共查询到20条相似文献，搜索用时 20 毫秒
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考虑深水S型铺设中离散均布托辊对上弯段管道的支撑作用,提出了管道铺设形态和内力的分段解析求解方法,通过迭代搜索算法确定管道最佳反弯点和升离点的位置,结合刚性悬链线理论和欧拉梁弯曲理论,推导了管道的变形和内力的解析表达式。依据所建立的分段解析方法编制了相应的数值计算程序,以某3 000 m水深铺设12英寸管道为例,计算了管道形态和内力响应,与商用有限元软件的数值分析结果进行对比,表明了分段解析方法的准确性和有效性。建立的方法具有较高的计算效率,为进一步开展S型铺设参数的优化或可靠性研究提供了有力的手段。 相似文献
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水下运动物体间相互作用力的计算探讨 总被引：3，自引：0，他引：3
本文首先用体内奇点分布法建立了水下多个运动回转体的数学模型,基此提出了一种新的计算多物体相互作用力的方法──等价拓展体法,达到考虑粘性、简化边界层计算的目的。以上方法都以两个运动回转体为例作了数值计算与比较。 相似文献
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1 .ＩｎｔｒｏｄｕｃｔｉｏｎＷｈｅｎａｔａｎｋｅｒｉｓｂｅｒｔｈｅｄｏｒｍｏｏｒｅｄｔｏａｎｏｃｅａｎｐｌａｔｆｏｒｍ ,ｗｈｉｃｈｉｓｕｓｕａｌｌｙｉｎｏｐｅｎｓｅａｓ,ｔｈｅｔａｎｋｅｒｗｉｌｌｓｕｆｆｅｒｆｏｒｃｅｓｇｅｎｅｒａｔｅｄｂｙｗａｖｅｓ ,ｗｉｎｄａｎｄｃｕｒｒｅｎｔ.Ｉｎｍｏｓｔｏｆｔｈｅｐｒｅｖｉｏｕｓｓｔｕｄｉｅｓ ,ｔｈｅｉｎ ｆｌｕｅｎｃｅｏｆｃｕｒｒｅｎｔｏｒｔｈｅｃｏｍｂｉｎｅｄｗａｖｅａｎｄｃｕｒｒｅｎｔｗａｓｃｏｎｓｉｄｅｒｅｄｔｏｂｅｔｈｅｍａｉｎｏｂｊｅｃｔ.Ｉｎｓ… 相似文献
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Gu Jianming Pan Bin Postgraduate Dept. of Naval Architecture Ocean Engineering Shanghai Jiao Tong University Shanghai Lecturer Dept. of Naval Architecture Ocean Engineering Shanghai Jiao Tong University Shanghai 《中国海洋工程》1993,(1)
- In this paper, an engineering method is employed to calculate the horizontal and vertical wave forces on the mat of the submersible platform under Froude-Krylov hypothesis. According to some model tests, appropriate diffraction coefficients are selected. And the results of the formulae given in the paper agree satisfactorily with those experimental data now available. The proposed computational method is effective and convenient to use in evaluating the horizontal and vertical wave forces on the mat. An exmaple is also given in this paper. Finally, the effects of the vertical wave force on the platorm's sit-on-bottom stability are analyzed. 相似文献
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M. Söylemez 《Ocean Engineering》1996,23(5):423-445
This paper presents the derivation of a general method for calculating wave forces on the cylindrical members of offshore structures. By means of the proposed method one can calculate the wave loading on cylindrical members of fixed or floating offshore structures orientated randomly in waves. This method of calculating wave forces is based on the linear Airy wave theory. Calculation procedure of wave force components is presented in great detail on the basis of wave particle kinematic properties obtained from the linear Airy wave theory. In the procedure of calculating wave forces presented, definitions of the wave reference system for propagating wave, the structure reference system for the platform and the member reference system for the tubular members of the structure are first established, and then the calculation of wave forces is given in terms of its components, which are pressure, acceleration and velocity forces, including current forces. At the end of the paper, expressions of total heave, sway and surge forces and total roll, pitch and yaw moments acting on the platform are given as a sum of these forces acting on each member of the platform. The calculation procedure derived in this paper provides a very efficient means of calculating wave forces and moments during the time-domain simulations of a floating platform experiencing large amplitude motion in intact, progressive flooding and damaged conditions. Comparisons of the predictions with the measurements which will be presented elsewhere reveal that the calculation procedure developed can predict large amplitude oscillatory and steady motion characteristics of an intact and damaged platform in waves with an acceptable degree of accuracy. 相似文献
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H. Wibisono 《Ocean Engineering》1996,23(6):545-550
An alternative floating system for an offshore airport and other reclamation works is presented. It consists of precast boxes filled with FRP hollow spheres which sit on pile system. A top slab system consisting of precast and cast in situ concrete slabs will make the whole system monolithic. The light weight but strong spheres will enable the system to make use the uplift force from water. The precast boxes and slab system will transfer the difference between the gravity and uplift forces, as well as any lateral forces to the pile system. Finally, a proposed method of any lateral forces to the pile system. construction is also presented. 相似文献
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《Oceanic Engineering, IEEE Journal of》2006,31(2):432-453
Precise control of trawl systems is assumed to be beneficial from both economic and environmental reasons. Using the trawl doors as actuators could increase the amount of available control forces. Adequate mathematical models of the hydrodynamic fores on the trawl doors are needed for control system design and verification. This paper presents a method for mathematical modeling of the hydrodynamic forces on the trawl doors. These forces are divided into steady-state forces and transient effects. The six degrees of freedom (six dof) steady-state hydrodynamic coefficients of a trawl door have been found as a function of its angles of attack and slip, based on wind-tunnel experiments. The coefficients are parameterized for smoothing and computational performance, and methods for extending the validity of the model in terms of orientation and trawl door shape are presented. The transient effects are described as functions of relative accelerations between the trawl door and the ambient water, angular velocities of the trawl door and circulation buildup. These effects are manifestations of variations in the flow around the trawl door and its wake, and a numerical method based on potential theory is employed to investigate them. A computational efficient, nonlinear, state–space model of the hydrodynamic forces is finally proposed. It accounts for steady-state and unsteady hydrodynamic forces and moments in six dof, suitable for trawl control system design and analysis. 相似文献
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In the present study, a novel method is proposed for the separation of the second-order sum- and difference-frequency wave forces—that is, quadratic transfer functions (QTFs)—on a floating body into three components due to wave–wave, wave–motion, and motion–motion action. By applying the new QTF components, the second-order wave forces on a floating body can be strictly computed in the time domain. In this work, the boundary value problems (BVPs) corresponding to the three kinds of QTF components were derived, and non-homogeneous boundary conditions on the free surface and the body surface were obtained. The second-order diffraction potentials were determined using the boundary integral equation method. In the solution procedure, the highly oscillatory and slowly converging integral on the free surface was evaluated in an accurate and effective manner. Furthermore, the application of the QTF components in the time domain was demonstrated. The second-order exciting forces in the time domain were divided into three parts. Each part of these forces was computed via a two-term Volterra series model based on the incident waves, the first-order motion response, and the QTF components. This method was applied to several numerical examples. The results demonstrated that this decomposition yields satisfactory results. 相似文献
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A numerical method is proposed to predict the effective wake profiles of high speed underwater vehicles propelled by contra-rotating propellers (CRPs), in which the hydrodynamic effects of the CRPs are simulated by distributed body forces. First, Reynolds-averaged Navier-Stokes (RANS) simulations are conducted for identical body-force distributions in open-water and self-propulsion conditions. The effective wake profiles at the CRP disks are then obtained by subtracting the velocities induced by the body forces in the open water from those induced by the body forces in the self-propulsion condition. The effective wake profiles were then predicted for a generic underwater vehicle with an established CRP design. Next, the hydrodynamic performance of the CRPs in the effective wake was computed using an in-house vortex-lattice code. The potential-flow results agree well with those provided by the RANS simulation under the self-propulsion condition, indicating that the proposed method can predict the effective wake profiles for CRPs with reasonable accuracy. The influences of different wake components on the blade forces were investigated, determining that for CRPs, and especially for the aft propeller, the circumferential wake cannot be neglected in the design. 相似文献
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《Coastal Engineering》2006,53(10):857-864
This paper presents a neural network model of simulating tides at multi-points considering tide-generating forces. A comparison on the root mean square and correlation coefficient of three-year mixed tides at a single point computed with harmonic method, response–orthotide method, the NAO.99b model and the proposed model was made to show the prediction accuracy of each method. The proposed model is examined efficient as the harmonic method to estimate the tides at a single point. Extended application of the proposed model to predicting tides at some points neighboring to an original interest point identifies accurately simulating multi-point tides as the NAO.99b numerical model. 相似文献
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With the development of marine energy in full swing, an increasing number of pipelines are being installed in deep-sea areas, which inevitably pass through extremely complex topographic conditions, to form natural sections of suspension over submarine canyons. The seabed is easily eroded and shaped by active deep-sea bottom currents and watercourses, resulting in different span heights for pipelines originally laid on the seabed. In particularly, deep-sea geological hazards frequently occur, and submarine landslides seriously threaten the safe operation of the pipelines. To address these problems, an improved numerical analysis method combined with low-temperature rheological models of landslides and the optimization design method of the geometric model, is developed to simulate the landslides’ impacts on pipelines. Based on these, the effect of the span heights on the pipelines’ impact forces induced by deep-sea landslides is systematically investigated, and three modes of the forces on pipelines under the impact of landslides and related mechanism are proposed. Further, the span height ratio is put forward, and four formulas for evaluating the forces on pipeline are established. Through the analysis of calculation results, the lift force coefficient even increases nearly 20 times considering different span heights. This research provides a theoretical basis for the design and protection of deep-sea pipelines. 相似文献
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This study deals with the general numerical model to simulate the two-dimensional tidal flow, flooding wave (long wave) and shallow water waves (short wave). The foundational model is based on nonlinear Boussinesq equations. Numerical method for modelling the short waves is investigated in detail. The forces, such as Coriolis forces, wind stress, atmosphere and bottom friction, are considered. A two-dimensional implicit difference scheme of Boussinesq equations is proposed. The low-reflection outflow open boundary is suggested. By means of this model,both velocity fields of circulation current in a channel with step expansion and the wave diffraction behind a semi-infinite breakwater are computed, and the results are satisfactory. 相似文献
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《中国海洋工程》2015,(3)
The effect of biofouling on the hydrodynamic characteristics of the net cage is of particular interest as biofouled nettings can significantly reduce flow of well-oxygenated water reaching the stocked fish. For computational efficiency, the porous-media fluid model is proposed to simulate flow through the biofouled plane net and full-scale net cage. The porous coefficients of the porous-media fluid model can be determined from the quadratic-function relationship between the hydrodynamic forces on a plane net and the flow velocity using the least squares method. In this study, drag forces on and flow fields around five plane nets with different levels of biofouling are calculated by use of the proposed model. The numerical results are compared with the experimental data of Swift et al.(2006) and the effectiveness of the numerical model is presented. On that basis, flow through full-scale net cages with the same level of biofouling as the tested plane nets are modeled. The flow fields inside and around biofouled net cages are analyzed and the drag force acting on a net cage is estimated by a control volume analysis method. According to the numerical results, empirical formulas of reduction in flow velocity and load on a net cage are derived as function of drag coefficient of the corresponding biofouled netting. 相似文献
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The effect of biofouling on the hydrodynamic characteristics of the net cage is of particular interest as biofouled nettings can significantly reduce flow of well-oxygenated water reaching the stocked fish. For computational efficiency, the porous-media fluid model is proposed to simulate flow through the biofouled plane net and full-scale net cage. The porous coefficients of the porous-media fluid model can be determined from the quadratic-function relationship between the hydrodynamic forces on a plane net and the flow velocity using the least squares method. In this study, drag forces on and flow fields around five plane nets with different levels of biofouling are calculated by use of the proposed model. The numerical results are compared with the experimental data of Swift et al. (2006) and the effectiveness of the numerical model is presented. On that basis, flow through full-scale net cages with the same level of biofouling as the tested plane nets are modeled. The flow fields inside and around biofouled net cages are analyzed and the drag force acting on a net cage is estimated by a control volume analysis method. According to the numerical results, empirical formulas of reduction in flow velocity and load on a net cage are derived as function of drag coefficient of the corresponding biofouled netting. 相似文献
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An investigation has been conducted to quantify the effect of waterway geometry on the form and magnitude of forces and moment experienced by a berthed ship due to a passing ship.By using the dynamic mesh technique and solving the unsteady RANS equations in conjunction with a RNG k?ε turbulence model,numerical simulation of the three-dimensional unsteady viscous flow around a passing ship and a berthed ship in different waterway geometries is conducted,and the hydrodynamic forces and moment acting on the berthed ship are calculated.The proposed method is verified by comparing the numerical results with existing empirical curves and a selection of results from model scale experiments.The calculated interaction forces and moment are presented for six different waterway geometries.The magnitude of the peak values and the form of the forces and moment on the berthed ship for different cases are investigated to assess the effect of the waterway geometry.The results of present study can provide certain guidance on safe maneuvering of a ship passing by a berthed ship. 相似文献
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Current paper presents a mathematical model based on 2D-asymmetric wedge water entry to model heave and pitch motions of planing hulls at non-zero heel angles. Vertical and horizontal forces as well as heeling moment due to asymmetric water entry are computed using momentum theory in conjunction with added mass of impact velocity in vertical and horizontal directions. The proposed model is able to compute sway and yaw forces, roll moment, as well as heave and pitch motions in calm water and regular waves. Validity of the proposed model is verified by comparing the results against existing experimental data in both symmetric and asymmetric conditions. Ultimately, different parametric studies are conducted to examine the effects of non-zero heel angle on dynamic vertical motions. The resulting sway and yaw forces due to asymmetric motion are also derived and effects of heel angle on these side forces are investigated. 相似文献