Formulation of the thermal problem

This paper describes the thermal problem and presents the experimental data for validation. The thermal problem involves validating a model for heat conduction in a solid. The mathematical model is based on one-dimensional, linear heat conduction in a solid slab, with heat flux boundary conditions. Experimental data from a series of material characterization, validation, and accreditation experiments related to the mathematical model are provided. The objective is to use the series of experiments to assess the model, and then use the model to predict regulatory performance relative to a regulatory requirement. The regulatory requirement is defined in terms of the probability that a surface temperature not exceed a specified temperature at the regulatory conditions.     

Determination of persistence effects in spatio-temporal patterns of upward long-wave radiation flux density from an urban courtyard by means of Time-Sequential Thermography

This research analyses upward long-wave radiation flux density from urban surfaces using a high-resolution thermal-infrared (TIR) camera and meteorological measurements in the city of Berlin, Germany. We report spatio-temporal patterns of the difference between upward long-wave radiation flux density from courtyard surfaces and the roof. For temporal analysis, the TIR camera recorded one TIR image per minute over a period of two days from 3rd to 5th May 2007. Three-hourly averaged thermal patterns show persistence effects due to shadow, sky-view factor (SVF) distribution in the courtyard, thermal properties of the surface materials, human activities and turbulence characteristics of the surface-atmosphere interface. The history of shadow influences the 24-hourly mean pattern. Shadow caused by temporarily parked cars results in a lower upward long-wave radiation flux density compared to the non-shadowed surface close to it. Immediately after car departure, this difference decreases. We propose a method to derive the thermal admittance of a concrete surface based on TIR data from this attenuation process. This study shows that ground-based high-resolution TIR imagery is highly suitable to investigate surface thermal properties and dynamic processes controlling thermal patterns within a complex three-dimensional (3D) urban structure.     

Wearer related performance standards for conditioned clothing

Abstract

Estimates, based on American experience of work in the heat, indicate that in the UK, half a million workers or more may be working in thermally uncomfortable and stressfully hot environments. In addition, many will be experiencing cold working conditions and associated discomfort. The role of protective clothing as one of the factors involved in imposing thermal stress is emphasized.

One method of thermal stress control is to provide conditioned garments which warm or cool the wearer as required. The use of ‘air supplied’ garments for cooling is specifically dealt with and the methods of defining their performance reviewed. The application of the concept of ‘per cent wetted skin surface area’ is discussed as one method of defining the performance of air ventilated garments if thermal comfort cannot be achieved. The use of low pressure air for ventilating garments is proposed. The performance of such a system employing a small battery powered blower is defined in terms of the wearers work rate and supply air temperature and volume using the wetted surface area concept. The necessary steps to be taken by manufacturers if they are to develop the market for such conditioned garments are outlined.     

SEAs导纳控制的μ综合方法

SEAs (Series elastic actuators)具有在确保机器人性能的基础上兼顾其安全性的特点, 因此被广泛地应用在康复机器人中. 为实现良好的康复训练效果, 机器人需根据实际要求呈现不同的阻抗特性. 本文采用μ综合技术解决了SEAs导纳控制器的设计问题. 首先, 考虑参数摄动、传感器噪声、输入干扰及控制输入限制等不确定性因素, 建立SEAs模型. 其次, 应用混合稳定性原理分析系统的交互稳定性. 由于无源环境的阻抗在高频段必然呈现小增益特性, 所以, 当端口导纳在低频段满足无源性, 高频段具有小增益时, 就能确保交互的稳定性. 然后, 将SEAs的导纳控制综合问题转化为实际端口导纳与期望导纳匹配的μ综合问题. 最后, 通过调节加权函数, 不仅让SEAs闭环系统的端口导纳逼近期望的端口导纳, 还能同时满足交互稳定性条件, 从而可以独立于环境因素来设计导纳控制器. 仿真结果表明, 基于μ综合方法设计的控制器, 能精确地逼近期望的端口导纳, 且确保交互稳定性. 另外, 通过Hankel逼近方法得到的降阶控制器也具有满意的控制效果.     

Numerical characterization and experimental verification of an in-plane MEMS-actuator with thin-film aluminum heater

In this paper, a novel concept of a thermo-mechanical MEMS actuator using aluminum thin-film heaters on a thermal oxide for electrical insulation is presented. The actuator is part of an universal tensile testing platform for thermo-mechanical material characterization of one dimensional materials on a micro- and nano-scopic scale under different environmental conditions, as varying temperatures, pressure, moisture or even vacuum and is realised in BDRIE technology. It is shown, that the actuator concept fulfills the requirements for the use in a tensile loading stage along with heterogeneously integrated nanofunctional elements, following a specimen centered approach in line with bottom-up self-assembly processes. Simulation and experiment agree very well in the thermal and mechanical domain and allow subsequent optimisation of the actuator performance.     

Fast, curvature-based prediction of rolling forces for porous media based on a series of detailed simulations

Using thermal spraying various surface coatings consisting of different material compositions can be manufactured. Besides different solid phases the resulting coating microstructure often contains a non-negligible amount of pores. In this context a roller burnishing process with a hydrostatic ball-point-tool is examined to compact the thermally sprayed coating, thereby reducing porosity. The rolling process is performed by a robot on free-formed workpieces. A simulation concept for the prediction of forces in a robot-guided roller burnishing process based on a series of detailed ABAQUS simulations is presented. It is shown that, based on these test configurations, the process forces can be calculated much faster and with sufficient precision. Thereby an optimal rolling path, which requires the least amount of normal force to be applied, can be determined efficiently leading to the decision whether a specific robot is equipped to handle the path. Furthermore, the described approach may be used as a pattern to apply similar methods to other engineering problems where accurate simulative solutions exist, but cannot be applied to problems of realistic size due to their expenditure of time.     

A review of solid shape modelling based on integrity verification

The potential benefits of using a canonical model for representing the shapes of solid objects has led to the design and implementation of a number of geometric modellers, with varying capabilities. This paper reviews the approaches taken in solid modelling by defining the well-formedness conditions which must be implemented in any modelling system. The methods for satisfying the well-formedness constraints in the various solid modelling methods are reviewed, using the concept of integrity constraint. The incorporation of integrity constraints, both explicitly and implicitly, into solid modellers are considered, with particular focus on boundary modellers. The use of integrity constraints for defining shape families and assembly families are also presented. The result is a unified view of solid shape modelling systems that enables their classification and extension into particular application areas.     

具有非线性时变滑模面的变结构控制系统设计

以二阶系统为研究对象,提出一种具有非线性连续时变滑模面的变结构控制器设计方法.用该方法设计的变结构控制系统,系统的初始状态位于滑模面上,通过滑模面斜率的连续变化,能消除系统状态变量到达滑模面的过程,极大地提高对参数摄动和外部干扰的鲁棒性,应用Lyapunov法证明时变滑模面的存在,计算机仿真结果证明该方法的正确性.     

Numerical prediction of three-dimensional time-dependent viscoelastic extrudate swell using differential and algebraic models

The dynamic behavior of a droplet on a solid surface is simulated by the lattice Boltzmann method (LBM) for two-phase fluids with large density differences; the wetting boundary condition on solid walls is incorporated in this simulation. By using the method, the dynamic behavior of a droplet impinging on a horizontal wall is investigated in terms of various Weber numbers. The dynamic contact angle, the contact line velocity, and the wet length are calculated, and found to be in good agreement with available experimental data. In addition, the method is applied to simulations of the collision of a falling droplet with a stationary droplet on a solid surface. The behavior of the droplets and the mixing process during their collision are simulated in terms of various impact velocities and several static contact angles on the solid surface. It is seen that mixing occurs around the rim of the coalescent droplet due to the circular flows. Also, the relationship between the mixing rate of the primary coalescent droplet and Weber number is investigated.     

Numerical simulation of fluid–structure interaction by SPH

A Lagrangian model for the numerical simulation of fluid–structure interaction problems is proposed in the present paper. In the method both fluid and solid phases are described by smoothing particle hydrodynamics: fluid dynamics is studied in the inviscid approximation, while solid dynamics is simulated through an incremental hypoelastic relation. The interface condition between fluid and solid is enforced by a suitable term, obtained by an approximate SPH evaluation of a surface integral of fluid pressure.The method is validated by comparing numerical results with laboratory experiments where an elastic plate is deformed under the effect of a rapidly varying fluid flow.     

Precise and full extraction of the coupling-of-mode parameters with periodic Green''''s function

Due to the more and more stringent requirements on surface acoustic wave (SAW) filters performances, recently considerable attention has been focused on the investigation of low-loss SAW filters in the last decade. Most low-loss filters, such as single phase unidirectional transducers (SPUDT), employ the electrodes multi-reflection effects to realize low insertion loss. In the design of low-loss filters, the phenomenological coupling-of-mode (COM) model[1] method is frequently used. Its …     

反应堆堆芯围筒结构热流固耦合热变形分析

针对反应堆堆芯围筒热流固耦合问题,采用三维有限元法研究堆芯围筒的热变形.考察ANSYS的三维实体热单元SOLID 70,三维实体单元SOLID 45,三维表面热效应单元SURF 152和三维热-流耦合管单元FLUID 116等单元类型的特点和实用性.建立堆芯围筒、吊篮和冷却剂的温度分析有限元模型：堆芯围筒和吊篮采用SOLID 70,结构表面与冷却剂的对流传热表面采用SURF152,堆芯围筒与吊篮之间冷却剂采用FLUID 116.采用SOLID 45建立堆芯围筒有限元模型,根据得到的堆芯围筒、吊篮和冷却剂的温度场结果分析堆芯围筒热变形.结果表明,在考虑堆芯围筒及吊篮固体和流体的交叉耦合的基础上,采用三维有限元法能比较客观地模拟反应堆堆芯处的复杂运行环境.     

线性离散时变系统的鲁棒自适应控制

利用滑模控制的概念,提出一种线性离散时变系统的自适应控制设计方法.在等价 控制信号外,用两个补偿项代替切换信号,避免了传统滑模控制中的抖动现象.文中证明了自 适应闭环系统的稳定性.     

上肢康复外骨骼机器人的模糊滑模导纳控制

为了辅助上肢运动功能障碍患者进行不同模式的康复训练,基于上肢康复外骨骼机器人系统,提出了一种模糊滑模导纳控制策略,实现训练过程的人机协调控制.首先,介绍了康复外骨骼的整体结构和实时控制平台.然后,分析了模糊滑模导纳控制算法的推导过程,并根据李亚普诺夫稳定性判据证明系统的稳定性.最后,在不同系统导纳参数条件下,分别进行被动训练模式和主动训练模式实验,并对比分析了实验过程中运动偏差、人机交互力以及肱二头肌表面肌电信号的变化特点.实验结果表明,选择合适的目标导纳模型可以优化康复训练强度与难度,提高人机交互柔顺性与患者参与度,满足不同瘫痪程度和康复进度患者的训练需求.     

Controllable C1 continuous blending of time-dependent parametric surfaces

This paper proposes the concept of blending time-dependent varying surfaces, and develops a new method to create a controllable C1 continuous blending surface between primary parametric surfaces whose position and shape change with time. We treat it as a boundary-valued problem defined by the mathematical model of a vectored dynamic fourth-order partial differential equation subjected to time-dependent C1 continuous blending boundary constraints. High performance blending surface generation is achieved through the development of an approximate analytical solution of the mathematical model. We investigate the accuracy and efficiency of the solution, study the effective shape control of the blending surfaces, and apply the obtained solution to tackle surface blending problems. The applications demonstrate that our proposed approach is very effective and efficient in dealing with controllable C1 continuous surface blending between time-dependent varying parametric surfaces.     

Fuzzy logic based adaptive admittance control of a redundantly actuated ankle rehabilitation robot

Ankle rehabilitation robots have recently attracted great attention since they provide various advantages in terms of rehabilitation process from the viewpoints of patients and therapists. This paper presents development and evaluation of a fuzzy logic based adaptive admittance control scheme for a developed 2-DOF redundantly actuated parallel ankle rehabilitation robot. The proposed adaptive admittance control scheme provides the robot to adapt resistance/assistance level according to patients' disability level. In addition, a fuzzy logic controller (FLC) is developed to improve the trajectory tracking ability of the rehabilitation robot subject to external disturbances which possibly occur due to human-robot interaction. The boundary scales of membership functions of the FLC are tuned using cuckoo search algorithm (CSA). A classical proportional-integral-derivative (PID) controller is also tuned using the CSA to examine the performance of the FLC. The effectiveness of the adaptive admittance control scheme is observed in the experimental results. Furthermore, the experimental results demonstrate that the optimized FLC significantly improves the tracking performance of the ankle rehabilitation robot and decreases the steady-state tracking errors about 50% compared to the optimized PID controller. The performances of the developed controllers are evaluated using common error based performance indices indicating that the FLC has roughly 50% better performance than the PID controller.     

Topology optimization of thermoelastic structures: mean compliance minimization or elastic strain energy minimization

In this work, two different formulations that minimize the mean compliance and elastic strain energy of a structure as the objective function are comparatively investigated for topology optimization of thermoelastic problems. As thermal load is a design-dependent load compared with mechanical load, the particularity of the problem and the difference between both formulations are highlighted in terms of sensitivity analysis and related optimization results based on numerical tests. The concept of load sensitivity is used to interpret quantitatively the underlying influences of thermal and mechanical loads upon optimized results in both formulations.     

Concept drift and how to identify it

This paper studies concept drift over time. We first define the meaning of a concept in terms of intension, extension and label. Then we study concept drift over time using two theories: one based on concept identity and one based on concept morphing. A qualitative toolkit for analysing concept drift is proposed to detect concept shift and stability when concept identity is available, and concept split and strength of morphing chain if using the morphing theory. We apply our framework in four case-studies: a political vocabulary in SKOS, the DBpedia ontology in RDFS, the LKIF-Core ontology in OWL and a few biomedical ontologies in OBO. We describe ways of identifying interesting changes in the meaning of concept within given application contexts. These case-studies illustrate the feasibility of our framework in analysing concept drift in knowledge organisation schemas of varying expressiveness.     

Speed-accuracy characteristics of human-machine cooperative manipulation using virtual fixtures with variable admittance

This work explores the effect of virtual fixture admittance on the performance, defined by error and time, of task execution with a human-machine cooperative system. A desired path is obtained using computer vision, and virtual fixtures for assistance in planar path following were implemented on an admittance-controlled robot. The admittance controller uses a velocity gain, so that the speed of the robot is proportional to the force applied by the operator. The level of virtual fixture guidance is determined by the admittance ratio, which is the ratio of the admittance gain of the force components orthogonal to the path to the gain of the force components parallel to the path. In Experiment 1, we found a linear relationship between admittance ratio and performance. In Experiment 2, we examined the effect of admittance ratio on the performance of three tasks: path following, off-path targeting, and obstacle avoidance. An algorithm was developed to select an appropriate admittance ratio based on the nature of the task. Automatic admittance ratio tuning is recommended for next-generation virtual fixtures. Actual or potential applications of this research include surgery, assembly, and manipulation at the macro and micro scales.     

Adaptive robust control and admittance control for contact-driven robotic surface conditioning

This work presents a hybrid position/force control of robots for surface contact conditioning tasks such as polishing, profiling, deburring, etc. The robot force control is designed using sliding mode ideas to benefit from robustness. On the one hand, a set of equality constraints are defined to attain the desired tool pressure on the surface, as well as to keep the tool orientation perpendicular to the surface. On the other hand, inequality constraints are defined to adapt the tool position to unmodeled features present in the surface, e.g., a protruding window frame. Conventional and non-conventional sliding mode controls are used to fulfill the equality and inequality constraints, respectively. Furthermore, in order to deal with sudden changes of the material stiffness, which are forwarded to the robot tool and can produce instability and bad performance, adaptive switching gain laws are considered not only for the conventional sliding mode control but also for the non-conventional sliding mode control. A lower priority tracking controller is also defined to follow the desired reference trajectory on the target surface. Moreover, the classical admittance control typically used in force control tasks is adapted for the proposed surface contact application in order to experimentally compare the performance of both control approaches. The effectiveness of the proposed method is substantiated by experimental results using a redundant 7R manipulator, whereas its advantages over the classical admittance control approach are experimentally shown.