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1.
The response of a long flexible cylinder excited by random waves in a large model basin was investigated. The linear and non-linear physical mechanisms associated with the wave–cylinder interaction were analysed using system identification and modelling techniques. A third-order frequency domain Volterra model and its orthogonalized counterpart were used to analyse the relationships between wave elevations at various locations in the vicinity of the cylinder and cylinder acceleration data at various cylinder longitudinal locations. It was found that linear mechanisms dominate, particularly at the frequency band where the majority of the wave energy is located. At higher frequencies, the cubic component of the Volterra model is the main contributor to the total model coherence, i.e. the fraction of the measured output power that can be approximated by the model output, whereas the quadratic component's contribution to the total model coherence was in general quite small. This process of identification and quantification of the non-linear mechanisms of the unknown physical system can lead to the design of improved parametric models for the cylinder response, which should by design simulate non-linearities such as the ones identified by the Volterra model. The estimated linear and non-linear Volterra transfer functions were also used to predict the cylinder acceleration under excitation inputs not used in the estimation of the model transfer functions. The good match between predicted and measured output auto-power spectra suggests that the estimated transfer functions are indeed true models of the underlying physical mechanisms of the interaction. However, the latter can only be achieved if a minimum number of data segments, as determined by an error analysis involving modelling and prediction errors, is used in the estimation of the Volterra transfer functions. 相似文献
2.
Developments in the study of wave forces and construction techniques in deep water by the offshore oil industry have increased the use of marine terminals at deep water locations. A thorough understanding of moored ship dynamics when subjected to waves, wind and current combined with the use of flexible mooring lines would help to design berthing terminals for exposed areas. In this paper, the three dimensional problem of wave interactions with a barge moored to a single point is dealt with, based on the finite element method. The effect of flexibility of the mooring line and the point of mooring on the response of the barge as well as the mooring line tension is investigated. The paper compares the numerical results with model tests carried out on a barge moored to a fixed support under regular and random waves in head sea. The effect of stiffness of the mooring line on the barge response for different mooring points is discussed, which would be useful for the designers. The effect of viscous damping is also considered. The analytical results are in good agreement with the experimental results in both regular and random waves. 相似文献
3.
The development of a definitive predictive model that accurately accounts for the nonlinear hydrodynamics and structural response behavior observed in arrays of closely spaced risers on deep water structures will require a more detailed understanding of this fluid–structure interaction. Through the analysis and interpretation of data from model basin tests on single and paired tandem cylinder configurations this study is directed at uncovering the nature of some aspects of this nonlinear response behavior using an orthogonal third-order Volterra technique that can delineate between linear, quadratic and cubic nonlinear frequency dependent behavior. As part of the analysis procedure the data was organized in input–output pairs that would provide logical groupings of the measured quantities. The data pairs presented in this study include wave excitation and inline cylinder displacement, wave excitation and transverse cylinder displacement, wave excitation and inline reaction force, and, upstream cylinder and downstream cylinder response. This information is presented in terms of spectral and coherence plots. The single cylinder data is presented as a means to contrast the behavior of the tandem cylinders. Both configurations were analyzed at two different pretensions adding another dimension to this investigation. It is shown that although a primary variable such as displacement may be more easily measured, pretension and force measurements provide an important key to our understanding of this difficult problem. 相似文献
4.
港口内靠码头系泊船运动的计算 总被引：11，自引：1，他引：11
本文以英国南海岸处Ｓｈｏｒｅｈａｍ港内系泊船为例，研究了港口内靠码头系泊船运动的数值计算问题。该船的实船实验和模型实验已经完成，为验证本文计算结果提供了依据。运动方程在时域内求解。在计算船体脉冲响应函数时，引入了船体阻尼系数在频率很低时的渐近表达式和一迭代算法。分析了港内共振波浪和其对船体的作用力。讨论了靠码头系泊船运动的非线性特征。计算结果与实验结果符合很好。 相似文献
5.
For the study of the parametric vibration response of submerged floating tunnel tether under random excitation,a nonlinear random parametric vibration equation of coupled tether and tube of submerged floating tunnel is set up.Subsequently,vibration response of tether in the tether-tube system is analyzed by Monte Carlo method.It may be concluded that when the tube is subjected to zero-mean Gaussian white noise random excitation,the displacement and velocity root mean square responses of tether reach the peak if the circular frequency of tube doubles that of tether;the displacement and velocity root mean square responses of tether increase as the random excitation root mean square increases;owing to the damping force of water,the displacement and velocity root mean square responses of tether decrease rapidly compared with tether in air;increasing the damping of the tether or tube reduces the displacement and velocity root mean square responses of tether;the large-amplitude vibration of tether may be avoided by locating dampers on the tether or tube. 相似文献
6.
A fuzzy logic controller for ship path control in restricted waters is developed and evaluated. The controller uses inputs of heading, yaw rate, and lateral offset from the nominal track to produce a commanded rudder angle. Input variable fuzzification, fuzzy associative memory rules, and output set defuzzification are described. Two maneuvering situations are evaluated: track keeping along a specified path where linearized regulator control is valid; and larger maneuvers onto a specified path where nonlinear modeling and control are required. For the track keeping assessment, the controller is benchmarked against a conventional linear quadratic Gaussian (LQG) optimal controller and Kalman filter control system. The Kalman filter is used to produce the input state variable estimates for the fuzzy controller as well. An initial startup transient and regulator control performance with an external hydrodynamic disturbance are evaluated using linear model simulations of a crude oil tanker. A fully nonlinear maneuvering model for a smaller product tanker is used to assess the larger maneuvers 相似文献
7.
The application of a Smoothed Particle Hydrodynamics (SPH) model to simulate the nonlinear interaction between waves and a moored floating breakwater is presented. The main aim is to predict and validate the response of the moored floating structure under the action of periodic waves. The Euler equations together with an artificial viscosity are used as the governing equations to describe the flow field. The motion of the moored floating body is described using the Newton’s second law of motion. The interactions between the waves and structures are modeled by setting a series of SPH particles on the boundary of the structure. The hydrodynamic forces acting on the floating body are evaluated by summing up the interacting forces on the boundary particles from the neighboring fluid particles. The water surface elevations, the movements of the floating body and the moored forces are all calculated and compared with the available experimental data. Good agreements are obtained for the dynamic response and hydrodynamic performance of the floating body. The numerical results of different immersion depths of the floating body are compared with that of the corresponding fixed body. The effects of the relative length and the density of the structure on the performance of the floating body are analyzed. 相似文献
8.
Seismic load has a significant effect on the response of a free spanning submarine pipeline when the pipeline is con-structed in a seismically active region. The model experiment is performed on an underwater shaking tahle to simulate the response of submarine pipelines under dynamic input. In consideration of the effects of the terrestrial and submarine pipeline , water depth, support condition, distance from seabed, empty and full pipeline, and span on dynamic response, 120 groups of experiments are conducted. Affecting factors are analyzed and conclusions are drawn for reference. For the con-trol of dynamic response, the span of a submarine pipeline is by far more important than the other factors. Meanwhile, the rosponse difference between a submarine pipeline under sine excitation and that under random excitation exists in ex-periments. 相似文献
9.
Dynamic Response Analysis of the Equivalent Water Depth Truncated Point of the Catenary Mooring Line
The real-time computer-controlled actuators are used to connect the truncated parts of moorings and risers in the active hybrid model testing system. This must be able to work in model-scale real time, based on feedback input from the floater motions. Thus, mooring line dynamics and damping effects are artificially simulated in real time, based on a computer-based model of the problem. In consideration of the nonlinear characteristics of the sea platform catenary mooring line, the equations of the mooring line motion are formulated by using the lumped-mass method and the dynamic response of several points on the mooring line is investigated by the time and frequency domain analysis method. The dynamic response of the representative point on the mooring line is analyzed under the condition of two different corresponding upper endpoint movements namely sine wave excitation and random wave excitation. The corresponding laws of the dynamic response between the equivalent water depth truncated points at different locations and the upper endpoint are obtained, which can provide technical support for further study of the active hybrid model test. 相似文献
10.
系泊方柱在畸形波与波群伴生波浪作用下运动响应试验研究 总被引：1，自引：1，他引：0
畸形波与波群伴生波浪作用于系泊浮体,和常规随机波浪作用比较,运动响应时频域特征均将发生显著变化。基于物理模型试验,采用小波方法计算伴生波浪和常规随机波浪作用下系泊浮体运动响应的时频域特征变化及波群因子与浮体运动响应时频域特征的定量关系。结果表明:伴生波浪作用下浮体运动响应显著大于常规随机波浪的作用结果,且波群因子G A对浮体运动响应时频域特征有显著影响;伴生波浪作用下浮体纵荡运动的广义能量谱E(t)统计特征值E max(t)、E 1/10(t)、E 1/3(t)、E average(t)均明显大于相同波谱下常规随机波浪的结果,且随着波群因子G A增大显著增大;伴生波浪作用下各运动响应能量集中度δE显著大于常规随机波浪作用结果,且能量集中时域分布范围参数ΔT E以纵荡运动分量最为显著。 相似文献
11.
According to linear random wave theory, water particle kinematics at different nodes of an offshore structure form a set of correlated jointly Gaussian random variables. Thus, using principal component analysis, all the foregoing kinematics can be expressed as linear combinations of a few independent Gaussian random variables. This technique can be used to generate statistically independent hydrodynamic load and response values, as opposed to time simulation technique that leads to correlated response values. The sampling variability of the statistics generated from a set of independent data points is considerably smaller than that of a set (of the same size) of correlated values. Therefore, a much smaller number of simulated data points are necessary for accurate prediction of the statistical properties of response. Furthermore, simulating N data points by principal component technique (PCT) has proved to be at least two times faster than simulating the same number of data points by the time simulation technique (TST). As a result, PCT is considerably more efficient (about 25 times) than TST. The forgoing conclusions have been verified by applying both techniques to two test structures under different environmental conditions. 相似文献
12.
The present study considers the prediction of extreme values of the second-order hydrodynamic parameters related to offshore structures in waves, where the application of Gaussian distribution is not valid. Particularly, this study focuses on a characteristic function approach in the frequency domain to estimate the probability distribution of the second-order quantities, and the results are compared with direct simulations in the time domain. The stochastic behaviors of the second-order hydrodynamic quantities are investigated with the characteristic function approach, which involves eigenvalue analyses of Hermitian kernels constructed with quadratic transfer functions. Three different second-order responses are considered: the springing responses of TLP tendons representative of the sum-frequency problem, the slow-drift motions of a semi-submersible platform moored in waves as a representative of the difference-frequency problem, and the wave run-up around a vertical column for regular and irregular waves. The applicability of the present approach in predicting extreme values is assessed by comparing the results with the values obtained from time-domain signals. 相似文献
13.
Physical model tests were conducted to validate numerical models of moored-buoy systems. Three buoy types (sphere, spar and discus) were tested for intrinsic properties, three-dimensional impulse response and three-dimensional dynamic response to two-dimensional regular and random wave excitation. Buoy kinematics were measured using advanced video imaging techniques. Other data collected included upper and lower mooring line tension and mooring line inclination. Physical model development, test and measurement procedures and data collected are discussed. 相似文献
14.
Mario Alberto Jordn 《Ocean Engineering》2006,33(8-9):1161-1213
This work presents an approach to identify hydrodynamic models for incident, diffraction and viscous forces acting on a moored floating structure. An important aspect treated here is the analysis of the unknown initial condition of the hydrodynamic state for the potential-radiation force. There is established its influence on the parameter convergence and the long-term effects. Afterwards the persistency of excitation of the regressor is analyzed in the case of both poor and rich excitation conditions. Theoretical results show that asymptotic convergence of the estimates takes place under arbitrary conditions of the wave excitation. A case study consisting in the identification of a moored semisubmersible is carried out to exemplify the application of the approach. 相似文献
15.
不规则波作用下的船舶撞击作用 总被引：2，自引：1，他引：2
随着波谱理论研究的发展,各种海工结构及船舶的荷载及其内力分析也日趋应用不规则波的计算方法。目前对于外海码头在波浪作用下的船舶撞击荷载还应用规则波的研究方法,对其应用不规则波分析方法的途径以及在考虑波谱作用后会有怎样的结果等问题目前还较少研究。本文试图对此问题进行初步的分析。 相似文献
16.
Reliable performance is the key requirement for instruments used in offshore moored buoys for cyclone monitoring, as under performance of the sensors can have a serious impact on the societal protection, and in addition, lead to costly repair and reinstallations. The instrument selection and application practices are based on the experiences of the global scientific community, and their performances are monitored based on IEC61508 standards. Reliability modeling based on experiences in the operation and maintenance of moored surface buoys for approximately two decades has identified that the sensor suite used for cyclone monitoring has a Mean Time Between Failure of 0.6 years, which is the basis of the implemented reliability centered maintenance strategies. As this is the first attempt to study the performance of such moored buoy instruments which have cumulatively clocked more than 7.3 million demanding offshore instrument-hours, the data presented shall serve as input for the offshore environmental instrument system design. 相似文献
17.
Kiho Kim Sung Bae Kim Powers E.J. Miksad R.W. Fischer F.J. 《Oceanic Engineering, IEEE Journal of》1994,19(2):183-192
This paper presents an adaptive second-order Volterra filter and its application to model-test data of a prototype tension leg platform (TLP). The least-squares approach of a second-order Volterra model and its adaptive filtering algorithm based on recursive least-squares are introduced. The second-order Volterra filter is applied to identify the linear and quadratically nonlinear relationship between irregular sea wave excitation and the surge response of a tension leg platform. Next, a deconvolution technique, based on the impulse invariance standard Z-transform, is utilized to recover the linear and quadratic forces exerted on the TLP 相似文献
18.
In this paper, studied are the dynamics of a moored buoy near the surface subjected to wave excitation. According to the physical structure, submersible buoy moored by tethered line is modeled firstly. Then from the differential equations, the natural frequencies are estimated by neglecting the coupling between tangential and normal direction. By use of numerical integration method, solutions are obtained. On this basis, strange attractors and bifurcation phenomena are obtained by applying Poincare map, pha... 相似文献
19.
For evaluation of the permanent deformation of a sea embankment under stochastic earthquake excitation, a robust dynamic risk analytical method is presented based on conventional permanent deformation analysis and stochastic seismic response analysis. This method can predict not only the mean value of maximum permanent deformation but also the reliability corresponding to different deformation control standards. The earthquake motion is modelled as a stationary Gaussian filtered white noise random process. The predicted average maximum horizontal permanent displacement is in agreement with the conventional result. Further studied are the reliability of permanent deformation due to stochastic wave details at one seismic motion level and the risk of permanent deformation due to stochastic seismic strength, i. e., the maximum acceleration in a long period. Therefore, it is possible to make the optimal design in terms of safety and economy according to the importance of a sea embankment. It is suggested tha 相似文献
20.
This paper presents an artificial neural network (ANN)-based response surface method that can be used to predict the failure probability of c-? slopes with spatially variable soil. In this method, the Latin hypercube sampling technique is adopted to generate input datasets for establishing an ANN model; the random finite element method is then utilized to calculate the corresponding output datasets considering the spatial variability of soil properties; and finally, an ANN model is trained to construct the response surface of failure probability and obtain an approximate function that incorporates the relevant variables. The results of the illustrated example indicate that the proposed method provides credible and accurate estimations of failure probability. As a result, the obtained approximate function can be used as an alternative to the specific analysis process in c-? slope reliability analyses. 相似文献