Application of Sound Intensity Measurement Method in Spotting the Noise Source of Engine Surface

During the study of noise emitted by accelerating mini-vehicle control, using theory of sound intensity measurement, it is actualized spotting the noise sources with the mini-vehicle engine. In the procees of the contour of sound intensity and frequency spectrum analysis, main noises of the engine are from oil sump tank and delivery menifold shield and two-way branch exhaust pipe shield. These noises are produced from the engine combustion. According to all analysis, the authors bring forward methods of modifying structure of shield-shell parts and consider them as main methods of reducing noises.     

Analysis of Low frequency Noise of Bridge Considering the Vibration of Bridge Deck

Under the dynamic load of vehicle, the bridge will vibrate and radiate low frequency noise which is harmful to human health. A method for predicting the low frequency noise is proposed based on the analysis of vibration of bridge deck. The prediction includes the analysis of vehicle bridge coupling vibration considering the bridge deck and the analysis of sound radiation and propagation in the air. By taking a bridge with low frequency noise as example, the vibration and sound radiation of the bridge are analyzed respectively by the current method and the previous method based on the grillage model. The results show that the prediction based on the vibration of bridge deck is more accurate. Furthermore, the measures to reduce the noise of bridge are explored, and the results indicate that a smoother road surface leads to lower noise. But when the condition of road surface is up to the extremely good standard defined by ISO, the effect of reducing the roughness of surface is not significant. Also, strengthening the crossbeam in the bridgehead is a simple and effective way to reduce the low frequency noise of bridge.     

Identification of combustion noise and mechanical noise in internal combustion engine

To identify internal combustion engine (IC engine) noise, a mathematical model is established, and the corresponding program is developed. By introducing global thresholds to decrease noise in the wavelet transforms program, the anti-interference of the program can be guaranteed, the spectrums of the combustion noise and mechanical noise are separated, and their A-weighted sound power levels are figured out. Taking a CG125 style motorcycle engine for an example, theoretical examples that include different interferential noises are constructed to simulate the identification and to validate the accuracy and practicability of the program. Results of the identification show that the spectrums of the combustion noise and mechanical noise before and after separation are agreed well; errors of A-weighted sound power level are all less than 0.6 dB.     

Identifying Research on Noise Sources of Rotary Vane Compressor

This paper describes the noise mechanism of rotary vane compressor JSS -96 by the method of running independently, spectrum and the measurement of the sound intensity. The noise sources of this type compressor mainly include noise of electromotor, outlet noise and intake noise. Electromotor noise and outlet noise among them have most influence on the compressor noise. This is the further basis of noise control for rotary vane compressor.     

Study on Surface Noise Distribution of Three ring Reducer

The three ring reducer is a kind of gear drive developed in the past decade. Adopting the new conception of "parallel and movable axis" of multiple mechanisms, this kind of gear drive has many characteristics such as large transmission ratio, high efficiency and so on. As the three ring reducer has been invented only for ten years, up to date the design of the gear drive is only made with analogue method, no design theory can be followed, there exist serious vibration and noise in transmission, which limit its wide application in industry. In this paper, the transmission principle of SHQ50 reducer is studied, the surface noise distribution of the reducer, transmission ratio 49.5 , is measured and analyzed by means of sound intensity method. The 3D distribution maps of noise on top of reducer, input side and output side of reducer, and left side and right side of reducer are drawn. With the sound intensity frequency maps of each measuring point, the sources of giving out noise are analyzed. The reducer of low vibration and noise can be designed rightly according to the analysis.     

Application of Sound Intensity Technique to Measure the Noise of Electromotor

This paper has explained the characteristics,virtue of sound intensity measurement and the principle. And compare with traditional sound pressure measurement. The principle and composing of virtual sound intensity measurement system based on two-channel FFT analysis are researched. The sound power of large turbogeneratorin operating site is determined by means of sound intensity measurement and sound pressuremeasurement. Itis demonstrated that the method of sound intensity measurement of engine is practicable and the measuring data are valid and the method conquers the problems of traditional method of sound pressure measurement which is apt to environmentinfluence and sound power measurement need to especially acoustic environment. It is proved that the sound intensity method is especially suited to determine highaccuratelythe sound Power level of the electrical machines operating in situated conditions especially in case of acoustically worst environments or on loadand themethod is so superiorityin noise measurement.     

Test Method of Indoor Noise for Micro-surfacing Mix

Micro-surfacing mix has been wildly used in the pavement maintenance for its water proofing, anti-skidding and wear resistance. However, micro-surfacing pavement has higher noise than the common asphalt pavement and its noise can not be measured effectively and accurately. Therefore, the indoor noise test method of micro-surfacing mix based on wet track abrasion test was explored. The micro-surfacing mix specimens were used to imitate the micro-surfacing pavement. The wet track abrasion tester was used to provide the vehicle loads. The sound level meter was used to measure the noise between tire and pavement. Furthermore, the indoor noise of nine kinds of micro-surfacing mixes with different gradation was examined. The results show that the equivalent sound level in the second time period has good relationship with the surface texture depth by sad patch method. Then the test method and test procedure for the indoor noise of micro-surfacing mix based on wet track abrasion test were given. Finally, two micro-surfacing mixtures with different gradations were made to validate the test method. The results show that the evaluation method can effectively distinguish the difference of micro-surfacing mixes with different gradation and can supplement the mix design method of micro-surfacing mixes.     

Analysis of Elevated Structure Radiated Noise with BEM-FEM Method

Urban rail transit is becoming an important means of transportation and elevated structure is one important part of urban rail transit. So the radiation noise induced by elevated structure attracts more and more attention. Based on the theory of Helmholtz integral equation of BEM and fluid-structure coupling system of FEM, the sound pressure transmission vector reflecting the relation between structural vibration acceleration and radiation of sound pressure is derived and solved by the element radiation superposition method. The calculated results are in good agreement with the experimental data from a viaduct section of the Beijing airport rapid rail transit.     

Experimental Research on Noise Reduction of Mini-car

By means of noise sources separation experiment of mini car and the surface acoustic intensity measurement of the engine, this paper finds that the main noise source of the mini car is the intake noise. According to the frequency spectrum analysis of the intake noise, the design frequency of the three cavity Helmholz intake silencer is determined. The results of the experiments show that the silencer, which is patented, has a remarkable effect, about 8 dB(A) decrement, on the noise reduction of the mini car.     

Junction stiffness analysis and vibration noise prediction of wind power speed-increase gearbox

In order to study the vibration characteristics and radiation noise of wind power speed-increase gearbox, a torsional vibration model of wind power speed-increase gearbox is established based on the analysis of supporting stiffness of bearing and contact stiffness of gear pairs. By solving the vibration differential equation with the help of Matlab, the frequency and corresponding vibration mode are obtained. With taking stiffness excitation, error exaction and meshing impact exaction into account, the dynamic finite element model of speed-increase gearbox is set up, and the dynamic response simulation is carried out. Regarding vibration displacement of the nodes on gearbox surface as boundary condition, an acoustic boundary element model of speed-increase gearbox is built. The surface acoustic pressure of gearbox and the radiation noise of field points are solved by the direct boundary element method. The results show that there is a great difference between torsion frequency and excitation frequency of wind power speed-increase gearbox, and so the resonance doesn't occur. The maximum structural noise and radiation noise mainly appear near the double octave of the gears meshing frequency of high-speed grade.     

Accelerated Vehicle Exterior Noise Control of Minicar SC6360B

This paper studyies the method of controlling SC6360B's accelerated vehicle Exterior noise. First, the main noise is found, which is from engine compartment and from exhaust noise by the identification of vehicle noise resource. Second, this paper carris out the farther noise identification experiment on engine and the insert-loss experiment on the exhaust gas muffler. In the end, the authors make sure that the noise is mainly infected by direct leaked noise from engine compartment, radiation-noise caused by the vibration of engine accessories and loud exhaust noise because the muffler has dficient elimination . The corresponding methods has been adopted according to the analysis. Through the test, the noise is lowered 2.5 dBA than it was and reach the new requirement.     

MEASUREMENT ON THE SOUND POWER LEVEL FOR MECHANICAL NOISE

Because of changeable distribution of noise fields in different room and the different absorption coefficients of walls and ceilings, average absorption coefficient of room surface hase to be estimated,which is really a great trouble . Now,this problem is solved,because,as discribed in this paper, the mechanical noise of the A weighted sound power level can be calculated after the absorption coefficient and environmental correction value is obtained. Experiences show that the result is accurate enough for engineering practice.     

Discussion on Limited Noise Value with Specific A-weighted Sound Level for Axial Flow Ventilators

The limited Value of specific A-weighted sound level in the present standard JB/TQh341-84 promulgated by the Ministry,which is applied to determine the unaccuracy of noise characteristics for axial-flow ven tilators has been discussed,Simultaneously a measure that should badopted to reduce the noise of high-pressure&great-flow axial flow ven tilators and a limited standard value for A-weighted Sound level have been also presented,This can not only keep the noise of ventilators up to A-weighted sound level.but also can decrcase the noise of ventilators properly. Purthermore this can make the noise standard for axlal flow ventilators be more scientific and more practica ble.     

风电齿轮箱传动误差分析及振动噪声预估

针对一级行星两级平行轴风电齿轮传动系统,综合考虑齿轮时变啮合刚度、啮合阻尼、传递误差等因素,建立31个自由度的弯扭轴耦合集中参数动力学模型,采用变步长Runge-Kutta法对系统动力学微分方程进行求解,得出齿轮传动系统各级传动误差;借助软件建立风电齿轮箱刚柔耦合动力学模型,并导入传动误差,采用模态叠加法求得齿轮箱轴承支反力,并将其作为声振耦合模型的边界条件,采用声学有限元法对风电齿轮箱进行振动噪声预估,并与试验结果对比分析,两者吻合良好。     

Research on Bridge Structure Noise of Railroads and Underground

This paper analyses the generating mechanism of radiation noise which produced by bridge structures and vibro-acoustic characteristics, and reviews the current situation of the researches on the relevant standards of structure noise at house and abroad. The author summarizes the method of measurement and calculation about structural noise at house and abroad, further notes their limits. This paper explores the impact of such factors as rain speed and other different fluids on structure noise. The noise characteristics of structures like cavity structure and thin-slab structure are also discussed. Strategies for reduce the bridge structure noise are summed up by reducing the vibration of track structure, altering the structure of boundary conditions, increasing the stiffness and changing the bridge cross section. Finally it comes to a conclusion that a combination of these strategies is the root way to settle the question of the bridge structure noise.     

Adaptive Enhancementt of Heart Sound Based on Simulink

In the course of recording heart sound, it is inevitable that many kinds of noise will be merged in the main signal. These kinds of noise disbennifit the heart sounds, even import awful influence to analysis result. So, before further processings of phonocardiographic records, noise must be suppressed. Because heart-sound is a highly nonstationary signal, this paper presents the application of adaptive filter method to the elimination of noise,and at the same time, employs the datum of heart-sound plot as the reference noise. With simulink, a modeling and simulation tool for dynamical systems, the model of LMS adaptive heart-sound enhancement is established.Tests prove this method makes effective denoising and heart-sound enhancement.     

Numerical simulation of dynamic response and radiation noise of gearbox

Considering the internal dynamic excitation produced by stiffness excitation, error excitation and mesh impact excitation, a dynamic finite element model of transmission system and structure system of gearbox is established. The normal mode and the dynamic responses of gearbox under the internal dynamic excitation are calculated by using the numerical simulation software ANSYS. Based on the result of dynamic responses, the boundary excitation condition is determined, and then the acoustic boundary element model is built. With the software of SYSNOISE, the surface acoustic pressure of gearbox and the radiation noise of field points are solved by the direct boundary element method. The test of airborne noise is carried out. The computational results obtained are in a good agreement with the data of experimental test.     

增补UV-B辐射对药用植物黄檗幼苗生长及光合生理影响

[目的]为了研究紫外辐射对药用植物生长和光合生理影响机制,[方法]通过设置三个实验处理对黄檗(Phellodendron amurense)幼苗进行40d的增补UV-B辐射处理,对照组(CK组)自然光照、T1组为自然光照下增补UV-B辐射强度为3.26 μw.cm_-2.nm_-1,T2组为自然光照下增补UV-B辐射强度为9.78 μw.cm_-2.nm_-1。[结果]结果表明黄檗幼苗在增补UV-B辐射处理后,与对照相比,不同辐射强度下单株生物量增长量显著低于对照组(P<0.05),而根冠比则显著降低(P<0.05),并且二者随辐射强度增大均减小;光合速率、蒸腾速率和气孔导度均显著低于对照(P<0.05),并随辐射强度升高而降低;叶绿素初始荧光(F₀)、最大荧光(Fm)、PSⅡ原初光能转换效率(Fv/Fm)、PSⅡ潜在光化学活性(F_V/F₀)、光化学猝灭系数(qP)和表观电子传递速率(ETR),均随UV-B辐射强度增大而降低(P<0.05),非光化学猝灭系数(qN)在低UV-B辐射强度下升高,随辐射强度增大而又降低,但仍高于对照组(P<0.05)。叶绿素a、叶绿素b、总叶绿素、类胡萝卜素和叶绿素a/b等光合色素含量均随增补UV-B辐射强度增大而降低。[结论]说明UV-B辐射处理抑制了黄檗幼苗的生长,降低了光合色素的含量和PSⅡ反应中心传递电子的能力,导致光合作用强度下降,并且上述作用均具有剂量效应。     

Virtual Sound Intensity Analyzer

The Virtual Sound Intensity Analyzer is a new instrument which has more advantages than the traditional Sound Analyzer. This Analyzer is based on fast Fourie transformation and virtual instrument technique.As an application, combining software and hardware, all kinds of weight noise sound level measurement and real-time noise octave analyzes realized synchronously. The design method has been introduced from three ways, which includes hardware, software and panel. An applied example and error analyze of Virtual Sound Intensity Analyzer are given.This Analyzer is low cost, small volume. and it is also easy to operate. It can be widely used in actual applications.     

Experimental Investigation on Characteristics and Evaluation Indexes of Ground-borne Noise Induced by Subway

In-situ experiments and investigation of evaluation indexes were performed to study the subway-induced ground-borne noise in buildings along the subway lines. The characteristics of ground-borne noise in buildings were summarized from various aspects by analyzing the experimental data. The factors such as the spectrum width, the analyzing time and background noise effect on the results of evaluation indexes, were further investigated. The correlation between different evalution indexes was analyzed, and the deficiencies of the indexes of noise evaluation in the environmental noise control codes of China were discussed.