波浪作用下海洋立管试验研究及ANSYS数值模拟

海洋立管在石油工业生产中有着非常广泛的应用,同时也是薄弱易损的构件之一。立管管内有高温高压的流体流过,管外承受海洋环境荷载尤其是波浪荷载的作用,受力比较复杂。由于中国大部分的海上油田水深都比较浅,所以重点研究浅水中的海洋立管。运用相似理论将实际立管模型缩放为试验模型,在管内流体流动及管外波浪荷载作用下,测量立管动力响应,并与Ansys有限元数值模拟结果进行了比较。     

海洋深水立管最小壁厚计算方法

深水立管钢管的壁厚是决定钢管承受安装和操作期间内、外荷载作用的关键因素,也是影响工程费用的关键因素,深水海洋立管因其受外部静水压力和内部介质压力共同作用,而使其在壁厚计算上与浅水海洋立管壁厚计算不同,且所遵循的规范也不同.本文以API RP2RD为基础,以SCR立管结构型式为例,简要介绍海洋深水立管壁厚计算中应主要考虑的设计因素和计算方法,供海底管道设计者参考.     

椭圆余弦波对圆弧型固立防波堤的绕射波浪力

基于椭圆余弦波绕射理论,应用特征函数展开法,推导浅水波对圆弧型固立防波堤绕射的波势解,据此计算作用于防波堤的水平波浪载荷。结果表明:浅水波入射角与非线性影响参数、海况条件以及防波堤几何条件等因素的相对变化对波浪作用均存在一定的影响。与微幅波理论对比可知:在一定浅水条件下采用椭圆余弦波一阶分量模型所计算的最大无量纲波浪力均明显高于微幅波理论的对应估值,反映了水波非线性因素的影响效应。     

附加重量缓波立管数值分析

对浅水海域使用的新型附加重量缓波立管进行数值计算,分析管内流体密度对柔性立管的动力特性影响,进行附加装置对立管平面外运动影响的分析,同时引入一种模型简化的计算方法,结果表明,内流密度对立管位形、最大曲率和最大有效张力的影响较大,附加装置的应用减小了立管碰撞的概率,同时发现该模型简化方法不仅计算准确,而且易收敛、计算时间短。     

关于浅水影响及其改善技术

通过浅水船型试验研究实例讨论浅水影响问题,强调内边界条件对船舶浅水性能的影响,并通过一例双体船的试验研究提出通过加装尾后水翼改善船舶浅水性能的技术方案。     

浅水效应对船舶航行安全的影响及对策

为保障船舶在相对浅水水域的航行安全,阐述界定浅水水域的3种方法,介绍浅水效应对船舶航行造成的影响,提出浅水区安全航行的对策:自主减速航行;利用船舶测深仪不断测深;忌用自动舵;提前备车备锚;正确对待浅水效应对停船冲程的作用;船舶会遇时提前减速避让。在相对浅水水域谨慎驾驶,正确对待浅水效应可提高浅水域航行安全水平。     

不同航速下船舶浅水摇荡运动规律

浅水效应是船舶安全操纵所需考虑的重要因素。本文采用三维势流理论,以某NPL型船模为例,分别对其在次浅水、浅水、超浅水3种不同相对水深条件下的纵摇和垂荡运动幅值响应情况进行计算,并对纵摇和垂荡运动随航速的变化规律进行总结。本文计算结果可作为船舶驾驶员判断是否发生浅水效应的参考依据。     

浅水效应对船舶的影响及经验估算方法

当船舶由深水区域航行至浅海、内河和港口等浅水区域时,因航道受限而遭受浅水效应,进而其安全航行和操纵性受到影响。针对这一问题,对浅水效应的概念、发生条件及其对航行安全的影响进行分析。针对浅水效应的下沉和阻力增加,介绍比较常用的经验公式估算法,以便对浅水效应进行定量分析。根据该经验估算方法,船长可在船舶遭受浅水效应时做出快速反应,从而保证船舶安全航行。     

南海沙质地和珊瑚礁地质浅水区域波浪衰减实测研究

波浪从深水区域传播到浅水区域,海底摩擦是引起波浪衰减的主要因素。南海浅水区域以沙质和珊瑚礁地质为主要特征,与世界其他地方浅水区域有较大不同,至今未有海底摩擦导致波浪衰减的实测资料。论文采用海洋环境实测设备—方向波潮仪(directional wave recorder,DWR),在沙质地浅水区域和珊瑚礁地质浅水区域进行波浪参数实测,基于动谱平衡方程波浪模型的处理方法获得了波浪衰减系数,首次定量描述南海浅水区域的波浪衰减特征,为后续南海浅水区域波浪衰减系数的长期实测研究工作奠定了基础。     

中国、英国、美国、日本规范关于直墙波谷力计算方法的对比

文章介绍了英国标准BS6349、美国陆军工程兵团《海岸工程手册》、日本《港口设施技术标准》中直墙所受波谷力的计算原理、应用范围和参数选取,并借助工程实例与中国《港口与航道水文规范》中计算方法进行了对比。对于立波波谷力的计算,各国较常用的均为森弗罗公式,但在公式使用过程中应注意特征波高的选取。当d/L在0.139～0.2范围内时,应用中国规范的波谷力计算值介于美国与日本规范、英国规范之间,英国规范水平波谷力计算值偏大17%左右。当d/L在0.05～0.139时,中国规范浅水立波法计算值与美国及日本规范接近,均远低于英国规范值。由于英国规范采用了特征波H_(max)与T_s计算,在波浪浅水变形较显著的工况下,计算可能偏离实际较大。美国规范及日本规范计算值则较中国规范偏低,偏低幅度根据相对水深及波陡等参数的不同而在5%～10%波动。     

非线性立波作用下砂质海床动力响应及液化研究

利用傅立叶级数近似法求解非线性立波作用下海床表面波压力,基于波浪作用下海床动力响应的二维准静态模型以及液化判定标准,模拟非线性立波作用下海床动力响应以及液化深度。线性与非线性立波计算结果比较表明:当相对水深较大时,非线性立波波峰处波压力出现双峰,波谷处的波压力明显大于线性立波波谷处波压力;海床中孔隙水压力在波峰时也表现出双峰型特性,且波谷时的海床压力增大;在相同波浪条件下,非线性立波作用下海床更易液化,且液化深度大于线性立波作用下液化深度。     

海堤波浪浅水变形的简化计算

对浙江地区海堤工程涉及的波浪浅水变形计算问题进行了分析研究,基于《浙江省海塘工程技术规定》及微积分原理,推导了波浪浅水变形后的波高直接计算解析式,并对平底海床、单斜坡海床、分段折线海床及三次抛物曲线海床情形下的波浪浅水变形计算进行了研究,分别给出了简洁计算解析式,以便于工程师计算参考,达到提高设计进度的目的。最后通过工程实例计算,验证了该波高直接计算解析式的精度完全满足工程要求。     

An analytical investigation for oscillations in a harbor of a parabolic bottom

Based on the linear shallow water approximation, longitudinal and transverse oscillations in a rectangular harbor with a parabolic bottom are analyzed. The longitudinal ones are combinations of the Legendre functions of the first and second kinds and the transverse ones are expressed with modified Bessel equations. Analytic results for longitudinal oscillations show that the augmentation of rapidity of variation of the water depth shifts the resonant wave frequencies to larger values and slightly changes the positions of the nodes for the resonant modes. For the transverse oscillations trapped within the harbor which are typically standing edge waves, the dispersion relationship is derived and the spatial structures of the first four modes are presented. The solutions illustrate that all the trapped modes are affected by the varying water depth parameters, especially for the higher modes whose profiles extend farther and the distribution of the energy of transverse oscillations is influenced by the rapidity of variation of the bottom within the harbor.     

变密度深水中的内波向水面的垂直传播

本文探讨了内波向上传播的衰减形式和处于海洋深处潜艇兴起的内波有无可能被微波探测到的问题.旨在将自航体内波的研究与星载(机载)合成孔径雷达(SAR)的微波探测联系起来,供潜艇非声探测和SAR制造单位参考.     

采用Green-Naghdi方程和有限元法计算浅水船波

采用波动方程／有限元法求解Green-Naghdi(G-N)方程计算船舶在有限水深区域的兴波和波浪阻力。把行驶船舶对水面的扰动作为移动压力直接加在Green-Naghdi方程里，以描述运动船体和水面的相互作用，并经此来计算不面波动、船底水动压力和波浪阻力。G－N方程比浅水方程增加一个非线性的频散项，以补充有限水深对浅水船波的影响。采用随船运动网格的有限方法，以Series 60 CB=0.6船作为算例给出浅水船波的计算结果，并与浅水方程的结果进行了比较。计算结果表明，当船速小于临界速度时，由于频散的影响，G－N方程级出的船后尾波波高比浅水方程的结果大，同时波浪阻力也比浅水方程的结果有所提高。当船速大于临界速度时，G－N方程的计算结果与浅水方程基本相同，频率散射无明显影响。     

浅水区域浮箱式防波堤结构形式的试验研究

介绍了2种浮箱结构型式的防波堤(L型中浮箱和L型边浮箱),3种类型(L型边浮箱、H型边浮箱、T型边浮箱)的浮式防波堤,对浅水区域浮箱式防波堤结构形式进行了实验室物理模型试验研究。得到了在规则波作用下的浮式防波堤的消浪效果和透过率。本次试验结果表明,在浅水波情况下,相同周期时的防波堤越宽波浪的透过率较小;同一形式尺寸的防波堤,透过率随着周期加长而逐渐增大。     

Green-Naghdi理论的全非线性浅水波数值模拟(英文)

Green-Naghdi (G-N) theory is a fully nonlinear theory for water waves. Some researchers call it a fully nonlinear Boussinesq model. Different degrees of complexity of G-N theory are distinguished by “levels” where the higher the level, the more complicated and presumably more accurate the theory is. In the research presented here a comparison was made between two different levels of G-N theory, specifically level II and level III G-N restricted theories. A linear analytical solution for level III G-N restricted theory was given. Waves on a planar beach and shoaling waves were both simulated with these two G-N theories. It was shown for the first time that level III G-N restricted theory can also be used to predict fluid velocity in shallow water. A level III G-N restricted theory is recommended instead of a level II G-N restricted theory when simulating fully nonlinear shallow water waves.     

On the dispersion relation of hydroelastic waves in a plate

This paper deals with the dispersion relation of hydroelastic waves in pontoon-type very large floating structures (VLFS) using a simple beam modeling, where the term hydroelastic waves means propagation of deflection vibrations in VLFS. The purpose of this paper is to show the properties of the hydroelastic waves. The dispersion relation of hydroelastic waves propagating in an infinite plate floating on the water is derived based on the linear water wave theory. The effects of the water depth and of the bending rigidity of the floating plate on the wavelength, phase velocity, and group velocity of the hydroelastic waves are shown theoretically or numerically. Then, the dispersion relation of hydroelastic waves in a finite plate floating on shallow water is investigated. It is shown that the wavelength or the phase velocity of the hydroelastic waves varies with the location in the plate. Received for publication on April 7, 1999; accepted on Aug. 20, 1999     

浅水短波Degasperis-Procesi方程的环形孤立波解(英文)

An analytic method, i.e. the homotopy analysis method, was applied for constructing the solutions of the short waves model equations associated with the Degasperis-Procesi (DP) shallow water waves equation. The explicit analytic solutions of loop soliton governing the propagation of short waves were obtained. By means of the transformation of independent variables, an analysis one-loop soliton solution expressed by a series of exponential functions was obtained, which agreed well with the exact solution. The results reveal the validity and great potential of the homotopy analysis method in solving complicated solitary water wave problems.     

Shallow water effects on high order statistics and probability distributions of wave run-ups along FPSO broadside

Ship hydrodynamics in shallow water becomes especially complicated since the nonlinearities in both the incident waves and the wave–hull interactions will be affected by the water depth. For a ship-shaped Floating Production, Storage and Offloading unit (FPSO) operating in shallow water, the broadside often suffers from the wave run-up and green water incidents in non-collinear harsh ocean environments. By applying the methods of ordinary moments and L-moments and the empirical Weibull distribution on the data measured in a series of model experiments, the high order statistics and the exceedance probability distribution of the run-ups along the FPSO broadside are evaluated and the effects of the shallow water depth and the incident environments are analyzed in this paper. It is seen that both the incident waves and the wave run-ups are non-Gaussian in shallow water and that the wave run-up characteristics are significantly influenced by the water depth and the incident environments, while the contribution due to the vessel vertical motions is negligible for the FPSO used in this study. The exceedance probabilities of the wave run-ups show that the broadside will be more likely to suffer from serious wave run-up and green water incidents in shallower water, in a higher incident wave and a non-collinear environment, especially so at locations around the FPSO midship within a range of 3/8L_pp ∼ 5/8L_pp. The dependency of the shape and scale parameters of the wave run-up probability distributions on the locations and the environment is quantified by model tests. The present study leads to the conclusion that the wave run-up characteristics and the shallow water effects should be considered carefully in determining the wave loads and the freeboard of a large FPSO in non-collinear environment conditions.