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  • Artikel  (28.148)
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  • 2015-2019  (28.148)
  • 1980-1984
  • 1970-1974
  • 2018  (28.148)
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  • 1
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    Accurate and Efficient Explicit Approximations of the Colebrook Flow Friction Equation Based on the Wright ω-Function (2018)
    Molecular Diversity Preservation International
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    Publikationsdatum: 2018-12-31
    Beschreibung: The Colebrook equation is a popular model for estimating friction loss coefficients in water and gas pipes. The model is implicit in the unknown flow friction factor, f. To date, the captured flow friction factor, f, can be extracted from the logarithmic form analytically only in the term of the Lambert W-function. The purpose of this study is to find an accurate and computationally efficient solution based on the shifted Lambert W-function also known as the Wright ω-function. The Wright ω-function is more suitable because it overcomes the problem with the overflow error by switching the fast growing term, y=W(ex), of the Lambert W-function to series expansions that further can be easily evaluated in computers without causing overflow run-time errors. Although the Colebrook equation transformed through the Lambert W-function is identical to the original expression in terms of accuracy, a further evaluation of the Lambert W-function can be only approximate. Very accurate explicit approximations of the Colebrook equation that contain only one or two logarithms are shown. The final result is an accurate explicit approximation of the Colebrook equation with a relative error of no more than 0.0096%. The presented approximations are in a form suitable for everyday engineering use, and are both accurate and computationally efficient.
    Digitale ISSN: 2227-7390
    Thema: Mathematik
    Publiziert von Molecular Diversity Preservation International
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
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    Quaternionic Blaschke Group (2018)
    Molecular Diversity Preservation International
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    Publikationsdatum: 2018-12-31
    Beschreibung: In the complex case, the Blaschke group was introduced and studied. It turned out that in the complex case this group plays important role in the construction of analytic wavelets and multiresolution analysis in different analytic function spaces. The extension of the wavelet theory to quaternion variable function spaces would be very beneficial in the solution of many problems in physics. A first step in this direction is to give the quaternionic analogue of the Blaschke group. In this paper we introduce the quaternionic Blaschke group and we study the properties of this group and its subgroups.
    Digitale ISSN: 2227-7390
    Thema: Mathematik
    Publiziert von Molecular Diversity Preservation International
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
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    Parallel Computing Based Dynamic Programming Algorithm of Track-before-Detect (2018)
    Molecular Diversity Preservation International
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    Publikationsdatum: 2018-12-31
    Beschreibung: The conventional dynamic programming-based track-before-detect (DP-TBD) methods are usually intractable in multi-target scenarios. The adjacent targets may interfere with each other, and the computational complexity is increased with the number of targets. In this paper, a DP-TBD method using parallel computing (PC-DP-TBD) is proposed to solve the above problems. The search region of the proposed PC-DP-TBD is divided into several parts according to the possible target movement direction. The energy integration is carried out independently and parallel in each part. This contributes to reducing the computational complexity in each part, since the divided search region is smaller than the whole one. In addition, the target energy can only be integrated adequately in the part in which the search direction matches the target movement. This is beneficial to improve the ability to detect the targets with various movement directions in different parts with different search directions. The solution to the problem of the adjacent targets interfering with each other is discussed. The procedure of the parallel computing in the proposed PC-DP-TBD is presented in detail. Simulations are conducted to verify the superiority of the proposed PC-DP-TBD in terms of detection probability and computational complexity.
    Digitale ISSN: 2073-8994
    Thema: Mathematik
    Publiziert von Molecular Diversity Preservation International
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
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    Match-Mode Autoregressive Method for Moving Source Depth Estimation in Shallow Water Waveguides (2018)
    Hindawi
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    Publikationsdatum: 2018-12-31
    Beschreibung: Source depth estimation is always a problem in underwater acoustic area, because depth estimation is a nonlinear problem. Traditional depth estimation methods use a vertical line array, which has disadvantage of poor mobility due to the size of sensor array. In order to estimate source depth with a horizontal line array, we propose a matched-mode depth estimation method based on autoregressive (AR) wavenumber estimation for a moving source in shallow water waveguides. First, we estimate the mode wavenumbers using the improved AR modal wavenumber spectrum. Second, according to the mode wavenumber estimation, we estimate the mode amplitudes by the wavenumber spectrum, which is obtained by generalized Hankel transform. Finally, we estimate source depth estimation by the peak of source depth function wherein the data mode best matches the replica mode that is calculated using a propagation model. Compared with synthetic aperture beamforming, the proposed method exhibits a better performance in source depth estimation under low signal-to-noise ratio or the small range span. The robustness of the proposed method is illustrated by simulating the performance in mismatched environment.
    Print ISSN: 1024-123X
    Digitale ISSN: 1563-5147
    Thema: Mathematik , Technik allgemein
    Publiziert von Hindawi
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
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    EO Sensor Planning for UAV Engineering Reconnaissance Based on NIIRS and GIQE (2018)
    Hindawi
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    Publikationsdatum: 2018-12-31
    Beschreibung: When unmanned aerial vehicles (UAVs) support the Corps of Engineers in reconnaissance operations, in order to gather visible image information that should meet the mission’s need, we grouped the engineering reconnaissance information interpretation tasks into 10 levels by using the National Imagery Interpretability Rating Scale (NIIRS). The quantitative relationship between the engineering targets, sensor performance, and flight altitude was established through the general image quality equation (GIQE) and the geometrical property of the ground sampled distance (GSD). Through some simulations, the influence of variable factors of the EO sensor imaging quality was analyzed, and the imaging height of the sensor for an engineering reconnaissance scenario was calculated. The results showed that this study could solve the problem of poor image quality caused by the flight altitude not meeting the mission requirements.
    Print ISSN: 1024-123X
    Digitale ISSN: 1563-5147
    Thema: Mathematik , Technik allgemein
    Publiziert von Hindawi
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
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    Joint DOA and Polarization Estimation with Two Parallel Sparse Dipole Arrays (2018)
    Hindawi
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    Publikationsdatum: 2018-12-31
    Beschreibung: Electromagnetic vector sensors (EMVS) have attracted growing attention in recent years. However, the mutual coupling effects in practical EMVS arrays may seriously degrade the parameter estimation performance. In order to solve this problem, a novel array configuration consisting of two parallel sparse dipole arrays is proposed. Based on the spatially rotational invariance property between the two parallel arrays and the interdipole spacing inside each array, highly accurate but ambiguous direction-cosine estimates, coarse direction-of-arrival (DOA) estimates, and polarization parameter estimation can be obtained jointly. The coarse DOA estimates are then employed to disambiguate the phase ambiguities in the fine estimates. Compared with collocated EMVS, the proposed array overcomes the mutual coupling problem. Moreover, the DOA estimation accuracy is promoted due to the sparse array aperture extension. Simulation results demonstrate the effectiveness of the proposed algorithm.
    Print ISSN: 1024-123X
    Digitale ISSN: 1563-5147
    Thema: Mathematik , Technik allgemein
    Publiziert von Hindawi
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
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    Mapping Heterogeneous Elastic Property Distribution of Soft Tissues Using Harmonic Motion Data: A Theoretical Study (2018)
    Hindawi
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    Publikationsdatum: 2018-12-31
    Beschreibung: Characterizing heterogeneous elastic property distribution of soft tissues is of great importance in disease detection. In this paper, we investigate an inverse approach to map the heterogeneous material property distribution of soft solids using harmonic motion data. To examine the feasibility of this approach, a number of numerical examples are presented. We observe that the shear modulus distribution is recovered well using harmonic motion measurements. Compared to the static inverse approach, the proposed dynamic inverse method improves the quality of the recovered shear modulus distribution significantly. We also study the influence of the uncertainty in the driving frequency on the reconstruction results and observe that the influence is not very significant in recovering the shape of the inclusion. The proposed inverse algorithm has potential to be a promising tool to diagnose diseases in clinical medicine.
    Print ISSN: 1024-123X
    Digitale ISSN: 1563-5147
    Thema: Mathematik , Technik allgemein
    Publiziert von Hindawi
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
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    An Efficient Pedestrian Detection Method Based on YOLOv2 (2018)
    Hindawi
    Details
    Publikationsdatum: 2018-12-31
    Beschreibung: In recent years, techniques based on the deep detection model have achieved overwhelming improvements in the accuracy of detection, which makes them being the most adapted for the applications, such as pedestrian detection. However, speed and accuracy are a pair of contradictions that always exist and have long puzzled researchers. How to achieve the good trade-off between them is a problem we must consider while designing the detectors. To this end, we employ the general detector YOLOv2, a state-of-the-art method in the general detection tasks, in the pedestrian detection. Then we modify the network parameters and structures, according to the characteristics of the pedestrians, making this method more suitable for detecting pedestrians. Experimental results in INRIA pedestrian detection dataset show that it has a fairly high detection speed with a small precision gap compared with the state-of-the-art pedestrian detection methods. Furthermore, we add weak semantic segmentation networks after shared convolution layers to illuminate pedestrians and employ a scale-aware structure in our model according to the characteristics of the wide size range in Caltech pedestrian detection dataset, which make great progress under the original improvement.
    Print ISSN: 1024-123X
    Digitale ISSN: 1563-5147
    Thema: Mathematik , Technik allgemein
    Publiziert von Hindawi
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
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    A Stress Approach Model of Moderately Thick, Homogeneous Shells (2018)
    Hindawi
    Details
    Publikationsdatum: 2018-12-31
    Beschreibung: This paper presents the theoretical development of a new model of shells called SAM-H (Stress Approach Model of Homogeneous shells) and adapted for linear elastic shells, from thin to moderately thick ones. The model starts from an original stress polynomial approximation which involves the generalized forces and verifies the 3D equilibrium equations and the stress boundary conditions at the faces of the shell. Hellinger-Reissner functional and Reissner’s variational method are applied to determine the generalized fields and equations. The generalized forces and displacements are the same as those obtained in a classical, moderately thick shell model (CS model). The equilibrium and constitutive equations have some differences from those of a CS model, mainly in consideration of applied stress vectors at the upper and lower faces of the shell and the stiffness matrices. Another feature of the SAM-H model is the inclusion of the Poisson’s effect of out-of-plane normal stresses on in-plane strains. As a first application example to test the accuracy of the model, the case of a pressurized hollow sphere is considered. The analytical results of stresses and displacements of the SAM-H and CS models are compared to those of an exact 3D resolution. In this example, SAM-H model proves to be much more accurate than the CS model and its approximation of the normal out-of-plane stress is very precise. Finally, an implementation of the SAM-H model equations in a finite element software is performed and a case study is analyzed to show the advantages of using the SAM-H model.
    Print ISSN: 1024-123X
    Digitale ISSN: 1563-5147
    Thema: Mathematik , Technik allgemein
    Publiziert von Hindawi
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
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    Shared Mechanism-Based Self-Adaptive Hyperheuristic for Regional Low-Carbon Location-Routing Problem with Time Windows (2018)
    Hindawi
    Details
    Publikationsdatum: 2018-12-31
    Beschreibung: In this paper, we consider a variant of the location-routing problem (LRP), namely, the regional low-carbon LRP with reality constraint conditions (RLCLRPRCC), which is characterized by clients and depots that located in nested zones with different speed limits. The RLCLRPRCC aims at reducing the logistics total cost and carbon emission and improving clients satisfactory by replacing the travel distance/time with fuel consumption and carbon emission costs under considering heterogeneous fleet, simultaneous pickup and delivery, and hard time windows. Aiming at this project, a novel approach is proposed: hyperheuristic (HH), which manipulates the space, consisted of a fixed pool of simple operators such as “shift” and “swap” for directly modifying the space of solutions. In proposed framework of HH, a kind of shared mechanism-based self-adaptive selection strategy and self-adaptive acceptance criterion are developed to improve its performance, accelerate convergence, and improve algorithm accuracy. The results show that the proposed HH effectively solves LRP/LRPSPD/RLCLRPRCC within reasonable computing time and the proposed mathematical model can reduce 2.6% logistics total cost, 27.6% carbon emission/fuel consumption, and 13.6% travel distance. Additionally, several managerial insights are presented for logistics enterprises to plan and design the distribution network by extensively analyzing the effects of various problem parameters such as depot cost and location, clients’ distribution, heterogeneous vehicles, and time windows allowance, on the key performance indicators, including fuel consumption, carbon emissions, operational costs, travel distance, and time.
    Print ISSN: 1024-123X
    Digitale ISSN: 1563-5147
    Thema: Mathematik , Technik allgemein
    Publiziert von Hindawi
    Standort Signatur Erwartet Verfügbarkeit
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