Bottom effects on the tower base shear forces and bending moments of a shallow water offshore wind turbine

In this paper the tower base shear forces and bending moments of a shallow water offshore wind turbine have been rigorously calculated by using a nonlinear simulation method taking into account the bottom effects. It has been found that nonlinearly simulated realistic waves with bottom effects should be used as inputs in the stochastic time domain simulation in order to design an un-conservative support structure for the offshore wind turbine. In order to further improve the simulation efficiency, a transformed linear simulation method has been utilized in this paper for generating equivalent waves as those obtained from the nonlinear simulation method. The accuracy and efficiency of the transformed linear simulation method have been convincingly substantiated through the subsequent calculation examples in this article.     

A procedure for predicting the permanent rotation of monopiles in sand supporting offshore wind turbines

Foundations for Offshore Wind Turbines (OWTs) are designed following the limit state philosophy. One of the considered states is the Serviceability Limit State (SLS), which verifies that the permanent rotation of the foundation generated from accumulated strains in the soil is below a project specific criterion. Despite design codes requiring an estimation of the permanent rotation, there is not clear guidance on how to implement this. This paper describes a methodology to estimate the monopile permanent rotation for SLS and discusses its advantages and limitations. The methodology combines an accumulation method with results from 3D Finite Element Analyses (FEA) and a soil model that accounts for strain accumulation as a function of the number of cycles, relative density and load characteristics. The performance of the proposed methodology is compared against experimental centrifuge tests and results from advanced 3D FEA, indicating that it can predict the permanent rotation with satisfactory accuracy, and with a considerable reduction in computational effort. This is important for the design of OWTs, where different load histories might be required to be checked – often under tight time constraints – to find which load history leads to the largest permanent rotation, and therefore is more critical to SLS design.     

多种节能减排技术在VLCC上的应用分析

从节能、绿色环保的理念出发,以30万t级VLCC为对象,综合比较LNG燃料供气系统、弗莱特纳旋转风筒节能装置,以及空气润滑系统等船舶动力装置节能减排技术,分析对比表明,在VLCC上综合应用这3种节能减排技术,可直接满足EEDI第三阶段排放要求,经不同的航行路线测算,该型VLCC年度综合节省油耗可达8%~12%,节能减排效果显著。     

大直径钢管桩沉桩工艺及桩身垂直度控制

本文通过对单桩沉桩工艺、垂直度测量控制方法的剖析与总结,为后续海上风电场建设中无过渡段大直径钢管桩单桩基础的施工、质控提供实际经验。     

抗风浪浮码头试验研究

针对现有传统浮码头抗风浪能力不足的问题,进行原因分析。提出一种新型抗风浪浮码头方案,其设计思路是将浮码头存在过程分为正常工作与防御风浪两种工作状态,采取设置抗风浪滑动槽、工作约束和人字锚系统等关键措施,既保证其正常工作要求,又具有较高抵御风浪能力。对设计方案进行了模型试验验证,并提供确定关键参数的原则和方法。该方案为有效提高浮码头在海洋环境中的生存适应能力、发挥浮码头技术优势提供一种解决方案和技术支持。     

铁路沿线太阳能电池板及支架立柱的抗风性能

以西成(西安—成都)高速铁路沿线立柱式太阳能电池板支架立柱的布设为背景,通过数值计算、风洞试验及有限元分析研究其抗风性能。为避免结构共振,须获得高速列车脉动风压的振动特性,通过刚性模型测力试验获取了结构最不利风偏角,试验结果可作为调整结构布设方向的依据。铁路沿线结构抗风设计须考虑自然风荷载和列车脉动风荷载的综合作用。本文提出了一种验算铁路沿线结构抗风安全性的方法:基于数值计算得到结构受列车风荷载作用下的极限风压,以此反算结构所受极限风荷载,并利用风洞试验及有限元计算方法计算结构应力。     

Calibration of safety factors for offshore wind turbine support structures using fully coupled simulations

The offshore wind industry experienced a boost during the last decade in terms of size of wind farms and rated capacity of the wind turbines: towers are getting taller and blades are getting longer, constantly facing new and complex challenges. Because of the relative immaturity of the wind industry, and the fact that the offshore design standards stemmed from the oil and gas industry, it is generally acknowledged that the reliability levels achieved, although not very well understood, might result in partial safety factors not optimal for OWT. This paper addresses this situation by studying the reliability levels delivered by the current standards and assessing the validity of the safety factors through a reliability-based code calibration. The combination of the low probability of failure imposed on the design of OWTs and the computational cost of the aero-elastic time-domain simulations brings out the need to develop new approaches for reliability analyses. In this paper, the reliability analysis is performed using a Kriging surrogate model to approximate the load-effect from the aero-elastic simulations converting expensive-to-evaluate limit state functions to explicit functions. Subsequently, a calibration of the safety factors is carried out using the probabilistic models from literature. The approach is applied to an industry-reference turbine and support structure. The results showed very low probabilities of failure for the most severe design cases and confirm that the safety factors from the IEC are mostly adequate.     

Dynamic responses analysis of a 5 MW spar-type floating wind turbine under accidental ship-impact scenario

Ship impact against offshore floating wind turbine (OFWT) has been identified as one of the major hazards with the development of OFWTs. The dynamic responses of OFWTs under ship impact should be taken into consideration during the design phase. This paper addresses a study on the dynamic responses of an OFWT in ship collision scenarios. Firstly, a mathematical model for external mechanism of ship-OFWT collision scenario is developed. Secondly, this model is combined with an in-house programme, DARwind, which can be used to predict nonlinear dynamic responses of whole OFWT system in time-domain. With the newly combined analysis tool, simulation cases for different scenarios are conducted to investigate the nonlinear dynamic responses of OFWT system, including the cases of still water condition, wave-only condition and wind-wave condition. It is shown that in still water condition, the ship impact will more obviously change the responses of motions and mooring system, compared with those in wave and wave-wind conditions. In the wave-only condition, these motions responses of platform are suppressed by wave effect, but the tower vibration and tower top deformation are sensitive to ship collision. For the wave-wind combined condition, the motions increment in surge and pitch due to ship collision becomes smaller than that of wave-only condition, but yaw motion has a considerable variation compared with those of the other two conditions. Additionally, the blade tip deformation increment due to ship collision are analyzed and it is found that the edgewise tip deformation got more obvious increment than that of flapwise. To further asses the safety of OFWT, the acceleration at nacelle are analyzed because some equipment might be sensitive to acceleration. The analysis results indicate that even though the OFWT structure doesn't get critical damage by ship impact, the equipment inside may still fail to work due to the high value of acceleration induced by ship impact. The research outcomes can benefit the safety design of OFWT in the engineering practice.     

大风环境列车横截面外形优化

列车经过大风环境时引起的列车稳定性变化影响列车行车安全与乘坐舒适性。优化列车横断面可以提高列车在横风作用下气动性能,降低倾覆危险。借助数值模拟手段,通过优化截面内倾角位置高度等7个几何参数,得到倾覆力矩随参数变化的规律,确定优化中需重点关注的参数。研究结果表明,倾覆力矩随顶部折角与底部折角的变化为非单调增长,而随其他部位的变化呈现单调趋势,优化得到的组合截面比原始截面横向力下降28. 28%、升力大小下降42. 85%、倾覆力矩减小45. 91%。优化后的列车横截面模型与原始断面相比,横向力增长了24. 28%,升力和倾覆力矩分别下降了75. 99%和27. 19%。倾斜条件下,优化后的列车截面模型倾覆力矩较原车模型下降了11. 22%。