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Hydrodynamic performance of flexible risers subject to vortex-induced vibrations

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Journal of Hydrodynamics 2013年第1期25卷 156-164页

作者： ZHANG Hui YANG Jian-min xiao long-fei LU Hai-ning State Key Laboratory of Ocean Engineering Shanghai Jiaotong University

The Vortex-Induced Vibration （VIV） displacements are determined from both the measured accelerations and strains in a series of VIV experiments. Based on the results, the forces in the longitudinal, transversal and tangential directions are estimated by using the finite element method with and without considering the interactions between adjacent elements. The numerical simulation indicates that the method considering the interactions performs better in the estimation of the forces. The component of the transversal force in phase with the acceleration is associated with the added mass coefficient. The estimated added mass coefficients take abnormally high values at the locations where the displacements are small. An improved formula based on the L＇Hospital＇s rule is pro- posed to deal with this problem. The results show the advantage of this formula in estimating the added mass coefficients at the loca- tions with small VIV displacements.

关键词： Vortex-Induced Vibration (VIV) flexible risers hydrodynamic force added mass coefficient

Research on the Effects of in-Line Oscillatory Flow on the Vortex-Induced Motions of A Deep Draft Semi-Submersible in Currents

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China Ocean Engineering 2017年第3期31卷 272-283页

作者： WU Fan xiao long-fei LIU Ming-yue TIAN Xin-liang The State Key Laboratory of Ocean Engineering Shanghai Jiao Tong University Shanghai 200240 China

A Deep Draft Semi-submersible （DDS） under certain flow conditions could be subjected to Vortex-Induced Motions （VIM）, which significantly influences the loads on and life fatigue of the moorings and the risers. To investigate the VIM of a DDS with four rectangular section columns in waves coupled with a uniform current, a numerical study using the computational fluid dynamics （CFD） method was conducted. The issues of the VIM of multi-column floaters can be con＇,＇eniently converted to the issues of oscillating cylinders in fluid cross flows. This paper looks into the CFD numerical simulation of infinite cylinders having rectangular sections in a two-dimensional sinusoidal time- dependent flow field coupled with a uniform current. The resulted hydrodynamic forces and motion responses in different oscillatory flows plus currents both aligned in the same direction for the incidence of 135° of the DDS relative to the flow are compared with the ones in current only cases. The results show that the VIM response of this geometric arrangement of a DDS with four rectangular columns in a current combined with oscillatory flows is more evident than that in the current only case. The oscillatory flows and waves have the significant influence on the VIM response, forces and trajectory, in-plane motions of the DDS.

关键词： Vortex-Induced Motion (VIM) deep draft semi-submersible numerical simulation oscillatory flow uniform current

Classification and Comparison of Wave Impact Modes on Semi-Submersibles

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China Ocean Engineering 2021年第2期35卷 161-175页

作者： GUO Ying-hao xiao long-fei WEI Han-di LI Xin LI Lei DENG Yan-fei State Key Laboratory of Ocean Engineering Shanghai Jiao Tong UniversityShanghai 200240China SJTU-Sanya Yazhou Bay Institute of Deepsea Technology Hainan 572024China CIMC Offshore Co.Ltd. Shenzhen 518000China

Semi-submersibles for offshore oil exploration and exploitation often suffer from severe wave impacts in extreme ocean *** to the complex wave interactions among structural components of semi-submersibles,in-depth analyses on the characteristics of wave impact events are of significance for both industry and *** experimental study was carried out to investigate the local wave impact loads on a semi-submersible,with focus on understanding the wave impacts by identifying typical impact *** criteria are proposed to classify major wave impacts on the semi-submersible into six modes and two *** results show that the classification is reasonable and provides valuable information for studying wave impacts on *** incident wave characteristics at the fore column of the semi-submersible have important influence on the wave impact *** fore-column dominating wave impacts exert the most intense loads on the fore column and feature well-developed breaking waves or slightly breaking waves at the fore ***,the aft-column dominating wave impacts exert the most intense loads on the aft column or the deck bottom and feature non-breaking waves at the fore *** loss during the fore-column impact weakens the impact severity on the aft column in the fore-column dominating wave *** shoaling effect of the submerged pontoon and different motion configurations of the platform result in higher occurrence rate of the aft-column dominating wave *** impact modes are also distinguished by different spatial distributions of wave impact loads.

关键词： wave impact load semi-submersible wave breaking energy loss shoaling effect

EXPERIMENTAL INVESTIGATION OF EFFECTS OF INNER-TANK SLO-SHING ON HYDRODYNAMICS OF AN FLNG SYSTEM

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Journal of Hydrodynamics 2012年第1期24卷 107-115页

作者： ZHAO Wen-hua YANG Jian-min HU Zhi-qiang xiao long-fei State Key Laboratory of Ocean Engineering Shanghai Jiao Tong UniversityShanghai 200240China

The present research focuses on experimentally clarifying the effect of inner-tank sloshing on the hydrodynamics of an Floating Liquefied Natural Gas（FLNG）*** the comparisons of the results obtained from the model tests carried out with the vessel model ballasted with liquid and solid cargo separately,the effects of the inner-tank sloshing on the hydrodynamics of an FLNG system are highlighted and *** languages of the maximum,minimum,mean values and the standard deviations and power density spectra calculated with the help of the algorithm of Fast Fourier Transformation（FFT）are *** is concluded that the effects of the inner-tank sloshing on the responses of the FLNG system are sensitive to wave excitation frequencies,and that the effects of the inner-tank sloshing play an important role,particularly in the roll motion of the FLNG *** outcome of the proposed technique would offer constructive feedback,which can lead to more practical applications and can serve as a reference for the verification of the potential numerical simulations by other researchers.

关键词： Floating Liquefied Natural Gas(FLNG) hydrodynamics sloshing model tests coupled effects

EXPERIMENTAL INVESTIGATION ON WAVE RUN-UP CHARACTERISTICS Along COLUMNS AND AIR GAP RESPONSE OF SEMI-SUBMERSIBLE PLATFORM

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Journal of Hydrodynamics 2011年第5期23卷 625-636页

作者： SHAN Tie-bing YANG Jian-min LI Xin xiao long-fei State Key Laboratory of Ocean Engineering Shanghai Jiao Tong University Shanghai 200240 China

This article mainly concentrates on a large-volume drilling semi-submersible platform, aiming to reveal wave run-up characteristics along square columns and give the relationship between air gap distributions and wave parameters. The tests with fixed model were conducted firstly on its encountering a series of monochromatic waves. A wide range of wave slope （H/L ） were selected to investigate the air gap response in detail. As can be seen, larger wave steepness will generally cause smaller air gap in the same wave period, which indicates nonlinear effects of incoming wave can amplify wave elevation. Model tests with mooring condition were also conducted in the same wave conditions. As was expected, the maximum relative wave elevation reduces obviously compared with the fixed one. However, wave shape close to columns show higher harmonic characteristics due to interaction between waves and the columns of semi-submersible platform. Meaningful conclusions from the model tests are drawn in this article, which is helpful in air gap design of floating offshore platform to a certain extent. In addition, the experimental results will provide an important reference for further research on validation and update of theoretical models of air gap.

关键词： wave run-up air gap diffraction-radiation effects wave steepness

THEORETICAL RESEARCH ON HYDRODYNAMICS OF A GEOMETRIC SPAR IN FREQUENCY-AND TIME-DOMAINS

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Journal of Hydrodynamics 2008年第1期20卷 30-38页

作者： WANG Ying YANG Jian-min HU Zhi-qiang xiao long-fei State Key Laboratory of Ocean Engineering School of Naval Architecture Ocean and Civil Engineering Shanghai Jiaotong University Shanghai 200030 China

Considering the coupling effects of the vessel and its riser and mooring system, hydrodynamic analyses of a geometric spar were performed both in frequency- and time-domains. Based on the boundary element method, the 3-D panel model of the geometric spar and the related free water surface model were established, and the first-order and second-order difference-frequency wave loads and other hydrodynamic coefficients were calculated. Frequency domain analysis of the motion Response Amplitude Operators （RAO） and Quadratic Transfer Functions （QTF） and time domain analysis of the response series and spectra in an extreme wave condition were conducted for the coupled system with the mooring lines and risers involved. These analyses were further validated by the physical model test results.

关键词： geometric spar hydrodynamics coupled analysis frequency domain time domain

NUMERICAL SIMULATION OF IRREGULAR WAVE-SIMULATING IRREGULAR WAVE TRAIN

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Journal of Hydrodynamics 2010年第4期22卷 537-545页

作者： LIANG Xiu-feng YANG Jian-min LI Jun xiao long-fei LI Xin State Key Laboratory of Ocean Engineering Shanghai Jiao Tong University Shanghai 200030 China

In real sea states,damage incidents on offshore floating structures are not due to the whole time series of wave elevation characterized as statistical one but due to few extreme waves or wave groups in irregular wave ***,using CFD tools to precisely simulate predetermined irregular wave train will lay sound basis for understanding the local characteristic of the flow field and impact loads on offshore floating structures when damage incidents *** this article,the generation of single extreme wave is investigated in a numerical wave ***,experimental irregular wave train is decomposed into certain number of small-amplitude *** Fourier series expansion is performed to determine the amplitude and initial phase angle of each wave component.A hydrodynamic transfer function is used to calculate the amplitude of wave-maker motion associated with each wave *** superposition is carried out on all of the wave-maker motion components to get the final wave-maker *** the wave-maker motion as input,simulation of the single extreme irregular wave train is modeled *** the method is applied to simulating a much more complicated irregular wave *** again main features of the complicated irregular wave train are reproduced compared with experiment carried out in the new deepwater experimental basin at Shanghai Jiao Tong *** the simulation,dynamic mesh method is enabled to model the piston-type wave-maker,the Volume Of Fluid（VOF） method is employed to capture the free surface and a dissipation zone is introduced to deal with wave reflection.

关键词： numerical wave tank irregular wave train Volume of Fluid (VOF) dynamic mesh

Surface Polarization Effects on Collapse Transition of Polyelectrolyte Brushes

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Chinese Journal of Polymer Science 2024年第9期42卷 1313-1320,I0006页

作者： xiao-fei Xu State Key Laboratory of Chemical Engineering and School of Chemical Engineering East China University of Science and TechnologyShanghai200237China

Polyelectrolyte brushes(PEBs)are commonly used to modify surface that have attracted great research *** dielectric permittivity of the grafted surface is typically significantly different from that of solution,which results in surface polarization(SP)effect with a jump of electric *** is thus important to study how SP alters the PEB’s structure and *** this work,the SP effects on PEB structure was studied using a statistical thermodynamic *** free energy functional to describe SP effect was constructed by using the image-charge ***,the electrostatic potential was solved from a modified Poisson-Boltzmann equation taking the ion solvation effect into *** the absence of SP,the thickness of PEB exhibited a continuous collapse transition when decreasing the solvent *** the presence of SP,the collapse became a jump-like *** energy analysis showed that the long-range Coulombic interaction dominated the transition because of the enhanced counterion condensation in the presence of *** theory provides an effective tool to study SP effect on PEBs,and the results explain the underlying physics in PEB collapse transition.

关键词： Surface polarization Polyelectrolyte brush Image charge Ion solvation Polyelectrolyte collapse transition

Current landscape of preoperative neoadjuvant therapies for initial resectable colorectal cancer liver metastasis

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World Journal of Gastroenterology 2024年第7期30卷 663-672页

作者： xiao-fei Cheng Feng Zhao Dong Chen Fan-long Liu Department of Colorectal Surgery The First Affiliated HospitalZhejiang University School of MedicineHangzhou 310003Zhejiang ProvinceChina Department of Radiation Oncology The First Affiliated HospitalZhejiang University School of MedicineHangzhou 310003Zhejiang ProvinceChina

Colorectal cancer liver metastasis(CRLM)presents a clinical challenge,and optimizing treatment strategies is crucial for improving patient *** resection,a key element in achieving prolonged survival,is often linked to a heightened risk of *** the potential benefits of preoperative neoadjuvant chemotherapy in managing resectable liver metastases,this approach has gained attention for its role in tumor downsizing,assessing biological behavior,and reducing the risk of postoperative ***,the use of neoadjuvant chemotherapy in initially resectable CRLM sparks ongoing *** balance between tumor reduction and the risk of hepatic injury,coupled with concerns about delaying surgery,necessitates a nuanced *** article explores recent research insights and draws upon the practical experiences at our center to address critical issues regarding considerations for initially resectable *** the criteria for patient selection and the judicious choice of neoadjuvant regimens are pivotal areas of *** the right balance between maximizing treatment efficacy and minimizing adverse effects is *** dynamic landscape of precision medicine is also reflected in the evolving role of gene testing,such as RAS/BRAF and PIK3CA,in tailoring neoadjuvant ***,the review emphasizes the need for a multidisciplinary approach to navigate the comp-lexities of *** technical expertise and biological insights is crucial in refining neoadjuvant *** management of progression following neoadjuvant chemotherapy requires a tailored approach,acknowledging the diverse biological behaviors that may *** conclusion,this review aims to provide a comprehensive perspective on the considerations,challenges,and advancements in the use of neoadjuvant chemotherapy for initially resectable *** combining evidencebased insights with practical experiences,we aspire to contribute

关键词： Neoadjuvant therapy Colorectal cancer liver metastasis Multidisciplinary teams Chemotherapeutic regimens Resectability criteria