Theoretical analysis of the mode coupling induced by heat of large-pitch micro-structured fibers

In this paper,a theoretical model to analyze the mode coupling induced by heat,when the fiber amplifier works at high power configuration,is proposed.The model mainly takes into consideration the mode field change due to the thermally induced refractive index change and the coupling between modes.A method to predict the largest average output power of fiber is also proposed according to the mode coupling theory.The largest average output power of a large pitch fiber with a core diameter of 190 μm and an available pulse energy of 100 mJ is predicted to be 540 W,which is the highest in large mode field fibers.

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 1st-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.

The Nonlinear Bifurcation and Chaos of Coupled Heave and Pitch Motions of a Truss Spar Platform

This paper presents the results from a numerical study on the nonlinear dynamic behaviors including bifurcation and chaos of a truss spar platform. In view of the mutual influences between the heave and the pitch modes, the coupled heave and pitch motion equations of the spar platform hull were established in the regular waves. In order to analyze the nonlinear motions of the platform, three-dimensional maximum Lyapunov exponent graphs and the bifurcation graphs were constructed, the Poincaré maps and the power spectrums of the platform response were calculated. It was found that the platform motions are sensitive to wave frequency. With changing wave frequency, the platform undergoes complicated nonlinear motions, including 1/2 sub-harmonic motion, quasi-periodic motion and chaotic motion. When the wave frequency approaches the natural frequency of the heave mode of the platform, the platform moves with quasi-periodic motion and chaotic motional ternately. For a certain range of wave frequencies, the platform moves with totally chaotic motion. The range of wave frequencies which leads to chaotic motion of the platform increases with increasing wave height. The three-dimensional maximum Lyapunov exponent graphs and the bifurcation graphs reveal the nonlinear motions of the spar platform under different wave conditions.

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.

10MW海上浮式风机伺服控制系统设计及耦合动力特性研究

为支撑DTU 10 MW风力机,对5 MW无撑杆半潜浮式风力机支撑平台进行了放大设计,并对10 MW半潜浮式风机的伺服控制系统重新设计。其中,在额定风速以下实施转矩控制,以实现最大功率捕获;在额定风速以上,基于增益调度比例积分(GSPI)控制方法进行变桨控制系统设计,以保证浮式风机的安全运行。基于所设计的10 MW浮式风机伺服控制系统,采用“气动-水动-控制-弹性”全耦合模型对10 MW半潜式风机在恒定风和湍流风作用下的耦合动力特性进行了分析,验证了所设计控制系统的可靠性。研究发现,在伺服系统控制作用下,10 MW浮式风机的运动响应得到有效控制,湍流风对浮式风机的纵荡和纵摇激励作用明显,垂荡运动受到风载荷和波浪的共同激励。

振荡浮子式波能装置的功率计算分析及参数设计

波浪能是重要的可再生资源之一,提高波浪能装置的能量捕获率是波浪能规模化利用的关键。本文对波浪能的能量转换装置进行了研究,针对装置于不同摇荡条件下的最大平均输出功率、最优阻尼系数及相关参数进行演化分析及求解。利用牛顿定律及质心系、转动惯量等建立二自由度、四自由度波浪能转换装置耦合运动模型,基于时间离散化的差分原理求解,同时采用模拟退火算法降低时间复杂度,提出了改良的粒子群算法,得到较为准确的结果,为实际工程中波浪能的高效采集提供思路和途径。

双轴变距自动螺栓拧紧机构的联轴器断裂问题研究

双轴变距自动螺栓拧紧机构通过伺服电机驱动丝杠做直线运动达到变距目的。伺服电机与丝杠由双膜片联轴器连接,传递运动与动力,而安装误差、工作环境等因素会使双膜片联轴器在长期使用过程中,多次出现疲劳断裂现象。为此,文章基于实际运行工况,通过有限元法分析双膜片联轴器的受力情况,发现其最大受力点的应力超过材料的疲劳极限值。继而重新选取联轴器型号,并进行受力情况分析,验证所选的十字滑块式联轴器能够解决联轴器在不确定工况下的疲劳断裂问题,保证螺栓拧紧机构的有效性。

EXPERIMENTS AND ANALYSIS OF HYSTERESIS OF VORTEX BREAKDOWN OVER PITCHING-UP DELTA WINGS

An investigation of the hysteresis of vortex breakdown over pitching-up deltawings is presented. Based on experiments, there are two main reasons which can be usedto explain the hysteresis of vortex breakdown. One is the time or phase lag due to the ini-tial suPerPOsition of linearized small disturbance, which enlarges the range of the incidenceof keeping attached flow and postpones the initial incidence of vortex breakdown. Theother is the reduction of adverse pressure gradient due to the periphery centrifugal instabil-ity after the concentrated vortex has come into being, which is the key reason of hystere-sis of vortex breakdown- The structure of vortex over a pitching up delta wing can be di-vided into three layers, which is not a significant a1teration compared with that of vortexover a static delta wing.

Liquefied Natural Gas Tanks for Suppressing Pitching Motions of FLNG Facility

Floating liquefied natural gas (FLNG) facility using partially filled tanks for control of pitch motion response to wave-exciting forces is investigated in this paper. The governing equations for sloshing analysis of rectangular tanks under pitch motion excitation are first established, then the spatial (boundary- value) partial derivatives are approximated by finite differences. The uncoupled pitch equation of FLNG is derived by assuming that pitch is uncoupled from other modes of vibration. By using state-space model to represent fluid-memory effect, the pitch equation can be transformed to first- order ordinary differential equations which can be solved with sloshing equations simultaneously with the given initial conditions. By using the proposed coupling model for FLNG facility and the liquefied natural gas (LNG) tanks, the performance of partially filled tanks for suppressing pitching motions of FLNG facility is numerically assessed. The parametric studies on the example FLNG show that there is a beneficial filling level by which the pitch motion of FLNG can be considerably reduced.

单向耦合FitzHugh-Nagumo神经元的滞后同步研究

本文提出一种新的研究思路,将两个单向耦合的FitzHugh-Nagumo神经元之间的滞后同步视为一种特殊的广义同步,通过辅助系统方法来获得滞后同步发生的条件.首先建立原响应系统的辅助系统,将原系统中驱动系统和响应系统的滞后同步问题转换为响应系统与辅助系统之间的误差系统原点稳定问题.通过拉普拉斯变换方法,将原本用微分方程表示的误差系统等效为Volterra积分方程表示,而后利用积分方程理论中的逐次逼近方法解析地得到原误差系统原点稳定性条件.本文给出的滞后同步判据与信号传送中的时间滞后量大小无关,数值模拟验证了本文提出判据的有效性.

斜风来流下纵摇运动对机-舰耦合流场的影响

机-舰耦合流场是一个复杂紊乱的非定常流场,舰船的六自由度摇摆运动会进一步恶化飞行甲板上方的流场环境。为了探究舰船的摇摆运动对飞行甲板上方机-舰耦合流场的影响,基于简化护卫舰SFS2和旋翼的耦合模型,对两种斜风状态下、纵摇运动中的机-舰耦合流场进行了数值模拟,分析了纵摇运动对机-舰耦合流场结构和旋翼拉力的影响,对比了两种斜风状态下的流场差异。研究结果表明:随着舰船的纵摇运动,机库后方形成的不稳定混合涡结构和垂向气流会对旋翼气动力造成明显的影响,旋翼拉力出现了近似周期性的变化,与纵摇运动的周期一致,但各观测点处的速度分量均未出现周期性的变化;旋翼拉力在甲板上浮至水平位置附近时最大,在甲板下沉至水平位置附近时最小,对于左舷和右舷来流,拉力分别降低了约13%和6%,因此飞行员要认识到纵摇运动带来的拉力损失,确保直升机具有足够的操纵量,以便能及时调整总距来保证直升机在该状况下的起降安全性。

考虑导引头耦合作用的带落角约束制导律设计

针对制导火箭弹弹体与导引头之间的动力学耦合等问题,提出了一种带落角约束的制导律设计方法。首先,考虑到飞行过程中导引头和弹体之间的耦合作用,建立了方位俯仰捷联式导引头的二自由度数学模型以及制导火箭弹的六自由度数学模型,然后,考虑到实际工程应用中导引头与弹体之间的动力学耦合因素,将导引头框架偏转角作为制导信息,设计了一种带落角约束的制导律,实现最大毁伤效果。最后,通过仿真分析验证了所设计的带落角约束制导律能够在保证落角精度的同时降低脱靶量。

切出风速下大型风力机变桨故障叶片气动及结构特性研究

风力机叶片变桨故障极易引发不稳定超高负载而导致结构失效损毁。首先,基于计算流体力学方法对NREL 5 MW风力机变桨故障/成功叶片气动侧特征进行分析,然后,利用双向强流固耦合及屈曲分析对典型方位角下变桨故障叶片状态展开研究。结果显示,切出风速下变桨故障叶片挥舞力矩平均值为变桨成功叶片的13.8倍,且前者流场尾迹更明显。叶片在双向强流固耦合下挥舞力矩较之无流固耦合波动范围明显更广,且变桨故障叶片最大叶尖位移为变桨成功叶片的14.1倍。对于0°、60°、120°和180°四个典型方位角,随角度增大变桨故障叶片的弯矩大小、叶尖位移、弯曲程度、端部效应、尾迹范围和强度逐渐减小。屈曲分析发现随方位角增大,屈曲因子呈递增趋势,其中180°方位角较之0°方位角的一阶屈曲因子增加20.2%。

带自适应模糊神经网络补偿的自耦合PI在风力机变桨控制中的应用

风力机对于风能的捕获主要依靠主控制器和执行机构之间的协同工作。然而风速的幅值和方向是时刻变化的,它的这种非线性特性给能量转换带来了挑战。针对该问题,文章设计了一种基于混合控制方案的变桨距系统,用于超风速下功率吸收的恒定。所提方法利用一种新颖的自耦合PI获取转子速度跟踪性能。而风速的随机性变化被视为一个外在扰动,采用自适应模糊神经网络对其进行补偿控制。为了验证该变桨距控制系统的性能,在Matlab/Simulink中搭建了2 MW直驱式风机模型,并与传统的PI控制器进行仿真对比。仿真结果表明,文章所提算法在转子速度跟踪和输出功率恒定控制等方面拥有比传统PI更为优异的性能。

混捏成型沥青烟净化系统中高效吸附技术的应用

针对炭素企业混捏成型工段中传统炭粉吸附沥青烟净化系统存在的问题,沥青烟高效吸附净化系统提出“源头吸附”、“预混喷射”、“多相耦合吸附”技术,旨在提高净化系统的吸附效率,为获得理想的净化效果奠定基础。

基于虚拟飞行的混合翼身融合布局操稳特性

针对混合翼身融合布局面临的三轴运动耦合和大迎角失稳等潜在操稳问题,研制三自由度虚拟飞行试验系统,基于动力学相似模型开展纵向和横航向开环虚拟飞行试验,对飞机的本体操稳特性进行研究。结果表明:该混合翼身融合布局飞机纵向和航向开环操纵均存在三轴运动耦合现象。纵向操纵会引起大迎角极限环失稳现象,迎角振荡平衡位置约为28°、振荡幅值约为2.56°、振荡主频率为0.55 Hz,振荡过程中气动力呈现非定常特性;V型尾翼偏航操纵响应呈现横向运动幅值最大、偏航运动次之、俯仰运动最小的特点。

长输管道的全自动超声检测耦合监控设置方式

通过设置人工耦合不良区域,对比长输管道全自动超声检测时的两种常用耦合通道设置方法,分析了耦合监控设置对实际检测结果有效性的影响。结果可为长输管道全自动超声检测耦合监控方案的选择以及参数设置提供参考。

配偶夫妻疾病沟通与肠造口患者感知社会约束的交叉滞后模型

目的了解配偶夫妻疾病沟通与肠造口患者感知社会约束在患者出院后6个月内的变化趋势,并分析二者间的因果关系,为基于夫妻二元沟通视角的肠造口患者心理干预提供参考。方法使用一般资料调查表、社会约束量表、夫妻癌症相关沟通问题量表对206例肠造口患者及其配偶于出院后1个月、3个月、6个月进行调查。结果出院后6个月内,肠造口患者感知社会约束及配偶夫妻疾病沟通呈改善趋势(均P<0.05)。交叉滞后模型显示,出院后1个月配偶夫妻疾病沟通能够影响出院后3个月患者感知社会约束(β=0.254,P<0.05),出院后3个月配偶夫妻疾病沟通亦能够影响出院后6个月患者感知社会约束(β=0.153,P<0.05),而肠造口患者感知社会约束对配偶夫妻疾病沟通无预测作用(均P>0.05)。结论肠造口患者感知社会约束及配偶夫妻疾病沟通在出院后逐渐改善,配偶夫妻疾病沟通能够预测患者感知社会约束。医护人员应及时评估患者与配偶的沟通状态,促进患者配偶与患者的良性沟通,以缓解患者感知的社会约束。

大型渡槽结构考虑流固耦合的动力建模研究

该文依据符拉索夫(Volasov)和豪斯纳尔(Housner)理论建立考虑槽内水体与槽身动力相互作用以及槽身剪力滞后影响的渡槽薄壁结构横向动力分析模型,由能量变分原理推导出渡槽薄壁梁段单元刚度矩阵及质量矩阵表达式,通过数值算例验证了该模型的正确性;利用该模型对某大型渡槽进行了多种工况的频率计算,结果表明:大型渡槽在无水和设计水位时的振动频率有所变化;该文模型是考虑渡槽槽内水体横向流固动力相互作用的实用动力分析模型。

二维矩形水槽晃荡过程的SPH方法模拟

新型LNG船的液仓内液体晃荡涉及非线性自由表面大变形运动。针对容器的运动所激发的内部流体的强迫晃荡问题,该文运用光滑质点水动力学(SPH)方法对二维矩形水槽的纵荡过程和纵摇过程进行了数值模拟。纵荡过程中边界处的自由液面高度的时间历程曲线与前人的结果相比符合较好,结果还显示了当激励频率接近容器一阶固有频率时出现了对容器上边界的砰击和自由水面的破碎现象,并分析了砰击作用对计算的影响;同时考虑纵荡和纵摇激励时,模拟表明当相位相同时波面的运动幅度最小,而相位差为180度时波面的运动幅度最大,并且其综合效果是非线性的。