PVDF压力传感器标定及在激光推进实验中的应用

详细介绍了PVDF压力传感器的设计方法和2个等效测量电路.利用SHPB系统对PVDF压力传感器的动态灵敏度进行了标定,结果显示,不同并联电阻对于PVDF压力传感器动态灵敏度的影响不大,但对脉冲推力上升时间的测量结果有影响,选择较小的并联电阻可以获得更逼真的测试信号.     

Experimental measurements of flow and flame spread in the development of a fire testing facility

A fire testing facility named the “MSU Fire Tunnel” has been developed. The intent was to devise a testing apparatus that controlled the flow of oxidizing gas in the tunnel to an extent not heretofore accomplished. A novel approach was developed for mounting the flame-spread samples flush with the surface of an “airfoil”. This method avoids previous complications of determining the exact position of the leading edge of the velocity boundary layer. Data were gathered for the flow field using hot-wire anemometry. These data indicated that a zero-pressure gradient Blasius boundary layer flow was established along the airfoil and fuel sample surfaces. Opposed-flow flame-spread tests were conducted and correlations were produced that support the predictive capacity of this apparatus. It was shown that the opposed flow flame-spread data allowed distinctions to be made between correlations of previous researchers. No such comparisons were formerly possible. A finite-chemistry correlation was shown to be consistent with, and similar to, correlations derived in the previous work.     

Influence of temperature transients and centrifugal force on fast-response pressure transducers

This contribution focuses on the use of fast-response semi-conductor pressure transducers to measure accurately the mean and fluctuating total pressure or static pressure in a wind tunnel environment. The problem of angular sensitivity is briefly addressed when measuring total pressure. Then, the influence of temperature is described when testing under steady or transient temperature conditions. The influence of the rotational speed is analyzed when measuring with rotating transducers. The transfer function of a sensor-cavity system is also considered. Correction methods are proposed for both the effects of the temperature and the rotational speed. Several applications are presented covering turbulence measurement with a quasi-steady probe, static and total pressure measurements in the absolute frame and the relative frame.     

The development of acoustic generators and their application as a boundary layer transition control device

An experimental investigation of a controllable artificial boundary layer transition by means of electro-acoustic generators was carried out in flat-plate boundary layers. The acoustic generators were flush mounted with the model surface in order to minimize local surface roughnesses which may cause flow instabilities in the laminar boundary layer. The dependence of the input power, pulse ratio, and input frequency of the acoustic generators on the transition threshold values of the input power were determined with surface hot films. In addition, the functional application of the acoustic generators for a controllable artificial boundary layer transition was examined qualitatively by flow visualizations applying the liquid crystal technique.List of symbols A fluctuating component of the hot film anemometer output voltage - time mean hot film anemometer output voltage - ₀ time mean hot film anemometer output voltage at zero velocity - B spectral component of any measured quantity (the used dB-scale is referred to 1 Volt) - time mean hot wire anemometer output voltage - ₀ time mean hot wire anemometer output voltage at zero velocity - f frequency - I _av average input current of the acoustic generator - P mean input power of the acoustic generator - p pressure - Re Reynolds number, Re=U x t/ - t time - t _i period of pulse signal - t _p pulse width of input power - t _s time after switching off heating lamp - U freestream velocity - blowing or sucking velocity produced by the acoustic generator - x longitudinal coordinate from the leading edge (Fig. 2) - x _t distance from the flat plate to the transition location - y coordinate normal to the wall (Fig. 2) - z spanwise coordinate (Fig. 2) - angle of incidence - pulse ratio t _p /t _I - kinematic viscosity - density - ₀ wall shear stress     

The effect of oxidant flow rate on a coaxial oxy-fuel flame

The effect of oxidant flow rate on temperature, heat transfer, and NO_x formation of an oxy-fuel flame is investigated using numerical simulation. The finite volume approach is used to solve the governing equations. The realizable k-ε turbulence model and β-PDF model are adopted to simulate the turbulence-combustion interaction. There is a good agreement between the present numerical results and the reference experimental data. The exhaust temperature is decreased with decreasing the oxidant inlet flow rate. As an important result, the adiabatic flame temperature can be considered a key parameter in the oxy-fuel flame applications. Also, it is observed that increasing oxygen inlet angle causes a decrease in NO formation.     

Frequency characteristics of a laminar flame

A theoretical study is made of the effect of harmonic pressure oscillations on a flat laminar flame. Frequency characteristics of the flames are obtained at amplitudes of the pressure oscillations which are small compared with the average pressure. It is established that in a broad range of frequencies the disturbances in the integral rate of heat release occur in phase with the pressure oscillations and depend weakly on the frequency.Translated trom Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 84–94, January–February, 1974.The authors thank V. E. Doroshenko for attention to the work and discussions.     

Large deformation mechanics of a soft elastomeric layer under compressive loading for a MEMS tactile sensor application

The study is motivated by the need to develop highly sensitive tactile sensors for both robotic and bionic applications. The ability to predict the response of an elastomeric layer under severe pressure conditions is key to the development of highly sensitive capacitive tactile sensors capable of detecting the location and magnitude of applied forces over a broad range of contact severity and layer depression. Thus, in this work, a large deformation Mooney–Rivlin material model is employed in establishing the non-linear mechanics of an elastomeric layer of finite thickness, subjected to uniform displacement of controlled compression. Thus, an analytical non-linear model for the above described problem which is validated numerically via the method of finite elements is developed. Two dimensional, plane strain conditions of an infinitely long and of finite thickness elastomeric layer are assumed. The layer is subjected to a uniform vertical large displacement with symmetry conditions applied at the contact center. Cauchy normal and shear stress profiles as well as displacement profiles are established over a broad range of a layer compression including up to 40% of layer thinning. The model allows for the determination of the non-linear relationship between the relative separation of embedded conducting electrodes and thus the sensor capacitance during touch, to the force magnitude of the force concentrated at the symmetry plane or sensor center. The current model is expected to further improve the sensitivity and range of polymeric tactile sensors currently under development (Charalambides and Bergbreiter, 2013) [1]. As shown elsewhere (Kalayeh et al., 2015) [2], capacitance–force model predictions are found to be in remarkable agreement with experimental measurements for a broad family of self-similar pressure sensors.     

The effects of ionization on the compression of a gas by a converging shell

One of the effective methods of obtaining a dense high-temperature plasma is compression of the gas by converging shells, which can be accelerated to high velocities by the products of an explosion either as a result of ablation caused by laser radiation, or by an electron beam [1–3]. In order to interpret the results of such experiments, it is very important to construct satisfactory physical models which enable us to obtain plausible estimates for the parameters of the plasma which are realized as a result of the compression. In a number of cases the process of compression may be described with sufficient accuracy by a system of simple hydro-dynamic equations which have particular analytical solutions (see, for example, [4–7]); however, as a rule, for more realistic estimates it is necessary to take into account the complex of physical phenomena accompanying the process, and in such cases the most effective method is numerical simulation of the process, which enables a fuller study to be made of the effect of various factors [7–9]. Compression regimes corresponding to velocities of projection of the shells of some tens of kilometers a second (attainable in experiments with laser compression of shells of a width of some microns) have at present been considered in detail in studies devoted to a pulse thermonuclear synthesis (for example, [8–10]), from which it follows that the process corresponds with sufficient accuracy to the compression of a gas which is completely ionized at the initial moment. In experiments with more massive shells (of the order of 100 m and more), the velocities attained in practice do not exceed 5–20 km/sec [1]. At such velocities, the energy densities contained in the shock wave detaching from the shell may turn out to be insufficient for complete ionization of the gas which has been compressed, and this must have an effect on its further compression and heating. The present study considers precisely these regimes of compression of gas-filled targets. The studies were carried out by the numerical method. For comparison, the studies were made in a number of cases both with allowance for ionization of the gas which was being compressed, and also on the assumption that the gas was already completely ionized at the initial moment.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 155–160, January–February, 1935.In conclusion the author expresses his appreciation to S. I. Anisimov for his constant attention to this study, and to M. F. Ivanov for his help in carrying out the calculations.     

Digital image analysis of a turbulent flame

Digital image analysis of cine pictures of an unconfined rich premixed turbulent flame has been used to determine structural characteristics of the turbulent/non-turbulent interface of the flame. The results, comprising various moments of the interface position, probability density functions and correlation functions, establish that the instantaneous flame-interface position is essentially a Gaussian random variable with a superimposed quasi-periodical component. The latter is ascribable to a pulsation caused by the convection and the stretching of ring vortices present within the flame. To a first approximation, the flame can be considered similar to a three-dimensional axisymmetric turbulent jet, with superimposed ring vortices, in which combustion occurs.     

Transient behaviors of a flame over a Tsuji burner

The present study investigated numerically the physical mechanisms underlying the transient behaviors of the flame over a porous cylindrical burner. The numerical results showed that a cold flow structure at a fixed inflow velocity of Uin = 0.6 m/s in a wind tunnel could be observed in two co-existing recirculation flows. Flow variations occur repeatedly until t = 4.71 s, and then a vortex existed steadily behind the burner and no shading occurred. The ignition of flammable mixture led to a rapid rise in gas temperature and a sudden gas expansion. When it reached the stable envelope flame condition, Uin is adjusted to an assigned value. Two blow-off mechanisms were identified. It was also found in the study flame shapes with buoyancy effects agreed with the ones observed experimentally by Tsai. Furthermore, the lift-off flame would appear briefly between the envelopes and wake ones, and was stabilized as a wake flame.     

Propagation rate and limits of existence of a turbulent flame

In a theoretical study of turbulent burning it is usually assumed that the average rate of the chemical reaction (heat release) is determined only by the average temperature. Ya. B. Zel'dovich [1] and later T. Karman [2] noted the necessity of taking into account the effect of temperature pulsations on the reaction rate. A quantitative estimate of this effect on the reaction rate constant is given in [3]. A critical analysis of various approaches to the theoretical study of turbulent flames is given in the reviews [4, 5]. In the present article, it is shown that, taking the pulsation component of the temperature and concentration into account, the average rate of the chemical reaction depends on the gradient of the mean temperature and the scale of the turbulent pulsations. The case, where a first-order reaction takes place in the flame is studied in detail. Existence and uniqueness theorems which determine the limits of the propagation of flames are proven. Quantitative rules for the propagation rate, limit, and structure of a turbulent flame front are analyzed with respect to the results of a numerical calculation of a series of variants. Dimensional interpolation equations are presented for the total propagation rate of a flame.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 65–76, May–June, 1972.     

The application of controlled variable magnetic eddy current damping to the study of vortex-induced vibrations

A powerful variable magnetic eddy current damping system has been constructed and utilized in an experimental study of vortex-induced vibrations (VIV). This damping system allows us to impose precise values of nearly ideal viscous damping over a wide range of damping values of interest. This new damping system offers improvements over previously utilized damping methods. Unlike most studies of VIV, where the damping cannot be independently controlled, we are able to impose our system damping independent of the other system parameters. Also, because the system only requires that a thin conductive plate be attached to the oscillating system, the overall mass of the system does not increase dramatically and still allows the investigation of very low mass systems. Finally, the system can operate in a steady-state fashion, supplying a constant damping value for an extended period of time, or in a transient fashion, where the damping value is intentionally varied over time. With this damping system, we have systematically explored both steady and transient damping effects on VIV behavior and provide a brief overview of some sample results.     

The development of rheometry for strain-sensitive gelling systems and its application in a study of fibrin–thrombin gel formation

This paper reports simulated sequential frequency sweep data which have been reconstructed from time resolved viscoelastic data obtained by Fourier transform mechanical spectroscopy. Comparisons of the results show that the recording of anomalous values of the stress relaxation power law exponent α at the Gel Point under ‘rapid’ gelling conditions may be due to inappropriate rheological techniques. An appropriate rheometrical criterion is established for the application of sequential frequency sweeps in order to obtain accurate values of α in the formation of strain-sensitive, rapidly formed gels. Furthermore, using appropriate rheometry, we report values of α for fibrin–thrombin gels formed by the addition of thrombin to a physiologically relevant level of human fibrinogen, and relate these values to the microstructure of the fibrin gel network in terms of a fractal dimension. The present study is the first to report a modification of the fractal characteristics of incipient clots in fibrin–thrombin gels due to the availability of thrombin. This work confirms the hypothesis that the self-similar (fractal) stress relaxation behaviour recorded at the Gel Point of samples of coagulating blood (Evans et al. 2010a, b) is associated with the microstructural characteristics of the incipient blood clot’s fibrin network.     

基于虚拟传感器的陆地移动目标跟踪原理及其应用

随着无线通信、互联网以及数据库技术的发展和成熟,陆地移动目标导航系统经历了点、面、球三个时期的发展过程,由于数据传输网络等因素引起的时间延迟已严重影响了陆地移动目标监控服务系统的性能,传统的技术方法已不能解决问题,必须探讨新的方法新的技术.为此,本文结合当前技术发展现状,提出了基于实时交通信息的陆地移动目标跟踪原理,充分利用陆地移动目标所处环境的实时交通信息,研究目标状态信息更新策略.通过监控服务系统的应用实验结果显示,在保持原有硬件设备和系统精度条件下,通过本方法可减少90%以上的数据传输量.     

Theory of flame propagation in a gas and drop mixture

The equations of a reacting multiphase continuous medium [1] are used to investigate the problem of steady-state flame front propagation in a gas mixture with evaporating drops. A simple model for ignition of the liquid drops is proposed which is based on the application of the method of equally accessible surfaces [2] to the heat and mass exchange processes between the microflames surrounding the separate drops, the drops, and the carrying gas medium. The parameter distributions in the macroscopic flame front as well as the dependences of the flame propagation velocity in the gas suspension on a number of parameters governing the process under investigation are represented.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 4, pp. 101–108, July–August, 1973.     

Simultaneous velocity and temperature measurements in a premixed flame

Procedures which allow the correlation of velocity signals from a laser anemometer and temperature signals from a compensated, small-diameter thermocouple are described together with the error sources associated with the use of the technique in premixed flames. The digital compensation procedure includes the effect of velocity and temperature on the time constant of the thermocouple and the influence of its exposure to the solid particles required by the laser anemometer are quantified and shown to be able to cause large differences in the measured probability-density-distribution of the reaction progress variable. The technique has been used to measure the probability-density-distribution of temperatures, conditioned by the arrival of velocity signals and velocity conditioned by the temperature signal and sample results are presented to help quantify the accuracy of the measurements.