2021 Vol. 16, No. 3

2021, (3): 1-2.
Abstract:
Ship Design and Performance
Handling scheme simulation and scheduling optimization for carrier-borne aircraft
Mao ZHENG, Shiwei YAN, Xiumin CHU, Yunqi ZOU, Shuo XIE
2021, 16(3): 1-8, 23. doi: 10.19693/j.issn.1673-3185.01945
Abstract:
  Objectives  To improve the deck handling efficiency of carrier-borne aircraft, a study of rapid handling routes and scheduling schemes is carried out.  Methods  A fast planning method of deck handling routes based on network topology is established, and a simulation model is developed on the basis of an aircraft kinematic model and line-of-sight control method. Taking typical launching and recovery operations as examples, the carrier-borne aircraft deck handling constraints, principles and optimization objectives are discussed, and a rapid optimization method for deck handling scheduling is proposed.  Results  The simulation results show that the optimized algorithm can significantly shorten the total deck handling time of aviation operations, and the performance of the optimized deck handling scheme is close to the US Navy Surge Operation data from 1997.  Conclusions  A reasonable carrier-borne aircraft deck handling scheme can be obtained quickly using the proposed method, which is of reference value for research into carrier-borne aircraft sortie capability and human-machine deck handling scheme decision-making.
Layout algorithm for carrier aircraft in hangar based on basic spatial combination relationship
Zhuguo XU, Minghui YU, Jin WU, Mingqiang DAI
2021, 16(3): 9-16. doi: 10.19693/j.issn.1673-3185.01954
Abstract:
  Objectives  This paper proposes an algorithm for optimizing the layout of carrier aircraft in a hangar.   Methods  To solve the problem of the mixed layout of aircraft in a hangar, based on the basic spatial combination relationship, this paper sets up a combinatorial relationship library, optimizes the solution space and converts the constrained two-dimensional layout problem into a combinatorial optimization problem. A hangar layout model is established with the maximum number of carrier aircraft and maximum number of emergency dispatch aircraft, and a heuristic algorithm is used to solve the model.  Results  Using the case study of a USS Nimitz-class aircraft carrier, the resulting layout scheme can maximize the total number of carrier aircraft while ensuring the number of emergency dispatch aircraft, and the results satisfy actual business constraints and requirements. Compared with the layout scheme of USS aircraft carrier, the area utilization rate of hangar deck is increased by 16.92%.  Conclusions   The proposed algorithm can be used to effectively solve the layout problem of carrier aircraft in a hangar.
Analysis of temperature field and noise characteristics of impinging jet of carrier-based aircraft engine
Longzhou QI, Heying FENG, Yehui PENG, Kun ZHAO
2021, 16(3): 17-23. doi: 10.19693/j.issn.1673-3185.02063
Abstract:
  Objectives  As the deflection angle has great influence on temperature and noise radiation near the deflector of the impinging jet of a carrier-based aircraft, determining an appropriate deflection angle can expand the safe area around the aircraft.  Methods  This paper analyzes the flow field, temperature field and sound field characteristics near the deflector of a certain type of engine tail nozzle in full afterburner conditions under different deflection angles (β=35°, 45°, 55°) and different monitoring distances (S=20D, 30D, 50D, 80D). Using large eddy simulation (LES) and acoustic analogy methods, a calculation model of a supersonic jet impinging on an inclined plate is established, and the correctness of the model verified by experimental data.  Results  The deflection angle changes the distribution of the temperature field. When β=45°, the deflector has a better effect, personnel and equipment behind the deflector can be protected most effectively, and the high-temperature reflux on the countercurrent side of the deflector will affect the carrier aircraft. The rear wheel basically has no effect. The deflection angle also has great influence on far-field radiated noise. When noise monitoring distance S=40D, the total sound pressure level increases with the increase of the deflection angle. When β=35°, the noise radiation range affecting the normal work of personnel is at its smallest.  Conclusions  In general, when β=45°, personnel and equipment near the deflector suffer the least high temperature and noise threat. Even so, in order to ensure that the ground crew can work normally at any angle, the tail nozzle should be kept above 80D.
HEMP shielding performance on carbon fiber composite power supply cabinet
Fuqiang WANG, Peng LIU, Jiandong ZHANG, Qinglin SU, Yan LIU, Yi LIANG
2021, 16(3): 24-30, 43. doi: 10.19693/j.issn.1673-3185.01850
Abstract:
  Objectives  Regarding demands for the lightweight and high-altitude electromagnetic pulse (HEMP) protection properties of carrier-borne cabinets, through the oven process, a carbon fiber composite cabinet is constructed.  Methods  CST Studio is used to simulate and evaluate the protective performance of a composite chassis. Nickel-coated carbon fiber and metal foil are selected as electromagnetic reinforced materials on the basis of the carbon fiber composite structural design and electric connection design of interlamination and gap electromagnetic reinforcement. HEMP protection performance is tested by using bounded wave simulator.   Results  The results show that the HEMP shielding efficiency is above 65 dB.  Conclusions  The carbon fiber composite cabinet has lightweight, high-strength, HEMP shielding and anti-severe environment properties, giving it significant project value and application prospects.
Rapid prototyping manufacturing and equipment design used in ship maintenance support
Heng LUO
2021, 16(3): 31-37. doi: 10.19693/j.issn.1673-3185.01980
Abstract:
  Objectives   With the rapid development of naval equipment and its increasing use frequency and failure rate, the traditional repair mode has limitations. This paper puts forward a rapid prototyping manufacturing (RPM) and equipment design method used in ship maintenance support.   Methods   Based on the hardware, software, technology and materials, the integration technology of rapid prototyping equipment is researched according to the actual situation of the ship. The design method of quick removal and combination using the equipment movement mechanism is adopted, achieving rapid prototyping repair with nitrogen as the shielding gas. The key technologies and methods of rapid prototyping repair are then studied, including technology, shape coordination and control, and post-repair treatment.   Results   The results of this study show that mobile rapid prototyping repair equipment with quick removal and combination can help to settle the problems of the online repair of real ships; marine nitrogen can be used as the shielding gas, which is convenient and affordable; and the dust collection system module greatly reduces the pollution of equipment in prototyping repairing process.   Conclusions   The developed quick removal and combination equipment for prototyping repair, which helps to realize "repair in case of damage" for ships under on-site conditions, can help to meet the requirements of accompanying support for spare ship equipment parts under actual combat conditions.
Modeling and time domain simulation of surf-riding for water-jet propelled ships
Peiyuan FENG, Youlin CAI, Sheming FAN
2021, 16(3): 38-43. doi: 10.19693/j.issn.1673-3185.01892
Abstract:
  Objectives  Surf-riding/broaching is one of the five stability failure modes included in the second generation intact stability criteria by IMO. The current regulation is limited by only applying to ships using propellers. To address this issue, this paper carries out some investigations concerning the surf-riding stability failure of ships using water-jets, so that the regulation can be further completed.  Methods   Based on the mechanical model of the water-jet unit and the one-dimensional surge motion equation of sequential waves, a mathematical surf-riding model is established. The fourth order Runge-Kutta method is used to solve the equation, and a time domain surf-riding simulation for the water-jet propelled ship is achieved. Taking one high-speed wave-piercing tumblehome as a sample ship, the characteristics of the conditions for the occurrence of surf-riding are obtained through systematic time domain simulations.  Results  The result shows that, within the range of wave conditions required by IMO's second generation intact stability criteria, surf-riding occurs in 80.9% of cases when the Froude number is 0.4; when the Froude number is reduced to 0.3, the percentage drops to 59.4%.  Conclusions  This study provides the theoretical model and the numerical approach necessary to evaluate the surf-riding/broaching stability of ships propelled by water-jets, which can be used to evaluate the stability safety of this type of ship.
A SR-UKF-based method to identify submarine hydrodynamic coefficients
Bangjun LYU, Bin HUANG, Likun PENG
2021, 16(3): 44-49. doi: 10.19693/j.issn.1673-3185.01893
Abstract:
  Objectives  The square root unscented Kalman filter (SR-UKF) algorithm was developed for the identification of hydrodynamic coefficients, which are difficult to obtain accurately in submarine motion models.  Methods  Firstly, the hydrodynamic coefficients identification model was established based on the nonlinear mathematical model of submarine motion in the vertical plane, combined with the SR-UKF algorithm. Then, a sinusoidal maneuvering in the vertical plane was carried out by the automatic steering method and the generated data in addition to the measurement errors were chosen as the input for SR-UKF parameter identification. Finally, six viscous hydrodynamic coefficients in the vertical motion plane were identified through a numerical simulation.  Results  The simulation results show that, all identified hydrodynamic coefficients converge to fixed values within 3 000 seconds, and through the selection of appropriate initial values, the maximum error between the identification results and the standard values measured by a hydrodynamic test is only 1.5%.   Conlusions  SR-UKF can be effectively applied to identify submarine hydrodynamic coefficients, and can be further extended to real ship coefficients identification.
Numerical prediction of hydrodynamic performance of differently shaped flapping foil propulsors
Shenghao ZHANG, Lei MEI, Junwei ZHOU
2021, 16(3): 50-59, 66. doi: 10.19693/j.issn.1673-3185.01911
Abstract:
  Objectives  The hydrodynamic performance of three-dimensional hydrofoils with different shapes is studied in order to find the optimal hydrofoil geometry.  Methods   NACA 0012 hydrofoil model with different aspect ratios, tip ratios, forward-swept and back-swept shapes are used to simulated the flow field of the hydrofoil with multi-DOF coupling motion based on the NUMECA Fine/Marine solver. The reliability of the numerical method is validated by comparison with the experimental results and analysis of grid independence.  Results  The results show that a hydrofoil with a larger aspect ratio has better performance. By comparing the results of hydrofoils with the same aspect ratio and different tip ratios, it is found that tip ratio causes performance degradation. By comparing the results of forward-swept, back-swept and trapezoidal hydrofoils with the same tip ratio, it is found that the performance of the back-swept hydrofoil is optimal, and the shape of the trailing edge has great influence on hydrofoil performance.  Conclusions  This study obtains certain optimal geometrical parameters of flapping foil propulsors, and achieves greater understanding of the characteristics of wake vortex structures.
Research and development of 3D hull modeling and stability calculation system
Zhibiao CHEN, Qingren CHEN, Xianling ZHU
2021, 16(3): 60-66. doi: 10.19693/j.issn.1673-3185.01952
Abstract:
  Objectives  To realize the visualization and fast modeling and stability calculation of hulls and compartments, and extend the application scope to complex ship forms such as multi-body and combined hull, a three-dimensional hull modeling and stability calculation system is developed.  Methods  Model-View-Controller mode is used to build the system framework; 3D visualization, object pick-up, feature point snap, command stream, reference expression-linkage update, undo-redo, intelligent table and other functional elements are integrated to realize the 3D interactive modeling of ships and compartments for general users, and command stream rapid modeling for skilled users; moreover, a 3D surface grid integration algorithm is used to realize static hydraulic and stability calculation without the limitation of hull shape, and multiple regulation criteria are implemented for users to select from based on the technology of the derived classes.  Results  Real ship tests and a large number of engineering applications show that this system can realize the fast 3D modeling and accurate stability calculation of hulls and compartments, covering complex ship forms such as multiple stern, bulbous bow, head up, tail up and convex deck, as well as special ship types such as floating dock, catamaran, trimaran and assembled combined ship.  Conclusions  This system has reference value for the design and development of ship engineering software.
Large eddy simulation of contaminants dispersion in ship isolation room
Qi LIU, Chengli XIE, Weiguang LI, Wenchuan LIU, Xinping LONG
2021, 16(3): 67-73. doi: 10.19693/j.issn.1673-3185.01900
Abstract:
  Objectives  Conducting studies on contaminant dispersion during the door-opening process of isolation rooms and quantitatively comparing and evaluating the diffusion characteristics of contaminated air under different negative pressure conditions is of great significance for the design of negative pressure systems for the isolation rooms of ships.   Methods  Based on the large eddy simulation (LES) method and a combination of tracer gas component transport equations, numerical simulations were conducted to investigate contaminated air dispersion during the door-opening process of isolation rooms. The flow field characteristics and pollutant dispersion process during the dynamic opening of the door under different differential pressure conditions were then compared and analyzed.   Results   The results show that the sensitivity analysis of mesh resolution and time step with total pollutant diffusion as the evaluation index can ensure the reliability of the LES simulation results. Further analysis shows that under the combination of different differential pressures and door-opening induced flows, there is a significant difference between the magnitude of the fluid velocity peak and the time when the peak appears. Increasing the negative pressure value of the isolation room can reduce the peak of pollutant diffusion and shorten the time for the diffused pollutant to return to the isolation room under the differential pressure.   Conclusions  The results obtained in this paper can provide guidance for the design of ship isolation rooms.
Study on thermo-mechanical coupling method of ship cabin with ceiling vent under fire condition
Jinhui WANG, Xianda ZHANG, Keye CHEN
2021, 16(3): 74-85, 111. doi: 10.19693/j.issn.1673-3185.01903
Abstract:
  Objectives  The performance analysis of ship cabin steel structures in fire situations is fundamental to structural fire resistance design. Compared with research conducted under traditional standard fire conditions, research based on the real fire temperature field can more accurately analyze the mechanical response behavior of cabin structures. Aiming at an open cabin (i.e. engine room) structure, a fire-heat-structure coupling method combining FDS and ANSYS is developed.  Methods  First, the FDS simulation is utilized to obtain the temperature information of the inside ship wall exposed to the fire, which is then used as the boundary condition transferred to the structural finite element analysis software ANSYS. Transient thermal analysis concerning the temperature field of the cabin structure is then conducted, and the thermal-structural coupling analysis of the ship cabin structure carried out in a real fire scenario.  Results  The results of the case study using the proposed method demonstrate that the stress distribution is not uniform due to the uneven temperature distribution. The maximum stress is concentrated at the edge of the cabin, with a value of 19 MPa. The structure does not reach the failure limit after being exposed to fire.  Conclusions  Compared with the traditional standard fire curve method, the proposed method has two advantages for addressing structural response: the non-uniform elevated temperature of the structure and real fire temperature rise. More attention should be paid to the change in structural internal force caused by non-uniform temperature rise in an open ship cabin.
Simulation analysis of warship equipment maintenance and support system evolution based on system dynamic
Chunhui YANG, Shuowei ZHANG, Tao HU
2021, 16(3): 86-95. doi: 10.19693/j.issn.1673-3185.02021
Abstract:
  Objectives  The evolution of the equipment maintenance and support system of warships is the result of internal and external factors. Based on an analysis of the evolution dynamic mechanism and system dynamics theory, an evolution model of the warship equipment maintenance and support system is established, and the evolution trends and key factors of the system are simulated and analyzed.  Methods  The model is quantified on the basis of the hypothesis, and the evolution process and sensitivity analysis of the system are carried out using the simulation tool Anylogic.   results  The results show that the evolution of the maintenance and support system of warship equipment presents an increasing trend in an S-shaped curve. At the beginning of the evolution, the scale of the system grows slowly and the cost of completing tasks is high. It is necessary to increase the proportion of maintenance hardware and personnel investment at the same time in the early stages of system evolution, then increase the proportion of personnel investment in the transition period. In the middle and late stages of system evolution, measures such as increasing the participation of maintenance personnel in equipment development and design can improve the marginal benefits of investment and flexibility of maintenance organization while also bringing greater evolution benefits.  Conclusions  This evolution simulation method based on system dynamics can provide support for the capability evaluation and key investment directions of the equipment maintenance and support system of warships.
Ship Structure and Fittings
Research progress on dynamic characteristics and protective performance of multicellular filled impact resistant protective structure
Zhujie ZHAO, Hailiang HOU, dian LI
2021, 16(3): 96-111. doi: 10.19693/j.issn.1673-3185.02053
Abstract:
With the development of structural protection design concepts, numerous multicellular filled impact resistant protection structures have gradually emerged. As many studies at home and abroad show, great progress has been made in the strength and vibration characteristics of multicellular filled impact resistant protective structures compared with traditional structures. Meanwhile, the overall optimization direction of such structures has also progressed from traditional linear studies to various nonlinear and multi-material design methods. In this paper, the exposition of various multicellular filled impact resistant protective structures is carried out in terms of mechanical properties, failure modes and protection characteristics. By generalizing the theoretical calculation methods and response characteristics of various multicellular filled impact resistant protective structures, this paper puts forward the development prospects of such structures for use as references in the study of structural forms, optimal design and application directions.
Analysis of buckling failure modes of composite sandwich panels filled with aluminum foam
Pengcheng XING, Zhen CHEN, Guangmin DAI
2021, 16(3): 112-119. doi: 10.19693/j.issn.1673-3185.02029
Abstract:
  Objectives  The goal of this article is to grasp the influence of panel spacing, plate thickness and other dimension parameters on the web buckling failure modes of I-type sandwich panels with aluminum foam. The change rules of its bearing characteristics during out-of-plane compression are revealed.  Methods  The nonlinear finite element method was used to simulate the out-of-plane compression process of composite sandwich panels. The mechanical properties of aluminum foam were obtained from experiments. Aluminum foam was realized using an isotropic crushable foam model in the FEM simulation. The accuracy of the numerical simulation methods used in this article was verified by comparing the quasi-static test results with the simulation results.  Results  The results show that with the decrease in the slenderness ratio, the failure modes of webs gradually transformed from material yield to plastic buckling, and five deformation modes such as plastic compression and low-order buckling appeared successively. Under high-order buckling, the stress curve will have a minimum value whenever a whole period deformation wave is generated. Under different slenderness ratios, the compressive strength of the composite sandwich panel appeared near the strain of 0.12, and was always maintained at about 9.36 MPa.  Conclusions  The slenderness ratio is an important factor affecting the web buckling failure modes of composite sandwich panels. The compression mechanical properties of composite sandwich panels with different slenderness ratios have obvious differences which require attention in structural optimization design.
Numerical simulation and improvement design of air cushion skirt connecting structure
Luhan WANG, Wenyong TANG, Shengjie XU, Yichao YUAN
2021, 16(3): 120-127. doi: 10.19693/j.issn.1673-3185.02058
Abstract:
  Objectives  The design of air cushion skirt connection structures mostly uses empirical formulas, and the application of the numerical simulation method is rare. Aiming at the particularity of the connection structure, a method for constructing a 3D finite element model of a connector which considers the bolt connection, complex contact of multiple components and interaction between the skirt and metal members is proposed as an effective means of designing skirt connection structures.  Methods  Taking the skirt connection structure in the bow of a air cushion vehicle as an example, a refined model of the structure is constructed, and the lifting load and extreme conditions are obtained from the static uplift forming results of a air cushion vehicle. The stress distribution of each member under lifting conditions and extreme conditions is then obtained for the air cushion skirt under loading, and suggestions for improving the main components are put forward.  Results  The results show that the upper edge of the hull plate's bolt hole, end of the pin shaft and transition part of the hinge are the main high-stress areas. The proposed schemes for local thickening and closed buckle improvement reduce the maximum average stress of the skirt hinge by over 20%, proving that the proposed structural improvement recommendations, especially the closed buckle design, can effectively improve the bearing capacity of the hinge.  Conclusions   The numerical simulation proposals in this study can be used to effectively calculate and analyze the strength of connection structures, and the improved scheme can provide design support.
A simplified method for structural fatigue analysis of hovercraft
Shouqi TANG, Ning LIU, Huilong REN
2021, 16(3): 128-136. doi: 10.19693/j.issn.1673-3185.02103
Abstract:
  Objectives  The operation principle of a hovercraft is different from those of conventional ship, with special stresses and much higher speeds than conventional ships. At present, the simplified fatigue strength calculation method proposed by major classification societies is not fully applicable to hovercraft, so it is necessary to put forward a suitable simplified method.  Methods  According to the special structure and sailing mode of hovercraft, and combined with mainstream specifications, experiments and related research, this paper analyzes the working conditions, load calculations, cumulative damage derivation and other aspects, and puts forward a simplified method suitable for the fatigue analysis of hovercraft structures using a specific hovercraft as an example for calculation.  Results  The simplified calculation results show that the fatigue life of typical longitudinal nodes meets the requirements of fatigue strength, and the analysis results of the example show that this method has certain applicability.  Conclusions  The simplified method proposed in this paper can be used as a reference for the development, design and verification of hovercraft.
Analysis of vibration and sound characteristics of fluid conveying pipeline considering the effect of acoustic-solid coupling
Dejin CHEN, Jin YAN, Yangyang LUO, Chao HUANG, Lülong ZOU
2021, 16(3): 137-143, 151. doi: 10.19693/j.issn.1673-3185.02193
Abstract:
  Objectives  In order to accurately grasp the vibration and sound characteristics of pipelines, a numerical simulation is carried out.  Methods   Based on the theory of acoustic-solid coupling, a numerical model of a pipeline is established. The dispersion curve of the vibration and acoustic modes of the pipeline is solved by parametric scanning. The dispersion characteristics of the elastic wall pipeline with air, water and crude oil, as well as the absolute pressure stress distribution in the pipeline, are analyzed, and the effects of wall thickness, elastic wall and hard sound field wall on the dispersion characteristics of the pipeline are studied.  Results  The results show that wall thickness has little effect on the propagation mode of elastic waves in the pipeline, and the dispersion curve is shifted to high frequency with the increase in wall thickness, mainly influencing the cut-off frequency. Due to the effects of acoustic-solid coupling, the number of modes of the elastic pipeline increases, and the increased mode number is mainly the deformation mode of the pipeline wall. The absolute sound pressure distribution in the elastic wall is basically the same as that in the hard sound field wall. The dispersion characteristics of liquid or gas inside are different, while the dispersion characteristics of water or oil inside are similar, but the direct modes of the two are different.  Conclusions  The results of this study can provide a theoretical basis for the pipeline acoustic detection of ships.
Study of L-extension type ship vibration isolation pedestal based on impedance mismatch principle
Xinhao ZHAO, Yuanyuan LI, Yuchao YUAN, Wenyong TANG, Hongxiang XUE
2021, 16(3): 144-151. doi: 10.19693/j.issn.1673-3185.01983
Abstract:
  Objectives  As the traditional pedestal has limited vibration suppression ability, it is necessary to design a new type of pedestal structure to improve its performance in this aspect.  Methods  First, based on the principle of impedance mismatch, a kind of L-extension structural cell is constructed. The mechanical properties of the straight-wall pedestal and new integrated pedestal are then compared and analyzed, therefore, the new type of pedestal is designed as lightweight to obtain a block pedestal. Finally, by changing the ratio of the thickness of the L-shaped structure in the cell, the vibration isolation effects of the new block pedestal are further improved.  Results  The results show that under the premise that the weight of the pedestals are similar, the total vibration level drop of the new pedestal in the whole frequency band of 10-250 Hz is increased by 40.56% compared with that of the straight-wall pedestal.  Conclusions  It concludes that the L-extension cell structure proposed in this paper has obvious inhibitory effects on vibration wave transmission, and that the L-extension cell structure can provide references for the design of new marine vibration isolation pedestals.
Structure-acoustic design of floating foundation in high strength steel cabin
Lei HOU, Yiyang DONG, Liming GENG
2021, 16(3): 152-156. doi: 10.19693/j.issn.1673-3185.02139
Abstract:
  Objectives  This paper proposes a design for a floating foundation of a high strength steel cabin which simultaneously meets the requirements of impedance adaptation in acoustics and stiffness matching in mechanics.  Methods  Typical floating foundations which are not connected with the pressure hull are studied by adjusting the structural parameters of the foundation, analyzing the impedance characteristics and intrinsic modes with the finite element method, and calculating the strength of the pressure structure along with the original and improved foundations. A scheme of a floating foundation which satisfies the design requirements is obtained.  Results   The results show that the amplitude of the improved foundation is increased, the coupling of the intrinsic modes of the foundation with the mechanical equipment is reduced, the strength of the pressure satisfies the specification requirements, and the added weight is within the acceptable range.  Conclusions  This floating foundation scheme can provide references for the design of large foundations for high strength steel cabins which take into account both acoustic and mechanical requirements.
Experimental investigation into vibration control of stern structure excited by propeller forces
Shengpeng JIANG, Zixiang HUANG, Di WU, Zhizhong LIU, Zhiyi ZHANG
2021, 16(3): 157-163. doi: 10.19693/j.issn.1673-3185.01938
Abstract:
  Objectives  To reduce the vibration of stern structure excited by lateral propeller forces, the application of vibration isolation, vibration blocking masses and damping coating is carried out.  Methods  First, the vibration transmission characteristics of the shaft-stern coupled system are obtained through vibration testing, then the lateral excitation mainly transmits to the stern structure through the rear stern bearing is suppressed using three control methods based on the test results. Finally the validity of the respective proposed methods is verified.   Results  The test results show that vibration isolation has limited effectiveness in reducing vibration in the low to medium frequency range due to the limited range of stiffness variation; vibration blocking masses are more effective in isolating vibration transmission to the stern structure; and damping coating has significant effect on the attenuation of vibration in the high frequency range. The acceleration level of the stern structure is reduced by at least 6 dB under the comprehensive application of the three control methods.  Conclusions  The results obtained in this study have reference value for the vibration control of the stern structures excited by propeller forces.
Performance simulation and parameter analysis of viscous fluid damper based on orthogonal design
Yong WU, Yousong GUO, Ming HONG
2021, 16(3): 164-169, 206. doi: 10.19693/j.issn.1673-3185.01872
Abstract:
  Objectives  This paper investigates the flow field distribution inside a working viscous fluid damper (VFD) , and the sensitivity of the hole radius, hole length, number of holes and piston diameter to the damping coefficient and velocity index.  Methods  Parameter design schemes are obtained through orthogonal design, and a FLUENT flow field simulation is applied to study the flow field distribution, and calculate the impact degree of structural parameter on the damping coefficient and velocity index of each scheme.  Results  The results show that the internal flow field distribution basically conforms to the regular distribution of laminar flow in parallel flat plates and tubes, the impact degree of of each factor on the damping coefficient and the velocity is obtained in descending order, i.e. hole radius>piston diameter> number of holes>hole length, and hole radius>number of holes>hole length>piston diameter.  Conclusions  The combination of orthogonal design and FLUENT flow field simulation can minimize the design scheme, shorten the design cycle, and reduce experimental cost, giving it great significance for practical engineering applications.
Marine Machinery, Electrical Equipment and Automation
Investigation into abnormal heat transfer mechanism of supercritical carbon dioxide in vertically upward Tube
Juanjuan HU, Zengguang LI, Yimin GAO, Jian YANG, Lang LIU
2021, 16(3): 170-179. doi: 10.19693/j.issn.1673-3185.01921
Abstract:
  Objectives  The heat transfer techniques of supercritical CO2 (S-CO2) in small channels have been extensively used in nuclear reactor cooling, aerospace engine cooling and so on. To ensure the safety and high operation efficiency of the thermodynamic devices involved in the S-CO2 Brayton cycle system, it is necessary to systematically study the flow and heat transfer characteristics of S-CO2, and thoroughly analyze the abnormal heat transfer mechanism.  Methods  Through CFD numerical simulation, the heat transfer characteristics of S-CO2 in a vertically upward tube with an internal diameter of 2 mm at different mass flow rates are studied. At the same time, under conditions of heat transfer enhancement and deterioration, the change of radial physical properties at different sections is studied, and the mechanism of abnormal heat transfer is analyzed in depth.  Results   It is found that under conditions with mass flow rates of 500–1 000 kg/(m2·s), the heat transfer of S-CO2 moves from heat transfer enhancement to heat transfer deterioration. In the heat transfer deterioration cases, the peak value of the heat transfer coefficient in the recovery region gradually decreases with the increase in heat flux, then finally disappears. As the operating pressure is far from the critical pressure, heat transfer enhancement and deterioration are both weakened. As shown by mechanism investigation, in heat transfer enhancement cases, the heat transfer of the fluid is stronger near the pseudo-critical region than in other regions, and the increased heat transfer coefficient comes from the increased portion of the cross-section area occupied by the fluid with large specific heat. In heat transfer deterioration cases, the velocity profile of the fluid at the cross-section where the wall temperature has its peak value presents an M-shaped curve, the velocity gradient at the inflection point of the velocity profile decreases to 0, the turbulent kinetic energy reaches its lowest level and heat transfer deterioration occurs.   Conclusions  The results of this study are significant for improving the heat transfer characteristics of S-CO2 in small channels.
Investigation of flow and heat transfer of supercritical water in double-pipe heat exchanger
Lang LIU, Zengguang LI, Jian YANG, Wenqiang HE, Qingqing WANG
2021, 16(3): 180-188. doi: 10.19693/j.issn.1673-3185.01809
Abstract:
  Objective  The flow and heat transfer of supercritical fluid is complex, and most of the existing research is based on the conditions of constant wall temperature and constant heat flux. However, in practical engineering, heat transfer often occurs under the conditions of variable heat flux. In order to better understand the relevant performance, this paper studies the coupled flow and heat transfer of supercritical fluid in a double-pipe heat exchanger.  Method  The experimental section of this paper focuses on a double-pipe heat exchanger. The flow and heat transfer characteristics of supercritical water in the double-pipe heat exchanger are analyzed by collecting temperature and pressure data from the temperature and pressure measuring points arranged on the inside and outside of the double pipe.  Results   The experimental results show that great changes in physical parameters near pseudo-critical points are the main reasons for the phenomenon of supercritical water heat transfer, and they differ from those of ordinary heat transfer. There is a difference between the peak heat transfer coefficient temperature and pseudo-critical temperature which increases with the increase of pressure. This phenomenon is caused by the temperature gradient and variations in thermal-physical properties in the heat transfer section. The heat transfer coefficient of the outer pipe increases with the increase in water temperature at the inlet of the inner pipe when the mean bulk temperature is lower than the pseudo-critical temperature due to the buoyancy effect decreasing at the same time, while the buoyancy effect is almost independent of the water temperature at the inlet of the inner pipe when the mean bulk temperature is higher than the pseudo-critical temperature and the buoyancy effect is non-significant.   Conclusion  The results can provide valuable references for the design of double-pipe heat exchangers and research and mechanism analysis of the coupled flow and heat transfer of supercritical fluid in double-pipe heat exchangers.
Influence of various wear ring clearances of centrifugal pump on output characteristic and excitation force properties
Yunyi WEI, Cunsheng ZHAO, Zhe CUI
2021, 16(3): 189-193. doi: 10.19693/j.issn.1673-3185.01832
Abstract:
  Objectives  In order to analyze the influence of different wear ring clearances on the output characteristics and vibration performance of a centrifugal pump, an integrative test platform of closed-circuit output characteristics and vibration performance is established to carry out experimental study.  Methods  Taking a vertical centrifugal pump as the research object, seven groups of sealing rings with different internal diameters are designed, the power spectrum of the vibration signal from the pump body is collected using a 16-channel vibration accelerometer, and the operating characteristics of the pump under different clearance conditions are tested.  Results  The results show that the head and efficiency of the centrifugal pump decrease with the increase in wear ring clearance, and that wear ring clearance has a greater influence on the radial balance of the single-stage double-suction centrifugal pump and further affects shaft frequency vibration intensity. When the wear ring clearance increases, the reflux increases the fluid pulsation of the centrifugal pump and causes the vibration energy to concentrate at high frequencies.  Conclusions  The results of this study reveal the influence of the wear ring clearance of a centrifugal pump on its output characteristics and excitation force properties, and can provide theoretical guidance for the condition assessment and maintenance work of centrifugal pumps.
Dynamic characteristics analysis of disc-spring longitudinal shock absorber of ship shafting
Ji XIA, Quanchao LI
2021, 16(3): 194-199. doi: 10.19693/j.issn.1673-3185.01953
Abstract:
  Objectives  In order to suppress the longitudinal vibration transfer of ship shafting, this paper put forward a design approach of applying disc-spring longitudinal shock absorber to the ship shafting, and carried out a study of dynamic characteristics before and after applying this type of longitudinal shock absorber.   Methods  First, the static stiffness of shock absorber was studied by theoretical analysis and experimental test. Secondly, the influence of static load, excitation frequency, disc spring combination and other factors on the dynamic stiffness of shock absorber was investigated by experimental test. Finally, the optimized scheme of disc-spring shock absorber was applied to ship shafting to study the effect of vibration reduction.   Results   The results show that the selected four-piece dual disc-spring shock absorber has a low ratio of dynamic stiffness to static stiffness, and its dynamic stiffness is not sensitive to the variation of static load, system excitation frequency and other factors. The application of shock absorber has obvious effect on longitudinal vibration control of shafting.   Conclusions   The research results have reference value for the engineering application of ship shafting disc-spring longitudinal shock absorber.
Dual CPU redundant communication hybrid fault detection technology for shipborne electrical plant control system
Yue LU, Weibo LI, Wei LI, Qi LI, Wanfeng SUN
2021, 16(3): 200-206. doi: 10.19693/j.issn.1673-3185.01898
Abstract:
  Objectives  In order to improve the reliability of shipborne electrical plant control systems and solve the key problem of fault detection in dual CPU hot backup redundant communication, a comprehensive set of fault detection mechanisms is proposed.  Methods  After analyzing traditional dual CPU fault detection, this study proposes a hybrid fault detection mechanism combining the network fault detection method with the third-party monitoring heartbeat method. Based on the designed dual CPU redundant system architecture, the principles and software implementation of the two proposed fault detection methods are analyzed, and the proposed fault detection method is verified on an actual device.  Results  After actual device inspection, the results show that the proposed dual fault detection technology overcomes the shortcomings of traditional fault detection methods such as focusing on CPU faults but ignoring CPU peripheral communication faults, and susceptibility to the "dual host phenomenon". It also improves the speed and accuracy of fault detection to ensure the stable and reliable operation of the dual CPU redundant system.  Conclusions  The results of this study can provide references for the dual CPU redundant communication fault detection methods of shipborne electrical plant control systems.
Built-in test technology for electro-hydraulic servo-valve amplifier
Jianping YUAN, Hanbing SUN
2021, 16(3): 207-214. doi: 10.19693/j.issn.1673-3185.01905
Abstract:
  Objectives   The electro-hydraulic servo valve operates in a harsh working environment but lacks integrated testability. In order to improve the usability and maintainability of electro-hydraulic servo valves, it is necessary to design a built-in test (BIT).   Methods   A BIT method involving the characteristics of the valve amplifier is proposed. On this basis, the implementation of BIT software/hardware and the concrete design of anti-false alarm measures are given, and a closed-loop electro-hydraulic servo system is constructed for verification.   Results   The verification test results show that this design method is feasible and can quickly detect faults online.   Conclusions   The BIT method is an effective way to reduce the maintenance cost of the electro-hydraulic servo system life cycle, giving it certain engineering application value.