International Journal of Computational Methods

In this paper, a finite element model was built using ANSYS/LS-DYNA to study the effect of strain rate on the dynamic out-of-plane plateau stress of aluminum honeycombs under constant velocity impact. The strain rates vary from 10² to 10⁴ s^-1. It has been found that the t/l ratio (wall thickness to edge length ratio) and strain rate have great influence on deformation pattern and plateau stress. The effect of strain rate on the plateau stress under high velocity impact was found to be different from that under low strain rate compression. The threshold impact velocity is approximately 100 m/s for the aluminum honeycomb studied.

The transition from the steady to the unsteady coupled thermal boundary layers around a partition in a differentially heated partitioned cavity is investigated numerically. The partitioned cavity is filled with water, which is imposed a temperature difference between the two sidewalls of the cavity. The numerical results are consistent with the corresponding experiments. The development of the unsteady coupled thermal boundary layers following a sudden temperature difference between the fluids at the two sides of the partition at a high Rayleigh number of Ra = 10¹¹ is described. The transition from the steady to the unsteady coupled thermal boundary layers over a wide range of Rayleigh numbers from Ra = 10⁹ to 10¹¹ is observed. The dependence of traveling waves in the unsteady coupled thermal boundary layers on the Rayleigh number and heat transfer through the partitioned cavity are characterized and quantified.

In this study, we are focusing on the investigation of the effects of gradient patterns on mechanical behavior of functionally-graded carbon nanotube-reinforced nanocomposites and considering typical beams made of such nanocomposites. Both analytic and finite element-based numerical models were developed. Analytic model was developed based on the first-order shear deformation and Timoshenko beam theories meanwhile finite element models were developed using Abaqus in conjunction with user-defined subroutines for defining the continuously gradient material properties for different gradient patterns. Position-dependent elastic modulus equations for four continuously graded patterns were studied. A nongraded pattern was used for benchmarking with the same geometry and total carbon nanotube (CNT) contents. For validation and verification, the results on both deflection and stress of these nanocomposite beams were analyzed, which clearly showed high influence from gradient patterns on these mechanical behaviors of such beams.

Numerical simulations of quasi-static indentation and low velocity impact of low density polymethacrylimide (PMI) Rohacell 51 WF foam using indenters with different nose shapes (conical, truncated-conical, hemi-spherical and flat) were carried out using the finite element code LS-DYNA. A 2D axisymmetric model was generated. A strain-rate dependent material model and r-adaptive remeshing were used for low velocity impact simulations. Numerical predictions matched the available experimental data very well. Moreover, the predicted resistance force closely matched the empirical results. The results demonstrated the ability of the model to reproduce the deformation mechanisms of the penetration process of Rohacell 51 WF foam.

Various studies have been conducted to investigate the effects of impact loading on cartilage damage and chondrocyte death. These have shown that the rate and magnitude of the applied strain significantly influence chondrocyte death, and that cell death occurred mostly in the superficial zone of cartilage suggesting the need to further understand the fundamental mechanisms underlying the chondrocytes death induced at certain levels of strain-rate. To date there is no comprehensive study providing insight on this phenomenon. The aim of this study is to examine the strain-rate dependent behavior of a single chondrocyte using a computational approach based on finite element method (FEM). An FEM model was developed using various mechanical models, which were standard Neo-Hookean solid (SnHS), porohyperelastic (PHE) and poroviscohyperelastic (PVHE) to simulate atomic force microscopy (AFM) experiments of chondrocyte. The PVHE showed, it can capture both relaxation and loading rate dependent behaviors of chondrocytes, accurately compared to other models.

International Thermonuclear Experimental Reactor (ITER) Cable-in-conduit Conductor (CICC) presents a typical hierarchical twisted configuration. An unpredictable stress–strain distribution is generated in each-level subcable under experimental loading tests or realistic operating conditions. The mechanical response relates to the threshold of transport currents on CICC which indicates the performance and stability of ITER magnets. To quantitatively assess mechanical deformation we develop an analytical scheme based on the hierarchical approach in the classical wire rope theory, following a successive top-down algorithm from the highest cable level to the lowest. The determination and evaluation of complex contact occurrence among adjacent strands is a key aspect which is formulated via a friction–contact model. Finite element (FE) method is used to extend the analytical approach that treats only elastic and isotropic material to the anisotropy and plasticity. The results show that the interstrand friction acts as a moderation for the axial deformation, and the interaction among the conductors has a stronger impact on the cable deformation than that between the conductor and jacket. It is suggested that under tensile load, the displacement constraints at the end and the strand anisotropy help to reduce the cable longitudinal deformation. It is also recommended that increasing the subsequent pitch is beneficial to reducing the cable deformation level.

The use of proper data structures with corresponding algorithms is critical to achieve good performance in scientific computing. The need of sparse matrix vector multiplication in each iteration of the iterative domain decomposition method has led to implementation of a variety of sparse matrix storage formats. Many storage formats have been presented to represent sparse matrix and integrated in the method. In this paper, the storage efficiency of those sparse matrix storage formats are evaluated and compared. The performance results of sparse matrix vector multiplication used in the domain decomposition method is considered. Based on our experiments in the FX10 supercomputer system, some useful conclusions that can serve as guidelines for the optimization of domain decomposition method are extracted.

In this paper, we consider the nonlinear orbit tracking control of rotating multi-tethered satellite formations in Halo orbits. A dynamical formulation is first applied for a rotating multi-tethered formation arranged in a hub-spoke configuration. Then, a new nonlinear optimal tracking control method is proposed for the stabilization of the parent satellite to follow the predefined trajectory. Numerical simulations illustrating the effectiveness of the nonlinear controller are presented. The results show that the actual trajectory of the parent satellite tracks the nominal Halo orbit with good accuracy under the influence of initial injection errors and the perturbations of subsatellites. In addition, the control acceleration and the total fuel cost of the control can be quite reasonable. Furthermore, a number of the relevant parameters that affect the control costs are varied in order to demonstrate the robustness of the nonlinear controller.

Dual phase (DP) steels were modeled using 2D and 3D representative volume elements (RVE). Both the 2D and 3D models were generated using the Monte-Carlo-Potts method to represent the realistic microstructural details. In the 2D model, a balance between computational efficiency and required accuracy in truly representing heterogeneous microstructure was achieved. In the 3D model, a stochastic template was used to generate a model with high spatial fidelity. The 2D model proved to be efficient for characterization of the mechanical properties of a DP steel where the effect of phase distribution, morphology and strain partitioning was studied. In contrast, the current 3D modeling technique was inefficient and impractical due to significant time cost. It is shown that the newly proposed 2D model generation technique is versatile and sufficiently accurate to capture mechanical properties of steels with heterogeneous microstructure.

In this paper, atomistic simulations have been conducted to investigate the torsional mechanical behaviors of five-fold twinned nanowires (FTNs), including the torsional vibration properties, elasto-plastic deformation behaviors and activation process of the first partial dislocation nucleation. Simulation results show that the fundamental torsional vibration frequency is inversely proportional to the wire length and is independent of the wire radius. Provided that an effective shear modulus of FTNs is used, the classic elastic torsional theory may be applicable to nanoscale. Furthermore, it is found that the plastic deformation of FTNs is dominated by partial dislocation activities. The normalized critical torsional angle corresponding to the onset of plastic deformation increases with the decrease of the wire radius and temperature, while it is almost independent of the wire length and loading rate. In addition, the activation energy of the first partial dislocation nucleation is about several electric voltages and decreases with the increase of the wire radius and applied torsional load.

The feasibility of real-time calculation of parameters for an internal combustion engine via reconfigurable hardware implementation is investigated as an alternative to software computation. A detailed in-hardware field programmable gate array (FPGA)-based design is developed and evaluated using input crank angle and in-cylinder pressure data from fully instrumented diesel engines in the QUT Biofuel Engine Research Facility (BERF). Results indicate the feasibility of employing a hardware-based implementation for real-time processing for speeds comparable to the data sampling rate currently used in the facility, with acceptably low level of discrepancies between hardware and software-based calculation of key engine parameters.

Industrial transformer is one of the most critical assets in the power and heavy industry. Failures of transformers can cause enormous losses. The poor joints of the electrical circuit on transformers can cause overheating and results in stress concentration on the structure which is the major cause of catastrophic failure. Few researches have been focused on the mechanical properties of industrial transformers under overheating thermal conditions. In this paper, both mechanical and thermal properties of industrial transformers are jointly investigated using finite element analysis (FEA). Dynamic response analysis is conducted on a modified transformer FEA model, and the computational results are compared with experimental results from literature to validate this simulation model. Based on the FEA model, thermal stress is calculated under different temperature conditions. These analysis results can provide insights to the understanding of the failure of transformers due to overheating, therefore are significant to assess winding fault, especially to the manufacturing and maintenance of large transformers.