Three-dimensional Solid Structures Research Articles

Weakly-singular symmetric Galerkin boundary element method in thermoelasticity for the fracture analysis of three-dimensional solids

The Symmetric Galerkin Boundary Element Method has demonstrated significant advantages for the fracture mechanics analysis of three-dimensional solid structures. However, when dealing with structures in thermal environments, strongly-singular domain integrals resulting from the temperature field require meshing of the interior of the domain. In this paper, formulation and implementation of the weakly-singular SGBEM of three-dimensional thermoelastic intact and cracked solids are presented where temperature-induced domain integrals are transformed into boundary integrals. The strong singularity of these temperature-induced integrals is reduced to the weak singularity by exploring the feature of double-layer surface integrals in the SGBEM. Obtained temperature-induced boundary integrals affect only the right-hand-side vector of the SGBEM equation, and therefore the advantages of the SGBEM, such as the symmetry of the stiffness matrix, are retained. Several examples of three-dimensional solids with or without cracks subjected to thermal loadings are presented to validate the developed methods. Advantages and disadvantages of SGBEMs with different temperature-induced boundary integrals are also discussed.

Numerical and Experimental Approach for Failure Analysis of Soil Subjected to Surface Explosion Loading

Controlling the hazards to facilities caused by detonation waves is a high priority in engineering design. To protect an underground facility, soil can reduce the destructive effects of detonation waves. Soil dynamic characteristics and the area of the destructive zone are affected by shock wave energy. The material at ground zero is impacted by high-intensity stress and forms a crater. To ensure the safety of the facility, the protective soil layers must be sufficiently thick. Therefore, the purpose of this study was to analyze the destructive effects that caused the deformation and destruction of an external protective soil layer. The results of the explosion experiments and the numerical simulation analysis were compared to explore the dynamic characteristics of the soil affected by the shock wave and the crater effects of on-ground explosions. The analysis model adopted an 8-node hexahedral element to create a three-dimensional solid structure model of the fluid-solid interaction. The material failure analysis demonstrated that the detonation wave destabilized the interior of the soil body, and the nearby high-intensity stress was the key factor for material failure. The results can serve as a reference for the design of soil-covering layers that provide explosion hazard control.

Prediction of mechanical-hysteresis behavior and complex moduli using the phase field crystal method with modified pressure controlled dynamic equation

Damping materials have been used in numerous engineering applications. The important property that plays a key role in this type of material is a damping capacity which is related to mechanical-hysteresis behavior of viscoelasticity. During the last decade, the phase-field-crystal (PFC) model has emerged as a robust tool to predict various material phenomena. This density-functional-type model has the advantage over a conventional phase-field model in terms of atomistic resolution and molecular dynamics in terms of computational expense. In this work, we propose a method to predict mechanical-hysteresis behavior and its related complex moduli parameters using a modified-pressure-controlled dynamics (MPCD) equation incorporating with the PFC model, denoted as PFC-MPCD method, in a three-dimensional solid structure. We modify the previously proposed pressure-controlled dynamics (PCD) equation by introducing the pressure-time derivative term which allows us to produce the results consistent with the standard linear solid model (SLS) at the broader frequency range. We apply sinusoidal pressure oscillation and compare the results predicted by both models. The results demonstrate that mechanical-hysteresis behavior and complex moduli parameters predicted by PFC-MPCD method are in good agreement with those of SLS model and consistent with numerous experimental observations whereas the results produced by original PCD equation tends to exhibit inaccurate results at the very frequency. We expect that this new PFC-MPCD method can be extended to a more complex system and still be capable to exhibit the accurate mechanical-hysteresis behavior and complex moduli parameters which results in predicting more reliable damping capacity parameter in damping material design.

A Four-Node Tetrahedral Finite Element Based on Space Fiber Rotation Concept

Abstract The paper presents a four-node tetrahedral solid finite element SFR4 with rotational degrees of freedom (DOFs) based on the Space Fiber Rotation (SFR) concept for modeling three-dimensional solid structures. This SFR concept is based on the idea that a 3D virtual fiber, after a spatial rotation, introduces an enhancement of the strain field tensor approximation. Full numerical integration is used to evaluate the element stiffness matrix. To demonstrate the efficiency and accuracy of the developed four-node tetrahedron solid element and to compare its performance with the classical four-node tetrahedral element, extensive numerical studies are presented.

Optimal design of three-dimensional non-uniform nylon lattice structures for selective laser sintering manufacturing

As a kind of novel multifunctional structure with three-dimensional pores characterized by low relative density, lattice structures can attain a lightweight design while maintaining high specific mechanical properties in three-dimensional solid structures. Focusing on the challenge of finding the optimal design of lattice structures in the design object, a design and modeling method of non-uniform three-dimensional lattice structures is proposed while ensuring the selective laser sintering manufacturability. Optimization for cell type, cell size, and strut size distribution of lattices is specified with the mechanical properties analyzed and the material model calculated beforehand. The manufacturing constraints are analyzed and expressed in topology optimization and the optimal distribution of topology optimization results is mapped to the strut size distribution of lattice cells. The rapid and automatic computer-aided design modeling of optimized structures is realized by the parametric definition and assembling of lattice components. Finally, the non-uniform structures are successfully manufactured by selective laser sintering and it is shown by means of finite element analysis and experiments that the proposed design approach can improve the mechanical performance compared to the uniform lattice structure under the same weight reduction. And for the design object in this study, body-centered structure with cell size [Formula: see text]mm is chosen as the optimal cell type and cell size under the given selective laser sintering manufacturing constraints.

Application and prospects of 3D printing in orthopedic surgery

3D printing is a new printing technology through which a three-dimensional solid structure is manufactured through printing layer by layer. Its manufacturing of a three-dimensional solid object is based on digital model files and results from layer by layer stack accumulation of powdery metal or plastic and other adhesive materials. In this review, we focus on application of 3D printing technology in orthopedic surgery. We talk about mould-making, preoperative planning, surgical protocols, customization of a navigation template and a personalized prosthesis and its application in bone tissue engineering. It improves therapeutic efficacy by making operative treatment more accurate, shortening operative time and providing personalized implants for the patients. This paper also summarizes the current situation of 3D printing in orthopedics and its future profile. Key words: Surgery, computer-assisted; Prosthesis design; Tissue engineering; 3D printing

An Optimization Tool for Impact Analysis of Composite Structures

Composite materials exhibit complex failure behavior under impact loading especially such as that for composite landing gear structure. Possible failure modes in composites may include matrix cracking, fiber breakage, kinking, fiber-matrix debonding or delamination between composite plies. In order to better understand the damage mechanisms and non-linear response of composite structures under impact, complex geometries, materials, ply orientations and stacking sequence need to be considered. However, general drop test analysis for composite structures usually takes a lot of computational efforts, and it may be even more expensive for failure analysis and optimization when various structural geometries and design configurations are taken into account. This paper proposes a new methodology for evaluation and optimization of failure behavior of composite structures subjected to impact loading, whereby drop test analysis of composite structures is modeled by explicitly dynamics analysis of two-dimensional structures and implicit analysis of three-dimensional solid structures to predict delamination or out-of-plane failure. The above-mentioned modeling strategy helps speed up the optimization process and considerably save computational time and efforts. The proposed methodology together with reliable optimization algorithms and failure theory criteria are integrated and coded into a FE optimization tool by Python script. It is shown that the optimization tool effectively helps engineers and researchers perform optimization of general composite structures and fully take into account of various geometries, materials, loading configurations, composite stack-up and sequences and individual ply's orientation.

Automated FE Analysis for Heat Sink of LED Modules

This paper describes an automatic finite element (FE) mesh generation for FE analysis of LED modules. It is consisting of element generation, bubble packing and solid geometry modeler. This automated FE analysis system including bubble packing method consists of three sub-processes: (a) definition of geometric model, i.e. analysis model, (b) generation of bubbles, and (c) generation of elements. One of commercial solid modelers is employed for three-dimensional solid structures. Bubble is generated if its distance from existing bubble points is similar to the bubble spacing function at the point. The Delaunay method is introduced as a basic tool for element generation. The developed system allows designers to evaluate detailed physical behaviors of structures through some simple interactive operations to their geometry models. To demonstrate practical performances of the present system, the system was used to an analysis of heat sink. Practical performances of the present system are demonstrated through several examples for heat sink of LED modules.

A novel in vitro assay of tumor‐initiating cells in xenograft prostate tumors

The field of prostate cancer has been stymied by the difficulty of cultivating patient-derived samples in the laboratory. In order to help circumvent this challenge, we sought to develop an in vitro assay of human prostate cancer initiation employing a prostate-associated mesenchymal feeder layer. Rat seminal vesicle mesenchyme (rSVM) harvested from male neonatal rats was plated in 12-well plates and then irradiated with 30 Gy after approximately 75% confluence. Single-cell suspensions of two human non-adherent prostate cancer xenograft lines (TRPC and LAPC9) were then plated on irradiated rSVM. At 3-4 weeks, three-dimensional solid structures, termed glandoids, were harvested and analyzed or transplanted singly into the renal capsule of immunodeficient mice. Animals were assessed for tumor formation 8-12 weeks after engraftment. Finally, clonality assays were performed to determine whether glandoids usually arise from a single cell and are therefore clonal in origin. Glandoids form with reliable frequency (1/ approximately 300 plated cells), are constituted by relevant cell types (CK8+, CK5-, PSA+) and after implantation into immunocompromised mice, give rise to tumors that recapitulate original xenograft histology and cell composition; defining a glandoid as a tumor-initiating unit. In addition, assessment of red fluorescent protein (RFP)-labeled glandoids revealed either all red or non-red structures, with few areas of fusion, suggesting glandoids are clonal in origin. The above assay describes an adjunct technique to readily cultivate cells from prostate cancer xenografts in vitro and as such provides a platform on which tumor-initiating cell studies and high-throughput drug discovery may be performed.

피지이론과 버블기법을 이용한 3차원 구조물의 유한요소해석을 위한 요소생성기법

본 논문은 3차원구조물의 유한요소해석을 위한 자동 유한요소 생성에 관한 것으로 퍼지이론과 버블요소 생성기법, 상용 솔리드모델러로 구성되어진다. 새로운 요소생성과정은 (a) 해석모델인 형상모델링 정의, (b) 버블생성, 그리고 (c) 요소생성으로 이루어진다. 형상모델링에는 상용 솔리드모델러를 이용하였으며 버블은 각 지점에서의 버블간격함수에 의해 생성되어진다. 버블간격 함수는 지식처리수법에 의해 조절되어 진다. 요소생성을 위해서는 기본적으로 데로우니방법을 도입하였다. 이러한 3차원 구조물에 대한 유한요소의 자동생성은 해석을 위해 큰 잇점이 있다. 실제적인 현 시스템의 효용성을 검증하기위해 3차원 형상에 대한 예를 제시하였다. This paper describes an automatic finite element mesh generation for finite element analysis of three-dimensional structures. It is consisting of fuzzy knowledge processing, bubble meshing and solid geometry modeler. This novel mesh generation process consists of three subprocesses: (a) definition of geometric model, i.e. analysis model, (b) generation of bubbles, and (c) generation of elements. One of commercial solid modelers is employed for three-dimensional solid structures. Bubble is generated if its distance from existing bubble points is similar to the bubble spacing function at the point. The bubble spacing function is well controlled by the fuzzy knowledge processing. The Delaunay method is introduced as a basic tool for element generation. Automatic generation of finite element for three-dimensional solid structures holds great benefits for analyses. Practical performances of the present system are demonstrated through several mesh generations for 3D geometry.

퍼지이론을 이용한 FEM 모델링을 위한 자동 요소분할 시스템

This paper describes an automatic finite element (FE) mesh generation for three-dimensional structures consisting of free-form surfaces. This mesh generation process consists of three subprocesses: (a) definition of geometric model, i.e. analysis model, (b) generation of nodes, and (c) generation of elements. One of commercial solid modelers is employed for three-dimensional solid structures. Node is generated if its distance from existing node points is similar to the node spacing function at the point. The node spacing function is well controlled by the fuzzy knowledge processing. The Delaunay method is introduced as a basic tool for element generation. Automatic generation of FE meshes for three-dimensional solid structures holds great benefits for analyses. Practical performances of the present system are demonstrated through several mesh generations for three-dimensional complex geometry.

Development of High-Performance FEM Modeling System Based on Fuzzy Knowledge Processing

This paper describes an automatic finite element (FE) mesh generation for three-dimensional structures consisting of tree-form surfaces. This mesh generation process consists of three subprocesses: (a) definition of geometric model, (b) generation of nodes, and (c) generation of elements. One of commercial solid modelers is employed for three-dimensional solid structures. Node is generated if its distance from existing node points is similar to the node spacing function at the point. The node spacing function is well controlled by the fuzzy knowledge processing. The Voronoi diagram method is introduced as a basic tool for element generation. Automatic generation of FE meshes for three-dimensional solid structures holds great benefits for analyses. Practical performances of the present system are demonstrated through several mesh generations for three-dimensional complex geometry.

A three-dimensional shape optimization system—shop3D

A modular approach for shape optimization of three-dimensional solid structures is described. A major consideration in the development of this capability is the desire to use a commercially available finite element program, such as NASTRAN, for analysis. Since NASTRAN cannot be called as a subroutine, a system architecture was developed of independently executable modules in which sequential execution is controlled by job control language. Also, shape sensitivities are not commonly available in commercial programs. A hybrid approach which is based on the material derivative concept is developed to obtain shape sensitivities by post processing finite element results stored on files. A quick generation of a good optimization model combined with an efficient optimization system will result in a drastic design time saving. In this paper, different modeling approaches for shape optimization are discussed. Emphasis will be placed upon a special modeling technique which overlays the design model onto an already existing finite element model. Several automotive related examples are used to evaluate the program's effectiveness.

A modular approach for three-dimensional shape optimization of structures

An approach for shape optimization of three-dimensional solid structures is described. A major consideration in the development of this capability was the desire to use a commercially available finite-element program, such as NASTRAN, for analysis. Since NASTRAN cannot be called a subroutine, a system architecture of independently executable modules was developed, in which sequential execution is controlled by job control language. Also, sensitivities are not commonly available in commercial programs. A material derivative approach was developed to obtain shape sensitivities by postprocessing finite-element boundary stresses stored on files. A parameterized surface description and mesh generation are provided using isoparametric mapping patches. The feasible directions algorithm CONMIN is used for optimization. Several automotive-related examples are used to evaluate the program's effectiveness.

Structural Dynamics—Theory and Computations (2nd Ed.)

Part I: structures modelled as a single degree-of-freedom system undamped single degree-of-freedom system damped single degree-of-freedom system response of one-degree-of-freedom system to haarmonic loading response to general dynamic loading Fourier analysis and response in the frequency domain generalized co-ordinates and Rayleigh's method nonlinear structural response response spectra. Part II: structures modelled as shear buildings the multistory shear building free vibration of a shear building forced motion of shear buildings damped motion of shear buildings reduction of dynamic matrices. Part III: framed structures modeled as discrete multidegree-of-freedom systems dynamic analysis of beams dynamic analysis of plane frames dynamic anaylsis of grids three-dimensional frames dynamic analysis of trusses time history response of multidegree-of-freedom systems. Part IV: structures modelled with distributed properties dynamic analysis of systems with distributed properties discretization of continuous systems. Part V: introduction to finite element method dynamic analysis of plates dynamic analysis of shells dynamic analysis of three-dimensional solid structures. Part VI: random vibration. Part VII: earthquake engineering equivolent staic lateral force method - uniform Building Code 1994 dynamic method - uniform Building Code - 1994.