A level-set based variational method for design and optimization of heterogeneous objects

A heterogeneous object is referred to as a solid object made of different constituent materials. The object is of a finite collection of regions of a set of prescribed material classes of continuously varying material properties. These properties have a discontinuous change across the interface of the material regions. In this paper, we propose a level-set based variational approach for the design of this class of heterogeneous objects. Central to the approach is a variational framework for a well-posed formulation of the design problem. In particular, we adapt the Mumford-Shah model which specifies that any point of the object belongs to either of two types: inside a material region of a well-defined gradient or on the boundary edges and surfaces of discontinuities. Furthermore, the set of discontinuities is represented implicitly, using a multi-phase level set model. This level-set based variational approach yields a computational system of coupled geometric evolution and diffusion partial differential equations. Promising features of the proposed method include strong regularity in the problem formulation and inherent capabilities of geometric and material modeling, yielding a common framework for optimization of the heterogeneous objects that incorporates dimension, shape, topology, and material properties. The proposed method is illustrated with several 2D examples of optimal design of multi-material structures and materials.     

A component-based parallel infrastructure for the simulation of fluid–structure interaction

The Uintah computational framework is a component-based infrastructure, designed for highly parallel simulations of complex fluid–structure interaction problems. Uintah utilizes an abstract representation of parallel computation and communication to express data dependencies between multiple physics components. These features allow parallelism to be integrated between multiple components while maintaining overall scalability. Uintah provides mechanisms for load-balancing, data communication, data I/O, and checkpoint/restart. The underlying infrastructure is designed to accommodate a range of PDE solution methods. The primary techniques described here, are the material point method (MPM) for structural mechanics and a multi-material fluid mechanics capability. MPM employs a particle-based representation of solid materials that interact through a semi-structured background grid. We describe a scalable infrastructure for problems with large deformation, high strain rates, and complex material behavior. Uintah is a product of the University of Utah Center for Accidental Fires and Explosions (C-SAFE), a DOE-funded Center of Excellence. This approach has been used to simulate numerous complex problems, including the response of energetic devices subject to harsh environments such as hydrocarbon pool fires. This scenario involves a wide range of length and time scales including a relatively slow heating phase punctuated by pressurization and rupture of the device.     

三元相图中字符提取算法

针对三元相图的特点,提出了一种基于轮廓跟踪的文图分离方法,通过轮廓跟踪得到每个连通域的外接矩形,分离出大小在一定范围内的外接矩形,从而实现文字与图形的分离。     

基于非结构滑移网格技术的旋翼型无人机空气动力学并行数值模拟方法

在现代飞行器设计中,数值模拟方法以低成本、高效率和高灵活性等优点成为研究飞行器空气动力学的重要方法.在旋翼型无人机流场模拟中,由于旋翼与机身存在相互作用,为获得精确模拟结果需要对整个无人机的流场进行模拟,因此,有效地模拟旋翼与机身的相对运动是实现成功模拟的关键步骤,这使得此类模拟问题极具挑战性.文章设计了一套求解旋翼型无人机空气动力学数值模拟问题的基于非结构滑移网格技术的高可扩展并行计算方法.该方法对控制方程的离散,在空间方向采用非结构移动网格有限元方法,时间推进采用全隐式二阶向后差分格式,最后采用一种并行Newton-Krylov-Schwarz方法求解离散后的非线性方程组.作为应用,文章对一个真实旋翼型无人机模型在悬停状态下的外流场进行了数值模拟,获得了一些非常详细的流场信息.数值结果显示,算法在天河2号上使用4 096个处理器核时仍具有接近线性的并行加速比,这为下一步开展旋翼型无人机的高保真度快速模拟奠定了良好的基础.     

A front-tracking method for computational modeling of impact and spreading of viscous droplets on solid walls

A finite-difference/front-tracking method is developed for computational modeling of impact and spreading of a viscous droplet on dry solid walls. The contact angle is specified dynamically using the empirical correlation given by Kistler (1993). The numerical method is general and can treat non-wetting, partially wetting and fully wetting cases but the focus here is placed on the partially wetting substrates. Here the method is implemented for axisymmetric problems but it is straightforward to extend it to three dimensional cases. Grid convergence of the method is demonstrated and the validity of the dynamic contact angle method is examined. The method is first tested for the spreading and relaxation of a droplet from the initial spherical shape to its final equilibrium conditions for various values of Eotvos number. Then it is applied to impact and spreading of glycerin droplets on wax and glass substrates and, the results are compared with experimental data of Sikalo et al. (2005). The numerical results are found in a good agreement with the experimental data. Finally the effects of governing non-dimensional numbers on the spreading rate, apparent contact angle and deformation of the droplet are investigated.     

A hybrid strategy for the time- and energy-efficient trajectory planning of parallel platform manipulators

In planning the trajectories of motor-driven parallel platform manipulators, the objective is to identify the trajectory which accomplishes the assigned motion with the minimal travel time and energy expenditure subject to the constraints imposed by the kinematics and dynamics of the manipulator structure. In this study, the possible trajectories of the manipulator are modeled using a parametric path representation, and the optimal trajectory is then obtained using a hybrid scheme comprising the particle swarm optimization method and the local conjugate gradient method. The numerical results confirm the feasibility of the optimized trajectories and show that the hybrid scheme is not only more computationally efficient than the standalone particle swarm optimization method, but also yields solutions of a higher quality.     

An Attempt at the Classification of Energy Decaying Schemes for Structural and Multibody Dynamics

This paper analyzes the formulation of energy preserving/decaying schemes for dynamics problems. We argue that any energy preserving/decaying scheme can always be seen as composed of an underlying temporal discretization, that is then slightly modified in order to prove a discrete energy bound within a time step. While the details of the modified scheme depend in a critical way on the governing equations, the underlying discretization can in principle be applied to a variety of models. We review some of the temporal underlying schemes recently proposed in the literature, presenting them with a common notation. We show their similarities and highlight their differences.     

A model of (en)action to approach embodiment: a cornerstone for the design of virtual environments for learning

This paper presents a model of (en)action from a conceptual and theoretical point of view. This model is used to provide solid bases to overcome the complexity of designing virtual environments for learning (VEL). It provides a common grounding for trans-disciplinary collaborations where embodiment can be perceived as the cornerstone of the project. Where virtual environments are concerned, both computer scientists and educationalists have to deal with the learner/user’s body; therefore the model provides tools with which to approach both human actions and learning processes within a threefold model. It is mainly based on neuroscientific research, including enaction and the neurophysiology of action.     

A 3D mathematical model for the prediction of mucilage dynamics

We illustrate a three-dimensional mathematical model for the prediction of biological processes that typically occur in a sea region with minor water exchange. The model accounts for particle transport due to water motion, turbulent diffusion and reaction processes and we use a fractional-step approach for discretizing the related different terms.     

A Dynamic Network Model of the Color Visual Pathways for Attentive Recognition

A neural network architecture for the segmentation and recognition of colored and textured visual stimuli is presented. The architecture is based on the Boundary Contour System and Feature Contour System (BCS/FCS) of S. Grossberg and E. Mingolla. The architecture proposes a biologically-inspired mechanism for color processing based on antagonist interactions. It suggests how information from different modalities (i.e. color or texture) can be fused together to form a coherent segmentation of the visual scene. It identifies two stages of visual pattern recognition, namely, a global preattentive recognition of the visual scene followed by a local attentive recognition within a particular visual context. The global and local classification and recognition of visual stimuli use ART-type models of G. Carpenter and S. Grossberg for pattern learning and recognition based on color and texture. One example is presented corresponding to an figure-figure separation task. The architecture provides a mechanism for segmentation, categorization and recognition of images from different classes based on self-organizing principles of perception and pattern recognition.     

一种快速提取铜块图像感兴趣区域的方法

针对铜块合金样本感兴趣的区域(ROI)有效提取问题,提出了一种完整的单一背景下提取铜块合金样本ROI的方法,进而抽象ROI提取问题.将该问题分割为2个步骤:第一步为背景相关的种子点提取,第二步为背景无关的ROI确定,并提出了一种基于种子点的SBRE方法.复杂背景下的SBRE方法首先建立HSV颜色模型,然后通过不断更新步长收缩搜索矩形框最终使搜索矩形框完全位于铜截面内部,进而确定种子点,最终确定ROI.实际测试结果表明:该方法准确、快速.     

A hybrid fuzzy evaluation method for safety assessment of food-waste feed based on entropy and the analytic hierarchy process methods

The product safety of food-waste feed is the key factor limiting the development of its industrial chain. In this paper, we construct a method based on data from the testing of food-waste feed with comprehensive evaluation of its product safety by integrating fuzzy mathematics effectively, i.e., the entropy method (EM), and the model of the analytic hierarchy (AHP) process. Furthermore, a hierarchical three-level evaluation-index system including biological-safety and chemical-safety considerations is first established via data analysis, data surveys and expert experiential investigation as well, with an actual case in China being fully applied. In addition, we apply the EM and AHP process to calculate the weights of the individual evaluation indices. Finally, through the dimensionless treatment of test data from samples, we determine the degree of membership of each test value relative to the different levels of safety using a trapezoidal membership function. By adopting the developed three-level model of fuzzy mathematics for comprehensive evaluation, we derive the safety grades of tested samples. The comprehensive evaluation method developed in this paper can effectively overcome the shortcomings of traditional single-factor evaluation and offer the qualitative and quantitative advantages of expert survey and basic data research as well. As a result, it is considerably applicable for the product-safety analysis and production control of animal feed generated from food waste.