The Experts below are selected from a list of 7566 Experts worldwide ranked by ideXlab platform
Chongqing Kang - One of the best experts on this subject based on the ideXlab platform.
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probabilistic duck curve in high pv penetration power system concept modeling and empirical analysis in china
Applied Energy, 2019Co-Authors: Qingchun Hou, Ning Zhang, Miao Miao, Fei Peng, Chongqing KangAbstract:Abstract The high penetration of photovoltaic (PV) is reshaping the electricity net-load curve and has a significant impact on power system operation and planning. The concept of duck curve is widely used to describe the timing imbalance between peak demand and PV generation. The traditional duck curve is deterministic and only shows a single extreme or typical scenario during a day. Thus, it cannot capture both the probability of that scenario and the uncertainty of PV generation and loads. These weaknesses limit the application of the duck curve on power system planning under high PV penetration. To address this issue, the novel concepts of probabilistic duck curve (PDC) and probabilistic ramp curve (PRC) are proposed to accurately model the uncertainty and variability of electricity net load and ramp under high PV penetration. An efficient method is presented for modeling PDC and PRC using kernel density estimation, copula function, and dependent Discrete Convolution. Several indices are designed to quantify the characteristics of the PDC and PRC. For the application, we demonstrate how the PDC and PRC will benefit flexible resource planning. Finally, an empirical study on the Qinghai provincial power system of China validates the effectiveness of the presented method. The results of PDC and PRC intuitively illustrate that the ramp demand and the valley of net load face considerable uncertainty under high PV penetration. The results of flexible resource planning indicate that retrofitting coal-fired units has remarkable performance on enhancing the power system flexibility in Qinghai. In average, reducing the minimal output of coal-fired units by 1 MW will increase PV accommodation by over 4 MWh each day.
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an efficient approach to power system uncertainty analysis with high dimensional dependencies
IEEE Transactions on Power Systems, 2018Co-Authors: Yi Wang, Ning Zhang, Chongqing Kang, Miao Miao, Rui Shi, Qing XiaAbstract:The integration of high penetration of renewable energy brings greater uncertainties for the operation of future power systems due to its intermittency and lack of predictability. The uncertainties brought by wide scale renewables might have dependencies with each other because their outputs are mainly influenced by weather. However, an analysis of such uncertainties with complex dependencies faces the “curse of dimensionality”. This challenges the power system uncertainty analysis in probabilistic forecasting, power system operation optimization, and power system planning. This paper proposes an efficient approach that is able to handle high-dimensional dependencies. The approach uses the high-dimensional Copula theory and Discrete Convolution method to conduct a high-dimensional dependent Discrete Convolution (DDC) calculation. A recursive algorithm is proposed to decompose the computation of DDC into multiple Convolutions between each pair of stochastic variables so that the “curse of dimensionality” is solved. The computational complexity of the proposed method is linear with respect to the number of dimensions and guarantees computational efficiency. Finally, illustrative examples of power system reserve requirement evaluation and wind power capacity credit assessment analysis are used to verify the effectiveness and superiority of the proposed approach.
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dependent Discrete Convolution based probabilistic load flow for the active distribution system
IEEE Transactions on Sustainable Energy, 2017Co-Authors: Yi Wang, Ning Zhang, Qixin Chen, Jingwei Yang, Chongqing Kang, Junhui HuangAbstract:Active distribution system (ADS) plays a significant role in enabling the integration of distributed generation. The stochastic nature of renewable energy resources injects the complex uncertainties of power flow into ADS. This paper proposes a Discrete Convolution methodology for probabilistic load flow (PLF) of ADS considering correlated uncertainties. First, the uncertainties of load and renewable energy are modeled using the distribution of the corresponding forecasting error, and the correlation is formulated using a Copula function. A novel reactive power-embedded DC power flow model with high accuracy in both branch flow and node voltage is introduced into ADS. Finally, the distribution of power flow is calculated using dependent Discrete Convolution, which is capable of handling nonanalytical probability distribution functions. In addition, a reduced dimension approximation method is proposed to further reduce the computational burden. The proposed PLF algorithm is tested on the IEEE 33-nodes system and 123-nodes system, and the results show that the proposed methodology requires less computation and produces higher accuracy compared with current methods.
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Copula Based Dependent Discrete Convolution for Power System Uncertainty Analysis
IEEE Transactions on Power Systems, 2016Co-Authors: Ning Zhang, Chongqing Kang, Chanan SinghAbstract:Discrete Convolution (DC) is a generally accepted approach for the probabilistic analysis such as reliability assessment and probabilistic load flow. However, it has a strong precondition that the stochastic variables being convolved must be independent, which may not be fully satisfied in all cases. Using copula functions, this letter derives the formulation of DC for dependent variables. The performance of the proposed dependent Discrete Convolution (DDC) is illustrated using reliability assessment involving wind power. The result shows that the DDC inherits the efficient and reliable performance of DC, indicating a promising potential for practical applications.
Qian Wang - One of the best experts on this subject based on the ideXlab platform.
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a new fast method for solving contact plasticity and its application in analyzing elasto plastic partial slip
Mechanics of Materials, 2013Co-Authors: Leon M Keer, Shuangbiao Liu, Qian Wang, Zhanjiang Wang, Xiaoqing Jin, Jian CaoAbstract:Abstract This paper presents a new method of contact plasticity analysis, based on Galerkin vectors, to solve the stresses caused by eigenstrain or plastic strain. The plastic strain region below the contact surface is divided into a number of elementary cuboids, where the plastic strains are assumed to be constant in every cuboidal element. The influence coefficients, relating plastic strains to residual displacements or residual stresses, can be divided into four terms: one due to the plastic strains in the full space, and others due to the image plastic strains in the virtual half space. Each term can be solved quickly and efficiently by using the three-dimensional Discrete Convolution and fast Fourier transform or the three-dimensional combined Discrete Convolution and correlation and fast Fourier transform. This new method is used to analyze the contact plastic residual displacements and residual stresses for several contact cases to reveal its efficiency. Partial slip contact involving an elasto-plastic body is investigated. Results show that the stick–slip behavior is affected by the plastic strains, and the surface stresses exhibit more complex behavior than those from a pure elastic partial slip contact.
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Elastic Fields due to Eigenstrains in a Half-Space
Journal of Applied Mechanics, 2005Co-Authors: Shuangbiao Liu, Qian WangAbstract:Engineering components inevitably encounter various eigenstrains, such as thermal expansion strains, residual strains, and plastic strains. In this paper, a set of formulas for the analytical solutions to cases of uniform eigenstrains in a cuboidal region-influence coefficients, is presented in terms of derivatives of four key integrals. The linear elastic field caused by arbitrarily distributed eigenstrains in a half-space is thus evaluated by the Discrete correlation and fast Fourier transform algorithm, along with the Discrete Convolution and fast Fourier transform algorithm. By taking advantage of both the Convolution and correlation characteristics of the problem, the formulas of influence coefficients and the numerical algorithms are expected to enable efficient and accurate numerical analyses for problems having nonuniform distribution of eigenstrains and for contact problems.
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studying contact stress fields caused by surface tractions with a Discrete Convolution and fast fourier transform algorithm
Journal of Tribology-transactions of The Asme, 2002Co-Authors: Shuangbiao Liu, Qian WangAbstract:The knowledge of contact stresses is critical to the design of a tribological element. It is necessary to keep improving contact models and develop efficient numerical methods for contact studies, particularly for the analysis involving coated bodies with rough surfaces. The fast Fourier Transform technique is likely to play an important role in contact analyses. It has been shown that the accuracy in an algorithm with the fast Fourier Transform is closely related to the Convolution theorem employed. The algorithm of the Discrete Convolution and fast Fourier Transform, named the DC-FFT algorithm includes two routes of problem solving: DC-FFT/Influence coefficients/Green's, function for the cases with known Green's functions and DC-FFT/Influence coefficient/conversion, if frequency response functions are known. This paper explores the method for the accurate conversion for influence coefficients from frequency response functions, further improves the DC- FFT algorithm, and applies this algorithm to analyze the contact stresses in an elastic body under pressure and shear tractions for high efficiency and accuracy. A set of general formulas of the frequency response function for the elastic field is derived and verified. Application examples are presented and discussed.
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a versatile method of Discrete Convolution and fft dc fft for contact analyses
Wear, 2000Co-Authors: Shuangbiao Liu, Qian Wang, Geng LiuAbstract:The fast Fourier transform (FFT) technology has been introduced into the process of contact analyses. However, a problem may occur at the borders of the domain due to a periodic error involved. In order to obtain reasonable results, an expedient treatment requires a computational physical domain much larger than the target domain at the cost of calculation efficiency. This paper studies the source of the error and investigates the methods that can help avoid this error and improve the efficiency. Discrete Convolution and FFT (DC-FFT) is first adopted instead of the method of continuous Convolution and Fourier transform for the contact problems. A few approaches based on the DC-FFT method are presented and numerical results are compared.
Jane Q Wang - One of the best experts on this subject based on the ideXlab platform.
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Discrete Convolution and fft modified with double influence coefficient superpositions dcss fft for contact of nominally flat heterogeneous materials involving elastoplasticity
Computational Mechanics, 2021Co-Authors: Jane Q Wang, Linlin Sun, Ning Zhao, Mengqi ZhangAbstract:The contact of nominally flat surfaces can be treated as a bilateral periodic contact problem considering the stochastic surface similarity to the asperity distribution in a representative region. This similarity treatment method can be extended to material inhomogeneities. A novel numerical model for simulating the elastoplastic contact between nominally flat surfaces of materials containing inhomogeneities or coatings is developed via extending the concept of the Discrete Convolution and FFT (DC–FFT) algorithm with double superpositions of influence coefficients, which is named the DCSS–FFT algorithm. Several cases are analyzed with this new algorithm to examine its convenience, efficiency, and accuracy in dealing with complicated nominally flat–flat contact problems. The effects of surface roughness and material inhomogeneity are explored, and the mechanisms of contact surface failure are discussed.
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mixed elastohydrodynamic lubrication model for finite roller coated half space interfaces
Tribology International, 2019Co-Authors: Dong Zhu, Jane Q WangAbstract:Abstract This paper presents a mixed elastohydrodynamic lubrication (EHL) model for finite roller-coated half space interfaces. The model is built with the unified mixed lubrication approach and the influence coefficients (ICs) relating the pressure on a contact surface to surface deformations and subsurface stresses, converted from the frequency response functions (FRFs). The elastic deformation is solved with the Discrete Convolution and fast Fourier transform (DC-FFT) algorithm. This model is used to explore the EHL performance of rollers subjected to a wide range of operating conditions. A parameters study is conducted to reveal the effects of coatings, macro geometry, and surface roughness on the lubrication of rollers.
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an efficient model for the frictional contact between two multiferroic bodies
International Journal of Solids and Structures, 2018Co-Authors: Jane Q Wang, Zhanjiang Wang, Xin Zhang, Huoming ShenAbstract:Abstract This paper presents a semi-analytical model (SAM) for three-dimensional frictional magnetoelectroelastic (MEE) contact of two multiferroic bodies, together with a set of effective solution methods. The frequency response functions (FRFs) for the MEE fields in a multiferroic half-space are analytically derived with respect to a unit concentrated normal force, a unit concentrated tangential force, a unit electric charge, and/or a unit magnetic charge, which are then converted into the results of continuous Fourier transforms of the influence coefficients (ICs), followed by the Discrete Fourier transforms with a proper aliasing treatment. The conjugate gradient method (CGM) is used to obtain the unknown distributed pressure. Furthermore, the Discrete Convolution-fast Fourier transform (DC-FFT) algorithm is implemented to calculate the in-plane electric/magnetic potentials and subsurface stresses. The model is implemented to analyze the frictional sliding contact between a half-space and a sphere, and to study the coupled effects of surface electric/magnetic charges and friction on contact behaviors, including pressure, stresses, and electric/magnetic potentials. A sensitivity analysis is also conducted to evaluate the influences of friction and material properties on the contact-induced multifield coupling behaviors. A number of case studies are committed, and the results indicate that electric/magnetic charge densities and the friction coefficient strongly influence the contact pressure, stress, and electric potential.
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fast fourier transform based numerical methods for elasto plastic contacts of nominally flat surfaces
Journal of Applied Mechanics, 2008Co-Authors: Wei Chen, Shuangbiao Liu, Jane Q WangAbstract:This paper presents a three-dimensional numerical elasto-plastic model for the contact of nominally flat surfaces based on the periodic expandability of surface topography. This model is built on two algorithms: the continuous Convolution and Fourier transform (CC-FT) and Discrete Convolution and fast Fourier transform (DC-FFT), modified with duplicated padding. This model considers the effect of asperity interactions and gives a detailed description of subsurface stress and strain fields caused by the contact of elasto-plastic solids with rough surfaces. Formulas of the frequency response functions (FRF) for elastic/plastic stresses and residual displacement are given in this paper. The model is verified by comparing the numerical results to several analytical solutions. The model is utilized to simulate the contacts involving a two-dimensional wavy surface and an engineering rough surface in order to examine its capability of evaluating the elasto-plastic contact behaviors of nominally flat surfaces.
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contact analyses for bodies with frictional heating and plastic behavior
Journal of Tribology-transactions of The Asme, 2005Co-Authors: Vincent Boucly, Jane Q Wang, Daniel Nelias, Leon M KeerAbstract:The stress field within machine components is an important indicator for contact failures. Since both thermal stresses due to frictional heating and plasticity are significant in engineering application, it is critical to predict the total stress field. In this work, the steady-state thermal effect is considered and a thermo-elastic-plastic contact model is developed. The model is applicable for rolling and/or sliding contact problem, as far as small equivalent plastic strain hypothesis is respected. Influence coefficients for surface normal displacement, temperature, and strain and stress tensors are used with the Discrete Convolution and fast Fourier transform algorithm. The single-loop conjugate gradient iteration scheme is also applied to achieve fast convergence speed. Simulations are presented for several academic examples ranging from elastic to thermo-elastic-plastic. The thermo-elastic-plastic analyses show that the heat factor in a contact situation has significant effect not only on the critical Hertzian pressure and on the pressure distribution, but also on the magnitude and depth of the maximum von Mises stress during loading and the residual ones found after unloading.
Ning Zhang - One of the best experts on this subject based on the ideXlab platform.
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probabilistic duck curve in high pv penetration power system concept modeling and empirical analysis in china
Applied Energy, 2019Co-Authors: Qingchun Hou, Ning Zhang, Miao Miao, Fei Peng, Chongqing KangAbstract:Abstract The high penetration of photovoltaic (PV) is reshaping the electricity net-load curve and has a significant impact on power system operation and planning. The concept of duck curve is widely used to describe the timing imbalance between peak demand and PV generation. The traditional duck curve is deterministic and only shows a single extreme or typical scenario during a day. Thus, it cannot capture both the probability of that scenario and the uncertainty of PV generation and loads. These weaknesses limit the application of the duck curve on power system planning under high PV penetration. To address this issue, the novel concepts of probabilistic duck curve (PDC) and probabilistic ramp curve (PRC) are proposed to accurately model the uncertainty and variability of electricity net load and ramp under high PV penetration. An efficient method is presented for modeling PDC and PRC using kernel density estimation, copula function, and dependent Discrete Convolution. Several indices are designed to quantify the characteristics of the PDC and PRC. For the application, we demonstrate how the PDC and PRC will benefit flexible resource planning. Finally, an empirical study on the Qinghai provincial power system of China validates the effectiveness of the presented method. The results of PDC and PRC intuitively illustrate that the ramp demand and the valley of net load face considerable uncertainty under high PV penetration. The results of flexible resource planning indicate that retrofitting coal-fired units has remarkable performance on enhancing the power system flexibility in Qinghai. In average, reducing the minimal output of coal-fired units by 1 MW will increase PV accommodation by over 4 MWh each day.
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an efficient approach to power system uncertainty analysis with high dimensional dependencies
IEEE Transactions on Power Systems, 2018Co-Authors: Yi Wang, Ning Zhang, Chongqing Kang, Miao Miao, Rui Shi, Qing XiaAbstract:The integration of high penetration of renewable energy brings greater uncertainties for the operation of future power systems due to its intermittency and lack of predictability. The uncertainties brought by wide scale renewables might have dependencies with each other because their outputs are mainly influenced by weather. However, an analysis of such uncertainties with complex dependencies faces the “curse of dimensionality”. This challenges the power system uncertainty analysis in probabilistic forecasting, power system operation optimization, and power system planning. This paper proposes an efficient approach that is able to handle high-dimensional dependencies. The approach uses the high-dimensional Copula theory and Discrete Convolution method to conduct a high-dimensional dependent Discrete Convolution (DDC) calculation. A recursive algorithm is proposed to decompose the computation of DDC into multiple Convolutions between each pair of stochastic variables so that the “curse of dimensionality” is solved. The computational complexity of the proposed method is linear with respect to the number of dimensions and guarantees computational efficiency. Finally, illustrative examples of power system reserve requirement evaluation and wind power capacity credit assessment analysis are used to verify the effectiveness and superiority of the proposed approach.
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dependent Discrete Convolution based probabilistic load flow for the active distribution system
IEEE Transactions on Sustainable Energy, 2017Co-Authors: Yi Wang, Ning Zhang, Qixin Chen, Jingwei Yang, Chongqing Kang, Junhui HuangAbstract:Active distribution system (ADS) plays a significant role in enabling the integration of distributed generation. The stochastic nature of renewable energy resources injects the complex uncertainties of power flow into ADS. This paper proposes a Discrete Convolution methodology for probabilistic load flow (PLF) of ADS considering correlated uncertainties. First, the uncertainties of load and renewable energy are modeled using the distribution of the corresponding forecasting error, and the correlation is formulated using a Copula function. A novel reactive power-embedded DC power flow model with high accuracy in both branch flow and node voltage is introduced into ADS. Finally, the distribution of power flow is calculated using dependent Discrete Convolution, which is capable of handling nonanalytical probability distribution functions. In addition, a reduced dimension approximation method is proposed to further reduce the computational burden. The proposed PLF algorithm is tested on the IEEE 33-nodes system and 123-nodes system, and the results show that the proposed methodology requires less computation and produces higher accuracy compared with current methods.
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Copula Based Dependent Discrete Convolution for Power System Uncertainty Analysis
IEEE Transactions on Power Systems, 2016Co-Authors: Ning Zhang, Chongqing Kang, Chanan SinghAbstract:Discrete Convolution (DC) is a generally accepted approach for the probabilistic analysis such as reliability assessment and probabilistic load flow. However, it has a strong precondition that the stochastic variables being convolved must be independent, which may not be fully satisfied in all cases. Using copula functions, this letter derives the formulation of DC for dependent variables. The performance of the proposed dependent Discrete Convolution (DDC) is illustrated using reliability assessment involving wind power. The result shows that the DDC inherits the efficient and reliable performance of DC, indicating a promising potential for practical applications.
Shuangbiao Liu - One of the best experts on this subject based on the ideXlab platform.
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Discrete Convolution and FFT method with summation of influence coefficients (DCS-FFT) for three-dimensional contact of inhomogeneous materials
Computational Mechanics, 2020Co-Authors: Linlin Sun, Q. Jane Wang, Leon M Keer, Shuangbiao Liu, Mengqi Zhang, Ning Zhao, Wei ChenAbstract:Certain contact problems must be treated as three-dimensional (3D) axial periodic problems, such as the contact of cylinders with rough surfaces and/or inhomogeneities in the materials, whose structural features in contact are confined in a finite domain in one direction but extended infinitely in the other direction. A novel numerical model for simulating the contact of machined cylindrical components containing inhomogeneities is developed via extending the concept of the 3D line-contact fast Fourier transform (FFT) algorithms. Due to the stochastic similarity of asperity and inhomogeneity distributions in the length direction, the cylinder is divided into N segments in the length direction while taking the roughness and inhomogeneities in one of these segments as representatives. The periodic Convolution and FFT is used in the length direction, together with superposing the influence coefficients (ICs) of the N segments, while the Discrete (circular) Convolution and fast Fourier transformation (DC–FFT) is used in the non-periodic direction; this is named the DCS–FFT algorithm. The accuracy of the DCS–FFT algorithm is examined by the comparison of the numerical results for a degenerated cylindrical contact with the corresponding analytical solution, and its efficiency is evaluated through the comparison of its execution speed with that of two other FFT-based algorithms. The developed method is implemented to study the influence of inhomogeneities on subsurface stress distributions with/without the periodic length direction extension and superposition of inhomogeneity ICs. A criterion is provided to decide whether the DCS procedure is needed for the contact analysis of inhomogeneity-containing cylinders.
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a new fast method for solving contact plasticity and its application in analyzing elasto plastic partial slip
Mechanics of Materials, 2013Co-Authors: Leon M Keer, Shuangbiao Liu, Qian Wang, Zhanjiang Wang, Xiaoqing Jin, Jian CaoAbstract:Abstract This paper presents a new method of contact plasticity analysis, based on Galerkin vectors, to solve the stresses caused by eigenstrain or plastic strain. The plastic strain region below the contact surface is divided into a number of elementary cuboids, where the plastic strains are assumed to be constant in every cuboidal element. The influence coefficients, relating plastic strains to residual displacements or residual stresses, can be divided into four terms: one due to the plastic strains in the full space, and others due to the image plastic strains in the virtual half space. Each term can be solved quickly and efficiently by using the three-dimensional Discrete Convolution and fast Fourier transform or the three-dimensional combined Discrete Convolution and correlation and fast Fourier transform. This new method is used to analyze the contact plastic residual displacements and residual stresses for several contact cases to reveal its efficiency. Partial slip contact involving an elasto-plastic body is investigated. Results show that the stick–slip behavior is affected by the plastic strains, and the surface stresses exhibit more complex behavior than those from a pure elastic partial slip contact.
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fast fourier transform based numerical methods for elasto plastic contacts of nominally flat surfaces
Journal of Applied Mechanics, 2008Co-Authors: Wei Chen, Shuangbiao Liu, Jane Q WangAbstract:This paper presents a three-dimensional numerical elasto-plastic model for the contact of nominally flat surfaces based on the periodic expandability of surface topography. This model is built on two algorithms: the continuous Convolution and Fourier transform (CC-FT) and Discrete Convolution and fast Fourier transform (DC-FFT), modified with duplicated padding. This model considers the effect of asperity interactions and gives a detailed description of subsurface stress and strain fields caused by the contact of elasto-plastic solids with rough surfaces. Formulas of the frequency response functions (FRF) for elastic/plastic stresses and residual displacement are given in this paper. The model is verified by comparing the numerical results to several analytical solutions. The model is utilized to simulate the contacts involving a two-dimensional wavy surface and an engineering rough surface in order to examine its capability of evaluating the elasto-plastic contact behaviors of nominally flat surfaces.
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Elastic Fields due to Eigenstrains in a Half-Space
Journal of Applied Mechanics, 2005Co-Authors: Shuangbiao Liu, Qian WangAbstract:Engineering components inevitably encounter various eigenstrains, such as thermal expansion strains, residual strains, and plastic strains. In this paper, a set of formulas for the analytical solutions to cases of uniform eigenstrains in a cuboidal region-influence coefficients, is presented in terms of derivatives of four key integrals. The linear elastic field caused by arbitrarily distributed eigenstrains in a half-space is thus evaluated by the Discrete correlation and fast Fourier transform algorithm, along with the Discrete Convolution and fast Fourier transform algorithm. By taking advantage of both the Convolution and correlation characteristics of the problem, the formulas of influence coefficients and the numerical algorithms are expected to enable efficient and accurate numerical analyses for problems having nonuniform distribution of eigenstrains and for contact problems.
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studying contact stress fields caused by surface tractions with a Discrete Convolution and fast fourier transform algorithm
Journal of Tribology-transactions of The Asme, 2002Co-Authors: Shuangbiao Liu, Qian WangAbstract:The knowledge of contact stresses is critical to the design of a tribological element. It is necessary to keep improving contact models and develop efficient numerical methods for contact studies, particularly for the analysis involving coated bodies with rough surfaces. The fast Fourier Transform technique is likely to play an important role in contact analyses. It has been shown that the accuracy in an algorithm with the fast Fourier Transform is closely related to the Convolution theorem employed. The algorithm of the Discrete Convolution and fast Fourier Transform, named the DC-FFT algorithm includes two routes of problem solving: DC-FFT/Influence coefficients/Green's, function for the cases with known Green's functions and DC-FFT/Influence coefficient/conversion, if frequency response functions are known. This paper explores the method for the accurate conversion for influence coefficients from frequency response functions, further improves the DC- FFT algorithm, and applies this algorithm to analyze the contact stresses in an elastic body under pressure and shear tractions for high efficiency and accuracy. A set of general formulas of the frequency response function for the elastic field is derived and verified. Application examples are presented and discussed.