## Current Issue 2022, Volume 17,  Issue 2

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2022, 17(2): .
Abstract:
2022, 17(2): 1-7. doi: 10.19693/j.issn.1673-3185.02202
Abstract:
The design and construction of luxury cruise ships is currently a hot topic in the domestic shipbuilding industry, but the design skills are insufficient due to a lack of practical experience derived from real projects. First, based on a survey of the internal R&D and refitting design of luxury cruise ships and ferry/passenger ship projects with gross tonnages of 15 000–75 000, as well as referring to the latest developments in rules regarding cruise and passenger ships, and the design features of delivered ships across the world, this paper seeks to review the relevant advanced technologies employed in the international design and construction of luxury cruise ships, with a focus on 3D modelling, flexible design throughout the full life cycle, holistic ship performance optimal design and alternative design application. Moreover, the effects of the application of green fuel, digital and intelligent design, and health and hygiene safety requirements on the future design of cruise ships are discussed. It is hoped that this paper can provide valuable references for improving the domestic design level of luxury cruise ships.
2022, 17(2): 8-16. doi: 10.19693/j.issn.1673-3185.02219
Abstract:
Objectives  In order to minimize ship type changes and meet the new requirements of SOLAS 2020 for the damaged stability of passenger ships, starting with the layout optimization design of large cruise ships, the ideas and key design factors regarding the improvement of attained subdivision index A (hereinafter referred to as index A) in damaged stability are deeply explored.   Methods  Taking a large cruise ship as an example, this paper obtains the key design factors affecting index A through the calculation, analysis and comparison of the influence of different detailed design schemes for index A, as well as the analysis of the SOLAS 2020 requirements.   Results   The index A of a ship can be improved by increasing the reserve buoyancy, adding cross-flooding devices and openings on class-A fire resistant bulkheads, and controlling the relevant design layout according to safety zones and flood waterlines.   Conclusions  This study shows that the index A of cruise ships can be improved to a certain extent by considering the refined design and layout optimization in damaged stability calculation, thereby limiting the optimization of the main dimensions of the cruise ship to within the minimum range.
2022, 17(2): 17-27, 37. doi: 10.19693/j.issn.1673-3185.02167
Abstract:
Objectives  Considering the high-level requirements of cooperative design ability, along with the fact that the working interface between general arrangement and aesthetic design of luxury cruise ships is unclear to a certain degree, this paper focuses on the constraints of general arrangement on the aesthetic design.  Method  Based on regional deconstruction and an exploration of the parameter tree of influencing factors on the appearance design of luxury cruise ships, the main factors are selected, constraints in ship code conventions, ship safety and engineering design experience are analyzed, and the boundary conditions for the creativity of appearance design are obtained.  Results  In terms of appearance and shape features such as the overall outline, visual envelope of the side view, and funnel, functional zones at the bow and the stern of ship, the constraint conditions of appearance design are confirmed through the relative dimensions of different parameters to avoid obstructing the free flow of creative work.  Conclusions  The results of this study can provide significant references for exploring the cooperative mode between engineering design and appearance design, and improving the level of domestic innovative cruise ship design.
2022, 17(2): 28-37. doi: 10.19693/j.issn.1673-3185.02108
Abstract:
Objectives  This paper takes the perspective of user cognition to explore the current situation and influencing factors of the cruise ships' appearance brand images.  Methods  Based on the hierarchical clustering method, experiments are designed that allow users to observe the appearance of sample cruise ships and reassess the brand belonging to each ship. The experimental data is then collected and statistically analyzed using SPSS（statistical product and service solutions）software.  Results  The research results show that there are three kinds of the current situation about cruise ship's appearance brand image: most cruise ship have good appearance brand image; Among them, the development of the appearance brand image of mass cruise and luxury cruise are far better than that of professional cruise. And because of the continuity of appearance of the same brand and the difference of the appearance of the different brand, cruise ship's appearance brand image presents a chaotic situation of image crossing or faulting.  Conclusions  The appearance brand images of cruise ships are generally well constructed. The poor appearance brand images of cruise ships (such as some professional cruise ships) are objectively due to the lack of a typical appearance or family characteristics among ships, as well as the homogenization of appearance across brands. Subjectively, the aesthetics and objectives of cruise users will affect the value of the appearance brand image.
2022, 17(2): 38-48, 155. doi: 10.19693/j.issn.1673-3185.02214
Abstract:
Objectives  The design of interior decoration themes in cruise ships is crucial for the overall orientation and conception of the product, and it affects the whole process of aesthetic design including the promotion of cruise products, appearance design, functional organization and interior decoration style in the later stages. Therefore, on the premise of meeting the aesthetic needs of passengers and consumers, this paper studies the design principles and aesthetic design strategies of interior decoration themes.  Methods  Based on an investigation of the theme styles and aesthetic design characteristics of 40 popular cruise ships in the international market, the theme tendencies of international cruise ships are analyzed, and the principles and methods of theme planning and aesthetic design are summarized and discussed. Based on the elements of each space in the cruise ship, the correlation between interior theme design and aesthetic design is studied, and the design methods of the interior space and decoration of cruise ships are explored.  Results  On this basis, the transformation of a thematic conceptual scheme into a realized functional layout and interior decoration can be implemented in the interior decoration of cruise ships.  Conclusions  This study provides substantial references for the basis, ideas and practices of aesthetic design in the overall design of medium-large cruise ships.
2022, 17(2): 49-56. doi: 10.19693/j.issn.1673-3185.02154
Abstract:
Objective  The thermal comfort of a ship's cabin has an important influence on the life and work of the crew. However, it takes a long time to design the air supply parameters using experimental research and the traditional numerical simulation trial method. Therefore, an inverse design method based on proper orthogonal decomposition (POD) is applied to the design of air supply parameters in a typical cabin.   Method  In this paper, a three-dimensional numerical model is established using the computational fluid dynamics (CFD) method. After obtaining the results of the flow field, temperature field and concentration field, combined with the inverse design method based on POD, the optimal thermal comfort and minimum pollutant concentration in the breathing zone of a nine-person cabin are taken as the optimization objectives.   Results  The results show that the inverse design method based on POD can be used for the inverse optimization of multiple parameters and objectives. Compared with the traditional algorithm, it can save time by more than 90% and greatly improve the design efficiency of the transmission of cabin air supply parameters.   Conclusions  The POD method can be applied to the design of a ship's living quarters. The appropriate range of air supply parameters obtained by reverse design can provide references for the selection of the air supply parameters.
2022, 17(2): 57-62. doi: 10.19693/j.issn.1673-3185.02277
Abstract:
Objective  In the design stage of a luxury cruise ship, in order to save costs, it is necessary to use the computational fluid dynamics (CFD) method to predict the seakeeping performance of the cruise ship under design.   Method  The research object of this paper is a large luxury cruise ship. The self-developed ship hydrodynamics CFD solver naoe-FOAM-SJTU is used to simulate the seakeeping performance of the luxury cruise ship at model scale. The seakeeping simulation adopts the speed entrance input wave-making method, and predicts and summarizes the cruise movement under different wave heights and downwards.   Results   The evaluation finds that the designed cruise ship model basically meets the requirements of ship comfort at maximum speed and wave heights of 0.062 5, 0.1 and 0.15 m, and meets the requirements of ship safety at the design speed, wave height of 0.225 m and heading sea conditions.   Conclusion  Under the calculated working conditions, this cruise ship design conforms to the safety and comfort standards in the seakeeping evaluation standards of luxury cruise ships.
2022, 17(2): 63-72. doi: 10.19693/j.issn.1673-3185.02169
Abstract:
Objectives  This study seeks to optimize the total resistance and seakeeping performance of ships sailing in waves by adding appendages and changing their size.   Methods  First, numerical calculations are performed on a KCS ship with two anti-pitching fins and a stern flap, and both kinds of appendage separately, to study the effects of the appendages on the hull. Second, thirty KCS ships with deformed appendages are obtained by changing the width of the anti-pitch fins and the length of the stern flap. The in-house viscous flow solver naoe-FOAM-SJTU is used for the calculations. Third, a Kriging surrogate model is established and applied to a multi-objective genetic algorithm to obtain the Pareto front of the hull with optimal appendages. Three KCS ships with optimal appendages are selected from the Pareto front for further analysis.   Results  By adding appendages to a KCS ship, the pitch magnitude and average total resistance in an encounter period are reduced by about 12.7% and 12.5% respectively.   Conclusions  The resistance and pitch magnitude of a KCS ship in head waves can be optimized by adding appendages such as anti-pitch fins and stern flaps, and changing their principal dimensions.
2022, 17(2): 73-80. doi: 10.19693/j.issn.1673-3185.02123
Abstract:
Objectives  Two-equation models are the turbulence models most commonly used for RANS calculations in engineering applications. The SST k-ω turbulence model is self-adaptive of wall distance and capable of predicting adverse pressure gradient flows. However, as empirical constants are introduced to derive turbulence models, none of them are universal for all flow conditions. Flow control parameters are implemented in this study to improve the adaptability of turbulence models to ship flow fields.   Methods  The GEKO (Generalized k-ω) turbulence model is based on the classical SST k-ω turbulence model, while also introducing separation parameter CS and rotation parameter CRC in order to control the separation intensity and impact of the flow rotation respectively. The new turbulence model is then applied to predict the flow of a JBC ship. In order to inspect the influence of varying settings of CS and CRC, the experimental data is compared with the calculation results in terms of ship resistance, wake patterns and pressure distribution.   Results  The comparison results show that the setting of CS and CRC in the GEKO turbulence model can have an impact on the prediction of ship resistance and local wake flow compared to the classical SST k-ω turbulence model.   Conclusions  The reasonable parameter tuning of turbulence models has the potential to improve the accuracy and applicability of numerical prediction. This procedure can provide references for the modification of turbulence models in engineering applications.
2022, 17(2): 81-90. doi: 10.19693/j.issn.1673-3185.02183
Abstract:
Objectives  This paper studies the transient effects, different frequencies of spectral peaks and meaningful excitation amplitudes on liquid sloshing.   Methods  A numerical model is established using the computational fluid dynamics (CFD) method, and the reliability of the numerical model is validated through comparison with the analytical solution of linear potential flow and experimental data.   Results  The transient effects of random excitation have a significant influence on the fluctuation of the free water surface of liquid sloshing in the tank. By applying the buffer function, stable results can be obtained quickly. When the peak frequency of the excitation spectrum is close to the natural frequency of the tank, the energy of the wave-height response spectrum of the liquid sloshing in the tank is mainly concentrated at the natural frequency of the tank. When the peak frequency of the excitation spectrum is far from the natural frequency of the tank, the energy of the wave-height response spectrum is concentrated near the peak frequency. With the increase of the meaningful amplitude of the excitation spectrum, the amplitude deviation of the liquid sloshing response relative to the linear wave (the deviation degree is zero) increases, and the nonlinearity of the tank increases significantly.   Conclusions  For the random excitation simulation, especially when the excitation frequency is far from the natural frequency, it is necessary to buffer the excitation duration. It is found that when the peak frequency of the excitation spectrum moves away from the first natural frequency to higher frequencies, the energy is dominant at the i-th order of the natural frequency when the peak frequency is close to it.
2022, 17(2): 91-97. doi: 10.19693/j.issn.1673-3185.02299
Abstract:
Objective  In order to accurately locate the zone and size of flow energy loss during the operation of a ducted propeller, the flow energy loss characteristics are analyzed from the perspective of energy.  Method  Steady ducted propeller simulations are investigated under different advance coefficients and rotational speed conditions by solving the Reynolds-Averaged Navier–Stokes equations and entropy production equation, and the optimization of a ducted propeller with boss cap fins is carried out on this basis.  Results  The value of viscous dissipation entropy production increases with the increase of the advance coefficient, while the value of turbulent dissipation entropy production decreases with the increase of the advance coefficient at the same rotational speed. At the same advance coefficient, the two kinds of entropy production value increase significantly with the increase of rotational speed. The proportion of turbulent dissipation entropy production is larger than that of viscous dissipation entropy production in different operating modes, so the turbulent dissipation is the main reason for the irreversible flow energy loss. The main flow loss zone is behind the trailing edge of the duct and hub, in which the hub vortex zone formed behind the hub is exactly the high concentration zone of the flow energy loss. In addition, the improved ducted propeller with boss cap fins can significantly improve the vortex distribution at the tail of the propeller and reduce the flow energy loss caused by the hub vortex.  Conclusions  This study reveals the flow loss mechanism of ducted propellers and accurately locates the flow energy loss concentration zone, offering new insights into the energy-saving optimization design and flow energy loss identification analysis of ducted propellers.
2022, 17(2): 98-108. doi: 10.19693/j.issn.1673-3185.02236
Abstract:
Objectives  This paper presents a non-singular terminal sliding mode track control method based on a finite-time disturbance observer to solve the problem of accurately tracking and controlling an the 3D trajectory of an unmanned underwater vehicle under complex external disturbances.  Methods  A non-singular terminal sliding mode track controller is designed to ensure that the tracking error converges to zero accurately within a limited time. A finite-time disturbance observer is designed to improve the anti-jamming ability of the system under external multidimensional time-varying disturbances.  Results  The Lyapunov function is used to prove that the designed control strategy can remain stable for a limited time. MATLAB is used for the simulation experiment, and a comparison with the backstepping sliding mode control method under step disturbance shows that the method presented in this paper achieves accurate trajectory tracking.  Conclusions  The results of this paper can provide a solution for accurately tracking the 3D trajectories of unmanned underwater vehicles.
2022, 17(2): 109-118. doi: 10.19693/j.issn.1673-3185.02271
Abstract:
Objectives   Typically, the fixed kentledge laying scheme of a submersible requires a significant amount of work and can often produce unpleasant results in engineering practice. Intelligent algorithms are considered for application in order to optimize the scheme. This paper proposes a genetic algorithm based method to solve the problem.   Methods  First, by studying typical transverse sections of kentledge laying in a submersible and reverse-thinking the finite element method, a simplified equivalent mathematic model is constructed. Next, constraint functions and objective functions are extracted from the model. By using a genetic algorithm, improved fixed kentledge laying schemes are acquired with lower centers of gravity. By computing different examples, this method is proven to be effective in gaining good gravity center results with a much smaller workload.  Results  The result shows that the gravity center of the improved scheme can be 23% lower compared to the ordinary scheme. This method is also effective in balancing longitudinal moment and lateral moment at the same time.   Conclusions  This study shows that the equivalent mathematical model and optimization method are feasible, and can improve both work efficiency and gravity results. Several general principles are also concluded, which can be helpful in engineering practice.
2022, 17(2): 119-124. doi: 10.19693/j.issn.1673-3185.02293
Abstract:
Objectives  This paper aims to solve the problem of the long scheduled maintenance duration of warships.  Methods  Combining the characteristics of the maintenance management and control of warships, research on the application of scheduled maintenance cycle management and control for warships is carried out based on critical chain project scheduling. A "buffering period" is set to solve the problems that may be encountered in the formulation, implementation and monitoring of the maintenance cycle, and a management and control model of the maintenance cycle of warships is established on the basis of the critical chain method （CCM）. The feasibility and effectiveness of this model are then verified through actual case calculations.  Results  The results show that the use of CCM can reduce the overhaul period of a main engine by nearly 63% while ensuring maintenance quality.  Conclusions  The application of CCM to the management and control of warships scheduled maintenance cycle not only enriches the theoretical system, but also has great significance for optimizing the management and control, and improving operational availability of warships.
2022, 17(2): 125-134. doi: 10.19693/j.issn.1673-3185.02335
Abstract:
Objectives   In view of the incomplete evaluation of the ultimate strength of I-core sandwich panels in the past, a BP artificial neural network method is proposed to quantitatively determine the influence of relevant parameters on the ultimate strength of I-core sandwich panels.   Methods  First, the ultimate strength of I-core sandwich panels under axial compression are investigated using the nonlinear finite element method. Second, a BP neural network is constructed to predict the ultimate strength of I-core sandwich panels with different plate slenderness ratios between longitudinal webs, plate slenderness ratios of webs and column slenderness ratio of one longitudinal web. Finally, a formula for predicting the ultimate strength of I-core sandwich panels using the artificial neural network weight and bias method is proposed.   Results  The mean square error MSE and correlation coefficient R of ultimate strength prediction using the BP neural network method are 0.001 2 and 0.981 8 respectively. The proposed neural network model has good prediction accuracy, and the maximum error is less than 10%.   Conclusions  This study can provide references for the application of I-core sandwich panels in hull structures.
2022, 17(2): 135-141. doi: 10.19693/j.issn.1673-3185.02240
Abstract:
Objectives  The superstructure participates in the overall longitudinal bending of a ship, which leads to stress concentration in certain parts and threatens the safety of the ship's structure. The large-scale steel model test can truly reflect the structural response characteristics of superstructures.   Methods  This paper studies the structural strength of a certain ship's superstructure. Through the equivalent simplification of the main hull structure, a large-scale steel model including the superstructure and main body is designed, and structural strength model testing is carried out under hogging moment load.   Results  The test and finite element calculation results show obvious stress concentration phenomena in the corners of the side opening groups of the superstructure and the edges of the round transitions between the sidewall and main deck. The bending efficiency of the superstructure is 0.315.   Conclusions  The results of this study can provide references for the local structural strengthening and optimal superstructure design of target ships. The simplified design method of the ship hull model provided in this paper can also serve as a reference for the design of large-scale ship models.
2022, 17(2): 142-147. doi: 10.19693/j.issn.1673-3185.02237
Abstract:
Objectives  Q690 high strength steel (HSS) is usually employed in the fabrication of special parts for semi-submersible lifting and dismantling platforms. As such, the fracture strength assessment of its welded joints is essential to an investigation of the fracture mechanics behavior and service life of offshore structures.   Methods  First, the base material and butt-welding joints of Q690 HSS are taken as the research objects and subjected to uniaxial tension tests to obtain the corresponding stress-strain curves. Next, based on the GTN damage model, the tensile fracture curve equations of Q690 HSS and its butt-welded joints are established, while the corresponding calculation parameters of the GTN model are obtained through the exhaustive and particle swarm methods.   Results   The results show that the optimized values of the GTN model parameters can generally evaluate the fracture performance of Q690 HSS and its butt-welded joints, while a heuristic search algorithm based on the particle swarm method can effectively improve search efficiency with sufficiently accurate GTN model parameters.  Conclusion  Welding induced micro-defects and residual stress are eventually proposed to illustrate the difference in fracture performance between Q690 HSS and its butt-welded joints, which also influences the variation tendency of the GTN model parameters.
2022, 17(2): 148-155. doi: 10.19693/j.issn.1673-3185.02256
Abstract:
Objectives  As solving the robust optimization (RO) problem with interval uncertainty is unduly time-consuming when the nested differential evolution algorithm is directly used, a new RO design method is proposed.  Methods  In the proposed method, individuals' response values that have been accurately calculated within the critical distance are used to approximately predict the response values of other individuals and evaluate the robustness indexes accordingly. The accurate information of individuals' response values, which is gradually expanded in the evolutionary procedure, is also used to selectively re-evaluate the past robustness of individuals, and the critical distance is adaptively reduced on the basis of the robustness misjudgment rate.  Results  Two numerical and one engineering examples are tested to demonstrate the applicability of the proposed algorithm. The results show that the proposed algorithm saves more than 94% of computational resources, while the estimated error is less than 2.5%.  Conclusions  The proposed method can greatly reduce the calculation time of individuals' response values in the evolution process and maintain the adaptive balance between the accuracy and cost of robustness evaluation by using previous optimization knowledge, providing a new idea and method for RO design with interval uncertainty.
2022, 17(2): 156-164. doi: 10.19693/j.issn.1673-3185.02306
Abstract:
Objectives  Due to the complexity of hull structures, traditional optimization methods are prone to fall into the local optimum and have slow solution speeds.   Methods  For this reason, based on an adaptive mutation particle swarm optimization (AMPSO) algorithm, BP neural network and genetic algorithm (GA), combined with orthogonal experiments designed by Isight/Nastran, an AMPSO-BP-GA structural optimization method is proposed. Subsequently, the optimizations of cross-bar truss and gangboard structures are used as examples to verify the accuracy and feasibility of the algorithm.  Results  The calculation results show that under the same constraints, the weight of a cross-bar truss structure optimized by the AMPSO-BP-GA method is 2 272.1 kg, which is lighter than structures optimized by other methods; and using the AMPSO-BP-GA method, the weight of a gangboard is reduced by 33.3% compared with the 25.4% weight reduction of the GA-BP-GA method and 17.9% weight reduction of the PSO-BP-GA method, demonstrating that the AMPSO-BP-GA method has superior optimization results.  Conclusions  Compared with the three methods of BP-GA, PSO-BP-GA and GA-BP-GA, the AMPSO-BP-GA method has a better effect in the optimization of lightweight structure, and can provide references for the optimization design of hull structures.
2022, 17(2): 165-172. doi: 10.19693/j.issn.1673-3185.02232
Abstract:
Objective  Due to the difficulty of accurately converting the experimental results of acoustic radiation and vibration from scale models of complex stiffened combined shells into prototypes, the acoustic vibration similarity laws of this type of combined shell are studied in order to provide a basis for scale model experimental research on the acoustic vibration of such underwater structures.   Method  First, a complex stiffened cone-cylinder combined shell model and its scale model are constructed by shell element reinforcement simulation. Next, based on the hybrid finite element method-boundary element method (FEM-BEM) method, the acoustic vibration response of the combined shell is calculated. Combined with the model experiment, the accuracy of the calculated response of the complex shell structure using the hybrid FEM-BEM method is then verified. Finally, the acoustic vibration similarity laws of the complex stiffened cone-cylinder combined shell are studied systematically.   Results  The vibration modal frequency of the complex combined shell is in inverse proportion to the geometric scale ratio with the model under the same material parameter boundary conditions and excitation force, while the vibration modal in the corresponding frequency is the same. Under conditions of the same excitation force, the vibration response of the combined shell is also in inverse proportion to the geometric scale ratio, whereas the acoustic pressure is in inverse proportion to the product of the geometric scale ratio and measurement distance of the shell. The radiation efficiency and acoustic directivity of the scale model and prototype are the same.   Conclusion  The stiffened cone-cylinder combined shell shows good acoustic and vibration similarity under similar conditions to those of the model, and the model constructed using shell element reinforcement simulation is more consistent with the experimental results.
2022, 17(2): 173-182. doi: 10.19693/j.issn.1673-3185.02208
Abstract:
Objectives  This paper aims to study the coupling interaction between a truss box floating raft and submarine hull, and proposes a design approach for enhancing the vibration isolation effect of the truss box floating raft-hull coupling system.   Methods  First, modal analyses of the aforementioned coupling system and individual floating raft and hull structures are carried out respectively, and comparisons are made of the modal shapes between the floating raft of the coupling system and individual floating raft structure, as well as between the hull structure of the coupling system and individual hull structure. The effects of the thickness of the floating raft panel and isolator stiffness on the isolation of the coupling system in the full-frequency range are then investigated.   Results  The floating raft of the coupling system shows little difference in natural frequency or modal shape compared with the individual floating raft, and the vibration isolation effects are also the same. In addition, the increase in the thickness of the panel and the weakening of the stiffness of the lower vibration isolator will improve the vibration isolation capability of the coupling system.   Conclusions  The results of this study indicate that the mutual influence between the floating raft and hull is small, and can be considered a weak coupling relationship.
2022, 17(2): 183-189, 205. doi: 10.19693/j.issn.1673-3185.02323
Abstract:
Objective  The carbon fiber reinforced plastic (CFRP) propeller has such advantages as light weight, high strength, low vibration, low noise, corrosion resistance and fatigue resistance. In order to accurately ascertain the deformation and strain of CFRP propeller blades under hydrodynamic load, this paper proposes an online measurement method for CFRP propeller dynamic strain under submerged operation conditions.  Method  Fiber bragg grating (FBG) sensors are embedded in a CFRP propeller, and an underwater dynamic strain test system is built. Two types of test conditions are set: (1) the velocity is 0 m/s, and the rotation speed increases from 50 to 400 r/min; and (2) the rotation speed is 427 r/min, and the velocity increases from 0.0 to 1.6 m/s. The dynamic strain data of the CFRP propeller under the above conditions is obtained by the FBG sensors and analyzed in the time and spectrum domains.  Results  The results show that, the dynamic strain frequencies of each FBG sensor on the CFRP propeller are the same and related to the rotation speed, while the dynamic strain amplitude of each FBG sensor has no obvious relationship with the rotation speed or velocity, but depends on the position of the sensor, which reflects the structural mechanics features of the propeller.  Conclusion  The underwater online dynamic strain test of the CFRP propeller is realized, and test results are reasonable and reliable. This provides an important empirical basis for the theoretical design and analysis of the CFRP propeller, which is of great significance for the study of its vibration noise and hydrodynamic performance.
2022, 17(2): 190-197. doi: 10.19693/j.issn.1673-3185.02359
Abstract:
Objective   In order to resolve the difficulty of extracting the fault features of rolling bearings under conditions of multiple components and strong background noise, this paper proposes a rolling bearing fault feature extraction method based on modified Fourier mode decomposition (MFMD) and frequency band entropy (FBE) analysis. In order to solve the problem of the boundary frequency offset and over-decomposition of the Fourier decomposition method (FDM) under strong background noise, a method for selecting sensitive frequency bands and mode components based on band entropy and the envelope spectrum is proposed.   Methods  First, the minimum band entropy value is selected as the central frequency of the sensitive band, while the boundary of the sensitive band is determined by FBE analysis. Second, the signal is decomposed by band-limited Fourier mode decomposition in the sensitive frequency band, and several mutually orthogonal Fourier intrinsic mode functions (FIMF) and their marginal Hilbert spectra are obtained. Next, sensitive FIMFs which can reflect fault characteristics are selected according to the regional dependency relationship between the FIMFs and the FBE of the original signal. Finally, the selected FIMFs are analyzed by envelope spectrum analysis to extract the fault features.   Results  The accurate diagnosis of bearing faults can be realized by applying this method to bearing simulation data and experimental data.   Conclusions  The results prove the effectiveness and superiority of the proposed method, which can provide technical support for the health evaluation of rolling bearings.
2022, 17(2): 198-205. doi: 10.19693/j.issn.1673-3185.02341
Abstract:
Objectives  This paper proposes a theoretical calculation method for obtaining the impact load and dynamic response of shafting during the rapid engagement process of a combined gas turbine and gas turbine (COGAG) power plant.   Methods  According to the mechanical relationships between various components in the meshing process of a synchro-self-shifting (SSS) clutch, a dynamic analysis model of the clutch is established, and the dynamic simulation and bench test during the rapid engagement of COGAG are carried out.   Results  As the simulation results show, when the damping dashpot functions, a significant torque impact occurs on the clutch spiral spline which can result in a strong dynamic response on the shafting. It is also found that the relative position of the ratchet and pawl is random, which can cause the peak torque impact and dynamic response of the shafting to fluctuate within a certain range. Through a power plant experiment, the accuracy of the impact load calculation method and the randomness of the impact amplitude are verified, and the errors of the maximum and minimum torque response amplitudes are 3.56% and 8.86% respectively.   Conclusions  This paper finds that the rapid engagement of COGAG can produce an obvious torque impact which can affect the safety of the power plant. As such, it can provide references for the operation safety evaluation of COGAG power plants.
2022, 17(2): 206-211. doi: 10.19693/j.issn.1673-3185.02336
Abstract:
Objectives  Aiming at the vibration control problem, this paper puts forward a design approach involving longitudinal two-stage vibration isolation technology for ship propeller-shaft systems.   Methods  First, a mathematic vibration model of a ship propeller-shaft longitudinal two-stage vibration isolation system is established. The effects of design parameters such as mass ratio, stiffness ratio and damping ratio on the vibration characteristics of the system are analyzed. The design is then optimized by using a ship propeller-shaft system as an example.  Results  The results show that, for a ship propeller-shaft longitudinal two-stage vibration isolation system, the lowest natural frequency ratio control can be obtained according to the formula given in this paper under the given mass ratio or stiffness ratio. With the increase in damping ratio \begin{document}${\xi _1}$\end{document}, the attenuation of the vibration transmissibility at the second order natural frequency is more obvious. The optimized ship propeller-shaft longitudinal two-stage vibration isolation system has a better isolation effect than the single-stage vibration isolation system.   Conclusions  The results of this study have important reference value for the design of ship propeller-shaft longitudinal vibration isolation technology.
2022, 17(2): 212-219. doi: 10.19693/j.issn.1673-3185.02295
Abstract:
Objectives  In order to improve the working performance of gas turbines, this study examines the aerodynamic performance of variable geometry turbine clamshell guide vanes.  Methods  Taking a typical variable geometry turbine guide vane as a prototype, a clamshell turbine guide vane model with a fixed pressure side and rotating suction side is constructed. Numerical simulation based on the shear-stress transport (SST) model is then carried out to analyze the parameter variation laws of the clamshell turbine guide vane and ordinary variable geometry turbine guide vane under different working conditions.   Results  As the calculation results show, when the rotation angle of the guide vane varies from +3° to –3°, the aerodynamic performance of the clamshell turbine guide vane has certain advantages, a larger flow rate and a smaller total pressure loss coefficient. When the guide vane rotation angle exceeds +3°, its flow rate increase will decrease significantly and even stop or negatively increase. When the rotation angle of the suction surface gradually increases from a negative angle to 0°, the total pressure loss coefficient will gradually decrease. When the rotation angle is greater than 0°, the total pressure loss coefficient will increase with the rotation angle.  Conclusions  The adoption of clamshell turbine guide vanes can improve the aerodynamic performance of turbines to a certain extent.
2022, 17(2): 220-227. doi: 10.19693/j.issn.1673-3185.02379
Abstract:
Objective  As there is still no complete set of rules regarding the general engineering design process for towed array sonar system installation aboard a submarine, it is necessary to analyze approaches to the overall engineering design of the system and systematically ascertain the key points.  Methods  On the basis of a literature review, this paper carries out an in-depth analysis of the aforementioned issue in terms of the sensor system and retraction/release system respectively, covering design scheme selection (i.e., number of towed array sonars, types of sensing element and length of towed cable-array) and device design (i.e., winch, spooling gear, conduit, driving mode and release port location).   Results  This review derives the basic process and method of engineering design and computational formulae (i.e., calculation of cable array’s length) for a towed array sonar installation adaptable to a submarine.  Conclusions  Through striking a good balance of desirable properties and trading-off among many elements while considering the actual state of the submarine and the technical characteristics of towed array sonar hardware, submarine designers can flexibly use the relevant engineering design points discussed in this paper to achieve optimal installation schemes.
2022, 17(2): 228-232. doi: 10.19693/j.issn.1673-3185.02296
Abstract:
Objectives  Waveform diversity technology is an effective anti-jamming measure against range false target jamming. However, in an environment of strong energy jamming, the high side-lobe caused by the jamming signal mismatch will still affect the detection performance of the radar. To this end, a dictionary learning method is proposed in order to better suppress and eliminate high-power jamming.   Methods   First, an initialization dictionary corresponding to the target and jamming signals is established. Second, the initialization dictionary and selected atoms are used to generate an autocorrelation matrix template, and the matching coefficient is obtained using the non-homogeneous linear mean square estimation. Next, an approximate quasi-Karhunen-Loève transform（Q-KLT） basis corresponding to the target and jamming signals is constructed by template and matching coefficients respectively. Finally, a convex optimization algorithm is used to separate and recover the target and jamming signals.  Results  The simulation results show that the proposed method can effectively counter the jamming of one or multiple range false targets at a 30 dB jamming-to-signal ratio.  Conclusions  Compared with the traditional waveform diversity technology, the proposed method still maintains good anti-jamming performance in high jamming-to-signal ratio environments, and can be used by shipboard radar to counter range false target jamming.