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• Open Access

ARTICLE

### An Inverse Problem in Estimating Simultaneously the Time-Dependent Applied Force and Moment of an Euler-Bernoulli Beam

CMES-Computer Modeling in Engineering & Sciences, Vol.21, No.3, pp. 239-254, 2007, DOI:10.3970/cmes.2007.021.239

Abstract An inverse forced vibration problem, based on the Conjugate Gradient Method (CGM), (or the iterative regularization method), is examined in this study to estimate simultaneously the unknown time-dependent applied force and moment for an Euler-Bernoulli beam by utilizing the simulated beam displacement measurements. The accuracy of this inverse problem is examined by using the simulated exact and inexact displacement measurements. The numerical experiments are performed to test the validity of the present algorithm by using different types of applied force and moment, sensor locations and measurement errors. Results show that excellent estimations on the applied force and moment can be… More >

• Open Access

ARTICLE

### On Hole Nucleation in Topology Optimization Using the Level Set Methods

CMES-Computer Modeling in Engineering & Sciences, Vol.21, No.3, pp. 219-238, 2007, DOI:10.3970/cmes.2007.021.219

Abstract Hole nucleation is an important issue not yet fully addressed in structural topology optimization using the level set methods. In this paper, a consistent and robust nucleation method is proposed to overcome the inconsistencies in the existing implementations and to allow for smooth hole nucleation in the conventional shape derivatives-based level set methods to avoid getting stuck at a premature local optimum. The extension velocity field is constructed to be consistent with the mutual energy density and favorable for hole nucleation. A negative extension velocity driven nucleation mechanism is established due to the physically meaningful driving force. An extension velocity… More >

• Open Access

ARTICLE

### Analytical Investigation of Depth Non-homogeneity Effect on the Dynamic Stiffness of Shallow Foundations

CMES-Computer Modeling in Engineering & Sciences, Vol.21, No.3, pp. 209-218, 2007, DOI:10.3970/cmes.2007.021.209

Abstract The vertical response of a rigid circular foundations resting on a continuously non-homogenous half space is studied analytically. The half space is considered as a liner-elastic media with a shear modulus increasing continuously with depth. The system of governing differential equations, based on the mentioned assumption, consist of two partial differential equations, is converted to ordinary equations' system by employing Hankel Integral transform. Using the method of extended power series (Frobenius Method) led to the general solution for the latter system. The mixed boundary problem is solved by introduction of functional expansion for the stress distribution under the foundation using… More >

• Open Access

ARTICLE

### Asymptotic Analysis for the Coupled Wavenumbers in an Infinite Fluid-Filled Flexible Cylindrical Shell: The Axisymmetric Mode

CMES-Computer Modeling in Engineering & Sciences, Vol.21, No.3, pp. 193-208, 2007, DOI:10.3970/cmes.2007.021.193

Abstract The coupled wavenumbers of a fluid-filled flexible cylindrical shell vibrating in the axisymmetric mode are studied. The coupled dispersion equation of the system is rewritten in the form of the uncoupled dispersion equation of the structure and the acoustic fluid, with an added fluid-loading term involving a parameter$\epsilon$ due to the coupling. Using the smallness of Poisson's ratio$(\nu )$, a double-asymptotic expansion involving$\epsilon$ and$\nu ^2$ is substituted in this equation. Analytical expressions are derived for the coupled wavenumbers (for large and small values of$\epsilon$). Different asymptotic expansions are used for different frequency ranges with continuous transitions occurring between them. The… More >

• Open Access

ARTICLE

### Geometrically Nonlinear Analysis of Reissner-Mindlin Plate by Meshless Computation

CMES-Computer Modeling in Engineering & Sciences, Vol.21, No.3, pp. 177-192, 2007, DOI:10.3970/cmes.2007.021.177

Abstract In this paper, we perform a geometrically nonlinear analysis of Reissner-Mindlin plate by using a meshless collocation method. The use of the smooth radial basis functions (RBFs) gives an advantage to evaluate higher order derivatives of the solution at no cost on extra-interpolation. The computational cost is low and requires neither the connectivity of mesh in the domain/boundary nor integrations of fundamental/particular solutions. The coupled nonlinear terms in the equilibrium equations for both the plane stress and plate bending problems are treated as body forces. Two load increment schemes are developed to solve the nonlinear differential equations. Numerical verifications are… More >

• Open Access

ARTICLE

### Acoustic Scattering in Prolate Spheroidal Geometry via Vekua Tranformation -- Theory and Numerical Results

CMES-Computer Modeling in Engineering & Sciences, Vol.21, No.2, pp. 157-176, 2007, DOI:10.3970/cmes.2007.021.157

Abstract A new complete set of scattering eigensolutions of Helmholtz equation in spheroidal geometry is constructed in this paper. It is based on the extension to exterior boundary value problems of the well known Vekua transformation pair, which connects the kernels of Laplace and Helmholtz operators. The derivation of this set is purely analytic. It avoids the implication of the spheroidal wave functions along with their accompanying numerical deficiencies. Using this novel set of eigensolutions, we solve the acoustic scattering problem from a soft acoustic spheroidal scatterer, by expanding the scattered field in terms of it. Two approaches concerning the determination… More >

• Open Access

ARTICLE

### Wind Set-down Relaxation

CMES-Computer Modeling in Engineering & Sciences, Vol.21, No.2, pp. 149-156, 2007, DOI:10.3970/cmes.2007.021.149

Abstract We developed analytical solutions to the wind set-down and the wind set-down relaxation problems. The response of the ocean to the wind blowing over a long-narrow and linearly sloping shallow basin is referred to as wind set-down. The shoreline exhibits oscillatory behavior when the wind calms down and the resulting problem is referred to as wind set-down relaxation. We use an existing hodograph-type transformation that was introduced to solve the nonlinear shallow-water wave equations analytically for long wave propagation and obtain an explicit-transform analytical solution for wind set-down. For the wind set-down relaxation, the nonlinear shallow-water wave equations are solved… More >

• Open Access

ARTICLE

### Genetic Programming Metamodel for Rotating Beams

CMES-Computer Modeling in Engineering & Sciences, Vol.21, No.2, pp. 133-148, 2007, DOI:10.3970/cmes.2007.021.133

Abstract This paper investigates the use of Genetic Programming (GP) to create an approximate model for the non-linear relationship between flexural stiffness, length, mass per unit length and rotation speed associated with rotating beams and their natural frequencies. GP, a relatively new form of artificial intelligence, is derived from the Darwinian concept of evolution and genetics and it creates computer programs to solve problems by manipulating their tree structures. GP predicts the size and structural complexity of the empirical model by minimizing the mean square error at the specified points of input-output relationship dataset. This dataset is generated using a finite… More >

• Open Access

ARTICLE

### Slow Viscous Migration of a Conducting Solid Particle under the Action of Uniform Ambient Electric and Magnetic Fields

CMES-Computer Modeling in Engineering & Sciences, Vol.21, No.2, pp. 105-132, 2007, DOI:10.3970/cmes.2007.021.105

Abstract We examine the low-Reynolds-number migration of a conducting and arbitrarily-shaped solid particle freely immersed in a metal liquid of different conductivity when subject to uniform ambient electric and magnetic fields. The boundary formulation established elsewhere for an insulating particle is extended and the incurred particle's rigid-body motion is then obtained by determinating a very few surface quantities on the particle's surface. The behavior of either oblate or prolate conducting spheroids is analytically investigated and the poposed procedure for the challenging case of other non-trivial geometries is implemented and benchmarked against those solutions. The numerical implementation makes it possible to obtain… More >

• Open Access

ARTICLE

### A New Local Contact Search Method Using a Multi-Layer Neural Network

CMES-Computer Modeling in Engineering & Sciences, Vol.21, No.2, pp. 93-104, 2007, DOI:10.3970/cmes.2007.021.093

Abstract This paper describes a new local contact search method using a multi-layer neural network and its application to smoothed contact surface consisting of Gregory patches. A contact search process consists of two phases: a global search phase for finding the nearest node-segment pair and a local search phase for finding an exact local coordinate of the contact point within the segment. In the present method, the multi-layer neural network is utilized in the latter phase. The fundamental formulation of the proposed local contact search method is described in detail, and it is applied to smoothed contact surfaces consisting of Gregory… More >

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