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1.
The effects of free-surface waves on the floating structures are of great importance in the offshore industry. Among the six degrees of motions of a surface ship the absence of restoring forces in surge, sway and yaw led to critical situations for moored ships in the recent times. The order of forces in horizontal plane and their exciting frequencies are matters of interest. The resonance with the presence of moored chains led to many accidents in the recent past. The lines in dry conditions may not give good damping and in wet condition they may trigger the system to chaotic motions and jumps. Two different loading conditions of a container ship model are tested with waves in laboratory conditions in two different drafts. The mooring lines are chosen as per scale law and the energy under the response spectrum is determined from the plots. The results give new insights into the movement of a berthed ships subjected to waves. Response of the moored ship to different loading conditions in different water depths are discussed in this paper. The paper gives the order of energy due to first-order and slowly varying movement of a berthed container model in a towing tank. 相似文献
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随着全球经济的快速发展，海上运输由于其运力大、运费低而变得更具实用性。然而，这也意味着在海上航道行驶的船只正变得越来越多，这将导致在复杂的海洋环境中航海船只发生事故的可能性会很高。据相关历史的统计，在海域中航行缺乏高精度导航数据会导致大量事故，这种累积的事故信息可以被用来提高航海的安全性。本文通过将蕴含在AIS (Automatic Identification System) 大数据中的经验导航信息挖掘出来，以辅助实现复杂海事环境下安全可靠的船舶路径的生成。本文提出了一种基于大数据自动生成船舶路径的新方法。该方法首先在大量船舶轨迹上通过DBSCAN (Density-Based Spatial Clustering of Applications with Noise) 聚类形成不同的轨迹矢量簇。然后，迭代计算轨迹矢量簇的中心线，并从这些中心线之间的节点-弧段拓扑关系来构建航道网络。最后，基于航道网络来实现船舶路径的生成，对于航道网络未覆盖的海域，则通过海洋环境风险栅格的路径规划来实现船舶路径的生成。不同海域不同AIS数据集进行的多次实验结果表明，本文提出的船舶路径生成方法是有效性。 相似文献
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Chlorophyll-a concentration (C chl) variations in the cross section within and outside the Peter the Great Bay shelf during different stages of the winter–spring phytoplankton bloom in 2003–2005 has been considered based on a ship (obtained during the R/V Akademik M.A. Lavrent’ev voyage of February 26 to March 9, 2003) and MODIS-Aqua spectroradiometer and the SeaWiFS color-scanner satellite data. A comparison of the C chl variability obtained from the ship and satellite data indicates that these data are inconsistent. According to satellite data obtained at the MUMM atmospheric correction, the C chl variability is distorted less than the NIR-correction data. Studying the variations in the coefficients of light absorption by the detritus and yellow substance (a dg) and light backscattering by suspended particles (b bp), C chl, chlorophyll-a fluorescence (F chl) according to the satellite data allow us to state that the variations in the discrepancy between the satellite and ship C chl values are mainly caused by the variations in the content of the detritus and yellow substance in water. Based on the satellite data, it has been revealed that the a dg values increase with increasing wind mixing after the phytoplankton bloom (about 2–5 km areas where the a dg, C chl, F chl, and bbp values abruptly increased in 2005, apparently due to eddy formation). It has been indicated that the F chl characteristic, which is close to C chl, increases when the favorable conditions for the phytoplankton bloom deteriorate. Therefore, this characteristic cannot be used to identify C chl under the indicated conditions. 相似文献
5.
Martin J. Petersen 《Ocean Engineering》1982,9(4):295-329
This paper described a procedure for simulation of the outer dynamics in ship collisions.The simulation procedure is derived using the transient equations for the horizontal motion of a ship. The hydrodynamic forces acting on the ships' hull during the collision are calculated by a strip method, where the forces acting on each section are described by means of unit response functions. These functions are determined by cosine transformation of the sectional dampings. The sectional added masses and dampings, and thereby also the sectional unit response functions, are calculated by an approximate method. The deformations of the slip structures during the collisions are modelled as non-linear springs.The resulting system of non-linear equations is solved using a numerical time-integration procedure.A number of different collision situations are simulated by means of the procedure. 相似文献
6.
Jeom Kee Paik Anil K. Thayamballi P. Terndrup Pedersen Young Il Park 《Ocean Engineering》2001,28(8):51
For a ship hull with large deck openings such as container vessels and some large bulk carriers, the analysis of warping stresses and hatch opening deformations is an essential part of ship structural analyses. It is thus of importance to better understand the ultimate torsional strength characteristics of ships with large hatch openings. The primary aim of the present study is to investigate the ultimate strength characteristics of ship hulls with large hatch openings under torsion. Axial (warping) as well as shear stresses are normally developed for thin-walled beams with open cross sections subjected to torsion. A procedure for calculating these stresses is briefly described. As an illustrative example, the distribution and magnitude of warping and shear stresses for a typical container vessel hull cross section under unit torsion is calculated by the procedure. By theoretical and numerical analyses, it is shown that the influence of torsion induced warping stresses on the ultimate hull girder bending strength is small for ductile hull materials while torsion induced shear stresses will of course reduce the ship hull ultimate bending moment. 相似文献
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The tsunami warning system in the Russian Far East employs the medium-period magnitude MS (BB) by Vaniek–Soloviev. However, its use may lead to inadequacies and underestimates for the tsunamigenic potential of an earthquake. Specifically, this can happen in the case of a so-called tsunami–earthquake. This kind of earthquakes with a nonstandard spectrum was revealed by H. Kanamori in 1972. This problem can be overcome by using a magnitude scale that deals with longer period seismic waves. This study develops a technique for determining the magnitudes at regional distances (from 70 to 4500 km) using the amplitudes of surface seismic waves of periods of 40 and 80 s. At distances of 70–250 km, the amplitude of the joint group of shear and surface waves is used. For the new magnitudes designated M S(40) and M S(80), experimental calibration curves are constructed using more than 1250 three-component records at 12 stations of the region. The magnitudes are calibrated so as to produce an unbiased estimate of the moment magnitude M w in the critical range 7.5–8.8. The rms error of the single-station estimate M w is around 0.27. At distances below 250 km and M w ≥ 8.3, the estimate of M w obtained by the proposed technique becomes saturated at the level of M w ~ 8.3, which is acceptable for operative analysis because no missed alarms arise. The technique can be used in operational tsunami warning based on seismological data. This can markedly decrease the number of false alarms. 相似文献
8.
A general formulation is given of the hydrodynamic forces on a ship, oscillating about a state of rest in 6df in response to excitation by a harmonic wave in shallow water. A method is described to obtain a numerical approximation of the velocity potential, describing the flow around the moving ship by means of a distribution of discrete three-dimensional sources.With this method it is possible to take the influence of a quay into account.Calculated values of wave excited forces, hydrodynamic coefficients and motions of a 200,000 tdw tanker in shallow water are presented and compared with experimental results. 相似文献
9.
Unsteady forces, torques and bending moments were predicted for a model podded propulsor unit at various azimuth angles. Predictions in time history include propeller shaft thrust, propulsor unit thrust, normal forces to the propeller shaft bearing, total forces acting on the propulsor unit, propeller shaft torque, blade spindle torque, in-plane and out-of-plane bending moments, and propulsor unit stock shaft torque and bending moments. Analysis was performed for averaged forces and their fluctuations as well. A time-domain unsteady multi-body panel method code, PROPELLA, was further developed for this prediction work. Predictions were compared with a set of time averaged in-house experimental data for a puller-type podded propulsor configuration in the first quadrant operation. Unsteady fluctuations of forces were predicted numerically. Analysis was made for the bending moment on propeller blades, shaft and the propulsor unit stock shaft for azimuth angles from 0° to 45°. It indicates that the magnitude and fluctuation of the forces are significant and they are essential for structural strength and design optimization. The predicted bending moment and global forces on the propulsor unit provide some useful data for ship maneuvering motion and simulation in off-design conditions. 相似文献
10.
引入拖曳系数参数化的海冰自由漂流模拟研究 总被引：2，自引：0，他引：2
Many interesting characteristics of sea ice drift depend on the atmospheric drag coefficient(C_a) and oceanic drag coefficient(C_w).Parameterizations of drag coefficients rather than constant values provide us a way to look insight into the dependence of these characteristics on sea ice conditions.In the present study,the parameterized ice drag coefficients are included into a free-drift sea ice dynamic model,and the wind factor α and the deflection angle θ between sea ice drift and wind velocity as well as the ratio of C_a to C_w are studied to investigate their dependence on the impact factors such as local drag coefficients,floe and ridge geometry.The results reveal that in an idealized steady ocean,C_a/C_w increases obviously with the increasing ice concentration for small ice floes in the marginal ice zone,while it remains at a steady level(0.2-0.25) for large floes in the central ice zone.The wind factor α increases rapidly at first and approaches a steady level of 0.018 when A is greater than 20%.And the deflection angle θ drops rapidly from an initial value of approximate 80° and decreases slowly as A is greater than20%without a steady level like α.The values of these parameters agree well with the previously reported observations in Arctic.The ridging intensity is an important parameter to determine the dominant contribution of the ratio of skin friction drag coefficient(C_s' /C_s) and the ratio of ridge form drag coefficient(C_r'/C_r) to the value of C_a/C_w,α,and θ,because of the dominance of ridge form drag for large ridging intensity and skin friction for small ridging intensity among the total drag forces.Parameterization of sea ice drag coefficients has the potential to be embedded into ice dynamic models to better account for the variability of sea ice in the transient Arctic Ocean. 相似文献
11.
The Eulerian-Lagrangian method (ELM) has been used by many ocean models as the solution of the advection equation, but the numerical error caused by interpolation imposes restriction on its accuracy. In the present study, hybrid N-order Lagrangian interpolation ELM (LiELM) is put forward in which the N-order Lagrangian interpolation is used at first, then the lower order Lagrangian interpolation is applied in the points where the interpolation results are abnormally higher or lower. The calculation results of a step-shaped salinity advection model are analyzed, which show that higher order (N=3-8) LiELM can reduce the mean numerical error of salinity calculation, but the numerical oscillation error is still significant. Even number order LiELM makes larger numerical oscillation error than its adjacent odd number order LiELM. Hybrid N-order LiELM can remove numerical oscillation, and it significantly reduces the mean numerical error when N is even and the current is in fixed direction, while it makes less effect on mean numerical error when N is odd or the current direction changes periodically. Hybrid odd number order LiELM makes less mean numerical error than its adjacent even number order LiELM when the current is in the fixed direction, while the mean numerical error decreases as N increases when the current direction changes periodically, so odd number of N may be better for application. Among various types of Hybrid N-order LiELM, the scheme reducing N-order directly to 1st-order may be the optimal for synthetic selection of accuracy and computational efficiency. 相似文献
12.
As the maneuverability of a ship navigating close to a bank is influenced by the sidewall, the assessment of ship maneuvering stability is important. The hydrodynamic derivatives measured by the planar motion mechanism (PMM) test provide a way to predict the change of ship maneuverability. This paper presents a numerical simulation of PMM model tests with variant distances to a vertical bank by using unsteady RANS equations. A hybrid dynamic mesh technique is developed to realize the mesh configuration and remeshing of dynamic PMM tests when the ship is close to the bank. The proposed method is validated by comparing numerical results with results of PMM tests in a circulating water channel. The first-order hydrodynamic derivatives of the ship are analyzed from the time history of lateral force and yaw moment according to the multiple-run simulating procedure and the variations of hydrodynamic derivatives with the ship-sidewall distance are given. The straight line stability and directional stability are also discussed and stable or unstable zone of proportional-derivative (PD) controller parameters for directional stability is shown, which can be a reference for course keeping operation when sailing near a bank. 相似文献
13.
The use of an unsteady computational fluid dynamic analysis of the manoeuvring performance of a self-propelled ship requires a large computational resource that restricts its use as part of a ship design process. A method is presented that significantly reduces computational cost by coupling a blade element momentum theory (BEMT) propeller model with the solution of the Reynolds averaged Navier Stokes (RANS) equations. The approach allows the determination of manoeuvring coefficients for a self-propelled ship travelling straight ahead, at a drift angle and for differing rudder angles. The swept volume of the propeller is divided into discrete annuli for which the axial and tangential momentum changes of the fluid passing through the propeller are balanced with the blade element performance of each propeller section. Such an approach allows the interaction effects between hull, propeller and rudder to be captured. Results are presented for the fully appended model scale self-propelled KRISO very large crude carrier 2 (KVLCC2) hull form undergoing static rudder and static drift tests at a Reynolds number of 4.6×106 acting at the ship self-propulsion point. All computations were carried out on a typical workstation using a hybrid finite volume mesh size of 2.1×106 elements. The computational uncertainty is typically 2–3% for side force and yaw moment. 相似文献
14.
系泊船非线性波浪力时域计算:二维模型 总被引：7，自引：1，他引：6
为找到具有工程实用价值的港口系泊船波浪力的时域计算方法,建立了在港口中存在系泊船时非线性波浪力时域计算的垂直二维耦合模型:用Boussinesq方程计算船的两侧的外域,用欧拉方程计算船底面下的内域,两域在交界面处的连接条件是流量连续和压力相等.将复平面内的边界元方法应用于所研究问题,对耦合模型进行了验证.进行了相关模型实验,实验结果与数值计算结果比较表明这两种数值计算模型都具有满意的精度,但耦合模型的计算效率要远远高于边界元方法的计算效率.本耦合模型的数学处理简单,可适用于工程计算. 相似文献
15.
The analytical method developed by Svendsen (1968) for a forced heave motion is extended to the general problem of wave induced heave, roll and sway motions of a long ship at a depth of water which is only slightly larger than the draught of the ship. This corresponds, for example, to the situation of a fully loaded ship in a harbour area.After linearization of the problem, the water motion is considered for each of the three individual motions and for the wave reflection-transmission problem for a fixed ship. The ensuing results for the forces on the ship are then synthesized to form the equations of motion, which are presented with all coefficients given, including mooring forces.Analytical and numerical results are given for the three components of motion, for the associated resonance frequencies, and for the hydrodynamic masses and moments of inertia. Finally, the assumptions used are analyzed and evaluated by comparison with measurements and with other results for a special case. 相似文献
16.
In practical maritime conditions, ship hulls experience heave motion due to the action of waves, which can further drive the ship’s propellers to oscillate relative to the surrounding water. In order to investigate the motion of a propeller working behind a surface vessel sailing in waves, a numerical simulation is conducted on a propeller impacted by heave motion in cavitating flow using the Reynolds-averaged Navier-Stokes (RANS) method. The coupling of the propeller’s rotation and translation is fulfilled using equations of motion defined for this purpose. The heave motion is simplified as a periodic motion based on a sinusoidal function. The numerical transmission of information from the unsteady flow field is achieved using the overset grid approach. In this manner, the unsteady thrust coefficient and torque coefficient of propellers in different periods of heave motion are analyzed. A comparative study is implemented on the unsteady cavitation performance and wake characteristics of propeller. With the propeller’s heave motion, the flow field non-uniformity constantly changes the load on the propeller during each revolution period and each heaving period, the propeller load and the wake field are closely related to the variation of heave motion period. The results obtained from the numerical simulation are expected to serve as a useful theoretical reference for the numerical analysis of a propeller in a heave motion. 相似文献
17.
In this paper, using a second-order steady-state approach and a three-dimensional (3D) pulsating source distribution method derives the nonlinear hydrodynamic forces on a ship advancing in waves. The nonlinear hydrodynamic forces considered here consist of the mean lateral drifting force and the added resistance, which can be expressed as products of the ship-motion responses, the radiation potential, diffraction potential and the incident-wave potential. All related velocity potentials applied in the calculations are in 3D form. The Series 60 and Marine ship hulls are used for numerical calculations and the results are compared with existing experimental data and two-dimensional (2D) solutions. The comparisons show that the results obtained in the paper generally agree with experimental data well. It is also found that the nonlinear hydrodynamic forces obtained based on the present 3D source distribution methods are indeed improved in some calculations compared with the 2D method, especially for the mean lateral drifting force. 相似文献
18.
This paper firstly figures out a similar scale model regarding ultimate strength experiment of a typical ultra large container ship (ULCS) through combined ultimate longitudinal bending and torsion analysis, in which the similarity theory is proposed to design the scale model for reflecting the progressive collapse behaviors of true ships in ultimate strength model test. The present study presents the similarity between scale model and true ship in cross-section considering the height of neutral axis, the section modulus, the inertia moment about neutral axis and the polar inertia moment should fit the geometrical similarity theory, and in strength considering buckling strength and shear ultimate strength of plates and stiffened panels should fit the strength similarity theory. Numerical investigations are conducted on the ultimate strength of a 10,000 TEU container ship and the similar scale model under pure hogging bending, pure torsion and combined bending and torsion, respectively. The nonlinear finite element method (NFEM) is adopted considering the effects of initial deformations and both material and geometric nonlinearities. Finally, the numerical results are compared with each other and discussed showing a good agreement in both elastic and inelastic range during the progressive collapse behaviors, which means the similar scale model can represent the true ship regarding ultimate strength test. And the similarity theory is verified quite stable after the uncertainty analysis. 相似文献
19.
Based on Green–Naghdi equation this work studies unsteady ship waves in shallow water of varying depth. A moving ship is regarded as a moving pressure disturbance on free surface. The moving pressure is incorporated into the Green–Naghdi equation to formulate forcing of ship waves in shallow water. The frequency dispersion term of the Green–Naghdi equation accounts for the effects of finite water depth on ship waves. A wave equation model and the finite element method (WE/FEM) are adopted to solve the Green–Naghdi equation. The numerical examples of a Series 60 (CB=0.6) ship moving in shallow water are presented. Three-dimensional ship wave profiles and wave resistance are given when the ship moves in shallow water with a bed bump (or a trench). The numerical results indicate that the wave resistance increases first, then decreases, and finally returns to normal value as the ship passes a bed bump. A comparison between the numerical results predicted by the Green–Naghdi equation and the shallow water equations is made. It is found that the wave resistance predicted by the Green–Naghdi equation is larger than that predicted by the shallow water equations in subcritical flow
, and the Green–Naghdi equation and the shallow water equations predict almost the same wave resistance when
, the frequency dispersion can be neglected in supercritical flows. 相似文献
20.
Vessels operating in shallow waters require careful observation of the finite-depth effect. In present study, a Rankine source method that includes the shallow water effect and double body steady flow effect is developed in frequency domain. In order to verify present numerical methods, two experiments were carried out respectively to measure the wave loads and free motions for ship advancing with forward speed in head regular waves. Numerical results are systematically compared with experiments and other solutions using the double body basis flow approach, the Neumann-Kelvin approach with simplified m-terms, and linearized free surface boundary conditions with double-body m-terms. Furthermore, the influence of water depths on added mass and damping coefficients, wave excitation forces, motions and unsteady wave patterns are deeply investigated. It is found that finite-depth effect is important and unsteady wave pattern in shallow water is dependent on both of the Brard number τ and depth Froude number Fh. 相似文献