The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform

Kenjiro Terada - One of the best experts on this subject based on the ideXlab platform.

  • Structural topology optimization of vibrating structures with specified Eigenfrequencies and eigenmode shapes
    International Journal for Numerical Methods in Engineering, 2006
    Co-Authors: Yasunori Maeda, Shinji Nishiwaki, Kazuhiro Izui, Masataka Yoshimura, Kazumi Matsui, Kenjiro Terada
    Abstract:

    In vibration optimization problems, Eigenfrequencies are usually maximized in the optimization since resonance phenomena in a mechanical structure must be avoided, and maximizing Eigenfrequencies can provide a high probability of dynamic stability. However, vibrating mechanical structures can provide additional useful dynamic functions or performance if desired Eigenfrequencies and eigenmode shapes in the structures can be implemented. In this research, we propose a new topology optimization method for designing vibrating structures that targets desired Eigenfrequencies and eigenmode shapes. Several numerical examples are presented to confirm that the method presented here can provide optimized vibrating structures applicable to the design of mechanical resonators and actuators.

Changjun Zheng - One of the best experts on this subject based on the ideXlab platform.

  • sensitivity analysis of acoustic Eigenfrequencies by using a boundary element method
    Journal of the Acoustical Society of America, 2021
    Co-Authors: Changjun Zheng, Wenchang Zhao, Haifeng Gao, Yongbin Zhang
    Abstract:

    This paper presents a boundary element-based scheme for the sensitivity analysis of acoustic Eigenfrequencies of both interior and exterior acoustic systems. The nonlinear eigenvalue problem generated by the acoustic boundary element method is first reformulated into a generalized eigenvalue problem of reduced dimension through a contour integral approach. The sensitivity formulations for acoustic Eigenfrequencies are then derived based on an adjoint method that uses both the right and left eigenvectors. The adaptive cross approximation in conjunction with the hierarchical matrices is used to reduce the solution burden of the boundary element systems. The Burton-Miller-type combined formulation is applied to shift the spurious Eigenfrequencies and their sensitivities, and the strategies to identify the spurious results are suggested. Three numerical examples are used to verify the accuracy and applicability of the developed scheme.

  • Fictitious Eigenfrequencies in the BEM for interior acoustic problems
    Engineering Analysis with Boundary Elements, 2019
    Co-Authors: Changjun Zheng, Yongbin Zhang, Chuanzeng Zhang, Haibo Chen
    Abstract:

    Abstract It is widely known that the boundary element method (BEM) without any special treatment suffers from the fictitious eigenfrequency problem for the numerical solutions of exterior acoustic problems. This problem has drawn much attention and been extensively studied over the last several decades. However, this paper is concerned with the existence and influence of the fictitious Eigenfrequencies when using the BEM for the numerical solutions of interior acoustic problems. To this end, an eigenvalue analysis technique is developed for the acoustic BEM. The nonlinear eigenvalue problem caused by the acoustic BEM is converted into an ordinary linear one by using a contour integral method. Therefore, the conversion is fulfilled by solving a series of BEM systems of equations without any special or complicated treatment of the governing equations or the linear systems. Three interior acoustic examples including two with simply connected domains and one with a multiply connected domain are used to reveal the existence and influence of the fictitious Eigenfrequencies. Furthermore, the Burton–Miller formulation with a variable coupling parameter is found to be able to remove such fictitious Eigenfrequencies, and the optimal choice of the coupling parameter is investigated.

  • is the burton miller formulation really free of fictitious Eigenfrequencies
    Engineering Analysis With Boundary Elements, 2015
    Co-Authors: Changjun Zheng, Haibo Chen, Haifeng Gao
    Abstract:

    Abstract This paper is concerned with the fictitious eigenfrequency problem of the boundary integral equation methods when solving exterior acoustic problems. A contour integral method is used to convert the nonlinear eigenproblems caused by the boundary element method into ordinary eigenproblems. Since both real and complex eigenvalues can be extracted by using the contour integral method, it enables us to investigate the fictitious eigenfrequency problem in a new way rather than comparing the accuracy of numerical solutions or the condition numbers of boundary element coefficient matrices. The interior and exterior acoustic fields of a sphere with both Dirichlet and Neumann boundary conditions are taken as numerical examples. The pulsating sphere example is studied and all fictitious Eigenfrequencies corresponding to the related interior problem are observed. The reasons are given for the usual absence of many fictitious Eigenfrequencies in the literature. Fictitious eigenfrequency phenomena of the Kirchhoff–Helmholtz boundary integral equation, its normal derivative formulation and the Burton–Miller formulation are investigated through the eigenvalue analysis. The actual effect of the Burton–Miller formulation on fictitious Eigenfrequencies is revealed and the optimal choice of the coupling parameter is confirmed.

  • Is the Burton–Miller formulation really free of fictitious Eigenfrequencies?
    Engineering Analysis with Boundary Elements, 2015
    Co-Authors: Changjun Zheng, Haibo Chen, Haifeng Gao
    Abstract:

    Abstract This paper is concerned with the fictitious eigenfrequency problem of the boundary integral equation methods when solving exterior acoustic problems. A contour integral method is used to convert the nonlinear eigenproblems caused by the boundary element method into ordinary eigenproblems. Since both real and complex eigenvalues can be extracted by using the contour integral method, it enables us to investigate the fictitious eigenfrequency problem in a new way rather than comparing the accuracy of numerical solutions or the condition numbers of boundary element coefficient matrices. The interior and exterior acoustic fields of a sphere with both Dirichlet and Neumann boundary conditions are taken as numerical examples. The pulsating sphere example is studied and all fictitious Eigenfrequencies corresponding to the related interior problem are observed. The reasons are given for the usual absence of many fictitious Eigenfrequencies in the literature. Fictitious eigenfrequency phenomena of the Kirchhoff–Helmholtz boundary integral equation, its normal derivative formulation and the Burton–Miller formulation are investigated through the eigenvalue analysis. The actual effect of the Burton–Miller formulation on fictitious Eigenfrequencies is revealed and the optimal choice of the coupling parameter is confirmed.

Niels Olhoff - One of the best experts on this subject based on the ideXlab platform.

  • Topological design of freely vibrating continuum structures for maximum values of simple and multiple Eigenfrequencies and frequency gaps
    Structural and Multidisciplinary Optimization, 2007
    Co-Authors: Niels Olhoff
    Abstract:

    A frequent goal of the design of vibrating structures is to avoid resonance of the structure in a given interval for external excitation frequencies. This can be achieved by, e.g., maximizing the fundamental eigenfrequency, an eigenfrequency of higher order, or the gap between two consecutive Eigenfrequencies of given order. This problem is often complicated by the fact that the Eigenfrequencies in question may be multiple, and this is particularly the case in topology optimization. In the present paper, different approaches are considered and discussed for topology optimization involving simple and multiple Eigenfrequencies of linearly elastic structures without damping. The mathematical formulations of these topology optimization problems and several illustrative results are presented.

Niels Leergaard Pedersen - One of the best experts on this subject based on the ideXlab platform.

  • An optimality criterion for shape optimization in eigenfrequency problems
    Structural and Multidisciplinary Optimization, 2005
    Co-Authors: Pauli Pedersen, Niels Leergaard Pedersen
    Abstract:

    For a broad class of static problems an optimality criterion of constant energy density at the designed boundary is known. In the present paper we prove a similar criterion for eigenfrequency problems. This optimality criterion serves as the tool for more basic understanding and for idealized reference cases as well as the basis for recursive procedures. Eigenfrequencies for in-plane vibrations as well as for out-of-plane vibrations of plates are optimized. The focus is on simplicity and multiple Eigenfrequencies are not considered.

Zhaoyan Zhang - One of the best experts on this subject based on the ideXlab platform.

  • interaction between the thyroarytenoid and lateral cricoarytenoid muscles in the control of vocal fold adduction and Eigenfrequencies
    Journal of Biomechanical Engineering-transactions of The Asme, 2014
    Co-Authors: Jun Yin, Zhaoyan Zhang
    Abstract:

    Although it is known vocal fold adduction is achieved through laryngeal muscle activation, it is still unclear how interaction between individual laryngeal muscle activations affects vocal fold adduction and vocal fold stiffness, both of which are important factors determining vocal fold vibration and the resulting voice quality. In this study, a three-dimensional (3D) finite element model was developed to investigate vocal fold adduction and changes in vocal fold Eigenfrequencies due to the interaction between the lateral cricoarytenoid (LCA) and thyroarytenoid (TA) muscles. The results showed that LCA contraction led to a medial and downward rocking motion of the arytenoid cartilage in the coronal plane about the long axis of the cricoid cartilage facet, which adducted the posterior portion of the glottis but had little influence on vocal fold Eigenfrequencies. In contrast, TA activation caused a medial rotation of the vocal folds toward the glottal midline, resulting in adduction of the anterior portion of the glottis and significant increase in vocal fold Eigenfrequencies. This vocal fold-stiffening effect of TA activation also reduced the posterior adductory effect of LCA activation. The implications of the results for phonation control are discussed.

  • The influence of thyroarytenoid and cricothyroid muscle activation on vocal fold stiffness and Eigenfrequencies
    The Journal of the Acoustical Society of America, 2013
    Co-Authors: Jun Yin, Zhaoyan Zhang
    Abstract:

    The influence of the thyroarytenoid (TA) and cricothyroid (CT) muscle activation on vocal fold stiffness and Eigenfrequencies was investigated in a muscularly controlled continuum model of the vocal folds. Unlike the general understanding that vocal fold fundamental frequency was determined by vocal fold tension, this study showed that vocal fold Eigenfrequencies were primarily determined by vocal fold stiffness. This study further showed that, with reference to the resting state of zero strain, vocal fold stiffness in both body and cover layers increased with either vocal fold elongation or shortening. As a result, whether vocal fold Eigenfrequencies increased or decreased with CT/TA activation depended on how the CT/TA interaction influenced vocal fold deformation. For conditions of strong CT activation and thus an elongated vocal fold, increasing TA contraction reduced the degree of vocal fold elongation and thus reduced vocal fold Eigenfrequencies. For conditions of no CT activation and thus a resting or slightly shortened vocal fold, increasing TA contraction increased the degree of vocal fold shortening and thus increased vocal fold Eigenfrequencies. In the transition region of a slightly elongated vocal fold, increasing TA contraction first decreased and then increased vocal fold Eigenfrequencies.