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Parametric Resonance Analyses for Spar Platform in irregular waves

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China Ocean Engineering 2018年第2期32卷 236-244页

作者： YANG He-zhen XU Pei-ji School of Engineering University of GlasgowGlasgow G128QQUnited Kingdom School of Naval Architecture Ocean and Civil EngineeringShanghai Jiao Tong UniversityShanghai 200240China

The parametric instability of a spar platform in irregular waves is analyzed. Parametric resonance is a phenomenon that may occur when a mechanical system parameter varies over time. When it occurs, a spar platform will have excessive pitch motion and may capsize. Therefore, avoiding parametric resonance is an important design requirement. The traditional methodology includes only a prediction of the Mathieu stability with harmonic excitation in regular waves. However, real sea conditions are irregular, and it has been observed that parametric resonance also occurs in non-harmonic excitations. Thus, it is imperative to predict the parametric resonance of a spar platform in irregular waves. A Hill equation is derived in this work, which can be used to analyze the parametric resonance under multi-frequency excitations. The derived Hill equation for predicting the instability of a spar can include non-harmonic excitation and random phases. The stability charts for multi-frequency excitation in irregular waves are given and compared with that for single frequency excitation in regular waves. Simulations of the pitch dynamic responses are carried out to check the stability. Three-dimensional stability charts with various damping coefficients for irregular waves are also investigated. The results show that the stability property in irregular waves has notable differences compared with that in case of regular waves. In addition, using the Hill equation to obtain the stability chart is an effective method to predict the parametric instability of spar platforms. Moreover, some suggestions for designing spar platforms to avoid parametric resonance are presented, such as increasing the damping coefficient, using an appropriate RAO and increasing the metacentric height.

关键词： spar platform instability parametric resonance Mathieu equation irregular waves dynamic responses

Laboratory Study of the Nonlinear Transformation of irregular waves over A Mild Slope

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China Ocean Engineering 2014年第4期28卷 489-500页

作者：于博马玉祥马小舟董国海 State Key Laboratory of Coastal and Offshore Engineering Dalian University of Technology

This paper considers the nonlinear transformation of irregular waves propagating over a mild slope （1：40）. Two cases of irregular waves, which are mechanically generated based on JONSWAP spectra, are used for this purpose. The results indicate that the wave heights obey the Rayleigh distribution at the offshore location; however, in the shoaling region, the heights of the largest waves are underestimated by the theoretical distributions. In the surf zone, the wave heights can be approximated by the composite Weibull distribution. In addition, the nonlinear phase coupling within the irregular waves is investigated by the wavelet-based bicoherence. The bicoherence spectra reflect that the number of frequency modes participating in the phase coupling increases with the decreasing water depth, as does the degree of phase coupling. After the incipient breaking, even though the degree of phase coupling decreases, a great number of higher harmonic wave modes are also involved in nonlinear interactions. Moreover, the summed bicoherence indicates that the frequency mode related to the strongest local nonlinear interactions shifts to higher harmonics with the decreasing water depth.

关键词： irregular waves shallow water nonlinear interactions wave height distribution wavelet bicoherence

Statistical Analyses of Wave Height Distribution for Multidirectional irregular waves over A Sloping Bottom

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China Ocean Engineering 2021年第4期35卷 504-517页

作者： GAO Jun-liang CHEN Hong-zhou MEI Li-li LIU Zhen LIU Qian School of Naval Architecture and Ocean Engineering Jiangsu University of Science and TechnologyZhenjiang 212100China School of Marine Engineering Equipment Zhejiang Ocean UniversityZhoushan 316022China Henan Province Construction Engineering Quality Inspection and Testing Center Station Co.Ltd. Zhengzhou 450053China State Key Laboratory of Coastal and Offshore Engineering Dalian University of TechnologyDalian 116024China

The main objective of this paper is to examine the influences of both the principal wave direction and the directional spreading parameter of the wave energy on the wave height evolution of multidirectional irregular waves over an impermeable sloping bottom and to propose an improved wave height distribution model based on an existing classical *** numerical model FUNWAVE 2.0,based on a fully nonlinear Boussinesq equation,is employed to simulate the propagation of multidirectional irregular waves over the sloping *** of wave heights derived from wave trains with various principal wave directions and different directional spreading parameters are *** show that both the principal wave direction and the wave directional spread have significant influences on the wave height evolution on a varying coastal *** shoaling effect for the wave height is obviously weakened with the increase of the principal wave direction and with the decrease of the directional spreading *** the simulated data,the classical Klopman wave height distribution model is improved by considering the influences of both *** is found that the improved model performs better in describing the wave height distribution for the multidirectional irregular waves in shallow water.

关键词： wave height distribution multidirectional waves irregular waves sloping bottom FUNWAVE 2.0 model

Experimental Study on Local Scour Around A Large Circular Cylinder Under irregular waves

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海洋工程：英文版 2004年第2期18卷 245-256页

作者：周益人陈国平 Harbor and River Department

A series of physical model tests are conducted for local scour around a circular cylinder of a relatively large diameter (0 15< D/L <0.5) under the action of irregular waves. The laws of change of the topography ar... 详细信息

A series of physical model tests are conducted for local scour around a circular cylinder of a relatively large diameter (0 15irregular waves. The laws of change of the topography around the cylinder are systematically studied. The effects of wave height, wave period, water depth, sediment grain size and cylinder diameter are taken into account. The mechanism of formation of the topography around the cylinder is analyzed. A detailed analysis is given to bed sediment grain size, and it is considered that the depth of scour around the cylinder under wave action is not inversely proportional to the sediment grain diameter. On such a basis, an equation is proposed for calculation of the maximum depth of scour around a cylinder as well as its position under the action of irregular waves.

关键词： large circular cylinder local scour irregular waves

Response Analysis of Tension-Based Tension Leg Platform Under irregular waves

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China Ocean Engineering 2016年第4期30卷 603-614页

作者： D.S.Bhaskara Rao R.Panneer Selvam Department of Ocean Engineering Indian Institute of Technology Madras

Tension Leg Platform（TLP） is a hybrid structure used as oil drilling and production facility within water depths of 1200 m. The extension of this TLP concept to deeper waters is a challenge and warrants for some innovative design concepts. In this paper, a relatively new concept of TLP which is christened as Tension-Based Tension Leg Platform（TBTLP） and patented by Srinivasan（1998） has been chosen for study. Response analysis of TLP with one tension base under irregular waves for three different sea states has been performed using hydrodynamic tool ANSYS？ AQWA？. Results are reported in terms of RAOs, response spectrums for surge, heave and pitch degrees of freedom from which spectral statistics have been obtained. The statistics of TBTLP have been compared with TLPs（without tension base） for two different water depths to highlight the features of the new concept. The effect of viscous damping and loading effects on the RAOs are also investigated.

关键词： Tension-Based Tension Leg Platform irregular waves time domain response response amplitudeoperators spectrum statistics coupled analysis

Placement Effect on the Stability of Tetrapod Armor Unit on Breakwaters in irregular waves

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China Ocean Engineering 2017年第6期31卷 747-753页

作者： Yesim CELIKOGLU Demet ENGIN Yildiz Technical University Department of Civil Engineering Hydraulics and Coastal Engineering Laboratory Davutpasa 34210 Esenler-Istanbul Turkey

Tetrapod, one of the well-known artificial concrete units, is frequently used as an armor unit on breakwaters. Two layers of tetrapod units are normmaly placed on the breakwaters with different placement methods. In this study, the stability of tetrapod units with two different regularly placement methods are investigated experimentally in irregular waves. Stability coefficients of tetrapod units for both placement methods are obtained. The important characteristic wave parameters of irregular waves causing the same damage ratio as those of the regular waves are also determined. It reveals that the average of one-tenth highest wave heights within the wave train （H1/lo） causes the similar damage as regular waves.

关键词： breakwaters tetrapod unit stability placement methods irregular waves

URANS simulations of ship motion responses in long-crest irregular waves

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Journal of Hydrodynamics 2014年第3期26卷 436-446页

作者：沈志荣叶海轩万德成 State Key Laboratory of Ocean Engineering School of Naval Architecture Ocean and Civil EngineeringShanghai Jiao Tong University

In this paper, numerical prediction of ship motion responses in long-crest irregular waves by the URANS-VOF method is presented. A white noise spectrum is applied to generate the incoming waves to evaluate the motion responses. The procedure can replace a decade of simulations in regular wave with one single run to obtain a complete curve of linear motion response, considerably reducing computation time. A correction procedure is employed to adjust the wave generation signal based on the wave spectrum and achieves fairly better results in the wave tank. Three ship models with five wave conditions are introduced to validate the method. The computations in this paper are completed by using the solver naoe-FOAM-SJTU, a solver developed for ship and ocean engineering based on the open source code OpenFOAM. The computational motion responses by the irregular wave procedure are compared with the results by regular wave, experiments and strip theory. Transfer functions by irregular wave closely agree with the data obtained in the regular waves, showing negligible difference. The comparison between computational results and experiments also show good agreements. The results better predicted by CFD method than strip theories indicate that this method can compensate for the inaccuracy of the strip theories. The results confirm that the irregular wave procedure is a promising method for the accurate prediction of motion responses with less accuracy loss and higher efficiency compared with the regular wave procedure.

关键词： irregular waves white noise spectrum unsteady incompressible Reynolds-Average Navier-Stokes(URANS) equations ship motion response naoe-FOAM-SJTU solver OpenFOAM

Ince-Strutt Stability Charts for Ship Parametric Roll Resonance in irregular waves

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China Ocean Engineering 2017年第4期31卷 447-457页

作者： ZHANG Xiao YANG He-zhen XIAO Fei XU Pei-ji National Key Laboratory on Ship Vibration &Noise China Ship Development and Design Center State Key Laboratory of Ocean Engineering School of Naval Architecture.Ocean and Civil EngineeringShanghai Jiao Tong University School of Civil and Environmental Engineering Nanyang Technological University

Ince-Strutt stability chart of ship parametric roll resonance in irregular waves is conducted and utilized for the exploration of the parametric roll resonance in irregular waves. Ship parametric roll resonance will lead to large amplitude roll motion and even wreck. Firstly, the equation describing the parametric roll resonance in irregular waves is derived according to Grim’s effective theory and the corresponding Ince-Strutt stability charts are obtained. Secondly, the differences of stability charts for the parametric roll resonance in irregular and regular waves are compared. Thirdly, wave phases and peak periods are taken into consideration to obtain a more realistic sea condition. The influence of random wave phases should be taken into consideration when the analyzed points are located near the instability boundary. Stability charts for different wave peak periods are various. Stability charts are helpful for the parameter determination in design stage to better adapt to sailing condition. Last, ship variables are analyzed according to stability charts by a statistical approach. The increase of the metacentric height will help improve ship stability.

关键词： parametric instability parametric rolling multi-frequency irregular waves Ince-Strutt stability chart

Interaction of irregular waves with Vertical Breakwater and Characteristics of Secondary Wave Generated by Overtopping

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Journal of Ocean University of China 2021年第6期20卷 1353-1370页

作者： HAN Xinyu JIANG Yunpeng DONG Sheng College of Engineering Ocean University of ChinaQingdao 266100China Tianjin Research Institute for Water Transport Engineering Tianjin 300456China

This study investigated the interaction between irregular waves and vertical *** main goal was to determine the wave force on the breakwater for different depths,along with the evolution of the secondary wave generated by *** open source code DualSPHysics was used in the *** transform was employed to remove the acoustic components from the weakly compressible smoothed particle hydrodynamics pressure *** results of the experiments and simulations showed that although the wave height at the low water level(case 2 was smaller than that at the high water level(case 1,the horizontal and uplifting force of case 2 was higher than that of case *** case 2,a large impact pressure occurred because of the plunging wave and wave breaking *** the water level was close to the breakwater top in case 1,the secondary wave generated by overtopping was *** indicated that wave and breakwater interactions transfer wave energy from the leading wave component to higher *** main harmonics were identified in the secondary *** first harmonic was the incident peak frequency,which was still the dominant *** the wave propagation behind the breakwater,the frequencies of harmonics remained unchanged,but the amplitude of the first harmonic showed an obvious *** the same wave condition,the first and second harmonics did not change with depth.

关键词： irregular waves vertical breakwater wavelet wave force secondary wave