Fatigue crack growth rate test using a frequency sweep method

Fatigue crack propagation characteristics of a diesel engine crankshaft are studied by measuring the fatigue crack growth rate using a frequency sweep method on a resonant fatigue test rig. Based on the phenomenon that the system frequency will change when the crack becomes large, this method can be directly applied to a complex component or structure. Finite element analyses （FEAs） are performed to calibrate the relation between the frequency change and the crack size, and to obtain the natural frequency of the test rig and the stress intensity factor （SIF） of growing cracks. The crack growth rate i.e. da/dN-AK of each crack size is obtained by combining the testing-time monitored data and FEA results. The results show that the crack growth rate of engine crankshaft, which is a component with complex geometry and special surface treatment, is quite different from that of a pure material. There is an apparent turning point in the Paris＇s crack partition. The cause of the fatigue crack growth is also discussed.

Time frequency spectrum of atmospheric turbulence and sweeping hypothesis

The present study is focused on the structure of time frequency spectrum.A scaling law for Eulerian time frequency spectrum and the corresponding temporal structure function are calculated from the sweeping hypothesis and Kolmogorov’s similarity law regarding spatial structure function.An experiment is designed to study this scaling law in the atmospheric turbulent boundary layer.The results well support the conclusion derived from relevant theoretical analysis.

Second-order phase correction of NMR spectra acquired using linear frequency-sweeps

NMR spectra acquired with experiments using frequency-sweeps such as the wide-band uniform-rate smooth truncation(WURST)spin-echo and Carr-Purcell-Meiboom-Gill(CPMG)sequences cannot be absorptively phased by using only conventional zerothand first-order phase correction.Implementation of phase correction up to the secondorder is described for obtaining absorptive spectra,which have more desirable line shapes and noise properties than magnitude spectra.The relationship of the second-order phase to the parameters of frequency sweeps is derived.The second-order phasing in the frequency-domain is equivalent to a point spread in the time-domain signal.The application of second-order phase correction is demonstrated with a wideline 35Cl CPMG spikelet spectrum.

Frequency Sweep Linearization for Semiconductor Laser Using a Feedback Loop Based on Amplitude-Frequency Response

A scheme of frequency sweep linearization of semiconductor lasers using a feed-back loop based on amplitude-frequency response is demonstrated in this paper. The beat frequency signal is obtained by self-heterodyne detection. The frequency changes are converted to the envelope of beat frequency signal after amplitude-frequency response. The active frequency sweep linearization is realized by feeding envelope deviations back to the drive currents of the lasers by a feedback loop. A simulation model is built to verify this scheme by Simulink. This scheme does not need high-performance, expensive lasers, complex linearization or tedious post-processing processes, which are of great significance for related applications.

Numerical exploration of population transfer of Rydberg-atom by single frequency-chirped laser pulse

This paper has calculated that Rydberg atoms can be transferred to states of lower principal quantum number by exposing them to a frequency chirped microwave pulse. The atoms experience the consequence： 70p-69s-68p-67s-66p by a constant amplitude field in the adopted model. This study shows that the complete population transfer is related to the chirp rate and the carrier frequency.

Numerical Investigation of Flow Separation Control over an NACA0018 Airfoil Using Sweeping Jet Actuator

As an active flow control technology and with the advantages of no moving components, the Sweeping jet actuator has become a hotspot in the field of flow control. However, the linear relationship between oscillation frequency and momentum coefficient in a sweeping jet actuator makes it difficult to determine the dominant factors that affect control effectiveness. Decoupling the oscillation frequency and momentum coefficient, as well as determining the control mechanism, is the focus of studying the sweeping jet actuator. In this study, a novel sweeping jet actuator is designed using synthetic jets instead of feedback channels and applied to the flow separation control of NACA0018 airfoil. This article studies the control effect under three oscillation frequencies of F+ = f × c/U∞ = 1, 10, 100 and three momentum coefficients of Cμ = 0.45%, 0.625%, 0.9%. The numerical results indicate that all three oscillation frequencies have good control effects on flow separation, and the control effect is best when F+ = 1, with the maximum lift coefficient increasing by approximately 14% compared to the other two cases. And the sweeping jet actuator has a better ability to control flow separation as the momentum coefficient increases. By decoupling the characteristics of the sweeping jet actuator and conducting numerical analysis of the flow control effect, it will promote its better engineering application in the field of flow control. .

基于AFL的海上风电单桩基础冲刷动力响应研究

单桩式基础作为海上风电应用最为广泛的支撑型式,其周围普遍存在不同程度冲蚀。目前,海上风电基础冲刷后的结构动力响应研究较少考虑叶片、机舱、轮毂等细节特征,而是将上部结构简化为质点或静止状态,缺乏基础-结构-荷载一体化数值仿真方法,难以反映冲刷后风机结构振动规律。为此,依托菩提岛海上风电场,通过多波束扫测探明了单桩基础最大冲刷深度,基于AFL(等效嵌固长度)法考虑桩基柔性特征,计算不同冲刷深度下桩基等效嵌固长度,建立风、浪共同作用下风机仿真模型,揭示不同冲刷深度下单桩式海上风电动力响应规律。结果表明,现有桩基冲刷深度难以引起结构共振,且风机的整体振幅较小。塔架和桩基均在F-A(前后)向出现最大振幅,而S-S(侧)向和YAW(垂)向的位移幅值相对较小,故需要对F-A向振动进行重点监测。随着桩基局部冲刷深度增加,风机结构固有频率单调递减,当冲刷深度达到12 m,结构整体刚度不足,给出了海上风电单桩基础冲刷安全阈值。提出的单桩式海上风电动力响应分析方法可为工程中不同冲刷深度引起风机振动安全性评价提供依据。

基于稀疏恢复的调频引信抗扫频干扰方法

针对连续波调频引信在扫频式干扰作用下的早炸或者瞎火问题,提出基于时域干扰剔除及信号稀疏重构的抗干扰方法。通过时域异常值检测定位干扰位置和持续时间,并剔除异常数据抑制干扰对引信的影响;进一步地针对干扰剔除引起的信号时域稀疏,建立基于稀疏正则项的差频信号重构优化方程,并提出基于交替方向乘子法的迭代重构算法;通过仿真和实测数据验证方法的性能。研究结果表明:该方法能够在信噪比-15 dB,置零样本率不高于70%的情况下,抑制扫频干扰的影响,准确实现目标距离-速度信息的获取,提高了调频引信抗扫频干扰能力。

带限位隔振系统的主共振响应及隔振性能研究

针对舰船设备带限位隔振系统中普遍存在的非线性特性,文中建立包含分段线性刚度和分段线性阻尼的限位隔振系统数学模型,采用平均法对主共振响应进行解析求解,推导出系统力传递率方程,综合分析了限位器各参数对系统幅频特性和隔振性能的影响规律,通过扫频试验进行验证。结果表明:限位器阻尼对系统振动性能具有积极意义,大阻尼限位有效减小了幅频响应峰值,降低了力传递率,减小甚至避免了跳跃和滞后现象的产生;对于任意一组系统参数都存在一个最优刚度比,使得相对位移幅值最小、隔振性能最好,同时保证了跳跃区间相对较小;适当增大限位间隙可以减小跳跃区间,进一步改善系统的振动性能。

大型核桃树振动响应特性与落果试验研究

为确定大型核桃树的振动响应特性,探究大型果树机械化摇振采收方法,以南疆大型核桃树为研究对象,利用ANSYS进行有限元分析获取各分枝振动响应特性;应用自主研发摇振收获设备进行扫频试验及落果试验研究,对各主枝进行共振频率检测,通过各分枝上的传感器获取的频率-加速度幅值曲线,确定曲线峰值对应的共振频率;最后,进行摇振落果试验,对比各主枝在不同共振频率下的落果情况。结果表明:大型果树同一主枝及其上侧枝共振频率相同,各主枝共振频率在22~26 Hz之间;同一主枝上的各检测点加速度响应曲线整体呈现先增加后减小的趋势,距离激振位置越远,加速度响应幅值越大;在共振条件下收获,能够获得更高的落果率。为此,提出一种基于大型核桃树主枝共振频率的摇振采收方法,通过获取主枝处的共振频率,以各主枝共振频率进行多次摇振收获作业,实现共振条件下以较低激振能量获得最大振动响应收获,可有效提高收获效率和采净率。研究结果可为大型果树摇振采收方法提供理论基础。

基于扫频电阻法的变压器绕组材质辨识方法及实验验证

变压器生产中“以铝代铜”现象危害电力系统运行安全,为了简单有效地辨别变压器绕组材质,提出了一种基于扫频电阻法的辨识方法和实验方案,并根据该方案搭建了一套变压器绕组材质检测系统。首先对基于扫频电阻法的辨识方法进行了相关理论推导和证明,之后对基于该方法的检测系统性能进行了测试,最后对不同类型变压器进行了实验验证。实验结果表明该方法能够快速高效地辨别变压器绕组材质,具有较高的工程实用价值。

基于DQN和功率分配的FDA-MIMO雷达抗扫频干扰

频率分集阵列(Frequency Diversity Array,FDA)雷达由于其阵列元件的频率增量产生了许多新的特性,包括其可以通过发射功率分配进行灵活的发射波形频谱控制。在以扫频干扰为电磁干扰环境的假设下,首先,通过引入强化学习的框架,建立了频率分集阵列-多输入多输出(Frequency Diversity Array-Multiple Input Multiple Output,FDA-MIMO)雷达与电磁干扰环境交互模型,使得FDA-MIMO雷达能够在与电磁环境交互过程中,感知干扰抑制干扰。其次,本文提出了一种基于深度Q网络(Deep Q-Network,DQN)和FDA-MIMO雷达发射功率分配的扫频干扰抑制方法,使得雷达系统能够在充分利用频谱资源的情况下最大化SINR。最后,仿真结果证实,在强化学习框架下,FDA-MIMO雷达能够通过对发射功率分配进行优化,完成干扰抑制,提升雷达性能。

一种便捷的IFM自动化测试系统

随着微波组件集成度的提高及测试指标的增多,传统手动测试方法的低效率已对其可测试性造成了阻碍,导致了生产效率低下。为提高测试效率,设计了一种基于虚拟仪器开发软件的自动测试系统,并对其在瞬时测频接收机(IFM)自动化测试中的应用进行分析。结果表明:该测试系统具有测试速度快、测试结果准确、测试结果自动保存等优点,可极大地提高组件的测试效率。

自激扫掠喷嘴气液两相流场特性研究

为研究自激扫掠喷嘴内、外流场结构,分析高频扫掠液柱的变形和破碎过程,首先采用高速阴影成像法,在0.1~4.0 MPa压降范围内,对喷嘴的扫掠频率及扫掠张角等基本工作特性进行了测量;其次,采用实验测量结果对气液两相数值模型进行了校核;最后,采用校核后的数值模型对喷嘴内、外气液两相流场结构开展了模拟研究。研究结果表明:喷嘴内部为单相流动,无气相介质的回流;液柱的高频扫掠使其在喷嘴出口形成了一个扇形液面;液柱的自旋增强了气相对液柱的剪切作用;在扇形液面两侧,液柱的反向偏转会导致其变形和破碎;在扇形液面中间,液柱的横向扫掠形成一个高速气相区,气相速度可达液相的3倍,提高了韦伯数,使得“液丝状”的液柱进一步破碎并扩散。

基于电磁驱动的管道除垢系统设计研究

设计一种带有励磁线圈型结构的电磁式管道除垢系统。通过对线圈的阻抗和磁场的分析确定线圈的匝数和半径。通过扫频的方式确定激励线圈的频率。使用COMSOL仿真软件构建了管道模型,通过实验测得在有无励磁线圈对管道振动情况的影响。实现管道在交变磁场内磁致伸缩产生振动的剪切作用对管道除垢的效果。

Fast tunable and broadband microwave sweep-frequency source based on photonic technology

A high-speed broadband tunable microwave source utilizing the wavelength tunable characteristics of distributed Bragg reflector(DBR) laser is proposed and demonstrated.The wavelength tuning of the laser is achieved instantaneously by controlling the voltage of the phase section of the DBR laser.By means of optical delay self-heterodyne technology,the microwave signal with the property of frequency broadband tuning is generated.Sweep speeds of 5 and 40 μs of the sweep-frequency source prototype were achieved and the maximum tuning range was up to 38.45 GHz.

船用电子机柜力学性能仿真计算

为了指导和优化结构设计,提出了一种快速预测船用电子机柜力学试验性能的数值模拟方法。根据船用电子设备结构力学试验标准,对某型船用电子机柜进行力学试验仿真分析。首先,利用有限元软件ANSYS建立电子机柜的有限元模型;其次,基于有限元数值求解方法,计算机柜的模态频率、正弦扫频响应、颠震响应和冲击响应;最后,根据计算结果对机柜进行强度校核,验证机柜力学设计可靠性。结果表明,机柜壳体顶部和底部直角、侧面凸台以及背部直角附近的应力较高,但都低于机柜壳体铸件的最大许用应力;机柜在各个试验条件下具有较高的可靠性。船用机柜的力学性能仿真计算方法对同类型的其他电子设备力学分析具有较好的参考价值。

时变多辐射源跟踪任务的时频扫描方案评估方法

多辐射源跟踪任务受辐射源天线扫描方式、工作参数变化等因素影响,在目标种类、数量等方面存在一定的时变特征。对该特征的适应能力是评估电子支援措施(electronic support measures,ESM)辐射源跟踪能力的一项重要指标。据此,首先建立了一种迭代式时频扫描方案优化模型。然后,以评估ESM对多辐射源跟踪任务时变特性的适应能力为目标,提出了一种基于可行域的性能评估方法。仿真实验结果表明,在不同类型目标数量动态变化过程中,所提方法给出的评估结果都能与扫描方案实际性能保持一致,具备准确的动态评估能力。

八极轴向绕组式磁流变阻尼器的隔振平台模糊控制研究

为了更好研究磁流变阻尼器在隔振系统中的隔振性能与控制策略,以八极轴向绕组式磁流变阻尼器为控制对象,搭建磁流变阻尼器与压缩弹簧并联的隔振平台,利用电动振动台施加正弦位移激励,测试隔振平台在不同励磁电流、激振频率下的加速度传递率。根据测试结果设计模糊控制器,控制系统的输入为加速度传递率与激振频率,输出为磁流变阻尼器的阻尼力,最后对隔振平台进行正弦位移扫频的隔振实验。实验结果表明,在隔振平台发生共振的区间频率9.4~11.4Hz内,所设计的控制算法能减小加速度传递率14.3%以上。该研究可为磁流变阻尼器在隔振领域中的工程应用奠定基础。

一种核产品的振动试验夹具设计与验证

针对一种核产品系统需要在研制阶段验证其结构和功能振动可靠性[1]的要求,设计了一款专用的振动试验夹具。利用Solid Works进行了建模、模态分析、谐波分析和出具加工图纸,选择6061铝合金材料采用整体加工方法加工了实物夹具。在实验室对实物夹具进行了正弦扫频试验,验证了该夹具设计的合理性,通过谐波分析和正弦扫频试验结果的对比验证了有限元分析的网格划分、边界条件、载荷、阻尼设置的合理性[2]。可为以后的试验夹具设计和有限元分析提供参考。