Parameter identification of nonlinear roll motion equation for floating structures in irregular waves     

《Applied Ocean Research》2016

In order to predict the roll motion of a floating structure in irregular waves accurately, it is crucial to estimate the unknown damping coefficients and restoring moment coefficients in the nonlinear roll motion equation. In this paper, a parameter identification method based on a combination of random decrement technique and support vector regression (SVR) is proposed to identify the coefficients in the roll motion equation of a floating structure by using the measured roll response in irregular waves. Case studies based on the simulation data and model test data respectively are designed to validate the applicability and validity of the identification method. Firstly, the roll motion of a vessel is simulated by using the known coefficients from literature, and the simulated data are used to identify the coefficients in the roll motion equation. The identified coefficients are compared with the known values to validate the applicability of the identification method. Then the roll motion is predicted by using the identified coefficients. The prediction results are compared with the simulated data, and good agreement is achieved. Secondly, the model test data of a FPSO are used to identify the coefficients in the roll motion equation. Then the random decrement signature of the roll motion is predicted by using the identified coefficients and compared with that obtained from the model test data, and satisfactory agreement is achieved. From this study, it is shown that the identification method can be effectively applied to identify the coefficients in the nonlinear roll motion equation in irregular waves.  相似文献   

Hydrodynamic behavior of a straight floating pipe under wave conditions   总被引：2，自引：0，他引：2  

Yucheng Li  Fukun Gui  Bin Teng 《Ocean Engineering》2007,34(3-4):552-559

This paper examines the hydrodynamic behavior of a floating straight pipe under wave conditions. The main problem in calculating the forces acting on a small-sized floating structure is obtaining the correct force coefficients C_n and C_t, which differ from a submerged structure. For a floating straight pipe of small size, we simplify it into a 2D problem, where the pipe is set symmetrically under wave conditions. The force equations were deduced under wave conditions and a specific method proposed to resolve the wave forces acting on a straight floating pipe. Results of the numerical method were compared to those from model tests and the effects of C_n and C_t on numerical results studied. Suggestions for the selection of correct C_n and C_t values in calculating wave forces on a straight floating pipe are given. The results are valuable for research into the hydrodynamic behavior of the gravity cage system.  相似文献   

褐藻胶厂漂浮渣的脂肪酸成分分析     

吴志军  熊慧萍  李智恩  徐祖洪 《海洋科学》2001,25(10):48-49

我国的海带养殖是海水养殖业的支柱产业之一 ,是世界上海藻养殖业中规模最大的产业,其养殖产量连续多年居世界首位,目前年产量已达６０００００ｔ多干品［２］。我国生产的海带除了大部分作为食品食用外 ,还有部分作为工业原料,提取褐藻胶、褐藻淀粉、甘露醇、碘、氯化钾等产品。我国褐藻胶年产量已达１５０００ｔ,在生产过程中产生大量的漂浮渣,都把其当作废物排放掉,这样不仅污染了环境 ,而且造成了资源的大量浪费。为了进一步地综合利用海带资源,变废为宝 ,作者对青岛某一褐藻胶厂排放的漂浮渣进行了较深入的化学成分分析。现报道利用气…  相似文献   

On the use of the capability polar plots program for dynamic positioning systems for marine vessels   总被引：2，自引：0，他引：2  

Ayman B. Mahfouz  Hussein W. El-Tahan 《Ocean Engineering》2006,33(8-9):1070-1089

As the capability of polar plots becomes better understood, improved dynamic positioning (DP) systems are possible since the control algorithms greatly depend on the accuracy of the aerodynamic and hydrodynamic models. The measurements and estimation of the environmental disturbances have an important role in the optimal design and selection of a DP system for a marine vessel. The main objective of this work is to present a new software program capable of estimating the environmental forces, thrusters capability calculations, and capability polar plots for marine vessels. A flowchart illustrating the logic and data flow of a developed software program, the Capability Polar Plot Program (CPPP), and the estimated results for two case studies for a scientific drilling vessel and a survey vessel are presented. It is obvious from the obtained results that the developed program has a future potential for the estimation of the Capability Polar Plots for marine vessels. Moreover, the developed software program would be considered as a marine tool for the thrusters' selection and their configuration for marine vessels and floating production units for the Oil and Gas industries.  相似文献   

空间曲面真实感的全方位体视     

马洪明  景新娟 《成都信息工程学院学报》1998,(1)

利用求补色立体图屏幕坐标原理,采用浮动水平线法来绘出空间曲面的透视投影图形。通过参数变换可展示出不同视点、不同视角、不同视距下物体表面的形态,通过双眼视觉加强所展示物体表面的真实感。实验表明,该方法有广泛的应用价值。  相似文献   

A study of spar buoy floating breakwater     

Nai-Kuang Liang  Jen-Sheng Huang  Chih-Fei Li 《Ocean Engineering》2004,31(1):43-60

A floating breakwater produces less environmental impact, but is easily destroyed by large waves. In this paper, the spar buoy floating breakwater is introduced with a study on the wave reflection and transmission characteristics and mooring line tension induced by the waves. Mei (The Applied Dynamics of Ocean Surface Waves, Wiley, New York (1983) 740 p) proposed a theoretical solution for the reflection and transmission coefficients as the wave propagates through a one-layer slotted barrier. For a multiple-layer fence system, the analytical solution is proposed linearly. The results show that the theoretical computations agree well with the experimental trends. For a multiple-layer fence system, the transmission coefficients become maximal as the layer spacing to wavelength ratio moves to 1/2. Conversely, the coefficients become minimal, as the ratio moves to 0.3. To estimate the maximum tension of the mooring line, both numerical calculations and laboratory experiments were executed. The numerical calculation results were similar to the experimental results.  相似文献   

Diffraction–radiation of multiple floating structures in directional waves     

S. A. Sannasiraj  R. Sundaravadivelu  V. Sundar 《Ocean Engineering》2001,28(2):106

The dynamics of multiple floating structures have been studied using the finite element method. The emphasis is on the hydrodynamic behaviour of multiple bodies under a multi-directional wave field. A two-dimensional numerical model has been adopted to evaluate hydrodynamic coefficients and forces in an oblique wave field. The responses in sway, heave and roll modes are reported. The linear filter technique is then used to extrapolate the responses under directional waves. The effect of mean wave direction and directional homogeneity on the hydrodynamic behaviour of the structure is studied. Based on the present study, it is found that the two-dimensional model is applicable to investigate the wave-structure interaction problems of the type herein considered.  相似文献   

Gravity wave interaction with floating membrane due to abrupt change in water depth   总被引：1，自引：0，他引：1  

D. Karmakar  T. Sahoo   《Ocean Engineering》2008,35(7):598-615

Using the recently developed expansion formulae for wave structure interaction problems, the scattering of surface water waves by a semi-infinite floating membrane due to abrupt change in bottom topography is analyzed. Both the cases of finite and infinite steps are analyzed. In the present paper, the analysis is based on the linearized theory of water waves and small amplitude membrane response. Combining the linearized kinematic and dynamic surface conditions on the water surface with the dynamic pressure condition on the membrane, a third order differential equation is derived to describe the membrane covered free surface condition. General wave energy relation for wave scattering by floating horizontal membrane is derived by the application of law of conservation of energy flux and alternately by the direct application of Green's second identity. In the floating membrane covered region, the wave energy density is a combination of the kinetic and potential energy density due to the surface gravity waves, and the surface energy density which is due to the existence of the floating membrane on the free surface. Gravity wave transformations due to an abrupt change in bottom topography in the presence of a floating membrane in finite water depth are analyzed based on shallow water approximation. Numerical results are computed and analyzed to understand the wave transformation due to the floating membrane when there is an abrupt change in topography in different cases.  相似文献   

Effects of mooring line drag damping on response statistics of vessels excited by first- and second-order wave forces     

A. Sarkar  R. Eatock Taylor 《Ocean Engineering》2000,27(6):17

The drag-induced damping in a mooring cable due to combined first- and second-order wave excited motion of a moored vessel has been determined by statistical linearisation. A dynamic stiffness approach developed elsewhere is used to deal with the dynamics of the mooring cables. The power spectral densities of low- and wave-frequency responses are obtained which clearly show the influence of mooring line damping. The non-Gaussian probability density functions (pdf) and expected crossing rates of vessel responses and dynamic cable tensions are determined using the Kac–Seigert technique, and the influence of drag damping is highlighted.  相似文献   

Complete two-dimensional analysis of sea-wave-induced fully non-linear sloshing fluid in a rigid floating tank     

Bang-Fuh Chen  Hsuen-Weng Chiang 《Ocean Engineering》2000,27(9):935

A time-independent finite-difference method and a fifth-order Runge–Kutta–Felhberg scheme were used to analyze the dynamic responses of sea-wave-induced fully non-linear sloshing fluid in a floating tank. The interaction effect between the fully non-linear sloshing fluid and the floating tank associated with coupled surge, heave and pitch motions of the tank are analyzed for the first time in the present pilot study. For the analysis of fluid motion in the tank, the coordinate system is moving (translating and rotating) with tank motion. The time-dependent water surface of the sloshing fluid is transformed to a horizontal plane and the flow field is mapped on to a rectangular region. The Euler equations as well as the fully non-linear kinematic free surface condition were used in the analysis of the sloshing fluid. The strip theory for linearized harmonic sea-wave loading was adopted to evaluate the regular encounter wave force. In addition, the dynamic coefficients used in the dynamic equations of tank motion were also derived based on strip theory and a harmonic motion of the tank. The characteristics of free and forced tank motions with and without the sloshing effect are studied. By the damping effect, the response of free oscillation will damp out and that of forced oscillation will approach a steady state. Without sea-wave action, the contribution of the sloshing load would enlarge the angular response of tank motion as well as the rise of free surface and the sloshing effect will delay the damping effect on angular displacement. On the contrary, under sea-wave action, the sloshing effect will decrease the dynamic response of tank motion and rise of free surface. The interaction, sloshing and coupling effects are found to be significant and should be considered in the analysis and design of floating tanks.  相似文献