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581.
海底管道靠近海床表面处受海流冲刷,管道与海床表面产生一定间隙,该间隙与管道直径的比值定义为间隙比。通过数值模拟和物理模型试验,研究间隙比对管道绕流的水动力特性的影响。物理模型试验中,六分力天平测得管道的阻力和升力,数值模拟研究管道尾流流态和旋涡发放频率。结果表明:间隙比低于某临界值时,海床的存在阻碍了剪切层与层外流动间的相互作用,抑制层内涡量的传递,下游旋涡得不到充分发展,发放频率有所降低;海床壁面加剧管道两侧压力分布不均匀,压力差增加,因而管道阻力和升力增大;间隙比高于某临界值时,海床的抑制作用逐渐削弱,旋涡脱落趋于规则,海床未对绕流产生较大影响,管道受力随之趋于稳定。该研究可为海流冲刷引起的海底管道悬跨现象的安全设计提供理论指导。 相似文献
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583.
介绍了海天集装箱码头使用的柴油发电机的基本情况,并介绍了电子调速器的工作原理、组成和选型。阐述了使用电子调速器的注意事项,并分析了常见故障。 相似文献
584.
A self-tuning fuzzy PID (ST-FPID) control scheme is implemented within a joint interactive (Matlab/Simulink/Fluent) co-simulation framework for effective two degrees of freedom (2DOF) vortex-induced vibration (VIV) control of an elastically-mounted circular cylinder in laminar cross-flow of incompressible non-Newtonian power-law fluids based on the control action of a single transverse force actuator. The model-free controller, which systematically tunes the control parameters online in real time based on given rules, is well-known to be highly advantageous over the previously employed conventional PID controllers. It is particularly capable of handling the intricate non-linear dynamic effects inherent in the complex fluid rheology of non-Newtonian flow past the cylinder in presence of unmodeled system dynamics, high parametric uncertainties, diverse operational conditions, and time-varying external disturbances and control signals. Extensive numerical simulations reveal that the complex shear-thinning and shear-thickening behaviors of fluid viscosity can substantially influence the cylinder dynamic response, applied hydrodynamic forces, and flow structure. In particular, effectiveness and high performance of the adopted ST-FPID control strategy in substantial suppression of the high amplitude coupled 2DOF VIV of the elastically-mounted cylinder at selected critical reduced velocities in the lock-in region are established for a wide range of power-law index parameters (e.g., up to 83% reduction in RMS value of cylinder cross-flow displacement and up to 35% reduction in RMS value of cylinder in-line displacement for n=1and U* = 5 at Re = 100). Also, the vigorous action of the error-driven ST-FPID controller in forcing the high strength vortex shedding patterns of the uncontrolled cylinder out of the lock-in condition into the classical von Kármán vortex street of 2S-type mode of moderately weaker strengths is verified. 相似文献
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The flexible cantilever riser, as a special form of the marine riser, can be encountered in a deep-sea mining system, where the bottom of the long vertical lifting pipeline is connected with the intermediate warehouse. The main objective of this paper is to investigate the effects of the bottom weight caused by the intermediate warehouse and the flow speed on the dynamic responses of the cantilever pipeline. A quasi-3D coupling algorithm based on the discrete vortex method and finite element method is employed to calculate the unsteady hydrodynamic forces and vortex-induced vibrations of this pipeline in the time domain, respectively. We first simulate the VIV of a long flexible riser with two fixed ends in a stepped flow to validate the feasibility of the present method. Then, systematic simulations of cross-flow VIV of the cantilever riser are carried out under a wide range of bottom weights and different current speeds. The number of the vibration mode shows the decreasing tendency with the increase of the bottom weight. In a certain range of the weight, the number of the dominant mode remains unchanged, while the vibration amplitude declines with increasing weight. An amplitude jump phenomenon can be observed when the transition of the dominant mode in two contiguous mode clusters occurs. Moreover, the higher-order modes are excited with the increase of the current speed. 相似文献
588.
OC4半潜浮式风机综合性能较好,但其浮式基础结构质量和结构复杂性使其建造成本高昂,而WindFloat半潜浮式风机浮式基础具有结构简单、建造成本低和减摇效果好等优点,但是适应水深较小且只适合特定海域。结合OC4和WindFloat半潜浮式风机浮式基础的结构特点,针对200 m水深环境设计OC4-WindFloat半潜浮式风机基础。基于叶素理论、莫里森公式和势流理论,通过有限元软件对OC4-WindFloat半潜浮式风机的固有周期及风浪联合作用下的动态响应进行耦合分析,并与OC4半潜浮式风机结果进行对比研究。结果显示,OC4-WindFloat半潜浮式风机固有周期及动态响应均满足相关规定,且具有比OC4更低的建造成本,相比WindFloat可适用更深的海域。研究结果对于浮式基础型式研究有一定的指导意义。 相似文献