基于图像处理的膏体推进剂火焰测温

膏体推进剂火焰温度测量对推进剂配方的研制及火箭发动机的设计具有重要意义.为了测试推进剂燃料温度分布,采用彩色CCD比色测温技术,设计了一种非接触式膏体推进剂火焰测温系统.利用黑体炉对测温系统进行标定,通过现场本生灯试验对测温系统进行精度检验,最后,对青体推进剂在开放空间内的燃烧火焰进行图像测温.结果表明方法简单可靠,基本满足青体推进剂火焰测温要求,由于系统拍摄图像实际上是火焰在CCD靶面上投影叠加的效果,对最终处理结果具有一定影响,方法仍有待改进.     

管内紊流非稳态扩散方程数值解

51．引言沿同一条管道连续输送几种介质的工艺称为顺序输送，比如成品油管道输送常采用此法．该输送工艺的最大缺点是前后介质的混合，因此成品油管道输送的混油问题，在实际输送中应减少混油．研究浓度分布对于制订合理的输送工艺、减少前后介质混合量具有重要意义．顺序输送中影响介质混合的因素很多，此处仅分析管道截面上速度分布不均匀性对介质混合的影响．传统的一维非稳态对流扩散解析法不足以揭示管道截面速度分布不均匀性对介质混合的影响．本文根据笔者推导的顺序输送紊流工况下的对流扩散方程，用特征线法和隐式差分法求得混合区…     

煤泥输送管道压力分布模型研究

针对煤泥高浓度黏稠物料在煤泥输送管道中压力分布的非线性特性,通过实验数据分析管道压力与主要影响因素的关系,并提出一种基于量子遗传算法的BP神经网络建模方法。该方法采用量子遗传算法优化BP神经网络的权值和阈值,再用优化后的BP神经网络来逼近煤泥输送管道中压力分布的非线性特性,从而得到其数学模型。仿真结果表明,采用该方法建立的煤泥输送管道压力分布模型稳定性好,误差仅为0.063 2,满足了实际工程要求,且在寻优时间和准确性等方面均优于采用BP神经网络建立的模型。     

探头偏转角对皮托管测速精度影响分析

皮托管在进行流场风速测量过程中,其探头偏转角对测量精度有很大的影响.针对皮托管探头偏转角对测量精度的影响,根据皮托管测量原理和数据处理方法,建立了仿真分析模型,选取Fluent中Standard k-ε Model作为流体力学分析控制方程.通过分析现有锥形及球形感应头对流场的影响,并改变感应头偏转角,分析了偏转角对皮托管风速测量精度的影响.结果表明:锥形感应头对流场的扰动小于球形感应头,当锥形感应头偏转角为15°时,皮托管对被测管道内流场的扰动最小,测量精度最高.     

针栓式变推力火箭发动机内流场数值仿真研究

发动机推力室的工作过程直接影响到发动机的性能,在设计过程中,从理论上分析推力室内的燃烧流动过程具有非常重要.通过数值仿真,可以大大缩短发动机的研制和改进设计周期,减少研制经费.针对自燃推进剂针栓式变推力液体火箭发动机燃烧与流动的特点,借助CFD计算软件FLUENT,采用标准k-ε湍流模型及有限速率化学反应模型,对采用针栓式喷注器的变推力液体火箭发动机的推力室喷雾燃烧过程进行了数值仿真.计算结果得到了压强分布,温度分布,牛成物的摩尔分数分布,粒子轨迹分布、流强、混合比分布以及流动码赫数分布等,并对流场结构和影响发动机性能的喷注器参数进行了分析.数值计算结果可为变推力发动机喷注器和推力室的设计和优化提供参考.     

孙村煤矿“矸石换煤”技术有新突破

将煤炭开采过程中产生的矸石磨细后，与水泥等材料混合，制成近似膏体的浆体，从地面通过管道输送至煤矿井下需要充填的采场，把采空区充满后快速凝固，有效支撑起岩层，达到避免地表沉降的目的。近日，山东新汶矿业集团孙村煤矿似膏体矸石充填技术通过了山东省科技厅组织的技术鉴定。     

短讯

孙村煤矿“矸石换煤”技术有新突破将煤炭开采过程中产生的矸石磨细后,与水泥等材料混合,制成近似膏体的浆体,从地面通过管道输送至煤矿井下需要充填的采场,把采空区充满后快速凝固,有效支撑起岩层,达到避免地表沉降的目的。近日,山东新汶矿业集团孙村煤矿似膏体矸石充填技术通     

Y型喉管流场分析及结构优化

Y型喉管主要应用于粮食供料气力输送中,结构参数设计不当容易导致颗粒聚集管底,引起较大的压力损失,因此对喉管内流场的分析和结构参数的优化设计显得尤为重要.利用欧拉双流体模型,借助Fluent软件对Y型喉管内气固两相流进行数值仿真,重点研究颗粒不同入射角对喉管内流场的影响.针对颗粒易于聚集问题,提出增加横板改进方案.通过数值分析,得到压降与入射角之间的关系曲线图以及喉管内改进前后的流场情况.结果表明,颗粒入射角在45°到75°之间更有利于颗粒输送,横板方案能够有效避免颗粒在管道底部聚集.     

凝胶推进剂火箭发动机工作过程仿真研究

基于系统分解方式,建立凝胶推进剂火箭发动机工作过程的数学模型,并采用液流试验数据对其进行修正.由于同时考虑液体的惯性、粘性和压缩性,所以本文建立的常微分方程组能反映管道中推进剂流动的分布特性.通过对发动机工作过程仿真分析,为发动机型号研制提供参照和依据.     

超声探头外声场在测量管道上的仿真分析

针对超声探头安置于测量管道不同位置时,获取信号不同这一问题,利用有限元软件COMSOL建立了探头外输送管道内的声场分布,研究了在不同声波频率和不同声衰减系数下,管道上的声场分布情况.研究表明:声波频率增大时,指向角减小,管道壁上的主声束范围也随之减小;声衰减系数增大时,指向角不变,但管道壁上主声束范围内的声压值减小.说明接收探头的设计位置应该主要根据声波频率确定.当频率不同时,声压为零的点不同,探头的设计位置应该避开声压为零的点,另外由于主轴处声信号的强度大,为了获得比较好的测量精度,探头位置应该尽量靠近主轴.     

Microdevice end pressure evaluations with Bagley correction

In this study the end pressure of microdevices is derived through Bagley corrections with the use of an off-chip pressure transducer. Such approach has many advantages over the approaches using on-chip pressure transducers. In this study it has been used to measure the non-Newtonian fluid flow at the ends of microdevices. The experimental microdevices had a microchannel with a cross section of 149×158 μm², end angles of 36° or 180°, a contraction ratio of 24, and a reservoir aspect ratio of 0.04. Two linear aqueous polymer solutions which have very different entry flow patterns were tested. Experimental results disclosed that the end pressures of microdevices are dominated by the excess pressure before the contraction plane. This is different from the conventional fluidics conclusions, which consider the kinetic energy change and/or the excess pressure from the boundary layer formation being the dominant sources of the end pressure. This discrepancy also explains why many earlier microfluidics studies observed higher frictional factors in microdevices. Determined by the unique device characteristics, microdevices have exhibited higher end pressures than macrodevices. The microdevice end angle has negligible effects on the end pressure.     

Variation in sitting pressure distribution and location of the points of maximum pressure with rotation of the pelvis,gender and body characteristics

The pressure distribution and the locations of the points of maximum pressure, usually below the ischial tuberosities, were measured for subjects sitting on a flat, hard and horizontal support, and at various angles of the rotation of the pelvis. The pressure data were analysed for force- and pressure-related quantities. Multiple regression was applied to explore relationships between these quantities and (i) a set of body characteristics and (ii) the pelvis rotation. The maximum pressure and the pressure gradient were mainly found to be explained by the ectomorphic index and the distance between the maximum pressure points by gender and the angle of rotation of the pelvis.     

Variation in sitting pressure distribution and location of the points of maximum pressure with rotation of the pelvis, gender and body characteristics

The pressure distribution and the locations of the points of maximum pressure, usually below the ischial tuberosities, were measured for subjects sitting on a flat, hard and horizontal support, and at various angles of the rotation of the pelvis. The pressure data were analysed for force- and pressure-related quantities. Multiple regression was applied to explore relationships between these quantities and (i) a set of body characteristics and (ii) the pelvis rotation. The maximum pressure and the pressure gradient were mainly found to be explained by the ectomorphic index and the distance between the maximum pressure points by gender and the angle of rotation of the pelvis.     

弯管流量计测量特性的数值模拟与试验研究

为了优化弯管流量计的测量,综合运用流场数值模拟和实流标定试验两种方法,研究了弯管流量计的测量特性.在对安装有弯管流量计的流场数值模拟的基础上,根据压力分布特点确定了较优的取压口斜度;然后,在内径为100 mm的管道中用空气进行了实流标定试验.结果表明:为了增加差压测量的灵敏度和减小二次流对测量的影响,可将弯管流量计的取压口选取在与上游端面成45°夹角的地方;在试验范围内不同流量下,弯管流量计的流量系数都比较稳定,相对误差都介于±3%之间,能够满足大多数工业现场流量测量的要求.     

SMA丝驱动的手指康复机器人设计及实验研究

为了研制一种轻便、可穿戴的仿生手指康复机器人,在分析手指肌肉骨骼生物参数及致动机理的基础上,设计了一种形状记忆合金丝(Shape Memory Alloy, SMA)驱动的软体柔性手指康复机器人,建立了其运动学和力学模型。以手套为结构设计的原型,通过控制SMA丝的收缩来模拟手指肌肉肌腱的收缩,从而实现辅助手指屈曲伸展运动的功能。试验研究了手指康复机器人的运动性能和抓握性能。试验结果表明,手指柔性康复机器人最大弯曲角度接近正常人手关节角度,最大指尖力可达18N,能完成日常所需的屈曲伸展以及抓握功能。     

Corona discharge assisted thermal bonding of polymer microfluidic devices

We present a study on the use of corona discharge surface treatment to achieve a fast thermal diffusion bonding process for the creation of microfluidic chips. Wafer scale bonding at 100 mm diameter was attempted. Polymethyl methacrylate (PMMA) wafers were hot embossed to create microchannels before bonding to another blank PMMA wafer. Corona discharge treatment of the PMMA resulted in a more hydrophilic surface. The average water contact angle on PMMA surface decreased from 74.5° before treatment to 35.5° after the treatment. The optimized bonding condition was found to be: 108°C for 4 min at a contact pressure of 3.1 MPa. The bonded chips could withstand an internal gauge pressure in the microchannels of at least seven bars. The rectangular shape of the cross section of the microchannels was conserved with some contraction in the dimensions of 3.7% on the mean widths and 2.1% on the mean depths. Bonding strength was found to increase with the bonding temperature and time while the effect of bonding pressure is evident at lower pressures. At higher pressures, the effect of bonding pressure seemed to have reduced. These effects could be explained by the diffusion mechanisms of the process.     

Pressure loss in constriction microchannels

Constriction devices contain elements inserted into the fluid stream, which change the local streamwise flow area. One such element is the orifice-like obstruction with sharp corners, a back-to-back abrupt contraction and expansion, which could trigger flow separation. A series of microchannels, 40 μm × 1 μm × 4000 μm in nominal dimensions, with constriction elements at the centers of the channels has been fabricated using standard micromachining techniques. The channel widths at the constriction sections varied from 10 μm to 34 μm, with pressure sensors integrated in each channel. Nitrogen gas was passed through the microdevices under inlet pressure up to 50 psi. The mass flow rates were measured for all the devices as a function of the pressure drop. A monotonic decrease of the flow rate with decreasing constriction-gap width was observed. The pressure distribution along the microchannel with the smallest constriction gap showed a pressure drop across the constriction element. Both mass flow rate and pressure measurements indicate that flow separation from the constriction sharp corners could occur     

基于FLUENT的内啮合齿轮泵静压支撑研究

在分析内啮合齿轮泵胶合失效的基础上,设计了一种静压支撑方法。分析了内齿轮上液压力变化周期,创建了其网格模型,运用FLUENT仿真软件模拟出在一个周期内不同位置时内齿轮内壁所受油压分布以及液压力大小和方向。在此基础上,确定泵体内壁上静压支撑槽的角度范围,并比较了在开静压支撑槽前后的内齿轮受力大小。数值模拟和样机试验结果表明静压支撑方法可防止内啮合齿轮泵胶合失效。     

Stochastic contraction-based observer and controller design algorithm with application to a flight vehicle

This paper focuses on a stochastic version of contraction theory to construct observer-controller structure for a flight dynamic system with noisy velocity measurement. A nonlinear stochastic observer is designed to estimate the pitch rate, the pitch angle, and the velocity of an aircraft example model using stochastic contraction theory. Estimated states are used to compute feedback control for solving a tracking problem. The structure and gain selection of the observer is carried out using Itô's stochastic differential equations and the contraction theory. The contraction property of integrated observer-controller structure is derived to ensure the exponential convergence of the trajectories of closed-loop nonlinear system. The upper bound of the state estimation error is explicitly derived and the efficacy of the proposed observer-controller structure has been shown through the numerical simulations.     

Ankle angle effects on endurance time,median frequency and mean power of gastrocnemius EMG power spectrum: a comparison between individual and group analysis

Surface EMG of the gastrocnemius medialis muscle during sustained submaximal isometric contraction was recorded for eight subjects at two ankle angles (at a fixed knee angle). Power spectral median frequency and mean power was examined by means of Fourier analysed EMG and related to plantar flexion exertion time. A longer endurance time was found at the smaller ankle angle, for six of eight subjects. This is probably related to significantly smaller mean spectral power found for those subjects in that condition, indicating decreased voluntary excitation of the muscle despite equal net moment exertion relative to maximal voluntary contraction (60%) at both ankle angles. At exhaustion a significant decrease of spectral median frequency of 10% with respect to initial values was shown for the group of subjects at both ankle angles. However not every individual subject showed a significant decrease of median frequency. In fact such a decrease was only shown for 7 out of 16 experiments. An influence of ankle angle was found on initial median frequency. It is concluded that ankle angle may affect voluntary excitation of gastrocnemius and that the use of EMG spectral median frequency as an indicator of muscle fatigue is not valid for individual analysis.