共查询到20条相似文献,搜索用时 234 毫秒
1.
对石墨烯薄膜进行电-热-声耦合的三维建模计算,并将计算结果与实验测试值进行对比分析。首先建立了通电石墨烯薄膜焦耳热的三维模型,计算出石墨烯薄膜表面的温度振荡和稳态温度分布;在此基础上,建立了热黏性声学和压力声学耦合的声扩散模型,计算出空间中声压的分布;分析了基底和空气参数对石墨烯薄膜发声的影响;最后对通电石墨烯薄膜进行温度测试和声压测试。结果表明:三维模型数值计算的温度分布与测试结果吻合良好,数值计算的声压值比一维近似解析解更接近实验值,验证了数值计算方法的有效性。三维模型的数值计算方法在复杂边界条件下分析薄膜的声学性能更具优势。 相似文献
2.
复杂山地风场幅值特性试验研究 总被引:1,自引:0,他引:1
复杂山地具有与单个山体完全不同的风场特性,为了研究平均和脉动风速在复杂山地中的空间分布规律,进行了不同山体间隔距离、不同遮挡山体坡度和高度的复杂三维山体模型边界层风洞试验。试验结果表明:随着间隔距离增加,山顶近地平均风速最大加速比迅速减小;背风面山脚加速比迅速由正值减小为负值。随着遮挡山体坡度增大,山顶加速比迅速增大,最后趋于稳定。遮挡山体坡度小于临界坡度时,背风面山脚加速比为负值,反之则为正值。脉动风速均方根加速比随着遮挡距离的增大,逐渐线性向单个山体的结果靠拢;当受扰山体坡度大于遮挡山体坡度时,背风面山脚脉动风加速效应主要由受扰山体控制,反之则由遮挡山体控制。遮挡山体高度对平均风和脉动风速均方根加速比影响都较小。最后根据试验结果提出了复杂山地风场平均及脉动风速均方根计算修正模型。 相似文献
3.
三维有限元并行EBE方法 总被引:6,自引:1,他引:6
采用Jacobi预处理,推导了基于EBE方法的预处理共轭梯度算法,给出了有限元EBE方法在分布存储并行机上的计算过程,可以实现整个三维有限元计算过程的并行化。编制了三维有限元求解的PFEM(ParallelFiniteElementMethod)程序,并在网络机群系统上实现。采用矩形截面悬臂梁的算例,对PFEM程序进行了数值测试,对串行计算和并行计算的效率进行了分析,最后将PFEM程序应用于二滩拱坝-地基系统的三维有限元数值计算中。结果表明,三维有限元EBE算法在求解过程中不需要集成整体刚度矩阵,有效地减少了对内存的需求,具有很好的并行性,可以有效地进行三维复杂结构的大规模数值分析。 相似文献
4.
针对可见光遥感图像中海上舰船的复杂背景,包括粗糙海面,云层遮挡以及云层阴影所造成的舰船目标难以提取的情况,提出一种云层舰船模型.模型引入基于形状距离的舰船的形状先验信息,根据云区的亮度和阴影特征构建模型以及对应的能量函数.能量函数中与形状对应的形状能量大小通过与形状先验模板的相似程度来计算.基于图割的能量函数最小化过程实现了舰船目标的提取.实验结果表明了该模型及方法在云区无阴影和有阴影两种情况下对单个或多个舰船目标提取的有效性. 相似文献
5.
本文着重介绍了基于数码城市GIS的几种常用日照分析实现方法及其特点,包括实现动态的三维阴影,对不同地区,不同季节的各种复杂建筑物单点进行日照时间计算。基于数码城市GIS进行日照环境分析,在三维场景中再现一天内日照阴影的变化比二维中目照阴影分析更全面、生动、直观。 相似文献
6.
7.
8.
9.
:利用逆向工程技术对具有复杂曲面的翻领成型器进行了设计,采用三维激光扫描设备和逆向工程软件,经过数据预处理、曲面重构等过程,得到翻领成型器产品的初步结构模型,然后把得到的三维模型导入三维造型软件中,进行相关的结构再设计,为翻领成型器提供了一种新的设计思路. 相似文献
10.
11.
A. E. Bogdanovich 《Journal of Materials Science》2006,41(20):6547-6590
The very complex, multi-level hierarchical construction of textile composites and their structural components commonly manifests
via significant property variation even at the macro-level. The concept of a “meso-volume” (introduced by this author in early
1990s) is consistently applied in this work to 3-D stress/strain and failure analyses of 3-D woven composites at several levels
of structural hierarchy. The meso-volume is defined as homogeneous, anisotropic block of composite material with effective
elastic properties determined through volumetrically averaged 3-D stress and strain fields computed at a lower (“finer”) level
of structural hierarchy and application of generalized Hooke’s law to the averaged fields. The meso-volume can represent a
relatively large, homogenized section of a composite structural component, a lamina in laminated composite structure, a homogenized
assembly of several textile composite unit cells, a single homogenized unit cell, a resin-impregnated yarn, a single carbon
fiber, even a carbon nanotube assembly. When composed together, distinct meso-volumes constitute a 3-D Mosaic model at the
respective hierarchy level. A multi-scale methodology presented in this paper first illustrates 3-D stress/strain analysis
of the Mosaic unidirectional composite, computation of its effective elastic properties and their further use in 3-D stress/strain
analysis of the Mosaic model of 3-D woven composite Unit Cell. The obtained 3-D stress/strain fields are then volumetrically
averaged within the Unit Cell, and its effective elastic properties are computed. The predicted effective elastic properties
of 3-D woven composite are compared with experimental data and show very good agreement. Further, those effective elastic
properties are used in 3-D simulations of three-point bending tests of 3-D woven composite; theoretical predictions for central
deflection show excellent agreement with experimental data. Finally, a 3-D progressive failure analysis of generic 3-D Mosaic
structure is developed using ultimate strain criterion and illustrated on the 3-D woven composite Unit Cell. The predicted
strength values are compared to experimental results. The presented comparisons of theoretical and experimental results validate
the adequacy and accuracy of the developed material models, mathematical algorithms, and computational tools. 相似文献
12.
《低温学》2015
In order to select an effective approach to predict the pressurization characteristics of cryogenic tank during rocket launching, three computational models, defined as 0-D, 1-D and CFD models, are used to obtain the pressure evolution and thermal performance of a cryogenic tank during pressurized discharge period. Several pressurization cases are computed by all of the three models to evaluate their predictive abilities and effects, respectively. The comparative study shows that for the case with a diffuser-type injector at the tank inlet, the consistent results by the three models are obtained in the most of period, except that 1-D model has a peak departure prediction of pressure value at the beginning of process. All of the three models can be used to predict the pressurization performance, and their predictive abilities could be validated with one another. The CFD model is the unique suitable model to display the pressurization performance including physical distribution in radial direction especially for the system with no-diffuser-type injector. Based on the analysis, the application selection of three models for different cases is accomplished. The 0-D model is the priority selection for a simple pressure prediction of tank ullage, even for the situation that severe temperature distribution exists in the ullage range. The 1-D model is the optimal selection as considering both the convenience and the time consumption for the constant-pressure cases. But it is not recommended in a constant-inlet flux cases for its distinct predicting deviation at the beginning of the process. When the detailed distributions within the tank are concerned, the CFD model is the unique selection. The results of this paper may be beneficial to the model selection and optimization analysis of a pressurization system. 相似文献
13.
《低温学》2013
Finite-element models are a powerful and widely used tool for evaluating the ac losses of HTS tapes and wires as well as of assemblies such as cables and coils. The H-formulation, which uses the magnetic field components as state variables, has proved to be an efficient implementation to solve 2-D problems, involving infinitely long or axially-symmetric geometries; an excellent agreement with experimental data has been found in many cases. However, the simulation of certain applications requires a full 3-D model. In this paper we report on the development of a 3-D model based on the H-formulation. We describe the implementation of Maxwell equations, the imposition of current constraints and we discuss the issues related to meshing 3-D volumes. The model is validated by comparing the results with those obtained with 2-D models in cases that can be investigated in 2-D; then, it is used to simulate cases that can be handled only in 3-D. 相似文献
14.
With more accurate simulation models and more efficient algorithms becoming available, the binding constants of an affinity interaction can be obtained from much simpler experiments using capillary electrophoresis. With the enumeration algorithm, all possible combinations of the binding constant and the complex mobility in certain ranges that could result in the experimental migration time of an injected analyte are extracted from a 3-D surface, which depicts the migration times resulting from different values of the binding constant and the mobility of the complex formed between the interacting pair, to form a 2-D curve. When the experimental conditions are changed, the analyte migration time will also change. A new 2-D curve can be constructed from another 3-D surface on the basis of the pairs of binding constants and complex mobility values that could result in the new migration time. Because the true binding constant and complex mobility values have to be the same for both experimental conditions under the same temperature, there has to be a point where both 2-D curves will converge. The coordinates of the converging point give the values for a binding constant and a complex mobility that will fit all 2-D curves generated under certain experimental conditions. p-Nitrophenol is used as the analyte, beta-cyclodextrin is used as the additive, and a one-cell model is used to simulate affinity CE. The experimental conditions that can improve the accuracy of the binding constants are discussed. 相似文献
15.
Irshad R. Mufti Joseph T. Fou 《International journal of imaging systems and technology》1989,1(1):28-32
Two-dimensional finite-difference seismic models are excited by a line-source which leads to incorrect amplitudes. Moreover, in a structurally complex environment with strong three-dimensional (3-D) features, the results obtained from such models are often incorrect and do not include any out-of-plane events. On the other hand, 3-D models based on the ray-theory approximation fail to provide vital information such as diffractions and interference patterns which can strongly influence the seismic expression associated with hydrocarbon reservoirs. We present the results of a study in which an approximate version of mapped surfaces was used to carry out a synthetic 3-D finite-difference survey. This followed the necessary adjustment of various horizons and it involved the calibration of synthetic sections by comparing them with the corresponding unmigrated real-data sections. The simulation of reservoir characteristics was accomplished in reference to two key seismic horizons used in the model. 相似文献
16.
Cleavage fracture modeling of pressure vessels under transient thermo-mechanical loading 总被引:1,自引:0,他引:1
The next generation of fracture assessment procedures for nuclear reactor pressure vessels (RPVs) will combine non-linear analyses of crack front response with stochastic treatments of crack size, shape, orientation, location, material properties and thermal-pressure transients. The projected computational demands needed to support stochastic approaches with detailed 3-D, non-linear stress analyses of vessels containing defects appear well beyond current and near-term capabilities. In the interim, 2-D models become appealing to approximate certain classes of critical flaws in RPVs, and have computational demands within reach for stochastic frameworks. The present work focuses on the capability of 2-D models to provide values for the Weibull stress fracture parameter with accuracy comparable to those from very detailed 3-D models. Weibull stress approaches provide one route to connect non-linear vessel response with fracture toughness values measured using small laboratory specimens. The embedded axial flaw located in the RPV wall near the cladding-vessel interface emerges from current linear-elastic, stochastic investigations as a critical contributor to the conditional probability of initiation. Three different types of 2-D models reflecting this configuration are subjected to a thermal-pressure transient characteristic of a critical pressurized thermal shock event. The plane-strain, 2-D models include: the modified boundary layer (MBL) model, the middle tension (M(T)) model, and the 2-D RPV model. The 2-D MBL model provides a high quality estimate for the Weibull stress but only in crack front regions with a positive T-stress. For crack front locations with low constraint (T-stress < 0), the M(T) specimen provides very accurate Weibull stress values but only for pressure load acting alone on the RPV. For RPVs under a combined thermal-pressure transient, Weibull stresses computed from the 2-D RPV model demonstrate close agreement with those computed from the corresponding crack front locations in the 3-D RPV model having large negative T-stresses. Applications of this family of 2-D models provide Weibull stress values in excellent agreement with very detailed 3-D models while retaining practical levels of computational effort. 相似文献
17.
D. H. Robbins J. N. Reddy 《International journal for numerical methods in engineering》1993,36(4):655-677
The layerwise laminate theory of Reddy1 is used to develop a layerwise, two-dimensional, displacement-based, finite element model of laminated composite plates that assumes a piecewise continuous distribution of the tranverse strains through the laminate thickness. The resulting layerwise finite element model is capable of computing interlaminar stresses and other localized effects with the same level of accuracy as a conventional 3-D finite element model. Although the total number of degrees of freedom are comparable in both models, the layerwise model maintains a 2-D-type data structure that provides several advantages over a conventional 3-D finite element model, e.g. simplified input data, ease of mesh alteration, and faster element stiffness matrix formulation. Two sample problems are provided to illustrate the accuracy of the present model in computing interlaminar stresses for laminates in bending and extension. 相似文献
18.
Shen YT Daoud MI Lacefield JC 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2010,57(12):2627-2636
Two methods for simulation of ultrasound wavefront distortion are introduced and compared with aberration produced in simulations using digitized breast tissue specimens and a conventional multiple time-shift screen model. In the first method, aberrators are generated using a computational model of breast anatomy. In the second method, 10 to 12 irregularly shaped, strongly scattering inclusions are superimposed on the multiple-screen model to create a screen-inclusion model. Linear 2-D propagation of a 7.5-MHz planar, pulsed wavefront through each aberrator is computed using a first-order k-space method. The anatomical and screen-inclusion models reproduce two characteristics of arrival-time fluctuations observed in simulations using the digitized specimens that are not represented in simulations using the multiple-screen model: non-Gaussian first-order statistics and sharp changes in the rms arrival-time fluctuation as a function of propagation distance. The anatomical and screen-inclusion models both produce energy- level fluctuations similar to the digitized specimens, but the anatomical model more closely matches the pulse-shape distortion produced by the specimens. Both aberration models can readily be extended to 3-D, and the screen-inclusion model has the advantage of simplicity of implementation. Both models should enable more rigorous evaluation of adaptive focusing algorithms than is possible using conventional time-shift screen models. 相似文献
19.
In this paper, 2-D and 3-D finite element (FE) models for particle removal mechanisms are constructed to study the interaction between brush tines and debris in road sweeping processes. A 2-D contact FE analysis is first performed to analyse the contact behaviour between a flicking brush tine and an object to sweep. Using this model, the removal mechanisms are studied and analysed. Furthermore, the effect of brush penetration on debris removal is investigated. The 2-D sweeping model is extended to an accurate 3-D contact model, which overcomes some geometric errors in the 2-D model. From the results, it is suggested that the major removal mechanisms are a horizontal dragging force and a rolling moment generated by the external forces. It is also found that penetration has a positive contribution when it is relatively small in a non-sticky environment. Furthermore, in this environment, it is found that sweeping loads have a small effect on the removal process as either flicking tines or cutting tines can produce adequate removal loads. 相似文献
20.
A multi-dimensional constitutive model for shape memory alloys 总被引:3,自引:0,他引:3
This paper presents a multi-dimensional thermomechanical constitutive model for shape memory alloys (SMAs). This constitutive relation is based upon a combination of both micromechanics and macromechanics. The martensite fraction is introduced as a variable in this model to reflect the martensitic transformation that determines the unique characteristics of shape memory alloys. This constitutive relation can be used to study the complex behavior associated with 2-D and 3-D SMA structures. A simple example using this constitutive model is also presented, which reveals a new and interesting phenomenon of 3-D SMA structures. 相似文献