半潜式海洋平台浮箱阻尼分析方法

本文依据CMA方法建立海浪波高与周期的联合模型,根据IFORM方法确定北大西洋百年一遇波高-周期的等概率曲线,设计了一组百年一遇波浪海况。由于海洋平台经受的波浪波长有几米到几百米,而半潜平台浮箱一般长度在100 m左右,宽度和高度在10~20 m范围,浮箱的粘性阻尼是否要考虑,如何考虑目前工程界做法不一。本文以典型四立柱半潜式平台为研究对象,运用忽略浮箱粘性阻尼、用Morison方程来考虑粘性阻尼和增加临界阻尼来修正的3种方法,分别对半潜式平台的运动响应、气隙、波浪二阶平均漂移力分别进行短期预报分析研究,并对3种分析方法结果进行对比分析。

作业水深对半潜平台气隙影响的比较研究

结合水池试验结果,对数值模拟粘滞曳力和辐射阻尼进行了修正。考虑平台所受的风、浪、流载荷以及全尺寸锚泊系统对平台运动的影响,基于锚泊和ATA定位方式,选取四种典型计算工况,对平台在不同作业水深下气隙和波浪砰击进行研究。研究结果表明:平台在同等工况下,工作水深对两种定位方式下平台运动响应能量谱、关注点气隙响应能量谱影响敏感。关注点处负气隙以及波浪砰击次数随着工作水深的增加而加剧。ATA定位平台较之于锚泊定位平台的随动性更好,可有效减小平台与水质点相对运动。工作水深引起ATA定位下平台关注点的砰击次数、气隙变化以及改善幅值优于锚泊定位。在平台设计过程中应该重视工作水深对平台气隙和波浪砰击的影响。

作业水深对浮式平台气隙的影响机理研究

本文结合模型试验,基于数值重构后的计算模型,采用时域全耦合分析方法,探索了作业水深对平台气隙的影响规律;针对作业水深对浮式平台系泊系统刚度、系泊力的影响特性进行了深入分析,揭示其对气隙的影响机理。研究结果表明:浮式平台关注点处负气隙对作业水深的影响较敏感,平台的运动响应能量谱受工作水深的影响显著,在同等环境工况下,关注点处负气隙随着作业水深的增加进一步加剧。随着作业水深的增加,系泊系统刚度呈现出减小趋势,平台系统的恢复力变弱,平台的运动增强,导致平台的垂向位移发生变化,平台发生负气隙的概率增大。水深变化引起的波浪砰击严重影响平台作业安全,在实际工程设计中要充分考虑工作水深对平台气隙运动的影响。

水平波浪冲击载荷对柱稳式平台局部结构设计的影响

当柱稳式平台的气隙计算结果为负值时,需要对该平台进行气隙评估,其中包括波浪水平载荷的计算分析。在工程设计技术基础上,依据相关规范方法,总结出一套工程实用方法,以改进柱稳式平台局部结构的加强设计。典型案例选取某柱稳式平台的前舱壁模型,计算平台局部上浪抨击载荷,并通过有限元方法进行平台前舱壁受波浪抨击载荷下的瞬态时域计算,最终得到前舱壁在波浪抨击载荷下的应变及变形。计算结果表明,水平波浪冲击载荷对于甲板箱垂直表面产生较为严重的破坏,不可忽视。应基于数值计算结果,对局部结构进行加强设计,直至设计符合相关规范要求。

Sensitivity Analysis of the Effect of Speed and Inclination Angle on Water-Entry Slamming Pressure of the Bow

In this paper,a method about the water-entry slamming of a two-dimensional(2D)bow structure has been proposed based on the experimental and simulation results.According to this method,the sensitivity analysis has been carried out about the effect of speed and inclination angle on the slamming pressure of the bow.Firstly,a 2D ship bow experimental model was performed to obtain the slamming pressure distribution at different measuring points under different speeds.Then,numerical simulation for the water-entry slamming of this experimental model was conducted to obtain the pressure distribution on the experimental model under different working conditions.Finally,the experimental results were compared with the numerical simulation results to evaluate the effect of speed and inclination angle on the slamming pressure of the bow.The results show that the slamming pressure is more sensitive to speed variation within the low-speed range.The effect of inclination angle on the slamming pressure is more obvious in the small angle condition.When the inclination angle is larger than 45°,the effect is limited.

Impact Analysis of Air Gap Motion with Respect to Parameters of Mooring System for Floating Platform

In this paper, the impact analysis of air gap concerning the parameters of mooring system for the semi-submersible platform is conducted. It is challenging to simulate the wave, current and wind loads of a platform based on a model test simultaneously. Furthermore, the dynamic equivalence between the truncated and full-depth mooring system is still a tuff work. However, the wind and current loads can be tested accurately in wind tunnel model. Furthermore, the wave can be simulated accurately in wave tank test. The full-scale mooring system and the all environment loads can be simulated accurately by using the numerical model based on the model tests simultaneously. In this paper, the air gap response of a floating platform is calculated based on the results of tunnel test and wave tank. Meanwhile, full-scale mooring system, the wind, wave and current load can be considered simultaneously. In addition, a numerical model of the platform is tuned and validated by ANSYS AQWA according to the model test results. With the support of the tuned numerical model, seventeen simulation cases about the presented platform are considered to study the wave, wind, and current loads simultaneously. Then, the impact analysis studies of air gap motion regarding the length, elasticity, and type of the mooring line are performed in the time domain under the beam wave, head wave, and oblique wave conditions.

Strength Analysis on Brace Structure for Semi-Submersible in Consideration of Wave Slamming

Slamming on bracings of column stabilized units shall be considered as a possible limiting criterion under transit condition based on the requirements in DNV-OS-C103. However, the wave slamming loads under survival condition were ignored for the strength analysis of the brace structures in many semi-submersible projects. In this paper, a method of strength analysis of brace structure is proposed based on the reconstruction and extrapolation of numerical model. The full-scale mooring system, the wind, wave and current loads can be considered simultaneously. Firstly,the model tests of the semi-submersible platform in wind tunnel and wave tanker have been carried out. Secondly,the numerical models of the platform are reconstructed and extrapolated based on the results of model tests. Then, a nonlinear numerical analysis has been conducted to study the wave slamming load on brace in semi-submersible platform through the reconstructed and extrapolated numerical model. For the randomness of wave load, ten subcases under each condition have been carried out. The value of the 90% Gumble distribution values of the ten subcases are used. Finally, the strength on brace structure has been analyzed considering the wave slamming. The wave slamming loads have been compared between the survival condition and transit condition with the method. The results indicate that wave slamming under survival condition is more critical than that under transit condition.Meanwhile, the wave slamming is significant to the structural strength of the brace. It should be overall considered in the strength analysis of the brace structure.

定位方式对浮式半潜平台气隙的影响特性及机理研究

本文结合模型试验,采用数值重构的模型,以一浮式半潜平台为算例进行时域全耦合分析,就锚泊定位与动力辅助锚泊定位对平台气隙影响的敏感性展开研究,深入探索了定位方式差异对平台气隙的影响特性及其机理。研究得到如下结论:动力辅助锚泊定位平台较之于纯锚泊定位平台,锚链对平台的垂向约束相对较小,在垂向方向,平台与波浪之间的随动性更好,从而减小了平台与水质点之间的相对运动,对气隙有着较好的改善效果。在同等工况下,锚泊定位方式平台发生负气隙的概率大于动力辅助锚泊定位方式平台,其波浪砰击也更为剧烈。在平台气隙数值模拟时,应充分考虑定位方式差异对平台安全作业的影响。

Numerical Study on the Effect of Gap Diffraction on the Hydrodynamic Performance of A Floating Breakwater

Two-dimensional(2D)flume experiments are useful in investigating the performances of floating breakwaters(FBs),including hydrodynamic performances,motion responses,and mooring forces.Designing a reasonable gap between the flume wall and the FBs is a critical step in 2D flume tests.However,research on the effect of the gap on the accuracy of 2D FB experimental results is scarce.To address this issue,a numerical wave tank is developed using CFD to estimate the wave-FB interaction of a moored dual-cylindrical FB,and the results are compared to experimental data from a previously published work.There is good agreement between them,indicating that the numerical model is sufficiently accurate.The numerical model is then applied to explore the effect of gap diffraction on the performance of FBs in2D experiments.It was discovered that the nondimensional gap length L_(Gap)/W_(Pool)should be smaller than 7.5%to ensure that the relative error of the transmission coefficient is smaller than 3%.The influence of the gap is also related to the entering wave properties,such as the wave height and period.