The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Yiqiang Wang - One of the best experts on this subject based on the ideXlab platform.
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a topology optimization method for geometrically nonlinear structures with meshless analysis and independent Density Field interpolation
Computational Mechanics, 2014Co-Authors: Zhan Kang, Yiqiang WangAbstract:Based on the element-free Galerkin (EFG) method, an analysis-independent Density variable approach is proposed for topology optimization of geometrically nonlinear structures. This method eliminates the mesh distortion problem often encountered in the finite element analysis of large deformations. The topology optimization problem is formulated on the basis of point-wise description of the material Density Field. This Density Field is constructed by a physical meaning-preserving interpolation with the Density values of the design variable points, which can be freely positioned independently of the Field points used in the displacement analysis. An energy criterion of convergence is used to resolve the well-known convergence difficulty, which would be usually encountered in low Density regions, where displacements oscillate severely during the optimization process. Numerical examples are given to demonstrate the effectiveness of the developed approach. It is shown that relatively clear optimal solutions can be achieved, without exhibiting numerical instabilities like the so-called "layering" or "islanding" phenomena even in large deformation cases. This study not only confirms the potential of the EFG method in topology optimization involving large deformations, but also provides a novel topology optimization framework based on element-free discretization of displacement and Density Fields, which can also easily incorporate other meshless analysis methods for specific purposes.
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An adaptive refinement approach for topology optimization based on separated Density Field description
Computers & Structures, 2013Co-Authors: Yiqiang Wang, Zhan Kang, Qizhi HeAbstract:This paper presents an adaptive Density point refinement approach for continuum topology optimization on the basis of an analysis-mesh separated material Density Field description based on nodal design variables. The Shepard interpolants are used to construct a strictly range-restricted Density Field over the design domain with the Density design variables defined on a Density point grid. Since the Density points are defined independent of the finite element mesh, it is easy to refine the Density point grid without remeshing the finite element model. A refinement criterion is given to identify the gray transitional regions to be adaptively refined in the subsequent optimization iterations. With such a refinement scheme, the topology optimization can start from a relatively coarse Density point grid but still yields a desired higher resolution of the structural boundaries in the final design. Because refinements are only performed when and where necessary, this method is able to improve the boundary description quality of the optimal result with much less design variables as compared with the case of global refinement, and therefore can greatly reduce the computational burden involved in the sensitivity analysis and optimization process. Moreover, the percentage of transitional regions in the final solutions can also be reduced. Compared with using a uniformly globally-dense Density point arrangement, this approach can achieve similar optimal designs but with much less computational cost. Numerical examples are given to demonstrate the effectiveness and efficiency of the present approach.
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structural topology optimization based on non local shepard interpolation of Density Field
Computer Methods in Applied Mechanics and Engineering, 2011Co-Authors: Zhan Kang, Yiqiang WangAbstract:Abstract This paper presents a non-local Density interpolation strategy for topology optimization based on nodal design variables. In this method, design variable points can be positioned at any locations in the design domain and may not necessarily coincide with elemental nodes. By using the Shepard family of interpolants, the Density value of any given computational point is interpolated by design variable values within a certain circular influence domain of the point. The employed interpolation scheme has an explicit form and satisfies non-negative and range-restricted properties required by a physically significant Density interpolation. Since the discretizations of the Density Field and the displacement Field are implemented on two independent sets of points, the method is well suited for a topology optimization problem with a design domain containing higher-order elements or non-quadrilateral elements. Moreover, it has the ability to yield mesh-independent solutions if the radius of the influence domain is reasonably specified. Numerical examples demonstrate the validity of the proposed formulation and numerical techniques. It is also confirmed that the method can successfully avoid checkerboard patterns as well as “islanding” phenomenon.
Michał Chodorowski - One of the best experts on this subject based on the ideXlab platform.
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Comparing the redshift-space Density Field with the real-space velocity Field
Monthly Notices of the Royal Astronomical Society, 2000Co-Authors: Michał ChodorowskiAbstract:I derive a non-linear local relation between the redshift-space Density Field and the real-space velocity Field. The relation accounts for the radial character of the redshift distortions and is not restricted to the limit of the distant observer. Direct comparisons between the observed redshift-space Density Fields and the real-space velocity Fields possess all of the advantages of the conventional redshift-space analyses, while at the same time they are free of their disadvantages. In particular, neither the model-dependent reconstruction of the Density Field in real space, nor the reconstruction of the non-linear velocity Field in redshift space is necessary, the latter being questionable because of its vorticity at second order. The non-linear redshift-space velocity Field is irrotational only in the distant observer limit, and that limit is not a good approximation for the shallow catalogues of peculiar velocities currently available. Unlike the conventional redshift-space comparisons, the comparison proposed here does not have to be restricted to the linear regime. Accounting for non-linear effects removes one of the sources of bias in the estimation of β. Moreover, the non-linear effects break the Ω–bias degeneracy plaguing all analyses based on linear theory.
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Comparing the redshift-space Density Field to the real-space velocity Field
Monthly Notices of the Royal Astronomical Society, 2000Co-Authors: Michał ChodorowskiAbstract:I derive a nonlinear local relation between the redshift-space Density Field and the real-space velocity Field. The relation accounts for radial character of redshift distortions, and it is not restricted to the limit of the distant observer. Direct comparisons between the observed redshift-space Density Fields and the real-space velocity Fields possess all of the advantages of the conventional redshift-space analyses, while at the same time they are free of their disadvantages. In particular, neither the model-dependent reconstruction of the Density Field in real space is necessary, nor is the reconstruction of the nonlinear velocity Field in redshift space, questionable because of its vorticity at second order. The nonlinear redshift-space velocity Field is irrotational only in the distant observer limit, and that limit is not a good approximation for shallow catalogs of peculiar velocities currently available. Unlike the conventional redshift-space comparisons, the comparison proposed here does not have to be restricted to the linear regime. Accounting for nonlinear effects removes one of the sources of bias in the estimate of beta. Moreover, the nonlinear effects break the Omega-bias degeneracy plaguing all analyses based on linear theory.
Zhan Kang - One of the best experts on this subject based on the ideXlab platform.
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a topology optimization method for geometrically nonlinear structures with meshless analysis and independent Density Field interpolation
Computational Mechanics, 2014Co-Authors: Zhan Kang, Yiqiang WangAbstract:Based on the element-free Galerkin (EFG) method, an analysis-independent Density variable approach is proposed for topology optimization of geometrically nonlinear structures. This method eliminates the mesh distortion problem often encountered in the finite element analysis of large deformations. The topology optimization problem is formulated on the basis of point-wise description of the material Density Field. This Density Field is constructed by a physical meaning-preserving interpolation with the Density values of the design variable points, which can be freely positioned independently of the Field points used in the displacement analysis. An energy criterion of convergence is used to resolve the well-known convergence difficulty, which would be usually encountered in low Density regions, where displacements oscillate severely during the optimization process. Numerical examples are given to demonstrate the effectiveness of the developed approach. It is shown that relatively clear optimal solutions can be achieved, without exhibiting numerical instabilities like the so-called "layering" or "islanding" phenomena even in large deformation cases. This study not only confirms the potential of the EFG method in topology optimization involving large deformations, but also provides a novel topology optimization framework based on element-free discretization of displacement and Density Fields, which can also easily incorporate other meshless analysis methods for specific purposes.
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An adaptive refinement approach for topology optimization based on separated Density Field description
Computers & Structures, 2013Co-Authors: Yiqiang Wang, Zhan Kang, Qizhi HeAbstract:This paper presents an adaptive Density point refinement approach for continuum topology optimization on the basis of an analysis-mesh separated material Density Field description based on nodal design variables. The Shepard interpolants are used to construct a strictly range-restricted Density Field over the design domain with the Density design variables defined on a Density point grid. Since the Density points are defined independent of the finite element mesh, it is easy to refine the Density point grid without remeshing the finite element model. A refinement criterion is given to identify the gray transitional regions to be adaptively refined in the subsequent optimization iterations. With such a refinement scheme, the topology optimization can start from a relatively coarse Density point grid but still yields a desired higher resolution of the structural boundaries in the final design. Because refinements are only performed when and where necessary, this method is able to improve the boundary description quality of the optimal result with much less design variables as compared with the case of global refinement, and therefore can greatly reduce the computational burden involved in the sensitivity analysis and optimization process. Moreover, the percentage of transitional regions in the final solutions can also be reduced. Compared with using a uniformly globally-dense Density point arrangement, this approach can achieve similar optimal designs but with much less computational cost. Numerical examples are given to demonstrate the effectiveness and efficiency of the present approach.
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structural topology optimization based on non local shepard interpolation of Density Field
Computer Methods in Applied Mechanics and Engineering, 2011Co-Authors: Zhan Kang, Yiqiang WangAbstract:Abstract This paper presents a non-local Density interpolation strategy for topology optimization based on nodal design variables. In this method, design variable points can be positioned at any locations in the design domain and may not necessarily coincide with elemental nodes. By using the Shepard family of interpolants, the Density value of any given computational point is interpolated by design variable values within a certain circular influence domain of the point. The employed interpolation scheme has an explicit form and satisfies non-negative and range-restricted properties required by a physically significant Density interpolation. Since the discretizations of the Density Field and the displacement Field are implemented on two independent sets of points, the method is well suited for a topology optimization problem with a design domain containing higher-order elements or non-quadrilateral elements. Moreover, it has the ability to yield mesh-independent solutions if the radius of the influence domain is reasonably specified. Numerical examples demonstrate the validity of the proposed formulation and numerical techniques. It is also confirmed that the method can successfully avoid checkerboard patterns as well as “islanding” phenomenon.
S De La Torre - One of the best experts on this subject based on the ideXlab platform.
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rapid modelling of the redshift space power spectrum multipoles for a masked Density Field
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: Michael Wilson, J A Peacock, A N Taylor, S De La TorreAbstract:In this work we reformulate the forward modelling of the redshift-space power spectrum multipole moments for a masked Density Field, as encountered in galaxy redshift surveys. Exploiting the symmetries of the redshift-space correlation function, we provide a masked-Field generalisation of the Hankel transform relation between the multipole moments in real and Fourier space. Using this result, we detail how a likelihood analysis requiring computation for a broad range of desired $P(k)$ models may be executed $10^3-10^4$ times faster than with other common approaches, together with significant gains in spectral resolution. We present a concrete application to the complex angular geometry of the VIPERS PDR-1 release and discuss the validity of this technique for finite-angle surveys.
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Rapid modelling of the redshift-space power spectrum multipoles for a masked Density Field
Mon.Not.Roy.Astron.Soc., 2017Co-Authors: M.j. Wilson, J A Peacock, A N Taylor, S De La TorreAbstract:In this work, we reformulate the forward modelling of the redshift-space power spectrum multipole moments for a masked Density Field, as encountered in galaxy redshift surveys. Exploiting the symmetries of the redshift-space correlation function, we provide a masked-Field generalization of the Hankel transform relation between the multipole moments in real and Fourier space. Using this result, we detail how a likelihood analysis requiring computation for a broad range of desired P(k) models may be executed 10^3–10^4 times faster than with other common approaches, together with significant gains in spectral resolution. We present a concrete application to the complex angular geometry of the VIMOS Public Extragalactic Redshift Survey PDR-1 release and discuss the validity of this technique for finite-angle surveys.
Heqizhi - One of the best experts on this subject based on the ideXlab platform.
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An adaptive refinement approach for topology optimization based on separated Density Field description
Computers & Structures, 2013Co-Authors: Wangyiqiang, Kangzhan, HeqizhiAbstract:This paper presents an adaptive Density point refinement approach for continuum topology optimization on the basis of an analysis-mesh separated material Density Field description based on nodal de...