风冷散热器热阻流阻测试系统风洞和试验段设计

热阻和流阻是电力半导体用散热器的两个重要热工参数.本文介绍了风冷散热器的热阻和流阻测试系统中风洞和试验段的设计方法和过程.试验段最大尺寸为500mm×250mm,最大风速为15m/s,散热器最大压损800Pa.风洞气动结构采用了低速直流风洞设计,动力段布置在风洞入口,后面依次为扩张段、稳定段、收缩段和试验段,包括试验段在内,风洞总长度为5.2m,收缩比为5.76.根据气动计算结果,空风洞压力损失为201Pa,总输入功率为1.9kW.通过在试验段箱体内部设置由横板和立板组成的抽屉板,实现风道截面尺寸可调.横版与立板通过滑槽连接,两个立板之间距离在一定范围内无级可调.立板设计成几个尺寸可以更换,实现不同高度散热器的测量.     

Ti-48Al-2Nb-2Cr合金铸造收缩特性研究

目的 研究TiAl合金铸造过程的收缩特性。方法 采用Ti4822合金,通过设计长方体、圆柱体、回字形和环形4种典型结构,开展了熔模精密铸造工艺实验。结果 基础尺寸在10~80 mm时,Ti4822合金的自由线收缩率在3.11%~2.09%之间,受阻收缩比自由收缩低30%~50%左右,同时随着基础尺寸的增加,自由线收缩量增加,而收缩率呈降低趋势。结论 收缩数据和规律的获得,为TiAl合金铸件尺寸精度控制提供了基础数据。     

在一米投影仪上用直角座标法绘制放大图

在大型投影仪上检查曲线样板,一般都需要画放大图。如何把放大图画得准确,是一个关键。如下图所示的断面型线是由多段半径大小不同的弧线组成。其中最大的半径为145mm,最小半径为0.4mm,曲线轮廓尺寸约40×50mm。原始样板曲线部分的误差要求不大于0.03mm。     

4D炭/炭复合材料试样尺寸对剪切性能的影响

以4D炭/炭复合材料为研究对象,对不同尺寸规格冲剪试样和三点短梁压剪试样进行了剪切性能测试,分析了试样尺寸对剪切性能的影响。研究表明,试样的尺寸规格对其剪切性能有着显著影响。对于冲剪试样,Φ50mm×4mm试样剪切强度测试值高于Φ50mm×6mm试样,Φ50mm×4mm试样呈韧性断裂特征;Φ50mm×6mm试样呈脆性断裂特征。对于三点短梁压剪试验,在所用的各尺寸规格试样中,40mm×6mm×6mm试样采用26mm跨距时,测试数据的离散性最小。     

4D炭/炭复合材料试样尺寸对剪切性能的影响

以4D炭/炭复合材料为研究对象,对不同尺寸规格冲剪试样和三点短梁压剪试样进行了剪切性能测试,分析了试样尺寸对剪切性能的影响。研究表明,试样的尺寸规格对其剪切性能有着显著影响。对于冲剪试样,Φ50mm×4mm试样剪切强度测试值高于Φ50mm×6mm试样,Φ50mm×4mm试样呈韧性断裂特征;Φ50mm×6mm试样呈脆性断裂特征。对于三点短梁压剪试验,在所用的各尺寸规格试样中,40mm×6mm×6mm试样采用26mm跨距时,测试数据的离散性最小。     

锦屏一级水电站大坝高压、高流速流道钢衬接触灌浆施工技术

锦屏一级水电站大坝设置2个放空底孔和5个泄洪深孔,其中放空底孔底部高程位于EL1750.00m,放空底孔布置有钢衬,钢衬断面均为矩形,包括渐变段和水平直段,其水平直段断面净尺寸为5.0m(宽)×9.2m(高),出口高度向下收缩至6.082m(净高尺寸);泄洪深孔底部高程EL1792.0m,泄洪深孔布置有钢衬,断面均为矩形,泄洪深孔包括渐变段和水平直段,其水平直段断面净尺寸为5.448m(宽)×9.2m(高),出口高度向下收缩。钢衬由顶衬、侧衬和底衬组成,施工为先进行钢衬安装,后进行混凝土浇筑,最后进行钢衬的接触灌浆施工。     

利用CFD对不同尺寸上下冲击式速冻机静压腔流场的研究

为进一步优化上下冲击式速冻机的冻结效果,本文以静压腔尺寸为4 m×1. 5 m×2 m的实体速冻机为基础,保证入口压力为190 Pa、入口体积流量为2. 64 m3/s不变,提出了4 m×1. 5 m×1. 5 m、4 m×2 m×1. 5 m、4 m×2 m×2 m、4 m×2. 5 m×1. 5 m、4 m×2. 5 m×2 m等5种不同的静压腔尺寸,通过CFD来模拟静压腔尺寸变化对于速冻机内部流场的改变,从速冻机喷嘴出口风速、钢带表面气流的矢量分布、钢带表面换热强度及换热均匀性等方面来综合分析静压腔内部换热特性。结果表明:在静压腔入口流量相同、压力不变的情况下,唯有4 m×1. 5 m×1. 5 m的出口风速与原有尺寸的出口风速相差较小,其余尺寸的出口风速略小但变化幅度不明显。而该尺寸的换热强度以及换热均匀性却远不如4 m×2. 5 m×1. 5 m、4 m×2. 5 m×2 m。此外,静压腔尺寸为4m×2 m×2 m的换热强度虽然比4 m×1. 5 m×2 m的换热强度高约4. 85%,但均匀性较差,不足以成为优选设计。4 m×2. 5 m×1. 5m与4 m×2. 5 m×2 m的换热强度达到177. 76和177. 39,比原有尺寸下钢带表面换热强度高约6. 81%和6. 59%,且均匀性也为最佳。结合上述因素,4 m×2. 5 m×1. 5 m和4 m×2. 5 m×2 m在出口风速、换热强度及均匀性方面均为5种尺寸中最优的设计。     

微喷管内气体流动特性研究

研究旨在提高微型空间推进器和微型气体涡轮机等微器件的性能。采用硅微加工技术在硅片上制作出矩形截面三维收缩扩张微喷管,喉部宽度为16mm,深度为20mm,收缩比为1.6251。实验测量了不同进出口压比条件下微喷管内氮气流量特性。实验设定进出口压比范围为1.0~5.0,由此出口体积流量范围为0~0.2mL/s,出口截面特征雷诺数小于500。基于两种数值模拟方法(有限体积法和Boltzmann气体动力学方法)对微喷管内部流动特性进行了数值模拟。数值模拟结果与实验结果相吻合。数值模拟结果发现几点不同于宏观流动的异常现象随着压比的提高,声速截面逐渐偏离喉部,向下游区移动,并且下游区的流动不断加速。当压比达到5.0时,出口截面中心区域的马赫数达到1.26。沿程压力分布呈现非线性下降的趋势。这些现象主要是由于相比于常规尺度管道,微小尺度下表面效应引起的粘性附面层效应和三维效应更显著。     

基于Cape Pack与Load Expert多包装配送的优化

目的运用科学方法合理优化运输方案。方法利用运输设计软件Cape Pack和Load Expert,从运输包装物品的排列方式入手进行空间优化设计。结果听装运输包装尺寸为200 mm×300 mm×103 mm、PET瓶装运输包装尺寸为169 mm×173 mm×224 mm、冲剂袋装盒式运输包装尺寸为250 mm×568mm×166 mm时的组合运输更加经济。结论优化后的方案可节约运输货车的使用,提高配送效率,降低物流业运输配送的成本。     

微型拉瓦尔喷管的流体仿真分析和优化

采用Fluent软件对微型模块化液化气微推进系统的拉瓦尔喷管进行了流体仿真,得到了喷管各个尺寸因素对有效比冲和推力的影响曲线关系,并给出了喷管的最终优化结果。喷管有五个尺寸因素:入口直径、喉部直径、出口直径、收缩段长度和扩张段长度。其中,喉部直径越大,推力越大,有效比冲越小;出口直径越大,推力和有效比冲越大;收缩段长度较小时,对有效比冲影响较大,对推力几乎无影响;入口直径和扩张段长度对推力和有效比冲的影响很小可忽略。     

拉曼激光相位噪声对原子干涉重力仪测量分辨力的影响

为了保证相控阵雷达的性能,它的天线现场校准越来越受到重视。本文首先介绍相控阵雷达天线现场校准的现状, 提出目前存在的问题。然后分析光学电磁场探测技术优势,阐述基于光子技术的相控阵雷达天线现场校准实现的可行性,建立了现场校准装置。通过实验验证,该技术能实现对相控阵雷达天线现场校准,具有高精度,对天线的辐射场的影响较小,能满足相控阵雷达天线现场校准要求。     

Diagnostic of phased arrays with faulty elements using the mutual coupling method

The ability to calibrate phased array antennas by utilising the mutual coupling method (MCM), which takes advantage of the mutual coupling effect between adjacent elements, is addressed. The basic assumption of the method is that the mutual coupling between adjacent elements is equal for all elements in the array and its major deficiency is its failure in the case of faulty elements. A parametric study to identify the effect of faulty elements in the array has been conducted. It has been shown that displacement of one element in the array may cause a significant error in the calibration, which affects its radiation characteristics (increase in the far side lobe level). The main contribution is the presentation of the effect of faulty elements in the calibration process and the proposal of a way to detect and bypass the faulty elements in a phased array calibrated by the MCM.     

基于DDS的收发全DBF相控阵技术

对DDS技术实现任意频率信号产生给予了理论上的解释,介绍了基于DDS的发射全DBF相控阵天线技术的基本思想和性能特点,并给出了4单元发射全DBF相控阵雷达试验系统的和,差波束形成结果。     

一种相控阵雷达天线极化特征的外场测试方法

为了解决相控阵雷达天线极化特征的外场测量问题,研究了极化的幅相测量法和斜天线测试场的布局方法,设计了基于双通道接收技术的相控阵雷达天线极化特征的一种外场测试方法。给出了应用该种方法的测量装置、测量布局、测量内容、测量步骤,分析了测量误差。该种测试方法在相控阵雷达天线极化特征测试任务中得到成功应用,为某武器系统的研制提供了准确的测量数据和宝贵的研究资料。     

Metric tensor approach to surveillance analysis of phased array radar

The author shows that the metric tensor gab is sufficient to accurately derive some of the most important system surveillance characteristics of static and rotating phased array radars. The author presents a novel and generalised method using metric spaces on Riemann manifolds as a viable approach for investigating phased array radar system design characteristics that is mathematically tractable and avoids complex iterative and non-analytic procedures.     

Shape calibration of a conformal ultrasound therapy array

A conformal ultrasound phased array prototype with 96 elements was previously calibrated for electronic steering and focusing in a water tank. The procedure for calibrating the shape of this 2D therapy array consists of two steps. First, a least squares triangulation algorithm determines the element coordinates from a 21×21 grid of time delays. The triangulation algorithm also requires temperature measurements to compensate for variations in the speed of sound. Second, a Rayleigh-Sommerfeld formulation of the acoustic radiation integral is aligned to a second grid of measured pressure amplitudes in a least squares sense. This shape calibration procedure, which is applicable to a wide variety of ultrasound phased arrays, was tested on a square array panel consisting of 7-×7-mm elements operating at 617 kHz. The simulated fields generated by an array of 96 equivalent elements are consistent with the measured data, even in the fine structure away from the primary focus and sidelobes. These two calibration steps are sufficient for the simulation model to predict successfully the pressure field generated by this conformal ultrasound phased array prototype     

Multiple-element crosseye

An extension to the traditional two-element array crosseye interferometric electronic jamming technique is investigated. Simulations are performed to obtain excitations for multiple-emitter linear arrays that produce distorted wavefronts over desired regions of space. This results in a greater number of degrees-of-freedom and a better ability to control the desired field pattern. The crosseye effect can be achieved over wider sectors, but only by increasing array power. The technique is extended to two-dimensional arrays and is applicable to multi-function radar antennas. Experimental measurements performed on a four-emitter array demonstrate the feasibility of the technique. Good agreement with predictions is shown     

Self-calibration of large phased-array antennas for radar

Self-calibration of a phased antenna array is required when distortions in the array are not known a priori and cannot be measured, or when turbulence in the propagation medium perturbs the radiation field. Two types of self-calibration procedures are discussed that have proved successful in experimental high-resolution two-dimensional microwave radar imaging. Each extracts information from the backscattered reradiation field to deduce a compensating weight vector for the phased array antenna. The first depends upon the presence of a strong reflector in the field of view of the transmitter. The second calibrates the array from correlation estimates of wavefront samples in the array. The basic algorithm in each group is described, along with two more sophisticated algorithms in the latter class. Two-dimensional radar images of airplanes are shown with resolution comparable to human vision. The performance of each algorithm and comparisons between them are illustrated by these images of targets and by simulation experiments.©1993 John Wiley & Sons Inc     

Angle density functions for active sensor imaging

A new target density function (TDF) is proposed for active sensor imaging. The TDF, called the angle density function, is studied by utilising the angular distribution of targets at a fixed range. Active sensor imaging based on the angle density function is achieved using a phased array radar system. The phased array system is arranged for stationary radar-stationary target configuration. The imaging algorithm is applied for the whole target area. Instead of pointwise imaging, an approach including the whole target area globally is developed. An advantage of the technique is the use of standard Fourier-based analysis. This makes it possible to use of simple functions for global radar imaging. Although the imaging is accomplished by way of the phased array radars, beamforming is not necessary with the proposed technique.     

Novel ferroelectric materials for phased array antennas

Various composites of barium strontium titanium oxide (BSTO) combined with other nonelectrically active oxide ceramics have been formulated for application in phased array antennas. In general, the composites have adjustable electronic properties which can be tailored for use in phased array antennas and other phase shifting devices. The dielectric constant and the loss tangents have been reduced to enhance the overall impedance matching and thereby lowering the insertion loss of the device. In addition, the overall tunability, the change in the dielectric constant with applied voltage, is maintained at a sufficiently high level. In order to address a broad frequency range in the microwave region, the composites have been fabricated in bulk ceramic, thick film, and thin film form. This article discusses the processing, material characterization, and electronic properties of the composites in MHz and GHz frequencies