Current Issue

2021, Volume 16,  Issue 5

2021, 16(5): 1-2.
Symposium of Polar ship and ocean engineering
Advances in application of peridynamics for ships and marine structures in ice zones
Yanzhuo XUE, Renwei LIU, Qing WANG, Baoyu NI
2021, 16(5): 1-15, 63. doi: 10.19693/j.issn.1673-3185.02233
As a non-local theory, peridynamics can spontaneously simulate material failure and damage through bond failure. It has achieved preliminary research results in the ocean engineering sector, especially in the field of ships and marine structures in ice zones. In order to better understand the application of peridynamics to ships and marine structures in such environments, this paper presents relevant applications including the ice constitutive model, ice-structure interaction model, ice-water coupling method, structural mechanics model, application of icebreaking through underwater explosion, application of structure surface deicing, etc. Finally, an attempt is made to comprehensively review the existing published research, analyze its characteristics and challenges, and provide corresponding solutions and future research directions.
Survey on polar marine navigation and positioning system
Jianhua CHENG, Jiaxin LIU, Lin ZHAO
2021, 16(5): 16-29. doi: 10.19693/j.issn.1673-3185.02045
The marine navigation system is a precondition for all kinds of military and civilian marine vehicles to sail safely to and within the polar regions. However, the special polar environment reduces the performance of such systems, sometimes to the point at which they cannot even be applied. In order to fundamentally understand the application of marine navigation systems in polar regions, this paper systematically expounds upon the development history of such systems, and comprehensively analyzes the impact of the special polar environment in four aspects: Earth kinematics, geophysical field, marine environment and geographic environment. As such, this survey provides valuable references by exploring the research context and future development of marine navigation technology, and analyzing the research status and future trends of the deployment of marine navigation systems in polar regions.
Design and application of moonpool system in polar icebreaker Xuelong 2
Qingman CHEN, Shuoren WANG, Yanping ZHAO, Dongfang YUAN, Yinyue XIA, Yue SHEN, Zhouxin LIAO
2021, 16(5): 30-38. doi: 10.19693/j.issn.1673-3185.02032
  Objective  In the polar regions, the operation mode of launching and recovering detection and sampling devices for scientific research by shipside is limited due to dense ice floes around the ship. To achieve the smooth acquisition of data records and samples in densely packed ice floe regions, a square-shaped moonpool system was designed in the midships of the Xuelong 2 icebreaker.  Methods  Benefiting from the accumulated experience of decades of polar surveys, and taking ice zone operation characteristics into full account, the design option of a reasonable switching process between shipside and moonpool operation was put forward. Specifically, innovative techniques such as the watertight bottom cover of the moonpool, special track docking plan and deicing of movable joints in low temperature environments were implemented.  Result  Field tests in the Antarctic area have demonstrated that the proposed scheme can effectively deal with the problem of launching and recovering scientific survey devices in densely packed ice floe regions.  Conclusions  The proposed moonpool scheme meets the actual needs of Chinese polar expeditions by increasing the sampling capability of Xuelong 2 in densely packed ice floe regions and matching the icebreaking capacity of the ship.
Review of research on ice loading of offshore structures in level ice fields
Chaoge YU, Yukui TIAN, Weibo WANG
2021, 16(5): 39-53. doi: 10.19693/j.issn.1673-3185.02084
The physical and mechanical properties of sea ice and the failure modes of ice sheets significantly affect the ice loading of offshore structures. This paper first introduces the physical and mechanical characteristics of sea ice, then describes the physical processes of the interaction of ice sheets with offshore structures. Finally, the progress of research on the ice loading of offshore structures is briefly analyzed, including the three main approaches of formula estimation, experimental testing and numerical simulation. By discussing the applicability of formula estimation, the research focus and difficulties of experimental testing, and the development trends of numerical simulation, we find that the model testing of ice loading is an effective method. This paper covers the research trends and problems faced by ice loading on offshore structures, and it can provide certain guiding references for the related research of scholars in the field.
Measurement and identification of ice loads on hull structures in far field based on dynamic effects
Shuaikang HE, Xiaodong CHEN, Shuai KONG, Shunying JI
2021, 16(5): 54-63. doi: 10.19693/j.issn.1673-3185.02065
  Objectives  This study presents an identification method for ice loads which takes the dynamic effect into consideration.   Methods   Due to the convolution relation between ice-ship interaction and structural response, the ice load described by the convolution integral equation can be established with Green's functions. Considering the ill conditions of the solution matrix and the influence of random noise, a regularization method is introduced to solve the ill-posed problem in the identification calculation, and the numerical-approximate stable solution of the time history of the dynamic ice load is obtained. For the arctic voyage of the polar class carrier vessel Tian'en, the ice-induced response was measured by installing strain sensors on the bow. Based on the full-scale measurement of Tian'en, the ice load is identified from the ice-induced strain during navigation in icy waters.  Results  The results show that the Green's function method can effectively identify the time history of far-field ice loads.  Conclusions   The effectiveness of load identification strongly depends on strain signal intensity. In addition, the size of ice and ice-structure contact area are key factors which dominate the ice load characteristics in different ice failure modes.
Numerical analysis of ice load on floating platform in polar region based on high-performance discrete element method
Shuai KONG, Shunying JI, Shaopeng JI, Yinghui WANG, Xuhao GANG
2021, 16(5): 64-70. doi: 10.19693/j.issn.1673-3185.02192
  Objectives  Ice load is an important input for floating platforms in polar regions in terms of structural safety analysis and integrity management. As such, the establishment of fast and effective ice load forecasting techniques can guarantee the safe operation of floating platforms.  Methods  A high-performance discrete element method (DEM) used for sea ice modeling based on the CUDA-C parallel processing technique is established. The pack ice around a platform during operation is generated using the Voronoi algorithm, and the ice sheet is constructed from sphere elements considering the bond-break effect controlled by the failure criterion. The hull structure is constructed from triangular elements and treated as a six-degrees of freedom system under the action of buoyancy, ice load and restoring force of mooring line. The global ice load on the moored structure is calculated under the continuous action of ice.  Results  The influence of ice thickness is studied statistically and the numerical results validated with field test results from Kulluk.  Conclusions  Ice thickness has a significant impact on the ice load of a floating platform during operation in ice-covered waters, so an ice-breaking service should be supplied to weaken the ice conditions in the operation area.
Finite element analysis of typical structure of side stringer skeleton under ice load
Xuehang YANG, Yanwu WANG, Pengfei LI, Yigang XU, Chuang LI
2021, 16(5): 71-77. doi: 10.19693/j.issn.1673-3185.02196
  Objectives  The force on the typical side skeleton nodes of a cross-skeleton icebreaker under ice load action is explored through the numerical analysis of such nodes.  Methods  First, based on a PC2 heavy icebreaker, according to China Classification Society (CCS) specifications, the ice load is calculated according to the relevant ice load specifications; next, MSC/PATRAN software is used to create a finite element model of the typical side skeleton nodes, and a representative ice load is applied to the outer plates of the icebreaker so as to obtain the stress state of the typical nodes; finally, by constantly changing the forms of the typical nodes, the stress distribution difference in the area of interest is obtained.  Results  The stress levels of different typical node forms are compared and analyzed, and it is concluded that the superior choices are ribs that cross through the side stringer area, and a structural form of rib disconnection in the deck area.  Conclusions  This paper summarizes and puts forward the design points of the typical structure form of an icebreaker's side skeleton, providing useful references for rib-crossing structural design.
Numerical simulation analysis of the collision between ship side and small iceberg
Biye YANG, Zhigang HUANG, Ning LIU, Zhe SUN, Guiyong ZHANG
2021, 16(5): 78-86. doi: 10.19693/j.issn.1673-3185.02220
  Objectives  Collisions between a side structure of ship and a small iceberg are investigated.  Methods  a nonlinear finite element model is established, involving the penalty function method and arbitrary Lagrangian-Eulerian (ALE) algorithm. A numerical simulation of the interaction between the double-sided structure of a tanker and a spherical iceberg is conducted. The numerical model considers the structural deformation, iceberg damage and hydrodynamic effects during the collision process. The effects of collision angle on collision velocity, contact force and structural energy absorption are also analyzed.  Results  The results show that the numerical model simulates the interaction between the structure on ship side and small iceberg in as much detail as possible. During the collision process, the peak value of the contact force is closely related to the collision angle and iceberg damage. The contact force increases with the collision angle. Compared to other collision angles, fluid has a significant effect on the iceberg's velocity decay in a normal contact case. Among the structural components of the side structure of tanker, the side shell appears to absorb the most energy. Besides, when the small iceberg is broken, the structural energy absorption decreases and the increasing degree is smaller than in unbroken cases due to the energy loss during the breaking process.  Conclusions  To ensure the safety of polar ships, the strength of the side structure should be enhanced and a wide collision angle avoided when colliding with small icebergs.
Simulation analysis on collision performance of polar cruise vessel based on JH-2 sea ice model
Zongpeng TONG, Linchang YE, Zhaowang XIA, Bin XUE, Rui CAO
2021, 16(5): 87-94. doi: 10.19693/j.issn.1673-3185.02085
  Objectives  When a polar cruise vessel collides with floating sea ice, the comfortability and safety of the passengers are affected.  Methods  A mechanical model of sea ice is established on the basis of the Johnson-Holmquist-2 (JH-2) model. The collision between a polar cruise vessel and sea ice is studied using the coupling method of the smoothed particle Galerkin-finite element method (SPG-FEM). The failure mode of sea ice in the collision process is explored in combination with the equivalent stress and plastic strain of sea ice.   Results  The results show that the large crack propagation phenomenon will not appear during the collision process between a polar cruise vessel and sea ice layer when the ice is 1.6 m thick. The sea ice will only be damaged in a small range of direct contact with the bow. At both sides of the bow, local strain will appear in the indirect collision area.   Conclusions  The results of this study can provide technical support for analyzing the passenger's comfortability and safety design of polar cruise vessel.
Prediction method for plastic dynamic response of hull plate subjected to ice floe impact
Wei CAI, Ling ZHU, Luze BI
2021, 16(5): 95-100. doi: 10.19693/j.issn.1673-3185.02217
  Objectives  Polar ships are often subjected to ice floe impact during navigation, particularly, hull plates may suffer permanent plastic deformation under extreme ice impact loads, affecting the safety and working performance of the ship, and greatly increasing the maintenance costs. Therefore, it is necessary to propose a method to predict the dynamic plastic response of hull structure under ice floe impact loads.   Methods  This paper analyzes the energy sharing mechanism of ice-hull interaction based on the energy analysis method and rigid-plastic theoretical method to predict the plastic dynamic response of hull plates. An analytical formula for the dynamic response of a hull plate under ice floe impact is proposed, and comparisons between the analytical and numerical results are made.   Results  The comparisons show that the presented analytical method is reliable, this simplified theoretical analysis method can provide designers with rapid prediction regarding the maximal plastic deformation and collision force of a hull plate under ice floe impact.   Conclusions  The research has giving it great significance for engineering applications.
Prediction of ice resistance of icebreaker during continuous icebreaking
Rui CHEN, Wugang HUANG, Xiaolu CHEN, Meize KANG
2021, 16(5): 101-108, 120. doi: 10.19693/j.issn.1673-3185.02164
  Objective  In order to accurately assess the ice resistance experienced by an icebreaker during continuous icebreaking when sailing in a level ice zone, and understand the characteristics of different prediction methods, this paper uses the empirical formula method, numerical simulation method and ship model test method to evaluate an icebreaker's continuous sailing in smooth ice and predict the ice resistance.   Method  In this paper, the nonlinear finite element software DYNA is used to construct ice numerical simulation models based on the traditional finite element and cohesive element methods respectively, and simulations are performed of the bending fracture and interaction process that occurs when level ice interacts with an icebreaker. At the same time, using the empirical formula method, three different empirical formulas are used to calculate the ice resistance, and a sensitivity analysis of the parameters affecting the prediction results of the empirical formula method is also carried out.   Results  The study finds that ice resistance shows an upward trend with the increase in speed, ice thickness and bending strength. Among them, ice thickness has the greatest influence on ice resistance. Among the three empirical formulas, the prediction results of the Lindqvist formula are closer to the ship model test results, while those of the Vance and Lewis formulas are more conservative. The traditional finite element and cohesive element methods obtain more accurate ice resistance prediction results when the thickness is small. When the thickness is large, the error is about 25%. In case of small ice thickness and high speed, the ice resistance value predicted by the cohesive element method is more accurate than that of the traditional finite element method, and the accuracy error is within 10% compared with the ship model test results.   Conclusion  In the actual ice resistance prediction, the empirical formula method and numerical simulation method can be combined to take into account the accuracy and efficiency of the prediction results.
Study on power matching of podded propulsor for polar ships
Yan HUANG, Anbin ZHENG, Aibing LIU, Hanfeng JIANG, Yufeng TIAN
2021, 16(5): 109-120. doi: 10.19693/j.issn.1673-3185.02281
  Objective  To enhance the pertinence and applicability of polar ships with podded propulsion design, the power matching problem should be researched.  Methods  Based on the overseas classification rules of ice classes and the results of ship investigation, the seaworthiness ranges of ships in different polar classes over the four seasons of the Arctic are confirmed. Based on the Lindqvist formula, the ice resistance levels of three typical podded propulsion ships in the polar regions are calculated, and the required power of a podded propulsion ship is obtained. Based on an investigation of mature pod thruster products on the market, a preliminary selection method for the pod thrusters of polar ships is established.   Results  Combined with the current single machine power and arrangement types of pod thrusters, the power matching results and preliminary suggestions for the selection of various ship types under different ice levels are obtained.   Conclusion  The results of this study can provide references for thruster selection in the design stage.
Selection and evaluation of polar cruise fin stabilizer based on combination weighting-TOPSIS method
Yunrui ZHAO, Haibo GAO, Zhiguo LIN, Yunhua GUO, Jianfeng ZHANG
2021, 16(5): 121-126, 149. doi: 10.19693/j.issn.1673-3185.02037
  Objectives   Many factors should be taken into consideration in the selection of a fin stabilizer for a polar cruise ship, such as environmental adaptation and device performance, and it should not be chosen via subjective judgment. To this end, a comprehensive fin stabilizer selection and evaluation method based on a combined weighting-TOPSIS (technique for order preference by similarity to ideal solution) method is proposed.   Methods   The selection principle of a fin stabilizer for a polar cruise ship with a gross tonnage of 8 035 is confirmed according to the PC6 guidelines for polar class ships, and the initial area of the fin stabilizer is calculated using the experimental mathematical model. Three design schemes are put forward for the fin stabilizer. A selection and evaluation index system is built by consulting experts, including five primary indexes and fourteen secondary indexes. The weights of the indexes are determined using the analytic hierarchy process (AHP) and entropy weight method (EWM), and the TOPSIS method is introduced to calculate the degree of closeness between the alternative and ideal solutions.   Results   According to the ranking results, Design Scheme 1 (Aquarius A100 fin stabilizer) is selected as the optimal fin stabilizer for meeting the decision-makers' requirements.   Conclusions   The method proposed in this study has valuable guiding significance for the selection of fin stabilizers for polar cruise ships by reducing the blindness of the shipbuilders and decision-makers.
Optimization design and sensitivity analysis of diesel/battery hybrid propulsion system for polar icebreaker
Wenlong DU, Fengxiang GUO, Li CHEN
2021, 16(5): 127-136. doi: 10.19693/j.issn.1673-3185.02260
  Objectives  For the economic and environmental requirements of polar ice-breakers, a hybrid propulsion system composed of diesel generator sets and a rechargeable battery is proposed.   Methods  First, the resistance model is established on the basis of ice scale, and the energy flow model of the diesel/battery hybrid propulsion system is established using the inverse simulation method. The component parameters of the propulsion system are then optimized on the basis of an elitist nondominated sorting genetic algorithm-II (NSGA-II) with "annual fuel consumption" and "total cost of entire life cycle" as the optimization objectives, and the optimal design is obtained via the technique for order of preference by similarity to ideal solution (TOPSIS) method. Finally, the sensitivity analysis of the optimization objectives to seven design parameters is conducted.   Results  The results show that the optimal design scheme of the diesel/battery hybrid propulsion system can save 1.89% in fuel consumption compared with the traditional diesel-electric propulsion system, and the pure electric navigation time accounts for 31.22% of the whole voyage, but the rechargeable battery reduces the economy of the system. The sensitivity analysis shows that the optimization objectives ("annual fuel consumption" and "total cost of entire life cycle") of the hybrid propulsion system are sensitive to main engine capacity, number of battery packs and battery state of charge, while less sensitive to reducer ratio, motor capacity and propeller size.   Conclusions  The results of this study can provide references for the research and design of polar icebreakers and other diesel/battery hybrid electric ships.
Numerical simulation analysis of icing process in ice model tank
Shifeng DING, Jinyan CAI, Li ZHOU, Yajun ZHOU
2021, 16(5): 137-142. doi: 10.19693/j.issn.1673-3185.02113
  Objectives  The icing process in an ice model tank is numerically simulated to study the characteristics and influencing factors of icing.  Methods  The volume of fluid (VoF) two-phase flow model in computational fluid dynamics software FLUENT is used to build the numerical model of the tank and set the thermodynamic boundary conditions, in order to observe the dynamic change process of the temperature field and ice surface in the calculation domain, and analyze the influence of the air-conditioning inlet setting scheme on the icing process.   Results  The research results show that as the number of air-conditioning inlets increases, the ice model tank freezes faster and it is easier to form a uniform layer of ice.   Conclusions  The numerical simulation results of the icing process reveal the relationship between cold air and icing, which can provide references for controlling icing in ice model tanks.
Numerical simulation analysis of flexural strength of columnar saline ice model
Xuhao GANG, Yukui TIAN, Chaoge YU, Shaopeng JI, Ying KOU
2021, 16(5): 143-149. doi: 10.19693/j.issn.1673-3185.02195
  Objective   As flexural failure is one of the main failure modes of ships navigating in level-ice region, research into flexural strength has great significance for engineering practices.  Methods  First, numerical prediction calculation is carried out for a model ice in a CSSRC (China Ship Scientific Research Center) ice tank; second, the discrete element method (DEM) is used to carry out the numerical simulation of the flexural strength of a columnar saline ice model, the calculation parameters are obtained through ice mechanics experiments, the rectangular element is used to discretize the ice layer, and cell array is used to transfer the control force. The calculation results are then verified using the flexural strength test data to ensure the reliability of the numerical simulation model.  Results  The variation law of flexural strength with velocity, ratio of width to thickness and ratio of length to thickness is obtained through the numerical model, and the basic scope of the flexural strength of the ice model is obtained through the error of the calculated results.  Conclusion  This numerical simulation method can provide references for predicting the mechanical properties of ice models.
Ship Design and Performance
Design of AUV depth controller based on L1 adaptive theory
Jianghang HUO, Xiangyuan JIANG, Yizhong LUAN, Xiaojing MA
2021, 16(5): 150-157. doi: 10.19693/j.issn.1673-3185.02114
  Objectives  An adaptive controller is designed for the longitudinal control channel of autonomous underwater vehicles (AUV) in order to suppress the influence of hydrodynamic parameters and complex external environment disturbance during AUV motion.   Methods  First, a dynamic model of the AUV system is established and the L1 adaptive controller is then designed on the basis of the longitudinal control model of the REMUS AUV system. Finally, Matlab/Simulink is used to simulate the L1 adaptive controller under different disturbance conditions, and the effects are compared with a PID controller in the same environment.   Results  Under the condition of strong external interference, the control effects of the L1 adaptive controller are more stable than those of the PID controller. When the hydrodynamic parameters of the AUV motion model change, the L1 adaptive controller can still maintain stability.   Conclusion  The simulation results show that the controller designed on the basis of L1 adaptive theory has good dynamic response and can guarantee anti-interference ability and robustness.
New identification algorithm for ship model parameters based on sinusoidal function processing innovation
Xianku ZHANG, Huiying ZHU
2021, 16(5): 158-162. doi: 10.19693/j.issn.1673-3185.02122
  Objective  When few ship test data samples are available, it is difficult to identify ship model parameters quickly and accurately.  Methods  On the basis of the original least-square system identification algorithm, an innovative sinusoidal function process is introduced, and a new ship model parameter identification method based on the nonlinear sinusoidal function is proposed.The ship Yukun, a teaching and training ship of Dalian Maritime University, is selected for the identification experiment. With only 26 test data samples, the identification effects of the original least square method and improved least square algorithm are compared.   Results  The simulation results show that the parameter identification accuracy of the algorithm is improved by about 15%, and the effectiveness of the algorithm is verified using the ship Yupeng.  Conclusion  This algorithm provides valuable references for the parameter identification of ship models with few test data samples.
The drag reduction mechanism of liquid-infused surface based on lattice boltzmann method
Shenglei QIN, Guoxiang HOU, Wenqiang GUO, Binbin ZHOU, Siyuan JIANG
2021, 16(5): 163-171, 197. doi: 10.19693/j.issn.1673-3185.02168
  Objectives  Newly proposed in recent years, the liquid-infused surface (LIS) is a drag reduction surface which replaces the residual air conserved by the microgrooves of a traditional superhydrophobic surface with a lubricant, thereby vastly improving the stability of the drag reduction level. To fully understand the drag reduction stability of LIS, this paper focuses on the influence of lubricant solubility on drag reduction.   Methods  Based on the lattice Boltzmann method (LBM), we simulated a conserving lubricant microstructure with microflow and studied the influence of the lubricant's dissolved density and shear velocity on slip length.   Results  The liquid-infused surface results in a slip phenomenon, and there exists a linear relationship between slip length and cohesion force strength among its particles when the lubricant is completely dissolved or difficult to dissolve.   Conclusions  With greater cohesion force strength among its particles, a lubricant can result in more promising drag reduction when it is difficult to dissolve. The lubricant's shear velocity has little influence on slip length. The properties of the lubricant are similar to those of a traditional superhydrophobic surface.
Ship near-miss duration model and application analysis
Jiaxuan YANG, Yangyu ZHOU, Jiaguo LIU
2021, 16(5): 172-180. doi: 10.19693/j.issn.1673-3185.02015
  Objectives  The near-miss of two ships is a special situation that ships will encounter, and it can be modeled in terms of the time-dimension perspective for evaluating potential maritime traffic risks.  Methods   In this paper, a temporal near-miss model is first established using the Fujii ship domain to detect near-miss situations, and the near-miss duration and average duration are then defined. An algorithm for calculating near-miss duration is proposed on the basis of the time synchronization processing of automatic identification system (AIS) data. Furthermore, the near-miss duration is used to analyze the time-dimension characteristics of maritime traffic risks. The Bohai Sea area is used as the research example to verify the model.  Results  The correlations between the average near-miss duration and ship type and length are determined. According to ship type analysis, the longest average near-miss duration is 252.63 s for an oil tanker and at least 180 s for a passenger ship. According to ship size analysis, the longest average near-miss duration is 272.65 s for a large ship and at least 180 s for a mid-size ship.  Conclusions  The proposed model can be used to accurately calculate near-miss duration, providing a new approach to studying maritime traffic risks from the time-dimension perspective.
Ship Structure and Fittings
Ultimate strength analysis of typical perforated high web frame structure in cruise ships
Jin GAN, Ou SHAN, Weiguo WU, Yongshui LIN
2021, 16(5): 181-188. doi: 10.19693/j.issn.1673-3185.01895
  Objectives  The perforate high web structure is a special structure widely used in the superstructures of large cruise ships. In order to establish the design method of this kind of structure, it is necessary to fully grasp the mechanical characteristics of typical perforated high web structures used in the superstructures of large cruise ships.  Methods  Using the nonlinear finite element theory and classical stiffened plate theory, an analysis is made of the influence law of initial deck defects, longitudinal girder specifications and web openings on the ultimate bearing capacity of the plate frame under longitudinal compression.  Results  The thin plate frame is more sensitive to initial defects, and the initial deformation mode is different from that of the thick plate frame. The longitudinal girder ultimate capacity contribution is bigger and the sensitivity of longitudinal pressure limit capacity to the proportion and shape of holes is low. The locations of the collapse failure buckling zones are determined by the locations of the holes. The failure modes of perforated high web frame structures are revealed.  Conclusions  The results of the influence law of key factors such as initial deck defects, geometrical dimensions of longitudinal girders and web openings on the ultimate strength of perforated high web frame structures provide guidance for the lightweight design and safety assessment of cruise ship superstructures.
Fatigue strength analysis of aluminum alloy trimaran considering corrosion effects
Chenyan ZHOU, Jianing ZHANG, lin CHEN, qiao MENG
2021, 16(5): 189-196. doi: 10.19693/j.issn.1673-3185.02070
  Objective  This study evaluates the fatigue strength of an aluminum alloy trimaran in a corrosive environment.  Method  Taking a 120 m aluminum alloy trimaran as an example, the direct calculation method/spectral analysis method is used to calculate its fatigue life based on Miner's linear cumulative damage theory. At the same time, four types of corrosion model are established to compare the hot spot fatigue strength calculation results under different corrosion models and explore the effects of corrosion on the fatigue life of the trimaran.  Results   The results show that the new corrosion model is closer to the actual corrosion process. The effects of different corrosion models on the hot spots of the aluminum alloy trimaran are related to corrosion years, and the fatigue strength of the connection between the cross-deck and the main and side bodies is strong.  Conclusion  The results of this study have reference significance for the fatigue assessment of trimarans in corrosive environments.
Effects of air cushion on slamming load of trimaran cross-deck structure
Yichen JIANG, Zhendong SUN, Zhi ZONG, Yifang SUN, Guoqing JIN
2021, 16(5): 197-205. doi: 10.19693/j.issn.1673-3185.01919
  Objectives  The hull plate of a trimaran cross-deck bottom is often subjected to slamming loads under high-level sea conditions, potentially causing severe structural damage. The objective of this study is to analyze the influence of the air cushion effect on the impact load of a trimaran cross-deck plate and propose a new type of hull plate for the cross-deck bottom in order to reduce the slamming load.  Methods  The two-phase flow problem of a trimaran ship section is simulated using the computational fluid dynamics (CFD) method. First, the accuracy of the numerical model is verified by comparing the predicted results with the experimental measurements. The influence of the air cushion on the slamming load of the trimaran cross-deck structure is then obtained by analyzing the evolution of the flow field. Finally, the influence of the air cushion is analyzed and the effects of different shapes and sizes of the proposed hull plate are evaluated.  Results  The numerical results show two slamming peaks that appear during the process of a trimaran entering the water. The rectangular shaped plate reduces the slamming load by around 20% compared with the flat plate bottom.  Conclusions  The air cushion has a significant effect on the slamming load. A rectangular shaped hull plate can be used to cover the trimaran cross-deck bottom.
Data transformation technology of 3D ship structure model for approval
Lisi HE, Rong CAO, Deyu WANG
2021, 16(5): 206-215. doi: 10.19693/j.issn.1673-3185.01874
  Objectives  Chinese ship design and approval institutions usually use different 3D design platforms, which can cause the problems of unsmooth model transfer and ineffective data conversion. This paper addresses the data conversion techniques of 3D ship structure models to ascertain whether a converted model can be directly used by classification societies for approval.  Methods  By analyzing the model data of the CAD and CAE systems, the required data for generating an approval-oriented 3D hull structure model is summarized. The storage format of the required data and the interface between the stored data and common 3D software platforms are introduced. Taking a cargo tank section of a ship as an example, the required data of the 3D model of the target section is stored in an XML data file. Based on this data file, the design model and FE analysis model of the target section are reconstructed through CATIA and Patran software, and equipped with a secondary developed interface.  Results  The reconstructed model has been submitted to Bureau Veritas (BV) for direct approval of the structural design.  Conclusions  The data conversion method proposed in this paper simplifies model transfer among different platforms, and can provide valuable references for realizing the paper-free approval of 3D ship models.
Marine Machinery, Electrical Equipment and Automation
Review of hybrid ship energy management
Hui HOU, Ming GAN, Xixiu WU, Kun XIE, Zeyang FAN
2021, 16(5): 216-229. doi: 10.19693/j.issn.1673-3185.02133
The advantages of hybrid ships in energy conservation and emission reduction are increasingly prominent in the context of countries around the world paying increasing attention to such matters. Energy management is the key to achieving energy conservation and emission reduction on the premise of ensuring power performance. This paper summarizes the research progress and status of hybrid ship energy management. First, the energy management objectives are summarized in the three aspects of reliability objectives, economy objectives and environmental protection objectives. Second, the energy management strategies are compared and analyzed from the perspectives of rules and optimization, and the advantages, disadvantages and application conditions of the existing energy management strategies are summarized and analyzed deeply and comprehensively. Finally, according to the gaps in the existing research, the future research directions of hybrid ship energy management are predicted.
Design and Realization of hybrid digital twin based on carbon steel corrosion
Huafeng LI, Yan LIU, Jianru CHEN, Tao ZHANG, Jiaming ZHU, Ze WANG
2021, 16(5): 230-237. doi: 10.19693/j.issn.1673-3185.02008
  Objectives  IoT technology is used to build up a digital twin model to comprehensively and directly reflect the corrosion process of metal structure in the whole life-cycle, realize the intelligent prediction and maintenance of metal corrosion, and improve the reliability of metal structure work.  Methods  Combining a finite element model with a real-time data-driven model, a hybrid digital twin model of the atmospheric corrosion process and an experimental platform design scheme of IoT monitoring are proposed to establish a link between the corrosion digital simulation and the actual corrosion process.  Results  A physical corrosion model is combined with a real-time data-driven corrosion model into a "hybrid digital twin" which can realize the whole life-cycle management of metal structures and   Conclusion  The hybrid digital twin model combining real-time data-driven and physical models can provide references for corrosion research and the application of corrosion prevention technology.
Vibration energy leakage analysis and diagnosis of vibration-isolation thrust bearing
Chongjian WU, Zhiyang LEI, Zhigang CHEN, Kun DU, Quanchao LI
2021, 16(5): 238-243. doi: 10.19693/j.issn.1673-3185.02322
  Objectives  The vibration-isolation thrust bearing is a new device for the longitudinal vibration control of propulsion shafts. Experimental results show that the dynamic transmission characteristics of the propulsion shaft are quite different from those of theoretical calculation predictions. Analysis shows that there is serious vibration energy leakage from the vibration-isolation thrust bearing. For better understanding the cause of poor acoustical property of the system, a study is conducted with the focus upon the flexible assemblies of the thrust bearing to determine directions for optimization improvement design.   Methods  The dynamic characteristic analysis is conducted concentrated on the coil spring and coil spring cylinder which are key vibration isolation components of the thrust bearing to research the vibration energy leakage. Then, the dynamic model of the coil spring cylinder is established based on both vibration isolation theory and experiment analysis. Moreover, the dynamic characteristic test bench in vertical state is also built up.   Results  The experimental analysis results show that the vibration resonance peak of the coil spring is sharp and smooth, while that of the coil spring cylinder is flat with more harmonic components induced by contact friction. When there is contact friction, there will be additional stiffness and damping, which significantly change the dynamic characteristics of the coil spring cylinder.   Conclusion  The dynamic model of the coil spring cylinder is verified by experiments. The dynamic transmission characteristics of the coil spring can be used as an evaluation standard for design improvement. The results of this study can provide theoretical support for the design optimization and improvement of the vibration-isolation thrust bearing, which can have great significance for practical engineering.
Analysis and evaluation of marine motor cooling system
Jun WANG, Hongdong WANG, Jianyao WANG, Jian WANG, Xiaofeng LIANG, Hong YI
2021, 16(5): 244-254. doi: 10.19693/j.issn.1673-3185.02028
  Objective  As the design of the cooling system directly affects the reliability of marine motors, it is necessary to evaluate the influence of the cooling system on the motor.  Method  Taking a high-power-density marine motor as an example, an overall model of the motor is established using the electronic thermal simulation software ANSYS Icepak, and the 3D temperature fields of three typical heat dissipation systems of the axial water jacket, spiral water jacket and annular water jacket are calculated. The cooling effects of the components and temperature gradients are then compared and evaluated, and an optimal scheme based on a combination of forced air-cooling and water-cooling is proposed.  Results  The calculation results show that the water-cooling system can solve the heat dissipation problems of the casing and stator, and reduce the axial and circumferential temperature gradients. The annular water jacket works best. However, the water-cooling system has a poor effect on the rotor and end casing. After optimization, the rotor temperature and overall temperature gradients of the motor are greatly reduced.  Conclusion  The annular water jacket is recommended to be chosen as the water-cooling system for marine motors, and an auxiliary cooling system should be considered to make up for the defects of the water-cooling system.