Ship Engineering

Longitudinal-Torsional Coupled Vibration Characteristics of LNG Carrier Propulsion Shafting System

[Purpose] To address the core technical challenges of insufficient modeling accuracy and poor adaptability of solution methods for longitudinal-torsional coupled vibration in low-speed diesel engine propulsion shafting, [Method] it focuses on the propulsion shaft system of a low-speed diesel engine on a specific type of liquefied natural gas(LNG) carrier.Based on Timoshenko's beam theory and combining the spatial continuous beam method with the lumped parameter method,it proposes a longitudinal torsional coupling modeling method that accounts for shear deformation and the phase coupling effects between adjacent cranks.The method is validated through simulation and actual ship trials. [Result] The results indicate that most natural frequencies of the coupled system are close to single vibration frequencies,but some modes are generated by the coupling effect;compared with traditional models,the natural frequency prediction error is controlled within 1.46%;increasing the main journal radius increases the peak axial displacement but has little effect on the torsional angle;the simulation results agree well with the experimental measurements. [Conclusion] The proposed method can effectively improve the accuracy of shaft system dynamic analysis,providing a basis for the design and vibration control of propulsion shaft systems.

Vibration and Noise Reduction

A Review of Research on Hydraulic Design of Low-Noise Marine Centrifugal Pumps

[Purpose] To enhance the comfort of vessels,vibration level have emerged as a critical parameter for assessing the performance of centrifugal pumps.Once the design and production of a centrifugal pump are completed,postproduction vibration control measures tend to be limited in effectiveness.Consequently,it becomes imperative to effectively suppress flow-induced excitation during the design stage. [Method] Based on the internal flow characteristics of the impeller,this paper takes the jet-wake structure at the impeller outlet as the research entry point,analyzes the generation mechanism of secondary flow within the impeller,and clarifies the influence mechanism of potential flow and wake effects on the unsteady flow field.[Result] The results show that it is necessary to clarify the induction mechanism of blade passing frequency excitation in centrifugal pumps and systematically summarize the flow-induced excitation control methods targeting the suppression of rotor-stator interaction. [Conclusion] The research resultss can provide a reference for the hydraulic design of low-noise marine centrifugal pumps.

Fire Resistance Tests of Marine Asbestos Boards and Nano-Porous Aerogel Composite Structures

[Purpose] The fire performance of composite structures is a key factor restricting their application in marine engineering.The fire resistance characteristics of composite structures under ship fire conditions are investigated. [Method] Fire resistance tests are conducted on fireproof composite structures made of asbestos boards and nano-porous aerogels,respectively.The flame-retardant and thermal insulation effects of fireproof thermal insulation layers made of different materials and the same material with different thicknesses are analyzed.The fireproof and thermal insulation properties as well as failure morphologies are comparatively studied. [Result] The backplate temperature of the composite structure containing nano-porous aerogels is far lower than that of the composite structure with asbestos boards under the same combustion time.According to the international maritime organization(IMO) Fire Resistance Test Procedure Rules,the fire resistance test is carried out on the fireproof composite structure with a 15 mm-thick nano-porous aerogel.Within 38 min of combustion testing,the maximum temperature on the exposed surface reached 949.6℃,and the maximum temperature on the unexposed surface reached 98.1℃,meeting the A30 fire resistance grade standard. [Conclusion] The research results provide a reference for the fire safety of marine carbon fiber composite structures.

Impact Load and Damage Evolution of Ship Under Hard Grounding of Rock Reefs

[Purpose] To address the insufficient quantitative characterization of damage in hard-grounding accidents,the unclear coupling effects of speed and trim angle,and the lack of a sound basis for component-level energy absorption allocation, [Method] the real reef-grounding accident of the 1 350 TEU containership Longhui is investigated.Based on site survey data,a coupled finite element model of the ship-reef-fluid system is established,and a parametric analysis is conducted with respect to vertical initial impact velocity and bow-down trim angle. [Result] The results show that,as the initial velocity increased from 2 m/s to 4 m/s,the peak horizontal and vertical grounding forces rose from approximately 27 MN to 55 MN and from approximately 218 MN to 273 MN,respectively,while the time to peak decreased.Compressive-shear tearing initiated in the outer bottom plating,after which the load is progressively transferred to the longitudinal stiffeners,transverse floors,longitudinal girders,and inner bottom plating.The outer bottom plating and bottom longitudinal girders are identified as the primary energy-absorbing components,accounting for approximately 31.3% and 23.7% of the absorbed energy,respectively.At the same velocity,when the bow-down trim angle increased from 10°to 20°,the horizontal force component decreased whereas the vertical force component increased,while the total energy-absorption curves remained nearly coincident. [Conclusion] The findings clarify the mechanisms of impact-load transfer and damage evolution under hard grounding on rocky reefs,and provides a basis for anti-grounding structural design,full-accident-scenario damage modeling,and salvage strength assessment.

Research Status and Key Technological Advancement of Ship Hull Spray Painting Robots

[Purpose] To break through the bottleneck of low efficiency， poor quality， and heavy pollution in manual spraying of ship hull outer plates， and to provide a reference for the industry's green transformation， this paper systematically reviews the progress of key technologies for spray painting robots and clarifies the characteristics and applicable scenarios of different technical routes.. [Method] From five dimensions—drive technology， 3D reconstruction， path planning， quality control， and environmental protection technology—this paper surveys domestic and international achievements， compares and analyzes the performance differences among three drive forms: wall climbing， track based， and elevated， and summarizes the accuracy of 3D reconstruction， the influence of process parameters on coating quality， and the effectiveness of environmental emission reduction measures. [Result] The results indicate that wall climbing type is flexible but has limited payload and tends to damage the coating; the track based type offers high precision but requires heavy preliminary work and lacks self adaptation to curvature changes; the elevated type covers a wide range with high efficiency but is restricted in mobility. All three types have achieved considerable development， yet they still share common bottlenecks in curved surface adaptability， multi robot collaboration， closed loop inspection， and versatility. [Conclusion] In the future， efforts should be directed toward developing flexible conformal mechanisms， swarm intelligence collaboration， integrated environmental protection， online inspection closed loop control， and digital twin virtual platforms. These synergistic developments will help break through the bottlenecks， promote spray painting robots from pilot demonstrations to large scale applications， and facilitate the intelligent and green transformation of coating operations.

The Evaluation Method for the Operating State Fluctuations of Thrust Bearings

[Purpose] A volatility evaluation method for podded propulsion system (POD) thrust bearing condition monitoring is proposed. [Method] A dynamic time warping (DTW) algorithm is employed to extract fluctuation difference sequences from bearing signals. Signal complexity is quantified using sample entropy and multiscale sample entropy (MSE). A modified membership function (MMF) is designed to overcome the limitations of traditional hard-thresholding functions， and a condition assessment framework based on entropy flow analysis， multivariate accumulation of Markov chains， and minimum entropy space is established for comprehensive evaluation and anomaly prediction. [Result] Simulation results show that the MMF method achieves Pearson correlation coefficients of 0.9995 (Sine signal) and 0.9996 (Logistic signal)， with sensitivity values of 1.8703 and 1.9476， respectively， significantly outperforming the hard-thresholding function (HF) and the power-function-based membership function (PFMF). [Conclusion] The proposed volatility evaluation system effectively characterizes the fluctuation behavior of POD thrust bearing operation and demonstrates significant advantages in bearing condition monitoring and anomaly prediction.

On Manoeuvrability Prediction for Multipurpose Cargo Ship

In this paper,taking an 27000 DWT multipurpose cargo ship as an example, the calculation has been carried out both for the model and actual ship.Moreover, the comparison between theoretical and experimental results has also been made in the paper.

Present Situation of Welding Production and Development Trend of Welding Technology in China

In this paper, it is verified that the consumption of steel for welded structures in China in 2004 has exceeded 100 million tons, which makes China the world number one welding manufacture country. Since the beginning of the reforming and opening policy in China, many important and large welded structures have been made and welding has played an indispensable role in the development of national economy. The production and application of welding consumables, the distribution of welding robots, the education and training of welding professional are analyzed. Although the yield of welding consumables and welding wires have been expanded rapidly and China has become the largest welding consumables production and consumption country, the rate of manual welding electrodes is still beyond 75%, the welding mechanization and automation rate is around 35% and the ratio between the annual yield of welding consumables and steel is up to 0.77%. These problems should be solved in a shorter time. According to the development trend of welding technology, the applications of welding robot system, fully digital welding power sources, laser and laser hybrid welding, friction stir welding as well as high efficient welding processes should be emphasized in China’s shipbuilding industry. Our international competition strength should be improved by attracting excellent welding professional to the production front and improving the cooperation between governments, enterprises, universities and research institutes as well as with our predominance of high quality, high efficiency and low production costs.

A Review of Approaches to Mechanism of Ship-bridge Collision And Its Nonlinear FEM Simulation

An overview on the mechanism of the ship bridge collision is given in this paper. Employing MSC/DYTRAN program, a normal collision between ship and bridge is simulated. The history of ship bridge collision force, the exchange of energy, the displacements and the stress distribution of the ship bow and various parts of the bridge are presented. Some mechanical rules and characters during the simulated collision are given which are of great value for bridge design, maintenance and damage estimation.

Application study on the Turbulence Models of k-ε Quadratic Equation on CFD Calculation

The paper applies the turbulence models of k-ε quadratic equation to carry on numerical simulation calculation on the circumfluence problem about the slender body,and then the influences of the setting of turbulence parameters in turbulence models on calculation results are compared.The turbulent intensity and the span of viscosity ratio have better flexibility by simulation calculation.By the nonsteady motion calculation on the two-dimensional section,the paper explains the reasonable preferences of turbulence models and verifies the practicability of the turbulence models.

Present Situation of Welding Production and Development Trend of Welding Technology in China

In this paper, it is verified that the consumption of steel for welded structures in China in 2004 has exceeded 100 million tons, which makes China the world number one welding manufacture country. Since the beginning of the reforming and opening policy in China, many important and large welded structures have been made and welding has played an indispensable role in the development of national economy. The production and application of welding consumables, the distribution of welding robots, the education and training of welding professional are analyzed. Although the yield of welding consumables and welding wires have been expanded rapidly and China has become the largest welding consumables production and consumption country, the rate of manual welding electrodes is still beyond 75%, the welding mechanization and automation rate is around 35% and the ratio between the annual yield of welding consumables and steel is up to 0.77%. These problems should be solved in a shorter time. According to the development trend of welding technology, the applications of welding robot system, fully digital welding power sources, laser and laser hybrid welding, friction stir welding as well as high efficient welding processes should be emphasized in China’s shipbuilding industry. Our international competition strength should be improved by attracting excellent welding professional to the production front and improving the cooperation between governments, enterprises, universities and research institutes as well as with our predominance of high quality, high efficiency and low production costs.

Design Study of a Single Point Mooring System in Ultra Shallow Water

On the study of the main form,the type characteristics and the application scope of single point mooring(SPM) system,soft yoke single point mooring system is chosen for the new SPM of "HaiYangShiYou 113" FPSO.The difficulties in the design is studied and the key factors for the design of a SPM in ultra shallow water should be paid more attention,which are design basis,low frequency wave force,bottom striking and green water.The experience is significant for other SPM design in ultra shallow water.