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1.
Capsizing of ships constitutes a primary group of casualties that leads to loss of life and money. Unfortunately, its mechanism has yet to be fully resolved due to underlying complex dynamics and parameters. Upon studying the causes in more detail, designing safer ships against capsizing may become a reality. In the present study, a relatively different approach called “reserve of stability” or “stability margins” which utilizes both statical and nonlinear dynamical aspects of stability is employed to analyze ship hydrodynamics. For this purpose a nonlinear roll model in beam waves has been implemented. In order to apply the theory, a capsized vessel is chosen to be analyzed in terms of stability. The necessary data about the vessel at the time of capsizing were collected from the published work found in the naval architecture literature. Suggestions are made based on the results of the analysis to improve ship stability qualities in a seaway. 相似文献
2.
A brief history of recognition of the Kuroshio 总被引：2，自引：0，他引：2
Hideo Kawai 《Progress in Oceanography》1998,41(4):505-578
3.
There is increasing interest in optimizing ships for the actual operating condition rather than just for calm water. In order to optimize the propeller designs for operations in waves, it is essential to study how the propeller performance is affected by operation in waves. The effect of various factors that influence the propeller is quantified in this paper using a 8000 dwt chemical tanker equipped with twin-podded propulsion as a case vessel. Propeller performance in waves in terms of cavitation, pressure pulses, and efficiency is compared with the performance in calm water. The influence of wake variation, ship motions, RPM fluctuations and speed loss is studied. Substantial increase in cavitation and pressure pulses due to wake variation in the presence of waves is found. It is found that the effect of other factors is relatively small and easier to take into account as compared to wake variation. Therefore, considering the wake variation at least in the critical wave condition (where the wavelength is close to ship length) in addition to calm water wake is recommended in order to ensure that the optimized propeller performs well both in calm water and in waves. 相似文献
4.
İ. Resatözkan 《Ocean Engineering》1981,8(6):551-598
In this paper the “total (practical) stability” concept is introduced to nonlinear forced rolling motion of a ship. This is achieved by employing “boundedness” and “Lyapunov's function” approach. In this respect two new theorems are proved and conditions and domain of Practical Stability are evaluated. The Paper also contains a critical review of the present status of international intact ship stability regulations. A qualitative discussion of oscillatory rolling motion and the capsizing phenomena is presented. 相似文献
5.
H. Schwanecke 《Ocean Engineering》1982,9(3):271-280
The thrust produced by a marine propeller operating in a spatially non-homogeneous flow is reduced by inhomogenities depending on the angular co-ordinate. The loss of efficiency caused by this reduction of thrust is to a certain extent compensated by increasing the design thrust, a procedure called “unsteady wake adaption”. Numerical calculations show improvements of propeller efficiency which are dependent on the degree of inhomogenity of the flow fielf. 相似文献
6.
I&#x;.R.
zkan 《Ocean Engineering》1979,6(5):493-516
In this study, asymptotic and total stability of the non-linear free and forced pure rolling motions of a ship are investigated. A ship performing a rolling motion is taken as a dynamical system. Lyapunov's direct method is employed in the analysis. By generating a time-invariant Lyapunov function, conditions and the domain of asymptotic stability are obtained for free rolling motion. Results of the work on “boundedness” and “uniform boundedness” of the solutions of the equation of forced rolling motion, done by Özkan (1977), that is, conditions of total (practical) stability and its domain in the phase-plane are given and illustrated. 相似文献
7.
Helmut Schwanecke 《Ocean Engineering》1979,6(6):571-580
The propulsive efficiency of marine vehicles has been investigated from the point of view of the effect of restricted waters of the propulsion characteristics. Model tests have been performed for both single-screw and twin-screw vessels. Also optimum propulsion data for modern sea-going single-screw merchant ships operating in unrestricted waters are presented for the sake of general comparison. 相似文献
8.
Ice ridges form a difficult obstacle for ice navigation. Despite this fact, the resistance of ships in ridges has been investigated very little.A trial was performed with the Finnish icebreaker APU (propulsion machinery power of 8·8 MW) in April 1974 in the Baltic, in order to measure its resistance in ridges.Most of the 11 ridges were so massive that the ship could not penetrate through them by a continuous mode, the ramming mode had to be used.When the ship was penetrating a ridge, its speed and the propeller revolutions were registered for determining the resistance. A doppler radar was used for measuring ship spped.In case the ship was stopped in the ridge it was extracted, reversed and accelerated for the next ram. The time history was registered for determining the ship's speed of advance.Before starting a test, the ridge profile above the water level was measured. This was simply done by using a levelling instrument.The main object of the test was to determine the ship's speed of advance. The results, i.e. ice resistance, ship speed and ridge characteristics were analysed on three levels: momentary values average values for rams and average values for a series of rams in one ridge.The test series presented in the article was the first one in full scale in which the speed of the advance of a ship moving by ramming was determined and the ridge profiles were mapped. The measuring system developed worked well. As results the tests gave data of the ship's resistance and of the ship's speed of advance in ridges. 相似文献
9.
Marine cycloidal propulsion system is efficient in maneuvering ships like tugs, ferries, etc. It is capable of vectoring thrust in all direction in a horizontal plane. When used in pair, the system enables a vessel to perform maneuvers like moving sideways, perform rotation about a point, i.e. turning diameter of its own length, etc. In this system, the propeller blades have to change their angle of attack at different angular position of the disc. Due to this reason, the inflow velocity vector to propeller blades changes continuously. The propeller blade oscillates about a vertical axis passing through its body and at the same time rotates about a point. Superposed on these motions is the dynamics of the ship on which the propulsion system is installed. This results in a formidable and challenging hydrodynamics problem. Each of the propeller blade sections could be considered as an aerofoil operating in combined heave and pitch oscillation mode. Due to the constantly varying inflow velocity, the hydrodynamic flow is unsteady. The unsteady hydrodynamic flow is simulated by incorporating the effect of shed vortices at different time instant behind the trailing edge. Due to the kinematics of the problem, the blade is subjected to higher structural deformation and vibration load. The structural deformation and vibration when coupled with the hydrodynamic loading add another level of complexity to the problem. In this paper, the variation of hydrodynamic load on the propeller blade due to steady and unsteady flow is compared. We also model the structural dynamics of the blade and study its effect on the hydrodynamic loading. Finally, we couple the structural dynamics with hydrodynamics loading and study its influence on the propeller blade for different operating regimes. 相似文献
10.
Resistance and propulsion characteristics of various commercial ships based on CFD results 总被引：2，自引：0，他引：2
This paper uses computational tools to examine the speed performance of various types of commercial ships including resistance and propulsion characteristics. Eight commercial ships built in the last decade were selected for the study. They include four large-sized container carriers, one bulk carrier, one VLCC, and two LNG carriers. The Reynolds averaged Navier-Stokes equation has been utilized, and the computations were executed under the same conditions of the model tests to predict the speed performance, i.e., resistance and self-propulsion. The self-propulsion point was obtained from load-varying tests. The speed performance was predicted based on the model-ship performance analysis method of the revised ITTC’78 method. The limiting streamlines on the hull, wave characteristics around the model ship, and the wake characteristics on the propeller plane were also investigated. After completing the computations, a series of model tests were conducted to evaluate the accuracy of the computational predictions. The predictions clearly reveal the differences in the resistance and propulsion characteristics regarding the various types of commercial ships, and may be applicable to hull-form design. 相似文献
11.
Starting from the regression analysis, equations are provided to determine the hydrostatic data for single-screw ships, fixing the block coefficient CB and the principal dimensions L0, B0and T0, with values T = (0÷1.5)T0. This paper continues and develops a former one, in which the hydrostatic data were obtained in nondimensional form by means of graphs for tive parent hulls of the “Series 60”, with volume 0 = 10,000 m3 at designed draught T0.Numerical examples show the usefulness of the equations, both with respect of the direct calculations starting from the half-breadth values, and with respect to other methods. 相似文献
12.
针对十万吨级深远海养殖工船在波浪中的阻力和运动响应开展了船模试验与模拟计算,并对其最小推进功率进行了校核。以试验流体力学（EFD）模型试验与模型尺度计算流体力学（CFD）模拟计算的结果进行对比作为方法验证,将实尺度CFD模拟计算的结果直接用于最小推进功率的校核。结果显示,EFD模型试验结果与模型尺度CFD计算结果误差在10%左右,计算精度满足工程要求。在规定的恶劣海况下该船型波浪增阻占总阻力的比例最高可达56.3%,螺旋桨转矩可达最大转矩的63.9%。等级2简化评估法得到的最小推进功率为等级1线评估法给出的最小功率线值的58.9%。研究表明实尺度CFD模拟计算可直接用于船舶最小推进功率的校核,此深远海养殖工船使用等级2简化评估方法进行校核更容易满足规范要求,其最小推进功率应不小于6 833 kW。 相似文献
13.
This paper presents the results of a numerical performance analysis to demonstrate the worthiness of a recently patented new concept propulsor, the so-called “thrust-balanced propeller (TBP)”. The main advantage of this unconventional propulsor is its inherent ability to reduce the unsteady effect of blade forces and moments when it is operating in a non-uniform wake flow. The propulsor comprises a pair of diametrically opposed blades that are connected to one another and mounted so as to be rotatable together through a limited angle about their spindle axis. A quasi-hydrodynamic approach is described and applied to perform the numerical analysis using a state-of-the-art lifting surface procedure for conventional propellers. Performance comparisons with a conventional fixed-pitch propeller are made for the blade forces and moments, efficiency, cavitation extents and fluctuating hull pressures. Bearing in mind the quasi-static nature of the analyses, the results present favourable performance characteristics for the thrust-balanced propeller and support the worthiness of the concept. However, the concept needs to be proved through physical model tests, which are planned to take in a cavitation tunnel. 相似文献
14.
By means of Lagrange's equation, the “coupled” equations of motion for a horizontal plate carrying a U-type tuned liquid damper (TLD) are derived. The “uncoupled” equations of motion for the liquid (in the TLD) and the structural system are then obtained by decoupling the “coupled” ones. Unlike the existing literature to indirectly determine the natural frequencies of a damped vibrating system by using the resonant method, the “complex” eigenvalues of the coupled damped system are obtained directly from the associated eigenvalue equations. Besides, the pressure intensities in the two air chambers and the sizes of the two vertical tanks together with the horizontal conduit are arbitrary in the formulation of this paper. The influence of some key parameters of the TLD on the dynamic responses of the structural system is studied. 相似文献
15.
In this paper, a beam without contact with water is called the “dry” beam and the one in contact with water is called the “wet” beam. For a partially (or completely) immersed uniform beam carrying an eccentric tip mass possessing rotary inertia, the conventional analytical (closed-form) solution is achieved by considering the inertial forces and moments of the tip mass and rotary inertia as the boundary conditions at the tip end of the beam. However, it has been found that the approximate solution for the last problem may be achieved by two techniques: Method 1 and Method 2. In Method 1, the basic concept is the same as the conventional analytical method; but in Method 2, the tip end of the beam is considered as a free end, while the inertial forces and moments induced by the tip mass and rotary inertia are considered as the external loads applied at the tip end of the beam. The main differences between the formulation of Method 1 and that of Method 2 are: In Method 1, the “normal” shapes of the “dry” beam are functions of the frequency-dependent boundary conditions but the external loads at the tip end are equal to zero; On the contrary, in Method 2, the “normal” mode shapes of the “dry” beam are determined based on the zero boundary conditions at the tip end of the beam but the external loads at the tip end due to the inertial effects of the tip mass and rotary inertia must be taken into consideration for the free vibration analysis of the “wet” beam. Numerical results reveal that the approximate solution obtained from Method 2 are very close to that from Method 1 if the tip mass moment of inertia is negligible. Besides, the two approximate solutions are also very close to the associated analytical (closed-form) solution or the finite element solution. In general, it is hoped that there exist several methods for tackling the same problem so that one may have more choices to incorporate with the specified cases. It is believed that the two approximate methods presented in this paper will be significant from this point of view. 相似文献
16.
Catherine Schuur Duncan John A. Goff James A. AustinJr. Craig S. Fulthorpe 《Marine Geology》2000,170(3-4):395-421
Seafloor geomorphology and surficial stratigraphy of the New Jersey middle continental shelf provide a detailed record of sea-level change during the last advance and retreat of the Laurentide ice sheet (120 kyr B.P. to Present). A NW–SE-oriented corridor on the middle shelf between water depths of 40 m (the mid-shelf “paleo-shore”) and 100 m (the Franklin “paleo-shore”) encompasses 500 line-km of 2D Huntec boomer profiles (500–3500 Hz), an embedded 4.6 km2 3D volume, and a 490 km2 swath bathymetry map. We use these data to develop a relative stratigraphy. Core samples from published studies also provide some chronological and sedimentological constraints on the upper <5 m of the stratigraphic succession.The following stratigraphic units and surfaces occur (from bottom to top): (1) “R”, a high-amplitude reflection that separates sediment >46.5 kyr old (by AMS 14C dating) from overlying sediment wedges; (2) the outer shelf wedge, a marine unit up to 50 m thick that onlaps “R”; (3) “Channels”, a reflection sub-parallel to the seafloor that incises “R”, and appears as a dendritic system of channels in map view; (4) “Channels” fill, the upper portion of which is sampled and known to represent deepening-upward marine sediments 12.3 kyr in age; (5) the “T” horizon, a seismically discontinuous surface that caps “Channels” fill; (6) oblique ridge deposits, coarse-grained shelly units comprised of km-scale, shallow shelf bedforms; and (7) ribbon-floored swales, bathymetric depressions parallel to modern shelf currents that truncate the oblique ridges and cut into surficial deposits.We interpret this succession of features in light of a global eustatic sea-level curve and the consequent migration of the coastline across the middle shelf during the last 120 kyr. The morphology of the New Jersey middle shelf shows a discrete sequence of stratigraphic elements, and reflects the pulsed episodicity of the last sea-level cycle. “R” is a complicated marine/non-marine erosional surface formed during the last regression, while the outer shelf wedge represents a shelf wedge emplaced during a minor glacial retreat before maximum Wisconsin lowstand (i.e., marine oxygen isotope stage 3.1). “Channels” is a widespread fluvial subarial erosion surface formed at the late Wisconsin glacial maximum 22 kyr B.P. The shoreline migrated back across the mid-shelf corridor non-uniformly during the period represented by “Channels” fill. Oblique ridges are relict features on the New Jersey middle shelf, while the ribbon-floored swales represent modern shelf erosion. There is no systematic relationship between modern seafloor morphology and the very shallowly buried stratigraphic succession. 相似文献
17.
A surface panel method is employed for the thin boundary layer calculation of heavily loaded marine propellers in steady state conditions. Employing the surface panel method, known as the “Morino Method”, the flow field around the propeller is represented by an unknown potential. The majority of the flow field is governed by the potential theory while the viscosity is assumed to be largely confined to thin shear layer on the propeller surface. The boundary layer calculations are performed by using Cebeci-Smith two dimensional model and the local skin friction coefficients and blowing velocities are obtained along the pre-computed on-body streamlines. It is shown that the prediction of torque of the propeller is improved when the boundary layer calculations are used instead of the boundary layer corrections based on the formulae established for the flat plates. 相似文献
18.
In this study, a placement technique named as “alternative placement technique” was developed for antifer blocks and the results of its application to a breakwater model were presented. This placement technique was compared with the existing techniques such as the “regular placement technique”, the “irregular placement technique” and the “sloped wall placement technique” by experiments. The comparison was carried out considering armor layer stability, prototype placement, clarity of the placement technique’s definition, armor layer cost, and wave runup. As a result of this investigation the “alternative placement technique” was found to be superior to the other existing placement techniques. 相似文献
19.
随着船舶推进技术的不断发展,动力定位船舶将更多地使用快速转向推进器以提高其定位性能。快速转向推进器的使用将引入大角度变化率,这会造成优化分配求解域明显的非凸性,给优化问题的求解带来了挑战。针对装备快速转向推进器的动力定位船舶,运用区域外切近似法对其推力分配的非凸性问题进行了凸化,采用增广拉格朗日乘子法对控制力进行了优化分配。仿真结果表明:推荐的凸化处理方法能有效地解决推力分配的非凸问题,分配算法可以充分利用快速转向推进器的机械性能优势,寻找更优的可行解,从而显著地减少动力定位船舶的能耗,提高其定位性能。 相似文献
20.
This paper has two main sources of inspiration. Firstly, building on Flyvbjerg's “Making Social Science Matter”[Flyvbjerg B. Making social science matter: why social inquiry fails and how it can succeed again. Cambridge: Cambridge University Press; 2003], I argue that the contribution of the social sciences to fisheries resource management must essentially be “phronetic” (after Aristotle's phronesis, i.e. practical wisdom), in contrast to the “scientific” (Aristotle: episteme) contribution of the natural sciences. Secondly, inspired by the recent publication “Fish for Life: Interactive Governance for Fisheries” [Kooiman J, Jentoft S, Pullin R, Bavinck M, editors. Fish for life: interactive governance for fisheries. Amsterdam: Amsterdam University Press; 2005], I hold that phronesis is basically what the notion of governance adds to management. Governance is the broader concept, inviting a more reflexive, deliberative and value-rational methodology than the instrumental, means-end oriented management concept. I claim that for interdisciplinarity to work in fisheries it is essential to recognize the fundamental methodological differences that exist between the social and natural sciences. 相似文献