International Journal of Computational Methods

Determination of optimal placements of sensors/actuators in large structures is a difficult job as large number of possible combinations leads to a very high computational time and storage. Therefore, this kind of optimization problem demands a parallel implementation of the optimization schemes. Island model genetic algorithm (GA) being inherently parallel has been used for searching optimal placements of collocated sensors/actuators. Numerical simulations have been done for determination of optimal placements of collocated PZT sensors and actuators in smart fiber reinforced shell structures using island model parallel GA (IMPGA) in conjunction with electro-mechanical finite element analysis with an objective of maximizing the controllability index. It has been observed that the present IMPGA-based formulation (due to its migration scheme) not only makes it possible to determine optimal sensors/actuators locations for large structures but also leads to a better solution at a much reduced and achievable computational time. Results from scalability analysis also show that the efficacy of the present method of using IMPGA for determination of optimal sensors/actuators location based on FEA will be more pronounced when actually used for real life problems requiring large number of sensors and actuators.

Eigenvector analysis can be performed to determine the shapes of the undamped free vibration modes of a system. Eigenvector analysis involves solving the generalized eigenvalue problem, which considers the stiffness and mass matrix of a structure. For a geometric nonlinear study, both parts of the total stiffness matrix are required. As modal analysis depends on the stiffness, the effect of its reduction on the modal shape of vibration of the structure must be determined. Case studies were evaluated using the finite element method, considering and neglecting the geometric portion of the stiffness matrix. Mathematic functions were applied for comparison.

We investigate the convective heat and mass transfer in a magnetohydrodynamic nanofluid flow through a porous medium over a stretching sheet subject to heat generation, thermal radiation, viscous dissipation and chemical reaction effects. We have assumed that the nanoparticle volume fraction at the wall may be actively controlled. Two types of nanofluids, namely Cu-water and Al₂O₃-water are studied. The physical problem is modeled using systems of nonlinear differential equations which have been solved numerically using the spectral relaxation method. Comparing the results with those previously published results in the literature shows excellent agreement. The impact of porosity, heat generation, thermal radiation, magnetic field, viscous dissipation and chemical reaction on the flow field is evaluated and explained.

This paper presents the transient dynamic analysis of micro-cracks of arbitrary shape in two-dimensional, linear piezoelectric fiber reinforced composite materials. Interface cracks between fiber and matrix as well as cracks inside the matrix and fibers are investigated. For this purpose, a symmetric Galerkin time-domain boundary element method in conjunction with a multi-domain technique is developed. The time-domain fundamental solutions for linear piezoelectric materials are applied. The time discretization is performed by a collocation method. An explicit time-stepping scheme is obtained to compute the discrete boundary data including the generalized crack-opening-displacements (CODs). Iterative solution algorithms are implemented to solve the nonlinear semi-permeable electrical crack-face boundary conditions and for a crack-face contact analysis at time-steps when a physically unacceptable crack-face intersection occurs. Several numerical examples are presented to reveal the influences of the micro-cracks, the material combinations and the transient dynamic loading on the intensity factors and the scattered wave fields.

In this paper, numerical simulations of ship motion coupled with LNG tank sloshing in waves are considered. The fully coupled problems are performed by our in-house RANS/DES solver, naoe-FOAM-SJTU. The internal tank sloshing and external wave flow are solved simultaneously. The considered model is a three-dimensional simplified LNG FPSO with two prismatic tanks. The ship motion responses are carried out in beam waves to compare with existing experimental data to validate this solver. The coupling effects between ship motion and sloshing tanks are observed. The anti-rolling characteristics are found, and this kind of characteristic is obvious in low-filling conditions. Different incident wave amplitudes and frequencies are considered. When the incident wave frequency is close to ship motion natural frequency, the ship motion response is strong and an overturning behavior in sloshing tanks is observed. Meanwhile, impact pressures on bulkhead are also discussed. The pressure signal explains the phenomenon in tanks we discussed before.

In the paper, the grain growth of TC4-DT (Damage Tolerance) alloy joint during electron beam welding (EBW) process was simulated by using Cellular Automaton method. In order to consider the effects of the growth of neighborhood cellular on the center cells in the model, the solid fraction and solute distribution algorithms of classical CA model were improved. The growth of equiaxed grains and columnar crystals under uniform and nonuniform temperature fields was simulated successfully by applying the modified model, respectively. The temperature distribution near the fusion line of TC4-DT EBW joint was also calculated by using double ellipsoid heat source model. Then, coupling the CA model with the temperature field, the grain growth process of the cross-section of the welded zone was simulated. The simulation result fits well with experimental ones on the morphology and the size of the columnar crystals.

The analysis of the in-plane free vibration of the circular and annular FG disks by a meshfree boundary-domain integral equation method is presented in this paper. The material properties of the disks are assumed to vary in the radial direction obeying an exponential law. Based on the two-dimensional linear elastic theory, the motion equations of the FG disks are derived by using the static fundamental solutions. Radial integration method as an efficient tool is adopted to treat the domain integrals which are raised due to the material inhomogeneous and inertial effects. The natural frequencies and associate mode shapes are calculated for the FG disks with combinations of free and clamped boundary conditions. Parametric studies are also conducted to study the effects of the material gradients, radius ratios and boundary conditions on the frequency of the FG disks.

The parallel volume integral equation method (PVIEM) is applied for the analysis of two-dimensional elastic wave scattering problems in an unbounded isotropic solid containing various types of multiple multilayered anisotropic inclusions. It should be noted that the volume integral equation method (VIEM) does not require the use of the Green’s function for the anisotropic inclusion — only the Green’s function for the unbounded isotropic matrix is needed. A detailed analysis of the SH wave scattering problem is presented for various types of multiple multilayered orthotropic inclusions. Numerical results are presented for the elastic fields at the interfaces for square and hexagonal packing arrays of various types of multilayered orthotropic inclusions in a broad frequency range of practical interest. Standard parallel programming was used to speed up computation in the VIEM. The PVIEM enables us to investigate the effects of single/multiple scattering, fiber packing type, fiber volume fraction, single/multiple layer(s), multilayer’s shapes and geometry, isotropy/anisotropy, and softness/hardness of various types of multiple multilayered anisotropic inclusions on displacements and stresses at the interfaces of the inclusions and far-field scattering patterns. Also, powerful capabilities of the PVIEM for the analysis of general two-dimensional multiple scattering problems are investigated.

The paper presents principles of the simple method which makes possible approximate calculations of statically indeterminate truss systems in two stages. The two-stage method applies rules of other methods used for calculations of statically determinate trusses. In each of the two stages, there are considered statically determinate trusses, patterns of which are obtained as results of suitable withdrawing of appropriate members from the pattern of the basic statically indeterminate truss. There are presented results of calculations carried out for two cases of load for selected type of plane truss together with comparison of outcomes obtained by means of using appropriate computer software.

This work performs a topology optimization of the interior structure of engine blades in compressors with any given geometry of the desired outer-surface shape that may be determined by CFD and aerodynamic design software for the desired performance for thermal and fluid flows. A lofted compressor airfoil surface from the aerodynamic design was used to create a three-dimensional (3D) solid in SolidWorks. This was converted to an .IGS file that would be imported into HyperMesh® for the meshing and submitted to OptiStruct® for optimization. An optimization process is designed to produce an optimal interior structure, considering both pressure on the outer surface and centrifugal forces produced by rotational movements. The optimized blade becomes hollow in an optimal pattern with minimum materials needed for the pressure loading on outer skin and the distributed centrifugal forces. The final design was compared to the initial design using finite element method (FEM) to confirm that the mass, stress, strain, and displacement were reduced. The mass was reduced by 59.8% and the stresses reduced by a factor of 3.66! These results were validated by conducting a mesh independence study. 3D printers were used to produce the optimized blades in both plastic and metal.

We present a high fidelity numerical simulation technique to analyze the nonlinear behavior of a composite beam under cyclic loading. The analysis is performed by using the in-house software called E-Simulator. A constitutive model for concrete; extended Drucker–Prager model considering the compressive failure and the tensile crack has been employed and the parameters are identified so that compressive and tensile behavior of concrete can be reproduced. The relation between the bending moment and deflection angle of a composite beam has been analyzed and compared with experimental results. Damage propagation and stiffness degradation results of concrete slab are demonstrated.

A recently developed numerical method, multidomain quasilinearization, is applied on a steady laminar, natural convection boundary layer flow of MHD viscous and incompressible fluid from a vertical permeable flat plate with uniform temperature in this paper. Nondimensionless variables are used to transform the governing equations to a system of nondimensional nonlinear partial differential equations. Then the resulting equations are solved numerically by using multidomain quasilinearization method. The numerical results for tangential velocity, transverse velocity, and temperature, skin friction are calculated and shown in various tables and graphs.

The objective of this paper is to study the effect of loosely bonded interface on torsional surface wave propagation in a fiber reinforced composite medium constrained between dry sandy layer and an anisotropic gravitating poroelastic substrate. All the media are assumed to be under initial stress. The dispersion relation on this proposed multilayer ground structure has been derived in closed form under certain boundary conditions, which contain Whittaker function and its derivative, which is further expanded asymptotically, retaining up to only the linear terms. The numerical solution for the limiting case of torsional surface waves is also discussed. As a special case of the problem, when the entire medium is isotropic and one of the upper layer vanishes and removing the initial stress and gravity, the dispersion relation obtained is in agreement with the classical Love type wave equation. The influence of various technical constants, such as sandy parameter, reinforcement parameter, porosity parameter, Biot’s gravity parameter, loosely bonded parameters, initial stress of both the layers and half spaces on the phase velocity of torsional surface wave has been pointed out by means of graphs.

In this paper, an edge-based smoothed finite element method with the discrete shear gap using triangular elements (ES-DSG3) is presented for static, free vibration and sound radiation analyses of plates stiffened by eccentric and concentric stiffeners. In the present model, the ES-DSG3 for the plate element with the isoparametric thick-beam element is employed to formulate stiffened plate structures. The deflections and rotations of the plates and the stiffeners are connected at tying positions. By using Rayleigh integral, sound radiation of stiffened plates subjected to a point load can be obtained. The edge-based gradient smoothing technique is employed to perform the related numerical integrations over the edge-based smoothing domains. Compared with the original DSG3 model, the present ES-DSG3 model is relatively softer as a result of the edge-based gradient smoothing technique. From several numerical examples, it is observed that the ES-DSG3 can produce more accurate numerical solutions than the original DSG3 for stiffened plates.