考虑船舶影响的升船机结构动力特性

运用ANSYS有限元软件建立了包含塔柱、承船厢、水体、船舶、提升系统等构件的大型垂直升船机整体模型,计算分析了升船机结构的动力特性。计算结果表明:横荡、扭转、纵荡是承船厢结构低阶主要振型。厢内有船会降低承船厢系统的自振频率,其有船与无船工况下横荡自振频率分别为0. 130 9 Hz和0. 280 5 Hz;升船机整体结构低阶特征振型主要包括整体系统的横向摆动、绕竖向的扭转、纵向摆动。承船厢内有无船舶计算得到的同种振型下升船机整体结构的自振频率相差很小,表明船舶对升船机整体结构自振特性的影响不大;承船厢位置的升高会使得升船机整体结构的自振频率降低;承船厢位置的变化对升船机低阶振型影响较大,对高阶振型的影响较小。     

Super-low-frequency laser instrument for measuring hydrosphere pressure variations

The operating principle and specifications of a laser meter for measuring hydrosphere pressure variations are described in this article. The meter was designed to measure the hydrosphere pressure variations to a depth of 500 m within the frequency range of 0–1000 Hz at the level of background oscillations. Some results obtained using the apparatus under consideration when recording sea oscillations and waves of natural and artificial origin are presented.     

Time domain analysis procedures for fatigue assessment of a semi-submersible wind turbine

Long term time domain analysis of the nominal stress for fatigue assessment of the tower and platform members of a three-column semi-submersible was performed by fully coupled time domain analyses in Simo-Riflex-AeroDyn. By combining the nominal stress ranges with stress concentration factors, hot spot stresses for fatigue damage calculation can be obtained. The aim of the study was to investigate the necessary simulation duration, number of random realisations and bin sizes for the discretisation of the joint wind and wave distribution. A total of 2316 3-h time domain simulations, were performed.In mild sea states with wind speeds between 7 and 9 m/s, the tower and pontoon experienced high fatigue damage due to resonance in the first bending frequency of the tower from the tower wake blade passing frequency (3P).Important fatigue effects seemed to be captured by 1 h simulations, and the sensitivity to number of random realisations was low when running simulations of more than 1 h. Fatigue damage for the tower base converged faster with simulation duration and number of random realisations than it did for the platform members.Bin sizes of 2 m/s for wind, 1 s for wave periods and 1 m for wave heights seemed to give acceptable estimates of total fatigue damage. It is, however, important that wind speeds that give coinciding 3P and tower resonance are included and that wave periods that give the largest pitch motion are included in the analysis.     

泥浆泵舱顶部甲板减振研究

以某平台泥浆泵舱顶部甲板为研究对象，利用数值计算和振动测试结合的方法对其减振方案进行研究。设置两种泥浆泵运行工况，利用振动分析仪测量甲板上表面8个高振动测点的振动速度。利用有限元方法建立顶部甲板模型，通过模态分析和谐响应分析得到顶部甲板的前五阶固有频率和各测点振动速度-转速曲线。振动响应数值计算结果和测试结果吻合，验证数值模型可靠性。分析发现顶部甲板固有频率远离激励频率，结构振动属于强迫振动，主要由泥浆泵输出管系的管托固定在刚度较弱的顶部甲板纵骨引起。甲板振动速度不符合规范要求，因此提出两种增加刚度的减振措施。通过谐响应分析重新计算测点的振动速度响应，结果满足规范要求。研究结果为船体局部结构设计和减振设计提供参考。     

Design optimization of a TetraSpar-type floater and tower for the IEA Wind 15 MW reference wind turbine

We present an optimization study for the conceptual design of wind turbine floaters of the TetraSpar type. The optimization variables include all geometric dimensions of the floater, keel, mooring lines and tower design. A gradient based optimization method is applied to a mass proportional objective cost function. The objective function accounts for the different weight components of the floater, including secondary steel, the wind turbine tower, and the mooring system. A frequency domain response method is utilized, so that each design evaluation also takes into account the dynamic response for 12 wind speeds with associated wave conditions. Nineteen constraints are applied for static and dynamic response, natural frequencies, and fatigue at the bottom of the tower. Two reference designs are presented, namely one with a soft–stiff tower and one with a stiff–stiff tower. Due to the anti-phase coupling of the floater pitch and tower vibration, the soft–stiff tower needs a stronger floater stiffness in pitch. This design thus has a larger water plane area moment than the more compact stiff–stiff floater, which is found to be the least economical. A constraint analysis is next presented based on Lagrange multipliers and a relative cost index. We find that the strongest cost influence is exerted by the 3P tower frequency constraint for the stiff-stiff and soft-stiff designs. Finally, a third design variant with a free optimizable tower frequency is introduced. This design is found to be 11% cheaper than the soft–stiff design and highlights the potential cost savings of tower designs within the 3P region.     

基于重根模态特性的舵桨电机振动

针对某型船全回转舵桨电机出现的振动超标问题,通过振动位移传递分析发现电机-基座系统存在一对重根模态,且系统在1/2倍电磁频率附近产生共振。采用振动特性实时测试技术,对振动传递路径进行灵敏度分析,以识别电机振动源。基于PATRAN的模态分析结果,验证了电机-基座结构在17Hz附近存在一对重根模态,并对电机安装基座开展优化设计以避开电机-基座系统的共振频率。结果表明,电机顶部的振动速度从22 mm/s降低至8 mm/s。将有限元法与振动实测技术相结合,可有效解决舵桨电机的振动问题,对立式电机、全回转舵桨推进器等结构的设计与安装及类似振动故障问题的解决,具有一定指导意义。     

Rigid moorings in shallow water: A wave power application. Part I: Experimental verification of methods

Experimental work carried out at 1:60 scale in a wave flume assessed the pitch motion and anchor loading of 3 articulated tower installations in 50 m water depth while being exposed to north Atlantic storms with H_s of 15.2 m and T_p of 18.4 s. The three installations differ only in that their mass and buoyancy characteristics provide a natural period in pitch at equilibrium of 13 s, 20 s and 34 s respectively. It is verified that the dominant behaviour can be simulated by a relatively simple mathematical model, allowing the critical parameters of peak anchor loads and pitch angles to be calculated and extrapolated to full scale. It is demonstrated from the experimental and simulation results that the mass characteristics of a non surface piercing tower can be used to offset some of the challenges of moving to shallow water. If done correctly, it is possible to keep horizontal anchor loads under control and reduce vortex-induced transverse loading at the expense of increased pitch motions. Overall, the use of articulated tower installations in water depths of 50 m would appear to be technically feasible, even in exposed areas. The limitations on the size of such structures and the consequences of the resulting pitch accelerations and induced anchor loads are the subject of further study. It is proposed that the model verified herein can be used to further assess their potential at delivering viable wave power position mooring systems.     

Dynamics of an ultra-deepwater mooring line with embedded chain segment

A code is developed to study the mooring tensions on a line with an embedded segment considered, based on lumped mass method. The accuracy of this code is validated by published results. The influence of soil-chain interaction on the static and dynamic behaviour of a 1500 m mooring line is studied under two operational situations: shallow embedded taut mooring line and deep embedded semi-taut mooring line. The shallow case has an embedded depth setting as 10 m under seafloor, while the embedded depth is 20 m for deep water. To study the influence of soil on mooring dynamics, three simplified cases without soil force considered are investigated and the results are compared with the dynamics of embedded mooring. These three cases include: i) Case MA has the same spread distance to embedded mooring anchored on seafloor; ii) Case MB is anchored on seafloor and it has the same pretension with embedded mooring; iii) Case MC is anchored to the same point to the embedded mooring but the soil force is not considered. Furthermore, the effects of effective width parameters of tangential and bearing soil resistance on mooring dynamics are also discussed. In this work, three different oscillations are forced on fairlead to study the mooring dynamics, which are low frequency oscillation, hybrid oscillation (low frequency and wave frequency) and wave frequency oscillation.     

MTMD to increase fatigue life for OWT jacket structures using Powell's method

The Powell's method was developed to determine the optimal stiffness and damping of multi-tuned mass dampers (MTMD) in offshore wind turbine (OWT) support structures under fatigue loads. Numerical examples indicated that the Powell's method results are always better than those using MTMD formulations. With the exception of the blade passing (3P) frequency, it was found in this work that a positive integer (n) multiple of the 3P frequency will also result in a large wind-induced vibration, which can be excited by the frequency of the first structural vertical rotation mode and will cause significant fatigue damage. The first translation mode TMD installed at the tower top is efficient to increase fatigue life at the tower and brace connections, but it cannot reduce fatigue damage at the column and brace connections below the platform. The second translation mode TMD can reduce fatigue damage resulting from large wave loads and thus increase the fatigue life of the braces and columns. The mode-3 TMD with a reduction in the 3(3P) vertical rotation can effectively increase the fatigue life of the braces and columns. Thus, the appropriate use of these TMDs can be effective for the fatigue problem of OWT support structures.     

Model test investigation of a spar floating wind turbine

Several floating wind turbine designs whose hull designs reflect those used in offshore petroleum industry have emerged as leading candidates for the future development of offshore wind farms. This article presents the research findings from a model basin test program that investigated the dynamic response of a 1:50 scale model OC3 spar floating wind turbine concept designed for a water depth of 200 m. In this study the rotor was allowed to rotate freely with the wind speed and this approach eliminated some of the undesirable effects of controlling wind turbine rotational speed that were observed in earlier studies. The quality of the wind field developed by an array of fans was investigated as to its uniformity and turbulence intensity. Additional calibration tests were performed to characterize various components that included establishing the baseline wind turbine tower frequencies, stiffness of the delta type mooring system and free decay response behaviour. The assembled system was then studied under a sequence of wind and irregular wave scenarios to reveal the nature of the coupled response behaviour. The wind loads were found to have an obvious influence on the surge, heave and pitch behaviour of the spar wind turbine system. It was observed from the experimental measurements that bending moment at the top of the support tower is dominated by the 1P oscillation component and somewhat influenced by the incoming wave. Further it was determined that the axial rotor thrust and tower-top shear force have similar dynamic characteristics both dominated by tower’s first mode of vibration under wind-only condition while dominated by the incident wave field when experiencing wind-wave loading. The tensions measured in the mooring lines resulting from either wave or wind-wave excitations were influenced by the surge/pitch and heave couplings and the wind loads were found to have a clear influence on the dynamic responses of the mooring system.     

Monitoring of suction bucket jackets for offshore wind turbines: Dynamic load bearing behaviour and modelling

Suction bucket foundations for offshore wind turbines (OWT) have considerable advantages compared to conventional foundation types: Due to the installation process with dead weight and applied negative pressure, noise from pile driving can be completely avoided. In addition, the installation process of the whole substructure, consisting of the buckets connected to the jacket, can be carried out in one work step, which increases efficiency. A prototype of the suction bucket jacket was installed in the wind park ‘Borkum Riffgrund 1’ (North Sea) in August 2014. Due to the pre-installed and comprehensive measuring system, it was possible to monitor all installation and operating phases. The data analysis of a storm event show an amplitude and frequency-dependent behaviour of the soil stiffness and the suction bucket foundation without wind turbine. In the frequency range of the first and second eigenfrequency (0.2 Hz < f < 5 Hz), the system behaves linearly. Here, the Frequency Domain Decomposition is used for identification and monitoring. For the lower frequency band (0.05 Hz < f < 0.2 Hz) where higher forces and displacements occur, a non-linear multilayer perceptron is chosen to model the non-linear relations between measurements. By applying two mathematical models for the relevant frequency ranges, all the information from the measurement data can be used for system identification and novelty detection under varying environmental conditions.     

Dynamic impedances and load carrying mechanism for skirted foundations

Dynamic impedances of foundations include dynamic stiffness and damping which have important effect on the internal forces in the structure. In some cases, such as offshore wind turbines, the influence of the foundation impedances on the system's natural frequency and overall damping could potentially have a significant effect on the fatigue life of the structure. The vertical, horizontal and rocking impedances of a skirted foundation (also termed bucket foundation in offshore wind industry) embedded in a fully saturated poroelastic seabed are addressed in this paper. The vertical impedance is most relevant for jacket foundations supported on three or four bucket foundations, while horizontal and rocking impedances are applicable for mono-bucket foundations. The dynamic vibration problems are solved semi-analytically with the help of dual integral equations and Green's functions. Numerical results for dynamic impedances are obtained; damping ratio are also obtained to show the importance of radiation damping for bucket foundations, even at very small excitation frequencies. The influence of length-to-radius ratio, Poisson's ratio, permeability of soil, excitation frequency and thickness-to-radius ratio on the impedances are also studied. Besides, the dynamic load sharing among the top plate, bucket shaft and bucket tip is obtained for vertical load, horizontal load and moment to shed light on the carrying mechanism of bucket foundation at dynamic working loads. It is found that for a rigid bucket foundation, even when the length-to-radius ratio is small (e.g. l/a = 1.0), most of the loads are carried by the shaft, while the top plate and tip of the bucket take only a small portion of the loads. The results of this study will be helpful for understanding the load-carrying mechanism of offshore bucket foundations for normal operation conditions.     

Estimation of natural frequencies and damping using dynamic field data from an offshore wind turbine

The dynamic characteristics of offshore wind turbines are heavily affected by environmental loads from wave and wind action and nonlinear soil behaviour. In the design of the monopile structures, the fatigue load due to wind and wave loading is one of the most important problems to consider. Since the fatigue damage is sensitive to the foundation stiffness and damping, increasing the accuracy of analysis tools used in the design and optimization process can improve the reliability of the structure and reduce conservatism, thereby leading to a more cost-efficient design. In this context, analysis of field data is important for calibrating and verifying purposes. This paper presents analysis of measured accelerations and strains from a wind farm in the North Sea with monopile foundations. Field data during idling conditions, collected over long periods of operation, are analysed and the natural frequencies are determined, and damping is estimated. The measured natural frequencies are compared to calculated values using an aero-servo-hydro-elastic code, showing a good agreement in the frequency range below 2 Hz. Variation of the natural frequencies with intensity of loading may indicate effect of soil nonlinearity on the overall OWT response. Since the first natural bending modes have the largest potential to mobilize soil reactions, they are of primary interest in this context. The effect of load (wave, wind and dynamic bending moment) on the first natural frequency is investigated using different analysis techniques in the frequency domain and time domain. A clear correlation between load level and first natural frequency is demonstrated. A simple nonlinear SSI model of the tower/soil system is employed to numerically investigate the observed changes in the measured first natural frequency with the level of loading and increased overall damping. The simulated results reproduce the general trends in the observed reduction in the first natural frequency and increased damping ratio with the load level. However, the effect of the load level is less than that observed in the measurements, indicating contribution also from other factors than soil nonlinearity.     

舱壁打孔的环肋圆柱壳振动性能分析

为研究舱壁打孔对结构振动性能的影响,以环肋圆柱壳为研究对象,采用有限元法,计算结构在不考虑开孔加强结构的条件下,改变圆形孔的大小、位置、数量以及含圆形孔的舱壁数量时的均方法向速度级,得到不同工况下整个结构的均方法向速度级频率响应曲线。数值计算结果的比较和分析表明:激振频率在150～350Hz时,4种工况对模型均方法向速度级影响不大;350～1 000 Hz时,在部分激振频率下,4种工况对模型均方法向速度级的影响变大。可见舱壁开孔在满足工程需求的同时,也可有效减少艇体质量,但同时也会一定程度地改变结构振动特性,须在潜艇实际设计中予以考虑。     

Ultimate load analysis of a 10 MW offshore monopile wind turbine incorporating fully nonlinear irregular wave kinematics

Loads from storm waves can in some cases be dimensioning for offshore wind turbine substructures. Accurate determination of nonlinear wave loads is therefore important for a safe, yet economic design. In this paper, the fully nonlinear waves, realized by a fully nonlinear potential wave solver OceanWave3D, are incorporated into coupled aero-servo-hydro-elastic simulations for a reduced set of wave-sensitive design load cases, in comparison with the widely used linear and constrained waves. The coupled aero-elastic simulations are performed for the DTU 10 MW reference wind turbine on a large monopile at 33 m water depth using the aero-elastic code HAWC2. Effect of the wave nonlinearity is investigated in terms of the ultimate sectional moments at tower bottom and monopile mudline. Higher ultimate moments, 5% at tower bottom and 13% at monopile mudline as maximum, are predicated when the nonlinear waves are used. It could be explained by the fact that the extreme nonlinear waves, that are close to the breaking limit, can induce resonant ringing-type responses, and hereby dominate the ultimate load responses. However, the constrained wave approach shows marginal difference compared to the standard linear wave approach. It can be concluded at least for the present configuration that the industry standard approaches (linear and constrained wave approach) underestimate the ultimate load responses on offshore wind turbines in severe sea states.     

爆破振动对宋家湾隧道施工的影响

为评价在生产常规作业阶段爆破施工方式对隧道结构的影响,对宋家湾隧道爆破振动进行监测,以获取主振频率,最终以频率和振动速度2个指标评估隧道爆破作业振动效应。本次爆破的最大振动速度为3.1cm/s,主振频率范围为27.34～70.31Hz,最大振动速度远小于国家标准。可知对隧道支护结构影响有限频率范围为27.34～70.31Hz,远高于隧道的自振频率（一般在3～9Hz范围内）,不会出现共振放大现象。     

高速船尾部喷水推进局部振动分析

针对高速船尾部采用喷水推进装置的局部振动问题,建立了船体尾部包含喷水推进泵的有限元模型。考虑附连水质量的影响,将船体尾部离散成甲板,底板,喷水推进泵,尾板等局部结构,采用规范经验公式估算以及有限元分析的方法分别对各局部结构的板、板格、板架进行固有频率计算,将其结果与轴频和叶频激励频率进行储备频率校核,判断尾部采用喷水推进装置在振动问题上是否满足规范标准,并为下一步的船体设计提供参考。     

Effect of mass ratio on hydrodynamic response of a flexible cylinder

The effect of the mass ratio on the flow-induced vibration (FIV) of a flexible circular cylinder is experimentally investigated in a towing tank. A Tygon tube with outer and inner diameters of 7.9 mm and 4.8 mm, respectively, was employed for the study. The tube was connected to a carriage and towed from rest to a steady speed up to 1.6 m/s before slowing down to rest again over a distance of 1.6 m in still water. Reynolds number based on the cylinder’s outer diameter was 800–13,000, and the reduced velocity (velocity normalized by the cylinder’s natural frequency and outer diameter) spanned from 2 to 25. When connected, the cylinder was elongated from 420 mm to 460 mm under an axial pre-tension of 11 N. Based on the cylinder’s elongated length, the aspect ratio (ratio of the cylinder’s length to outer diameter) was calculated as 58. Three mass ratios (ratio of the cylinder’s structural mass to displaced fluid mass, m*) of 0.7, 1.0, and 3.4 were determined by filling the cylinder’s interior with air, water, and alloy powder (nickel-chromium-boron matrix alloy), respectively. An optical method was adopted for response measurements. Multi-frequency vibrations were observed in both in-line (IL) and cross-flow (CF) responses; at high Reynolds number, vibration modes up to the 3^rd one were identified in the CF response. The mode transition was found to occur at a lower reduced velocity for the highest tested mass ratio. The vibration amplitude and frequency were quantified and expressed with respect to the reduced velocity. A significant reduced vibration amplitude was found in the IL response with increasing mass ratios, and only initial and upper branches existed in the IL and CF response amplitudes. The normalized response frequencies were revealed to linearly increase with respect to the reduced velocity, and slopes for linear relations were found to be identical for the three cases tested.     

船舶上层建筑振动的最优控制分析

本文讨论了最优控制理论在船舶上层建筑振动控制中的应用。文中将船体和上层建筑简化为相应的船体梁和上层建筑梁模型，并将上层建筑梁的振动响应处理为支承激励下的响应。用模态分析法得到船体梁和上层建筑梁的动力特性（固有频率和固有振型），再用模态（振型）叠加法得到受控前上层建筑顶端的稳态动力响应，接着根据最优控制理论，设定目标函数，求解Riccati方程，得到主动控制力，将其作用在上层建筑梁的顶部，用模态（振型）叠加法得到受控后上层建筑梁顶部的稳态动力响应。以一条50000吨的油船为算例进行数值仿真，受控后上层建筑顶部的稳态振动位移减小了30％，可见最优控制在船舶上层建筑的振动控制中是可行的和有效的。     

大型舰船总振动固有频率近似计算研究

基于我国舰船的设计规律,提出了一种精确计算大型舰船总振动固有频率所需初始数据的虚拟设计方法。以某舰船为原型,设计出177～200 m船长范围内系列虚拟船型主尺度及船体等值梁数据。计算出系列舰船虚拟船型船体的总振动固有频率值,扩展了船体总振动固有频率近似公式中统计系数的统计样本范围,利用扩展的统计样本数据提出了适合估算大型舰船船体总振动固有频率的经验公式。