On the effect of pitch and yaw angles in oblique impacts of smallcaliber projectiles

A terminal ballistic analysis of the effects of 7.62 mm × 51 AP P80 rounds on inclined high-strength armor steel plates is the focus of the presented study.The findings of an instrumented ballistic testing combined with 3D advanced numerical simulations performed using the IMPETUS Afea? software yielded the conclusions.The experimental verification proved that slight differences in the pitch-andyaw angles of a projectile upon an impact caused different damage types to the projectile’s core.The residual velocities predicted numerically were close to the experimental values and the calculated core deviations were in satisfactory agreement with the experimental results.An extended matrix of the core deviation angles with combinations of pitch-and-yaw upon impact angles was subsequently built on the basis of the numerical study.The presented experimental and numerical investigation examined thoroughly the influence of the initial pitch and yaw angles on the after-perforation projectile’s performance.

Analysis of Influence on Aerodynamic Noise of Wind Turbine Blades under Different Pitch Angles

Aiming at the influence of blade pitch Angle on aerodynamic noise of wind turbines, the sound field and flow field distribution at 0˚, 5˚, 10˚ and 15˚ are calculated by numerical simulation. Then, through the distribution of pressure field and velocity field calculated by flow field, the influence of different pitch angles on wind turbine blade aerodynamic noise and the reasons for its influence are analyzed. The results show that when the pitch Angle increases within 0˚ - 10˚, the aerodynamic noise pressure level of the blade decreases. However, the sound pressure level of aerodynamic noise increases in the range of 10˚ - 15˚. The changes of static pressure gradient and pressure pulsation on the blade surface make the aerodynamic noise change, and the changes of the two are positively correlated. At the same time, the fluid velocity and fluid motion state on the blade surface are closely related to the aerodynamic noise of the blade. The greater the fluid velocity, the more complex the fluid motion state and the greater the turbulent kinetic energy of the wind turbine blade, and the aerodynamic noise of the wind turbine blade will also increase.

Proton pitch angle distributions in the Martian induced magnetosphere: A survey of Tianwen-1 Mars Ion and Neutral Particle Analyzer observations

The pitch angle distributions of ions and electrons can be affected by various processes;thus,they can serve as an important indicator of the physical mechanisms driving the dynamics of space plasmas.From observations from the Mars Ion and Neutral Particle Analyzer onboard the Tianwen-1 orbiter,we calculated the pitch angle distributions of protons in the Martian induced magnetosphere by using information from the magnetohydrodynamically simulated magnetic field,and we statistically analyzed the spatial occurrence pattern of different types of pitch angle distributions.Even though no symmetrical features were seen in the dataset,we found the dominance of the field-aligned distribution type over the energy range from 188 to 6232 eV.Maps of the occurrence rate showed the preferential presence of a trapped-like distribution at the lower altitudes of the surveyed nightside region.Although our results are more or less restricted by the adopted magnetic field,they indicate the complexity of the near-Mars proton pitch angle distributions and infer the possibility of wave–particle interactions in the Martian induced magnetosphere.

Investigation of fast pitch angle scattering of runaway electrons in the EAST tokamak

This paper reports that an experimental investigation of fast pitch angle scattering （FPAS） of runaway electrons in the EAST tokamak has been performed. From the newly developed infrared detector （HgCdTe） diagnostic system, the infrared synchrotron radiation emitted by relativistic electrons can be obtained as a function of time. The FPAS is analysed by means of the infrared detector diagnostic system and the other correlative diagnostic systems （including electron-cyclotron emission, hard x-ray, neutrons）. It is found that the intensity of infrared synchrotron radiation and the electron-cyclotron emission signal increase rapidly at the time of FPAS because of the fast increase of pitch angle and the perpendicular velocity of the energetic runaway electrons. The Parail and Pogutse instability is a possible mechanism for the FPAS.

Effect of Helix Pitch Angle on the Modal Dispersion Characteristic of Step-Index Optical Fiber

The general characteristic equation is derived for the helically cladded step-index optical fiber. The dispersion curves are drawn for the different pitch angles Ψ and mode order ν = 1. The effect of helix pitch angle on the dispersion characteristics and also on the modal cut-off condition is examined. Except for the lowest order mode, all the modes appear in pairs. The lowest order mode displays the negative dispersion for the some value of normalized frequency V and depends on the helix pitch angle Ψ.

Effect of blade pitch angle on aerodynamic performance of straight-bladed vertical axis wind turbine

Wind energy is one of the most promising renewable energy sources, straight-bladed vertical axis wind turbine(S-VAWT) appears to be particularly promising for the shortage of fossil fuel reserves owing to its distinct advantages, but suffers from poor self-starting and low power coefficient. Variable-pitch method was recognized as an attractive solution to performance improvement, thus majority efforts had been devoted into blade pitch angle effect on aerodynamic performance. Taken into account the local flow field of S-VAWT, mathematical model was built to analyze the relationship between power outputs and pitch angle. Numerical simulations on static and dynamic performances of blade were carried out and optimized pitch angle along the rotor were presented. Comparative analyses of fixed pitch and variable-pitch S-VAWT were conducted, and a considerable improvement of the performance was obtained by the optimized blade pitch angle, in particular, a relative increase of the power coefficient by more than 19.3%. It is further demonstrated that the self-starting is greatly improved with the optimized blade pitch angle.

Storm-Time Evolution of Energetic Electron Pitch Angle Distributions by Wave-Particle Interaction

The quasi-pure pitch-angle scattering of energetic electrons driven by field-aligned propagating whistler mode waves during the 9～15 October 1990 magnetic storm at L≈ 3 ～ 4 is studied, and numerical calculations for energetic electrons in gyroresonance with a band of frequency of whistler mode waves distributed over a standard Gaussian spectrum is performed. It is found that the whistler mode waves can efficiently drive energetic electrons from the larger pitchangles into the loss cone, and lead to a flat-top distribution during the main phase of geomagnetic storms. This result perhaps presents a feasible interpretation for observation of time evolution of the quasi-isotropic pitch-angle distribution by Combined Release and Radiation Effects Satellite （CRRES） spacecraft at L ≈ 3 ～ 4.

A Study on Relationship among Blade Camber Direction and Pitch Angle and Performance of a Small Straight-Blade Darrieus Wind Turbine by Using Scale Test Model and Gurney Flap

Straight-blade Darrieus vertical axis wind turbines are used as medium and small size wind turbine because of higher power output in vertical axis wind turbine (VAWT). In our previous study, the relationship between the performance and Reynolds number based on airfoil chord length had been investigated by using small-scale test models of lift-type VAWT, and the results showed that the performance of tested wind turbine models with small diameter was clearly lower than that of the large-scale field test machine, and its performance also varies significantly with the blade pitch angle. In this study, we focused on the performance of a small-scale straight-blade Darrieus VAWT, the relationship among the blade airfoil camber direction and the pitch angle, and the performance of the small-scale VAWT was examined experimentally by using a small-scale VAWT test model with Gurney flap which was a small flat plate. Gurney flaps with its height h, as a ratio to the blade chord length c, h/c = 0.036 to 0.055, were attached to the blades of the VAWT test model, in addition, the attaching direction of the Gurney flap on the blade was examined for both inward and outward of the rotor, and the pitch angle was also examined for a range of −5 to 10 degrees. These results are discussed comparing with the result of the VAWT without Gurney flap and considering the numerical results for the single blade with/without the Gurney flap. The results showed that the performance of the tested VAWT was reversed between the inward and outward Gurney flaps around a pitch angle of 10 degrees. That is, the inward Gurney flap was superior at a pitch angle of less than 10 degrees, while the outward Gurney flap was effective at a pitch angle of more than 10 degrees. Furthermore, for the tested small-scale VAWT model, the optimum pitch angle was about 5 degrees, and the inward and shorter Gurney flap showed higher power performance of the VAWT under this pitch angle condition.

Calculation on the pitch angle of rocker of a rocker lunar rover in uneven terrain and path planning

For the concerted motion of rocker lunar rover, the pitch angle of rocker of a rocker lunar rover in uneven terrain must be calculated. According to the character of passive shape-shifting adaptive suspension of rocker lunar rover, the model of rocker lunar rover and the model of terrain were both simplified. The pitch angle of rocker was calculated using forward solving, reverse solving and the method of offsetting the curve of terrain respectively. Because of the banishment of the nonlinearity of equation sets of calculation by reverse solving, the calculation of the pitch angle based on reverse solving was programmed by means of MATLAB. Simulations were carried out by means of ADAMS. The result verified the validity of the calculation based on reverse solving. It provides the theoretical foundation for motion planning and path planning of rocker lunar rover. As applications of the calculation of pitch angle of rocker, the multi-attribute decision making of path based on the concerted motion planning and the predictive control on lunar rover based on the Markov prediction model were introduced.

齿轮传动性能检测系统设计与试验

齿轮传动中的啮合角和重合度受制造精度、载荷、齿廓磨损、变形等因素影响会发生改变,导致传动的平稳性和连续性下降。为检测齿轮传动啮合参数,基于机器视觉技术设计了齿轮传动性能检测系统。该系统由轮系、传动装置、测量装置和图像分析系统等组成。使用工业摄像机拍摄齿轮啮合运动图像,基于最小二乘法进行数据分析,检测齿轮节圆、啮合角、重合度等啮合参数。检测结果表明,实际啮合角和重合度值检测结果与设计值相对误差低于5%。该检测系统具有高效、实时、非接触等优点,为齿轮智能制造及检测提供技术支持。

平行轴变齿厚齿轮接触应力解析计算

变齿厚齿轮作为一种新型齿轮,目前尚无成熟的接触应力理论和计算方法。为了从理论上计算变齿厚齿轮齿面上的最大接触应力,了解变齿厚齿轮在不同参数下接触应力的变化情况。文中在赫兹公式的基础上,考虑变齿厚齿轮的几何结构,确定了变齿厚齿轮重合度、曲率半径、法向载荷、接触线长、重合度系数和齿形角系数的计算方法。研究了不同节锥角、齿数、模数和压力角对变齿厚齿轮接触应力的影响,通过有限元分析验证了变齿厚齿轮接触应力理论计算公式的正确性。研究结果表明:推导出的变齿厚齿轮接触应力计算公式具有较高的精度,能够准确地反映齿面的真实接触应力值,为变齿厚齿轮的结构设计、强度校核等提供了一定的依据。

计及恒定减载桨距角控制的风电高占比电力系统频率动态特性分析

在新型电力系统中,风电主动参与电网频率调节已成为必然,如何评估风电参与调频对频率动态特性的影响也成为了研究热点。围绕现有的风电调频措施,提出一种可以在额定风速前减少变桨动作次数的恒定减载桨距角的改进风电机组变桨控制,推导出该控制下风电机组参与一次调频的调差系数表达式。基于此构建了含恒定减载桨距角控制的电力系统频率响应模型。推导出频率动态特性指标的解析表达式,揭示了风速、初始桨距角等对风电机组调差系数及频率动态特性的影响机理。通过改进的IEEE三机九节点系统验证了所构建频率等值模型的准确性以及所提调频方法的有效性和可行性。

一种弹丸全向入射弹着点定位模型的研究

立靶测量是射击训练及射击比赛中一种常用的弹着点位置测量方法,弹道俯仰角是立靶测量的重要参数之一,其偏差水平是影响测量精度的重要因素。重武器弹丸入射时由于重力、地形等各种因素的影响,使弹丸产生弹道俯仰角,因此以弹丸垂直入射为假设条件的传统T型报靶模型不再适用。针对上述情形,本文以单个激波传感器全向入射理论为基础,提出基于6个激波传感器组成H型阵列的弹丸全向入射弹着点定位模型,解决传统T靶模型传感器数目少、无法求解俯仰角与方位角的问题,以提高测量的精度。对该模型进行数学推导与仿真分析,并应用到靶场实验中进行验证。实验结果表明,通过该模型计算出的弹着点坐标与实际弹着点坐标相比误差较小。因此,该模型能够有效减小弹道俯仰角对报靶系统的影响,更具实用价值。

基于桨距角控制的永磁风电机组高电压穿越控制策略

为解决传统永磁风电机组高电压穿越控制策略存在超速脱网风险问题,提出一种基于桨距角控制的高电压穿越控制策略。高电压穿越期间,首先,按照并网要求向电网提供无功支撑;其次,考虑转子转速限制,当转子转速达到参考值时启动桨距角控制,抑制转子转速上升;最后,通过仿真试验,验证了所提控制策略的有效性。基于桨距角控制的永磁风电机组高电压穿越控制策略,既能向电网提供无功支撑,又能避免超速脱网。

基于图像比对的螺纹牙形补偿量算法研究

为研究牙形失真对螺纹参数测量精度的影响,在分析现有螺纹牙形失真量计算方法的基础上,提出了一种基于机器视觉螺纹牙型角和中径的补偿量算法。将螺纹参数一致的没有螺旋升角的螺纹环槽与有螺旋升角的螺纹塞规图片进行比对,获取螺纹牙型角补偿量,再利用几何关系计算出相应螺纹牙的中径补偿量。经过研究发现,螺纹大径处螺旋升角相同的一系列螺纹产生的牙侧角误差基本一致,且随着螺旋升角的增大,牙侧角误差也随之增大。以螺纹塞规为对象进行对比实验,数据表明采用所提方法获得补偿后的牙型角平均值为59.999°和补偿后的中径平均值为18.290 mm与接触式螺纹综合测量仪所测牙型角平均值60.015°和中径平均值18.326 mm接近,且补偿后的牙型角方差7.76×10^(-5)与中径方差8.65×10^(-4)均小于综合测量仪所测牙型角方差3.38×10^(-3)和中径方差8.55×10^(-3)。结果表明,所提出的补偿算法可行。

螺栓设计参数对连接状态的影响及轴向力可视化方法研究

螺栓结构的连接状态与轴向力密切相关,而轴向力受多因素的影响,在拧紧或者松动过程中不断变化且无法做到无传感器实时监测。首先,基于螺栓的外螺纹轮廓方程,建立了精细化的螺栓有限元模型。其次,基于此模型研究了螺纹接触面摩擦因数、牙型角、螺距对于螺栓预紧过程及松动过程的影响规律。最后,关联松动角度和轴向力,结合深度学习目标检测算法,将螺栓的轴向力信息可视化。研究结果表明:在拧紧和松动过程中,螺栓轴向力实现了可观和可控,同时螺栓在预紧相同角度的情况下,其轴向力随着螺距和牙型角的增大而增加;其预紧力矩随着螺纹接触面摩擦因数和螺距的增大而变大,但会随着牙型角的增大而变小。

海上大型风机单叶片吊装风载荷计算程序开发

随着叶片大型化发展,海上单叶片吊装技术以其风阻小、作业效率高和吊装安全等优势得到广泛的工程应用,准确计算吊装过程中的风载荷和吊装系统响应是工程中的重要问题。本文采用Matlab语言,开发了单叶片吊装风载荷计算程序。可以计算吊装过程随安装角度和变桨角度改变时的叶片风载荷。结合工程实际,计算了单叶片吊装过程的风载荷,并与其他程序的计算结果进行了比对验证,表明了本文开发的叶片吊装风载荷计算程序的可靠性和实用性,可用于单叶片起吊方案的制订。

航行体不同角度入水的空泡流体特性研究

为研究航行体不同俯仰角入水空化演变规律及空泡流体特性,基于Realizable k-ε湍流模型和VOF多相流模型,建立航行体不同俯仰角入水数值模型,开展数值方法验证,数值模拟结果与实验测试结果吻合。基于此,研究航行体入水空化过程演变机理及其不同俯仰角水空泡内流体分布规律和空化阶段演变特性。研究结果表明,依据空泡内流体分布变化规律空化过程可分为空泡的表面闭合阶段、饱和阶段、深度闭合阶段和溃灭阶段;在入水速度一定的情况下随航行体入水俯仰角增大空泡生成速率降低、空泡内的水蒸汽体积增长率减小、水蒸汽体积含量峰值变小、空泡饱和阶段的空气体积变大,体积范围为6%~9%;空泡表面闭合无量纲时间随入水俯仰角从-10°变化到10°呈对数趋势增长,空泡饱和无量纲时间近似线性递减,空泡深度闭合无量纲时间基本不受俯仰角变化影响。

智能喷灌系统设计及射程计算

目前智能化在各行各业发挥着巨大作用,绿化喷灌领域也不例外。结合现有传感器技术,进行按需设置的喷头喷灌时长设置、喷头转速。根据超声波测距,控制俯仰角,从而改变其射程,对比喷头射程的经验公式,提出模型及拟合公式。实验表明,该系统可提高园林喷灌效率,并节水节能,有较好的实用价值,为智能喷灌系统产品的设计系统提供一种新的方法,有较强的工程应用意义。

变螺距诱导轮出口角对氢泵流场及性能的影响

为了研究变螺距诱导轮出口角对氢泵流场及性能的影响,以某型液体火箭发动机带变螺距诱导轮的氢泵作为研究对象,选取3种诱导轮出口角(轮缘),分别为12°、14°和16°,采用数值仿真的方法分析了不同诱导轮出口角对氢泵流场分布、水力性能和汽蚀性能的影响,并且进行试验验证。结果表明:适当增大诱导轮出口角,可以改善诱导轮出口的流场分布;在一定范围内增大诱导轮出口角,氢泵不同流量点的扬程和总效率都会获得提升,但是继续增大出口角到16°时,氢泵扬程提升效果减弱,且总效率有所下降;随着诱导轮出口角增大,氢泵的汽蚀性能先提升后降低。