滑动电接触中最小温升的计算研究

在滑动电接触中,接触面温升会改变接触环境,为了降低温升对接触性能的影响,应保证接触温升最小。采用滑动电接触实验机,对其温升系统进行了实验研究,得到了以温升为输出,运行速度、接触载流以及载荷为输入的数据变化关系。采用神经网络拟合出数据所表现出的模型关系,得到从输入映射到输出变量的黑箱模型。在此基础上,通过对最小温升问题的分析,将其转化为最优问题的求解,进而采用粒子群优化算法实现最优载荷的确定,给出了部分运行工况下最小温升,结果表明了设计方法的有效性。     

Effects of moderate cold on performance of psychomotor and cognitive tasks

Two experiments were performed to study the effects of exposure to moderate cold ( + 5°C) on psychomotor and cognitive tasks requiring sustained attention. Twelve male and 12 female subjects participated. Skin and core temperatures, heart rate and subjective ratings were recorded. Considerable decrements in manual dexterity were found during exposure, but no effects on simple reaction time or speed of correct response were observed. The effects of cold on the performance of complex tasks were demonstrated as an increase in the number of errors and the speed of incorrect response and as an increase in the number of false alarms on two computerized performance tests. The results, indicating a negative effect of moderate cold exposure on tasks which require speed and which encourage erroneous responses, are discussed in terms of theories of arousal and distraction.     

Axisymmetric SPH simulation of elasto-plastic contact in the low velocity impact

This paper presents a new contact algorithm to analyze an elasto-plastic contact problem using the SPH (Smoothed Particle Hydrodynamics) method. This algorithm is available to both contact types, which are the particle-to-particle contact and the surface-to-particle one. It is employed to determine the actual boundary normal vector and apply the reproducing condition in the cylindrical coordinate. The variational equation based on the virtual work principle is derived and its solution is obtained by the penalty method, which includes both a penetration and a penetration rate. Numerical simulations are presented to show that the proposed algorithm can be applied to the elasto-plastic contact problem for the case that either both bodies are deformable or one is a rigid wall and the other is deformable. Two colliding bodies can be separated with the expected rebound velocity and the total contact force acting on between them similar to theoretical value. Results of the rod impact analysis are shown to be in agreement with the ones obtained by other solution and experiment.     

The effects of vibration-reducing gloves on finger vibration

Vibration-reducing (VR) gloves have been used to reduce the hand-transmitted vibration exposures from machines and powered hand tools but their effectiveness remains unclear, especially for finger protection. The objectives of this study are to determine whether VR gloves can attenuate the vibration transmitted to the fingers and to enhance the understanding of the mechanisms of how these gloves work. Seven adult male subjects participated in the experiment. The fixed factors evaluated include hand force (four levels), glove condition (gel-filled, air bladder, no gloves), and location of the finger vibration measurement. A 3-D laser vibrometer was used to measure the vibrations on the fingers with and without wearing a glove on a 3-D hand-arm vibration test system. This study finds that the effect of VR gloves on the finger vibration depends on not only the gloves but also their influence on the distribution of the finger contact stiffness and the grip effort. As a result, the gloves increase the vibration in the fingertip area but marginally reduce the vibration in the proximal area at some frequencies below 100 Hz. On average, the gloves reduce the vibration of the entire fingers by less than 3% at frequencies below 80 Hz but increase at frequencies from 80 to 400 Hz. At higher frequencies, the gel-filled glove is more effective at reducing the finger vibration than the air bladder-filled glove. The implications of these findings are discussed.     

Adaptive control of robot contact tasks with on-line learning of planar surfaces

In robot constrained motion problems on planar surfaces with frictional contacts, uncertainties on the contacted surface not only affect the control system performance but also distort control targets. The surface normal direction cosines are in this case uncertain parameters that are involved in both the control law and the control targets. This work proposes an adaptive learning controller that uses force and joint position/velocity measurements to simultaneously learn the surface orientation and achieve the desired goal. Simulation examples for a 6 dof robot are used to illustrate the theoretical results and the performance of the proposed controller in practical cases.     

Nonlinear viscoelastic contact and deformation of freeform virtual surfaces

This article is concerned with the haptic deformation display of discrete viscoelastic surfaces by means of a human fingertip. The virtual surface of a deformable quadrilateral mesh is interactively deformed by a Kelvin–Voigt soft fingertip model attached to the end-effector of a haptic interface device. In achieving this task, a nonlinear constitutive model approximating experimental data from literature is developed for determining the contact point deformations. By employing a new kernel weighting function, the deformations are distributed dependently on the discrete surface topology based on a nonlinear spring–damper net around the contact location. For illustration and evaluation of the proposed approach, a parallel robotic device with a constraint-based controller is adopted. The grip of the device is moved by the user to feel a sense of touch as the soft fingertip deforms the mesh surface of an ex vivo porcine liver tissue. Experimental data indicates stable realistic interactions thorough mechanical coupling between the soft fingertip and the deforming liver tissue. Dynamic response data of liver show rate-dependent hysteretic deformations and match closely with experimental indentation data from literature. A thorough analysis of mesh node count on the sample rate and the rendering quality is also presented.     

Effects of repeated exposures to severely cold environments on thermal responses of humans

Abstract

This study was conducted to investigate the effects of different exposure rates on thermal responses with the total cold exposure time the same under each of the conditions. After resting in a warm room (25°C) for 10 minutes, six male students wearing standard cold protective clothing entered an adjoining cold room (— 25°C). Each 5-, 10- and 20-minute cold exposure was repeated 12, 6 and 3 times, respectively. Each cold exposure was followed by a similar duration of rest at 25°C. Total cold exposure time was the same under the three conditions. Rectal temperature, skin temperatures, blood pressure, 17-hydroxycoyticoids (OHCS), counting task and subjective responses were measured. At the end of the cold exposure skin temperatures in the shorter exposures were higher than those in the other conditions, except on the foot. Discomfort due to cold was less in the shorter exposures and manifestation of discomfort was delayed. However, there were no differences among the three conditions in the fall of rectal temperature and urinary excretion of 17-OHCS, which are good indices of cold stress, Moreover, increase in blood pressure and decrease in counting task due to cold were not different among the three conditions. Even though the cold exposure time for each stay was short, when cold exposures were repeated frequently, cold stress of the whole body and decrease in manual task performance were the same as in the longer cold exposure.     

温控风机电源的研制

风冷形式是多数大功率电源采用的冷却方式,而风冷形式的关键器件就是风机。介绍了利用控制芯片MC34063A实现风机的温度控制,从而达到增加风机寿命的目的。     

Determination of maximum temperatures that can be tolerated on contact with hot surfaces

The knowledge that there is a risk of burning from touching hot surfaces is certainly nothing new. However, little progress has been made so far on the matter of the minimum surface temperature at which burning can be expected. Preparatory work on determining these threshold values has now been finished by the Berufsgenossenschaftlichen Institut für Arbeitssicherheit (Occupational Safety Institute of Industrial Injuries Insurance Institutes). The figures are included in UVV “Hitze” (Accident Prevention Regulation on “Heat”).     

Fuzzy logic system based prediction effort: A case study on the effects of tire parameters on contact area and contact pressure

Various methodologies of artificial intelligence have been recently used for estimating performance parameters of soil working machines and off-road vehicles. Due to nonlinear and stochastic features of soil–wheel interactions, application of knowledge-based Mamdani max–min fuzzy expert system for estimation of contact area and contact pressure is described in this paper. Fuzzy logic model was constructed by use of the experience of contact area and contact pressure utilizing data obtained from series of experimentations in soil bin facility and a single-wheel tester. Two paramount tire parameters: wheel load and tire inflation pressure are the input variables for our model, each has five membership functions. As a fundamental aspect of the fuzzy logic based prediction systems, a set of fuzzy if-then rules were used in accordance with fuzzy logic principles. 25 linguistic if-then rules were included to develop a complicated highly intelligent predicting model based on Centroid method at defuzzification stage. The model performance was assessed on the basis of several statistical quality criteria. Mean relative error lower than 10%, satisfactory scattering around unity-slope line (T), and high coefficient of determination, R², were obtained by the fuzzy logic model proposed in this study.     

高压开关柜触头温度场的数值仿真分析

为验证光纤温度传感器用于高压开关柜触头温度检测的可行性,调研了高压开关柜触头的几何结构,利用多物理场耦合分析软件COMSOL Multiphysics,结合传热学相关理论进行了触头的温度场数值仿真分析。计算了额定电流和短路电流2种情况下的触头温度分布情况,结果表明:触指为触头温度检测的最佳位置;短路电流通过时,触头温度最高可达564℃。在此基础上,在安装、量程、应变干扰三方面对光纤温度传感器进行了分析,证实光纤温度传感器可用于触头温度的检测。     

弓网电弧接触线温度分布仿真研究

为了分析弓网电弧对接触网导线温升的影响,以接触线为研究对象,建立了电弧作用下弓网系统滑动摩擦副的三维有限元模型,利用COMSOL Multiphysics仿真分析,得到不同类型的接触网导线在不同环境下的温度分布特征.结果表明:相同条件下,铜镁合金、纯铜、铜锡合金接触线的温升依次升高.接触线的截面积越大温升越高.同种接触导线分别处于正常、覆冰和潮湿状态时,接触线的温升依次升高.仿真结果对选择接触线以及降低弓网电弧对接触线的热损伤具有一定参考价值.     

The vibration characteristics of chain saws and their influence on vibration white finger disease

The vibration from chain saws can cause vibration-induced white finger disease (VWFD). Measurements of vibration levels on the front and rear handles of different chain saw-types, and on the operator's middle finger were collected at three logging camps on Vancouver Island. Factors effecting the vibration levels on the finger and handles were investigated. The acceleration at the firing frequency was found to be the dominant factor effecting handle and finger vibration. Other factors which were investigated were: grip force; the presence of handle covers; and chain sharpening procedure. Weighted acceleration levels are calculated and this information is used to assess the latency period for fallers to develop VWF disease.     

Evaluation of MODIS land surface temperature data to estimate air temperature in different ecosystems over Africa

The estimation of near surface air temperature (Ta) is useful for a wide range of applications such as agriculture, climate related diseases and climate change studies. Air temperature is commonly obtained from synoptic measurements in weather stations. In Africa, the spatial distribution of weather stations is often limited and the dissemination of temperature data is variable, therefore limiting their use for real-time applications. Compensation for this paucity of information may be obtained by using satellite-based methods. However, the derivation of near surface air temperature (Ta), from the land surface temperature (Ts) derived from satellite is far from straight forward. Some studies have tried to derive maximum Ta from satellites through regression analysis but the accuracy obtained is quite variable according to the study. The main objective of this study was to explore the possibility of retrieving high-resolution Ta data from the Moderate Resolution Imaging Spectroradiometer (MODIS) Ts products over different ecosystems in Africa. First, comparisons between night MODIS Ts data with minimum Ta showed that MODIS nighttime products provide a good estimation of minimum Ta over different ecosystems (with (ΔTs − Ta) centered at 0 °C, a mean absolute error (MAE) = 1.73 °C and a standard deviation = 2.4 °C). Secondly, comparisons between day MODIS Ts data with maximum Ta showed that (ΔTs − Ta) strongly varies according to the seasonality, the ecosystems, the solar radiation, and cloud-cover. Two factors proposed in the literature to retrieve maximum Ta from Ts, i.e. the Normalized Difference Vegetation Index (NDVI) and the Solar Zenith Angle (SZA), were analyzed. No strong relationship between (ΔTs − Ta) and (i) NDVI and (ii) SZA was observed, therefore requiring further research on robust methods to retrieve maximum Ta.     

抛光液温控装置结构设计及温度场分析

为精确控制超光滑表面抛光过程中抛光液的温度,根据温控基本原理设计温控装置结构.将用UG建立的温控装置模型导入GAMBIT中进行温度场分析.针对装置内部温度分布不均匀问题,对其结构进行优化：在装置内加入导热隔板将其分为工作区和调温区,制冷器被置于调温区内;将温控装置的外形结构加入过渡圆角.结果表明：优化后的温控装置形成内外环流,工作区温度波动范围为±0.01℃,温度分布均匀对称,满足高精度温控的恒温和匀温要求.     

Extending and correcting some research results on minimal and harmonic surfaces

In this article, we give necessary and beneficial extension for several important theorems by Monterde et al. on minimal and harmonic surfaces, so that they can be applied to all generic situations for n×m (n≠m or n=m) Bézier surfaces, instead of the special case of n×n Bézier surfaces. At the same time, we point out the errors in Monterde et al.?s six papers, and give the correct and precise answers.     

Contributions and co-ordination of individual fingers in multiple finger prehension

The contributions and co-ordination of external ringer grip forces were examined during a lifting task with a precision grip using multiple fingers. The subjects ( n = 10) lifted a force transducer-equipped grip apparatus. Grip force from each of the five fingers was continuously measured under different object weight (200 g, 400 g, and 800 g) and surface structure (plastic and sandpaper) conditions. The effect of five-, four-, and three-finger grip modes was also examined. It was found that variation of object weight or surface friction resulted in change of the total grip force magnitude; the largest change in finger force, was that for the index finger, followed by the middle, ring, and little fingers. Percentage contribution of static grip force to the total grip force for the index, middle, ring, and little fingers was 420%, 27·4%, 17·6% and 12·9%, respectively. These values were fairly constant for all object weight conditions, as well as for all surface friction conditions, suggesting that all individual finger force adjustments for light loads less than 800 g are controlled comprehensively simply by using a single common scaling value. A higher surface friction provided faster lifting initiation and required lesser grip force exertion, indicating advantageous effect of a non-slippery surface over a slippery surface. The results indicate that nearly 40% force reduction can be obtained when a non-slippery surface is used. Variation in grip mode changed the total grip force, i.e., the fewer the number of fingers, the greater the total grip force. The percent value of static grip force for the index, middle, and ring fingers in the four-finger grip mode was 42·7%, 32·5%, and 24·7%, respectively, and that for the index and middle fingers in the three-finger grip mode was 43·0% and 56·9%, respectively. Therefore, the grip mode was found to influence the force contributions of the middle and ring fingers, but not of the index finger.     

大型电机转子表面温度的网络系统测量

针对大型电机转子表面温度的非接触光纤测温方法和网络化传感器的基本特点,研究了大型电机转子表面温度的网络系统测量;提出了采用CAN总线作为TII接口协议完成STIM和NCAP的长距离连接方法,实现了大型电机转子表面温度的远程在线监测与控制,其测量精度达到0.2%。     

Diurnal variability in sea surface temperature in the Arctic

The formation of diurnal warming events in sea surface temperature (SST) observations in the Arctic is investigated using multiple satellite derived SST products and in situ buoy temperature measurements. Significant diurnal warming events (of the order of several K) are shown to occur even in the Arctic during summer months, when the total daily insolation at high latitudes is, in fact, higher than that at low and mid latitudes. The observed Arctic diurnal warming events are shown to usually happen in persistent low wind conditions, and are more frequent in shallow waters than deep waters. During the studied period of June and July 2008, significant diurnal warming events were observed over most of the studied area, although with smaller spatial extent and reoccurring less often when compared to events reported at low and mid latitudes.