Fully Coupled Effects of Hull,Mooring and Risers Model in Time Domain Based on An Innovative Deep Draft Multi-Spar

The coupled hull, mooring and riser analysis techniques in time domain are widely recognized as the unique approach to predict the accurate global motions. However, these complex issues have not been perfectly solved due to a large number of nonlinear factors, e.g. forces nonlinearity, mooring nonlinearity, motion nonlinearity and so on. This paper investigates the coupled effects through the numerical uncoupled model, mooring coupled model and fully coupled model accounting mooring and risers based on a novel deep draft multi-spar which is especially designed for deepwater in 2009. The numerical static-offset, free-decay, wind-action tests are executed, and finally three hours simulations are conducted under 100-year return period of GOM conditions involving wave, wind and current actions. The damping contributions, response characteristics and mooring line tensions are emphatically studied.

Time-Domain Simulation for Coupled Motions of Three Barges Moored Side-by-Side in Floatover Operation

Simulating the coupled motions of multiple bodies in the time domain is a complex problem because of the strong hydrodynamic interactions and coupled effect of various mechanical connectors. In this study, we investigate the hydrodynamic responses of three barges moored side-by-side in a floatover operation in the frequency and time domains. In the frequency domain, the damping lid method is adopted to improve the overestimated hydrodynamic coefficients calculated from conventional potential flow theory. A time-domain computing program based on potential flow theory and impulse theory is compiled for analyses that consider multibody hydrodynamic interactions and mechanical effects from lines and fenders. Correspondingly, an experiment is carried out for comparison with the numerical results. All statistics, time series, and power density spectra from decay and irregular wave tests are in a fairly good agreement.

Nonlinear Random Motion Analysis of Coupled Heave-Pitch Motions of a Spar Platform Considering lst-Order and 2nd-Order Wave Loads

In this study, the coupled heave-pitch motion equations of a spar platform were established by considering lst-order and 2nd-order random wave loads and the effects of time-varying displacement volume and transient wave elevation. We generated random wave loads based on frequency-domain wave load transfer functions and the Joint North Sea Wave Project （JONSWAP） wave spectrum, designed program codes to solve the motion equations, and then simulated the coupled heave-pitch motion responses of the platform in the time domain. We then calculated and compared the motion responses in different sea conditions and separately investigated the effects of 2nd-order random wave loads and transient wave elevation. The results show that the coupled heave-pitch motion responses of the platform are primarily dominated by wave height and the characteristic wave period, the latter of which has a greater impact. 2nd-order mean wave loads mainly affect the average heave value. The platform＇s pitch increases after the 2nd-order low frequency wave loads are taken into account. The platform＇s heave is underestimated if the transient wave elevation term in the motion equations is neglected.

A New Dual Polarized Aperture-Coupled Printed Array for SAR Applications

This paper presents a new design of dual polarized aperture coupled printed antenna array. The finite difference time domain (FDTD) analysis of an aperture coupled microstrip element is performed, and the effects of antenna parameters on its characteristics are obtained to guide the design of the printed array. Then an 8×2 dual polarized array design in X band is introduced with configuration plots. In order to improve its isolation and cross polarization, an outphase displacement feeding technique is adopted in the feed network. Also, the round bends are used instead of conventional right angle bends so as to achieve better VSWR performance. Experimental results are presented, indicating the validity of the design. This dual polarized array can be applied as a sub array of spaceborne SAR systems.

Real Time Power Monitoring Detection Based on Sequence Time Domain Reflectometry Approach

Sequence Time Domain Reflectometry (STDR) have been demonstrated to be a powerful technique for detecting the length of cable or length of open circuit or short circuit cables. Using this method along with using smart meter on the main electrical panel board to monitor consumption if load at each circuit, enable user to monitor power consumption at each node (power outlet) only by operating a smart digital meter and an STDR circuitry on each circuit at the main electrical panel board. This paper introduces this method and examines it on dead-wire and energized wire with a load connected across it. Experimental results are demonstrated for both types. Test result show the potential application of this approach to provide consumption information and potential cost saving via feedback for users.

Dynamic Positioning Control of Surge−Pitch Coupled Motion for Small-Waterplane-Area Marine Structures

For general dynamic positioning systems,controllers are mainly based on the feedback of motions only in the horizontal plane.However,for marine structures with a small water plane area and low metacentric height,undesirable surge and pitch oscillations may be induced by the thruster actions.In this paper,three control laws are investigated to suppress the induced pitch motion by adding pitch rate,pitch angle or pitch acceleration into the feedback control loop.Extensive numerical simulations are conducted with a semi-submersible platform for each control law.The influences of additional terms on surge−pitch coupled motions are analyzed in both frequency and time domain.The mechanical constraints of the thrust allocation and the frequency characters of external forces are simultaneously considered.It is concluded that adding pitch angle or pitch acceleration into the feedback loop changes the natural frequency in pitch,and its performance is highly dependent on the frequency distribution of external forces,while adding pitch rate into the feedback loop is always effective in mitigating surge−pitch coupled motions.

4-Port Octagonal Shaped MIMO Antenna with Low Mutual Coupling for UWB Applications

A4-port multiple-input multiple-output(MIMO)antenna exhibiting lowmutual coupling andUWBperformance is developed.The octagonal-shaped four-antenna elements are connected with a 50microstrip feed line that is arranged rotationally to achieve the orthogonal polarization for improving the MIMO system performance.The antenna has a wideband impedance bandwidth of 7.5GHz with S11<−10 dB from(103.44%)3.5–11GHz and inter-element isolation higher than 20 dB.Antenna validation is carried out by verifying the simulated and measured results after fabricating the antenna.The results in the form of omnidirectional radiation patterns,peak gain(≥4 dBi),and Envelope Correlation Coefficient(ECC)(≤0.01)are extracted to validate the suggested antenna performance.Aswell,time-domain analysis was investigated to demonstrate the operation of the suggested antenna in wideband applications.Finally,the simulated and experimental outcomes have almost similar tendenciesmaking the antenna suitable for its use in UWBMIMOapplications.

基于AQWA的船舶拖航耦合动力响应分析

船舶在长期航行中,会遇到船舶发生故障以及穿过狭窄航道的情况,需要拖船牵引船舶航行。本文以船舶拖航为研究对象,利用AQWA分析时域耦合过程中不同拖缆数目和不同拖速对船舶拖航的影响。从拖缆张力和运动响应2个方面进行对比分析,结果表明,在相同环境条件下,2根拖缆比1根拖缆时最大张力平均减少49.18%,拖速4 kn比拖速8 kn时拖缆最大张力平均减少53.78%,拖速6 kn比拖速8 kn时拖缆最大张力平均减少29.39%。

提高微腔孤子光频梳泵浦能量转换效率技术研究进展

分析了孤子微梳泵浦能量转换效率低的原因,介绍了目前已提出的几种提高孤子微梳泵浦光能量转换效率的技术方案,包括激发孤子晶体光梳利用多孤子结构、正常-反常色散双腔耦合泵浦光循环存储结构、微腔-光纤/波导环泵浦光反馈耦合干涉结构、主-副微环腔耦合超模谐振峰劈裂结构等,并分析了这些方案的优缺点。在此基础上,给出了本课题组对反馈耦合腔的优化设计,仿真模拟结果显示,单孤子微梳的泵浦光转换效率可超过25%。最后,对孤子微梳的低能耗产生方案作出总结和展望,为微腔孤子光频梳泵浦能量转换效率提高技术的发展与应用提供理论参考。

基于时域BLT方程的带绝缘线缆束场-线耦合模型

为研究外场辐照下复杂线缆系统(多导体、非线性负载、带绝缘层)终端电压/电流时域响应特性规律,提出了复杂线缆束在入射场激励下的终端响应建模方法。研究在时域内重塑多导体BLT方程,在兼顾计算效率、易于向线缆网络扩展的基础上,解决了线缆束端接非线性负载的终端时域响应求解问题;并通过引入介质层系数,修正了BLT方程源矢量项,解决了常规BLT方程忽视绝缘层对入射场畸变效应而导致的误差问题。最后,将计算结果同时域有限差分法和有限积分法计算结果进行对比,验证了模型在处理复杂线缆场线耦合问题上的准确性。

融合时频特征的多源无监督域自适应轴承故障诊断方法

无监督域自适应已成为多工况下轴承故障诊断的一种重要方法。然而,现有多源无监督域自适应方法往往忽略不同视角信号对于跨域故障诊断的贡献,不足以全面表达轴承的故障特征。此外,这些方法的不同源域对同一目标域的预测结果存在差异。为此,提出一种融合时频特征的多源无监督域自适应(time-frequency features fused multi-source unsupervised domain adaptation,TFFMUDA)轴承故障诊断方法。该方法以时域和频域信号为输入,通过特征耦合机制实现两种故障特征的互补,并利用分类器对齐策略增强了不同源域对于同一目标域的诊断一致性。通过实际轴承故障案例的试验结果表明,所提方法相较于现有无监督域自适应轴承故障诊断方法能获得更清晰的故障类决策边界并具有更好的目标域诊断精度。

核电磁脉冲对计算机机箱的时频域电场耦合特性研究

为研究计算机机箱对核电磁脉冲的时域和频域耦合特性,采用基于时域有限积分法的电磁仿真软件,对计算机机箱采取不同孔缝形状、孔缝布局和机箱内不同位置的电场耦合规律进行了数值仿真。结果表明:机箱的电场屏蔽效能随频率的增加而下降,在谐振频率处达到最小值;同样孔缝面积时,机箱采用圆形孔缝、多圆孔阵列的瞬时电场屏蔽效能和各频点电场屏蔽效能均最优;机箱内的瞬时电场屏蔽效能和各频点屏蔽效能随着与孔缝距离的增大而提升,电场极化方向上的电场屏蔽效能提升缓慢,非极化方向上的电场屏蔽效能提升较快。对提升计算机机箱的屏蔽效能,优化内部电子器件与线路的合理布局提供参考。

弱导电薄层介质材料电磁耦合等效计算方法研究

面向核电磁脉冲等强电磁环境下复合材料壳体平台的电磁环境效应分析需求,根据Maxwell-Ampere定理的积分形式,分析得到了时域有限差分方法在处理弱导电薄层介质材料参数时的等效计算方法,即当介质等效波长远大于模型厚度时,可将薄层模型适当增厚,同时等比例减小其电导率,参数等效前后模型的电磁耦合特性基本相同。该方法通过等效增厚薄层材料从而实现增大空间离散步长,减少网格量的目的,不需要改变传统时域有限差分方法的时间步进格式,不会破坏计算的稳定性。无限大有耗介质薄板、薄层球体、含薄层壳体无人机电磁耦合等算例表明,在包含毫米级厚度弱导电介质薄层壳体平台的核电磁脉冲耦合模拟中,该方法具有较好的适用性。

太赫兹光谱结合特征选择算法分选掺混稻种

农业生产安全是食品安全的重要组成,粳米作为日常食用的大米,劣质掺混种子的快速检验是相关领域的重要研究工作。本研究使用太赫兹时域光谱采集220份掺混稻种和纯品稻种样本的光谱信号,通过傅里叶变换(Fourier transform, FT)对光谱数据进行预处理,将时域信号转化为频域信号作为建模数据集,对QUSET等5种模式识别模型进行分选研究。结果表明,随机森林算法(RF)、连续投影算法(SPA)、变量集群分析耦合迭代保留算法(VCPA-IRIV)等3种算法分别选择9个、6个、25个重要的特征频率,其中VCPA-IRIV作为耦合算法选择的特征频率包含的光谱信息最为丰富。为进一步优化模型,对特征频率选择后建模,在分析速度和识别精准度上显著优于全光谱建模方法,经VCPA-IRIV算法筛选的25个特征频率建立的QUEST和KNN分类对是否掺混的鉴别准确率均能达100%。变量集群分析耦合迭代保留算法能够有效地选择包含信息丰富的太赫兹光谱特征频率,能够有效提升所建立的识别模型的准确率。基于太赫兹光谱和耦合特征选择算法建立的掺混稻种识别模型快速、准确,能够为检测劣质掺混粳米种子提供新的方法。

基于HIE-FDTD方法的电磁热耦合分析快速计算方法研究

基于混合显隐式时域有限差分(hybrid implicit-explicit finite-difference time-domain,HIE-FDTD)方法,提出了一种电磁热耦合分析快速计算方法。仿真电磁场时,采用HIE-FDTD方法求解Maxwell旋度方程;计算温度场时,采用时域有限差分(finite-difference time-domain,FDTD)方法求解热传导方程。由于HIE-FDTD方法只对1维空间偏导数采用隐式差分方法进行离散,因此时间步长不受电磁目标精细结构所在方向网格大小的限制。采用电磁热耦合分析快速计算方法对十字缝隙频率选择表面的电磁热耦合效应进行分析,并将仿真结果与采用传统FDTD方法、CST软件以及COMSOL软件的仿真结果进行对比,所有结果均相互符合。十字缝隙频率选择表面算例结果表明:在保证计算精度的前提下,采用HIE-FDTD方法的仿真时间仅为传统FDTD方法仿真时间的1/6,有效提高了电磁热耦合仿真的计算效率。

A Hybrid Method for Electromagnetic Coupling in Large Spaces

A hybrid method combining finite difference time domain(FDTD)with topology network was presented to treat with electromagnetic couplings and transmissions in large spaces A generalized matrix euqation expressing the relations among wave vectors at every port of the network nodes was give Scattering characteristics and electromagnetic distributions of every node was calculated independently using FDTD A structure of irises in a waveguide was taken as numerical examples This hybrid method has more advantages than the traditional FDTD method which includes saving calculation time,saving memory spaces and being flexible in setting up FDTD grids

基于MOSES软件的系泊下大型起重船吊装作业适用性分析

为降低大型锚泊定位起重船在不同水深区域吊装作业的安全风险,以7000 t起重船为例,采用数值模拟方法,在MOSES软件中建立起重船、吊物和系泊系统耦合分析模型,对系泊下大型起重船吊装作业工况进行模拟,结果表明,系泊吊装作业受浪向、波高、波周期、锚缆预张力和作业水深变化的影响,在实际操作中,根据作业水深采取相应的船位和预张力,可以有效地改善大型起重船系泊吊装作业的适用性。

各向异性的硼烯等离激元诱导透明超材料

等离激元诱导透明效应源于电磁明、暗模式之间的相消干涉.该文从理论上提出了两种简单且直观的单层硼烯超材料构型,基于时域有限差分方法的数值计算结果显示,其在光通信波段(~1 550 nm)具有显著的各向异性等离激元诱导透明特征.利用不同晶向电磁明、暗模式的近场耦合,在实现各向异性光学色散特性的同时,兼具了集成度更高的优点.其次,通过调控硼烯的载流子浓度,可以实现对透明窗口频谱位置的主动调控.此外,通过结合谐振子理论和Λ型原子三能级模型,定性描述了这类各向异性等离激元诱导透明超材料中的光学干涉路径,定量刻画了透明窗口随耦合距离的演化过程.研究结果将为设计高性能近红外波段的慢波器件提供科学依据.

相邻骨科植入物的磁共振射频致热耦合效应作用机理

该文研究了1.5 T/3.0 T磁共振(magnetic resonance imaging,MRI)环境下2个相邻的骨科植入物的射频场相互耦合对射频致热的作用。当患者佩戴多个相邻的植入物时,这些植入物之间的相互作用可能会增加射频致热。采用骨板和骨钉作为例子,通过基于惠更斯原理的数值模拟计算并提取热点位置的入射和散射电场向量的振幅和方向,以分析其他相邻植入物的影响。结果表明,不仅入射场的存在会导致强耦合效应,强散射场也会起作用,通过惠更斯源可以得到器械之间产生的一阶和二阶散射场,如果在一定区域内,一阶和二阶电场项相互叠加,则双植入物系统的射频致热风险会增加。

飞机气动伺服弹性地面试验与分析方法研究

飞机气动伺服弹性地面试验可测试飞控系统与结构模态耦合特性,验证结构弹性模态频率范围内飞控系统稳定性,从而为气动伺服弹性模型修正和分析提供依据,进一步降低试飞风险。本文介绍了飞机气动伺服弹性地面试验的原理及方法,结合工程经验和教训对可能影响试验结果准确性的因素进行分析,提出相应解决措施,并对结构滤波器优化改进和试验数据处理分析等方法进行了研究。