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Numerical Studies on Stratified Rock Failure Based on Digital Image Processing Technique at Mesoscale
Get PDFThis paper investigates the failure behaviors of stratified rocks under uniaxial compression using a digital image processing (DIP) based finite difference method (FDM). The two-dimensional (2D) mesostructure of stratified rocks, represented as the internal spatial distribution of two main rock materials (marble and greenschist), is first identified with the DIP technique. And then the binaryzation image information is used to generate the finite difference grid. Finally, the failure behaviors of stratified rock samples are simulated by FDM considering the inhomogeneity of rock materials. In the DIP, an image segmentation algorithm based on seeded region growing (SRG) is proposed, instead of the traditional threshold value method. And with the new proposed image segmentation algorithm, the mesostructure of stratified rocks can be fully acquired. In the process of simulation, to sufficiently capture the inhomogeneity of stratified rocks, mechanical properties of each rock material are all characterized by the Weibull statistical manner. Several cases of stratified rocks with different homogeneity indices of rock materials have been discussed under two compression loading conditions considering the anisotropy of stratified rocks to some extent. Results from numerical simulations show that the inhomogeneity of stratified rocks arising from the presence of different rock materials has a great influence on the failure behaviors of stratified rocks and that the numerical failure behaviors of stratified rocks without confining stresses applied agree quite well with the general observations reported in the literature
Finite Deflection of Slender Cantilever with Predefined Load Application Locus using an Incremental Formulation
Get PDFIn this paper, a class of problems involving space constrained loading on thin beams with large deflections is considered. The loading is such that, the locus of the force application point moves along an arbitrarily predefined path, fixed in space. Both linear elastic as well as elastic-perfectly plastic materials are considered. A simplification is realized using the moment-curvature relationship directly. The governing equation obtained is highly non-linear owing to inclusion of both material and geometric non-linearity. A general algorithm is described to solve the governing equation using an incremental formulation coupled with Runge Kutta 4th order initial value explicit solver. Additionally, the presented method is capable of handling unloading and reverse loading conditions. An example problem where the load application point locus is an inclined straight line is solved to demonstrate the performance of the method. It is found that, the force response due to the inclined locus is stiffer than the vertical locus. This response is akin to dry friction condition on a vertical locus case
Bending Response of Foldcore Composite Sandwich Beams
Get PDFIn order to solve bending behavior difference of corrugated structure in L andWorientation, bending response for composite sandwich beams with foldcores of three different wall thicknesses were experimentally and numerically investigated. Effect of the cell walls thickness on the strength and failure behavior of the composite sandwich beams with L and W orientations was also examined. The deformation mode was obtained by the numerical method; a constitutive law of laminated material has been incorporated into a finite element (FE) analysis program. Numerical calculations give accurate prediction to the bending response of foldcore composite sandwich beams comparing with experiments. Structural flexural stiffness, strength and failure mechanism at a given topological geometry depended on the nature of core itself: the bending stiffness and strength of the sandwich beam increased with the core wall thickness (relative density). Also, bending isotropy was shown in this study for foldcore composite sandwich beams with selected core geometry
A Macro Element Method to Improve Computational Efficiency in Large-scaled Nonlinear Analysis
Get PDFCompared with dealing with a linear system, solving a nonlinear system equation in numerical simulation requires generally more CPU time since iterative approach is usually used in the latter. To cut down the computing cost, a direct way is to reduce the degree of freedoms (DOF) of the problem under investigation. However, this kind of treatment may result in poorer accuracy. In this manuscript, a macro element method is proposed to improve computational efficiency in large-scaled nonlinear analysis. When this concept is incorporated into finite element analysis (FEA), all the members in the linear zones of a structure can be grouped into just one macro element. By using weak member approach, the stiffness matrix of this macro element can be evaluated through unit force method. Numerical examples prove that the proposed macro element method can increase the computational efficiency significantly without obvious negative influence on accuracy
Static and Dynamic Analysis of Laminated Thick and Thin Plates and Shells by a Very Simple Displacement-based 3-D Hexahedral Element with Over-Integration
Get PDFA very simple displacement-based hexahedral 32-node element (denoted as DPH32), with over-integration in the thickness direction, is developed in this paper for static and dynamic analyses of laminated composite plates and shells. In contrast to higher-order or layer-wise higher-order plate and shell theories which are widely popularized in the current literature, the proposed method does not develop specific theories of plates and shells with postulated kinematic assumptions, but simply uses the theory of 3-D solid mechanics and the widely-available solid elements. Over-integration is used to evaluate the element stiffness matrices of laminated structures with an arbitrary number of laminae, while only one element is used in the thickness direction without increasing the number of degrees of freedom. A stress-recovery approach is used to compute the distribution of transverse stresses by considering the equations of 3D elasticity. Comprehensive numerical results are presented for static, free vibration, and transient analyses of different laminated plates and shells, which agree well with existing solutions in the published literature, or solutions of very-expensive 3D models by commercial FEM codes. It is clearly shown that the proposed methodology can accurately and efficiently predict the structural and dynamical behavior of laminated composite plates and shells in a very simple and cost-effective manner
EvaluatingWater Vapor Permeance Measurement Techniques for Highly Permeable Membranes
Get PDFThe cup method and dynamic moisture permeation cell (DMPC) method are two common techniques used to determine the water vapor permeation properties of a membrane. Often, ignoring the resistance of boundary air layers to the transport of water vapor results in the water vapor permeance of the membrane being underestimated in practical tests. The measurement errors are higher with highly permeable membranes. In this study, the two methods were simulated using COMSOL Multiphysics platform and the extent of the error was evaluated. Initial results showed that the error is equally high in both methods. With the correction for the still air gap, the cup method produces a relatively reduced error. In the DMPC method, reducing the error caused by the boundary air layer by increasing the sweep speed can produce higher instrument error. Highly accurate and precise instrument is needed for DMPC method; however, its error is still higher than that in the cup method. Simulations also show that lowering the test pressure is favorable to both methods
On the Buckling Response of Offshore Pipelines under Combined Tension, Bending, and External Pressure
Get PDFIn this paper, the buckling and collapse analysis of offshore pipeline under combined tension, bending moment, and external pressure has been presented with theoretical analysis and FE (finite element) simulation method respectively. Based on the model initially proposed by Kyriakides, a 2-D theoretical model has been further developed. To verify the correctness and accuracy of the model proposed in this paper, numerical simulations have been conducted with 3-D FE model using ABAQUS software. Good consistency has been shown between the calculation results which validate the availability of the theoretical analysis. On this basis, the influence of load path, material properties, and diameter-to-thickness ratio on the buckling behaviors of the pipes have been discussed. Based upon the discussion mentioned above, some significant conclusions have been drawn
Development and Optimization of an Unstructured Kinetic Model for Sodium Gluconate Fermentation Process
Get PDFThis study proposed a modified unstructured kinetic model for sodium gluconate fermentation by Aspergillus niger. Four specific growth rate equations (Monod, Tessier, Contois, and logistic) were considered in the biomass growth equation. The growth, instantaneous biomass concentration, instantaneous product, and substrate concentration were considered in the equations of product formation and substrate consumption. Option parameters were introduced to determine the form of the unstructured model. A double-nested optimization strategy was proposed to optimize the option and kinetic parameters. The proposed unstructured kinetic model based on the estimated optimal parameters efficiently simulated sodium gluconate fermentation. The obtained option parameters of the kinetic model indicated that the Monod equation-based unstructured model displayed better performance than the three other specific growth rate equation-based kinetic models
Study on Lateral Nonlinear Dynamic Response of Deepwater Drilling Riser with Consideration of The Vessel Motions in Its Installation
Get PDFIn this paper, the mechanical model to analyze the riser lateral vibration displacement and stress distribution in installation has been established via variational approach and the principle of minimum potential energy. In this model, the influence of vessel motion on riser lateral vibration has been taken into consideration. The specific expression of lateral vibration has also been figured out according to the boundary conditions and initial conditions. At last, the variations of riser maximum lateral displacement and stress distribution on water depth (WD), wave height, wave period, riser OD, BOPS weight have been discussed
Preliminary Validation of Fluid-Structure Interaction Modeling for Hypersonic Deployable Re-Entry Systems
Get PDFThe aim of the present work is to provide a first attempt to set an aero-thermo-elastic methodology for deployable atmospheric re-entry decelerators operating at high Mach number and high dynamic pressure. Because of the severity of re-entry conditions such as high temperatures, high pressures and high velocities, the behavior of their flexible structures is a hard target to assess. In this paper a partitioned Fluid Structure Interaction (FSI) approach based on the integration of different commercial software (STAR-CCM+ and ABAQUS) is presented. In order to validate the specific codes and the overall strategy for structural and fluid dynamics analyses of flexible structures, different test cases are considered, including numerical and experimental literature results related to the problem under investigation. The paper shows that a good description of the physical behavior is possible with the proposed FSI partitioned approach. The model is preliminarily applied to investigate structural, fluid dynamic and aero-thermal behavior of a flexible deployable umbrella-like configuration along a typical suborbital re-entry trajectory based on sounding rocket