PROCEEDINGS OF THE 2ND INTERNATIONAL SYMPOSIUM ON COMPUTATIONAL MECHANICS AND THE 12TH INTERNATIONAL CONFERENCE ON THE ENHANCEMENT AND PROMOTION OF COMPUTATIONAL METHODS IN ENGINEERING AND SCIENCE
1233(2010); http://dx.doi.org/10.1063/1.3452242View Description Hide Description
The 2.5D finite/infinite element approach for simulating the ground vibrations by surface or underground moving trains will be briefly summarized in this paper. By assuming the soils to be uniform along the direction of the railway, only a two‐dimensional profile of the soil perpendicular to the railway need be considered in the modeling. Besides the two in‐plane degrees of freedom (DOFs) per node conventionally used for plane strain elements, an extra DOF is introduced to account for the out‐of‐plane wave transmission. The profile of the half‐space is divided into a near field and a semi‐infinite far field. The near field containing the train loads and irregular structures is simulated by the finite elements, while the far field covering the soils with infinite boundary by the infinite elements, by which due account is taken of the radiation effects for the moving loads. Enhanced by the automated mesh expansion procedure proposed previously by the writers, the far field impedances for all the lower frequencies are generated repetitively from the mesh created for the highest frequency considered. Finally, incorporated with a proposed load generation mechanism that takes the rail irregularity and dynamic properties of trains into account, an illustrative case study was performed. This paper investigates the vibration isolation effect of the elastic foundation that separates the concrete slab track from the underlying soil or tunnel structure. In addition, the advantage of the 2.5D approach was clearly demonstrated in that the three‐dimensional wave propagation effect can be virtually captured using a two‐dimensional finite/infinite element mesh. Compared with the conventional 3D approach, the present approach appears to be simple, efficient and generally accurate.
1233(2010); http://dx.doi.org/10.1063/1.3452149View Description Hide Description
Bioreactors play important role in tissue engineering, as they simulate physiological environment required for the development of tissue substitutes. The significant parameters involved in the efficient working of a bioreactor are the transfer of nutrients and removal of wastes. Use of carbon nanotube polymeric scaffolds for tissue engineering applications has gained recent attention, primarily due to the enhanced mechanical properties of carbon nanotubes. In this study, a hierarchical approach to determine the atomistic properties of carbon nanotube based polymers using molecular dynamics and coupling between the scales through complex multi‐scale mathematical homogenization models is discussed. A new computational methodology for the analysis of tissue‐fluid interaction problem based on a biphasic representation of fluid and tissue domain is also presented. The significance of this work lies in the use of a multi‐physical modelling of complex material geometry as well as physical processes that represent different physiological systems, leading to an efficient multiscale‐multi‐physical computational algorithm.
1233(2010); http://dx.doi.org/10.1063/1.3452170View Description Hide Description
Our recent studies on kinetic behaviors of gas flows are reviewed in this paper. These flows have a wide range of background, but share a common feature that the flow Knudsen number is larger than 0.01. Thus kinetic approaches such as the direct simulation Monte Carlo method are required for their description. In the past few years, we studied several micro/nano‐scale flows by developing novel particle simulation approach, and investigated the flows in low‐pressure chambers and at high altitude. In addition, the microscopic behaviors of a couple of classical flow problems were analyzed, which shows the potential for kinetic approaches to reveal the microscopic mechanism of gas flows.
1233(2010); http://dx.doi.org/10.1063/1.3452181View Description Hide Description
A fully coupled meshfree algorithm is proposed for numerical analysis of Biot’s formulation. Spatial discretisation of the governing equations is accomplished using radial point interpolation method. Temporal discretization is achieved based on a novel three‐point approximation technique with variable time step, which has second order accuracy and avoids oscillatory response observed in the conventional methods of time discretization. Application of the model is demonstrated using two numerical examples with analytical solution. It is shown that the model proposed is efficient in simulating the coupled flow deformation behavior in fluid saturated porous media with good accuracy and stability irrespective of the magnitude of the time step adopted.
1233(2010); http://dx.doi.org/10.1063/1.3452196View Description Hide Description
The massive increase in the speed of computers over the past forty years changed the way that social scientists, applied economists and statisticians approach their trades and also the very nature of the problems that they could feasibly tackle. The new methods that use intensively computer power go by the names of “computer‐intensive” or “simulation”.
My lecture will start with bird’s eye view of the uses of simulation in Economics and Statistics. Then I will turn out to my own research on uses of computer‐ intensive methods. From a methodological point of view the question I address is how to infer marginal distributions having estimated a conditional quantile process, (Counterfactual Decomposition of Changes in Wage Distributions using Quantile Regression,” Journal of Applied Econometrics 20, 2005). Illustrations will be provided of the use of the method to perform counterfactual analysis in several different areas of knowledge.
1233(2010); http://dx.doi.org/10.1063/1.3452208View Description Hide Description
This paper reports our recent research works on crack analysis in continuously non‐homogeneous and linear elastic functionally graded materials. A meshless boundary element method is developed for this purpose. Numerical examples are presented and discussed to demonstrate the efficiency and the accuracy of the present numerical method, and to show the effects of the material gradation on the crack‐opening‐displacements and the stress intensity factors.
Detection of Multiple Cracks on a Partially Obstructed Plate Structure Following the Probabilistic Approach1233(2010); http://dx.doi.org/10.1063/1.3452230View Description Hide Description
This paper addresses the problem of detecting multiple cracks on thin plates utilizing measured dynamic responses from only a few points on the target plate. Most existing model‐based methods in the literature focus on the detection of single‐crack or multi‐crack with given crack number on beams. Only very limited number of researches have been carried out for the detection of multiple cracks for plate‐type structures following the model‐based method. There are two phase contained in the proposed crack detection methodology. The number of cracks is first identified by adopting the Bayesian model class selection method in the first stage. After that, the posterior (updated) probability density function (PDF) of the crack parameters, such as crack locations, lengths and depths are identified in the second phase following the Bayesian statistical identification framework. Very encouraging results are obtained for the case studies showing that the proposed methodology can correctly identify the number of cracks, the corresponding crack parameters and their associated uncertainties. Some useful discussions are also made through the case studies.
1233(2010); http://dx.doi.org/10.1063/1.3452241View Description Hide Description
A methodology is presented in this paper for the identification of an effective way to install a given number of sensors on a structure to extract as much information as possible for structural model identification utilizing measured dynamic data. The information entropy is employed as a measure to quantify the uncertainties of the set of identified model parameters. The problem of optimal sensor placement is then formulated as a discrete optimization problem, in which the information entropy measure is minimized, with the sensor configurations as the minimization variables. The methodology is illustrated numerically and experimentally using shear building models. The performance of the optimal sensor placement technique is verified using the identification results based on the measured acceleration responses of a 4‐storey shear building model under laboratory conditions.
1233(2010); http://dx.doi.org/10.1063/1.3452253View Description Hide Description
One of recent experimental progresses in strengthening and toughening metals simultaneously is to adopt techniques of surface mechanical attrition treatment (SMAT) and warm co‐rolling to 304 stainless steel (SS). To capture deformation behavior and associated damage initiation/evolution process in the co‐rolled SMATed 304SS, cohesive finite element method (CFEM) is employed in this paper and simulation results are in agreement with experimental results. Both strengthening effect due to high yield stress of the nanograin layer and toughening effect due to non‐localized damage in the nanograin layer are captured. Effect of energy release rate of nanograin layer on failure strain of layered co‐rolled SMATed 304SS is investigated. It is found that the more brittle the nanograin layer is, the more potential necking sites in the nanograin layer are, and the more ductile the layered co‐rolled SMATed 304SS is.
Simulation of the Optical Parameters and Study of the Physical Properties of the ITO Films Prepared by the IBAD1233(2010); http://dx.doi.org/10.1063/1.3452265View Description Hide Description
Indium tin oxide (ITO) thin films have been deposited onto glass substrates at room temperature by ion beam assisted deposition technique at different deposition rates. During all the deposition processes, the parameters of the Kaufman ion source and the oxygen gas flow are maintained constants. And only the deposition rate is varied from 0,1 nm/s to 0,3 nm/s by adjusting the e‐beam power supply. The effects of the deposition rate on the properties of the deposited films have been studied. The structural, optical and electrical properties of the deposited films have been characterized by X‐ray diffraction, AFM, transmittance, FTIR, and Hall effect measurements. The optical constants of the deposited films have been calculated by fitting the transmittance spectra. It has been found that although the film prepared at low deposition rate (0,1 nm/s) shows a high transmittance in the visible region, it has a poor electrical conductivity. The films prepared at 0,2 nm/s deposition rate shows a good electrical conductivity, high IR reflectance which is useable for some electromagnetic wave shielding applications and a reasonable transmittance in the visible region.
1233(2010); http://dx.doi.org/10.1063/1.3452276View Description Hide Description
A MD simulation study of 2:1 clay minerals is carried out using a new MD simulation method which is capable of simulating a system under the most general external stress conditions by considering the changes of MD cell size and shape. The tensor defining the cell size and shape is correlated with the atomic level stress tensors (both internal and external) through a Lagrangian formulation. Due to this feature, the method is able to predict the crystal transformation of molecular structures which is compatible with the imposed external stress and boundary conditions.
In this paper, the new method has been applied for the first time to the simulations of dehydrated montmorillonite sheets, and has successfully revealed unforeseen structural transformations of clay minerals upon relaxation under different normal stress conditions. In order to first achieve the correct coupled simulation of atomic structural change and MD cell deformation, parametric studies were made on the effects of the time step and the “imaginary” mass M of the MD cell on the model behavior. It is found that the time step essentially controls the convergence behavior of the system, while the “imaginary” mass M has large influences on the final equilibrated structure of the system. Results of the parametric study suggest that values of sec for the time step and for the “imaginary” mass M are appropriate for the simulation of 2:1 clay minerals using the current method.
Simulation results reveal the strong correlations between the degrees of constraints imposed on the simulation cell (i.e., whether the cell size or shape change is allowed) and the final equilibrated crystal structure of clay minerals. It is found during the relaxation process that large shear distortions of clay minerals will occur if full allowance is given to the cell size and shape change, while large shear stress in the sheet plane will be retained if only the cell size change is allowed. These structural changes are shown to be essentially correlated with the internal shear stresses of the clay mineral.
1233(2010); http://dx.doi.org/10.1063/1.3452288View Description Hide Description
Two‐dimensional, time‐dependent, reactive Navier—Stokes equations involving the effects of viscosity, thermal conduction, molecular diffusion and turbulence etc. were solved to obtain a deep insight into gaseous detonation vortex‐like structures and its induced mechanism. Detailed chemical reaction model, together with standard κ‐ε turbulence model, was employed in this paper. Numerical simulation indicates that a large amount of vortex‐like structure emerges in detonation flow field due to its intrinsic three‐dimensional structure. Vortex‐like structure can also be induced by wall geometry with an abrupt cross‐section area change. Shock wave interacts with slip line, which in turn causes the formation of vortex‐like structure. In nature, all these induce the instability of slip line, so it is the slip line instability that is the essential reason for the emergence of vortex‐like structure. Additionally, the difference of vortex‐like structure between an ordinary detonation and a marginal detonation was compared. In an ordinary detonation, the vorticity magnitude of vortex‐like structure is different, even for two vortex‐like structures in the same pair. With increasing the distance away from leading front, the vorticity magnitude gradually decays. Slip line in a marginal detonation is more unstable and produces more vortex‐like structures.
1233(2010); http://dx.doi.org/10.1063/1.3452299View Description Hide Description
In this paper, we present a study of hemoglobin‐hemoglobin interaction with model reduction methods. We begin with a simple spring‐mass system with given parameters (mass and stiffness). With this known system, we compare the mode superposition method with Singular Value Decomposition (SVD) based Principal Component Analysis (PCA). Through PCA we are able to recover the principal direction of this system, namely the model direction. This model direction will be matched with the eigenvector derived from mode superposition analysis. The same technique will be implemented in a much more complicated hemoglobin‐hemoglobin molecule interaction model, in which thousands of atoms in hemoglobin molecules are coupled with tens of thousands of T3 water molecule models. In this model, complex inter‐atomic and inter‐molecular potentials are replaced by nonlinear springs. We employ the same method to get the most significant modes and their frequencies of this complex dynamical system. More complex physical phenomena can then be further studied by these coarse grained models.
1233(2010); http://dx.doi.org/10.1063/1.3452310View Description Hide Description
A systematic investigation is being performed to understand the combined size, loading rate and thermal effects on the responses of nanostructures such as nanofilms and nanowires. This paper summarizes what has been found so far, and presents the recent molecular dynamics simulations of the mechanical behaviors of single crystal fcc nanowires and nanofilms under different temperatures and extremely high strain rates. Based on the model‐based simulation results, the mechanism of the nanostructural responses will be explored and future research tasks will be discussed.
1233(2010); http://dx.doi.org/10.1063/1.3452040View Description Hide Description
In this paper, finite element models were developed to simulate fibre metal laminates subjected to various blast loadings with typical pressure‐time patterns. The aluminium (alloy grade 2024‐0) layer was modelled as an isotropic elasto‐plastic material up to the on‐set of post failure stage, followed by shear failure and tensile failure to simulate its failure mechanism. The glass fibre laminate (woven glass‐fibre/polypropylene matrix composite) layer was modelled as an orthotropic material up to its on‐set of damage, followed by damage initiation and evolution using the Hashin criterion. The damage initiation was controlled by failure tensile and compressive stresses within the lamina plane which were primarily determined by tests. The damage evolution was controlled by tensile/compressive fracture energies combined both fibre and matrix. Discussions were given to cover difficulties faced during development of the modelling. The FE models developed for 2/1 and 3/2 fibre metal laminates with different GFPP layer thicknesses were validated against the corresponding experimental results. Good correlation was obtained in terms of failure modes and permanent displacements. Using validated models, parametric studies may be further carried out to cover FMLs made with various stack sequences and layer thicknesses.
1233(2010); http://dx.doi.org/10.1063/1.3452051View Description Hide Description
This paper studies the parametric instability of functionally graded beams with open edge cracks subjected to an axial excitation. The beam is clamped at both ends and movable in the longitudinal direction with materials properties varying exponentially through the thickness direction. Theoretical formulations are based on Timoshenko beam theory and the linear rotational spring model. The governing equations of motion are derived by using the Hamilton’s principle and solved by using Galerkin’s technique and the Least Squares method. The boundary points on the unstable regions are determined by Bolotin’s method. Numerical results are presented to show the influences of crack location, crack depth, material property gradient, and beam slenderness ratio on the principal unstable region of the cracked functionally graded beams.
1233(2010); http://dx.doi.org/10.1063/1.3452062View Description Hide Description
A structural damage detection method integrating the damage locating vector (DLV) method and ARX model for system identification of frame structures from seismic acceleration responses has been explored in this paper. The concept of the DLV method is to identify the members with zero stress under some specific loading patterns derived from the changes in flexibility matrix of the structure before and after the damage state. Success of the DLV method requires clear identification of the flexibility matrix for at least the first few dominant modes. In this study, a five‐storey steel frame with diagonal bracings is considered as the objective building. The damage condition of the structure is simulated by partially removing some of the diagonals. With the flexibility matrices of both the intact and damaged structure identified from seismic structural responses via shaking table tests, results indicate that the damaged locations can be successfully identified by the DLV method if sufficient modes of vibration are taken into account in the realization of the flexibility matrices. The feasibility of using DLV method for damage detection of frame structures using seismic response data is confirmed.
1233(2010); http://dx.doi.org/10.1063/1.3452073View Description Hide Description
The nonlinear vibrations of two flexible cantilever beams with different sections, which are subjected to harmonic vertical base excitation, are studied experimentally. The periodic motions and chaotic motions are demonstrated. And the multi‐pulse orbits, which imply the existence of chaos under the Smale horseshoes sense, are also observed.
1233(2010); http://dx.doi.org/10.1063/1.3452084View Description Hide Description
Xihoumen Bridge is a suspension bridge with main span of 1650 m, and the bridge pylon is 211.286 m high. The problem of structural internal force response of bridge pylon under wind loads is a major concern in design as the bridge is located in a typhoon‐prone region. Firstly, according to two status of the north bridge pylon, namely the construction longest cantilever stage and the bridge service stage under the wind velocity with a return period of 100 years, three‐dimensional finite element model of pylon was established. Then, considering two types of wind yaw angles of 0° and 90°, the structural internal force response under wind loads and the gust response factor of the pylon were studied. The static structural internal force responses were computed by the static finite element method, while the fluctuating structural buffeting internal force responses were computed by the dynamic finite element method and the pseudo‐excitation method. The results show that the structural internal force responses of the pylon gradually increased with the lower elevation. On the above two status of the north bridge pylon, in the case of wind yaw angle of 0°, the structural longitudinal bending moment in pylon bottom cross‐section were 38529 t⋅m and 50158 t⋅m, respectively; while in the case of wind yaw angle of 90°, the structural lateral bending moment in pylon bottom cross‐section were 70722 t⋅m and 21991 t⋅m, respectively.