基于齿轮传动与红外遥感技术测量流速实验的设计与实现

流体流速是流体力学研究中最重要的参数之一,是判断流动稳定性与力学计算的基础,流速测量是实验研究中最必要的环节.本文主要对齿轮的各项物理特性及红外遥感技术进行深入的研究,设计了一组可以同时测出水流的平均速度与当前时刻水流瞬时速度的实验装置,以解决目前实验室测水流速课程中测量数据单一,实验仪器繁多等问题.设计的实验内容包括齿轮传动比的测量、基于单片机和齿轮组的路程时间测量,以及红外测速仪的瞬时速度读取,实验环节环环相扣,可以更好地锻炼学生的独立研究能力及培养学生的思维缜密性.通过上述实验,可以较为准确地测量出流体的平均流速以及在当前时刻的瞬时流速,并通过灵敏度的计算判断出各个参数对流速的影响比例.     

Nonlinear parametric identification using periodic equilibrium states

The subject of this paper is the development and assessment of a new nonlinear parametric identification method for dynamic systems using periodic equilibrium states or outputs. The method consists of a modified Bayesian point estimation technique which can be used in combination with a time discretization method or a shooting method to obtain the periodic equilibrium states. It is assumed that the specific excited and measured periodic solution can be computed directly from a static initial guess. An important feature of this estimator is the possibility to estimate the best parameters based on all experiments of the complete experimental set-up. The choice of using periodic states appears to be computationally efficient compared to using transient states. The new method is applied to multiple sets of nonlinear shaker-test measurements of a uniaxially loaded F-16 nose landing gear damper, for which a standard 1 dof mechanical model and a more comprehensive 2 dof thermo-mechanical model are postulated. Finally, the predictive power of the method is assessed by comparison of predictions for a transient drop-test load case of the best 2 dof model with corresponding parameters and real drop-test measurements.Notation a,b partial derivative of a with respect to vector b - % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaCbiaeaaca% WGHbaaleqabaGaaiOlaaaaaaa!37CD!\[\mathop a\limits^. \] total derivative of a with respect to time t - a total derivative of a with respect to the dimensionless time - â predicted value of a - mean value of a - ã approximate equations a - e residuals - f output equations - f _e external excitation frequency - F force - g ordinary differential equations - l number of parameters - n number of samples in each experiment - N number of experiments - % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWefv3ySLgznf% gDOfdaryqr1ngBPrginfgDObYtUvgaiuGacqWFneVtdaWgaaWcbaGa% amyyaaqabaGccaGGOaGaamOyaiaacYcacqWFce-qcaGGPaaaaa!4710!\[{\cal N}_a (b,{\cal C})\] a-dimensional normal distribution (mean b and covariance C) - p pressure - q degrees of freedom - s number of outputs - t time - T absolute temperature     

Dynamics Modeling and Experimental Investigation of Gear Mechanism with Coupled Small Clearances

Internal gear mechanism is widely used in micro-nano satellites due to its compact structure and high precision transmission. However, the vibration coupling caused by the small clearance coupling is more obvious and cannot be ignored under low speed, light load and zero gravity conditions. Based on the geometric relationship between radial clearance and backlash, a coupled model between dynamic backlash and radial clearance of internal meshing gear is established. Based on the conformal contact theory, the radial collision force model of the gear shaft and shaft sleeve considering the small clearances is established. Additionally, a multi-clearance gear rotor system test device is built to measure the vibration acceleration of the internal gear rotor system by an acceleration sensor and transmitted to the industrial computer through a signal collector for data processing. Through the comparison of simulation and experiment, the accuracy of the gear dynamics model is verified. The analysis results show that, compared with the traditional model, the calculation results of the gear mechanism model considering the small clearance coupling is closer to the experimental data.     

起落架结构参数对飞机机轮摆振的影响

建立了飞机机轮摆振运动方程,详细研究了起落架三个重要结构参数;稳定距、支柱刚度和减摆器传动系统扭转刚度对飞机机轮摆振的影响,考虑了各参数之间的耦合作用,严格区分“轮胎型”摆振和“结构型”摆振,并分别予以研究,所得结论为新机防摆设计和现役飞机防摆维护提供了理论依据。     

Dynamics of a Gear System with Faults in Meshing Stiffness

Gear box dynamics is characterised by a periodically changing stiffness. In real gear systems, a backlash also exists that can lead to a loss in contact between the teeth. Due to this loss of contact the gear has piecewise linear stiffness characteristics, and the gears can vibrate regularly and chaotically. In this paper we examine the effect of tooth shape imperfections and defects. Using standard methods for nonlinear systems we examine the dynamics of gear systems with various faults in meshing stiffness.     

含磨粒油润滑齿轮胶合失效的计算模型与试验研究

在机械设备的运转过程中，齿轮润滑油都含有很多不同尺寸的磨粒，研究表明，磨粒产生的机械效应和热效应都不容忽视，前者可以导致齿轮的磨粒磨损，后者能够造成齿轮的胶合失效。尽管目前人们已经对磨粒导致胶合失效的机理有所认识，但还没有建立起相应的计算方法和模型，有关的试验分析方法也还没有看到文献报道。因此，从机理，计算方法和试验等方面对含磨粒润滑工况下的齿轮胶合失效进行了分析与研究，在给定的条件下，通过几种含     

基于断裂力学理论的表面淬火齿轮疲劳寿命的数值计算

基于二维线性断裂力学理论，提出了一种表面淬火齿轮的弯曲疲劳寿命预测方法，并开发了相应的计算程序。在程序中，用权函数法估计应力强度因子，运算速度快，节省了计算时间。在估计应力强度因子时，考虑了热处理后产生的残余应力的影响。用开发的软件对表面淬火齿轮的弯曲疲劳寿命作了预测，并与试验数据进行了比较。预测值与试验结果基本相符，特别是高应力时，二者符合的更好。     

The influence of variable stiffness of teeth on dynamic loads in single-gear transmission

Summary In this paper, the influence of the variable stiffness of mating gear teeth on dynamic loads occurring between teeth in a single-gear transmission is investigated using a discrete-continuous model consisting of two torsionally deformable ponderable shafts and four rigid bodies. The stiffness is described by a harmonic function of time. Considerations by means of the wave method enable to determine dynamic loads in steady as well as in transient states. Numerical calculations are concentrated on the determination of the amplitudes of dynamic loads on gear teeth with respect to revolution per minute. Received 4 March 1997; accepted for publication 12 September 1997     

OPTIONS FOR THE REGULATION OF MEDITERRANEAN DEMERSAL FISHERIES

Research and management actions are reviewed with respect to demersal fisheries of the Mediterranean since the Second World War, as reflected in the activities of the General Fisheries Council for the Mediterranean, (GFCM). The scientific background to the priority concern expressed for minimum size limits in the 1960's and 1970's is discussed, and in particular, the mesh selectivity experiments that formed the basis for yield per recruit calculations, with respect to the trawl fishery. More recent considerations, changing our perception of the appropriateness of size at first capture of demersal fish as a management tool in trawl fisheries, are reviewed. It is concluded that for multispecies fisheries where the first priority for fishing effort control is not respected, size limits based on size at maturity, rather than yield per recruit criteria, are more feasible, but that changes in mesh size need to take into account subsequent changes in equity between inshore and offshore fleets, and changes in species composition and areas of distribution during the life history. They also need to consider the high landed value of small fish in many Mediterranean fisheries. Alternative, or supplementary, measures to mesh size regulation that affect capture of small fish are also reviewed, including seasonal closures, closed areas, bans on trawling inshore, and regulations on minimum size at sale. A range of problems to be considered prior to deciding on an increase in mesh size are reviewed, including changes in total effort exerted, changes in increases in fishing power (and especially the impacts on the spawning stock), changes in discard rate, “meshing” of small fish, and indirect mortality during fishing. A strategy for introducing new mesh sizes is suggested, with emphasis, where possible, on the experimental approach, and on supplementary measures to control fishing effort. The paper concludes by considering an alternative paradigm to minimum size regulation for demersal fisheries management; namely, the exploitation of juvenile fish, with provision for escapement of a small proportion of large, mature fish offshore, for which exploitation rate declines and remains low. It is suggested that this strategy may be, de facto, the one prevailing in the small mesh size inshore trawl fishery prior to development of offshore fisheries. The implications of this possibility have to be considered seriously if high effort levels are to be maintained while effective size limits are raised.