Study on Floating Properties and Stability of Air Floated Structures

In this paper, the buoyancy, kinetic properties and stability of air floated structures have been studied by theoretical and experimental methods. The equations for calculation of the buoyancy of the air floated buoy are derived according to the Boyler law and the equilibrium equations of the air floated structure are established. Through simplification of the air floated structure as a single freedom rigid body and spring system, the natural period of heaving and some kinetic properties are discussed. In the stability analysis, the formulas for calculation of the meta centric height are presented. The theoretical results are in good agreement with the data observed from the model test and prototype test. The air buoyancy decrease coefficient presented in this paper has a large influence on the floating state, stability and dynamic properties of the air floated structure. The stability of the air floated structure can also be judged by the parameter of meta centric height, and calculations show that the air floated structure is less stable than the conventional float.

Optimal Skirt Spacing for Subsea Skirted Foundation Considering Floating Stability

A hydraulics model is built in Moses to find the optimal internal skirt spacing for the maximum floating stability of the skirted foundation. The results show that the increase in the internal skirts’ number can help improve the floating stability of the skirted foundation. However, with the increase in the internal skirts’ number, the improvement of floating stability becomes more and more weak. In this study, an optimal number of four are found for the internal skirt spacing. Moreover, to testify the feasibility of internal skirt spacing, a practical project is modeled, which indicates that the optimal internal skirt spacing can satisfy the requirements of towing. © 2017, Tianjin University and Springer-Verlag Berlin Heidelberg.

基于COMPASS iStability的浮船坞稳性计算

为比对分段建模与整体建模工作量及稳性计算结果,选取某浮船坞,采用命令流方法,对坞墙无开口,做5分段建模和整体建模稳性计算,对坞墙有开口,做7分段建模和借助体过渡整体建模稳性计算,结果表明,无论坞墙有无开口,整体建模比分段建模节省约一半工作量,两种建模方式稳性计算精度相同,建模过程表明,命令流方法整体建模计算稳性,高效快捷。

Dynamic Response of Offshore Wind Turbine on 3×3 Barge Array Floating Platform under Extreme Sea Conditions

Offshore wind farm construction is nowadays state of the art in the wind power generation technology.However,deep water areas with huge amount of wind energy require innovative floating platforms to arrange and install wind turbines in order to harness wind energy and generate electricity.The conventional floating offshore wind turbine system is typically in the state of force imbalance due to the unique sway characteristics caused by the unfixed foundation and the high center of gravity of the platform.Therefore,a floating wind farm for 3×3 barge array platforms with shared mooring system is presented here to increase stability for floating platform.The NREL 5 MW wind turbine and ITI Energy barge reference model is taken as a basis for this work.Furthermore,the unsteady aerodynamic load solution model of the floating wind turbine is established considering the tip loss,hub loss and dynamic stall correction based on the blade element momentum(BEM)theory.The second development of AQWA is realized by FORTRAN programming language,and aerodynamic-hydrodynamic-Mooring coupled dynamics model is established to realize the algorithm solution of the model.Finally,the 6 degrees of freedom(DOF)dynamic response of single barge platform and barge array under extreme sea condition considering the coupling effect of wind and wave were observed and investigated in detail.The research results validate the feasibility of establishing barge array floating wind farm,and provide theoretical basis for further research on new floating wind farm.

Numerical Simulation on Floating Behavior of Buoyancy Tank Foundation of Anemometer Tower

The intact stability and damage stability of a model of an anemometer tower with buoyancy tank foundation are computed by the finite element software MOSES in this paper. The natural period of the anemometer tower is discussed through frequency domain analysis. The influence of a single factor, such as towing point position, wave height, wave direction and wave period, on towing stability is discussed through time domain analysis. At the same time, the towing stability under the condition of various combinations of many factors is analyzed based on the measured data of the target area. Computer simulation results show that the intact stability is preferable and the damage stability is sufficient under the condition of plenty of subdivisions. Within the scope of the buoyancy tank foundation,the higher the towing point position is, the better the stability is. Wave height has a great impact on the motion amplitude of buoyancy tank foundation, but the effect on the acceleration is not obvious; wave period has a great impact on the acceleration, while the effect on the motion amplitude is not obvious; following-waves towing is more conducive to safety than atry.

A Multidisciplinary Method for Evaluating Ship Stability

The aim of this paper is to present the main results arisen from the joint efforts of the public-private partnership in being between CCII （Centro Cultura Innovativa d＇Impresa） of University of Salento and Apphia s.r.l.. This paper will focus on the results of the core of the OBSS （on board stability system） module that, starting from the exact 3D geometry of a ship hull, described by a discrete model in a standard format, the distribution of all weights onboard and the data acquired by the system, calculates ship floating conditions （in draught, heel and trim）. The proposed approach is based on geometry meshes represented by an universally accepted file format （named OBJ） first developed by Wavefront Technologies. Demonstration of the validity of the results is done by the authors using as hull model a simple rectangular box.

Optimal Design for Main Dimensions of a 75000t Floating Production and Storage Vessel

The basis, process and results of the demonstration of the main dimensions of a 75000t floating production and storage vessel are discussed in this paper. A simple but reliable orthogonal design method is applied in the main dimension optimization. The ideas of gradual approximation and feedback from various aspects are put into effect. During the demonstration, in order to make the model tally with the actual situation, the draft design is closely related to the computational analysis, so that the demonstration model can be verified at any time; the handling of the overall system is closely related to the research of each item, which is beneficial not only to the mastery of various regularities, but also to the balance of decisions. Finally, according to the computational results and the regularities obtained from analysis, the main dimensions are determined.

Optimization of block-floating-point realizations for digital controllers with finite-word-length considerations

The closed-loop stability issue of finite-precision realizations was investigated for digital control-lers implemented in block-floating-point format. The controller coefficient perturbation was analyzed resultingfrom using finite word length (FWL) block-floating-point representation scheme. A block-floating-point FWL closed-loop stability measure was derived which considers both the dynamic range and precision. To facilitate the design of optimal finite-precision controller realizations, a computationally tractable block-floating-point FWL closed-loop stability measure was then introduced and the method of computing the value of this measure for a given controller realization was developed. The optimal controller realization is defined as the solution that maximizes the corresponding measure, and a numerical optimization approach was adopted to solve the resulting optimal realization problem. A numerical example was used to illustrate the design procedure and to compare the optimal controller realization with the initial realization.

Case Study: Hydraulic Model Experiment to Analyze the Hydraulic Features for Installing Floating Islands

The viewpoint of a river is changing as people regard the river as water-friendly space where they can enjoy and share the space beyond the simple purpose of flood control alongside the improving social level. The floating islands installation was planned featuring three islands. The river’s flow and channel stability could be changed when new structures are built in a river. Hence an analysis of the hydraulic characteristic changes should need. The hydraulic model experiment in this study sought to review the impacts of the floating islands installation on the safety of flood control and stability of river channel. This study analyzed the hydraulic features affecting the surrounding stability when installing floating islands and proposed stable floating islands layout in terms of hydraulics based on the experiment results.

Numerical simulation of multi-body floating piers to investigate pontoon stability

The objective of this study is to develop a procedure to analyze the motions of a floating pier comprised of several pontoons that are modeled as rigid bodies and connected to each other by flexible and rigid connectors.Recently,the use of floating piers has increased because of their advantages,such as faster and higher-quality construction,seismic force isolation for a full-scale mooring system,low dependence on local soil conditions and tides,ability to relocate or reconfigure the pier modules during the operation period and 75-100 years of repair-free service.A floating pier consists of a pier,access bridge,mooring system and fender system,each of which comes in many variations to suit different usages and construction considerations.The typical loads used in the design of these piers are dead loads,live loads,mooring loads,fender loads and environmental loads induced by wind,currents and waves.For numerical simulation,three types of piers are used:passenger piers,light-cargo piers and semi-heavy-cargo piers.The selected piers consist of several large pontoons joined by pivots and have a pile-based mooring system.These piers are modeled by SAP2000software as two-dimensional frames that are linked together.As the first step,each type of pier is subjected to loading,and its general behavior is assessed.According to this behavior,the major load combinations are described for the design of piers and analyzed to determine the behavior of the modules.Lastly,according to the analysis results and the safe use and stability considerations,such as the maximum draft and longitudinal gradient,the dimensions of each module in each pier type are presented.

浮式风机平台设计研究综述

大力发展风力发电技术是国家推动能源低碳转型、实现“双碳”目标的核心路径。随着陆上风电和近海风电资源开发逐渐饱和,风电开发从近岸走向深远海成为风电行业发展必然的趋势,而浮式风机平台的研发与优化是推进海上风电向深远海区域发展的关键。基于对国内外浮式风机平台发展现状的研究,进一步分析浮式风机平台设计中气动载荷、水动力载荷、系泊系统、耦合分析方法以及常用数值模拟工具的研究现状,重点梳理以提升结构稳性和降低成本为驱动的浮式风机平台的关键技术思路及构型特点,总结浮式风机平台优化的研究现状,以及其设计中存在的问题与挑战,以期为相关领域研究人员提供技术参考。

道岔区敷设橡胶弹簧浮置板轨道的动力仿真分析

道岔区剧烈的轮轨冲击引起的振动超标问题十分突出。由于良好的弹性和阻尼特性,橡胶弹簧能够有效地起到隔振作用,且与钢弹簧相比造价更低,因此在道岔区敷设橡胶弹簧浮置板轨道为解决振动超标问题提供了有效途径。为探明道岔区敷设橡胶弹簧浮置板轨道的可行性,基于车辆-轨道耦合动力学理论和有限元分析理论,建立车辆-道岔-浮置板刚柔耦合模型和环境振动计算模型。与既有研究相比,不仅分析了地铁列车直/侧逆向通过9号道岔时的安全性指标、平稳性指标和轨道结构形位变化指标,而且计算了在9号道岔区敷设橡胶弹簧浮置板轨道的减振效果。经检算,可得出以下结论:当地铁列车直/侧逆向通过敷设橡胶弹簧浮置板的9号道岔区时,轮轨垂、横向力和脱轨系数的最大值分别为166,30 kN和0.4,均在相关技术标准允许的范围内,能够确保列车的安全运营;列车直/侧逆向通过道岔时的车体垂、横向加速度和Sperling指标计算结果最大值分别为0.14,0.64 m/s^(2)和2.58 m/s^(2),满足列车平稳运行要求,在9号道岔区敷设橡胶弹簧浮置板对列车乘坐的舒适性影响不大;列车直/逆向通过道岔时的钢轨位移最大值为3.78 mm,未超过相关技术标准要求;在9号道岔区敷设橡胶弹簧浮置板减振效果达到18 dB,能够满足高减振需求。以上成果可为在道岔区敷设橡胶弹簧浮置板的相关工程及研究提供理论指导。

非线性静水恢复力影响下的海上漂浮式Spar型风机水动力特性

研究非线性静水恢复力对海上漂浮式Spar型风机的水动力特性的影响。通过解析法推导非线性静水恢复刚度系数,并使用AQWA中的非线性模型验证当前推导的解析解的准确性。考虑非线性静水恢复刚度系数,采用编程程序对Spar型浮式风机进行时域分析,将结果与线性静水恢复力作用下的运动响应进行对比,并分析Spar型浮式风机的水动力特性以及静水非线性带来的影响。结果表明:流体静力非线性对浮式风机垂荡响应有显著影响,且这种影响随浮式风机旋转运动增大而增大;在极限海况下,由静水非线性引起的垂荡、横摇和纵摇响应差异为16%~40%,显示非线性静水力在运动响应中应予以重视。

计入热效应的浮环轴承稳定性研究

以径向浮环轴承为研究对象,建立轴承压力场和温度场耦合的热流体模型。采用有限差分法联立求解Reynolds方程、能量方程、黏度和密度方程,推导出油膜扰动方程,并求解轴承的动态特性系数;分析等温、绝热和热传导3种模型对浮环轴承环速比、临界质量和失稳转速等稳定性参数的影响。结果表明:等温模型中,环速比随主轴转速的增大先上升后逐渐平缓,在绝热和热传导模型中环速比先增大后减小,呈非线性关系,绝热模型相较于热传导模型,环速比有所降低;绝热模型对轴承动态特性系数的影响要高于热传导模型;临界质量稳定区域出现在高偏心工况下,失稳转速稳定区域则出现在低偏心工况下;计入热效应后,轴承临界质量和失稳转速均减小,且绝热模型对轴承临界质量和失稳转速的影响高于热传导模型。

低频非线性浮筏隔振装置设计及特性研究

低频振动噪声影响水下装备声隐身性能。在原气囊隔振装置基础上,通过结构改进设计,使得侧向气囊能够为系统提供负刚度,通过与垂向气囊并联,设计了一种新型非线性浮筏隔振装置,提升了隔振装置的低频隔振能力。新型隔振装置由“侧向气囊-万向节-垂向气囊”非线性隔振器组和浮筏组成。分析了侧向气囊为系统提供负刚度原理,建立了非线性浮筏隔振装置六自由度动力学模型,设计了新型隔振装置样机并开展了相关性能试验。理论分析和试验结果表明,新型非线性浮筏隔振系统垂向一阶固有频率约为原系统的50%,垂向隔振性能提升了约6 dB,侧向隔振性能与原系统相当。此外,也研究了非线性浮筏隔振系统的摇摆稳定性。研究结果表明,在重载情况下,新系统能够具备较好的摇摆稳定性。

城市水环境生态修复技术研究进展

随着我国城镇化进程的不断加速发展,生活、工业污水排放量逐年增加,城市水环境问题正变得愈发突出。近几年,生态修复技术作为一种绿色环保、可持续的水处理工艺,被逐渐应用于城市水环境的修复研究。在此基础上,综述了城市水环境生态修复技术的研究进展,主要包括生物浮岛,人工湿地、稳定塘等技术,并进一步总结了城市水环境生态修复技术的工程技术要点,讨论了水生植物在生态修复中的作用;最后对城市水环境生态修复技术的经济效益进行了分析,旨在呼吁城市水环境管理中更加重视生态修复技术的应用,以实现城市水环境的可持续发展。

High-precision gyro-stabilized control of a gear-driven platform with a floating gear tension device

This study presents an improved compound control algorithm that substantially enhances the antidisturbance performance of a gear-drive gyro-stabilized platform with a floating gear tension device.The tension device can provide a self-adjustable preload to eliminate the gap in the meshing process.However,the weaker gear support stiffness and more complex meshing friction are also induced by the tension device,which deteriorates the control accuracy and the ability to keep the aim point of the optical sensors isolated from the platform motion.The modeling and compensation of the induced complex nonlinearities are technically challenging,especially when base motion exists.The aim of this research is to cope with the unmeasured disturbances as well as the uncertainties caused by the base lateral motion.First,the structural properties of the gear transmission and the friction-generating mechanism are analyzed,which classify the disturbances into two categories:Time-invariant and time-varying parts.Then,a proportional-integral controller is designed to eliminate the steady-state error caused by the time-invariant disturbance.A proportional multiple-integral-based state augmented Kalman filter is proposed to estimate and compensate for the time-varying disturbance that can be approximated as a polynomial function.The effectiveness of the proposed compound algorithm is demonstrated by comparative experiments on a gear-drive pointing system with a floating gear tension device,which shows a maximum 76%improvement in stabilization precision.

风荷载对全潜式浮式风机拖航运动响应的影响

[目的]为了解决浮式风机拖航运输的安全问题,对全潜式浮式基础风机的拖航运动特性展开研究。[方法]针对全潜式浮式风机拖航过程,通过Moses软件建立了“全潜式浮式风机-拖缆绳-拖船”一体化拖航系统数值模型,设置了五组不同的海况对拖航过程进行计算。文章研究风速和风浪方向对全潜式浮式风机拖航运动响应的影响,并根据分析结果,提出有助于全潜式浮式风机拖航安全的建议。[结果]结果表明:相比于横摇运动,全潜式浮式风机的纵摇和垂荡运动受风速影响较为明显,风速越大,运动幅度越大;当风浪方向为90°时,风机的横摇运动受风浪方向影响较大,风浪方向为0°时,风机的纵摇和垂荡运动受风浪方向影响较大。[结论]在保证拖航过程在拖航窗口期的前提下,实际工程中建议对全潜式浮式风机采用逆风拖航的方式,以降低风机振动和共振的风险。同时,应尽量避免风向与拖航方向垂直的情况,两者垂直容易引发较大程度的横摇运动,使拖航过程较为危险。逆风拖航时,在超过平均海况的较大风速30.9 m/s下,全潜式浮式风机的运动响应及拖缆力仍能满足安全拖航的要求。

5兆瓦级V型浮式风机平台设计及稳性分析

基于静力学原理和规范要求,设计了一种搭载NREL 5 MW风机的V型半潜式平台,计算并验证了其结构完整稳性。结果表明平台设计优良合理,在工作工况和自存工况的各个倾斜轴下均能保证足够的结构稳性。自存工况时平台的最小许用重心高度为12.2 m,而实际重心高度为9.4 m,并未超出许用限值。值得注意的是,30°倾斜轴为平台危险轴,此时稳性相对较差,需要注意平台在此倾斜轴下的横倾运动。

超大型双壁钢套箱围堰整节段吊装施工关键技术

新建G3铜陵长江公铁两用大桥主跨为988 m的斜拉-悬索协作体系桥梁,主桥3#墩采用整体式圆端哑铃型承台、群桩基础。围堰采用竖向分节制作、整节段运输、现场双浮吊整节段吊装施工工艺。通过将双浮吊由常规的并行站位调整为正交站位,解决了浮吊在长江高水位、快流速、窄航道、忙航运下的抛锚定位难题,降低了吊装风险;同时辅以缜密的竖向分节,使首节围堰在自浮稳定后,围堰后续节段以“蒸笼”方式一节节接高,从而将超大型双壁钢套箱围堰在长江洪汛期间以最短的时间、最省的材料和最安全的方式拼装完成。