Numerical modeling on a scaled shaft-hull model is made using the finite element method firstly. Then the experimental data is used to verify and modify the dynamics model. Direct boundary element method is applied to compute the acoustic radiation signature of the hull when subjected to the propeller exciting force in both transverse and longitudinal direction. The acoustic pressure and far-field pressure distribution is obtained. The energy method is also used to compare the acoustic power under different loading conditions.

Abstract:In this paper,a study on an inline-four diesel engine mounting system is conducted.Using the dynamics simulation software for internal combustion engine named GT-CRANK,a virtual ptototype model of engine mounting system is set up.Then the vibration isolation performance of the mouting system is simulated under differernt schemes of mount stiffness.The law that how the variation of mount stiffness in differert directions influences the vibration isolation performance of the mounting system is found after analyzing the simulation result.Ultimately,combined with the influence law ,the optimization of the mount stiffness is conducted to improve the mounting system performance of vibration isolation.

The frequency-domain analysis is the most important and applicable signal processing technology in fault diagnosis for machinery. In the literature, a number of frequency-domain-based methods have been applied to detect faults in machinery and each method has its special features. Therefore, selecting appropriate method plays a pivotal role in inspecting defects based on vibration signals. Characteristics of fault-caused vibration signals and frequency-domain-based methods are summarized in this paper using representative examples, so as to establish a rule of selecting appropriate signal methods of extracting vibration features for different mechanical equipments. The results can be used to improve the precision and reliability of many kinds of fault diagnoses for key components in different machinery.

In this paper, several wavelet denoising methods are compared and analyzed. On these bases, a new threshold function is constructed. The improvement of threshold selecting is made. Simulation experiment of signal denoising is carried out using MATLAB software. The advantage of improved wavelet denoising method is demonstrated, and better denoising effect is gained.

A survey on the research of the unbalanced magnetic pull(UMP) in the motors is given in the paper. The mechanism of UMP is analyzed and summarized. The developing status of the research of UMP, especially the nonlinear UMP, is also introduced. The ways to preventing and reducing UMP are also summarized. Finally, the future research orientation of UMP is also discussed.

Least-squares complex frequency-domain (LSCF) method developed to be implemented in modal parameter estimation recent years. An expect result was received either in the system of weak damping or heavy damping. An User Interface was designed based on Matlab consisting of the LSCF method. Different parameters were set based on different coefficient matrixes and solution modification of the pole of the system was given. A test was used to validate the consistency of the different coefficient matrixes and that the User Interface was correct.

This paper describes an investigation about the frequency characteristics of the various types of vehicles in different speed. The noise samples were recorded to analyze the spectrum and the energy ratio of different frequency bands. The results showed that most of the vehicle noise energy was mainly located between 400Hz and 2.5kHz. The noise energy distribution of small cars was almost from 1kHz to 2.5kHz, the noise energy of large cars was evenly distributed from 400Hz to 2.5kHz and the noise energy distribution of middle cars was in between. Most of buses noise energy was located in low-frequency band from 10Hz to 315Hz. As the speed increased, the energy distribution of small cars and middle cars was more concentrated, the noise frequency of large cars has no significant relationship with speed and the ratio of bus noise energy in low-frequency band was increased.

By measurement of a laptop thermal system, the noise characteristics are obtained. The fan outlet is confirmed as the major noise source. Mathematical relationship of the fan rotating speed and noise of the fan outlet is set up. Through simulation of the airflow field, fin arrangement angle is found out effected to the outflow quantity and pressure, but much less effected to the noise. The fin is redesigned, which leads to a big increase of the cooling efficiency, so that the fan rotating speed is decreased, as a result noise of the thermal system is lowed. The experimental results show that the rotating speed can get a reduction of 16.8 % and noise is 2.0 dB(A) lower than the original one.

Electric Vehicles have been serving as taxis and public buses in many cities. The subject of this paper are electric and fuel vehicles. An analysis and comparison of the maximum A sound level and spectrum of electric and fuel cars and buses under different speed is provided in this paper. The aim is to offer some references to the prevention of transport noise in cities.

Transmission loss is an important index in evaluating muffler’s acoustic performance. A new method called acoustic mode in pipeline instead of the traditional method was proposed in this paper to estimate transmission loss. It was applied in the muffler with the smaller sectional area on the inlet and outlet whose result is nearly correct and the process is very simple compared with the traditional method, improving the efficiency in computing the transmission loss. For the muffler with the larger sectional area on the inlet and outlet, because of amount of high secondary wave appears in the medium-high frequency, the traditional method has become invalid; but in the low frequency the result is consistent with the traditional method for the plane wave is the main acoustic wave in the pipeline. So the method of acoustic mode in pipeline can estimate the transmission loss at express speed.

Abstract: Aerodynamic characteristics and vibration characteristics of a micro quad-rotor aircraft were studied based on finite element method. A three dimensional physical model of the fluid fields was established. By adding boundary conditions, the fluid fields were analyzed numerically using the finite volume method and the aerodynamic characteristics were obtained. Then the aerodynamic force was loaded to the aircraft structure to get the stress distribution and find out where the maximum stress is. At last, the first six vibration modes and their vibration characteristics were obtained after the modal analysis of the micro quad-rotor aircraft.

Negative stiffness mechanism can be used to isolate the low frequency vibration of the system. In this paper, an analytical expression of the force and stiffness was derived by using the equivalent magnetic charge method. Meanwhile, the optimal arrangement and magnetization of the rectangular permanent magnets were obtained to accomplish the negative stiffness. Finally, the trimagnets quasi-zero-stiffness vibration isolation was designed. The simulation results proved that the correctness of the theoretical analysis and the excellent low frequency vibration isolation performance was achieved without affecting the load ability.

Vibration test of a certain type of scroll compressor was conducted according to its vibrations and the high-frequency vibration spectrum for each of the major components of the compressor was achieved. Modal analysis of scroll compressor was carried out through finite element analysis software ANSYS and the first six natural frequency was achieved. The result of vibration spectrum analysis and comparison of the vibration spectrum and natural frequency shows that there is resonance phenomenon on upper shell and the shell contacting with housing is prone to fatigue damage. Three improvement programs have been putted forward. They are increasing the thickness of the upper shell, increasing the radian of the upper shell and increasing the thickness of the shell contacting with housing. The programs were verified through ANSYS. The result of verication shows that increasing the thickness of the shell contacting with housing and increasing the radian of the upper shell are effective.

The structural characteristics of hybrid electric vehicle (HEV) are analyzed in this paper. The changes of the noise and vibration sources and their characteristics due to the structural change are studied. The methods for controlling the noise and vibration of the HEV are put forward. Finally, the difficulty and the development trend of the noise and vibration control of the HEV are summarized.

The importance of impact noise control of hydraulic pile drivers is elaborated. The theory of acoustic fluidstructure coupling and the corresponding finite element method are introduced. According to the theoretical characteristics of impact frequency spectrum, the relation of noise and buffer time is analyzed. Using the finite element software ANSYS/LSDYNA, the numerical simulation of impact of a pile driver is carried out. The results show that the impact noise can be reduced by prolonging the buffer time.

In the case of high frequency sound waves incident, sound transmission loss formula of orthotropic composite laminates was introduced on basis of transfer matrix method. Audio calculated model was established by composite laminates plate, transmission loss was analyzed by researching the laminate lay angle, plate thickness and density of structural parameters of the laminated plate. The results showed that, effected by fabric and basic performance, laying method, laying angle and other factors, Mass Law can not reflect correctly the sound insulation feature of laminated composite plate. Comparison and analysis can show that there is no obvious linearity between composite material density and sound transmission loss; the greater thickness of laminated plate, the greater of sound transmission loss, also, the thickness of each layer is different, which also can cause the change of sound transmission loss; the greater of angel of laminated plate, the greater of sound transmission loss.

This paper systematically analyzes the basic principle,calculation methods and control standards of the noise metrics of the world’s major countries and regions.A series of experiments were taken on based on the noise monitoring data of a large busy airport.Through the experimental analysis demonstrated the similarities and differences of the airport noise metrics,pointing out that the existing airport noise metrics are not complete and need improvement.

Applying the tensioncompression viscoelastic model of metallic rubber (MR), the constitutive law of MR is obtained by means of ANSYS code with quilibrium iteration. The computation result is in good accordance with the experimental data. This work provides a reference for further study of MR.

The transmission loss is one of the important characteristics to appraises the muffler performance. But in the experiment, it should been pay attention to the acoustic source stability and sound wave reflection questions.In this article summarized some differences which the insertion loses and transmits loses, Simultaneously pointed out the merits of application transmission loss test noise elimination performance，And for avoided the sound reflection proposed one new transmission loss test way. Discussed the transmission loss value change situation when the muffler be inputed different intensity sound pressure, which through the massive experiments.

In this paper, principium of exhaust system standing wave was analyzed from theory and simulation calculate . The exhaust system tailpipe noise acoustic model was built with GT-power. Seen from acoustic characters of the exhaust system tailpipe noise, a long tailpipe stand wave is the root cause for peak of the common frequency. Therefore, two proposals was adopted. One proposal is to change the tailpipe length, keep away from the frequency, decrease the stand wave effect; another proposal is to design a resonator for solve this common frequency, eliminate this frequency noise; The simulation of the two proposals proved to improve the acoustic performance and achieve the target.

With the vigorous development of civil aviation, the development trend of large passenger aircraft airworthiness noise, the average every 10 years, Airworthiness noise reduction 6EPNdB. ICAO is studying the more stringent noise standards, 2016, large passenger aircraft the airworthiness noise than the fourth phase noise is expected to limit the low 10EPNdB above. To make the design and manufacture of civil aircraft meet the noise standard international practice, the need to update the noise certification standards, this article studies the noise certification standards for aircraft engine project.

Abstract: The load state of the stern bearing of the propulsion shafting system is affected by factors such as the propeller and the shafting alignment. Unreasonable design or installation of the shafting system will result in poor lubrication of the rubber bearing, which probably causes the stick-slip motion between the shaft and the bearing and abnormal bending and torsional vibration of the shafting system. In this paper, the bending and torsional vibration induced by the friction between the stern bearing and the propulsion shaft is analyzed thoeretically, revealing the characteristics of friction induced shaft vibration and noise.

The test research on the noise causes of the washer machine motor is discussed in the paper, and to determine the mechanical noise is the main reason. A modal analysis with pre-stress of the entire motor structure is established by ANSYS software, and the weakness positions of the motor structure are found by FEA simulated analysis. The practical sound tests of the washer machine are run to verify the simulated result, and reduce the motor noise in the washer machine. The modal calculate and analysis results provide the reference standard for structural design and realize the project optimization.

This paper briefly described the aircraft noise monitoring system, and analyzed the the location of noise monitoring terminal, the method of locate the terminal can be divided into two steps, general arrangement and specific location. The method is applied at Shanghai Hongqiao International Airport, and the practices shows that mensurability of aircraft noise, control of background noise, the influence of local sound field and some other factors should be paid Special attention during the design of monitoring terminal site.

Given the longitudinal vibration of ship propulsion shafting, the dynamic model of longitudinal vibration of Propeller-Shafting is established, and its first three modal shapes are derived in this paper. At the same time, the finite element modal of the shafting has been established, the calculated results and the analytical solution were compared. In this paper, a method of using the dynamic absorber to suppress the longitudinal vibration of the ship shafting was put forward. By simulating the longitudinal vibration of the shafting under the actual speed of ship, it is evident that the actual vibration is very close to the first modal, so it is used to approximate the response of the shafting. After assembled absorber, the dynamic differential equation was established and the response was deduced. Then, an idea was conceived that using magnetorheological elastomer to manufacture broadband dynamic vibration absorber, and a simple conceptual design was introduced. A new method of suppressing the shafting vibration is introduced in this paper.

Several renowned software and methods in the world for prediction of acoustic signature from ships are presented in this article: evaluation software of radiated noise—NDES, evaluation software of target strength—ARTES, integrated radiated noise and self-noise modeling software—FNVNOISE. Prediction of the acoustic signature by above methods have been presented on the basis of theoretical calculation as practical as possible and dedicated database helping designers for essential calculations has been developed for excessively complicated issues. The database and calculation algorithm will be constantly improved and updated through addition and verification of new data in order to provide solutions to problems during future design work.

Vehicle launch shudder is the severe torsional vibration phenomenon of driveline under different gear and throttle opening while launching in different road load. The phenomenon undergoes three stages, including vehicle launching, severe shudder and smoothly riding. The frequency components and amplitudes of the vibration acceleration signal have significant time-varying characteristics. This paper introduces three methods of time-frequency analysis, such as short time Fourier transform, Wigner-Ville distribution and continuous wavelet transform. On this basis, the appropriate time-frequency method is chosen to analyze the acceleration signal of different positions in the car under the conditions of M2 gear and small throttle opening. Then, the vibration time-frequency characteristics of three stages are revealed. Finally, this paper studies the frequency characteristic of the three stages combined with the FFT.

Impulse excitation experiments of Gough-Stewart manipulator were conducted at typical configurations with different structural parameters, and the frequency varying with structural parameters and configurations were studied. Firstly, the mechanism was assembled according to certain structural parameters, and accelerometers were laid-out on the moving platform at feature points. Then, pulse excitation was executed at typical configurations, and the acceleration response at three degrees of freedom was recorded. The frequency response function curves were obtained and the resonant frequencies were identified using the analysis software. The resonant frequency varying with configurations were analyzed. Finally, the mechanism was reassembled according to the changed structure parameters, and the experiment process was repeated. The resonant frequency varying with the structure parameters were analyzed. The analysis results can be used for robot dynamic optimization and controller design.

In order to investigate how to choose active noise control algorithm in practical engineering, the performances of typical ANC algorithms are investigated in different conditions by simulations and experiments. The conditions of application of the algorithms are also studied. It is concluded that if the secondary path is linear and the requirement of the convergence speed is not strictly demanded，FxLMS algorithm is the best choice. If the noise to be actively controlled (i.e. the primary noise) is non-stationary or the requirement of convergence speed is strictly demanded, GSFxAP algorithm is a suitable choice. If the correlation between the primary noise and reference signal is poor, FsLMS algorithm is the choice. It provides a theoretical guide for the choice of active control algorithm in practical engineering.

A certain type of car exhaust muffler is taken as the object to research the acoustic performance. The muffler is divided into basic silencing units based on the transfer matrix method , and silencing units are analyzed to get muffler’s total transfer matrix , and its acoustic model is established. The frequency characteristic of transmission loss is calculated using Matlab software. Finite element simulation software , Sysnoise and Fluent are used for the simulation calculation to get the accurate frequency characteristic of transmission loss. The results obtained with both methods are compared to verify the accuracy of the acoustic model ,and the basis for improvement and optimization of the muffler is provide.

The sound transmission performance of the acoustical material can be measured in the standing-wave pipe by using the two-microphone method. The front surface impedances of the acoustical material can be determined if the beck surface impedances are known, so the arguments which are associated with the four elements of the transfer matrix can be calculated, and the sound transmission loss of the acoustical can be easily obtained. Several samples have been tested in the standing-wave pipe, compared with the experimental results from the four-microphone method, we know that the two-microphone method can be used to measure the sound transmission loss.

As for M1 class vehicle sound quality, this paper first proposed subjective evaluation test by considering the subjective feelings. First, collected a large number of sound signals of vehicles as for the database of sound quality evaluation, collected a large number of sound signals as for the database of sound quality evaluation, according to different frequency bands of sound signals show different characteristics, sound signals were divided to different frequency band. Then determined the best proportion of male and female while do subjective evaluation test. And then did sound quality subjective evaluation test by specific paired comparison. Finally, analyzed the test results and obtained: M1 class vehicle sound characteristic is most influenced by the frequency band 500-4000Hz, followed by 20-150Hz, the frequency band above 4000Hz has minimal impact.

The drum of a washing machine rotates at a high speed during dehydration work, while the clothes in the drum rotate together with the drum, yielding pressure on the drum wall which causes the drum to deform. With software Pro-E and ANSYS the finite element model of a washing machine drum with its support is established. Dynamic analysis of the drum structure in the case of dehydration work is carried out. The natural frequencies and vibration modes are obtained. The critical positions and the critical rotating speed are found. Some improvement suggestions for the washing machine drums are esented.

Operational transfer path analysis is an effective in-situ method for measuring the vibration transmission path. OTPA requires only operational measurements of the path references and target response(s) to establish a transmissibility matrix between references and target(s) from operational data under different test conditions. There is no need to measure operational forces and transfer function comparing to traditional method. It is easier and can operate in-situ. This article analyzes the basic theory of the operational transfer path analysis and the cause of the error. A car’s vibration analysis is given as an analysis example. The implementation procedures of operational transfer path analysis are given in detail. The noise sources were found out, and reasonable noise and vibration reduction suggestion was given.