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1.
Time-varying coefficient vector autoregressive (T-VVAR) modeling with instantaneous responses is applied to spectrum analysis
based on the nonstationary motion data of ships. Because of the ship's maneuvers, changes such as course and speed, the ship
motions in waves are regarded as a nonstationary random process, although the seaway can be considered as a stationary stochastic
process. The T-VVAR model is transformed into a state space model, and the time-varying coefficients can be evaluated by using
the Kalman filter algorithm. Using the estimated time-varying coefficients, the instantaneous cross spectra of the ship motions
can be calculated at every moment. In order to examine the reliability of the proposed procedure, on-board tests were carried
out. Under stationary conditions, at a constant speed and course, the proposed method shows good agreement with stationary
vector autoregressive (SVAR) modeling analysis. Moreover, it is confirmed that the proposed method can estimate the instantaneous
cross spectra of the ship motions even under nonstationary conditions, showing that this is a powerful tool for on-line analysis
of the nonstationary motion data of ships.
Received: August 2, 2002 / Accepted: November 28, 2002
Acknowledgments. The authors thank the captain and crew of the training ship Shioji Maru, Tokyo University of Mercantile Marine.
Address correspondence to: T. Iseki (iseki@ipc.tosho-u.ac.jp)
Updated from the Japanese original, which won the 2002 SNAJ prize (J Soc Nav Archit Jpn 2001;190:161–168) 相似文献
2.
《船舶与海洋工程学报》2018,(3)
The paper presents an empirical method to calculate bow flare slamming pressure and the green water load. Many empirical formulae for various types of vessels have been provided by rules of ship classification societies. In the present work, attempt is made to develop generalized formulations for all types of displacement vessels. Extreme sea conditions are considered. Bow flare pressure is derived in terms of flare and waterline angles. Specific condition for limiting waterline angle is derived based on 2 D numerical simulations. Deck wetness is derived in terms of static and dynamic swell-up and the relative motion. Variation of static swell along the length is determined based on potential solution based analyses considering variation in vessels' hull. 2 D wedge simulations are carried out to validate the formulation of dynamic swell-up. Results of the calculated bow flare and deck pressures are compared with various ship classification society formulations and the trends are found to be in good agreement in general barring at bow flare where lower pressure is found in most of the presented cases. Also IACS UR S21 A(2018) governing minimum pressure for deck scantlings is found to be conservative in few of the presented cases. Although scantlings assessment is not performed, the presented new formulations may help in realistic assessment of scantlings. 相似文献
3.
Naoya Umeda Hirotada Hashimoto Akihiko Matsuda 《Journal of Marine Science and Technology》2003,7(3):145-155
We have attempted to develop a more consistent mathematical model for capsizing associated with surf-riding in following
and quartering waves by taking most of the second-order terms of the waves into account. The wave effects on the hull maneuvring
coefficients were estimated, together with the hydrodynamic lift due to wave fluid velocity, and the change in added mass
due to relative wave elevations. The wave effects on the hydrodynamic derivatives with respect to rudder angles were estimated
by using the Mathematical Modelling Group (MMG) model. Then captive ship model experiments were conducted, and these showed
reasonably good agreements between the experiments and the calculations for the wave effects on the hull and the rudder maneuvring
forces. It was also found that the wave effects on restoring moments are much smaller than the Froude–Krylov prediction, and
the minimum restoring arm appears on a wave downslope but not on a wave crest amidship. Thus, an experimental formula of the
lift force due to the heel angle of the ship is provided for numerical modelling. Numerical simulations were then carried
out with these second-order terms of waves, and the results were compared with the results of free-running model experiments.
An improved prediction accuracy for ship motions in following and quartering seas was demonstrated. Although the boundaries
of the ship motion modes were also obtained with both the original model and the present one, the second-order terms for waves
are not so crucial for predicting the capsizing boundaries themselves.
Received: June 20, 2002 / Accepted: October 10, 2002
Acknowledgments. This research was supported by a Grant-in-Aid for Scientific Research of the Ministry of Education, Culture, Sports, Science
and Technology of Japan (No. 13555270). The authors thank Prof. N. Rakhmanin of the Krylov Ship Research Institute for providing
the Russian literature, as well as Mr. H. Murata of NHK (Japan Broadcasting Corporation) for translating it into Japanese.
Address correspondence to: N. Umeda (e-mail: umeda@naoe.eng.osaka-u.ac.jp) 相似文献
4.
舰船的砰击载荷与结构响应的研究一直备受关注.对于双体船来说,砰击按部位可分为底部砰击、外飘砰击和甲板上浪,和连接相邻船体的甲板下侧,即湿甲板砰击.目前对于双体船的砰击计算还不完善,因此对于该船型的砰击研究十分必要.本文分别利用规范计算和直接计算的方式,对砰击载荷作用下双体船强度影响进行研究.规范计算主要基于中国船级社规范计算砰击载荷,直接计算则是通过线性势流理论预报船波相对速度,借助相关规范确定砰击压力系数,实现砰击载荷的直接计算.通过有限元软件加载计算,分析比较2种载荷计算方法对双体船强度的影响,以指导砰击载荷作用下双体船局部结构的设计实践. 相似文献
5.
A nonlinear time-domain procedure is presented which is used to calculate the vertical responses of a container ship advancing
in head waves. The method assumes linear radiation forces represented by time convolution of memory functions, infinite frequency
added masses, and radiation restoring coefficients. The nonlinear hydrostatic restoring and Froude–Krilov forces are computed
exactly over the instantaneous wetted surface of the ship's hull. Forces due to green water on deck are calculated using the
momentum method. Nonlinear effects are identified on different vertical ship responses, namely on the heave and pitch motions,
the vertical accelerations, and the vertical bending moment. These non-linear effects are expressed by the variation of the
transfer function with the wave amplitude, the higher-order harmonics of the time signals, the offset of the time series,
and the asymmetry of the peaks. The numerical results and the quantified nonlinear effects are compared with experimental
results showing an ability to reproduce the main nonlinear effects.
Received: December 17, 2001 / Accepted: January 31, 2002 相似文献
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7.
Masahiko Fujikubo Taoyun Xiao Kazuhiro Yamamura 《Journal of Marine Science and Technology》2003,7(3):119-127
A structural safety assessment of a pontoon-type very large floating structure (VLFS) surrounded by a gravity-type breakwater
was carried out for extreme wave conditions by considering the damage to the breakwater. Bending and shear collapses are considered
to be a failure mode of the floating structure, while overturning damages the breakwater. The probability of the breakwater
overturning, and the transmitted wave height before and after damage to the breakwater, are evaluated using design formulae
for port and harbor facilities in Japan. The ultimate bending and shear strengths of the floating structure are calculated
by the idealized structural unit method (ISUM) and FEM, respectively. The calculated failure probability for the floating
structure is compared with the specified target safety level. It was found that the floating structure under consideration
is most likely to fail by bending in transverse waves, and that the corresponding failure probability satisfies the target
level.
Received: September 12, 2002 / Accepted: October 4, 2002
Acknowledgment. The authors are grateful to Dr. Shigeo Ohmatsu, National Maritime Research Institute, Japan, for allowing us to use the program
of hydroelastic response analysis.
Address correspondence to: M. Fujikubo (e-mail: fujikubo@naoe.hiroshima-u.ac.jp)
Updated from the Japanese original, which won the 2002 SNAJ prize (J Soc Arthit Jpn 2002;190:337–345) 相似文献
8.
考虑甲板运输船的甲板相对较宽,容易导致尺度比超出规范的限定,因此其强度分析应该特殊考虑.利用有限元分析软件MSC.Patran/Nastran建立舱段有限元模型,对甲板运输船的艏部舱段在总纵外载荷、外部水压力和甲板局部载荷作用下的强度进行直接计算和分析. 相似文献
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10.
The theory and procedure established by Wu and Moan in 1996 and 2005 and Wu and Hermundstad in 2002 were applied to a high-speed
transatlantic pentamaran containership. Nonlinear time-domain simulations of ship motions and load effects were carried out
in different sea states. The simulated responses were validated against model tests with satisfactory results. The short-term
probabilities of exceedance were estimated by using different stochastic analysis procedures. The long-term probabilities
of exceedance were obtained based on the short-term results. These served as information about loading in a reliability-based
design approach. The load effects in a semiprobabilistic design were also calculated at an appropriate probability of exceedance
level. 相似文献
11.
《船舶与海洋工程学报》2019,(4)
In this paper, the influence of heave and pitch motions on green water impact on the deck is numerically investigated. The vessel motions are determined using a potential theory based method and provided as input to finite volume based CFD computations of green water phenomenon. A dynamic mesh approach is adopted to determine instantaneous body positioning in the fluid domain.Detailed validation studies with published experimental results for 2D and 3D fixed vessel cases are initially performed to validate the present numerical approach before studying the moving vessel problem. The results show that inclusion of heave and pitch motion changes the disturbed wave field near the bow which influences the free surface as well as the impact loading due to green water. The effect of wave steepness on green water impact is also investigated and it is seen that the present numerical method is capable of capturing green water load. It is observed that the effects of vessel motions on green water load are not negligible and one should consider this effect too. The incorporation of vessel motions in the vertical plane affects the green water loading on the deck. 相似文献
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13.
On the numerical accuracy of the wave load distribution on a ship advancing in short and steep waves
Satu K. Hänninen Tommi Mikkola Jerzy Matusiak 《Journal of Marine Science and Technology》2012,17(2):125-138
Defining numerical uncertainty is an important part of the practical application of a numerical method. In the case of a ship advancing in short and steep waves, little knowledge exists on the solution behaviour as a function of discretisation resolution. This paper studies an interface-capturing (VOF) solution for a passenger ship advancing in steep (kA = 0.24) and short waves (L w /L pp = 0.16). The focus is to estimate quantitative uncertainties for the longitudinal distributions of the first–third harmonic wave loads in the ship bow area. These estimates are derived from the results of three systematically refined discretisation resolutions. The obtained uncertainty distributions reveal that even the uncertainty of the first harmonic wave load varies significantly along the ship bow area. It is shown that the largest local uncertainties of the first harmonic wave load relate to the differences in the local details of the propagating and deforming encountered waves along the hull. This paper also discusses the challenges that were encountered in the quantification of the uncertainties for this complex flow case. 相似文献
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对开式艏门作为某型船的关键设备在波浪载荷下容易损坏。文章阐述了采用模型试验、理论计算、规范计算、实船试验等方法研究艏门波浪载荷,进行艏门有限元建模计算,从而找到薄弱环节并进行优化改装设计的方法。 相似文献
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In this research,a commercial CFD code "Fluent" was applied to optimization of bulbous bow shape for a non ballast water ships(NBS).The ship was developed at the Laboratory of the authors in Osaka Prefecture University,Japan.At first,accuracy of the CFD code was validated by comparing the CFD results with experimental results at towing tank of Osaka Prefecture University.In the optimizing process,the resistances acting on ships in calm water and in regular head waves were defined as the object function.Following features of bulbous bow shapes were considered as design parameters: volume of bulbous bow,height of its volume center,angle of bow bottom,and length of bulbous bow.When referring to the computed results given by the CFD like resistance,pressure and wave pattern made by ships in calm water and in waves,an optimal bow shape for ships was discovered by comparing the results in the series of bow shapes.In the computation on waves,the ship is in fully captured condition because shorter waves,λ/Lpp 0.6,are assumed. 相似文献
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