A Simple Empirical Formula for Predicting the Ultimate Strength of Ship Plates with Elastically Restrained Edges in Axial Compression

An investigation is conducted on the static ultimate limit state assessment of ship hull plates with elastically restrained edges subjected to axial compression. Both material and geometric non-linearities were considered in finite element(FE) analysis. The initial geometric imperfection of the plate was considered, while the residual stress introduced by welding was not considered. The ultimate strength of simply supported ship hull plates compared well with the existing empirical formula to validate the correctness of the applied boundary conditions, initial imperfection and mesh size. The extensive FE calculations on the ultimate strength of ship hull plates with elastically restrained edges are presented. Then a new simple empirical formula for plate ultimate strength is developed, which includes the effect of the rotational restraint stiffness, rotational restraint stiffness, and aspect ratios. By applying the new formula and FE method to ship hull plates in real ships, a good coincidence of the results between these two methods is obtained, which indicates that the new formula can accurately predict the ultimate strength of ship hull plates with elastically restrained edges.     

Ultimate Strength Analysis of Offshore Jacket Platform

- The ultimate strength analysis of offshore jacket platforms is a research project which has been developed in recent years. With the rapid development of marine oil industry, the departments of design and IMR (Inspection, Maintenance and Repair) in the offshore engineering have attached great importance to this project. The research procedure applies to both the stress check of new design platforms and the whole safety assessment of existing platforms. In this paper, we combine the pseudo non-linear technique with the linear analysis program and successfully analyze the ultimate strength of the space frame structure subject to the concentrated load and a real jacket platform subject to the dead load and environmental load.     

Ultimate Strength of Ship Plating under Axial Compression

The failure of a ship hull girder is governed by buckling and plastic collapse of the deck, bottom and side shell steel stiffened plates. The stiffened steel plating in ships is generally subjected to both in-plane and out-of-plane loading and is more important to understand the characteristics of these panels under buckling. Tests are reported on the collapse load of stiffened plates with and without cutout and with reinforced cutout under uniaxial compression. A generalized computer program for the semi-analytical solutions proposed by various investigators based on strut approach and orthotropic plate approach, and a finite element analysis program based on orthotropic plate approach are developed. The panels are also analysed using the finite element analysis software ANSYS. An approximate method based on strut approach is proposed to calculate the collapse load of stiffened plates with cutouts and initial imperfections. The reduction in strength of the panels due to the presence of square cutout, rectangular cutout and increase in strength due to reinforcement around rectangular cutout are calculated based on the test results. Comparisons are made between the test results and predictions based on semi-analytical solutions and finite element analyses, and the uncertainty parameters calculated are discussed. Based on this study it is concluded that the cutout can be reinforced with a maximum increase in strength up to 19% for plate initiated failures.     

Ultimate Bending Capacity of Strain Hardening Steel Pipes

Based on Hencky’s total strain theory of plasticity, ultimate bending capacity of steel pipes can be determined analytically assuming an elastic-linear strain hardening material, the simplified analytical solution is proposed as well. Good agreement is observed when ultimate bending capacities obtained from analytical solutions are compared with experimental results from full-size tests of steel pipes. Parametric study conducted as part of this paper indicates that the strain hardening effect has significant influence on the ultimate bending capacity of steel pipes. It is shown that pipe considering strain hardening yields higher bending capacity than that of pipe assumed as elastic-perfectly plastic material. Thus, the ignorance of strain hardening effect, as commonly assumed in current codes, may underestimate the ultimate bending capacity of steel pipes. The solutions proposed in this paper are applicable in the design of offshore/onshore steel pipes, supports of offshore platforms and other tubular structural steel members.     

Restoration of Ultimate Strength of Dented Hemispheres Under External Hydrostatic Pressure

China Ocean Engineering - This study aimed to restore the ultimate strength of dented stainless-steel hemispheres with a radius of 90 mm and a thickness of 0.86 mm. All of the hemispheres were...     

An Improved Formulation for the Ultimate Static Strength of Tubular Joints subjected to Combined Loads

"The effect of interaction of loads on the ultimate static strength of tubular joints of offshore fixed platforms, is a practical problem. But there is still absence of rigorous theory to explain available experimental data and empirical criteria for the static strength of tubular joints. The idea of yield at hot spot of tubular joints is introduced in this paper. The interaction equations of plastic capacity for the tubular joints under combined loads (two and three different kinds) are derived. Thereafter the Yura's test data and empirical criteria of ultimate static strength for the tubular joints can be explained. The idea of classification of category of loads in accordance with experimental data and the present theory is suggested. Finally, the improved ultimate capacity equations for tubular joints are recommended. The physical significance of the coefficient of plastic reservation Qp is discussed.     

Experimental Investigation on Vortex-Induced Vibration of Steel Catenary Riser

Steel catenary riser(SCR) is the transmission device between the seabed and the floating production facilities. As developments move into deeper water, the fatigue life of the riser can become critical to the whole production system, especially due to the vortex-induced vibration(VIV), which is the key factor to operational longevity. As a result, experimental investigation about VIV of the riser was performed in a large plane pool which is 60 m long, 36 m wide and 6.5 m deep. Experiments were developed to study the influence of current speed and seabed on VIV of SCR. The results show that amplitudes of strain and response frequencies increase with the current speed both in cross-flow(CF) and in-line(IL). When the current speed is high, multi-mode response is observed in the VIV motion. The amplitudes of strain in IL direction are not much smaller than those in CF direction. The seabed has influence on the response frequencies of riser and the positions of damage for riser.     

Experimental Investigation on Vortex-Induced Vibration of Steel Catenary Riser

Steel catenary riser (SCR) is the transmission device between the seabed and the floating production facilities. As developments move into deeper water, the fatigue life of the riser can become critical to the whole production system, especially due to the vortex-induced vibration (VIV), which is the key factor to operational longevity. As a result, experimental investigation about VIV of the riser was performed in a large plane pool which is 60 m long, 36 m wide and 6.5 m deep. Experiments were developed to study the influence of current speed and seabed on VIV of SCR. The results show that amplitudes of strain and response frequencies increase with the current speed both in cross-flow (CF) and in-line (IL). When the current speed is high, multi-mode response is observed in the VIV motion. The amplitudes of strain in IL direction are not much smaller than those in CF direction. The seabed has influence on the response frequencies of riser and the positions of damage for riser.     

A Discusion on Limited Load-Carrying Capacity of Rectangular Plates

The elastic-plastic method is often used in designing the inner flat bulkhead plates of submarines, and the upper structure of ships and drilling platforms. Such bulkhead plates can bear the load only once. For the improvement of the load-carrying capacity or the reduction of the weight of plates, the yield line analytical method is employed in this paper to design the bulkhead plate to improve economy and increase the effiective load. Besides, a further sutdy of this method has been made theoretically and experimentally, and the data of the limited load-carrying capacity of the plate have been obtained. Furthermore, the safety coefficients for such a method are presented, which can be used as reference for related departments and staffs.     

导管架式海洋平台结构极限承载力分析的整体推进法及其软件

根据非线性有限元逐步分析的思想,以已有的结构弹性分析软件为计算核心,提出了一种近似分析结构极限承载力的方法——整体推进法;采用整体推进法,以导管架式海洋平台结构线弹性分析软件ＥＮＳＡ为计算核心,考虑结构构件的损伤影响和维修加固效果,编制了导管架式海洋平台结构极限承载力近似分析软件ＵＡＰ,为导管架式海洋平台结构的安全度评定提供了方法和手段;最后对渤海八号生产／储油平台在１９９３年的状态和ＪＺ２０２ＭＵＱ平台的完好状态进行了极限承载力分析     

导管架式海洋平台结构极限承载力分析的 整体推进法及其软件

根据非线性有限元逐步分析的思想,以已有的结构弹性分析软件为计算核心,提出了一种近似分析结构极限承载力的方法——整体推进法;采用整体推进法,以导管架式海洋平台结构线弹性分析软件ENSA为计算核心,考虑结构构件的损伤影响和维修加固效果,编制了导管架式海洋平台结构极限承载力近似分析软件UAP,为导管架式海洋平台结构的安全度评定提供了方法和手段;最后对渤海八号生产／储油平台在1993年的状态和JZ20-2MUQ平台的完好状态进行了极限承载力分析。     

Computational and Empirical Investigation of Propeller Tip Vortex Cavitation Noise

In this study, non-cavitating and cavitating flow around the benchmark DTMB 4119 model propeller are solved using both viscous and potential based solvers. Cavitating and non-cavitating propeller radiated noises are then predicted by using a hybrid method in which RANS(Reynolds-averaged Navier-Stokes) and FWH(Ffowcs Williams Hawkings) equations are solved together in open water conditions. Sheet cavitation on the propeller blades is modelled by using a VOF(Volume of Fiuld) method equipped with Schnerr-Sauer cavitation model.Nevertheless, tip vortex cavitation noise is estimated by using two different semi-empirical techniques, namely Tip Vortex Index(TVI, based on potential flow theory) and Tip Vortex Contribution(TVC). As the reference distance between noise source and receiver is not defined in open water case for TVI technique, one of the outputs of this study is to propose a reference distance for TVI technique by coupling two semi-empirical techniques and ITTC distance normalization. At the defined distance, the starting point of the tip vortex cavitation is determined for different advance ratios and cavitation numbers using potential flow solver. Also, it is examined that whether the hybrid method and potential flow solver give the same noise results at the inception point of tip vortex cavitation.Results show that TVI method based on potential flow theory is reliable and can practically be used to replace the hybrid method(RANS with FWH approach) when tip vortex cavitation starts.     

北方港口城市的组群发展战略探讨

本文在总结和研究了国内外港口城市组群发展战略的基础上,重点对北方环渤海地区的天津市、大连市和青岛市等港口城市的组群发展战略进行了探讨,提出了“一个龙头,三个中心”的分区分级组群发展战略模式。     

The Effect of Marine Fouling Organisms on the Corrosion of Steel

An annual in situ corrosion experiment of carbon steel and low alloy steel is reported in this paper. The results show that the corrosion rate varies with the beginning month of immersion. The corrosion rates of 09CuWSn steel panels immersed at the end of April and May when larger fouling organisms grow heavily are 0.1180 and 0.1342 mm/y respectively,     

Numerical Investigation of the Effect of Current on Wave Focusing

A numerical study on the acoustic radiation of a propeller interacting with non-uniform inflow has been conducted. Real geometry of a marine propeller DTMB 4118 is used in the calculation, and sliding mesh technique is adopted to deal with the rotational motion of the propeller. The performance of the DES (Detached Eddy Simulation) approach at capturing the unsteady forces and moments on the propeller is compared with experiment. Far-field sound radiation is predicted by the formation 1A developed by Farassat, an integral solution of FW-H (Ffowcs Williams-Hawkings) equation in time domain. The sound pressure and directivity patterns of the propeller operating in two specific velocity distributions are discussed.     

Effect of Rate-Dependent Soil Strength on Cylinders Penetrating Into Soft Clay

This paper presents a predictive model for undrained penetration of cylinders into soft seafloor soils. The penetration depth will depend on the velocity of the cylinder as it touches down at the seafloor, and the net deceleration of the cylinder as it is acted on by forces of self-weight, soil buoyancy, and soil-shearing resistance. The soil-shearing resistance force increases as a function of penetration depth and, due to the dependence of undrained shear strength on strain rate, penetration velocity. This paper presents finite element (FE) simulations that quantify both effects and form the basis of a simplified soil-resisting force model. Strain-rate effects are modeled within a framework of rate-dependent plasticity, with shearing resistance increasing semilogarithmically with increasing strain rate above a certain threshold strain rate. With all forces acting on the cylinder, estimated penetration depths are predicted from simple equations of motion for a single particle. Comparisons to laboratory tests involving penetration of cylinders into soft reconstituted marine clay show reasonable agreement between model predictions and measurements.     

Strength Characterization of Sand-Bentonite Mixtures and the Effect of Cement Additives

This article studies the strength properties of compacted sand-bentonite landfill barrier material with and without cement addition at different periods of aging. Test results indicated that strength values, both in compression and tension, increased up to threefold in cement added samples, as well as enhancing the ductile behavior. Cubic modulus, described as the slope of the elastic portion of the cubic compressive stress versus strain curves, is determined along with initial and flexural moduli, and all the strength and moduli values were correlated with each other. Finally, it is concluded that there is a marked improvement in strength properties and moduli with cement inclusion and that the effect of aging has been very effective.     

Effect of Sample Disturbance on Unconfined Compression Strength of Natural Marine Clays

1 .IntroductionCoastalstructuresoftenencountersettlementandstabilityproblemsofsoftmarinefoundation (Liuetal.,1 999;Zhouetal.,2 0 0 0 ;Liuetal.,2 0 0 3) .Manyresearchershaveillustratedthatnaturalmarineclaysaregenerallysubjectedtotheeffectsofsoilstructureduringtheirdepositionalandpost depositionalprocesses (Zhangetal.,1 995;Hongetal.,2 0 0 3a ;2 0 0 3b) .Thesoilstructureofnat uralmarineclaysiseasilydamagedduringsamplingandhandlingbecausenaturalmarineclaysgeneral lyhavehighwatercontentandlowsti…     

Influence of the Spudcan Angle on the Ultimate Bearing Capacity of Jack-up Platform

Jack-up platforms of the Ocean engineering structures always withstand the vertical gravity loads which are applied to the seabed by spudcan, so it is important to determine the bearing capacity and the penetration depth of the spudcan for its geometry. In fact, it is up to the deformation law and the failure modes of soil surrounding the spudcan which can calculate the ultimate bearing capacity of the spudcan foundation on the soil seabed. By using the finite element analysis software Abaqus, the deformation law of soil around the spudcan is analyzed in detail, and the failure modes of soil surrounding the spudcan foundation are achieved. At the same time, based on the limit equilibrium theory, by use of static permissible slip-line field, the ultimate bearing capacity of the spudcan foundation is analyzed and the lower limit solution is derived theoretically, and the effect of the spudcan angle on the ultimate bearing capacity is investigated. The numerical results are compared with those obtained by the theoretical formulas deduced in this paper. On the basis of the lower limit solutions in this paper, the effect of the spudcan angle on the ultimate bearing capacity is revealed, and a practical bearing capacity formula is given to take the effect of the spudcan angle into consideration.