新型准零刚度空气悬架系统的设计与分析

为提高商用汽车在低频外部激励环境下的隔振性能以及行驶平顺性,基于准零刚度理论,采用正负刚度并联的方式,将负刚度碟形弹簧组与正刚度空气弹簧相结合,设计一种新型准零刚度悬架系统。通过静力学特性分析,建立力位移和刚度位移表达式,得到系统达到准零刚度的参数条件;通过动力学特性分析,建立系统的二自由度模型和简谐力作用下的非线性运动微分方程,得到力传递率特性曲线并对其进行分析。结果表明新结构的低频隔振性能显著提升。基于刚度位移表达式建立2自由度1/4悬架模型,分别对准零刚度系统与传统系统的垂向加速度、悬架动行程和轮胎动载荷等平顺性指标的差异性进行分析,仿真结果表明,该准零刚度系统的平顺性改善效果亦优于传统结构。

准零刚度隔振座椅的理论与实验研究

针对车辆座椅的低频隔振问题,基于经典三弹簧准零刚度(Quasi-zero Stiffness,QZS)模型,建立座椅隔振实验模型,采用仿真和实验方法评价座椅模型的隔振性能。首先,对于三弹簧QZS模型,讨论参数对QZS的影响,获得QZS条件。其次,采用ADAMS仿真分析三弹簧QZS座椅模型,仿真和理论位移传递率具有较好的一致性。然后,制作三弹簧QZS座椅实验模型,通过静态实验调整实验模型获得QZS特性。最后,采用振动台对QZS座椅在1~10 Hz频率范围内开展大幅谐波位移激励隔振实验,同时采用Polytec激光测振仪分别获得振动台和座椅的位移响应,通过实验位移传递率评价QZS座椅隔振性能并验证理论分析正确性;相比对应的线性刚度隔振座椅,三弹簧QZS座椅具有较宽隔振频带和较小传递率。研究三弹簧QZS座椅的隔振性能可为后续可供实际工程应用的QZS座椅研究提供参考,同时也指出QZS座椅研究中存在的困难。

零群速度特征导波在焊缝损伤评估中的应用

通过数值模拟方法研究了零群速度特征导波(zero-group-velocity feature guided waves,ZGV-FGWs)在焊缝损伤检测中的应用。建立了焊缝结构的二维频域有限元模型,损伤程度用不同的杨氏模量表征,验证了焊缝结构中的共振现象并确定了能量集中在焊缝特征区附近时的共振频率。利用三维时域有限元方法确定了ZGV-FGWs共振模式的存在,并分析了不同杨氏模量焊缝的ZGV-FGWs传播特性。结果表明:随着材料杨氏模量的减小,ZGV-FGWs频谱信号幅值显著单调减小,且ZGV-FGWs频谱信号幅值的变化趋势与激励信号的频谱曲线吻合。基于此特性可以设置合适的激励信号,获得幅值变化更强的ZGV-FGWs频谱信号,进而准确评价焊缝的损伤状态。

基于优化暂态零序方向与改进首半波的综合决策选线方法

针对现有小电流接地选线判据适应性较差、选线精度较低的问题,提出了基于优化暂态零序方向与改进首半波的综合决策选线方法,通过带通数字滤波器的设计及暂态首半波特性分析,综合利用首半波短窗、首半波长窗以及带通滤波数据窗内极性满足特性的采样点统计,确定各自相关系数,形成综合选线判据。基于该综合决策选线方法开发了对应的选线保护装置,并进行了RTDS动模测试及真型试验。结果表明,该选线方法能适应各种系统运行方式及故障条件,验证了其有效性和可靠性。

Estimation of JONSWAP Spectral Parameters by Using Measured Wave Data

- This paper presents the method of determining JONSWAP spectrum by using measured wave data. If Hs, Tz and Tc are the measured significant wave height, average zero-up crossing wave period and average period between wave crests respectively and let y = T Z / TC; this paper provides equation to solve y fromf(y,y) = 0. From the solutions of this equation and by using LSM, the expression relating y as a function of y (for 2.54<y< 15.34 and 1.6 <y < 1,79) may be written as y -5546.721 - 9586.533y + 5568.168/- 1089/+ 2/, for other intervals the related formulas are also given. When y is known, the rest of parameters in JONSWAP spectrum can be obtained. In addition, this paper also provides alternatives for determining JONSWAP spectral parameters by using Hs, Tz and (, or Hs, Tz and S(w0) or other three given data. The JONSWAP spectra given in this paper satisfy the following formulas HS= 4.0 = 2 Tc = 2

ZERO DISSIPATION LIMIT OF THE COMPRESSIBLE HEAT-CONDUCTING NAVIER-STOKES EQUATIONS IN THE PRESENCE OF THE SHOCK

The zero dissipation limit of the compressible heat-conducting Navier–Stokes equations in the presence of the shock is investigated. It is shown that when the heat conduction coefficient κ and the viscosity coefficient ε satisfy κ = O（ε）, κ/ε≥ c 〉 0, as ε→ 0 （see （1.3））, if the solution of the corresponding Euler equations is piecewise smooth with shock wave satisfying the Lax entropy condition, then there exists a smooth solution to the Navier–Stokes equations, which converges to the piecewise smooth shock solution of the Euler equations away from the shock discontinuity at a rate of ε. The proof is given by a combination of the energy estimates and the matched asymptotic analysis introduced in [3].

深空探测中磁强计在轨标定研究进展

磁场测量是深空探测的重要任务之一,高精度的磁场测量对研究行星宜居性、空间等离子体环境等具有重要意义.磁通门磁强计是空间探测任务中最广泛使用的仪器之一.然而其磁补偿会随时间缓慢变化,因此,在卫星飞行期间需要定期对磁强计的磁补偿实施在轨标定.本文综述了基于空间物理现象对星载磁强计实施在轨标定的方法.根据计算磁补偿的方式,这些方法可分为两类.第一类方法通过公式计算磁补偿,如基于阿尔芬波动特征的Belcher方法、Hedgecock方法和Davis-Smith方法,以及一维和三维磁镜模方法;这类方法中,Davis-Smith方法被认为是计算磁补偿的最优方法.第二类方法通过概率获取磁补偿的最优解,该类方法被称为新一代在轨标定技术,目前已发展出六种算法;该技术可使用阿尔芬波动、磁镜结构和电流片中的一种或多种现象来实施在轨标定,另外,该技术也可以使用足够数据量(如4小时)的任意行星际磁场数据来计算磁补偿.与Davis-Smith方法相比,新一代在轨标定技术具有很好的兼容性(可同时使用不同的物理现象)和拓展性.除了太阳风,该技术还能在火星磁鞘中实施在轨标定.目前,该技术已为“天问一号”环绕器的磁场数据提供标定服务.

Robust Control Based on Feedback Linearization for Roll Stabilizing of Autonomous Underwater Vehicle Under Wave Disturbances

In the case of Autonomous Underwater Vehicle （AUV） navigating with low speed near water surface, a new method for design of roll motion controller is proposed in order to restrain wave disturbance effectively and improve roll stabilizing performance. Robust control is applied, which is based on uncertain nonlinear horizontal motion model of AUV and the principle of zero speed fin stabilizer. Feedback linearization approach is used to transform the complex nonlinear system into a comparatively simple linear system. For parameter uncertainty of motion model, the controller is designed with mixed-sensitivity method based on H-infinity robust control theory. Simulation results show better robustness improved by this control method for roll stabilizing of AUV navigating near water surface.

A Comparative Study of the Statistical Distributions of Wave Heights

Distribution of wave heights and surface elevations of wind-driven waves are studied. Records of surface elevations obtained from both field observations and laboratory measurements are analyzed. Wave heights can be approximated by normal, two-parameter Weibull, and/or Rayleigh distribution. However, while the first two models may have almost equal probabilities to fit measured data quite satisfactorily, the Rayleigh distribution does not appear to be a good model for the majority of the cases studied. Surface elevations from field data are well described by the Gaussian model, but as with increasing wind speeds, water surface in a wind-wave flume deviates from normality, and the Edgeworth/s form of the type A Gram-Charlier series is then applied.

Estimation of Wind Wave Frequency Spectra by Use of the Arcsine Law

In the present study, the surface elevation of wind waves observed in laboratory and in the Bohai Sea are adopted for the estimation of the wind wave frequency spectrtm by use of the method of the arcsine law （MAL）. The traditional method uses the surface elevation to calculate the correlation and then estimate the frequency spectrum while the MAL, presented by Yu and l.an （1979）, uses the time sequence of zero-crossing points of surface elevation rather than directly the surface elevation to calculate the correlation. 66 sets of wind wave data obtained in laboratory and 420 sets of data observed in the Bohai Sea are adopted for the examination of the method introduced by Yu and Lan. Results show that the MAL can give reliable estimation of wind wave spectra. Correlation and form of spectra estimated by the MAL are similar to those estimated by the traditional method. The peak frequency and the spectral density in peak frequency by the MAL are close to those obtained by the traditional method.

ZERO DISSIPATION LIMIT TO A RIEMANN SOLUTION FOR THE COMPRESSIBLE NAVIER-STOKES SYSTEM OF GENERAL GAS

For the general gas including ideal polytropic gas, we study the zero dissipation limit problem of the full 1-D compressible Navier-Stokes equations toward the superposition of contact discontinuity and two rarefaction waves. In the case of both smooth and Riemann initial data, we show that if the solutions to the corresponding Euler system consist of the composite wave of two rarefaction wave and contact discontinuity, then there exist solutions to Navier-Stokes equations which converge to the Riemman solutions away from the initial layer with a decay rate in any fixed time interval as the viscosity and the heat-conductivity coefficients tend to zero. The proof is based on scaling arguments, the construction of the approximate profiles and delicate energy estimates. Notice that we have no need to restrict the strengths of the contact discontinuity and rarefaction waves to be small.

What Is the Missing Dark Energy in a Nutshell and the Hawking-Hartle Quantum Wave Collapse

We reason that in quantum cosmology there are two kinds of energy. The first is the ordinary energy of the quantum particle which we can measure. The second is the dark energy of the quantum wave by quantum duality. Because measurement collapses the Hawking-Hartle quantum wave of the cosmos, dark energy cannot be detected or measured in any conventional manner. The quantitative results are confirmed using some exact solutions for the hydrogen atom. In particular the ordinary energy of the quantum particle is given by E(0) = (/2)(mc2) where is Hardy’s probability of quantum entanglement, =( - 1)/2 is the Hausdorff dimension of the zero measure thin Cantor set modeling the quantum particle, while the dark energy of the quantum wave is given by E(D) = (5/2)(mc2) where is the Hausdorff dimension of the positive measure thick empty Cantor set modeling the quantum wave and the factor five (5) is the Kaluza-Klein spacetime dimension to which the measure zero thin Cantor set D(0) = (0,) and the thick empty set D(-1) = (1,) must be lifted to give the five dimensional analogue sets namely and 5 needed for calculating the energy density E(0) and E(D) which together add to Einstein’s maximal total energy density E(total) = E(0) + E(D) = mc2 = E(Einstein). These results seem to be in complete agreement with the WMAP, supernova and recent Planck cosmic measurement as well as the 2005 quantum gravity experiments of V. V. Nesvizhersky and his associates. It also confirms the equivalence of wormhole solutions of Einstein’s equations and quantum entanglement by scaling the Planck scale.

DESIGN OF HIGH VOLTAGE POWER CONVERTER FOR TRAVELING WAVE TUBE AMPLIFIER

Traveling Wave Tubes(TWTs) are widely used in the radar and communications system as RF power amplifiers. A highly sophisticated power supply is required by TWT. In order to meet the severe requirements of Traveling Wave Tube Amplifier(TWTA), a novel two-stage topology high voltage converter for TWTA is proposed.The converter is based on Zero-Voltage Switching and Zero-Current Switching(ZVS/ZCS) resonant techniques. The high voltage converter operation principles are investigated and major features of the converter are discussed. The power switching mode of ZVS/ZCS is obtained. The experimental results show that the converter has good soft switching characteristics. Compared to the conventional hard switched Pulse Width Modulation(PWM) techniques, the high efficiency and low ripple of the converter for TWTA are realized. The efficiency of High Voltage Electronic Power Conditioners(HV-EPC) over 93.5% under the condition of 38~46 V input voltage and 260~300 W input power. The switching frequency of first-stage(preregulator) of HV-EPC is 89 k Hz and the switching frequency of second-stage(postregulator) is 44.5 k Hz. The highest output voltage of the HV-EPC is helix voltage which is about –6.8 kV. It is especially suitable for TWTA utilized in space satellite applications due to its high switching frequency and high power density.

一类等熵欧拉方程组的流近似

研究了一类带有流扰动的一般压力等熵欧拉方程组的黎曼问题,获得了包含5种不同结构的黎曼解.证明了当包含压力的3-参数流扰动消失时,任何包含2个激波的黎曼解收敛于零压流系统的狄拉克激波解;任何包含2个稀疏波的黎曼解收敛于零压流系统的真空解.还证明了当包含压力的2-参数流扰动消失时,任何满足一定初值条件的2-激波黎曼解收敛于一类Chaplygin型气体方程组的狄拉克激波解.最后,对狄拉克激波和真空状态的形成过程进行了数值模拟.

Interaction of Streamwise and Wall-Normal Velocities in Combined Wave-Current Motion

The aim of this paper is to present an analytical expression for the streamwise velocity distribution in a non-uniform flow in the presence of waves; the correlation between the horizontal and vertical velocity components has been compreheusively examined. Different from previous researches which attributed the deviation of velocity from the classical log-law to the wave Reynolds stress, i.e. - ρ uv^- only, this study demonstrates that the momentum flux caused by mean velocities, i.e., u^- and v^-, is also responsible for the velocity deviation, and it is found that the streamwise velocity for a flow in the presence of non-zero wall-normal velocity does not follow the classical log-law, but the modified log-law proposed in this study based on simplified mixing-length theorem. The validity of the modified log-law has been verified by use of available experimental data from published sources for combined wave-current flows, and good agreement between the predicted and observed velocity profiles has been achieved.

声表面波标签的相参阅读器设计

现有与声表面波标签匹配的阅读器通常采用非相参的超外差结构,并通过开关截断以产生激励脉冲信号。由于开关闭合时刻和本振信号初相位的随机性,该方案所测回波相位为一个不确定的值,无法与距离等待测量建立函数关系。本文设计了一种相参阅读器,在发射链路使用功分器将信号源产生的信号分为两路同相信号,并把其中一路引入接收链路的下混频器作为本振信号,由此可使回波相位为一确定值。实际制作了阅读器电路,测试了发射、接收链路,并结合声表面波标签进行了实验,通过与矢量网络分析仪测量结果对比,表明了该阅读器的有效性。

改进零视差像素点重组的图像数字水印算法

针对三维图像数字水印无法同时保证良好的视觉感受与抗攻击性能的问题,提出基于零视差点重组的三维图像数字水印算法。利用平面点-线模型描述三维图像,将色彩从红色、绿色、蓝色等分量转变为亮度、蓝色、红色等分量。根据视距、景深等参数,解得各像素点的视差值,基于零视差像素点及对应窗口归一化协方差,调整各像素点坐标,得到重组图像。将重组图像作为待嵌入水印的载体图像,结合轮廓波变换策略,取得能量最大的方向图像。通过分块处理,推导出轮廓波交换系数的交换判定条件,经轮廓波逆变换、拼接、融合等操作,完成数字水印嵌入。实验结果表明,所提算法嵌入的水印视觉感知程度较低,隐秘度与安全度较高,能保证水印在取得较好视觉效果的前提下,具备较强的攻击防御能力。

组合KdV方程孤立波解的轨道稳定性

组合KdV方程在物理学的许多领域都有应用,例如等离子体磁流波、离子声波等。粒子在传输过程中需要刻画其稳定性。本文主要通过平移变换,将研究带有非零渐近值的孤立波解的轨道稳定性,转化为研究具有零渐进值孤立波解的轨道稳定性,给出了稳定性的判定定理,应用Grillakis-Shatah-Strauss提出的轨道稳定性理论与谱分析理论得到了组合KdV方程的几种孤立波解的轨道稳定性结论。

配电网单相接地故障行波定位新方法

针对零、线模速度差和时间差行波定位原理中零模波速度难以确定的问题,提出了在无需时间同步的情况下,利用线路两端信息融合在线实时求取零模波速度的算法和一种配电网单相接地故障行波定位新方法。分析了行波分量在线路上的传播特性,将零、线模行波通过S变换后,发现在零、线模行波频率分别为50 k Hz和500 k Hz的分量下标定初始波头的到达时间,具有较高的灵敏度和稳定性。根据零模波速度与定位公式之间的关系,找出故障点所在最小区域,将该最小区域包含的线路区段分解成多组T型线路进行了故障定位。通过PSCAD/EMTDC进行了全面系统的仿真验证,结果表明所求得的零模波速度和定位方法具有较高的准确度,具有一定工程价值。

基于线模行波突变的配电网单相接地故障测距方法

为了消除线路结构多变性和不平衡负载对配电网单相接地故障测距的影响,提出三相同时注入高压脉冲后以线模行波突变为判据的测距新方法。通过分析配电变压器的行波传变特性和行波在故障点的传播方程,在理论上证明首端检测到的第一个线模电压行波波头来源于故障点零模电压入射波的反射,进而得到测距公式。根据色散原理及配电网线路一般较短的情况,将波头首个非零点作为行波到达时刻的判别,并选取波速度为光速。在PSCAD(power systemscomputer aided design)中仿真验证了方法的有效性和准确性。