Advanced Materials Research Vols. 199-200

Abstract: This paper optimized the design of the cooling fans of a light-duty diesel engine through numerical simulation. Using Fluent as a platform, a detailed Computational fluid dynamics (CFD) model was developed to simulate both the aerodynamic and the acoustics performance. The model developed was validated against experimental data obtained in this research. The validated model was then used to optimize the design of the cooling fan aiming to minimize the operation noise. With the guarantee of cooling performances, the aerodynamic noise of the two fans has been successfully reduced.

Abstract: Tortional vibration is a common phenomena in the rotary machine such as internal combustion engine. The measurement of tortional vibration is an usual test in the engine experiments. In this paper, the influences of some parameters of measurement instruments such as teeth number and diameter of gear wheel were investigated by experiment approach. Some useful results to guarantee the precision of measurement were obtained.

Abstract: Based on the power spectral density (PSD) function of stochastic irregularities of the standard grade road and by means of inverse fast Fouerier transform (IFFT) based on discretized PSD sampling, an equivalent sample of stochastic road surface model in time domain was built. A one-dimensional model of stochastic road was developed into a 2D model of stochastic road surface. Through computer simulation practice based on the MATlab, a 2D sample of stochastic road surface in time domain was regenerated. Furthermore, given the sample data, the PSD was estimated and then compared with the theoretical 2D PSD Equation deduced from the one-dimensional PSD expreesion so as to prove the effectiveness and accuracy of the time-domain model regeneration of 2D stochastic road surface by means of IFFT method. The 2D stochastic road surface model directly provided basic road excitation input data for virtual prototyping (VP) and virtual proving ground (VPG) technology.

Abstract: The noise of Diesel engine is the main source of vehicle noise, and engine noise is divided to 3 parts: the mechanical noise, the air flow noise and combustion noise. Combustion noise is the main part of in the three. In this paper, the combustion noise variation of a vehicle diesel with parameters of engine speed, engine load, pump and injector were analyzed by experiment method, the relationship between combustion noise and the double-peak of cylinder presser rise rate were analyzed carefully, some conclusions such as the second peak of PRR(pressure rise rate) is the suitable factor reflecting combustion noise and combustion noise is the function of diesel load were gotten.

Abstract: Sound source localization is always of great value in many engineering applications. In recent years, studies on orientation mechanisms of the auditory systems and research of bionic structures of subminiature creatures, especially of the parasitoid fly Ormia Ochracea which has a remarkable ability to detect the direction of the incident sound stimulus despite of its tiny body size, may provide preferable solutions for the miniaturization of acoustic localization structure. In this paper, the bionic acoustic sensing device are set up and taken as the research object to find feasible orientation mechanisms, and the dynamics of the bionic mechanical coupled diaphragms are analyzed. These works provide the basis for the manufacture of experimental acoustic sensing device. In the last part of this paper, experiments on bionic acoustic sensing device are conducted after the test system has been established. The measured data and the analyses based on the measured data demonstrate that the modeling methods and theoretical study in this paper are correct.

Abstract: The automotive interior noise subjected to different road excitations was analyzed with finite element simulation method, according to the analysis results of panel acoustic contribution; acoustic property of the vehicle was optimized. Firstly, B and C grade road spectra were generated by MATLAB. Secondly, the frequency response results of body structure subjected to different road excitations were computed by MSC.NASTRAN, and the response results were imported in LMS Virtual. Lab as velocity boundary condition via the coupling between the body structure and cab cavity, and the sound pressure level (SPL) around driver’s ears was predicted by using Acoustic Transfer Vector (ATV) technology. Also, the impact of cavity structure surface impedance on the interior noise was discussed, and the noise characteristics subjected to different road spectra were compared. And the contributions of body panels to the noise levels around the driver’s ears were achieved via panel acoustic contribution analysis (PACA). Finally, taking the vibration velocity of panels as the main goal, the body structure was optimized to reduce the automotive interior noise.

Abstract: The fault of a bearing may cause the breakdown of a rotating machine, leading to serious consequences. A rolling element bearing is an important part of, and is widely used in rotating machinery. Therefore, fault diagnosis of rolling bearings is important for guaranteeing production efficiency and plant safety. Although many studies have been carried out with the goal of achieving fault diagnosis of a bearing, most of these works were studied for rotating machinery with a high rotating speed rather than with a low rotating speed. Fault diagnosis for bearings under a low rotating speed, is more difficult than under a high rotating speed. Because bearing faults signal is very weak under a low rotating speed. This work acquires vibration and acoustic emission signals from the rolling bearing under low speed respectively, and analyzes the both kinds of signals in time domain and frequency domain for diagnosing the typical bearing faults contrastively. This paper also discussed the advantages using the acoustic emission signal for fault diagnosis of rolling speed bearing. From the results of analysis and experiment we can find the effectiveness of acoustic emission signal is better than vibration signal for fault diagnosis of a bearing under the low speed.

Abstract: A study of the Herschel-Quincke (HQ) tube concept for the reduction of noise in circular ducts is presented here, which contain the models, the attenuation conditions and the acoustic characteristics of HQ tube without flow and with mean flow. Then the simulations have been done by using GT-POWER, which explain the influences on the acoustic characteristics of the angle between the main duct and the bypass duct and the changes of the diameters. The results show that the angle has an impact with flow, no effect without flow, and both of them are affected by the changes of the diameters.

Abstract: The properties of the SW and its transmission law in the low-speed rolling bearing were studied in this paper. Firstly, the three-dimension contact model of the bearing was set up. The defects which occurred on the outer race were simulated in the model. According to the model, the stress, the strain and the contact stress distribution was computed. Then, the stress and strain distribution law and the contact stress distribution law of the interface on good and fault bearing were compared. In the real-world testing, fault signals were acquired using stress wave transducer. Fault characteristic parameters were extracted and the background noise was reduced using wavelet analysis. Both simulation and real-world testing result obtained indicate that SW and wavelet transform can be the effective method in the fault diagnosis of low-speed bearing.

Abstract: As the requirements for industrial operation and military work, the frequency characteristics should be changed artificially sometimes. Active control is a good choice, but the current active control mainly focuses on time domain for vibration control. In this paper, the structural active control on frequency domain is studied through theory and experiment. Firstly, multivariable wavelet finite element method with two kinds of variables (TWFEM) which is suitable for modeling of great and complex structures with high efficiency and precision is used to construct the mathematical model for the controlled structure and do static and dynamic analysis. Then the control algorithm based on neural network including two parts, identification implement and controller is constructed. The present study takes frequency response as control objective, and can not only do vibration control but also change the vibration frequency characteristics, providing a new perspective for active control.