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The moving particle semi-implicit (MPS) method has demonstrated its usefulness in practical engineering applications. Although it has wide applicability, it is still hard to predict the pressure precisely using the MPS method. A pressure-convection particle method based on the MPS method is proposed to overcome this problem. The improved performance of this new method is validated with computational and measured results. The approach is also applied to compute the problem of sloshing associated with floating body motion in waves. The pressure-convection MPS method demonstrated its capability to improve the prediction of pressure.
This study has focused on developing numerical procedures for the static and dynamic nonlinear analysis of mooring lines. A geometrically nonlinear finite element method using isoparametric cable element with two nodes is briefly presented on the basis of the total Lagrangian formulation. The static and dynamic equilibrium equations of mooring lines are established. An incremental-iterative method is used to determine the initial static equilibrium state of cable systems under the action of self weights, buoyancy and current. Also the Newmark method is used for dynamic nonlinear analysis of ocean cables. Numerical examples are presented to validate the present numerical method, and examine the effect of various parameters.
Hurricane Katrina and Rita resulted in the largest number of platforms destroyed and damaged in the history of Gulf of Mexico operations. With the trend of global warming, sea level rising and the frequency and intensity of typhoon increase. How to determine a reasonable deck elevation against the largest hurricane waves has become a key issue in offshore platforms design and construction for the unification of economy and safety. In this paper, the multivariate compound extreme value distribution (MCEVD) model is used to predict the deck elevation with different combination of tide, surge height, and crest height. Compared with practice recommended by American Petroleum Institute (API), the prediction by MCEVD has probabilistic meaning and universality.
An optimal active sliding mode controller with specified decay rate design is proposed to control the wave-induced offshore jacket-type platform with active mass damper (AMD). Irregular wave loading is approximated by finite sums of Fourier series, and its dynamic characteristics are governed by an exosystem that derived from the linearized Morison equation. The offshore platform system is first decomposed into two virtual subsystems based on a linear transformation. By considering the velocity of AMD as a virtual control force for the first subsystem, the optimal virtual controller is derived. Furthermore, an optimal sliding mode surface with specified decay rate is proposed. Then, the active sliding mode controller is designed to ensure that the state trajectories reach the sliding surface in finite time and remain on it thereafter. Numerical simulation is employed to verify the effectiveness of the proposed approach.
An impedance analytical method (IAM) is developed to study the interaction of plane water wave with a slotted-wall caisson breakwater. The non-linear boundary condition at the slotted-wall is expressed in terms of flow resistance. A set of algebraic expressions are obtained for free surface elevation inside and outside chamber, and reflection coefficient. The prediction of the reflection coefficients shows that the relative widths of the chamber inducing the minimum reflection coefficient for a slotted-wall caisson breakwater are in a range of 0.10 and 0.20, which are smaller than that (0.15~0.25) for a perforated-wall caisson breakwater. The reflection coefficients and free surface elevation by the present model are compared with that of laboratory experiments by previous researchers.
The Saemangeum project includes well-developed tidal flats, two estuaries of the Mankyeong and Dongjin rivers, and a chain of small islands in the outer area off the dike by reclaiming a surface area of 40100 ha. A long sea dike of 30 km has been constructed in the mid-west area of Korea. This paper describes the construction of tidal dikes focusing on the final closure operation performed in April, 2006 employing intermediate technology.Predictive modelling was also carried out to predict the real-time flow fields during the gradual closure operation of the final stage.
A series of hydraulic model tests are carried out to investigate random wave run-up and overtopping on smooth, impermeable single slope and composite slope. Based on analysis of the influences of wave steepness, structure slope, incident wave angle, width of the berm and water depth on the berm and the wave run-up, empirical formulas for wave run-up on dike are proposed. Moreover, empirical formula on estimating the wave run-up on composite slope with multiple berms is presented for practical application of complex dike cross-section. The present study shows that the influence factors for wave overtopping are almost the same as those for wave run-up and the trend of the wave overtopping variation with main influence parameters is also similar to that for wave run-up. The trend of the wave overtopping discharge variations can be well described by two main factors, i.e. the wave run-up and the crest freeboard of the structure. A new prediction method for wave overtopping discharge is proposed for random waves. The proposed prediction formulas are applied to case study of over forty cases and the results show that the prediction methods are good enough for practical design purposes.
In this paper, the focused wave groups with different parameters and their actions on a vertical cylinder are experimentally studied. The harmonic wave characteristics of the focusing waves are analyzed by the addition and subtraction of the crest and trough focusing waves. The analyzed results show that higher order harmonics can be generated because of the interaction of component waves. Nonlinearity increases with the inputted wave amplitude and the frequency width increment. Further, the wave run-up around the vertical circular cylinder is experimentally studied. It increases with the wave steepness and the relative cylinder diameter increase. However, the variations of wave run-up around the circular cylinder are different. The researches provide a reference for further numerical studies.
Generally the underwater bio-robots take the tail fin as propulsor, and combined with pectoral fin they can manoeuvre agilely and control their position and movement at will. In nature, a lot of fishes realize to suspend itself in water to go forward and to move back up by the pectoral fin moving complexly. So that it is significant theoretically and valuable for practical application to investigate the propulsive principle and hydrodynamic performance of pectoral fin, and find the method utilizing the pectoral fin to manoeuvre the underwater bio-robot agilely. In this paper, a two degree of freedom (DoF) motion model is established for a rigid pectoral fin, and the hydrodynamic performances of the pectoral fin are studied by use of the pectoral fin propulsive experimental platform developed by Harbin Engineering University, simultaneously the hydrodynamic performance of the pectoral fin is analyzed when some parameters changed. Then, through the secondary development of FLUENT (CFD code) software, the hydrodynamic performances of rigid pectoral fin in viscous flows are calculated and the results are compared with the latest experimental results. The research in this paper will provide the theoretical reference for the design of the manoeuvring system imitating pectoral fin, at the same time will become the foundation for the developing of the small underwater bio-robot.
Stiffness degradation will occur due to the generation of accumulated pore pressure in saturated soft clays under cyclic loading. The soil static-dynamic multi-purpose triaxial and torsional shear apparatus in Dalian University of Technology was employed to perform different types of test on saturated soft marine clay in the Yangtze estuary. Undisturbed samples of the clay were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotorpic consolidation with different initial consolidation parameters. Investigated were the effects of the initial orientation angle of the major principal stress, initial ratio of deviatoric stress, initial coefficient of intermediate principal stress and continuous rotation of principal stress axes on the stiffness degradation. It is found that the degradation index decreases (or degradation degree increases) significantly with increasing initial orientation angle of the major principal stress and initial ratio of deviatoric stress. Compared to the effects of the initial orientation angle of the major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate principal stress is less evident and this trend is more clearly reflected by the results of the cyclic torsional shear tests than those of the cyclic coupling shear tests. At the same cycle number, the degradation index obtained from the cyclic torsional shear test is higher than that from the cyclic coupling shear test. The main reason is that the continuous rotation in principal stress directions during cyclic coupling shear damages the original structure of the soil more than the cyclic torsional shear does. Based on a series of experiments, a mathematical model for stiffness degradation is proposed and the relevant parameters are determined.
In order to research the strengthening effects of aramid fiber reinforced polymer (AFRP) sheets on the flexural performance of corroded beams, the static and fatigue performance of corroded RC beams strengthened with non-prestressed AFRP sheets under different degrees of corrosion (minor: reinforcement mass loss is 2.0%, medium: reinforcement mass loss is 6.0%) have been researched experimentally in this paper, to compare with that of the control beams (un-strengthened and un-corroded) and un-strengthened corroded beams, and additionally compare with fatigue performance of those medium corroded RC beams strengthened with prestressed AFRP sheets with permanent anchors. The results show that, (1) compared with un-strengthened corroded beams under the same degrees of corrosion, the cracking, yield and ultimate monotonic loads of minor corroded RC beam strengthened with non-prestressed AFRP sheets is respectively increased by 20%, 27% and 60%, whereas for medium corroded RC beam strengthened with non-prestressed AFRP sheets increased by 15%, 36% and 83% respectively. The ultimate deflection of the medium corroded beam strengthened with non-prestressed AFRP sheets is 166% larger than that of corroded un-strengthened beam under monotonic load. (2) The fatigue life of the non-prestressed AFRP strengthened medium corroded beam is 10.4 times more than that of the un-strengthened corroded beam, but lower than that of the unstrengthened-uncorroded (virgin) beam. (3) Fatigue experiments of the beams strengthened with prestressed AFRP sheets and with those non-prestressed AFRP sheets shows that the fatigue life of the retrofit RC beams increase with increasing prestress level of AFRP sheets. (4)The use of AFRP sheets for strengthening corroded RC beams is an efficient technique that can maintain the structural integrity and enhance the structural behavior of such beams.
The purpose of this paper is to develop a functional method for designing a series of submerged breakwaters on practical topography. The method is used to verify the feasibility and effectiveness of Bragg breakwaters for coastal protection by using field topography. The first part of this paper provides definitions and procedures needed in the design process for applying the mechanism of Bragg reflection. Next, Bragg breakwaters are designed on the basis of the cross-sectional topography and then on the plane topography of the Mi-Tuo coast by following the proposed process and procedure. Numerical modeling (Hsu et al., 2003; Wen and Tasi, 2008) was used as a design and assessment tool. Finally, the effectiveness and feasibility of a Bragg breakwater was assessed by practical cases. Based on the mechanism of Bragg reflection, an optimum layout for a series of submerged breakwaters is proposed to protect the Mi-Tuo coast. The results indicate that the proper layout of a series of submerged breakwaters can achieve the objective of beach protection.
Owing to the long propagation delay and high error rate of acoustic channels, it is very challenging to provide reliable data transfer for underwater sensor networks. Moreover, network coding is proved to be an effective coding technique for throughput and robustness of networks. In this paper, we propose a Reliable Braided Multipath Routing with Network Coding for Underwater Sensor Networks (RBMR-NC). Disjoint multi-path algorithm is used to build independent actual paths, as called main paths. Some braided paths on each main path are built according to the braided multi-path algorithm, which are called logic paths. When a data packet is transmitted by these nodes, the nodes can employ network coding to encode packets coming from the same group in order to further reduce relativity among these packets, and enhance the probability of successful decoding at the sink node. Braided multi-path can make the main paths to be multiplexed to reduce the probability of long paths. This paper mainly employs successful delivery rate to evaluate RBMR-NC model with theoretical analysis and simulation methods. The results indicate that the proposed RBMR-NC protocol is valuable to enhance network reliability and to reduce system redundancy.
In this paper, the formula calculating ship impact forces on light wharf structures is presented when the elastic deformation of the hull and the pier structures as well as the nonlinear deformation of the fender are taken into account. The ship impact forces are statistically analyzed with the Monte-Carlo method according to the known probability distribution types of random variables. Based on the simulated results, the distribution of ship impact forces which is characterized by bimodal distribution can be expressed as the combining probability density function of beta distribution and normal distribution. The corresponding parameters of the probability density function can be estimated with the maximum likelihood method. The results show that ship impact forces on light wharf structures follow the distribution of type I extreme value. The mean coefficient and variation coefficient are 1.11 and 0.008, respectively during 50 years of design reference period.
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- Volume 33
- Issue 6
- December 2019
- Superintended by:
CHINA ASSOCIATION FOR SCIENCE AND TECHNOLOGY
- Sponsored by:
Chinese Ocean Engineering Society （COES）
- Edited by:
Nanjing Hydraulic Research Institute
Adaptive Predictive Inverse Control of Offshore Jacket Platform Based on Rough Neural Network
Numerical Simulation of Water Exchange Characteristics of the Jiaozhou Bay Based on A Three-Dimensional Lagrangian Model
A Global Reliability Assessment Method on Aging Offshore Platforms with Corrosion and Cracks