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Failure Pressure Analysis of Corroded Moderate-to-High Strength Pipelines

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China Ocean engineering 2016年第1期30卷 69-82页

作者：苏晨亮李昕周晶 state key laboratory of coastal and offshore engineering Dalian University of Technology

Based on the elastic-plastic, large-deformation finite element method, burst capacity of steel pipeline with longitudinal corrosion defect subjected to internal pressure is studied. The appropriate stress-based criterion is used to predict the failure pressure of finite element model of corroded pipeline under internal pressure. By considering the pipe steel grades and geometries of corrosion defects, a series of finite element analyses is conducted. The effects of corrosion depth, length and width on burst capacity are also discussed. A specific failure pressure solution for the assessment of corrosion defects in moderate-to-high strength pipeline is proposed on the base of numerical results. The failure pressures predicted by the proposed method are in better agreement with the experimental results than the results by the other methods.

关键词： steel pipeline stress-based criteria failure pressure effect of corrosion width

A Study of the Stability Properties in Simulation of Wave Propagation with SPH Method

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China Ocean engineering 2017年第2期31卷 173-181页

作者： CHANG Jiang LIU Shu-xue LI Jin-xuan state key laboratory of coastal and offshore engineering Dalian University of Technology

When ordinary Smoothed Particle Hydrodynamics （SPH） method is used to simulate wave propagation in a wave tank, it is usually observed that the wave height decays and the wave length elongates along the direction of wave propagation. Accompanied with this phenomenon, the pressure under water decays either and shows a big oscillation simultaneously. The reason is the natural potential tensile instability of modeling water motion with ordinary SPH which is caused by particle negative stress in the computation. I＇o deal with the problems, a new sextic kernel function is proposed to reduce this instability. An appropriate smooth length is given and its computation criterion is also suggested. At the same time, a new kind dynamic boundary condition is introduced. Based on these improvements, the new SPH method named stability improved SPH （SISPH） can simulate the wave propagation well. Both the water surface and pressure can be well expressed and the oscillation of pressure is nearly eliminated. Compared with other improved methods, SISPH can truly reveal the physical reality without bringing some new problems in a simple way.

关键词： wave propagation SPH method instability sextic kernel function SISPH

Investigation on A Resistance-Type Porosity Model and the Experimental Coefficients

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China Ocean engineering 2019年第4期33卷 468-476页

作者： ZHAO Pei-hong SUN Da-peng WU Hao state key laboratory of coastal and offshore engineering Dalian University of Technology

The mathematical model based on the Volume-Averaged/Reynolds-Averaged Navier Stokes (VARANS) equations has been adopted in recent years to generally simulate the interaction between waves and porous structures. However, it is still hard to determine the two experimental coefficients (α and β) included in VARANS equations. In the present study, VARANS equation is adopted to describe the flow inside and outside the porous structures uniformly, with applying the volume averaged k ε model to simulate the turbulence effect. A new calibration method is used to evaluate the accuracy of numerical simulation of wave motion on porous seabed with different coefficients, by taking the wave damping rate as an index. The calibration is achieved by completing a simulation matrix on two calibration cases. A region can be found in the parameter space to produce a lower error, which means that the simulation results are better consistent with the experimental results.

关键词： porous media VARANS equations wave damping rate perforated caisson rubble-mound foundation

Establishment of Numerical Wave Flume Based on the Second-Order Wave-Maker Theory

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China Ocean engineering 2019年第2期33卷 160-171页

作者： ZHANG Hao-chen LIU Shu-xue LI Jin-xuan WANG Lei state key laboratory of coastal and offshore engineering Dalian University of Technology

With growing computational power, the first-order wave-maker theory has become well established and is widely used for numerical wave flumes. However, existing numerical models based on the first-order wave-maker theory lose accuracy as nonlinear effects become prominent. Because spurious harmonic waves and primary waves have different propagation velocities, waves simulated by using the first-order wave-maker theory have an unstable wave profile. In this paper, a numerical wave flume with a piston-type wave-maker based on the second-order wave-maker theory has been established. Dynamic mesh technique was developed. The boundary treatment for irregular wave simulation was specially dealt with. Comparisons of the free-surface elevations using the first-order and second-order wave-maker theory prove that second-order wave-maker theory can generate stable wave profiles in both the spatial and time domains. Harmonic analysis and spectral analysis were used to prove the superiority of the second-order wave-maker theory from other two aspects. To simulate irregular waves, the numerical flume was improved to solve the problem of the water depth variation due to low-frequency motion of the wave board. In summary, the new numerical flume using the second-order wave-maker theory can guarantee the accuracy of waves by adding an extra motion of the wave board. The boundary treatment method can provide a reference for the improvement of nonlinear numerical flume.

关键词： second-order wave generation nonlinear wave spurious harmonic wave numerical flume

Viscous Effects on Wave Forces on A Submerged Horizontal Circular Cylinder

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China Ocean engineering 2018年第3期32卷 245-255页

作者： TENG Bin MAO Hong-fei LU Lin state key laboratory of coastal and offshore engineering Dalian University of Technology

Numerical simulations are carried out for wave action on a submerged horizontal circular cylinder by means of a viscous fluid model, and it is focused on the examination of the discrepancies between the viscous fluid results and the potential flow solutions. It is found that the lift force resulted from rotational flow on the circular cylinder is always in anti-phase with the inertia force and induces the discrepancies between the results. The influence factors on the magnitude of the lift force, especially the correlation between the stagnation-point position and the wave amplitude, and the effect of the vortex shedding are investigated by further examination on the flow fields around the cylinder. The viscous numerical calculations at different wave frequencies showed that the wave frequency has also significant influence on the wave forces. Under higher frequency and larger amplitude wave action, vortex shedding from the circular cylinder will appear and influence the wave forces on the cylinder substantially.

关键词： submerged horizontal circular cylinder wave force lift force vortex effect

Dynamic Analysis of A 5-MW Tripod offshore Wind Turbine by Considering Fluid–Structure Interaction

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China Ocean engineering 2017年第5期31卷 559-566页

作者： ZHANG Li-wei LI Xin state key laboratory of coastal and offshore engineering Dalian University of Technology

Fixed offshore wind turbines usually have large underwater supporting structures. The fluid influences the dynamic characteristics of the structure system. The dynamic model of a 5-MW tripod offshore wind turbine considering the pile-soil system and fluid structure interaction （FSI） is established, and the structural modes in air and in water are obtained by use of ANSYS. By comparing low-order natural frequencies and mode shapes, the influence of sea water on the free vibration characteristics of offshore wind turbine is analyzed. On basis of the above work, seismic responses under excitation by E1-Centro waves are calculated by the time-history analysis method. The results reveal that the dynamic responses such as the lateral displacement of the foundation and the section bending moment of the tubular piles increase substantially under the influence of the added-mass and hydrodynamic pressure of sea water. The method and conclusions presented in this paper can provide a theoretical reference for structure design and analysis of offshore wind turbines fixed in deep seawater.

关键词： 5-MW tripod offshore wind turbine fluid-structure interaction natural frequency seismic analysis,hydrodynamic pressure

Observations of Freak Waves in Random Wave Field in 2D Experimental Wave Flume

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China Ocean engineering 2013年第5期27卷 659-670页

作者：李金宣李鹏飞柳淑学 state key laboratory of coastal and offshore engineering Dalian University of Technology

Long time series of wave field are experimentally simulated by JONSWAP spectra with random phases in a 2D wave flume. Statistic properties of wave surface, such as significant wave height, skewness and kurtosis, are analyzed, and the freak wave occurrence probability and its relations with Benjamin-Feir index （BFI） are also investigated. The results show that the skewness and the kurtosis are significantly dependent on the wave steepness, and the kurtosis increases along the flume when BFI is large. The freak waves are observed in random wave groups. They occur more frequently than expected, especially for the wave groups with large BFI.

关键词： freak waves Benjamin-Feir instability random wave groups

Experimental Investigation on the Extreme Waves Induced by Single Wave Packets in Finite Water Depth

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China Ocean engineering 2018年第4期32卷 375-387页

作者： HE Yan-li MA Yu-xiang MA Xiao-zhou DONG Guo-hai state key laboratory of coastal and offshore engineering Dalian University of Technology

Single Gaussian wave groups with different initial wave steepness εand width N are produced in laboratory in finite depth to study the nonlinear evolution, the extreme events and breaking. The results show that wave groups with larger εwill evolve to be several envelope solitons(short wave groups). By analyzing geometric parameters, a break in the evolution of the wave elevation and asymmetric parameters after extreme wave may be an indicator for the inception of refocus and the maximal wave moving to the middle, namely, wave down-shift occurs. The analysis of the surface elevations with HHT(Hilbert-Huang Transform), which presents the concrete local variation of energy in time and frequency can be exhibited clearly, reveals that the higher frequency components play a major role in forming the extreme event and the contribution to the nonlinearity. Instantaneous energy and frequency in the vicinity of the extreme wave are also examined locally. For spilling breakers, the energy residing in the whole wave front dissipates much more due to breaking, while the energy in the rear of wave crest loses little, and the intra-wave frequency modulation increases as focus. It illustrates that the maximal first order instantaneous frequency fand the largest crest tend to emerge at the same time after extreme wave when significant energy dissipation happens, and vice versa. In addition, it shows that there is no obvious relation of the CDN(combined degree of nonlinearity) to the wave breaking for the single Gaussian wave group in finite water depth.

关键词： wave group wave breaking Hilbert-Huang transform instantaneous frequency extreme waves

Prediction of Load Carrying Capacity of Corroded Reinforced Concrete Beam

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海洋工程：英文版 2004年第1期18卷 107-118页

作者：范颖芳周晶冯新 state key laboratory of coastal and offshore engineering School of Civil engineering

A novel method for prediction of the load carrying capacity of a corroded reinforced concrete beam (CRCB) is presented in the paper. Nine reinforced concrete beams, which had been working in an aggressive environment for more than 10 years, were tested in the laboratory. Comprehensive tests, including flexural test, strength test for corroded concrete and rusty rebar, and pullout test for bond strength between concrete and rebar, were conducted. ne flexural test results of CRCBs reveal that the distribution of surface cracks on the beams shows a fractal behavior. The relationship between the fractal dimensions and mechanical properties of CRCBs is then studied. A prediction model based on artificial neural network (ANN) is established by the use of the fractal dimension as the corrosion index, together with the basic information of the beam. The validity of the prediction model is demonstrated through the experimental data, and satisfactory results are achieved.

关键词： corrosion reinforced concrete beam load carrying capacity prediction fractal artificial neural network