Effects of structural flexibility on the dynamic responses of low-height lifting mechanism for offshore wind turbine installation

Installation complexities are one of the major challenges in the floating offshore wind turbine (OWT) industry. The modern concept introduced by the SFI-MOVE project is an effort to overcome the complexities by utilizing a low-height lifting mechanism. It is common to idealize a crane in the lifting mechanism as a rigid body since the structural deflections are smaller than the responses introduced by the other system components. However, structural flexibility can play an essential role in demanding offshore operations with smaller acceptable tolerances. In this study, lifting cranes are modeled using the finite element method and simplified by implementing equivalent 3D beam elements. Dynamic analysis is performed for various environmental conditions, and the responses of the crane structure and the OWT are calculated for each load case. This research reveals that crane structure flexibility influences the relative motion between a floating spar buoy and an OWT during mating operations. Crane structural flexibility contributes significantly to the OWT rotations. In addition, the response deviation between using rigid and flexible cranes increases as the excitation force increases. Therefore, it is recommended to consider the crane structural flexibility in the calculation when strict installation tolerances are needed.     

Underactuated control and analysis of single blade installation using a jackup installation vessel and active tugger line force control

The assembly and installation costs account for a large share in the overall expenditures of an offshore wind farm project. Single blade installation is suitable for large scale wind turbines due to the lower crane capability requirement and lower transportation time. By introducing active tension control on the tugger lines, an automatic single blade installation approach can accomplish operations in higher sea states, reduce the waiting-on-weather time, and improve the operational efficiency. Compared to early research, a more complicated control objective is achieved in this paper, i.e., a two-tugger-line configuration is applied to stabilize the suspended blade in three degrees of freedom during crane rotation and blade root-hub mating processes. The pulleys on the crane boom, i.e., the ends of the tugger lines, are assumed to be fixedly placed, resulting in tugger line time-varying inclinations. A novel backstepping-like controller is designed and proved. It is able to stabilize the blade around its equilibrium and make it track the desired path. Sensitivity studies are conducted to evaluate the influence of the tugger line inclinations. In addition, the influence of the installed blades on a three-blade horizontal wind turbine with a monopile foundation is discussed. The proposed active control setup improves the installation success rate and reduces the risks for blade impacts that may occur during mating.     

35t×4/62m万能杆件组拼式跨桥龙门吊的设计和安装

中山市35号路长江大桥两个不对称外倾的拱肋构成了一个蜿蜒起伏、翻腾向上的动感钢环,通过缕缕钢丝轻轻挽起曲线形的桥身,别致的构思,优美的造型却给结构安装提出了新的难题。采用万能杆件组拼大型的跨桥门吊,把整个桥梁结构揽入掌中,较好的解决了蝴蝶拱桥各个构件空中吊装定位的问题。本文主要介绍该门吊的结构选型、设计计算和安装工艺。     

高精度水下导航定位技术在考古打捞中的应用

高精度水下导航定位技术已被广泛应用于水下工程.但在考古打捞中的应用还很少.结合某考古打捞工程,分析考古打捞的技术特点,阐述控制系统、使用设备、设备安装调试、作业过程、以及可能存在的主要问题等,全面介绍高精度水下导航定位技术在考古打捞中的应用.     

A review of the effect of a／W ratio on fracture toughness （Ⅰ）—experimental investigation in EPFM

Many experimental investigations have previously been performed and recently done on different shipbuilding structural steels where the specimens size and crack depth/specimen width (a/W) were varied. A series of interesting results have been gained. It is worthwhile to have a review on the effect of a/W ratio on fracture toughness, and further theoretical analysis is necessary. In this paper, experimental work in elasticplastic fracture mechanics (EPFM) was discussed. Tests had been carried out on 10 kinds of strength steels. Results showed that J _i and δ₁ values increased with decreasing a/W when a/W<0.3 for three-point bend specimens and that shallow crack specimens which have less constrained flow field give markedly higher values of toughness than deeply notched specimens. However, for a/W>0.3, the toughness was found to be independent of a/W. Slip line field analysis shows that for shallow cracks, the hydrostatic stress is lower than that from standard deeply cracked bend specimen which develops a high level of crack tip constraint, provides a lower bound estimate of toughness, and will ensure an unduly conservative approach when applied to structure defects especially if initiation values of COD/J-integral are used.     

A review of the Effect of α/W ratio on fracture toughness （Ⅱ） experimental investigation in LEFM

In part I of this series, experimental investigation in EPFM （elastic-plastic fracture mechanics） had been discussed. In this paper, experimental investigation in LEFM （ linear elastic fracture mechanics） is given. Fracture toughness tests had been carried out on three different strength steels, using both through-cracked specimens with different α/W ratio and semi-elliptical cracked specimens with variable crack size and shape. Results show that the fracture toughness KIC increases with decreasing α/W when α/W 〈 0.3 for three-point-bend specimens, and that for α/W 〉 0.3, it is independent of α/W. Shallow crack specimens, both through-cracked and surface-cracked, gave markedly higher values than deeply notched specimens. However, the effect of crack shape on fracture toughness is negligible. Results also show that the LEFM approach to fracture is not tenable for design stresses where αc is often very small, far less than 2.5 （ KIC/σy）^2.     

Learning tracking controllers under unknown disturbances for the installation of rigid and flexible structures

During the installation operations of underwater structures, offshore structures such as semisubmersibles, the steady nonlinear hydrodynamic force due to the ocean current, the tidal current, and the hydrodynamic interaction between structures are regarded as major disturbances. Generally, it is difficult and very expensive to collect information about these disturbances in advance, although such knowledge would be important and necessary for precise installation. Because of this situation, we have proposed a learning tracking controller (LTC) for automated tracking/docking operations of offshore structures. The LTC can be operated without any information about current, and can be applied to the installation problem of flexible structures whose flexibility cannot be ignored. In order to confirm the effectiveness of the LTC, basin tests were carried out using experimental models with an unknown current. Two types of basin experiment were executed using an ultrasound ranging system and thrusters. One was trajectory tracking of a semisubmersible, and the other was the precise mating of flexible underwater structures. In both cases the LTC showed good performance, and in the latter case in particular, two flexible models were successfully made to track the given trajectory and dock to the docking targets with an accuracy of ±5 mm, after the trajectory had been tracked six to seven times for learning purposes. No elastic responses were excited in the flexible model. Received for publication on Dec. 1, 1999; accepted on March 13, 2000     

港口起重机金属结构件的焊接应力控制方法

针对港口起重机主要部件的结构特点、工作环境和受载情况,分析控制焊接结构件焊接应力的重要性;以箱形截面吊臂为例,介绍其焊接工艺及焊接前后的辅助处理方法。这些工艺、方法的正确运用有助于控制港口起重机的主要结构件的焊接应力。     

半潜式钻井平台推进器水下安装工艺研究与分析

推进器在半潜式钻井平台的定位系统中起到提供动力定位所需推力的作用。大型的推进器通常都需要进行水下安装,而水下安装推进器的风险及其大。所以,推进器的水下安装工艺显得尤为重要,既要考虑到各个厂家推进器的安装程序和技术要求,同时又要考虑安装场地的实际情况,只有将两者有机地结合起来,才能够保证在安全、快速、经济的情况下圆满完成推进器的水下安装工作。     

深水软基半圆体弧线段安装施工关键技术

根据半圆体结构特点和现场工况,对起重船安装半圆体工艺进行技术创新,介绍施工工艺关键技术。解决了弧线段安装中遇到的问题,为类似工程提供一定的参考依据。     

高桩码头构件吊装新技术

在高桩码头预制构件安装中,传统工艺一般都采用起重船施工。在某些工程中,天气恶劣、海况复杂,在利用起重船安装时,受风浪等因素的影响,施工进度缓慢,配套船机投入大、利用率低、成本大,安全风险高。主要介绍一种码头预制构件吊装技术,转水上施工为陆上施工。采用该技术安装码头预制构件,作业时间长,安装速度快,风险小,精度高,造价低,在外海无掩护海域作业时尤为明显。     

鱼雷型无人水下航行器鲁棒控制器设计

针对鱼雷型无人水下航行器航行过程中外界环境干扰复杂,航行体系统内部干扰严重的特殊问题,并同时考虑系统参数剧烈变化造成的系统不确定性,设计纵向鲁棒控制器。该控制器采用 PID控制器作为标称控制器控制标称受控对象。利用非线性状态观测器估计受控系统中的不确定性和外界环境干扰,并通过补偿控制律补偿,使整个闭环控制系统具有鲁棒性。将此方法应用于鱼雷型无人水下航行器鲁棒控制器的设计,可大大提高鱼雷型无人水下航行器航行过程中对干扰的抑制和对不确定性的适应能力,保证鱼雷型无人水下航行器在整个航行过程中的姿态稳定,以保证航行任务的完成。     

潜艇机械噪声控制技术综述

机械噪声是潜艇低速巡航时最主要的噪声源,有效控制机械噪声是潜艇实现安静化的首要环节。本文从潜艇机械设备选用评估、设备布置与弹性安装、管路系统布置和设计、基座和壳体设计、消声瓦隔声处理等几个方面评述国内外潜艇机械噪声控制技术的现状及存在的主要问题,并提出实现机械噪声定量设计与控制的关键问题。     

Application of H∞ filtering in the initial alignment of strapdown inertial navigation system

In this paper , the principle of H∞ filtering is discussed and H∞ filter is constructed, which is used in the initial alignment of the strapdown inertial navigation systems(SINS). The error model of SINS is derived. By utilizing constructed H∞ filter, the filtering calculation to that system has been conducted. The simulation results of the misalignment angle are given under the condition of unknown noises. The results show that the process of alignment with H∞ filter is much faster and with excellent robustness.     

海洋平台振动模糊控制研究

在过去的三十年里,模糊逻辑控制在结构振动控制中得到了广泛的研究和应用.模糊逻辑控制具有很强的鲁棒性并且能够有效地处理非线性以及被控系统和外载荷的不确定性和不精确性,本文对于海洋平台振动模糊控制进行了研究.通过模态阻尼比的不确定性显示了模糊控制的鲁棒性,研究表明海洋平台的振动模糊主动控制是有效的、可行的,并且提高了平台的适用性和生存性.本文的方法毫无疑问为今后的海洋平台振动控制提供了一条新的途径.     

Daily and seasonal variations of the partial pressure of CO2 in surface seawater along Belgian and southern Dutch coastal areas

The variations of the partial pressure of CO₂ (pCO₂) and related parameters were determined in surface seawater along the Belgian coast, from January 1995 to June 1996, at both daily and seasonal time scales. The distribution of pCO₂ in this area is regulated by river input from the Scheldt, biological activity and hydrodynamics. The contribution of each of these processes varies as a function of the considered time scale: (i) the daily variation of pCO₂ depends on the tide although modulated by the biological diel cycle; (ii) the seasonal variation of pCO₂ depends on the input from the Scheldt and the seasonal variations of phytoplanktonic biomass. During winter, the plume of the river Scheldt is oversaturated in pCO₂ with respect to the atmosphere. During spring and summer, phytoplankton blooms occur both in the lower Scheldt estuary and in the river plume and may lead to undersaturation of pCO₂ in the easternmost area of the river plume. However, the degradation of phytoplankton induces oversaturation of pCO₂, in the westernmost area of the plume. Furthermore, the inter-annual variation of pCO₂ depends partly on the fluctuations of the discharge of the Scheldt. Our preliminary results strongly suggest that, on an annual basis, the Scheldt plume behaves as a net source of CO₂ to the atmosphere.     

H∞ Robust Fault-Tolerant Controller Design for an Autonomous Underwater Vehicle＇s Navigation Control System

In order to improve the security and reliability for autonomous underwater vehicle (AUV) navigation, an H_∞ robust fault-tolerant controller was designed after analyzing variations in state-feedback gain. Operating conditions and the design method were then analyzed so that the control problem could be expressed as a mathematical optimization problem. This permitted the use of linear matrix inequalities (LMI) to solve for the H_∞ controller for the system. When considering different actuator failures, these conditions were then also mathematically expressed, allowing the H_∞ robust controller to solve for these events and thus be fault-tolerant. Finally, simulation results showed that the H_∞ robust fault-tolerant controller could provide precise AUV navigation control with strong robustness.     

水下机器人结构形式及其发展趋势分析

水下机器人的结构是影响其运动性能的重要因素。按框架式、刚性外壳仿生式、柔性外壳仿生式、球形、滑翔式和链式6类结构,对水下机器人结构形式的发展现状和存在的关键技术问题进行分析。重点分析各类结构的驱动速度、加装载重和运动灵活性,以及在水下环境中的运动性和适应性。研究结果表明,水下机器人的结构形式正朝着高度柔性化、整体与局部结构之间高度变形化和多体结构可分离化的方向发展。     

Expert S-surface control for autonomous underwater vehicles

S-surface control has proven to be an effective means for motion control of underwater autonomous vehicles （AUV）. However there are still problems maintaining steady precision of course due to the constant need to adjust parameters, especially where there are disturbing currents. Thus an intelligent integral was introduced to improve precision. An expert S-surface control was developed to tune the parameters on-line, based on the expert system, it provides S-surface control according to practical experience and control knowledge. To prevent control output over-compensation, a fuzzy neural network was included to adjust the production rules to the knowledge base. Experiments were conducted on an AUV simulation platform, and the results show that the expert S-surface controller performs better than an S-surface controller in environments with currents, producing good steady precision of course in a robust way.     

多变量解耦控制在潜操系统中的仿真研究

针对潜艇的水下垂直面运动,提出了一种多变量解耦自抗扰控制器的研究方案,通过仿真验证了其控制效果;在分析自抗扰控制器在低噪声控制方面存在的不足和缺陷的基础上,给出了一种独立通道控制器的设计方案,根据仿真结果,证明了方案的有效性。