低成本车载GPS/INS组合导航姿态角更新算法

低成本INS系统的元件误差严重影响INS导航精度.针对车载系统,提出一种低成本车载GPS/INS组合导航姿态角更新算法.首先在GPS/INS组合导航Kalman滤波方程基础上,给出两种姿态角更新的观测方程.然后给出利用GPS测速确定航向角的原理,并且对低成本车载INS系统的俯仰角和翻滚角进行了分析,指出由INS随机误差造成的俯仰角和翻滚角误差比其本身量值要大,建议令俯仰角和翻滚角数值保持不变.利用实测算例确定了不同速度下的航向角精度,并且验证了该算法的有效性,以及相对于基于位置、速度组合的Kalman滤波,导航精度有明显提高.     

Optimization of energy extraction in transverse galloping

A numerical method to analyse the stability of transverse galloping based on experimental measurements, as an alternative method to polynomial fitting of the transverse force coefficient C_z, is proposed in this paper. The Glauert–Den Hartog criterion is used to determine the region of angles of attack (pitch angles) prone to present galloping. An analytic solution (based on a polynomial curve of C_z) is used to validate the method and to evaluate the discretization errors. Several bodies (of biconvex, D-shape and rhomboidal cross sections) have been tested in a wind tunnel and the stability of the galloping region has been analysed with the new method. An algorithm to determine the pitch angle of the body that allows the maximum value of the kinetic energy of the flow to be extracted is presented.     

Effects of Oblique Inflow in Vortex-Induced Vibrations

We investigate the validity of the independence principle for fixed yawed circular cylinders and free yawed circular rigid cylinders subject to vortex-induced vibrations (VIV) at subcritical Reynolds number using direct numerical simulation (DNS). We compare forces on the cylinder and cylinder responses for different angles of yaw and reduced velocities, and investigate the value of the critical angle of yaw. We also present flow visualizations and examine flow structures corresponding to different angles of yaw and reduced velocities.     

Two noncircular cross-section bodies and a high wing-body configuration at incidence in a low subsonic free stream

This experimental study examines the flow characteristics over a square cross-section body with sharp edges, a rectangular one with rounded edges, and a high wing-body configuration, in a low subsonic free stream. Pressure, velocity, force measurements and flow visualization provide a picture of the flow behaviour, locally and globally. Flow visualization and velocity measurements clearly depict the presence of two axial counter-rotating vortices in the leeside of the first two bodies, being mainly responsible for the asymmetric loading at nonzero roll angles, maximizing the side-force at a roll angle of about 25°. For all body orientations there is always a recirculation region at the nose-afterbody junction leeside area, the extent of which depends mainly on the roll angle. Pressure gradients take high values at the corners of the after body cross-section, even when these are rounded. No asymmetries were practically detected for a zero roll angle and pitch angles up to 20° for the examined three models. The wing-body configuration exhibits a higher lift slope and a more negative zero lift angle, compared to the wing-alone case, and the side-force increases monotonically with the roll angle, without showing any maximum in contrast to the other two models.     

A free gait algorithm for quadrupedal walking machines

A free gait is a computer generated, rule-based gait for a walking machine to walk on rough terrain. Based on a given terrain map, the gait algorithm selects footholds for leg placements and determines the movements of legs and body. In the past, a few free gaits for hexapods have been developed. For quadrupeds, the only report on free gait was briefly mentioned in a paper by Hirose [Int. J. Robotics Res., 3(2) (1984)]. In this paper, a free gait algorithm for a quadrupedal walking chair is developed. For quadrupeds, the stability margin is small due to a small number of legs and the choices of a leg to be lifted are limited. Hence, deadlock situations may occur quite often. Many special techniques are incorporated into the algorithm in order to reduce deadlocks. This free gait algorithm adopts the wave-crab gaits as the primary gait because they are periodic and can provide good stability. The algorithm also adopts a non-periodic free gait to handle terrain with higher concentration of forbidden areas. This algorithm is evaluated under different terrain conditions using computer simulations. The results show that the performance is satisfactory on randomly generated rough terrain and needs improvement on manually generated rough terrain.     

火箭弹大动态单轴平台惯导系统姿态算法

火箭弹在飞行中常采用滚转稳定的控制方式,其滚转角速度的动态范围很大,因此实时、准确地测量滚转角速度和滚转姿态角成为制导火箭弹控制的关键问题。大动态单轴平台惯导系统将IMU安装在沿滚转方向的稳定平台上,通过伺服电机驱动单轴平台相对于弹体反旋,隔离滚转方向的大动态角速度,为IMU提供平稳的测试环境。介绍了大动态单轴平台惯导系统的组成和功能,搭建了样机,推导了惯导姿态解算的数学模型。经过120 s半实物仿真试验,系统俯仰姿态角误差<4°,偏航姿态角误差<3°,滚转姿态角误差<25°,结果验证了整体方案的可行性和姿态解算模型的正确性。为进一步提高姿态解算精度,搭建单轴平台组合导航系统,实现全部导航信息的高精度测量打下了基础。     

A thermodynamic approach to isotropic-nematic phase transitions in liquid crystals

We propose a dynamical model for (non-isothermal) phase transitions in liquid crystals. Macroscopic motions of the liquid crystal (LC) are neglected, while the coupling with the electromagnetic field is considered. The LC is described in terms of the classical order tensor Q, which is split as Q=s N, where N is a normalized tensor; two independent evolution laws are given for s and N. The model includes an evolutive equation for the temperature field obtained from an appropriate form of the energy balance, in which the internal powers associated to the equations for s and N are accounted for. The thermodynamic restrictions in the constitutive relations which ensure the Clausius–Duhem inequality have been pointed out.     

Influence of streamwise pitch on the local heat transfer characteristics for in-line arrays of circular jets with crossflow of spent air in one direction

Influence of the streamwise pitch on local heat transfer distribution due to a rectangular in-line array of circular air jets of length-to-diameter ratio (l/d) of 1.0 is studied experimentally. The flow, after the impingement, is constrained to exit in one direction. Mean jet Reynolds number is varied from 3000 to 10000 and jet-to-plate spacing from d to 3d. Streamwise jet-to-jet distances of 3d, 4d and 5d and a constant spanwise pitch of 4d are considered. A flat target surface is made of thin stainless steel metal foil. The local temperature distribution on a target plate is measured using thermal infrared camera. The jet exit pressures are measured to estimate the cross-flow velocities and individual jet velocities. The streamwise distribution of the jet-flow and the cross-flow is least influenced by the streamwise pitch variation for the range of parameters investigated. Heat transfer characteristics are explained partially on the basis of flow distribution. The cooling performance, based on strip averaged Nusselt number per unit mass flow rate of coolant per unit area of cooled surface, deteriorates for lower streamwise pitch and higher jet-to-plate distance.     

Discrete element method analysis of single wheel performance for a small lunar rover on sloped terrain

The purpose of this study is to analyze the performance of a lugged wheel for a lunar micro rover on sloped terrain by a 2D discrete element method (DEM), which was initially developed for horizontal terrain. To confirm the applicability of DEM for sloped terrain locomotion, the relationships of slope angle with slip, wheel sinkage and wheel torque obtained by DEM, were compared with experimental results measured using a slope test bed consisting of a soil bin filled with lunar regolith simulant. Among the lug parameters investigated, a lugged wheel with rim diameter of 250 mm, width of 100 mm, lug height of 10 mm, lug thickness of 5 mm, and total lug number of 18 was found, on average, to perform excellently in terms of metrics, such as slope angle for 20% slip, power number for self-propelled point, power number for 15-degree slope and power number for 20% slip. The estimation of wheel performance over sloped lunar terrain showed an increase in wheel slip, and the possibility exists that the selected lugged wheel will not be able to move up a slope steeper than 20°.     

Attenuation of the fourth sound in liquid helium II via extended thermodynamics

This work continues a study begun in previous works, where a non-standard model of liquid helium II is proposed, in which a small entropy transfer is associated with the superfluid component. In this work the influence of this superfluid entropy on the propagation of the fourth sound is analyzed. From experimental data for velocities and attenuations of the first and second sound, the model provides speed and attenuation coefficient of the fourth sound in a porous medium as a function of the ratio s_s/s between the superfluid entropy s_s and the total entropy s. These values are determined in the two limiting cases s_s/s=0 and =0.02, for various values of temperature and pressure.     

A Weak-L p Prodi–Serrin Type Regularity Criterion for the Navier–Stokes Equations

We give simple proofs that a weak solution u of the Navier–Stokes equations with H ¹ initial data remains strong on the time interval [0, T] if it satisfies the Prodi–Serrin type condition u ∈ L ^s (0, T;L ^r,∞(Ω)) or if its L ^s,∞(0, T;L ^r,∞(Ω)) norm is sufficiently small, where 3 < r ≤ ∞ and (3/r) + (2/s) = 1.     

Multi-shock structure of roll wavesStructure multi-chocs d'ondes à rouleaux

The special class of periodic travelling waves which is known as roll waves is investigated for nonhomogeneous hyperbolic equations of gas dynamics type. In this Note these equations are applied to shallow water flows in inclined open channels, but the results obtained are more general and far-reaching. The necessary conditions for the existence of a roll wave are derived. It is shown that for a nonconvex pressure term, multi-shock configurations of roll waves of finite amplitude exist. A new type of periodic travelling wave, which corresponds to the slug flow regime in two-layer flows, is found. To cite this article: A. Boudlal, V.Yu. Liapidevskii, C. R. Mecanique 332 (2004).     

Modeling of the phase lag causing fluidelastic instability in a parallel triangular tube array

Fluidelastic instability is considered a critical flow induced vibration mechanism in tube and shell heat exchangers. It is believed that a finite time lag between tube vibration and fluid response is essential to predict the phenomenon. However, the physical nature of this time lag is not fully understood. This paper presents a fundamental study of this time delay using a parallel triangular tube array with a pitch ratio of 1.54. A computational fluid dynamics (CFD) model was developed and validated experimentally in an attempt to investigate the interaction between tube vibrations and flow perturbations at lower reduced velocities U_r=1–6 and Reynolds numbers Re=2000–12 000. The numerical predictions of the phase lag are in reasonable agreement with the experimental measurements for the range of reduced velocities U_g/fd=6–7. It was found that there are two propagation mechanisms; the first is associated with the acoustic wave propagation at low reduced velocities, U_r<2, and the second mechanism for higher reduced velocities is associated with the vorticity shedding and convection. An empirical model of the two mechanisms is developed and the phase lag predictions are in reasonable agreement with the experimental and numerical measurements. The developed phase lag model is then coupled with the semi-analytical model of Lever and Weaver to predict the fluidelastic stability threshold. Improved predictions of the stability boundaries for the parallel triangular array were achieved. In addition, the present study has explained why fluidelastic instability does not occur below some threshold reduced velocity.     

Experimental,numerical and analytical studies of abrasive wear: correlation between wear mechanisms and friction coefficient

The transport of granular material often generates severe damage. Understanding the correlation between the friction coefficient, particle geometry and wear mechanisms is of primary importance for materials undergoing abrasive wear. The aim of this study is to investigate the effect of particle geometry on wear mechanisms and the friction coefficient. Numerical and analytical simulations and experimental results have been compared. The process to be studied is the scratch made by a rigid cone with different attack angles on a 5xxx aluminium alloy (Al–Mg) flat surface. A scratch test was used and the wear mechanisms were observed for different attack angles. A numerical study with a finite element code was made in order to understand the effect of attack angle on the friction coefficient. The contact surface and the friction coefficient were also studied, and the results compared to the Bowden and Tabor model. The superposition of the numerical, analytical and experimental results showed a better correlation between the wear mechanisms and the friction coefficient. It also showed the importance of the model hypothesis used to simulate the scratch phenomenon. To cite this article: S. Mezlini et al., C. R. Mecanique 333 (2005).     

Effect of strain rate,moisture and temperature on the deformation behavior of polymer roll covers

Soft polymer roll covers, which are used in certain positions of paper manufacturing machines, have a vital role in the dynamics of two mating rotating rolls (i.e., nip dynamics). The polymer covers are often used in moist conditions where the loading rates are rather high and temperatures may vary from 45 to 60°C. In this paper, we study the dynamic mechanical behavior of two soft polyurethane composite roll covers under different conditions of temperature, moisture, and loading rate. For the tests in compression, both servohydraulic materials testing machines and the split Hopkinson pressure bar technique were used in the strain rate range of 0.001–1500 s⁻¹. The specimens, which were to be tested under moist conditions, were immersed in paper machine water (pH 4.5) until saturated moisture content was reached. The materials showed remarkable softening as well as decrease in the strain rate sensitivity in moist conditions.     

Stability of roll waves in open channel flowsStabilité de trains d'ondes dans un canal découvert

The stability of finite amplitude roll waves that may develop at a liquid free surface in inclined open channels of arbitrary cross-section is studied. In the framework of shallow water theory with turbulent friction the modulation equations for wave series are derived and a nonlinear stability criterion is obtained. To cite this article: A. Boudlal, V.Yu. Liapidevskii, C. R. Mecanique 330 (2002) 291–295.     

A continuum description of partially coherent interfaces

A continuum model of a two-phase crystal-crystal system is constructed in which the structure of the interface between the phases is determined by energy minimization, rather than by being specified a priori. The interfacial structure is parameterized by a variable? corresponding to the jump in the surface deformation gradient (or strain) at the interface, so that coherence is defined locally by the condition? = 0. The energy of the system is taken to be the sum of the bulk and interfacial energies, where the interfacial energy densityf ^xs depends on?. In order to explore how the equilibrium interfacial structure depends on the functionf ^xs (?), a model system consisting of an elastic film on a rigid substrate is studied, and the interfacial energy density is taken to be nonconvex with a sharp minimum associated with coherence. In this case, it can be shown that the energy of the system is driven to its infimum by separating the interface into coherent and incoherent regions, which may be viewed as a continuum analog to a partially coherent interface. Further, this solution only appears above a certain critical thickness of the film, in agreement with misfit dislocation models of partially coherent interfaces.     

Effect of flow regime change from subsonic to transonic on the air loads of an oscillating airfoil

In this research, the effect of flow regime change from subsonic to transonic on the air loads of a pitching NACA0012 airfoil is investigated. To do this, the effect of change in flow regime on the lift and pitching moment coefficients hysteresis cycles is studied. The harmonic balance approach is utilized for numerical calculation due to its low computational time. Verifications are also made with previous works and good agreements are observed. The assessment of flow regime change on the aforementioned hysteresis cycles is accomplished in the Mach number range of M=0.65–0.755. The reduced frequency and pitch amplitude also vary from k=0.03 to 0.1 and α₀=1–2.51°, respectively. Results show that the effect of increase in Mach number is to increase and decrease the lift coefficient during downstroke and upstroke, respectively, whereas at low reduced frequencies, the effect of increase in Mach number may lead to a reverse manner when airfoil moves toward its extremum angle of attack. Results also reveal that as the pitch amplitude varies, the shape of lift coefficient hysteresis cycle depends more on the pitch amplitude than on the appearance of shock. It is shown that as the Mach number increases, the incidence angles correspond to the extremum pitching moment, and depending on the reduced frequency, lie between zero and extremum angle of attack. These incidence angles shift toward the extremum angle of attack as the reduced frequency decreases. Results also show that the increase in pitch amplitude at low Mach number, in such a way that leads to the formation of shock around the extremum angle of attack, causes the extremum pitching moment to appear around these angles and at high Mach number, depending on the reduced frequency, the extremum pitching moment incidence angles would be between zero and extremum incidence angle.     

Calibration of a four-hole pyramid probe and area traverse measurements in a short-duration transonic turbine cascade tunnel

A four-hole pyramid probe has been calibrated for use in a short-duration transonic turbine cascade tunnel. The probe is used to create area traverse maps of total and static pressure, and pitch and yaw angles of the flow downstream of a transonic annular cascade. This data is unusual in that it was acquired in a short-duration (5 s of run time) annular cascade blowdown tunnel. A four-hole pyramid probe was used which has a 2.5 mm section head, and has the side faces inclined at 60° to the flow to improve transonic performance. The probe was calibrated in an ejector driven, perforated wall transonic tunnel over the Mach number range 0.5–1.2, with pitch angles from -20° to + 20° and yaw angles from-23° to +23°. A computer driven automatic traversing mechanism and data collection system was used to acquire a large probe calibration matrix (～ 10,000 readings) of non dimensional pitch, yaw, Mach number, and total pressure calibration coefficients. A novel method was used to transform the probe calibration matrix of the raw coefficients into a probe application matrix of the physical flow variables (pitch, yaw, Mach number etc.). The probe application matrix is then used as a fast look-up table to process probe results. With negligible loss of accuracy, this method is faster by two orders of magnitude than the alternative of global interpolation on the raw probe calibration matrix. The blowdown tunnel (mean nozzle guide vane blade ring diameter 1.1 m) creates engine representative Reynolds numbers, transonic Mach numbers and high levels (≈ 13%) of inlet turbulence intensity. Contours of experimental measurements at three different engine relevant conditions and two axial positions have been obtained. An analysis of the data is presented which includes a necessary correction for the finite velocity of the probe. Such a correction is non trivial for the case of fast moving probes in compressible flow.     

Heat transfer in asymmetric transverse flows over bundles of tubes

Heat transfer was studied on a separate transverse row of tubes with the relative pitch ofs ₁/d=1.5 and a staggered bundle with the relative pitches ofs ₁/d×s ₂/d=1.15×0.98. A test tube in the transverse row was used with a variable displacement from the symmetric position. The tube bundle was placed at different gaps from the shell wall. Experiments were performed in air and water in the range ofRe from 10³ to 6×10⁵. Asymmetric flows over transverse rows are accompanied by augmented heat transfer rates and steady state lift force which becomes higher with the amount of displacement. The presence of the shell wall introduces alterations in the thermal and fluid dynamics over outside tubes in a bundle.