Emerald | Engineering Computations | Table of Contents http://www.emeraldinsight.com/0264-4401.htm Table of contents from the most recently published issue of Engineering Computations Journal en-gb Mon, 28 Apr 2014 00:00:00 +0100 2014 Emerald Group Publishing Limited editorial@emeraldinsight.com support@emeraldinsight.com 60 Emerald | Engineering Computations | Table of Contents http://www.emeraldinsight.com/common_assets/img/covers_journal/eccover.gif http://www.emeraldinsight.com/0264-4401.htm 120 157 A Two-Step Taylor Galerkin formulation for fast dynamics http://www.emeraldinsight.com/journals.htm?issn=0264-4401&volume=31&issue=3&articleid=17107695&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - This paper presents a new stabilised low order finite element methodology for large strain fast dynamics.<B>Design/methodology/approach</B> - The numerical technique describing the motion is formulated upon the mixed set of first order hyperbolic conservation laws already presented in [Lee, Gil and Bonet, DOI: 10.1016/j.compstruc.2012.12.008] where the main variables are the linear momentum, the deformation gradient tensor and the total energy. The mixed formulation is discretised using the standard explicit Two-Step Taylor Galerkin (2TG) approach, which has been successfully employed in Computational Fluid Dynamics (CFD). Unfortunately, the results display non-physical spurious (or hourglassing) modes, leading to the breakdown of the numerical scheme. For this reason, the 2TG methodology is further improved by means of two ingredients, namely a curl-free projection of the deformation gradient tensor and the inclusion of an additional stiffness stabilisation term.<B>Findings</B> - A series of numerical examples are carried out drawing key comparisons between the proposed formulation and some other existing numerical techniques recently published [Lee, Gil and Bonet, DOI: 10.1016/j.compstruc.2012.12.008].<B>Originality/value</B> - Both velocities (or displacements) and stresses display the same rate of convergence, which proves ideal in the case of industrial applications where low order discretisations tend to be preferred. The enhancements introduced in this paper enable the use of linear triangular (or bilinear quadrilateral) elements in two dimensional nearly incompressible dynamics applications without locking difficulties. In addition, an artificial viscosity term has been added into the formulation to eliminate the appearance of spurious oscillations in the vicinity of sharp spatial gradients induced by shocks. Article literatinetwork@emeraldinsight.com (Izian Abd. Karim, Chun Hean Lee, Antonio Javier Gil, J Bonet) Mon, 28 Apr 2014 00:00:00 +0100 Method of lines solutions for the 3-wave model of Brillouin equations http://www.emeraldinsight.com/journals.htm?issn=0264-4401&volume=31&issue=3&articleid=17107725&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - The method of lines (MOL) solution of the SBS equations (a system of three first-order hyperbolic PDEs ), describing the three-wave interaction resulting from a coupling between light and acoustic waves, is presented. The system has complex numbers and boundary values.<B>Design/methodology/approach</B> - System of three first-order hyperbolic PDEs are first transformed and then spatially discretized. Superbee flux limiter is proposed to offset numerical damping and dispersion, brought on by the low order approximation of spatial derivatives in the partial differential equations (PDEs). In order to increase computational efficiency, the structured structure of the PDE Jacobian matrix is identified and a sparse integration algorithm option of the ODE solvers is used. The flux limiter based on higher order approximations eliminates numerical oscillation. Examples are presented, and the performance of the Matlab ODE solvers is evaluated by comparison.<B>Findings</B> - This type of solution provides a rapid means of investigating SBS (stimulated Brillouin scattering) as a tool in fiber optic sensing. <B>Originality/value</B> - To the best of our knowledge, MOL solution is proposed for the first time for the modeling of three-wave interaction in a SBS based fiber optic sensor. Article literatinetwork@emeraldinsight.com (Fikri Serdar Gokhan, Graham W. Griffiths, William E. Schiesser) Mon, 28 Apr 2014 00:00:00 +0100 Numerical study on the dynamics and mass transfer characteristics of a radial offset jet http://www.emeraldinsight.com/journals.htm?issn=0264-4401&volume=31&issue=3&articleid=17107713&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - A radial offset jet has the flow characteristics of a radial jet and an offset jet, which are encountered in many engineering applications. The purpose of this paper is to study the dynamics and mass transfer characteristics of the radial offset jet with an offset ratio 6, 8 and 12.<B>Design/methodology/approach</B> - Three turbulence models, namely the SST k–? model, detached eddy simulation model (DES), and improved delayed detached eddy simulation (IDDES), were applied to the radial offset jet with an offset ratio eight and their results were compared with experimental results. The contrasting results, such as the distributions of mean and turbulent velocity and pressure, show that the IDDES model was the best model in simulating the radial offset jet. The results of the IDDES were analyzed, including the Reynolds stress, turbulent kinetic energy, triple-velocity correlations, vertical structure and the tracer concentration distribution.<B>Findings</B> - In the axisymmetric plane, Reynolds stresses increase to reach a maximum at the location where the jet central line starts to be bent rapidly, and then decrease with increasing distance in the radial direction. The shear layer vortices, which arise from the K-H (Kelvin-Helmholtz) instability near the jet exit, become larger scale results in the entrainment and vortex-pairing, and breakdown when the jet approaches the wall. Near the wall, the vortex swirling direction is different at both front and back of attachment point. In the wall-jet region, the concentration distributions present self-similarity while it keeps constant below the jet in the recirculation region.<B>Research limitations/implications</B> - The radial offset jet with other offset ratio and exit angle is not considered in this paper, which should be investigated furthermore.<B>Originality/value</B> - The results obtained in this paper will provide guidance for studying similar flow and a better understanding of the radial offset jet. Article literatinetwork@emeraldinsight.com (Zhiwei Li, Wenxin Huai, Zhonghua Yang, Zhongdong Qian, Yuhong Zeng) Mon, 28 Apr 2014 00:00:00 +0100 A Mie-Grüneisen mixture Eulerian model for underwater explosion http://www.emeraldinsight.com/journals.htm?issn=0264-4401&volume=31&issue=3&articleid=17107676&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - The main purpose of this paper is to provide an improved Mie-Grüneisen mixture model to simulate underwater explosion (UNDEX).<B>Design/methodology/approach</B> - By using Mie-Grüneisen equations of state (EOS) to model explosive charge, liquid water and solid structure, the whole fluid field is considered as a multi-phases mixture under Mie-Grüneisen EOS. Then by introducing auxiliary variables in Eulerian model and using mass fraction to establish a diffusion balance, a new improved Mie-Grüneisen mixture model is presented here. For the new reconstructed mixture model, a second order MUSCL scheme with TVD limiter is employed to solve the multi-phase Riemann problem. <B>Findings</B> - Numerical examples show that the results obtained by Mie-Grüneisen mixture model are quite closed to theoretical and empirical data. And the model can be also used in 2-D fluid-structure problem of UNDEX effectively, it is proved that the deformation of structure can be clearly described by mass fraction.<B>Research limitations/implications</B> - The FVM model based on mass fraction can only describe the motion of compressible material under impact. Material failure or large deformation needs a modification about the EOS or implementations of other models (i.e. FEM model).<B>Originality/value</B> - An improved non-oscillation Mie-Grüneisen mixture model, which based on mass fraction, is given in the present paper. The present Mie-Grüneisen mixture model provides a simplified and efficient way to simulate UNDEX. The feasibility of this model to simulate the detonation impacts on different mediums, including water and other metal mediums, is tested and verified here. Then the model is applied to the simulation of underwater contact explosion problem. In the simulation, deformation of structure under explosion loads, as well as second shock wave, are studied here. Article literatinetwork@emeraldinsight.com (Zongduo Wu, Z Zong, Lei sun) Mon, 28 Apr 2014 00:00:00 +0100 An innovative strategy to create equivalent elements for modelling assembly points in joined structures http://www.emeraldinsight.com/journals.htm?issn=0264-4401&volume=31&issue=3&articleid=17107712&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - Large structures (e.g. plane, bridge, etc.) often include several hundreds of assembly points. Structural computations often use over-simplistic approximations for these points; among others, they do not take into account the thermo-mechanical history due to the assembling process. Running computations with each assembly point modelled completely would require too much time to achieve a simulation. There is thus a need to create equivalent elements for assembly points in order to: - take into account the mechanical state of the assembly point in the design stage - while reducing the computational time cost at the same time <B>Design/methodology/approach</B> - This paper introduces a innovative strategy based on a coupling procedure between: - a finite element tool for modelling the assembly process in order to access to the mechanical state of the assembly point - an optimisation algorithm in order to identify the equivalent element parameters <B>Findings</B> - The strategy has proven to be successful. A connector model easier to use and much faster than the complete model, has been obtained. Results obtained with this element are in good agreement with experimental tests in the case of multipoint assemblies and with the simulation results of the complete numerical model. Finally the connector model appears to be easier to use and much faster than the complete model, more difficult to model properly. <B>Originality/value</B> - The main innovative aspects of this strategy lie in the fact that: - The creation of this equivalent element is based on a complete numerical approach. - The thermomechanical history due to the assembly process is considered - The element parameters are identified thanks to an evolution strategy based on the coupling between a finite element model and a zero-order minimisation algorithm. Article literatinetwork@emeraldinsight.com (Maxime Bérot, Julien Malrieu, François Bay) Mon, 28 Apr 2014 00:00:00 +0100 A computational method for evaluating the damage in a solder joint of an electronic package subjected to thermal loads http://www.emeraldinsight.com/journals.htm?issn=0264-4401&volume=31&issue=3&articleid=17107715&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - The purpose of this paper is to introduce a novel computational method to evaluate damage accumulation in a solder joint of an electronic package, when exposed to operating temperature environment. A procedure to implement the method is suggested, and a discussion of the method and its possible applications is provided in the paper.<B>Design/methodology/approach</B> - Methodologically, interpolated response surfaces based on specially designed finite element simulation runs, are employed to compute a damage metric at regular time intervals of an operating temperature profile. The developed method has been evaluated on a finite-element model of a lead-free PBGA256 package, and accumulated creep strain energy density has been chosen as damage metric.<B>Findings</B> - The method has proven to be two orders of magnitude more computationally efficient compared to finite element simulation. A general agreement within 3% has been found between the results predicted with the new method, and finite element simulations when tested on a number of temperature profiles from an avionic application. The solder joint temperature ranges between +25°C and +75°C. <B>Practical implications</B> - The method can be implemented as part of reliability assessment of electronic packages in the design phase.<B>Originality/value</B> - The method enables increased accuracy in thermal fatigue life prediction of solder joints. Combined with other failure mechanisms, it may contribute to the accuracy of reliability assessment of electronic packages. Article literatinetwork@emeraldinsight.com (Jonas Arwidson, Ilja Belov, Erland Johnson, Peter Leisner) Mon, 24 Mar 2014 00:00:00 +0000 Numerical Analysis of Characteristics of the Wind Caused by Methane- air Explosion http://www.emeraldinsight.com/journals.htm?issn=0264-4401&volume=31&issue=3&articleid=17107708&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - The high velocity wind caused by a methane-air explosion is one of the important hazardous effects in explosion events of coal mines, and however until now it has not been received much attention from scientific works. <B>Design/methodology/approach</B> - In consideration of the difficulties in observing particle velocities of high velocity flows, this work presented a study to reveal the regularity during a methane-air explosion happening in the tunnel of coal mine through the numerical analysis approach.<B>Findings</B> - The strong wind caused by a methane-air explosion is a significant hazard and can cause damage in the accidents of methane-air explosion in underground coal mines, especially at structural opening, according to this work. obtained results show that maximum particle velocity of the high velocity wind occurs in the outside region of the premixed area, with a peak value of 400~500m/s, and the peak velocity of the high velocity wind decreases exponentially with distance beyond the premixed area.<B>Originality/value</B> - The objective of this work was to examine the effect of wind caused by a methane-air explosion in a tunnel. Other information, such as shock wave and flame and temperature distribution, has been reported in the previous literatures. However, in the accidents of methane-air explosion in underground coal mines, some phenomena (structural opening is destroyed badly) can not be understood by using shock wave and flame and temperature distribution caused by the explosion. The strong wind caused by a methane-air explosion is another significant hazard and can cause damage in the accidents of methane-air explosion in underground coal mines, especially at structural opening, according to this work. Article literatinetwork@emeraldinsight.com (Qi Zhang, Lei Pang, Dachao Lin) Mon, 28 Apr 2014 00:00:00 +0100 Numerical Evaluation of the Side Wall Effect on the Flow around a Hydrofoil http://www.emeraldinsight.com/journals.htm?issn=0264-4401&volume=31&issue=3&articleid=17107714&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - Studies of the three-dimensional flow characteristics during hydrofoil cavitation have shown that the side walls strongly affect the flow field around the hydrofoil. The purpose of this paper is to analyze the side wall effect for three-dimensional non-cavitating flows around a hydrofoil. <B>Design/methodology/approach</B> - A three-dimensional non-cavitating flow field around a hydrofoil is analyzed for different attack angles using the RNG turbulence model and Large Eddy Simulations (LES). The effect of the hydrofoil span was analyzed using LES simulations for various spans.<B>Findings</B> - The lift coefficient, drag coefficient and pressure coefficient on the suction side are compared with experimental values. The results from the LES model (Smagorinsky-lilly subgrid-scale model) agree better with the experimental data than those from the RNG turbulence model.<B>Originality/value</B> - This paper shows that the flow around the hydrofoil has significant three-dimensional characteristics due to the side wall. For wide hydrofoils, the wall vortex region becomes essentially stable, and the width of the span has little effect on the middle region. Article literatinetwork@emeraldinsight.com (Min He, Lingli Yuan, Lingjiu Zhou, Jing Yang, Zhengwei Wang) Mon, 28 Apr 2014 00:00:00 +0100 Transient Heat Conduction across Thermal Barrier Coating on an Anisotropic Substrate http://www.emeraldinsight.com/journals.htm?issn=0264-4401&volume=31&issue=3&articleid=17107711&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - This paper examines the transient heat conduction in a 2D anisotropic substrate coated with a thin layer of thermal barrier coating. Nowadays, materials with anisotropic properties have been extensively applied in various engineering applications for enhanced strength. However, under an extreme operating environment of high temperature, the strength of the materials may largely decline. As a common practice in engineering, thermal barrier coatings (TBC) are usually applied to thermally insulate the substrates so as to allow for higher operating temperature. This research provides engineers an numerical approach for properly designing the TBC to protect the anisotropic substrate.<B>Design/methodology/approach</B> - For this investigation, a finite difference scheme using the domain mapping technique, transforming the anisotropic domain into isotropic one, is employed. The analysis considers three respective boundary conditions, namely Dirichelete condition, Neumann condition, and also forced convection, and studies the effect of various variables on the heat conduction in the coated system. Additionally, formulas for the steady-state temperature drop across the coating layer at the center are analytically derived. By comparing the numerical results with the analytical solutions, the veracity of the formulas is verified.<B>Findings</B> - A few interesting phenomena are observed from the numerical results. First, the rotation of the substrate’s principal axes affects the temperature on the TBC front surface in a more obvious manner for the Neumann condition than that for convection. Second, the temperature profile of the Dirichelete condition rises faster than the other cases, although all their profiles present a similar pattern. Third, the transient temperature drop across the TBC under the convection condition presents a complicated pattern, depending on the TBC thickness. At last, the increase of TBC thickness under the Dirichelete condition may provide better insulation than the other cases. In this paper, approximate analytical formulations for the steady-state temperature drop across the TBC are also presented. Numerical results by the FDM indicate excellent agreements with the analytical solutions.<B>Originality/value</B> - In the past, the finite element method is usually applied for analyzing the heat conduction problem of thermal barrier coating (TBC). However, one serious deficiency of applying the FEM to the TBC problem lies in the demand for a vast amount of elements (or cells) when the TBC thickness is far smaller than the substrate dimension. For ultra-thin coating, an enormous amount of elements are required that may lead to an extremely heavy computational burden. The paper is to present an innovative finite difference approach that can be applied to analyze the heat conduction across the TBC coated on an anisotropic substrate. On the interface between the TBC and the substrate, a special heat equilibrium condition and the compatibility condition of identical temperature on the adjacent materials are used to propose three new models to predict the temperature drop across the TBC. Article literatinetwork@emeraldinsight.com (Yung-Ming Lee, Tsun-Wen Tsai, Yui-Chuin Shiah) Mon, 28 Apr 2014 00:00:00 +0100 Techniques to derive geometries for image-based Eulerian computations http://www.emeraldinsight.com/journals.htm?issn=0264-4401&volume=31&issue=3&articleid=17107705&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - The performance of three frequently used level set-based segmentation methods is examined for the purpose of defining features and boundary conditions for image-based Eulerian fluid and solid mechanics models. The focus of the evaluation is to identify an approach that produces the best geometric representation from a computational fluid/solid modeling point of view. In particular, extraction of geometries from a wide variety of imaging modalities and noise intensities, to supply to an immersed boundary approach, is targeted.<B>Design/methodology/approach</B> - Two- and three-dimensional images, acquired from optical, X-ray CT, and ultrasound imaging modalities, are segmented with active contours, k-Means, and adaptive clustering methods. Segmentation contours are converted to level sets and smoothed as necessary for use in fluid/solid simulations. Results produced by the three approaches are compared visually and with contrast ratio, signal-to-noise ratio, and contrast-to-noise ratio measures.<B>Findings</B> - While the active contours method possesses built-in smoothing and regularization and produces continuous contours, the clustering methods (k-Means and adaptive clustering) produce discrete (pixelated) contours that require smoothing using speckle-reducing anisotropic diffusion (SRAD). Thus, for images with high contrast and low to moderate noise, active contours are generally preferable. However, adaptive clustering is found to be far superior to the other two methods for images possessing high levels of noise and global intensity variations, due to its more sophisticated use of local pixel/voxel intensity statistics.<B>Originality/value</B> - It is often difficult to know a priori which segmentation will perform best for a given image type, particularly when geometric modelling is the ultimate goal. This work offers insight to the algorithm selection process, as well as outlining a practical framework for generating useful geometric surfaces in an Eulerian setting. Article literatinetwork@emeraldinsight.com (Seth Ian Dillard, James Buchholz, Sarah Vigmostad, Hyunggun Kim, H. S. Udaykumar) Mon, 28 Apr 2014 00:00:00 +0100 Polyhedra faster than spheres? http://www.emeraldinsight.com/journals.htm?issn=0264-4401&volume=31&issue=3&articleid=17107707&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - To present a new and efficient technique for discrete element modelling using non-convex polyhedral grain shapes. <B>Design/methodology/approach</B> - The efficiency of the technique follows from the use of grains that are dilated versions of the basic polyhedral grain shapes. Dilation of an arbitrary polyhedral grain is accomplished by placing the center of a sphere of fixed radius at every point on the surface. The dilated vertices become sphere segments and the edges become cylinder segments. The sharpness of the vertices and edges can be adjusted by varying the dilation radius. Contacts between two dilated polyhedral grains can be grouped into three categories; vertex on surface, vertex on edge, and edge on edge, or in the grammar of the model, sphere on polygonal surface, sphere on cylinder, and cylinder on cylinder. Simple, closed-form solutions exist for each of these cases.<B>Findings</B> - The speed of the proposed polyhedral discrete element model is compared to similar models using spherical and ellipsoidal grains. The polyhedral code is found to run about 40% as fast as an equivalent code using spherical grains and about 80% as fast as an equivalent code using ellipsoidal grains. Finally, several applications of the polyhedral model are illustrated.<B>Originality/value</B> - Few examples of discrete element modeling studies in the literature use polyhedral grains. This dearth is because of the perceived complexity of the polyhedral coding challenges and the slow speed of the codes compared to codes for other grain shapes. This paper presents a much simpler approach to discrete element modeling using polyhedral grain shapes. Article literatinetwork@emeraldinsight.com (Mark Hopkins) Mon, 28 Apr 2014 00:00:00 +0100 Combined equivalent & multi-scale simulation method for 3-D seismic analysis of large-scale shield tunnel http://www.emeraldinsight.com/journals.htm?issn=0264-4401&volume=31&issue=3&articleid=17107693&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - Purpose – The great magnitude differences between the integral tunnel and its structure details make it impossible to numerically model and analyze the global and local seismic behavior of large-scale shield tunnels using a unified spatial scale, even with the help of supercomputers. This paper aims to present a combined equivalent & multi-scale simulation method, by which the tunnel’s major mechanical properties under seismic loads can be represented by the equivalent model, and the seismic responses of the interested details can be studied efficiently by the coupled multi-scale model.<B>Design/methodology/approach</B> - Design/methodology/approach – The nominal orthotropic material constants of the equivalent tunnel model are inversely determined by fitting the modal characteristics of the equivalent model with the corresponding segmental lining model. The critical sections are selected by comprehensive analyzing of the integral compression/extension and bending loads in the equivalent lining under the seismic shaking. And the coupled multi-scale model containing the details of interest is solved by the mixed time explicit integration algorithm.<B>Findings</B> - Findings – The combined equivalent & multi-scale simulation method is an effective and efficient way for seismic analyses of large-scale tunnels. The response of each flexible joint is related to its polar location on the lining ring, and the mixed time integration method can speed-up the calculation process for hybrid FE model with great differences in element sizes.<B>Originality/value</B> - Originality/value – The orthotropic equivalent assumption is, to the best of the authors' knowledge, for the first time, used in the 3-D simulation of the shield tunnel lining, representing the rigidity discrepancies caused by the structural property. Article literatinetwork@emeraldinsight.com (Weiwei Zhang, Xianlong Jin, Zhihao Yang) Mon, 28 Apr 2014 00:00:00 +0100