Projection 2 Goes Turbulent - and Fully Implicit

We describe and demonstrate both our newest projection method (fully implicit) for the incompressible Navier-Stokes equations via the finite element method and our newest turbulence model - a somewhat sophisticated nonlinear (cubic) eddy viscosity model that does not employ wall functions or normal distances to walls - the combination providing a method and a model that is each applicable in arbitrary geometry. We demonstrate both via a flow simulation past an automobile-like body at a Reynolds number of 4.3 million.     

A computational approach for eliminating error in the solution of the location set covering problem

The location set covering problem continues to be an important and challenging spatial optimization problem. The range of practical planning applications underscores its importance, spanning fire station siting, warning siren positioning, security monitoring and nature reserve design, to name but a few. It is challenging on a number of fronts. First, it can be difficult to solve for medium to large size problem instances, which are often encountered in combination with geographic information systems (GIS) based analysis. Second, the need to cover a region efficiently often brings about complications associated with the abstraction of geographic space. Representation as points can lead to significant gaps in actual coverage, whereas representation as polygons can result in a substantial overestimate of facilities needed. Computational complexity along with spatial abstraction sensitivity combine to make advances in solving this problem much needed. To this end, a solution framework for ensuring complete coverage of a region with a minimum number of facilities is proposed that eliminates potential error. Applications to emergency warning siren and fire station siting are presented to demonstrate the effectiveness of the developed approach. The approach can be applied to convex, non-convex and non-contiguous regions and is unaffected by arbitrary initial spatial representations of space.     

Nonlinear model-predictive control with hysteresis compensation of an electro-pneumatic clutch for truck applications

This contribution presents two real-time capable nonlinear model-predictive control (NMPC) approaches for an electro-pneumatic clutch for heavy trucks: a centralized control approach and a cascaded one. A clutch is necessary at start-up or during gear shifts to connect or disconnect the combustion engine and the gear box. This automated actuator disburdens the driver and provides the necessary actuation force according to the large torque typically transmitted through the drive train. The force characteristic of the clutch, however, is subject to hysteresis, which is described by a generalized Bouc–Wen model and used for a feedforward hysteresis compensation in the control algorithm. The proposed NMPC-algorithm involves (i) a minimization of the difference between the desired and predicted state vector at the end of the prediction horizon and (ii) flatness-based techniques to compute desired trajectories for the complete state vector as well as the control input. The optimal control is given by an additional, minimum-norm control input that minimizes the difference between the predicted state vector and the desired one at the end of the prediction horizon. Thereby, the computation effort of the NMPC approaches can be kept relatively small, and a real-time evaluation becomes possible. A reduced-order observer estimates an effective pressure in the clutch that also accounts for an uncertain disturbance force. Thereby, a disturbance compensation and a high tracking accuracy is achievable for the piston position as controlled variable. The efficiency of the two proposed control structures is emphasized by experimental results from a dedicated test rig.     

Boundary regularity for Maxwell's equations with applications to shape optimization

The dynamic Maxwell equations with a strictly dissipative boundary condition is considered. Sharp trace regularity for the electric and the magnetic field are established for both: weak and differentiable solutions. As an application a shape optimization problem for Maxwell's equations is considered. In order to characterize the shape derivative as a solution to a boundary value problem, the aforementioned sharp regularity of the boundary traces is critical.     

New series of AB2‐type hyperbranched polytriazoles derived from the same polymeric intermediate: Different endcapping spacers with adjustable bulk and convenient syntheses via click chemistry under copper(I) catalysis

In this article, according to the concept of “suitable isolation group,” six new AB₂‐type polytriazoles containing azo‐chromophore moieties, derived from the same hyperbranched polymer intermediate, were successfully prepared through click reaction under copper(I) catalysis by modifying the synthetic route, in which different isolation groups in different size were introduced to the periphery of the hyperbranched polymers as end‐capping moieties. With the different end‐capping groups, these hyperbranched polymers, P1 – P6 , exhibited different solubility and processability; also, their nonlinear optical properties were modified accordingly, realizing the adjustment of the properties of hyperbranched polymers through the structural design. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Chiral crystal of a C2v‐symmetric 1,3‐diazaaulene derivative showing efficient optical second harmonic generation

Achiral nonlinear optical (NLO) chromophores 1,3‐diazaazulene derivatives, 2‐(4′‐aminophenyl)‐6‐nitro‐1,3‐diazaazulene (APNA) and 2‐(4′‐N,N‐diphenylaminophenyl)‐6‐nitro‐1,3‐diazaazulene (DPAPNA), were synthesized with high yield. Despite the moderate static first hyperpolarizabilities (β₀) for both APNA [(136 ± 5) × 10^?30 esu] and DPAPNA [(263 ± 20) × 10^?30 esu], only APNA crystal shows a powder efficiency of second harmonic generation (SHG) of 23 times that of urea. It is shown that the APNA crystallization driven cooperatively by the strong H‐bonding network and the dipolar electrostatic interactions falls into the noncentrosymmetric P2₁2₁2₁ space group, and that the helical supramolecular assembly is solely responsible for the efficient SHG response. To the contrary, the DPAPNA crystal with centrosymmetric P‐1 space group is packed with antiparalleling dimmers, and is therefore completely SHG‐inactive. 1,3‐Diazaazulene derivatives are suggested to be potent building blocks for SHG‐active chiral crystals, which are advantageous in high thermal stability, excellent near‐infrared transparency and high degree of designing flexibility. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

PORTFOLIO OPTIMIZATION TECHNIQUES FOR A MIXED‐GRAZING SCENARIO FOR AUSTRALIA'S RANGELANDS

Abstract Currently pastoralists in Australia view native mammal species as one of many variables that impact, usually negatively, on their productivity and therefore profitability. This does not necessarily have to be the case. The species with the largest impact, kangaroos, have a value that could be incorporated into their income stream as a method of both reducing risk and increasing biodiversity, and therefore increasing resilience. An investigation of the idea of optimally allocating stocking rates using techniques analogous to classical portfolio selection optimization is conducted. Using historical pricing data for beef, wool, and kangaroo meat, an efficient frontier is formed to analyze the best scenario dependent on an investors risk aversion. It is shown that there is a clear opportunity for pastoralists to benefit economically by the inclusion of kangaroos in a mixed‐grazing strategy for Australian rangelands.     

道路约束条件下的移动机器人跟踪

为提高移动机器人的位置估计精度和跟踪效果,提出一种基于道路约束条件下的移动机器人鲁棒约束H∞滤波(CHF)跟踪算法.首先,将机器人移动的道路网络作为跟踪的约束条件,并利用当前统计模型对机器人的运动进行建模.其次,将道路约束条件作为机器人跟踪的非线性状态约束,利用最小协方差估计推导了鲁棒CHF递推方程.通过拉格朗日乘子法对非线性约束优化估计问题进行求解,并利用约束信息对CHF算法的状态更新过程进行了改进.最后,通过对CHF算法和无约束的H∞滤波算法的跟踪性能进行了对比分析和验证.仿真结果表明,该算法可以实现机器人的跟踪,且跟踪精度优于HF算法.     

Initial guess by improved population-based intelligent algorithms for large inter-frame deformation measurement using digital image correlation

Digital image correlation (DIC) has received a widespread research and application in experimental mechanics. In DIC, the performance of subpixel registration algorithm (e.g., Newton-Raphson method, quasi-Newton method) relies heavily on the initial guess of deformation. In the case of small inter-frame deformation, the initial guess could be found by simple search scheme, the coarse-fine search for instance. While for large inter-frame deformation, it is difficult for simple search scheme to robustly estimate displacement parameters and deformation parameters simultaneously with low computational cost. In this paper, we proposed three improving strategies, i.e. Q-stage evolutionary strategy (T), parameter control strategy (C) and space expanding strategy (E), and then combined them into three population-based intelligent algorithms (PIAs), i.e. genetic algorithm (GA), differential evolution (DE) and particle swarm optimization (PSO), and finally derived eighteen different algorithms to calculate the initial guess for qN. The eighteen algorithms were compared in three sets of experiments including large rigid body translation, finite uniaxial strain and large rigid body rotation, and the results showed the effectiveness of proposed improving strategies. Among all compared algorithms, DE-TCE is the best which is robust, convenient and efficient for large inter-frame deformation measurement.