敏感器正常和故障模式下微小卫星的姿态确定方法

围绕某日-地空间环境组网探测系统中微小卫星定姿系统的设计需求,基于MEMS陀螺、小型CMOS太阳敏感器、微磁强计,研究了该微小卫星各敏感器正常工作模式以及敏感器故障模式下的系统建模和姿态确定方法。各敏感器正常工作模式下,用陀螺、太阳敏感器和磁强计进行组合定姿;陀螺故障时,用太阳敏感器和磁强计进行组合定姿;太阳敏感器故障时,用陀螺和磁强计进行组合定姿;陀螺/太阳敏感器同时故障时,用磁强计进行定姿。仿真结果表明,本文定姿方法的姿态确定精度满足该系统中微小卫星在轨运行时的定姿精度要求,为该微小卫星的半物理仿真系统的研究及其在轨运行时的姿态确定提供了依据。     

Evaluation of the performance of high-speed PIV compared to standard PIV in a turbulent jet

In this paper, a comparison between two particle image velocimetry (PIV) systems, one based on a standard cross-correlation charge coupled device (CCD) camera with pulsed laser and another using high-speed complementary metal oxide semiconductor (CMOS) camera with continuous laser is performed. The objective of the paper is to point out advantages and disadvantages of the two systems when computing large and small flow scale statistics. The comparison is performed on velocity measurements in the near and far fields of a circular water jet: on this flow several experimental data and empirical self-similarity laws are available for comparisons. The results show that both systems are suitable for measurements with a preference for the standard one when investigating small-scale statistics. This result depends on the lower number of effectively independent samples acquired by a high-speed system and on the higher noise levels of CMOS sensors in comparison to CCDs.     

基于电容检测接口ASIC的闭环微机械加速度计

对于采用微传感器和接口ASIC两芯片方案来实现的电容式微机械加速度计来说,寄生电容是影响其性能的重要因素之一。采用采样电荷结构,设计实现了电容检测接口ASIC电路,该电路具有对寄生电容不敏感的特点,并在0.35-μm CMOS标准工艺下流片实现。基于流片得到的电容检测ASIC样片,以梳齿式硅微传感器为敏感元件,采用滞后比例积分调节器,通过力平衡反馈方案设计实现了一种闭环微机械加速度计。实验结果表明:该闭环微加速度计的灵敏度为650 mV/g,噪声基底为23.17μg Hz。     

Development of a strain multiplier for fatigue-sensor applications

The successive imposition of strain cycles on the fatigue sensor causes a progressive increase in its unstrained resistance which is thus a measure of fatigue experience. Consideration of the sensor as an equivalent device to the counting accelerometer, having the advantages of negligible size and mass, implies its application to a wide range of structural locations which, in most instances, will receive cyclic strain intensities of only moderate amplitude. For such applications, the low sensitivity of the sensor requires the employment of a strain multiplier. The development of a multiplier having the required characteristics is described, and its construction and application detailed. Typical results for the sensor and multiplier combination under static and fluctuating strains are given.     

Optically interrogated MEMS pressure sensor array

A novel pressure measurement technique is presented for wireless recording of time-averaged surface pressure distributions in wind tunnel surveys. An array of silicon micro-plate resonators acts as pressure sensing element. The pressure is recorded by measuring the sensor diaphragms’ resonance frequency using optical interferometry. Dependent on the quasi-static deflection caused by a pressure load, the resonance frequency varies with an average pressure sensitivity of 3 Hz/Pa in a frequency range between 30 and 150 kHz. A smart-pixel CMOS camera, narrow-band acoustic noise excitation and a specific sensor surface structure allow for the interrogation of a large number of sensors in parallel without the need for alignment between sensor and detector. Experimental tests reveal increased sensing performance with acoustic excitation of the higher vibration modes.     

Toward real-time particle tracking using an event-based dynamic vision sensor

Optically based measurements in high Reynolds number fluid flows often require high-speed imaging techniques. These cameras typically record data internally and thus are limited by the amount of onboard memory available. A novel camera technology for use in particle tracking velocimetry is presented in this paper. This technology consists of a dynamic vision sensor in which pixels operate in parallel, transmitting asynchronous events only when relative changes in intensity of approximately 10% are encountered with a temporal resolution of 1 μs. This results in a recording system whose data storage and bandwidth requirements are about 100 times smaller than a typical high-speed image sensor. Post-processing times of data collected from this sensor also increase to about 10 times faster than real time. We present a proof-of-concept study comparing this novel sensor with a high-speed CMOS camera capable of recording up to 2,000 fps at 1,024 × 1,024 pixels. Comparisons are made in the ability of each system to track dense (ρ >1 g/cm³) particles in a solid–liquid two-phase pipe flow. Reynolds numbers based on the bulk velocity and pipe diameter up to 100,000 are investigated.     

Development and Application of a Novel Technique for Direct Heat Flux Measurements in Turbomachinery Flows

The high performance and efficiency of modern gas turbines are only possible with temperatures inside the engine exceeding the allowed material temperatures in some areas by several hundred degrees. Therefore effective cooling methods are one of the key factors for the success of these engines. In order to achieve reliable predictions of the heat load of rotor or stator blades numerous research activities were performed to understand the nature of heat transfer in complex unsteady flows. Even numerical methods have made significant progress in recent years detailed experimental data are still necessary for validation and further development of the engines and the design tools. Here a new method to directly measure the heat flux at the material surface and accurately determine the heat transfer coefficienth is presented. The new sensor is based on the anisotropic characteristics of single crystals and allows the determination of the time varying heat flux on the surface of a model turbine airfoil. This feature is of special interest to study the influence of periodically disturbed flow conditions on the heat transfer characteristics of cooled turbine blades. The working principle of an anisotropic heat flux (AHF) sensor is briefly described together with the design of the actual sensor used in this study. Prior to the application of the sensor in a cascade test rig, comprehensive test of the sensor, the electronics and the data acquisition system were performed using a pulsed laser beam as heat source. To test the sensor under realistic conditions a large number of sensor was installed in a test blade and heat transfer measurements were performed in a cascade test rig equipped with a spoke-wheel wake generator. The results showed good agreement in the time mean results compared with standard techniques. Additionally time resolved data could be extracted from the sensor signals providing detailed information on the unsteady heat transfer characteristics and boundary layer development. This revised version was published online in July 2006 with corrections to the Cover Date.     

Design and modeling of an endoscopic piezoelectric tactile sensor

The paper presents a proof-of-concept design of a tactile sensor capable of measuring compliance of a contact tissue/sensed object. The main objective of this study is to design and model a piezoelectric sensor capable of measuring the total applied force on the sensed object as well as its compliance. The sensor consists of a rigid and compliant cylindrical element. Determination of the compliance of sensed objects is based on the ratio of force experienced by the rigid cylinder to the total force applied to the sensor. To obtain this force ratio, a circular PVDF film is sandwiched between rigid cylinder and plate to measure the force applied on the rigid element and a rectangular PVDF film is sandwiched between the two base plates to measure the total force applied on the sensor. The detailed design of the senor was performed using finite element analysis. A prototype was fabricated and tested and it has been shown that good agreement exists between the finite element results and experimental values. The proposed sensor exhibits high force sensitivity and good linearity and offers the potential for future miniaturization in order to be integrated with the commercial endoscope graspers used in minimally invasive surgery.     

Spatial distribution of void fraction in the liquid slug in the whole range of pipe inclinations

A wire mesh sensor was used to detect the local instantaneous cross-sectional distribution of the phases in gas-liquid slug flow. Data were obtained for a wide range of flow rates and for pipe inclinations ranging from shallow to vertical. Processing of the wire mesh sensor data yielded detailed information of the 3D void fraction distribution in the liquid slug. These results shed additional light on the hydrodynamics of slug flow, in particular, regarding the formation and distribution of dispersed bubbles in the liquid slug. Comparison with available data was carried out. The present results compared favorably with model predictions.     

Two-color digital PIV employing a single CCD camera

 An extension of two color particle image velocimetry (PIV) is described where the color images are recorded onto a single high-resolution (3060×2036 pixel) color CCD sensor. Unlike mono-color CCD sensors, this system not only eliminates the processing time and the subsequent digitization time of film-based PIV but also resolves the directional ambiguity of the velocity vector without using conventional image-shifting techniques. For comparing the spatial resolutions of film and CCD data, a calibration experiment is conducted by recording the speckle pattern onto 35 mm color film and using a CCD sensor under identical conditions. This technique has been successfully implemented for simulated turbine film-cooling flows in order to obtain a more detailed characterization of the coolant-injection phenomenon and its interaction with freestream disturbances. Received: 20 November 1996/Accepted: 29 January 1998     

Model for measurement of thermal expansion coefficient of concrete by fiber optic sensor

The existence of a coating on an optical fiber results in a difference between the strain of the matrix concrete and that sensed by the embedded fiber optic sensor. This paper deals with the theoretical model for measurement of thermal expansion coefficient of concrete by embedded fiber optic sensor. The fiber core, the coating of the optical fiber, and the matrix concrete were all supposed to be elastic. And the bonding surfaces were supposed to be intact, that is to say, there is no relative slip deformation at the interface between the matrix concrete and the coating of the optical fiber, and that between the coating and the fiber core. Based on these assumptions, a theoretical model was developed for measurement of thermal expansion coefficient of concrete. Some experiments were done to verify the validation of the theoretical model. And the comparison indicates a good agreement between the experimental and theoretical results.     

流管声传播与膜结构相互作用的机理研究

以等价分布源方法为基础研究流管声传播与膜结构相互作用的机理. 根据广义格林函数 给出任意截面管道的通用模型. 并在此基础上研究了结构参数、流动马赫数、高阶模态波对 膜结构消声器降噪量及临界频率的影响. 此外，还讨论了流体介质对声波与膜片相互作 用的影响，可以看出膜结构消声器在水下也能得到广泛的应用.     

A Mesh Adaptation Strategy to Predict Pressure Losses in LES of Swirled Flows

Large-Eddy Simulation (LES) has become a potent tool to investigate instabilities in swirl flows even for complex, industrial geometries. However, the accurate prediction of pressure losses on these complex flows remains difficult. The paper identifies localised near-wall resolution issues as an important factor to improve accuracy and proposes a solution with an adaptive mesh h-refinement strategy relying on the tetrahedral fully automatic MMG3D library of Dapogny et al. (J. Comput. Phys. 262, 358-378, 2014) using a novel sensor based on the dissipation of kinetic energy. Using a joint experimental and numerical LES study, the methodology is first validated on a simple diaphragm flow before to be applied on a swirler with two counter-rotating passages. The results demonstrate that the new sensor and adaptation approach can effectively produce the desired local mesh refinement to match the target losses, measured experimentally. Results shows that the accuracy of pressure losses prediction is mainly controlled by the mesh quality and density in the swirler passages. The refinement also improves the computed velocity and turbulence profiles at the swirler outlet, compared to PIV results. The significant improvement of results confirms that the sensor is able to identify the relevant physics of turbulent flows that is essential for the overall accuracy of LES. Finally, in the appendix, an additional comparison of the sensor fields on tetrahedral and hexahedral meshes demonstrates that the methodology is broadly applicable to all mesh types.     

The velocity field of the turbulent very near wake of a circular cylinder

Hot-wire measurements were conducted in the very near wake (x/d10) of a circular cylinder at a Reynolds number based on cylinder diameter, Re _d of 3900. Measurements of the streamwise velocity component with the use of single sensor hot-wire probes were found to be inaccurate for such flowfields where high flow angles are present. An X-array probe provided detailed streamwise and lateral velocity component statistics. Frequency spectra of these two velocity components are also presented. Measurements with a 4-sensor hot-wire probe confirmed that the very near wake region is dominantly two-dimensional, thus validating the accuracy of the present X-array data.This study has been funded by the NASA-Ames University Consortium Cooperative Agreement, NCC2-5003. We wish to thank Patrick Beaudan for providing us with the LES results for comparison and Parviz Moin for his interest in and encouragement of this experiment to provide validation data for the LES. We also wish to thank loseph Murray for his help with the look-up-table data reduction program.     

A method to observe and record vibration modes of rotating circular objects

A method has been developed to make a record of the vibration modes of a rotating circular disk, in our case a circular saw, at various rotating speeds. A picture is produced on a cathode-ray-tube display and photographed. The vibrations are measured by means of a sensor at a variable position along a radius of the saw. The signal is fed to the intensity input of the display, the oscilloscope beam being swept circularly in synchronism with the saw to derotate the pattern. Exposures are made at successively increasing sensor radius and corresponding sweep radius. The picture obtained is less detailed than a holographic picture, but the method is easy to apply, even for rotating objects with a certain skewness.     

A NOTE ON MORI-TANAKA＇S METHOD

Explicit expressions of Mori-Tanaka＇s tensor for a transversely isotropic fiber rein- forced UD composite are presented. Closed-form formulae for the effective elastic properties of the composite are obtained. In a 3D sense, the resulting compliance tensor of the composite is symmetric. Nevertheless, the 2D compliance tensor based on a deteriorated Mori-Tanaka＇s tensor is not symmetric. Nor is the compliance tensor defined upon a deteriorated 2D Eshelby＇s tensor. The in-plane effective elastic properties given by those three approaches are different. A detailed comparison between the predicted results obtained from those approaches with experimental data available for a number of UD composites is made.     

Heat flux sensor with minimal impact on boundary conditions

A technique for determining the heat transfer on the far surface of a wall based on measuring the heat flux and temperature on the near wall is presented. Although heat transfer measurements have previously been used to augment temperature measurements in inverse heat conduction methods, the sensors used alter the heat flow through the surface, disturbing the very quantity that is desired to be measured. The ideal sensor would not alter the boundary condition that would exist were the sensor not present. The innovation of this technique in that it has minimal impact on the wall boundary condition. Since the sensor is placed on the surface of the wall, no alteration of the wall is needed. The theoretical basis for the experimental technique as well as experimental results showing the heat flux sensor performance is presented.     

Some fast 3D finite element solvers for the generalized Stokes problem

This paper is devoted to a comparison of various iterative solvers for the Stokes problem, based on the preconditioned Uzawa approach. In the first section the basic equations and general results of gradient-like methods are recalled. Then a new class of preconditioners, whose optimality will be shown, is introduced. In the last section numerical experiments and comparisons with multigrid methods prove the quality of these schemes, whose discretization is detailed.     

仿生推进装置翼盘变速运动的数值仿真与试验研究

根据水母游动原理扩展设计了一种仿生推进装置,该装置以曲柄滑块机构驱动剪式结构串联体、两端仿生合页式翼盘,实现大行程直线往复运动的仿生推进.在数值分析的基础上,根据仿生推进装置运动的特点,运用直线位移与拉压力传感器,对翼盘在水中运动时的推进力及运动位移进行测试和数据采集.考虑运动过程中翼盘速度变化,运用FLUENT软件对不同张角的翼盘产生的推进力进行数值仿真.通过仿真与试验分析,并以推进力最大化为原则,确定了翼盘最大张角为160°,推进力仿真值与实际测试值基本吻合,初步验证了所提出仿真方法准确性.