静水及波浪中四筒型基础的动力及运动特性研究

以四筒型基础为研究对象,通过模型试验和数值模拟的形式对影响结构静水和规则波浪中动力及运动特性的因素进行分析。结果表明：MOSES能较好地预测结构在静水中的动力特性以及波浪中的运动响应的变化趋势;结构摇荡运动的附加质量系数取值在1.4~1.6之间,大于船舶动力学的建议值1.2;随着吃水的增加,结构的垂荡运动呈增大趋势,但结构的摇摆运动呈下降趋势;随着水深的增加,结构的摇荡运动呈下降趋势,即浅水可增强结构的竖向运动。     

四角架筒型基础气浮过程中运动特性研究

以四角架筒型基础为研究对象,通过在静水及规则波作用下的模型试验对影响结构气浮过程中运动特性的因素进行分析.结果表明,结构摇荡运动的附加质量系数随吃水的增加呈下降趋势,都大于船舶动力学的建议值1.2;随着吃水的增加,垂荡运动呈先减小后增大的趋势,而纵摇运动呈减小的趋势;较浅水深增强了结构的竖向运动,垂荡和纵摇运动的最大幅...     

海上风电多筒导管架基础湿拖过程稳性控制研究

目的 为探究合理的三筒导管架基础湿拖方式以及研究其自浮湿拖浮运特性, 方法 结合某海上风电三筒导管架项目,使用数值模拟软件MOSES对比分析了实浮体及气浮体两种方案的静稳性以及在拖航过程中的运动响应,得到在相同环境荷载影响下,海上风电三筒基础气浮与实浮结构的静稳性及浮运特性的差异。 结果 研究表明：气浮结构的静稳性要优于实浮结构,但在浮运过程中,实浮结构的运动响应幅度要低于气浮结构。 结论 所提方法是正确并有效的,可为实际应用提供指导。     

叶片质量不平衡下风机基础的疲劳性能

为探究基础环式风机基础在叶片质量不平衡时的疲劳性能,文章通过重构风力发电机组叶片质量不平衡模型推导了附加载荷,基于谐波合成法理论对脉动风速谱做单点模拟以计算风电机组气动荷载等基本运行载荷,并以实际工程为例建立了风机叶片—塔筒—基础一体化有限元模型,计算了结构自振特性和基本运行载荷与附加载荷共同作用下的载荷响应。结果表明：风机叶片质量不平衡程度加深会导致基础结构的应力集中现象,加剧应力幅增加,进而影响结构的疲劳性能与寿命;结构中混凝土的受力特性受影响较大,钢筋笼次之,基础环最小。     

粉质黏土中厚壁筒型基础沉放及受力分析

筒型基础具有海上施工效率高、建造成本低等优点,已成功应用于实际工程。为了进一步降低筒型基础结构的制造成本,避免建造、运输、安装过程中钢制筒裙的屈曲,文章研究并优化了混凝土筒壁和钢质内分舱板的组合式筒型基础结构。首先,针对厚壁筒型基础沉放安装难度增加问题,开展了室内试验,研究了粉质黏土中厚壁沉放阻力计算方法;然后,利用三维有限元模型对该组合式筒型基础在位状态下的结构受力进行了分析。研究结果表明：考虑形状和深度系数的端阻力计算公式可以用于该新型风电基础;混凝土筒壁+钢质内分舱板组合式筒型基础倾斜率、结构强度和自振频率满足设计要求,且在造价上更为经济。     

海上风电筒型基础结构体系阻尼特性研究

针对某筒型基础海上风电结构,基于实测振动响应数据,采用随机子空间法对所测海上风电结构的阻尼进行识别,研究海上风电筒型基础结构在停机及运行状态下阻尼的变化规律。结果表明：在停机状态下,海上风电筒型基础结构的顺风向阻尼和横风向阻尼均随外界风速的增大呈增长趋势,两者的平均值分别为0.952%和0.973%;当风电机组处于运行状态时,顺风向运行阻尼随外界风速的增大呈增长趋势,阻尼平均值在3.87%~5.28%之间变化,而对于横风向运行阻尼,其变化趋势受外界因素的影响较小,阻尼平均值在整个风速范围内在1.74%~3.37%之间变化,横风向运行阻尼小于顺风向运行阻尼。     

遗留桩坑对临近复合筒型基础倾斜率的影响

针对某海上风电项目,基于ABAQUS三维数值软件定量分析桩坑与复合筒型基础的距离、桩坑尺寸及深度等参数变化对复合筒型基础结构泥面倾斜率的影响,引入可反映桩坑充盈固结程度的系数γ与切线斜率K。结果表明：随着桩坑尺寸增加,复合筒型基础泥面倾斜率呈非线性增长,且均向桩坑所在方向倾斜;桩坑深度大于复合筒型基础入土深度时,基础倾斜率增长较快;研究表明筒型基础泥面倾斜率对大深度、近距离桩坑内部土体强度尤为敏感,拟通过该文研究为复合筒型基础风电机组安装船舶选型及布置提供理论依据。     

风电场脉动风模拟及风机塔架动力响应研究

为掌握风载作用下风机结构的动力学特性,采用Davenport脉动风功率谱,基于Shinozuka理论模拟某沿海风电场的脉动风速谱;采用Shiotani简化表达式,以相关系数矩阵考虑脉动风竖向相关性,推导空间脉动风随机过程表达式.建立风机塔底固接和考虑桩基刚度的两种有限元模型,计算自振特性和模拟风载作用下的动力响应.结果表明,该模拟方法能较好地反映风电场实际风况;风机结构自振周期与脉动风变化周期处于同一量级,两者接近时易产生顺风向振动和涡激振动;结构的低阶振型对风致动力响应有重要影响;考虑脉动风效应后,作用于风机上的风荷载和动力响应显著增大.该文成果为进一步开展风机结构的疲劳评价、振动控制及破坏分析奠定基础.     

极限海况下三种海上风力机半潜平台的动态响应对比

采用水动力学软件AQWA和有限元方法,分别对三浮体平台、四浮体平台和五浮体平台在极限海况下的工作状态进行数值仿真,并对3种半潜平台的频域和时域运动响应进行分析。结果表明:在频域分析中,三浮体平台、四浮体平台和五浮体平台在纵荡、垂荡和纵摇方向上的附加质量依次增大,运动响应依次减小;在时域分析中,3种半潜平台在横荡、垂荡和横摇方向上的运动响应均减小;平台的稳定性随平台结构复杂度的增加而提高,但与四浮体平台相比,五浮体平台稳定性的提高不显著。     

新型重力式海上风力机基础结构动力特性分析

提出一种新型海上风力机重力式基础结构形式,介绍其构造与特点。以5 MW风力机为例建立该新型基础及上部结构的整体有限元模型,进行自振特性与地震响应分析,并重点讨论环境水体对结构动力特性的影响。结果表明:1)该新型结构,塔筒柔而基础刚,形成"二元"刚度体系;2)考虑环境水体作用的结构自振频率较未考虑水体作用时小,且振型中的水体淹没部位参与越多,自振频率的减小越显著;3)因水体"附加质量"效应,水下结构地震反应增强,水上结构则不然,其反应略微减小。建议进行重力式海上风力机基础的抗震设计时,应考虑环境水体影响,否则计算偏于危险。     

基于浮式风力机平台的分形特征垂荡板强迫振荡水动力特性

垂荡板因其具有增大水动力阻尼及附加质量的优点而广泛应用于海洋工程领域。将分形理论应用于垂荡板的结构设计,提出一种具有分形特征孔的垂荡板,运用Fluent的自定义函数并结合动网格技术对不同垂荡板模型进行数值模拟,研究其水动力特性。对比分析了不同振幅下实心、不同分形阶数(透空率)以及规则孔垂荡板的水动力特性,得到了不同垂荡板垂向力时间历程曲线、附加质量系数C_m和阻尼系数C_d以及涡量云图。结果表明:振动周期不变时,随振幅的增大,各垂荡板C_d值随之减小,最终趋于平稳,而C_m值随之增大;比较不同分形阶数时,C_m值随分形阶数增加而减小,C_d值随分形阶数增加而先增大后减小,在分形阶数为二阶时,C_d值最大;相同透空率时,分形孔和规则孔垂荡板C_m值大致相等,分形孔C_d值较规则孔有较大提升,最大提升为17.83%,平均为14.74%。由此可见,较之普通开孔垂荡板,分形特征垂荡板具有优越的性能。     

Experimental and theoretical study on single-phase natural circulation flow and heat transfer under rolling motion condition

Experimental and theoretical studies of single-phase natural circulation flow and heat transfer under a rolling motion condition are performed. Experiments with and without rolling motions are conducted so the effects of rolling motion on natural circulation flow and heat transfer are obtained. The experimental results show the additional inertia caused by rolling motion easily causes the natural circulation flow to fluctuate. The average mass flow rate of natural circulation decreases with increases in rolling amplitude and frequency. Rolling motion enhances the heat transfer, and the heat transfer coefficient of natural circulation flow increases with the rolling amplitude and frequency. An empirical equation for the heat transfer coefficient under rolling motion is achieved, and a mathematical model is also developed to calculate the natural circulation flow under a rolling motion condition. The calculated results agree well with experimental data. Effects of the rolling motion on natural circulation flow are analyzed using the model. The increase in the flow resistance coefficient is the main reason why the natural circulation capacity decreases under a rolling motion condition.     

基于流固耦合的卧式轴流泵叶轮模态分析

研究轴流泵转轮的振动特性,对于避免轴流泵工作时发生共振、保证水泵安全稳定运行有重要意义。运用有限元软件ANSYS Workbench,结合流固耦合方法,分析某泵站卧式轴流泵的模态,计算轴流泵叶轮转子在空气和水中的各阶固有频率及其振型,并分析了叶轮固有频率的变化规律及其原因。结果表明,水介质会引起叶轮各阶固有频率的降低,各阶固有频率降低系数的范围为0.10~0.38,降低系数大小与各阶振型有关,水中振型和空气中的振型相似,振幅有所减小,水体的附加振动质量是引起叶轮各阶自振频率降低的原因。     

直管型中心管波能模型的数值计算和实验研究

中心管波浪能模型利用浮体自身振荡运动吸收波浪能,使管内水柱产生相对运动,通过外加气动阻尼转换俘获的波浪能.运用HydroStar水动力学软件计算了直管型中心管模型在不同波况下的水动力学性能,对比分析了不同外加气动阻尼对模型俘获宽度比的影响,得到了最佳气动阻尼;研究了模型在3种不同总质量下的性能,得到了最佳响应波周期与模...     

Operational characteristics of oscillating heat pipes under micro-gravity condition

A mathematical model to investigate the oscillating motion characteristics of liquid slugs and vapor plugs/bubbles in oscillating heat pipes (OHPs) was developed considering the contact angle hysteresis (CAH) and interconnected-tube induced pressure fluctuations. Results show that a short period less than 1 s is available to attain the steady state after startup and then the oscillation amplitudes and frequencies for both of slug/bubble displacement and velocity are kept fixed. The slug/bubble displacement and velocity display quasi-sine oscillating waves with small pressure fluctuations induced by the interconnected-tube. However, small oscillation waves are superimposed on a main quasi-sine oscillation wave and cause a chaotic oscillating behavior of slug/bubble inside the OHP if the induced pressure fluctuation is large enough. Besides, the effects of filling ratio, tube length, inner diameter, temperature difference between the evaporator and condenser sections, and working fluid on the oscillating motion were numerically analyzed and discussed. The numerical model provides a physical insight to understand the operational mechanism of OHPs under the microgravity condition.     

Numerical simulation and analysis of periodically oscillating pressure characteristics of inviscid flow in a rolling pipe

Floating liquefied natural gas (LNG) plants are gaining increasing attention in offshore energy exploitation. The effects of the periodically oscillatory motion on the fluid flow in all processes on the offshore plant are very complicated and require detailed thermodynamic and hydrodynamic analyses. In this paper, numerical simulations are conducted by computational fluid dynamics (CFD) code combined with user defined function (UDF) in order to understand the periodically oscillating pressure characteristics of inviscid flow in the rolling pipe. The computational model of the circular pipe flow is established with the excitated rolling motion, at the excitated frequencies of 1–4 rad/s, and the excitated amplitudes of 3°–15°, respectively. The influences of flow velocities and excitated conditions on pressure characteristics, including mean pressure, frequency and amplitude are systematically investigated. It is found that the pressure fluctuation of the inviscid flow remains almost constant at different flow velocities. The amplitude of the pressure fluctuation increases with the increasing of the excitated amplitude, and decreases with the increasing of the excitated frequency. It is also found that the period of the pressure fluctuation varies with the excitated frequency. Furthermore, theoretical analyses of the flow in the rolling circular pipe are conducted and the results are found in qualitative agreement with the numerical simulations.     

NONISOTHERMAL CHARACTERIZATION OF THIN-FILM OSCILLATING BEARINGS IN THE PRESENCE OF ULTRAFINE PARTICLES

The effects of viscous dissipation and thermal dispersion due to the presence of ultrafine particles in the lubricating fluid are studied on flow and heat transfer inside a non-isothermal and incompressible bearing during relief and squeezing stages. The governing equations are nondimensionlized and reduced to simpler forms based on an order-of-magnitude analysis. Analytical solution for the energy equation for a special case is obtained. Further, the influence of the thermal squeezing parameter, Eckert number, thermal dispersion coefficient, the motion characteristics of an oscillating bearing, and the perturbation parameter are determined. It is shown that the average heat transfer parameter decreases by an increase in the thermal squeezing parameter and dispersion coefficient, while it increases as both the Eckert number and amplitude motion parameter are increased.     

Effects of plate vibration on the mixing and combustion of transverse hydrogen injection for scramjet

Transverse injection is an effective mixing enhancement technique for the combustor of scramjets. Vibration of the plate structure in combustor will easily be induced due to aerodynamic load and harsh aerothermodynamic load simultaneously. Effects of the plate vibration on the mixing and the combustion of the transverse hydrogen injection have been investigated numerically in this study. Finite rate chemistry model is used as combustion model. The supersonic jet experimental model of the Stanford University is modified slightly and used as the analysis model. Effects of the frequency and the amplitude of the plate vibration on combustion performance and flow field structure have been investigated in detail. The results show that the plate vibration increases the mixing efficiency, the combustion efficiency and the total pressure loss coefficient. Besides, it can change the flame structure and the shock wave structure, as well as increase the shock wave intensity at downstream of the injection. The vibration frequency has relatively little effect on the combustion efficiency and the total pressure loss coefficient. When the vibration frequency is large, it presents some high frequency pulsations for the total pressure loss coefficient. However, the vibration amplitude has large effect on combustion efficiency and the total pressure loss coefficient. When the vibration amplitude is small, the combustion efficiency presents regular periodic change with time. When the vibration amplitude is large, it diverges with time, and the flow tends to be unstable. The large vibration amplitude changes the stability of the original flow. Consequently, the combustion with large amplitude fluctuation can critically damage the combustion stability.