Simulation and experiment research of vibration characteristic on star compressor

Aiming at the vibration defects of star compressor, simulation and experiment are carried out to investigate the compressor. By drilling holes in the valve stem, the pressure changes of each cylinder are measured without damaging the cylinder block. The dynamic model of crank-connecting rod mechanism is established. After the measured cylinder pressure loaded on the dynamic model, the force acting on the main motion pair is obtained. The finite element model of the compressor is established for the first time, the force of the motion pair is loaded on the finite element model by MPC coupling method, and the vibration acceleration of the machine base is tested. The result shows that the main modal shapes between 50-150 Hz are body deformation, modal shapes between 150-200 Hz are base deformation, the simulation acceleration of the base is higher than that of the experiment, and the main working frequency and frequency doubling can correspond. The conclusions provide reference for vibration isolation design of star compressor

Control measures about vibration and noise of pipeline onboard marine vessels

The pipeline noise is an important part of the sources of vibration and noise for high performance marine vessels. It is vital to control the vibration and noise of the onboard pipeline to improve the acoustic stealth and life level in marine vessels. The vibration and noise caused by the onboard pipeline system was analyzed. Some methods and advices were put forwards to reduce the vibration and noise caused by the pipeline system, including the control of vibration, structural noise and fluid noise. In addition, a new concept “pressure-stabilized bladder” was created

Underwater vibration and acoustic radiation calculation of double cylindrical shell by three-dimensional sono-elasticity of ships

As common structure of underwater vehicle, the accurate prediction of underwater vibration and acoustic radiation of double cylindrical shell is always a difficult problem in the research of vibration and noise. Establish finite element model of double cylindrical shell in Abaqus software. Based on the three-dimensional sono-elasticity theory of ships, analysis vibration and acoustic radiation characteristics of underwater double cylindrical shell by the use of Thafts-acoustic software, and compared with experimental result. Results show that error of prediction result and experiment result at single frequency point is about 10 %~20 %, and error of total level of acceleration and sound pressure is less than 5 dB. It is accurate to predict the underwater vibration and acoustic radiation characteristics of double cylindrical shell with three-dimensional sono-elasticity theory of ships, which can provide new effective guidance for the engineering application

Multi-objective optimization design of ship propulsion shafting based on the multi-attribute decision making

The expression of field transfer matrix of a ship propulsion shafting is deduced based on the modified Timoshenko beam theory using the transfer matrix method. Moreover, the power flow of each bearing of the propulsion shafting is carried out numerically. The Pareto optimal solution set is obtained by selecting the aft stern bearing stiffness, front stern bearing stiffness, thrust bearing stiffness and the bearing spacing length as the optimization design variables and selecting the sum of the power flow of each bearing of the propulsion shafting as the optimization objectives. Then, the Pareto optimal solution set is sorted by the TOPSIS method and MADM approach. The analysis results show that it is feasible and effective to avoid the blindness of selecting optimization results by optimizing the propulsion shafting multi-objectives based on the TOPSIS method and MADM approach

Study on vibration isolation performance of elastic coupling under longitudinal excitation

According to longitudinal vibration differential equations of ship propulsion shafting, deduced transfer matrix of propeller, uniform shaft segment and thrust bearing which composed propulsion shafting. Given longitudinal vibration natural frequency of propulsion shafting using the transfer matrix solver, and compared with finite element simulation results to verify the accuracy of the finite element model. Then analysis the effect of elastic coupling axial stiffness on modal frequencies of shafting longitudinal vibration and vibration isolation performance through simulation. Results show that: elastic coupling can effectively isolate the propulsion shafting vibration transmitted to the propulsion motor; when the axial stiffness ratio of thrust bearing and elastic coupling is greater than 50, the impact of elastic coupling axial stiffness on longitudinal vibration natural frequency of propulsion shafting and acceleration level and axial displacement of thrust bearing is very small; when the stiffness ratio is greater than 100, the elastic coupling can achieve better vibration isolation effect

Analysis of hydrodynamic noise characteristics of rudder-wing

The flow field and sound field of trapezoidal rudder-wing under different rudder angles are numerically predicted by CFD LES theory, Lighthill acoustic analogy theory and vibro-acoustic theory. And characteristics of hydrodynamic noise including flow noise and vibroacoustics under hydrodynamic excitations are analyzed. Results show that: at the same speed, the hydrodynamic noise raises with the increase of rudder angle; sound pressure level spectrum band of flow noise is wide and there is no obvious dominant frequency while there is a very obvious peak value of vibroacoustics under hydrodynamic excitations corresponding to the first order modal frequency in the band of 520-530 Hz; sound intensity at the front of leading edge and after trailing edge is higher than that at both sides of rudder-wing; the vibration of trailing edge is large, so it is the concentrated area of noise source

THREE CONDITIONS LYAPUNOV EXPONENTS SHOULD SATISFY

ABSTRACT In contrast to the unilateral claim in some papers that a positive Lyapunov exponent means chaos, it was claimed in this paper that this is just one of the three conditions that Lyapunov exponent should satisfy in a dissipative dynamical system when the chaotic motion appears. The other two conditions, any continuous dynamical system without a fixed point has at least one zero exponent, and any dissipative dynamical system has at least one negative exponent and the sum of all of the 1-dimensional Lyapunov exponents id negative, are also discussed. In order to verify the conclusion, a MATLAB scheme was developed for the computation of the 1-dimensional and 3-dimensional Lyapunov exponents of the Duffing system with square and cubic nonlinearity. KEYWORDS: Lyapunov exponent, chaos, three conditions, Duffing system INTRODUCTION Recently, chaotic motions that arise from the nonlinearity of dissipative dynamical systems have received a great concern in both physical and non-physical fields. The most striking feature of chaos is the unpredictability of the future despite a deterministic time evolution. This unpredictability is a consequence of the inherent instability of the solutions, reflected by what is called sensitive dependence on initial conditions. The tiny deviations between the initial conditions of all the trajectories are blown up after a short time. A more careful investigation of this instability leads to two different, although related, concepts. One is the loss of information related to unpredictability, quantified by the Kolmogorov-Sinai entropy. The other is a simple geometric one, namely, that nearby trajectories separate very fast, or more precisely, separate exponentially over time. The properly averaged exponent of this increase is the characteristics for th

Analysis of vibration traits of underwater vehicle propulsion shafting and optimization design of support parameters

In this paper, the calculation model of the propulsion shafting structure was established to solve the problem of flexural vibration of the shafting system for the underwater vehicle with relatively small scale. By using the transfer matrix method and the finite element method, the vibration characteristics of the shafting system subjected to the transverse unsteady excitation force were calculated by MATLAB software and ABAQUS software. Two aspects of the displacement response and the vibration power flow were analyzed and compared. Analysis showed that the results of the two methods were very close to each other and all met the requirements of vibration engineering calculation. The influence of the mass of propeller and the bearing stiffness in different positions on the vibration characteristics were analyzed by using the transfer matrix method. Finally, based on the transfer matrix method, the parameters of the bearing stiffness at different supports were optimized with design optimization, and then use ABAQUS software to verify the effectiveness of the optimization. The analysis results showed that, after optimization calculation, the vibration power flow input to the bases of different bearings were significantly decreased

Numerical simulation of fluctuation pressure with liquid-filled pipes based on large eddy simulation method

Pipeline is an important part of mechanical system on ship. Fluctuation pressure produced on the pipe wall is a significant source of noise, and more and more scholars pay attention to it. In this paper, by using large eddy simulation and subgrid turbulence theory, pipeline fluctuation pressure simulation model is established, and influence of flow velocity, wall roughness and step offset of pipeline connection on pipe fluctuation pressure are studied. This provides theoretical guidance for low-noise installation and maintenance of ship piping system

The NAH based on complex cepstrum method in a closed space

NAH method in non-free sound field reconstruction of the sound source will lead to considerable error. This paper proposes a method to reconstruct the sound source in a closed space. In the closed space, the total sound pressure is the sum of the source radiation pressure and the reflected sound pressure from medium interface. Reflections from medium interface is a convolution noise, rather than additive noise. In order to reconstruct a sound source in the closed space, in this paper we first adopt the complex cepstrum method to separate and radiation pressure and the reflected sound pressure, then filter them to reduction of reflected sound pressure, and then reconstruct the sound source. The simulation results show the correctness and effectiveness of the method