A survey of CAD model simplification techniques for physics-based simulation applications

Automated CAD model simplification plays an important role in effectively utilizing physics-based simulation during the product realization process. Currently a rich body of literature exists that describe many successful techniques for fully-automatic or semi-automatic simplification of CAD models for a wide variety of applications. The purpose of this paper is to compile a list of the techniques that are relevant for physics-based simulations problems and to characterize them based on their attributes. We have classified them into the following four categories: techniques based on surface entity based operators, volume entity based operators, explicit feature based operators, and dimension reduction operators. This paper also presents the necessary background information in the CAD model representation to assist the new readers. We conclude the paper by outlining open research directions in this field.     

A physics-based electromigration reliability model for interconnects lifetime prediction

Dear editor,When the technology node scales down to 14 nm,the back-end-of-line (BEOL) in IC design faces the more serious chal-lenges[1,2].The high-density int...     

Meshless methods for physics-based modeling and simulation of deformable models

As 3D digital photographic and scanning devices produce higher resolution images, acquired geometric data sets grow more complex in terms of the modeled objects’ size, geometry, and topology. As a consequence, point-sampled geometry is becoming ubiquitous in graphics and geometric information processing, and poses new challenges which have not been fully resolved by the state-of-art graphical techniques. In this paper, we address the challenges by proposing a meshless computational framework for dynamic modeling and simulation of solids and thin-shells represented as point samples. Our meshless framework can directly compute the elastic deformation and fracture propagation for any scanned point geometry, without the need of converting them to polygonal meshes or higher order spline representations. We address the necessary computational techniques, such as Moving Least Squares, Hierarchical Discretization, and Modal Warping, to effectively and efficiently compute the physical simulation in real-time. This meshless computational framework aims to bridge the gap between the point-sampled geometry with physics-based modeling and simulation governed by partial differential equations. Supported by the National Science Foundation (Grant Nos. CCF-0727098, IIS-0710819)     

On elliptical model for forest fire spread modeling and simulation

A new approach for the derivation of elliptical model of steady-state forest fire spread in time based on classical envelope theory is described. The derivation of this model known in the literature is based on the introduction of a special transform of co-ordinate system which allows to utilize geometrical properties of points lying on common tangent line of two circles. However, the use of this transform means the necessity to apply some specific assumptions onto the model. The proposed new procedure allows us to derive the model without the use of this transform. The new approach enables to better explain the internal coherence of studied problem, assumptions and limitations of the model, as well as to suggest its further generalizations.     

A physics-based model of hyperabrupt varactors for nonlinear transmission line applications

This article presents a physics-based varactor-diode model for exponentially graded doping profiles. The capacitance–voltage characteristic and the bias dependence of the series resistance are discussed in detail. The model is validated by frequency and time domain measurements on GaAs varactors. The optimum design for nonlinear transmission line (NLTL) applications is discussed. © 1997 John Wiley & Sons, Inc. Int J Microwave Millimeter-Wave CAE 7 : 278–288, 1997.     

A fire risk simulation system for multi-purpose building based fire statistics

Statistical data over the past 24 years detailing the number of fires and building floor areas published by the Taiwan government was employed to determine the fire probability, frequency, and cycle for each building category. By applying a matrix calculation, the fire probability, frequency, cycle, and risk ratio for each functional area within a multi-purpose building were obtained. With assistance from the Taiwan government, the fire case investigation and statistical data for building fires were established. By adopting the risk ratio concept, the weight values for 20 fire safety assessment criteria and 4 fire safety strategies for a multi-purpose building were acquired to indicate the possible causes of fires and the quantitative extent of fire influence.     

A GIS-based urban simulation model for environmental health analysis

This paper introduces an urban simulation model for environmental health analysis (SIENA). SIENA is a novel tool to explore urban interactions and processes with regard to exposure assessments. It is based on urban structures and relationships observed in real-world cities making it a realistic representation of a functioning city. The development of SIENA involved identifying and quantifying fundamental processes and similarities in urban areas in Great Britain and using those to guide the building of SIENA within a GIS. An internal validation confirmed SIENA's realism. Its generality, achieved through the pooling of information from different real-world cities, makes it particularly useful for developing and testing spatial epidemiological concepts and models; simulating processes and interactions relating to environmental exposure; and exploring theoretical and methodological problems in the spatial analysis of environmental health. SIENA ultimately provides a much needed tool in the form of a controlled, simplified urban simulation model.     

A simulation model for the analysis of machine deterioration and repair

One particular methodology for machine replacement and repair analysis encompasses a Markov or semi-Markov model consisting of states reflecting various stages of machine deterioration. In this paper the “bathtub curve” of replacement analysis is used as the basis for modeling the time in each state of a state-dependent, control-limit replacement policy. A repair queue is also embedded in the model. Specifically, a Q-GERT network simulation is developed and demonstrated via a case example of the weaving operation of a textile company. Output statistics related to the state movement of machines, new machines acquired, and machine repair are presented and discussed.     

A simulation model for risk analysis of toxic chemical storage

With the increasing complexity of chemical plants and the growing public concern for the safe manufacture, transport, and disposal of these chemicals, there exist a need to assist decision-makers in project evaluation with regard to risk.

Extensive work has been done in risk analysis area related to nuclear industry. The amount of research and applications of risk analysis methodology in chemical industry is seriously lacking. Direct application of some of the risk analysis techniques used for nuclear risk studies is not always appropriate to the chemical industry.

The use of simulation models to overcome some of the problems of direct application of probabilistic risk assessment (PRA) methodologies is evaluated in this paper. A simulation model is developed for a toxic chemical storage risk analysis problem. The results of the simulation model are compared to the results of using standard fault tree methodology.     

火焰动画快速模拟的新方法

针对火焰动画难以快速建模和绘制的问题,提出了完全利用GPU过程化生成火焰动画的高效算法。先用建模工具在预处理阶段构建一个由平面正方形组成的三维模型,在绘制阶段通过GPU编程对这些方形进行Billboard方式的变换,并用一些简单公式对他们的运动方式、大小和颜色来用过程化方式进行控制,最后通过alpha混合得到最终结果。算法完全在GPU里实现,能满足实时的绘制要求。     

A network simulation model for police patrol vehicle maintenance and replacement analysis

Research in the field of urban police patrol-car analysis has tended to concentrate in the areas of vehicle deployment, fleetsize and location, etc., with very little emphasis in the area of vehicle maintenance and replacement policy. As such, the purpose of this paper is to develop and demonstrate a simulation model for patrol-vehicle replacement and maintenance analysis. The simulation model will encompass a Markov-type framework of state movements where the states represent the various stages of a patrol vehicle's life from new to inoperable. The model will be developed in the form of a Q-Gert network, and, demonstrated via a case example of an urban patrol fleet of 100 vehicles.     

隧道火灾疏散模型实时仿真算法的实现

由于隧道火灾的人员疏散难题,提出一种基于网格选择的隧道火灾人员疏散模型算法,设计了人员类型、奔跑速度、奔跑方向、人员所在环境等疏散属性参数,建立基于网格化离散场变量和坐标值的仿真模型。该算法克服了常用的元胞自动机算法计算量大,实时仿真比较困难的缺点。最后,利用Open Inventor进行了计算机仿真,并应用该仿真模型进行了分析,从逃生通道对疏散时间的影响及诱导标志设计对疏散时间的影响两方面验证了模型的有效性,并可直观地为安全疏散设计提供理论依据。     

A semi-distributed,physics-based hydrologic model using remotely sensed and Digital Terrain Elevation Data for semi-arid catchments

A practical, hydrologic model (DPHM-RS) is developed for the semi-arid climate of the Canadian Prairies that could adequately account for a river basin's terrain features by sub-dividing it to sub-basins of uneven shapes and sizes (semi-distributed) based on topographic information derived from the digital terrain elevation (DTED) data. Even though computationally modest, DPHM-RS is scientifically vigorous, can effectively assimilate remotely sensed (RS) data, and has most of its parameters determined through RS data and measurements. The hydrologic processes are estimated for each land cover and then aggregated according to percentage of each land cover present within each sub-basin. As evapotranspiration (ET) usually dominates the hydrology of the Canadian Prairies, ET from each land cover is estimated at three levels by the two-source model that separately considers evaporation from soil and plants. The soil moisture at the top active and the transmission zones are estimated by a water budget approach, while the groundwater dynamics by the topographic soil index obtained from DTED. The surface runoff from each sub-basin is routed to the channel network by a kinematic wave response function, and then routed to the basin outlet by the Muskingum-Cunge model. DPHM-RS, is applied to the Paddle River Basin (265?km²) of Central Alberta divided to five sub-basins. It was calibrated with hourly hydroclimatic and RS data collected in the summer of 1996 and validated with data of 1997 and 1998. In both stages, there are good agreements between simulated runoff at the basin outlet with the observed, between simulated surface temperature and net radiation with the observed, between soil moisture and that retrieved from Radarsat-SAR data, and between simulated ET and that estimated by water balance. Encouraging results from these multi-criteria assessments demonstrate the feasibility of semi-distributed, physics-based hydrologic modelling in the dry climate of Canadian Prairies, and the usefulness of RS and DTED data in basin hydrology.     

实时图仿真中畸变模型的分析与建立

实时图的仿真生成是景像匹配仿真研究中的重要内容之一。系统研究了实时图仿真中的各种畸变模型的建立问题。分析了实时图与基准图之间存在的主要差异,设计了包括噪声干扰、几何畸变、灰度畸变等形式的十种畸变模型,给出了相应的实验结果。通过匹配仿真实验验证了这些模型在匹配算法性能评估及基准图可匹配性检验中的实用意义。     

改进的GPSR模型及其仿真分析

为最大限度保证路由QoS需求,引入概率传输机制在前向区域内选择下一跳节点,对无线传感器网络GPSR算法进行改进,提出一种新的无线传感器路由算法IGPSR,与现有GPSR算法主要有两点不同：（1）根据邻居节点剩余能量对前向区域实行分区;（2）在选定的前向区域分区内采用概率传输机制来选择下一跳节点。仿真实验结果表明,IGPSR算法能有效均衡网络节点能量消耗和延长网络生命周期。     

A hybrid model for smoke simulation

A smoke simulation approach based on the integration of traditional particle systems and density functions is presented in this paper.By attaching a density function to each particle as its attribute,the diffusion of smoke can be described by the variation of parti-each particle as its attribute ,the diffusion of smoke can be described by the variation of parti-cles‘ density functions ,along with the effect on airflow by controlling particles‘ movement and fragmentation.In addition.a continuous density field for realistic rendering can be generatd quickly through the look-up talbes of particle‘s density functions .Compared with traditional particle systems,this approach can describe smoke diffusion,and provide a continuous density field for realistic rendering with much less computation.A quick rendering scheme is also presented in this paper as a useful preview tool for tuning appropriate parameters in the smoke model.     

Spectral indices and fire behavior simulation for fire risk assessment in savanna ecosystems

The lack of information on the vegetation status before the use of fire as a management tool in protected areas leads to drastic destruction of the natural vegetation and biodiversity. This paper describes the use of spectral indices and simulation of savanna burning to assess risk of intensive fire propagation in a National Park (Niokolo Koba, Senegal, West Africa). Spectral parameters corresponding to thematic information (wetness, brightness, and greenness) were retrieved using an orthogonal transformation, the Tasseled Cap approach on LANDSAT-ETM images. Wetness and brightness indices were normalized (σ=1 and mean=0) and then combined in a simple semi-empirical algorithm of fire risk levels discrimination. These two indices are proven to reflect qualitatively both fuel moisture and its distribution, which constitute the most foreseen determinants of fire propagation in savanna areas. The fire risk assessment algorithm (FIRA algorithm) was used to produce a fire risk map at the beginning of the management fire implement period. In parallel, a fire area simulator (FARSITE) developed by USDA was used with randomly spaced fire sources to determine areas which can be potentially burned in the study site. These simulated burned areas and the FIRA algorithm results were cross-compared to a real fire scars dated at the end of the same burning period and to land cover map. A great consistency was found between the different sources of information. More than 85% of fire prone areas identified by the FIRA algorithm or simulated by FARSITE were located in trees-shrub, woodland, and shrub savannas. These cover types included also 95% of real fire scars. Almost 88% and 84% of real fire scars were found in the risk zones determined by the FIRA algorithm and the simulated burned areas by FARSITE, respectively. The method used is simple and suited for an operational use for management fire implementation in savanna ecosystems.     

Data analysis for parallel car-crash simulation results and model optimization

The paper discusses automotive crash simulation in a stochastic context, whereby the uncertainties in numerical simulation results generated by parallel computing. Since crash is a non-repeatable phenomenon, qualification for crashworthiness based on a single test is not meaningful, and should be replaced by stochastic simulation. But the stochastic simulations may generate different results on parallel machines, if the same application is executed more than once. For a benchmark car model, differences between the position of a node in two simulation runs of PAMCRASH or LS-DYNA of up to 10 cm were observed, just as a result of round-off differences in the case of parallel computing. In this paper, some data mining algorithms are described to measure the scatter of parallel simulation results of car-crash and then provide hints to overcome this scatter to get more stable car model.     

Numerical simulation of forest fire propagation based on modified two-dimensional model

A modified two-dimensional two-phase mathematical model of forest wildfires propagation is considered. The model is based on the averaging of three-dimensional equations of two-phase medium over the height of the forest fuel (FF) layer and it includes the (k?ε)-turbulence model with additional turbulence production and dissipation terms in the forest layer and the Eddy Break-up Model for the combustion rate in the gas phase. The developed model can be used to carry out numerical simulation of the forest fire-front propagation under the conditions of a heterogeneous FF distribution, the presence of obstacles to the fire propagation, and the wind effects. This model can be used for real-time computation of the fire propagation, for expert assessments of emergency situations, and for assessments of the damage caused by forest fires.