Calculation method of underwater acoustic and vibration response of cabin segment based on onshore vibration test北大核心CSCD

[Objective]This paper proposes a method for calculating the acoustic and vibration response of underwater cylindrical shell structures based on land-based vibration test results.[Methods]An axisymmetric boundary element method (BEM) is introduced to describe the radiation acoustic field of the shell. The relationship of acoustic pressure at the nodal point of the generatrix with velocity is obtained by solving the numerical solution of the boundary element integral equation, then the acoustic radiation impedance matrix of the outer surface of the shell and acoustic transfer vector (ATV) are constructed. Based on the assumption that the low-order vibration mode of an underwater cylindrical shell is the same as that of an onshore cylindrical shell, combined with the modes and acoustic radiation impedance matrix of an onshore cylindrical shell, the modal added mass and damping are calculated. [Results]The natural frequency calculation formula of the underwater cylindrical shell is established on the basis of the onshore mode, and the calculation method of underwater vibration response and acoustic radiation characteristics with the vibration response in air as input is obtained based on mode superposition method.[Conclusion ] The numerical results of a typical cylindrical shell with internal structure show that the method meets the engineering accuracy requirements. © 2023 Chinese Journal of Ship Research. All rights reserved.     

Technology application and development trend of intelligent unmanned system北大核心CSCD

Intelligent unmanned system combat is moving from concepts to actual combat applications. The military applications of intelligent unmanned systems are emphasized by focusing on the needs of the combat missions that they will undertake on future battlefields and summarizing the development statuses of land, air and maritime unmanned systems. Aiming at the key problems faced by intelligent unmanned systems and the practical difficulties that will be faced on the battlefield in the future, we analyze the key technologies required for intelligent unmanned systems, including autonomous perception and understanding in complex environments, behavioral decision-making and trajectory planning, autonomous navigation and positioning, multi-scenario autonomous skill learning and intelligent control, unmanned cluster cooperative control, natural human-computer interaction, etc. At the same time, aiming at the problems that will be encountered in the further development of intelligent unmanned systems on the battlefield in the future, we start with individual enhancement and cluster enhancement, and conduct a detailed analysis of the development trends of intelligent unmanned systems. © 2022 Palaeobulgarica. All rights reserved.     

Galvanic corrosion behaviour of aluminium 3004 and copper in tropical marine atmosphere

The galvanic corrosion behaviour of aluminium 3004 and copper with different area ratios were studied in the tropical marine atmosphere at Tuticorin harbour over a period of 426 days. The area ratios OfAAI： Acu, studied were l：l, 1：2, l：4, 1：8, 2：1, 4：1 ＆ 8：1. The galvanic corrosion behaviour of metals was studied in terms of relative increase in the corrosion rate of aluminium due to galvanic coupling with copper, relative decrease in the corrosion rate of copper due to galvanic coupling with aluminium, and the susceptibility of aluminium to pitting owing to galvanic coupling with copper, The galvanic potential and galvanic current of the system were monitored. Pits of different dimensions ranging from mild etchings to perforations were experienced on the borders and the surfaces of the interface of aluminium in contact with copper. The weathering parameters and the environmental pollutants which have a major role in influencing the galvanic corrosion of metals were also monitored. The corrosion products resulting from galvanic corrosion were analysed using XRD and the pitting on aluminium resulting from galvanic corrosion has been highlighted in terms of pit depth, size and density of pit, using a high resolution microscope.     

New analysis method of seismic passive earth pressure and its distribution on a retaining wallEI北大核心

Research purposes: At present, the analysis methods about seismic passive earth pressure and its distribution have several defects, including unreasonable distribution rule and position, complex derivation, harsh application conditions and so on. The seismic passive earth pressure problem is translated into non-seismic passive earth pressure problem in this paper by using the transform method with rotating calculation model of retaining wall. This method has large reference value to simplify the calculation process of seismic passive earth pressure and its distribution. Research conclusions: Based on the non-seismic passive earth pressure formulations with horizontal slices analysis method, the analytical formulas of seismic passive earth pressure intensity distribution, resultant force of earth pressure and its point position are obtained directly, and the explicit solution of critical rupture angle is got by graphic method. The influencing factors including horizontal and vertical seismic accelerations, different angle of wall back, cohesion and external friction angle between filler and back of retaining wall, equispaced overloading are considered. The formulas can be used for seismic passive earth pressure calculations of cohesive soil with common border condition. The deducing process of seismic passive earth pressure formulations is simplified and unified greatly by using the method in this paper. The seismic passive earth pressure theory is perfected much more. The research results can be applied to do fast computation about seismic passive earth pressure of retaining wall.     

Large eddy simulation of cavitation development on highly skewed propellers

This paper deals with numerical simulations of the cavitating flow around two highly skewed propellers operating in open water and mounted on an inclined shaft. The aim of the study is to check the ability of our numerical method in distinguishing the variation in flow features resulting from different blade designs. Moreover, a secondary aim is also to improve the knowledge about the physics that control the growth and collapse of cavitation, and hence also the generation of cavitation noise and erosion on this type of propellers. The investigation is based on incompressible large eddy simulation (LES) in combination with a volume-of-fluid implementation to represent the two phases of liquid and vapour, and a transport equation-based method for the mass transfer between the phases. High-speed video recordings from experiments were made available for comparison. The simulations demonstrate that the current method makes it possible to analyse the main difference in flow features caused by modest design alternation. Furthermore, with suitable grid resolution, LES is demonstrated to be capable of capturing the mechanisms that are important in the cavitation development, and that numerical simulation is a reliable supplement to experiments in advanced propeller design.     

Brake pad taper wear on brake moan noise

Automotive brake systems today have many factors that can contribute to brake noise. Modern approaches to reduce the propensity of brake noise mostly target high frequency brake squeal. A more difficult constituent of brake noise to address is low frequency moan, which is typically caused when the brake system excites a suspension member with a constrained natural frequency in the range of excitation. Although most modern CAE techniques utilized to diagnose and solve brake noise issues focus on new brake pad condition, this paper will show the benefit of understanding a common wear mechanism “Taper Wear,?and attempt to correlate its effects on brake moan. In order to study this phenomenon, a finite element model of a disc brake is established, and a complex eigenvalue analysis (CEA) of the brake system is performed. The propensity of brake moan noise is evaluated on basis of damping ratio of a dynamic brake system model. By using the finite element model, effects of the brake pad taper wear on brake moan noise is studied. The results show that the brake pad taper wear is a significant factor for generating the instability causing the brake moan noise. The study is performed at various levels of brake pad taper wear. When the brake pad taper wear is more than 0.5 mm, the value of negative damping ratio rapidly increases, and the propensity of brake moan noise is greatly magnified. In this study, the simulation result correlated well with the test result, which provides the theory and guidance for brake moan noise control.     

Comparison of PMP and DP in fuel cell hybrid vehicles

Pontryagin’s Minimum Principle (PMP) and Dynamic Programming (DP) are both from the optimal control theory and can both achieve optimal trajectories when they are applied to power management strategies of hybrid vehicles. However they have totally different control concepts. In order to select the superior one, the PMP-based and the DP-based power management strategies are introduced and compared for a fuel cell hybrid vehicle (FCHV) in this paper. The two power management strategies are applied to the FCHV in a computer simulation environment, and the simulation results from the two strategies are compared when the control variable for the PMP is fuel cell system (FCS) net power and for the DP is battery power. As a result, the superiority of the PMP-based power management strategy is proved.     

Prediction procedure for wear distribution of transient rolling tire

As a research method, finite element analysis (FEA) with ABAQUS can help researchers to study throughout the whole process of abnormal tire wear. For precise tread wear simulation, this paper introduces a tire finite element model building method. Then, the model is verified by comparing its simulation results with experiment data. Based on the verified model, tire high-speed rolling procedure is presented by combining steady-state transport analysis and dynamic analysis. To predict the wear distribution, micro tread wear calculation method is described. Finally, the wear prediction procedure of tread mesh evolving is introduced and tire polygonal wear pattern is simulated by this procedure.     

Discerning the operational state of a vehicle’s distributed electronic systems from vehicle network traffic for use as a fault detection and diagnosis tool

This paper suggests a novel approach to finding faults in a vehicle’s electronic systems by monitoring the network traffic directly and generating statistical traits. The nature of the data in a CAN network is considered, and a case for the use of statistical analysis presented. Statistical traits extracted from the temporal behavior of network messages are investigated as a metric for fault detection. It is shown how this trait information can be extracted from network data, and how this information could be used for fault detection of an unknown fault on a CAN network. It is then demonstrated that combining multiple types of trait data can be used to correctly identify a fault once detected.     

Optimization of drying performance considering driving conditions

Compressed air can be used as an energy source for brake systems in medium-heavy and heavy-duty commercial vehicles. The moisture in compressed air, which is due to high temperature and humidity, can be eliminated by using an air dryer. In this paper, drying performance data for a cartridge were obtained and used to develop a drying performance program, to predict the moisture and relative humidity in the air tanks of vehicles. The on-load time, off-load time, air flow, duty cycle, humidity and dew point temperature were calculated according to air consumption. The validity of the program was verified, and it was shown to be able to predict humidity changes in the air tank. The air tank capacity was increased from 100 to 130 to reduce the duty cycle. Therefore, the regeneration rate decreased from 18% to 15%, but the dew point depression temperature (ΔT) remained above 30°C. The duty cycle decreased from 50% to 43%, and the total operation time and power consumption of the air compressor were reduced. In conclusion, fuel savings were obtained by changing the parameters to optimize the system.