LNG bunkering pontoons are presented to solve the fueling difficulty of LNG ships on inland waterways with a great variation of water height and channel width by seasonal change.First,the background of this concept wa...LNG bunkering pontoons are presented to solve the fueling difficulty of LNG ships on inland waterways with a great variation of water height and channel width by seasonal change.First,the background of this concept was analyzed as well as the demand of LNG bunkering pontoons,and the involved idea of levels management.Then,from the safety barrier perspective,safety design principles were discussed,the safety principles and implement measures of LNG storage were provided,LNG tanks for the pontoon were analyzed in detail in terms of their types,design pressure,material selection and leakage protection principles.Also,the safety concerns of LNG supply and bunkering process were raised,and an improved handy bunkering arm&hose,lighter and more flexible than ever before,was introduced.Berthing and unberthing are related to the survival of the pontoon so that the key points of such design were highlighted.It is concluded that(1)based on the levels management,the pontoon equipped with IMO Type C tanks,with reasonable berthing/unberthing and safety designs adopted,is proved to be safe and reliable by practices;(2)by 2025,nearly 30 such improved LNG bunkering pontoons with a fueling capacity of 500 m^(3) each will be required on Yangtze and Pearl Rivers;and(3)the pontoon's safety and reliability has been verified by practices and its fourth generation has been developed.展开更多
The perfection of labor law and enhanced legal awareness among employees have caused an increase in labor disputes in China.However,there are only a few studies that systematically analyzed conflict resolutions within...The perfection of labor law and enhanced legal awareness among employees have caused an increase in labor disputes in China.However,there are only a few studies that systematically analyzed conflict resolutions within organizations in China.In attempt to address this research gap,this study used the conflict management theory and classified the various mechanisms of the conflict management system using a quantitative research design approach,focusing on positing tools specific to the situation in China,as well as analyzed the effect of different conflict management mechanisms on employee outcomes,in hope that the findings would provide constructive suggestions for improving the management of Chinese organizations.展开更多
Hydrogen fuel cell ships are one of the key solutions to achieving zero carbon emissions in shipping.Multi-fuel cell stacks(MFCS)systems are frequently employed to fulfill the power requirements of high-load power equ...Hydrogen fuel cell ships are one of the key solutions to achieving zero carbon emissions in shipping.Multi-fuel cell stacks(MFCS)systems are frequently employed to fulfill the power requirements of high-load power equipment on ships.Compared to single-stack system,MFCS may be difficult to apply traditional energy management strategies(EMS)due to their complex structure.In this paper,a two-layer power allocation strategy for MFCS of a hydrogen fuel cell ship is proposed to reduce the complexity of the allocation task by splitting it into each layer of the EMS.The first layer of the EMSis centered on the Nonlinear Model Predictive Control(NMPC).The Northern Goshawk Optimization(NGO)algorithm is used to solve the nonlinear optimization problem in NMPC,and the local fine search is performed using sequential quadratic programming(SQP).Based on the power allocation results of the first layer,the second layer is centered on a fuzzy rule-based adaptive power allocation strategy(AP-Fuzzy).The membership function bounds of the fuzzy controller are related to the aging level of the MFCS.The Particle Swarm Optimization(PSO)algorithm is used to optimize the parameters of the residual membership function to improve the performance of the proposed strategy.The effectiveness of the proposed EMS is verified by comparing it with the traditional EMS.The experimental results show that the EMS proposed in this paper can ensure reasonable hydrogen consumption,slow down the FC aging and equalize its performance,effectively extend the system life,and ensure that the ship has good endurance after completing the mission.展开更多
Considering both the axial force on the spanning pipeline and influence of sea waves and currents, a perpendicular nonlinear vibration equation which satisfies given boundary conditions is .set up according to the fac...Considering both the axial force on the spanning pipeline and influence of sea waves and currents, a perpendicular nonlinear vibration equation which satisfies given boundary conditions is .set up according to the factual soil supports for the pipeline. Based on the inherent modes of vibration determined from the equation of motion describing free vibrations, the differential equations for the time domain of the equation solution are deduced and established. By the application of time and frequency domain analysis, the sea wave and current force spectrum is derived from wave spectrum and is used as the input spectrum of the vibration equation to deduce the output spectrum, and further determine the probability distribution of displacement and strain. On this basis, the fatigue invalidation probability of the spanning pipeline is found out according to the theory of reliability. Finally, by means of calculation and analysis of a practical sample, the degree of effect of some important parameters on fatigue invalidation of the spanning pipeline span is determined.展开更多
SAW308L submerged arc welding wire and SJ601A submerged arc welding flux were selected to weld the 12 mm 08Cr19MnNi3Cu2N low nickel and high nitrogen austenitic stainless steel plates with three different welding heat...SAW308L submerged arc welding wire and SJ601A submerged arc welding flux were selected to weld the 12 mm 08Cr19MnNi3Cu2N low nickel and high nitrogen austenitic stainless steel plates with three different welding heat input,and microstructure,tensile properties,microhardness and corrosion properties of the welded joints were studied.The results show that no defects are found in the three groups of welded joints,and the welded joints have better performance.The tensile strength of 08Cr19MnNi3Cu2N stainless steel welded joints with different heat input is slightly lower than that of the base metal,and fracture occurs in the weld zone,and the hardness of the weld zone is lower than that of the base metal.The weld microstructure of stainless steel welded joints with different heat input is composed of austenite+δferrite,and ferrite is uniformly distributed in austenite.With the increase of the welding heat input,the ferrite content in the weld zone decrease gradually,the grain size in the thermal affected zone increase gradually,and the impact toughness reduce.展开更多
The influence of Cr on the initial corrosion behavior of low-alloy steels exposed to a CO2–O2–H2S–SO2 wet–dry corrosion environment was investigated using weight-loss measurements, scanning electron microscopy, N2...The influence of Cr on the initial corrosion behavior of low-alloy steels exposed to a CO2–O2–H2S–SO2 wet–dry corrosion environment was investigated using weight-loss measurements, scanning electron microscopy, N2 adsorption tests, X-ray diffraction analysis, and electrochemical impedance spectroscopy. The results show that the corrosion rate increases with increasing Cr content in samples subjected to corrosion for 21 d. However, the rust grain size decreases, its specific surface area increases, and it becomes more compact and denser with increasing Cr content, which indicates the enhanced protectivity of the rust. The results of charge transfer resistance(Rct) calculations indicate that higher Cr contents can accelerate the corrosion during the first 7 d and promote the formation of the enhanced protective inner rust after 14 d; the formed protective inner rust is responsible for the greater corrosion resistance during long-term exposure.展开更多
The failure of one or even more components usually does riot lead to the collapse of the whole structure. Most of the analysis of fatigue is centered on only a single component which the researchers are interested in ...The failure of one or even more components usually does riot lead to the collapse of the whole structure. Most of the analysis of fatigue is centered on only a single component which the researchers are interested in or Much attention should be paid to. However, the collapse of a structure is the result of failure of a series of components in a specific order or path. This paper proposes an integrated approach to fatigue life prediction of whole structural system for offshore platforms, mainly describing the basic principles and prediction method. A method is presented for determining the failure path of the whole structure system and calculating the fatigue life in the determined failure path, The corresponding final collapse criteria for the whole structure system are discussed, A simple method of equivalent fatigue stress range calculation and a mathematical model of structural component fatigue life estimation in consideration of sea wave and sea ice loads are provided. As an application of the proposed approach, a fixed production platform Bohai No. 8 is chosen for the predication of fatigue life of the whole structure system by means of the software OSFAC developed based on the present methods.展开更多
Polar ships need to meet stringent safety and environmental requirements.Usually those ships are classified by diferent ice classes based on ice operation capability.However,the polar ships are also trapped by severe ...Polar ships need to meet stringent safety and environmental requirements.Usually those ships are classified by diferent ice classes based on ice operation capability.However,the polar ships are also trapped by severe ice condition due to low propulsion power.Therefore,it is a realistic question to design the appropriate minimum propulsion power for ice operation.This paper focuses on the ice resistance and its related propulsion power for the ships with polar code(PC)classes.In consideration of seven typical polar ice conditions related to the PC rule of International Association of Classification Societies(IACS),a prediction method of ice resistance is developed by Lindqvist's model.The results are compared with those of Lindqvist's model and Riska's model by using two real ship lines.The comparison among propulsion requirements of representative classification societies is made,and a formula of minimum propulsion power is presented on the basis of ice resistance by revised Finnish-Swedish Ice Class Rules(FSICR)method.The results are verified by the actual values from seven ice class ships.A relatively good agreement is achieved.As a conclusion,the presented prediction method of ice resistance and minimum propulsion power is recommended for evaluation of ice resistance and its related propulsion power during the process of developing polar ships.展开更多
The insulation of membrane type liquefied natunal gas （LNG） carrier is composed of plywood boxes filled with perlite. Within the service period, considering of the effects of load conditions, such as sloshing, wave ...The insulation of membrane type liquefied natunal gas （LNG） carrier is composed of plywood boxes filled with perlite. Within the service period, considering of the effects of load conditions, such as sloshing, wave load, it is possible to have some damage of the plywood box, leakage of perlite, and failure of the insulation box. LNG carrier without whole protection of effective insulation is dangerous. Hull structure is extremely fragile when exposed to ultra-low temperature. In order to solve these problems, firstly a study on insulation boxes＇ character and work condition is carried out and some presuppositions of partial disabled insulation are put forward. Secondly the thermal system of LNG carrier is analyzed to find out an effective way to simulate the thermal action of close air between outer and inner hull. Then a calculation about temperature field and thermal stress is done by MSC/PATRAN＆NASTRAN. At the end it is concluded that LNG carrier with incomplete insulation is dangerous and needs to be avoided.展开更多
The element stiffness matrix of the equivalent beam or pipe element of the deformed leg of the platform is derived by the finite element method. The stresses and displacements of some damaged components are calculated...The element stiffness matrix of the equivalent beam or pipe element of the deformed leg of the platform is derived by the finite element method. The stresses and displacements of some damaged components are calculated, and the numerical solutions agree well with those obtained by the fine mesh finite element method. Finally, as an application of this method, the stresses of some platform structures are calculated and analyzed.展开更多
To solve the numerical divergence problem of the direct time domain Green function method for the motion simulation of floating bodies with large flare, a time domain hybrid Rankine-Green boundary element method is pr...To solve the numerical divergence problem of the direct time domain Green function method for the motion simulation of floating bodies with large flare, a time domain hybrid Rankine-Green boundary element method is proposed. In this numerical method, the fluid domain is decomposed by an imaginary control surface, at which the continuous condition should be satisfied. Then the Rankine Green function is adopted in the inner domain. The transient free surface Green function is applied in the outer domain, which is used to find the relationship between the velocity potential and its normal derivative for the inner domain. Besides, the velocity potential at the mean free surface between body surface and control surface is directly solved by the integration scheme. The wave exciting force is computed through the convolution integration with wave elevation, by introducing the impulse response function. Additionally, the nonlinear Froude-Krylov force and hydrostatic force, which is computed under the instantaneous incident wave free surface, are taken into account by the direct pressure integration scheme. The corresponding numerical computer code is developed and first used to compute the hydrodynamic coefficients of the hemisphere, as well as the time history of a ship with large flare; good agreement is obtained with the analytical solutions as well as the available numerical results. Then the hydrodynamic properties of a FPSO are studied. The hydrodynamic coefficients agree well with the results computed by the frequency method; the influence of the time interval and the truncated time is investigated in detail.展开更多
In this paper, a method is developed for determining the effective stiffness of the cracked component. The stiffness matrix of the cracked component is integrated into the global stiffness matrix of the finite element...In this paper, a method is developed for determining the effective stiffness of the cracked component. The stiffness matrix of the cracked component is integrated into the global stiffness matrix of the finite element model of the global platform for the FE calculation of the structure in any environmental conditions. The stiffness matrix equation of the cracked component is derived by use of the finite variation principle and fracture mechanics. The equivalent parameters defining the element that simulates the cracked component are mathematically presented, and can be easily used for the FE calculation of large scale cracked structures together with any finite element program. The theories developed are validated by both lab tests and numerical calculations, and applied to the evaluation of crack effect on the strength of a fixed platform and a self-elevating drilling rig.展开更多
The importance of risk thinking is emphasized in the ISO quality management system.In order to do a good job in quality management,we should use risk thinking to do a good job in risk management,improve the level of q...The importance of risk thinking is emphasized in the ISO quality management system.In order to do a good job in quality management,we should use risk thinking to do a good job in risk management,improve the level of quality management,and enhance customer satisfaction,so that enterprises can meet the international quality certification standards in the process of development,and have greater development space in the market.Therefore,this paper studies the risk thinking in the ISO quality management system,summarizes the concept of risk thinking in the ISO quality management system,analyzes the problems existing in the application of risk thinking in the ISO quality management system of Chinese enterprises,and puts forward some suggestions for improvement one by one.It is hoped that the analysis can promote Chinese enterprises to fully integrate risk-based thinking into quality management,calmly cope with risks and opportunities,and make customers more satisfied with their services and products.展开更多
In order to reduce waiting time in port for large LNG （liquefied natural gas） fueled ships, it is suggested that LNG STS （ship to ship） bunkering and cargo loading/unloading should be carried out simultaneously. T...In order to reduce waiting time in port for large LNG （liquefied natural gas） fueled ships, it is suggested that LNG STS （ship to ship） bunkering and cargo loading/unloading should be carried out simultaneously. This study investigated the safety zone of an LNG bunkering vessel with 10,000 cubic meters capacity transferring LNG fuel to an LNG fueled 18,000 TEU containership. Four LNG leakage scenarios were identified based on failure frequencies analysis of piping systems and severity of consequence, three-dimension CFD software FLACS was adopted to calculate flammable cloud dispersion after LNG leakage. As a result, we obtained a rectangle dangerous zone （41.3 m ~ 126 m）, outside of this dangerous zone can be def＇med as safety zone. It is concluded that safety zone of LNG STS bunkering and cargo loading/unloading SIMOPS （simultaneous operations） cannot keep the same, there are different results for different designs and operation locations. Due to high frequencies and severe consequences, two typical scenarios, the leakage of LNG hose and the natural gas releases from bunkering tank＇s safety relief valve during bunkering, cannot be ignored in similar study.展开更多
The independent LNG(Liquified Nature Gas)containment is widely used for small or medium-sized LNG carrier and ship using LNG as fuels.The common tank pattern includes single-spherical-cylindrical tank and double-spher...The independent LNG(Liquified Nature Gas)containment is widely used for small or medium-sized LNG carrier and ship using LNG as fuels.The common tank pattern includes single-spherical-cylindrical tank and double-spherical-cylindrical tank,which is the key to design the hull structure and its support.The support is designed to connect the hull structure and LNG tank.Its main functions are heat transferring and force loading.This paper focus on the temperature field distribution of hull and its support structure.The thermal boundary conditions are simulated according to the heat transfer action,such as thermal convection,heat conduction and thermal radiation.The method on how to carry out thermal analysis is presented for an independent LNG containment.The case study is carried out with two typical independent LNG tanks.One is a tank with double spherical cylindrical in the LNG carrier,and the other is a tank with single spherical cylindrical on the deck of the ship using LNG as fuels.The result shows the method presented in this paper is a good reference for the structural design with independent LNG containment.展开更多
Three types of ice loading, which are most commonly present when ice acts on structures, are chosen and simulated for use of fatigue crack propagation tests on offshore structural steel A131. The three types of ice ca...Three types of ice loading, which are most commonly present when ice acts on structures, are chosen and simulated for use of fatigue crack propagation tests on offshore structural steel A131. The three types of ice categorized in accordance with the failure modes when acting on structures called Crushing ice, bending ice, and buckling ice, respectively. This paper presents an experimental investigation on the fatigue crack propagation behavior of widely used high strength steel A131 for offshore jackets in the loading environment of ice crushing, bending, and buckling. The test results of fatigue crack propagation in steel A131 tinder these simulated ice loading at temperature 292K are presented and analyzed in detail in this paper, The amplitude root mean square stress intensity factor is optimized to be the fundamental parameter of fatigue crack propagation for all types of ice loading histories. The results are also compared with constant amplitude fatigue crack propagation conclusions as in wave load mode, and a joint investigation on the results from ice forces, ice-induced vibrations, and ice-induced fatigue crack propagation is conducted. Conclusions are drawn for reference in structural design and material selection for offshore structures in ice environments.展开更多
The purpose of this study is to investigate the suppression effect of a nonlinear energy sink(NES)on the wind-vortex-induced pipe vibration and explore the influence of damping,stiffness,and NES installation position ...The purpose of this study is to investigate the suppression effect of a nonlinear energy sink(NES)on the wind-vortex-induced pipe vibration and explore the influence of damping,stiffness,and NES installation position on the suppression effect.In this work,the wind-vortex-induced vibration of an elastic pipe of a deepwater jacket was studied,and vibrations were suppressed by using an NES.A van der Pol wake oscillator was used to simulate vortex-induced force,and the dynamic equation of the pipe considering the NES was established.The Galerkin method was applied to discretize the motion equation,and the vortex-induced vibration(VIV)of the pipe at reduced wind speeds was numerically analyzed.The novelty of this research is that particle swarm optimization was used to optimize the parameters of the NES to improve vibration suppression.The influence of the installation position,nonlinear stiffness,and damping parameters of the NES on vibration suppression was analyzed.Results showed that the optimized parameter combinations of the NES can effectively reduce wind-vortex-induced pipe vibration.The installation position of the NES had a significant effect on vibration suppression,and the midpoint of the pipe was the optimal NES installation position.An increase in stiffness or a 10% decrease in damping may cause vibration suppression failure.The results of this study provide some guidance for VIV suppression in deepwater jacket pipes.展开更多
The stress combination method for the fatigue assessment of the hatch comer of a bulk carrier was investigated based on equivalent waves. The principles of the equivalent waves of ship structures were given, including...The stress combination method for the fatigue assessment of the hatch comer of a bulk carrier was investigated based on equivalent waves. The principles of the equivalent waves of ship structures were given, including the determination of the dominant load parameter, heading, frequency, and amplitude of the equivalent regular waves. The dominant load parameters of the hatch comer of a bulk carrier were identified by the structural stress response analysis, and then a series of equivalent regular waves were defined based on these parameters. A combination method of the structural stress ranges under the different equivalent waves was developed for the fatigue analysis. The combination factors were obtained by least square regression analysis with the stress ranges derived from spectral fatigue analysis as the target value. The proposed method was applied to the hatch comer of another bulk carrier as an example. This shows that the results from the equivalent wave approach agree well with those from the spectral fatigue analysis. The workload is reduced substantially. This method can be referenced in the fatigue assessment of the hatch comer of a bulk carrier.展开更多
The main challenge in predicting global responses of floating vessels in deepwater and uhra-deepwater areas comes from the system＇s coupled effect, tn this paper, the coupled approach is used to analyze effects of ri...The main challenge in predicting global responses of floating vessels in deepwater and uhra-deepwater areas comes from the system＇s coupled effect, tn this paper, the coupled approach is used to analyze effects of riser on floating system in deepwater. The analysis results show that the coupling effects of risers will mainly affect the low frequency （LF） motions of the system. That is because risers will provide the system with a significant low frequency （LF） damping which will vary with the sea states. Under storm sea state, the excitation term from drag force will govern the response. While under the moderate conditions, the damping effect of risers is more significant. In the practical engineering, the combination effect should be considered by other ways when the risers are omitted from the model.展开更多
In the leg-lowering process,the offshore jack-up platform is in a floating state,and the spudcan may collide with the seabed due to the platform motion in waves,thereby threatening the safety and stability of the plat...In the leg-lowering process,the offshore jack-up platform is in a floating state,and the spudcan may collide with the seabed due to the platform motion in waves,thereby threatening the safety and stability of the platform.This paper first analyzed the hydrodynamic response of a jack-up platform under different sea states.Then a finite-element model was established which considered the material and geometrical nonlinearity in the structure and the nonlinear interaction between soil and structure to investigate the collision response between the spudcan and seabed during lowering jack-up legs.The results show that the dynamic response of the platform decreases and gradually tends to be stable as the wave period increases.The motion response of the platform reach the largest value when the wave period is 8 s and the wave direction is 0°.The collision angle between the spudcan and seabed has a large influence on the collision response,while the velocity of leg-lowering has little influence on the collision response.The collision response is also significantly affected by soil conditions.For clay,the increase in undrained shear strength and Young’s modulus will increase the impact force.展开更多
基金Project supported by the funding program of China Maritime Safety Administration and National Energy Administration“Research on the Application Safety of LNG-Fueled Vessels”(No.:MSA[2012]509).
文摘LNG bunkering pontoons are presented to solve the fueling difficulty of LNG ships on inland waterways with a great variation of water height and channel width by seasonal change.First,the background of this concept was analyzed as well as the demand of LNG bunkering pontoons,and the involved idea of levels management.Then,from the safety barrier perspective,safety design principles were discussed,the safety principles and implement measures of LNG storage were provided,LNG tanks for the pontoon were analyzed in detail in terms of their types,design pressure,material selection and leakage protection principles.Also,the safety concerns of LNG supply and bunkering process were raised,and an improved handy bunkering arm&hose,lighter and more flexible than ever before,was introduced.Berthing and unberthing are related to the survival of the pontoon so that the key points of such design were highlighted.It is concluded that(1)based on the levels management,the pontoon equipped with IMO Type C tanks,with reasonable berthing/unberthing and safety designs adopted,is proved to be safe and reliable by practices;(2)by 2025,nearly 30 such improved LNG bunkering pontoons with a fueling capacity of 500 m^(3) each will be required on Yangtze and Pearl Rivers;and(3)the pontoon's safety and reliability has been verified by practices and its fourth generation has been developed.
文摘The perfection of labor law and enhanced legal awareness among employees have caused an increase in labor disputes in China.However,there are only a few studies that systematically analyzed conflict resolutions within organizations in China.In attempt to address this research gap,this study used the conflict management theory and classified the various mechanisms of the conflict management system using a quantitative research design approach,focusing on positing tools specific to the situation in China,as well as analyzed the effect of different conflict management mechanisms on employee outcomes,in hope that the findings would provide constructive suggestions for improving the management of Chinese organizations.
基金supported by the National Key R&D Program of China(2022YFB4301403).
文摘Hydrogen fuel cell ships are one of the key solutions to achieving zero carbon emissions in shipping.Multi-fuel cell stacks(MFCS)systems are frequently employed to fulfill the power requirements of high-load power equipment on ships.Compared to single-stack system,MFCS may be difficult to apply traditional energy management strategies(EMS)due to their complex structure.In this paper,a two-layer power allocation strategy for MFCS of a hydrogen fuel cell ship is proposed to reduce the complexity of the allocation task by splitting it into each layer of the EMS.The first layer of the EMSis centered on the Nonlinear Model Predictive Control(NMPC).The Northern Goshawk Optimization(NGO)algorithm is used to solve the nonlinear optimization problem in NMPC,and the local fine search is performed using sequential quadratic programming(SQP).Based on the power allocation results of the first layer,the second layer is centered on a fuzzy rule-based adaptive power allocation strategy(AP-Fuzzy).The membership function bounds of the fuzzy controller are related to the aging level of the MFCS.The Particle Swarm Optimization(PSO)algorithm is used to optimize the parameters of the residual membership function to improve the performance of the proposed strategy.The effectiveness of the proposed EMS is verified by comparing it with the traditional EMS.The experimental results show that the EMS proposed in this paper can ensure reasonable hydrogen consumption,slow down the FC aging and equalize its performance,effectively extend the system life,and ensure that the ship has good endurance after completing the mission.
基金This work was financially supported bythe National Natural Science Foundation of China (Grant No.59979018)
文摘Considering both the axial force on the spanning pipeline and influence of sea waves and currents, a perpendicular nonlinear vibration equation which satisfies given boundary conditions is .set up according to the factual soil supports for the pipeline. Based on the inherent modes of vibration determined from the equation of motion describing free vibrations, the differential equations for the time domain of the equation solution are deduced and established. By the application of time and frequency domain analysis, the sea wave and current force spectrum is derived from wave spectrum and is used as the input spectrum of the vibration equation to deduce the output spectrum, and further determine the probability distribution of displacement and strain. On this basis, the fatigue invalidation probability of the spanning pipeline is found out according to the theory of reliability. Finally, by means of calculation and analysis of a practical sample, the degree of effect of some important parameters on fatigue invalidation of the spanning pipeline span is determined.
文摘SAW308L submerged arc welding wire and SJ601A submerged arc welding flux were selected to weld the 12 mm 08Cr19MnNi3Cu2N low nickel and high nitrogen austenitic stainless steel plates with three different welding heat input,and microstructure,tensile properties,microhardness and corrosion properties of the welded joints were studied.The results show that no defects are found in the three groups of welded joints,and the welded joints have better performance.The tensile strength of 08Cr19MnNi3Cu2N stainless steel welded joints with different heat input is slightly lower than that of the base metal,and fracture occurs in the weld zone,and the hardness of the weld zone is lower than that of the base metal.The weld microstructure of stainless steel welded joints with different heat input is composed of austenite+δferrite,and ferrite is uniformly distributed in austenite.With the increase of the welding heat input,the ferrite content in the weld zone decrease gradually,the grain size in the thermal affected zone increase gradually,and the impact toughness reduce.
文摘The influence of Cr on the initial corrosion behavior of low-alloy steels exposed to a CO2–O2–H2S–SO2 wet–dry corrosion environment was investigated using weight-loss measurements, scanning electron microscopy, N2 adsorption tests, X-ray diffraction analysis, and electrochemical impedance spectroscopy. The results show that the corrosion rate increases with increasing Cr content in samples subjected to corrosion for 21 d. However, the rust grain size decreases, its specific surface area increases, and it becomes more compact and denser with increasing Cr content, which indicates the enhanced protectivity of the rust. The results of charge transfer resistance(Rct) calculations indicate that higher Cr contents can accelerate the corrosion during the first 7 d and promote the formation of the enhanced protective inner rust after 14 d; the formed protective inner rust is responsible for the greater corrosion resistance during long-term exposure.
基金This paper was financially supported by National Natural Science Foundation of China(Grant No.59895410)
文摘The failure of one or even more components usually does riot lead to the collapse of the whole structure. Most of the analysis of fatigue is centered on only a single component which the researchers are interested in or Much attention should be paid to. However, the collapse of a structure is the result of failure of a series of components in a specific order or path. This paper proposes an integrated approach to fatigue life prediction of whole structural system for offshore platforms, mainly describing the basic principles and prediction method. A method is presented for determining the failure path of the whole structure system and calculating the fatigue life in the determined failure path, The corresponding final collapse criteria for the whole structure system are discussed, A simple method of equivalent fatigue stress range calculation and a mathematical model of structural component fatigue life estimation in consideration of sea wave and sea ice loads are provided. As an application of the proposed approach, a fixed production platform Bohai No. 8 is chosen for the predication of fatigue life of the whole structure system by means of the software OSFAC developed based on the present methods.
基金the National Natural Science Foun-dation of China(Nos.51809124 and 51911530156)the Natural Science Foundation of Jiangsu Province(No.BK20170576)+1 种基金the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province(No.17KJB580006)the Project of State Key Lab-oratory of Ocean Engineering of Shanghai Jiao Tong University(No.1704,1807)。
文摘Polar ships need to meet stringent safety and environmental requirements.Usually those ships are classified by diferent ice classes based on ice operation capability.However,the polar ships are also trapped by severe ice condition due to low propulsion power.Therefore,it is a realistic question to design the appropriate minimum propulsion power for ice operation.This paper focuses on the ice resistance and its related propulsion power for the ships with polar code(PC)classes.In consideration of seven typical polar ice conditions related to the PC rule of International Association of Classification Societies(IACS),a prediction method of ice resistance is developed by Lindqvist's model.The results are compared with those of Lindqvist's model and Riska's model by using two real ship lines.The comparison among propulsion requirements of representative classification societies is made,and a formula of minimum propulsion power is presented on the basis of ice resistance by revised Finnish-Swedish Ice Class Rules(FSICR)method.The results are verified by the actual values from seven ice class ships.A relatively good agreement is achieved.As a conclusion,the presented prediction method of ice resistance and minimum propulsion power is recommended for evaluation of ice resistance and its related propulsion power during the process of developing polar ships.
文摘The insulation of membrane type liquefied natunal gas （LNG） carrier is composed of plywood boxes filled with perlite. Within the service period, considering of the effects of load conditions, such as sloshing, wave load, it is possible to have some damage of the plywood box, leakage of perlite, and failure of the insulation box. LNG carrier without whole protection of effective insulation is dangerous. Hull structure is extremely fragile when exposed to ultra-low temperature. In order to solve these problems, firstly a study on insulation boxes＇ character and work condition is carried out and some presuppositions of partial disabled insulation are put forward. Secondly the thermal system of LNG carrier is analyzed to find out an effective way to simulate the thermal action of close air between outer and inner hull. Then a calculation about temperature field and thermal stress is done by MSC/PATRAN＆NASTRAN. At the end it is concluded that LNG carrier with incomplete insulation is dangerous and needs to be avoided.
文摘The element stiffness matrix of the equivalent beam or pipe element of the deformed leg of the platform is derived by the finite element method. The stresses and displacements of some damaged components are calculated, and the numerical solutions agree well with those obtained by the fine mesh finite element method. Finally, as an application of this method, the stresses of some platform structures are calculated and analyzed.
基金the financial support provided by the National Basic Research Program of China(No.2011CB3703)the National Natural Science Foundation of China(No.51079034)
文摘To solve the numerical divergence problem of the direct time domain Green function method for the motion simulation of floating bodies with large flare, a time domain hybrid Rankine-Green boundary element method is proposed. In this numerical method, the fluid domain is decomposed by an imaginary control surface, at which the continuous condition should be satisfied. Then the Rankine Green function is adopted in the inner domain. The transient free surface Green function is applied in the outer domain, which is used to find the relationship between the velocity potential and its normal derivative for the inner domain. Besides, the velocity potential at the mean free surface between body surface and control surface is directly solved by the integration scheme. The wave exciting force is computed through the convolution integration with wave elevation, by introducing the impulse response function. Additionally, the nonlinear Froude-Krylov force and hydrostatic force, which is computed under the instantaneous incident wave free surface, are taken into account by the direct pressure integration scheme. The corresponding numerical computer code is developed and first used to compute the hydrodynamic coefficients of the hemisphere, as well as the time history of a ship with large flare; good agreement is obtained with the analytical solutions as well as the available numerical results. Then the hydrodynamic properties of a FPSO are studied. The hydrodynamic coefficients agree well with the results computed by the frequency method; the influence of the time interval and the truncated time is investigated in detail.
文摘In this paper, a method is developed for determining the effective stiffness of the cracked component. The stiffness matrix of the cracked component is integrated into the global stiffness matrix of the finite element model of the global platform for the FE calculation of the structure in any environmental conditions. The stiffness matrix equation of the cracked component is derived by use of the finite variation principle and fracture mechanics. The equivalent parameters defining the element that simulates the cracked component are mathematically presented, and can be easily used for the FE calculation of large scale cracked structures together with any finite element program. The theories developed are validated by both lab tests and numerical calculations, and applied to the evaluation of crack effect on the strength of a fixed platform and a self-elevating drilling rig.
文摘The importance of risk thinking is emphasized in the ISO quality management system.In order to do a good job in quality management,we should use risk thinking to do a good job in risk management,improve the level of quality management,and enhance customer satisfaction,so that enterprises can meet the international quality certification standards in the process of development,and have greater development space in the market.Therefore,this paper studies the risk thinking in the ISO quality management system,summarizes the concept of risk thinking in the ISO quality management system,analyzes the problems existing in the application of risk thinking in the ISO quality management system of Chinese enterprises,and puts forward some suggestions for improvement one by one.It is hoped that the analysis can promote Chinese enterprises to fully integrate risk-based thinking into quality management,calmly cope with risks and opportunities,and make customers more satisfied with their services and products.
文摘In order to reduce waiting time in port for large LNG （liquefied natural gas） fueled ships, it is suggested that LNG STS （ship to ship） bunkering and cargo loading/unloading should be carried out simultaneously. This study investigated the safety zone of an LNG bunkering vessel with 10,000 cubic meters capacity transferring LNG fuel to an LNG fueled 18,000 TEU containership. Four LNG leakage scenarios were identified based on failure frequencies analysis of piping systems and severity of consequence, three-dimension CFD software FLACS was adopted to calculate flammable cloud dispersion after LNG leakage. As a result, we obtained a rectangle dangerous zone （41.3 m ~ 126 m）, outside of this dangerous zone can be def＇med as safety zone. It is concluded that safety zone of LNG STS bunkering and cargo loading/unloading SIMOPS （simultaneous operations） cannot keep the same, there are different results for different designs and operation locations. Due to high frequencies and severe consequences, two typical scenarios, the leakage of LNG hose and the natural gas releases from bunkering tank＇s safety relief valve during bunkering, cannot be ignored in similar study.
文摘The independent LNG(Liquified Nature Gas)containment is widely used for small or medium-sized LNG carrier and ship using LNG as fuels.The common tank pattern includes single-spherical-cylindrical tank and double-spherical-cylindrical tank,which is the key to design the hull structure and its support.The support is designed to connect the hull structure and LNG tank.Its main functions are heat transferring and force loading.This paper focus on the temperature field distribution of hull and its support structure.The thermal boundary conditions are simulated according to the heat transfer action,such as thermal convection,heat conduction and thermal radiation.The method on how to carry out thermal analysis is presented for an independent LNG containment.The case study is carried out with two typical independent LNG tanks.One is a tank with double spherical cylindrical in the LNG carrier,and the other is a tank with single spherical cylindrical on the deck of the ship using LNG as fuels.The result shows the method presented in this paper is a good reference for the structural design with independent LNG containment.
基金This research is financially supported by the National Natural Science Foundation of China (Grant No.5989410) Key Project Foundation of the Chinese Academy of Sciences China National Offshore Oil Corporation
文摘Three types of ice loading, which are most commonly present when ice acts on structures, are chosen and simulated for use of fatigue crack propagation tests on offshore structural steel A131. The three types of ice categorized in accordance with the failure modes when acting on structures called Crushing ice, bending ice, and buckling ice, respectively. This paper presents an experimental investigation on the fatigue crack propagation behavior of widely used high strength steel A131 for offshore jackets in the loading environment of ice crushing, bending, and buckling. The test results of fatigue crack propagation in steel A131 tinder these simulated ice loading at temperature 292K are presented and analyzed in detail in this paper, The amplitude root mean square stress intensity factor is optimized to be the fundamental parameter of fatigue crack propagation for all types of ice loading histories. The results are also compared with constant amplitude fatigue crack propagation conclusions as in wave load mode, and a joint investigation on the results from ice forces, ice-induced vibrations, and ice-induced fatigue crack propagation is conducted. Conclusions are drawn for reference in structural design and material selection for offshore structures in ice environments.
基金supported by the Tianjin Municipal Transportation Commission Project(No.2018-b2).
文摘The purpose of this study is to investigate the suppression effect of a nonlinear energy sink(NES)on the wind-vortex-induced pipe vibration and explore the influence of damping,stiffness,and NES installation position on the suppression effect.In this work,the wind-vortex-induced vibration of an elastic pipe of a deepwater jacket was studied,and vibrations were suppressed by using an NES.A van der Pol wake oscillator was used to simulate vortex-induced force,and the dynamic equation of the pipe considering the NES was established.The Galerkin method was applied to discretize the motion equation,and the vortex-induced vibration(VIV)of the pipe at reduced wind speeds was numerically analyzed.The novelty of this research is that particle swarm optimization was used to optimize the parameters of the NES to improve vibration suppression.The influence of the installation position,nonlinear stiffness,and damping parameters of the NES on vibration suppression was analyzed.Results showed that the optimized parameter combinations of the NES can effectively reduce wind-vortex-induced pipe vibration.The installation position of the NES had a significant effect on vibration suppression,and the midpoint of the pipe was the optimal NES installation position.An increase in stiffness or a 10% decrease in damping may cause vibration suppression failure.The results of this study provide some guidance for VIV suppression in deepwater jacket pipes.
基金Supported by the National Natural Science Foundation of China （50809019）.
文摘The stress combination method for the fatigue assessment of the hatch comer of a bulk carrier was investigated based on equivalent waves. The principles of the equivalent waves of ship structures were given, including the determination of the dominant load parameter, heading, frequency, and amplitude of the equivalent regular waves. The dominant load parameters of the hatch comer of a bulk carrier were identified by the structural stress response analysis, and then a series of equivalent regular waves were defined based on these parameters. A combination method of the structural stress ranges under the different equivalent waves was developed for the fatigue analysis. The combination factors were obtained by least square regression analysis with the stress ranges derived from spectral fatigue analysis as the target value. The proposed method was applied to the hatch comer of another bulk carrier as an example. This shows that the results from the equivalent wave approach agree well with those from the spectral fatigue analysis. The workload is reduced substantially. This method can be referenced in the fatigue assessment of the hatch comer of a bulk carrier.
文摘The main challenge in predicting global responses of floating vessels in deepwater and uhra-deepwater areas comes from the system＇s coupled effect, tn this paper, the coupled approach is used to analyze effects of riser on floating system in deepwater. The analysis results show that the coupling effects of risers will mainly affect the low frequency （LF） motions of the system. That is because risers will provide the system with a significant low frequency （LF） damping which will vary with the sea states. Under storm sea state, the excitation term from drag force will govern the response. While under the moderate conditions, the damping effect of risers is more significant. In the practical engineering, the combination effect should be considered by other ways when the risers are omitted from the model.
基金financially supported by the National Natural Science Foundation of China(Grant No.51779171)the Tianjin Municipal Natural Science Foundation(Grant No.18JCYBJC22800)。
文摘In the leg-lowering process,the offshore jack-up platform is in a floating state,and the spudcan may collide with the seabed due to the platform motion in waves,thereby threatening the safety and stability of the platform.This paper first analyzed the hydrodynamic response of a jack-up platform under different sea states.Then a finite-element model was established which considered the material and geometrical nonlinearity in the structure and the nonlinear interaction between soil and structure to investigate the collision response between the spudcan and seabed during lowering jack-up legs.The results show that the dynamic response of the platform decreases and gradually tends to be stable as the wave period increases.The motion response of the platform reach the largest value when the wave period is 8 s and the wave direction is 0°.The collision angle between the spudcan and seabed has a large influence on the collision response,while the velocity of leg-lowering has little influence on the collision response.The collision response is also significantly affected by soil conditions.For clay,the increase in undrained shear strength and Young’s modulus will increase the impact force.
