheds. The results of the study show that discharge and energy fluxes were found to follow power law distributions. Exponent of the resulting power laws does not show the universality suggested by previous investigations.

Description: This paper presents a novel optimization algorithm for the multi-area multi-fuel economic–emission dispatch problem and total power loss objective. The proposed method uses the uniform distribution to determine the control parameters and employs a two-stage initialization process. This enables various objectives to be optimized under practical constraints and device limits. We formulate a realistic generation cost that includes the cost of reactive power generation, shunt power injections, and total power losses, along with the conventional active power generation cost. A novel objective based on the concept of multi-fuel emissions makes the problem more realistic, and a generalized unified power flow controller (GUPFC) is considered. A detailed power injection model is developed for a GUPFC with two series converters, including switching losses of converters. A nondominated sorting methodology and particle swarm optimization algorithm are then used to solve the multi-objective problem on the standard IEEE-30 bus and real-time Indian-124 bus test systems.

Description: In the present paper, a modified optimal profit model with settings of production and process parameters is proposed, where the larger-the-better product characteristic with the one-sided lower specification limit is considered. The product characteristic is assumed to be normally distributed with unknown mean and known standard deviation. The selling price of product is assumed to be linearly proportional to its warranty period. We also assume that the retailer’s order quantity is negatively correlated with the wholesale selling price and is positively correlated with the warranty period. The single sampling rectifying inspection plan is adopted for determining the quality of product lot. The Taguchi’s quadratic quality loss function is addressed for measuring the used cost of customer for product. The optimal manufacturer’s process quality level, production run length, warranty period, and retailer’s order quantity can then be simultaneously determined by maximizing the expected total profit of society including both the manufacturer and the retailer. Numerical results show that the longer warranty period and the higher product quality level will lead to the larger expected total profit of society.

Description: Viscosity and specific electrical conductivity of polyacrylonitrile (PAN) in N , N -dimethylformamide (DMF) medium are studied in the presence and absence of anionic surfactants as sodium oleate, sodium dodecyl sulfate and palmitic. Critical micelle concentrations of these surfactants are determined in DMF medium. Thermodynamic functions ( \({\Delta H^{\circ}_{\rm m},\,\Delta G^{\circ}_{\rm m}}\) and \({\Delta S^{\circ}_{\rm m}}\) ) of micelle formation of sodium dodecylbenzene sulfonate and sodium dodecyl sulfate are determined. Curves of X-ray diffraction and differential thermal analysis showed that the PAN samples containing SDS lead to the development of the crystalline structure of PAN, and the initiation temperature decreases of the cyclization reaction of nitrile groups of PAN by 8.5 °C, respectively.

Description: Prediction model allows the machinist to determine the values of the cutting performance before machining. According to the literature, various modeling techniques have been investigated and applied to predict the cutting parameters. Response surface methodology (RSM) is a statistical method that only predicts effectively within the observed data provided. Most artificial intelligent systems mostly had an issue with user-defined data and long processing time. Recently, the extreme learning machine (ELM) method has been introduced, combining the single hidden layer feed- forward neural network with analytically determined output weights. The advantage of this method is that it can overcome the limitations due to the previous methods which include too many engineers’ judgment and slow iterative learning phase. Therefore, in this study, the ELM was proposed to model the surface roughness based on RSM design of experiment. The results indicate that ELM can yield satisfactory solution for predicting the response within a few seconds and with small amount of error.

Description: The aim of this paper is to achieve the 3D reconstruction of blood vessels from a limited number of 2D transversal cuts obtained from scanners. This is motivated by the fact that data can be missing. The difficulty of this work is in connecting the blood vessels between some widely spaced cuts to produce the graph corresponding to the network of vessels. We identify the vessels on each transversal cut as a mass to be transported along a graph which allows to determine the bifurcation points of vessels. Specifically, we are interested in branching transportation Brasco et al. (SIAM J Math Anal 43(2):1023–1040, 2011 ) to model an optimized graph associated with the network of vessels. At this stage, we are able to reconstruct a 3D level set function by using the 2D level set functions given by the transversal cuts and the graph information. When the whole scanner data are available, a global reconstruction is proposed in a simple manner, without using the mass transfer problem.

Description: A novel second-order time integration algorithm for solving dynamic problems is presented. To demonstrate the abilities of this formulation, several linear and geometrical nonlinear structures are solved. The outcomes of authors’ technique are compared with the ones obtained by other researchers. The findings not only confirm the improved accuracy of the new scheme but also indicate that the suggested method remains stable when the trapezoidal rule fails to produce a stable solution. Effectively maximizing high-frequency numerical dissipation, without inducing excessive algorithmic damping in the important low-frequency region, is one of the proposed tactic merits. Spurious oscillations are removed, and small numerical dispersion error is achieved, when using this approach.

Description: The present study focuses on evaluating the groundwater quality in parts of the Hail Province of Saudi Arabia. Hail province is the home to the Hail Agricultural Development Company and is dependent entirely on the groundwater resources available from the Saq aquifer for agricultural productivity. Twenty-four groundwater samples from agricultural farms were analyzed for their major ion concentrations. The TDS content of the collected samples ranged from 245.9 to 869.20 mg/l, whereas the EC values were below the maximum permissible limit of 1,400μS/cm prescribed by WHO for drinking water. The cation and anion concentrations were in the following order: \({{\rm Na}^{+} 〉 {\rm Ca}^{2+} 〉 {\rm Mg}_{2}^{+} 〉 {\rm K}^{+}\,{\rm and}\,{\rm HCO}_{3}^{2-} 〉 {\rm Cl}^{-} 〉 {\rm SO}_{4}^{2-} 〉 {\rm NO}_{3}^{2-}}\) . The major groundwater facies identified included the Ca(Mg)–Na(K)–Cl– \({{\rm SO}_{4}-{\rm HCO}_{3}}\) type, Ca(Mg)–Na(K)– \({{\rm HCO}_{3}-{\rm Cl}-{\rm SO}_{4}}\) type and the Na(K)–Ca(Mg)–Cl– \({{\rm SO}_{4}-{\rm HCO}_{3}}\) type. The samples fall in the rock–water interaction zone on the Gibb’s plot. Carbonate weathering, silicate weathering and reverse ion exchange are the major chemical processes which govern the chemistry of the groundwater in the area. The sodium adsorption ratio values for all the samples are below 10 and are excellent for irrigation. In terms of residual sodium carbonate, the values are 〈1.25 and are considered good for irrigation.

Description: The effect of triazole (TR), 3-amino-1,2,4-triazole (ATA) and cetyltrimethylammonium bromide (CTAB) on the inhibition of brass corrosion in simulated cooling water system has been studied using electrochemical measurements, scanning electron microscopy (SEM) observations and energy dispersive X-ray (EDX) analysis. The potentiodynamic polarization study reveals that these inhibitors inhibit both cathodic and anodic reactions, indicating a mixed-type control of inhibition and their inhibition depend on the nitrogen number in their structure. It shows that the ATA is the best inhibitor. The interference between CTAB and TR derivatives against corrosion has been also studied. So, a large passive current plate is observed directly from the corrosion potential in the presence of formulation. In addition, the operational parameters effect on the performance of this formulation is also investigated. It shows that its inhibition efficiency increases with pH, immersion time and the presence of corrosion products and takes its performance by increasing in temperature. The SEM/EDX data confirm that the formulation is a corrosion and scale inhibitor.

Description: Thin ZnS films were prepared by improved spray pyrolysis (ISP) method for precursor (Zn/S) ratios (1:1) to (1:6) in the initial solution. The ISP parameters such as carrier gas flow rate, solution flow rate and substrate temperature were controlled with an accuracy of \({\pm0.25\,{{\rm lpm}},\, \pm1\,{{\rm ml/h}}}\) and \({\pm1\,^{\circ}{{\rm C}}}\) , respectively. The solution was sprayed in a pulse mode. The chemical and physical properties for these thin films were investigated as a function of solution precursor ratio. The films were fairly smooth with satisfactory crystallinity. The films have exhibited a polycrystalline cubic structure. A gradual increase in (S/Zn) atomic ratio from 0.82 to 1.01 with the increase in solution precursor ratio was observed. The properties such as crystal size, texture coefficient, band gap, grain size and electrical resistivity for thin ZnS films showed a gradual improvement with the increase in their (S/Zn) atomic ratio. The behavior of non-stoichiometric (zinc excess) thin films was like n-type extrinsic semiconductors. The thin film (1:6) have the larger crystal size of 5.59 nm, grain size of 72 nm, band gap of 3.634 eV and electrical resistivity of \({6.85\times10^{6} \,\Omega\,{{\rm cm}}}\) . These features of ISP-prepared thin ZnS films make the films more appropriate for optical and photovoltaic applications.

Description: Thiosulfate is generated from various process industries, such as petrochemical, metallurgical, photography processing, pharmaceutical, pigment and dye manufacturing units, etc. Thiosulfate-bearing wastewater is also produced during the anaerobic treatment of wastewater. In the present work, oxidative removal of thiosulfate in the presence of UV light from aqueous solution has been investigated. The effect of thiosulfate concentration, oxygen partial pressure, UV light intensity and air flow rate on the kinetics of thiosulfate removal has been explored, and suitable rate equations were developed for the oxidation processes. 67 % of thiosulfate was removed from the aqueous solution by carrying out aerial oxidation for one hour. Using photooxidation by UV light, 1,200ppm thiosulfate could be oxidized by one hour. Overall reaction by aerial oxidation followed the second-order kinetics, whereas by photooxidation, it followed third-order kinetics.

Description: This paper investigates the sliding wear behaviour of nanoparticle-filled aluminium matrix nano-composites (AMNCs). Two different nano-reinforcements undertaken for this study are SiC and Al 2 O 3 . The percentage reinforcement is also varied from 0.5 to 1.5 wt%. For investigating the wear behaviour, factors such as applied normal load, sliding speed and sliding distance are considered. Also Taguchi design of experimental technique is employed for the study and analysis of sliding wear. Findings showed that nano-SiC particulate-reinforced AMNCs show better wear resistance than nano-Al 2 O 3 -reinforced AMNCs. Also regression and artificial neural network are used to develop a model to predict the wear rate of these composites.

Description: This paper proposes a new iso-parametric tool path generation scheme for trimmed parametric surface based on two discrete parameterization techniques, namely, the Partial Differential Equation method and the newly developed “Boundary Interpolation method”. The efficiency of the scheme is measured in terms of path length and computational time for machining some typical surfaces. The side-steps and forward-steps have been formulated to suit the discrete nature of the surface representation. Conventionally the forward-step is calculated by approximating the cutting curve with osculating circle. Due to this approximation there is a possibility that the tolerance can go beyond given limit. In this paper an improved tolerance constraint method has been presented to keep the tolerance in forward-step under given value by considering the true profile of the cutting curve. Case studies show that the method presented here significantly improves the path profile by maintaining the tolerance limit.

Description: An artificial neural network (ANN) has a wide application field for mathematical problems. Specifically, an ANN is successfully applied to problems that are difficult to solve or do not have any information on their operating techniques. In this article, an ANN was applied to predict the concrete mix composition for steel fiber-reinforced concrete (SFRC). Thus, an ANN model was developed and trained with data collected from literature. These data have SFRC mix compositions, workability measurements of fresh SFRC, compressive strength of SFRCs, and additional information that affects concrete quality. Additionally, the ANN included steel fiber volume fraction in the SFRC and steel fiber properties. With the goal of determining the concrete mix composition, which is cement dosage, amount of water, coarse aggregate content, fine aggregate content, and chemical admixture, an ANN model was developed. The inputs for the ANN were consistency class of SFRC, compressive strength of SFRC, maximum size of aggregate, steel fiber volume fraction, steel fiber length, and diameter. At the end of the study, a feed forward ANN model with six inputs and five outputs was successfully trained and used to produce the correct responses to testing data. Designing SFRC requires more trial mixtures to obtain the desired quality than does conventional concrete. In conclusion, artificial neural networks have a strong potential for predicting concrete mix composition for SFRC such that without trial mixes and loss of time, an SFRC design is possible with the desired workability and mechanical properties.

Description: In this paper, the mechanical and long-term durability behaviour of structural lightweight concrete (LWC) produced with natural lightweight scoria aggregate (LWSA) from the Azores is analysed. Among the properties studied are the compressive and tensile strength, modulus of elasticity, shrinkage, capillary absorption, carbonation and chloride resistance. To this end, a comprehensive experimental study was carried out on different concrete compositions involving common and high-performance structural concrete produced with coarse or coarse and fine volcanic scoria aggregate. Generally, all the mechanical properties worsened with the incorporation of LWSA. It is concluded that the most efficient LWC with LWSA can attain compressive strength up to about 35 MPa. On the other hand, the production of LWC of more than 50 MPa implies a marked reduction in compressive strength for a small reduction in density. The long-term shrinkage increased with the replacement of normal-weight aggregate by LWA and was higher when coarse and fine scoria were used. However, the early age shrinkage can be counterbalanced by the internal curing effect provided by LWSA. The capillary absorption, chloride and carbonation resistance were affected by the high porosity of LWSA. The absence of the outer shell in scoria aggregate and the surface effects during tests can partly explain the lower performance of the LWC. Nevertheless, it is shown that LWC with scoria can be durable, and even for low- to moderate-strength LWC the corrosion induced by carbonation may not be relevant.

Description: Load balancing is an important aspect of Grid resource scheduling. This paper attempts to address the issue of load balancing in a Grid, while maintaining the resource utilization and response time for dynamic and decentralized Grid environment. Here, to its optimum value, a hierarchical load balancing technique has been analysed based on variable threshold value. The load is divided into different categories, such as lightly loaded, under-lightly loaded, overloaded, and normally loaded. A threshold value, which can be found out using load deviation, is responsible for transferring the task and flow of workload information. In order to improve response time and to increase throughput of the Grid, a random policy has been introduced to reduce the resource allocation capacity. The proposed model has been rigorously examined over the GridSim simulator using various parameters, such as response time, resource allocation efficiency, etc. Experimental results prove the superiority of the proposed technique over existing techniques, such as without load balancing, load balancing in enhanced GridSim.

Description: An inverse analysis methodology for determining the parameters of the kinematic law of sheet metals is proposed. The sensitivity of the load versus displacement curves, obtained by reverse shear tests of rectangular and notched specimens, to the kinematic law parameters are studied following a forward analysis, based on finite element simulations. Afterwards, an inverse analysis methodology using a gradient-based Levenberg–Marquardt method is established, by evaluating the relative difference between numerical and experimental results of the shear test, i.e. the load evolution in function of the displacements of the grips. The use of a notched specimen is proposed in order to allow an easy and suitable numerical representation of the boundary conditions of the shear experimental test. This methodology has proven to be appropriate for determining the parameters of the kinematic hardening law.

Description: In this paper, we have investigated the role of dependencies in the design process of mechatronic products. Since explicit modeling of dependencies is largely considered unnecessary today, current languages do not support dependency modeling due to lack of sufficiently expressive language constructs. However, this paper argues that modeling dependencies is important in managing the overall design process. The paper highlights dependencies between two important viewpoints: system design and mechanical design. We have looked closely at how mechanical design (supported by CAD tools) establishes a backbone for the overall design concept. Mechanical design cannot be isolated from other design activities, and the mismanagement of dependencies there leads to problems in other domains too. To illustrate the process, the paper presents an example of modeling dependencies between system hierarchy in OMG SysML™ and the CAD assembly in Solid Edge for a mechatronic design example. The paper presents two different approaches to capturing dependencies—using a general purpose modeling language such as SysML and using a domain specific modeling language (DSML). We argue for using a DSML instead of a general purpose language and provide a DSML called the dependency modeling language (DML). An example DML model for a two degree of freedom robot use case is discussed. The paper also illustrates the complete process of capturing dependencies in a general purpose modeling language like SysML, which served as a good exercise on how to fetch data from a CAD tool and how to represent dependencies inside a significantly different modeling language. Lessons learned from doing this were applied to the construction of DML. Our aim for the future is to reduce the human effort required to build dependency models. Machine learning techniques and automated model transformations are valuable techniques to support this cause.

Description: In this research, influences of two factors in adaptive metamodeling, noise level of samples and initial size of samples, are investigated through comparative study. Two cases of adaptive metamodeling considering the best output point for optimization and the best fit in a specific output parameter space are considered. Three different metamodels, kriging, radial basis function, and multivariate polynomial, are employed in this study. Various test functions are used to create the sample data and evaluate the quality and efficiency of the adaptive metamodeling methods considering influences of noise and initial size of samples. The results of this research provide guidelines for selecting appropriate adaptive metamodeling methods to solve various engineering problems. Effectiveness of the developed guidelines has been demonstrated through case study applications.

Description: In geometric modeling, surface parameterization plays an important role for converting triangle meshes to spline surfaces. Parameterization will introduce distortions. Conventional parameterization methods emphasize on angle-preservation, which may induce huge area distortions and cause large spline fitting errors and trigger numerical instabilities.To overcome this difficulty, this work proposes a novel area-preserving parameterization method, which is based on an optimal mass transport theory and convex geometry. Optimal mass transport mapping is measure-preserving and minimizes the transportation cost. According to Brenier’s theorem, for quadratic distance transportation costs, the optimal mass transport map is the gradient of a convex function. The graph of the convex function is a convex polyhedron with prescribed normal and areas. The existence and the uniqueness of such a polyhedron have been proved by the Minkowski-Alexandrov theorem in convex geometry. This work gives an explicit method to construct such a polyhedron based on the variational principle, and formulates the solution to the optimal transport map as the unique optimum of a convex energy. In practice, the energy optimization can be carried out using Newton’s method, and each iteration constructs a power Voronoi diagram dynamically. We tested the proposal algorithms on 3D surfaces scanned from real life. Experimental results demonstrate the efficiency and efficacy of the proposed variational approach for the optimal transport map.

Description: This paper presents specific procedures for locally refining nodal connectivity of two-dimensional unstructured triangular meshes to improve the quality of the mesh as well as to increase solution accuracy and computational speed. Details of the procedure are outlined along with a discussion of similar work, and an example problem from hydrodynamics is shown.

Description: In recent days, due to the rapid technological advancements, the grid computing has become an important area of research in distributed systems. The load balancing is a very important and complex problem in grid computing. In this paper, we propose a dynamic-distributed load-balancing technique called the improved load balancing on enhanced GridSim with deadline control (IEGDC) for computational grids. Here, we provide a new mechanism of scheduling to enhance the utilization of the resources and to prevent the resource overloading. A selection method for scheduling by considering the state of resource bandwidth and capacity of various resources is presented. We simulate the proposed load-balancing strategy on the GridSim platform. The proposed mechanism on comparison is found to outperform the existing schemes in terms of response time, resubmitted time, finished and unfinished Gridlets. The simulation results are presented.

Description: Cuckoo search-based algorithm is presented for accurate estimation of thermal power plant heat curve (or fuel cost function) parameters. The fuel cost function of power plant reveals some of its economical characteristics that greatly impact many operational practices. Some of influential factors that affect the input–output characteristics of thermal power plants are ambient operating temperature and aging of generating units. Periodical and accurate extraction of fuel cost function characteristics is very important as it directly affects optimal power flow and economic dispatch calculations which in turn enhances the overall operational and economical practices. Convex and non-convex or smooth and non-smooth models that describe the input–output relationship of thermal units are considered including the one that accounts for the valve loading point. The objective is to minimize the total estimation error using cuckoo search algorithm via proper estimation of fuel cost function parameters. The proposed approach relieves some of the mathematical restrictions typically imposed on system modeling since it does not require convexity nor differentiability like in the case of many conventional estimation techniques. Various study cases are considered in this work to test the performance of the method. Results obtained are compared to those computed using competing estimation methods. Comparison results are in favor of Cuckoo search algorithm in all study cases considered.

Description: In this paper, the effect of compacting pressure (150–450 MPa) and copper (Cu) additions (2.5, 5, 7.5 and 10 wt%) on the microstructure and physical properties of NiTi-based shape memory alloys prepared by powder metallurgy is studied. Many characterization techniques were employed in this study such as X-ray diffraction method and scanning electron microscope. The chemical composition of the prepared alloys and microstructure was achieved by using scanning electron microscope equipped with EDS. Differential scanning calorimetric is utilized to measure the transformation temperature of the prepared alloys. Several physical tests such as particle size distribution measurements, density and porosity of green compacted samples and density and porosity after sintering are achieved. XRD test shows that the master sintered samples consist of three phases at room temperature: NiTi monoclinic phase, NiTi cubic phase and Ni 3 Ti hexagonal phase. Furthermore, (CuNi 2 Ti) intermetallic compound is appeared in the samples with 2.5, 5, 7.5 and 10 wt% of Cu. According to the results, it was found that compacting pressure has an essential effect on the decreases in porosity percentage and the results show that (Cu) additions increase porosity percentage in all weight percentages of additives.

Description: In the present study, ultrasonic-assisted Fenton process called sono-Fenton (SF) with low concentration of Fenton reagents was studied via degradation of Direct Blue 71. Influences of seven operational parameters including initial pH (pH 0 ), initial concentration of pollutant ( C 0 ), dose of Fenton reagents ( C Fe and C H2O2 ), ultrasound irradiation frequency (Fr S ), ultrasound irradiation power ( P S ), and treatment time ( t SF ) were investigated on the dye removal efficiency (DR). A combined design of experiments consists of full factorial for t SF , and Taguchi for other six parameters was designed, and experiments were conducted in accordance with the design. The experimental data were collected using a batch reactor equipped with controllable ultrasonic bath. The DR of 0–33.5 mg/l was achieved under experimental conditions. These results approved that the SF process can be a promising approach in terms of colored wastewater treatment. The data were used for model building by Taguchi and artificial neural network. Further statistical tests were applied to exhibit models goodness and to compare models. Finally, optimization process was carried out using Taguchi and genetic algorithm. The optimization procedure causes optimal point which gives an insight of optimal operating condition.

Description: Bottom intakes are frequently used as diversion structures in mountainous regions, because of their simplicity and low costs in comparison with other methods of river diversion. In this study, Flow-3D software is utilized to simulate the flow passing through the racks. Verification tests are performed on the results of numerical method by using the experimental results of Righetti and Lanzoni (J. Hydraul. Eng. 134(1), 15–22, 2008 ). Also, calibration tests and mesh sensitivity are performed on the mathematical model. The diverted discharge in the numerical model is compared with the experimental data, and a good correlation ( R 2  = 0.99) was obtained. Among the different existing turbulence models, the k ɛ RNG model performed best. Afterward, the racks with eight different cross-sectional geometries are simulated by the numerical method. The diverted discharge, velocity and pressure distributions around the racks for each cross section are obtained and compared with each other. Results revealed that lozenge shape is the most effective geometry in flow diversion.

Description: The use of traffic crash data-based methodologies for safety evaluation is inadequate due to the shortcomings such as unavailability and low quality of historical crash data. Other than crash data-based analysis, the use of empirical vehicle maneuvers and/or the development of micro-simulation models in conjunction with surrogate safety measures has been shown to potentially complement traditional safety analysis. However, several previous works found that existing surrogate measures for intersection safety assessment, such as post-encroachment time, time to collision and speed, fail to simultaneously represent conflict probability and severity. Thus, this study proposes a measurement of the crash hazard that considers crash occurrence probability as well as expected severity. By utilizing the change in the total kinetic energy before and after the collision, angle of collision and PET, the proposed conflict index is derived and its implications are discussed. Several video-recorded signalized intersections in Nagoya, Japan, were utilized to extract vehicle trajectories, through which conflict characteristics are estimated. The relationship between the estimated distributions of the proposed index and the records of severe crashes at the corresponding sites are compared. The proposed safety measure is successful in similarly ranking different signalized intersection to the severity of crashes that occurred at each site. The author expects the new safety assessment measure can be useful in assisting policy makers in prioritizing different sites for safety improvements by identifying hazardous locations which currently lack accurate and historical crash data.

Description: The paper presents entropy analysis of MHD generalized Couette fluid flow inside a composite duct. The composite duct is composed of two parallel walls. The upper wall is uniformly moving impermeable plate, whereas the lower wall is porous strata of finite thickness with impermeable bottom. The upper plate and the bottom are asymmetrically convectively cooled. The solutions obtained for the velocity and the temperature are exploited to enumerate entropy generation. The effects of pertinent parameters on the quantities of interest are portrayed graphically and are discussed.

Description: A new CMOS current-mode four-quadrant analog multiplier is presented. The design is based on the square-difference approach using short-channel MOSFETs operating in saturation region and a rectifier. The squaring circuit used is free of error due to carrier mobility reduction and hence an accurate multiplier is achieved. Tanner T-spice is used to confirm the functionality of the proposed design using 0.18μm TCMS CMOS process technology. Simulation results shows that the relative error is 1.8% and –3dB frequency is 230MHz.

Description: The purpose of this study was to conduct seismic hazard analysis for Al-Tajiat and Al-Zawraa stadiums using probabilistic and deterministic approaches. The stadiums of Al-Tajiat and Al-Zawraa are located at latitude of \({33^{\circ}}\) 25ʹ25.80ʺN, longitude of \({44^{\circ}}\) 17ʹ9.28ʺE and latitude of \({33^{\circ}}\) 20ʹ39ʺN, longitude of \({44^{\circ}}\) 22ʹ5.81ʺE, respectively. To assess the seismic hazard, the region was divided into five seismic sources, and the seismic parameters were calculated for each selected seismic source. According to the results obtained from probabilistic seismic hazard analysis, the maximum horizontal accelerations on bedrock for return periods of 75, 475, and 2,475 years are equal to 0.06, 0.12, and 0.21 g, respectively. The result of deterministic seismic hazard assessment proves that the maximum horizontal and vertical acceleration on bedrock are 0.31 and 0.16 g, respectively. In order to analyze the response of structures against calculated acceleration, studies related to response spectrum and design spectrum have been carried out based on statistical analysis of appropriate time histories. The computer program Equivalent linear Earthquake Response Analysis was used to process the selected records and to consider the effect of soil conditions. Design spectrum has also been presented based on the response spectrum of the selected time histories and then was compared with the corresponding ones in UBC 1997 and ISIRI 2800 codes. The comparison shows that the presented design spectrum is more conservative than the results provided by the above codes.

Description: This article addresses the problem of NURBS surface deformation design using surface feature transplantation. To represent the semantic surface feature, a new surface feature representation called normal feature membrane is proposed. In the proposed method, the base surfaces of the source surface with the feature that the designer is highly interested in and the target surface to be deformed are first constructed. This is followed by extracting the normal feature membrane of the source surface. The deformation design is then realized by transplanting the extracted normal feature membrane of the source surface to the base surface of the target surface through four main operations, which are normal feature membrane preprocessing, normal feature membrane transplanting, surface fairing, and boundary feature decaying, respectively. The proposed method provides an easy copy–paste operation of the semantic surface feature for surface deformation of complex product. The examples of the surface feature transplantation for the surface design of automobile bodies are given to verify the validity and feasibility of the proposed method.

Description: Backbreak is one of the undesirable effects of blasting operations causing instability in mine walls, falling down the machinery, improper fragmentation and reduction in efficiency of drilling. Backbreak can be affected by various parameters such as the rock mass properties, blasting geometry and explosive properties. In this study, the application of the artificial neural network (ANN), an adaptive neuro-fuzzy inference system (ANFIS) for prediction of backbreak, was described and compared with the traditional statistical model of multiple regression. The performance of these models was assessed through the root mean square error, correlation coefficient ( R 2 ) and mean absolute percentage error. As a result, it was found that the constructed ANFIS exhibited a higher performance than the ANN and multiple regression for backbreak prediction.

Description: We present a parametric model for generating unit cells with randomly distributed inclusions. The proposed algorithm possesses (1) robustness by yielding unit cells with fiber volume fraction of up to 45 % for aspect ratios as high as 20, (2) computationally efficiency accomplished through a hierarchy of algorithms with increasing computational complexity, and (3) versatility by generating unit cells with different inclusion shapes. A statistical study aimed at determining the effective size of the unit cell is conducted. The method has been applied to various random inclusion microstructure composites, including: (1) two-dimensional chopped tow composites employed in automotive applications, (2) polyurea or polyethene coating consisting of hard and soft domains (segments) employed for energy absorption in military and industrial applications, and (3) fiber framework called fiberform embedded in or free from an amorphous matrix used as heat shield on space crafts to prevent structural damage during reentry into the atmosphere.

Description: Integrating analysis and design models is a complex task due to differences between the models and the architectures of the toolsets used to create them. This complexity is increased with the use of many different tools for specific tasks during an analysis process. In this work various design and analysis models are linked throughout the design lifecycle, allowing them to be moved between packages in a way not currently available. Three technologies named Cellular Modeling, Virtual Topology and Equivalencing are combined to demonstrate how different finite element meshes generated on abstract analysis geometries can be linked to their original geometry. Cellular models allow interfaces between adjacent cells to be extracted and exploited to transfer analysis attributes such as mesh associativity or boundary conditions between equivalent model representations. Virtual Topology descriptions used for geometry clean-up operations are explicitly stored so they can be reused by downstream applications. Establishing the equivalence relationships between models enables analysts to utilize multiple packages for specialist tasks without worrying about compatibility issues or substantial rework.

Description: Grid-based methods for generating all-hex meshes show tremendous promise in automating and speeding up turnaround for computational simulations for solid mechanics. Recognizing some of the inherent weaknesses of grid-based methods, there has been hesitancy in accepting this technology as a viable option for critical FEA. The authors extend previous work on a grid-based method known as sculpt, and evaluate its effectiveness in practice. This study attempts to compare meshes generated with traditional manual pave-and-sweep technologies with those generated with sculpt’s automatic overlay grid method. We use a simple torsion pin analysis to understand both linear-elastic and non-linear elastic–plastic responses with grid-based meshes. We also introduce improvements to the sculpt grid-based procedure, including adaptive optimization-based smoothing, hex-dominant and pillowing to capture curve features as proposed techniques for improving mesh quality. This study demonstrates that in the cases tested, equivalent or superior results were achieved with grid-based meshes when compared to pave-and-sweep meshes.

Description: The modern engineering design process often relies on numerical analysis codes to evaluate candidate designs, a setup which formulates an optimization problem which involves a computationally expensive black-box function. Such problems are often solved using a algorithm in which a metamodel approximates the true objective function and provides predicted objective values at a lower computational cost. The metamodel is trained using an initial sample of vectors, and this implies that the procedure by which the initial sample is generated can impact the overall effectiveness of the optimization search. Approaches for generating the initial sample include the statistically based design of experiments, and the more recent search-driven sampling which generates the sample vectors with a direct-search optimizer. This study compares these two approaches in terms of their overall impact on the optimization search and formulates guidelines in which scenario is each approach preferable. An extensive analysis shows that: (a) the main factor affecting search-driven sampling is the size of the initial sample, and such methods performed better in large initial samples, (b) design of experiments methods tended to perform better in lower sample sizes, (c) generating a sample which is space-filling improved the overall search effectiveness

Description: The sweeping algorithm is one of the most robust techniques to generate hexahedral meshes. During one-to-one sweeping, the most difficult thing is to map an all-quad source surface mesh onto its target surface. In this paper, a harmonic function is used to map meshes from a source surface to its target surface. The result shows that it can generate an all-quad mesh on the target surface with good mesh quality for the convex, concave or multiply-connected surface and thus avoid expensive smoothing algorithm (untangling). Meanwhile, the cage-based deformation method is used to locate interior nodes between the source and target surface during sweeping. Finally, examples are provided and the execution time for our proposed algorithm is discussed.

Description: This paper describes an overset approach that comprised virtual boundary-layer -like near-body grid coupled with an off-body adaptive mesh refinement far-field mesh for viscous fluids simulations. Unlike most a priori grid generation systems for the Reynolds-Averaged Navier–Stokes equations, the strand meshing paradigm is automatic, fast and requires little memory to provide boundary-layer coverage. In addition, the stacks of elements implied by the strands can be used to the simulation’s advantage, where they naturally provide a line direction for semi-implicit solving.

Description: This work recovers an established technique for improving quadrilateral shell element performance in both out-of-plane and in-plane bending cases using a mixed formulation. A four-field variational principle is established and we relate, at the discrete level, the Lagrange multipliers and secondary right Cauchy–Green field with the displacement and rotation fields. This is the main contribution of this work. High coarse-mesh accuracy is observed for distorted meshes and the robustness is shown to be adequate for crack propagation simulations. A consistent director normalization is performed, as an alternative to our recent spherical interpolation. Covariant metric components are deduced and exact linearization of the shell element is performed. Full assessment of the element is accomplished, showing similar performance to more costly approaches such as enhanced assumed strain. Patch test is satisfied ab-initio and benchmarks present very accurate results. Numerical experimentation for geometrically and material nonlinear problems is presented, as well as one fracture example using our recently proposed cracked edge technique.

Description: This paper presents a method to compute accurate bounds on Jacobian determinants of high-order (curvilinear) triangular finite elements. This method can be used to guarantee that a curvilinear triangle is geometrically valid, i.e., its Jacobian determinant is strictly positive everywhere in its reference domain. It also provides an efficient way to measure the quality of triangles. The key feature of the method is to expand the Jacobian determinant using a polynomial basis, built using Bézier functions, that has both properties of boundedness and positivity. Numerical results show the sharpness of our estimates.

Description: In this work, we introduce a new method for generating Lagrangian computational meshes from Eulerian-based data. We focus specifically on shock physics problems that are relevant to Eulerian-based codes that generate volume fraction data on a Cartesian grid. A step-by-step procedure for generating an all-hexahedral mesh is presented. We focus specifically on the challenges of developing a parallel implementation using the message passing interface to ensure a continuous, conformal and good quality hex mesh.

Description: This paper introduces Voronoi squared distance minimization (VSDM), an algorithm that fits a surface to an input mesh. VSDM minimizes an objective function that corresponds to a Voronoi-based approximation of the overall squared distance function between the surface and the input mesh (SDM). This objective function is a generalization of the one minimized by centroidal Voronoi tessellation, and can be minimized by a quasi-Newton solver. VSDM naturally adapts the orientation of the mesh elements to best approximate the input, without estimating any differential quantities. Therefore, it can be applied to triangle soups or surfaces with degenerate triangles, topological noise and sharp features. Applications of fitting quad meshes and polynomial surfaces to input triangular meshes are demonstrated.

Description: Solving partial differential equations using finite element (FE) methods for unstructured meshes that contain billions of elements is computationally a very challenging task. While parallel implementations can deliver a solution in a reasonable amount of time, they suffer from low cache utilization due to unstructured data access patterns. In this work, we reorder the way the mesh vertices and elements are stored in memory using Hilbert space-filling curves to improve cache utilization in FE methods for unstructured meshes. This reordering technique enumerates the mesh elements such that parallel threads access shared vertices at different time intervals, reducing the time wasted waiting to acquire locks guarding atomic regions. Further, when the linear system resulting from the FE analysis is solved using the preconditioned conjugate gradient method, the performance of the block-Jacobi preconditioner also improves, as more nonzeros are present near the stiffness matrix diagonal. Our results show that our reordering reduces the L1 and L2 cache miss-rates in the stiffness matrix assembly step by about 50 and 10 %, respectively, on a single-core processor. We also reduce the number of iterations required to solve the linear system by about 5 %. Overall, our reordering reduces the time to assemble the stiffness matrix and to solve the linear system on a 4-socket, 48-core multi-processor by about 20 %.

Description: The development of parallel algorithms for mesh generation, untangling, and quality improvement is of high importance due to the need for large meshes with millions to billions of elements and the availability of supercomputers with hundreds to thousands of cores. There have been prior efforts in the development of parallel algorithms for mesh generation and local mesh quality improvement in which only one vertex is moved at a time. But for global mesh untangling and for global mesh quality improvement, where all vertices are simultaneously moved, parallel algorithms have not yet been developed. In our earlier work, we developed a serial global mesh optimization algorithm and used it to perform mesh untangling and mesh quality improvement. Our algorithm moved the vertices simultaneously to optimize a log-barrier objective function that was designed to untangle meshes as well as to improve the quality of the worst quality mesh elements. In this paper, we extend our work and develop a parallel log-barrier mesh untangling and mesh quality improvement algorithm for distributed-memory machines. We have used the algorithm with an edge coloring-based algorithm for synchronizing unstructured communication among the processes executing the log-barrier mesh optimization algorithm. The main contribution of this paper is a generic scheme for global mesh optimization, whereby the gradient of the objective function with respect to the position of some of the vertices is communicated among all processes in every iteration. The algorithm was implemented using the OpenMPI 2.0 parallel programming constructs and shows greater strong scaling efficiency compared to an existing parallel mesh quality improvement technique.

Description: We present different linear parametrization techniques for the purpose of surface remeshing: the energy minimizing harmonic map, the convex map, and the least square conformal map. The implementation of those mappings as well as the associated boundary conditions is presented in a unified manner and the issues of triangle flipping and folding that may arise with discrete linear mappings are discussed. We explore the optimality of these parametrizations for surface remeshing by applying several classical 2D meshing algorithms in the parametric space and by comparing the quality of the generated elements. We present various examples that permit to draw guidelines that a user can follow in choosing the best parametrization scheme for a specific topology, geometry, and characteristics of the target output mesh.

Description: We present a new method to construct a trivariate T-spline representation of complex solids for the application of isogeometric analysis. We take a genus-zero solid as a basis of our study, but at the end of the work we explain the way to generalize the results to any genus solids. The proposed technique only demands a surface triangulation of the solid as input data. The key of this method lies in obtaining a volumetric parameterization between the solid and the parametric domain, the unitary cube. To do that, an adaptive tetrahedral mesh of the parametric domain is isomorphically transformed onto the solid by applying a mesh untangling and smoothing procedure. The control points of the trivariate T-spline are calculated by imposing the interpolation conditions on points sited both on the inner and on the surface of the solid. The distribution of the interpolating points is adapted to the singularities of the domain to preserve the features of the surface triangulation. We present some results of the application of isogeometric analysis with T-splines to the resolution of Poisson equation in solids parameterized with this technique.

Description: This paper presents a method for detecting holes during the surface wrapping process which cause surface leaks into the volume parts that shall not be meshed. The method solves a heat-diffusion equation on the background octree mesh, which is generated based on user-defined parameters, and its resolution corresponds to the resolution of the wrapper surface mesh. The heat problem is posed with the constant heat source in the volume, and the holes are detected as regions of high temperature gradients. The method detects both holes with open-boundary edges and semantic holes due to some missing parts. The sensitivity of the method is controlled via user-adjustable parameter which represents the ratio between the volume that shall not be meshed and the area of the hole. In addition, it is demonstrated that the method can be used to correct the orientation of normals in the surface mesh by utilising the property that high temperature is always found inside the volume. The potential of the method is presented on complex engineering examples.

Description: In this paper, a novel approach to automatically sub-divide a complex geometry and apply an efficient mesh is presented. Following the identification and removal of thin-sheet regions from an arbitrary solid using the thick/thin decomposition approach developed by Robinson et al. [ 1 ], the technique here employs shape metrics generated using local sizing measures to identify long-slender regions within the thick body. A series of algorithms automatically partition the thick region into a non-manifold assembly of long-slender and complex sub-regions. A structured anisotropic mesh is applied to the thin-sheet and long-slender bodies, and the remaining complex bodies are filled with unstructured isotropic tetrahedra. The resulting semi-structured mesh possesses significantly fewer degrees of freedom than the equivalent unstructured mesh, demonstrating the effectiveness of the approach. The accuracy of the efficient meshes generated for a complex geometry is verified via a study that compares the results of a modal analysis with the results of an equivalent analysis on a dense tetrahedral mesh.