Experimental study on acoustic emission characteristics of coal rock at different confining pressure

This paper conducts experimental investigation on acoustic emission(AE) characteristics of coal rock at uniaxial and triaxial compression by MTS815 rock mechanics test system. The results show that the variation of AE has tendency effect at uniaxial compression and confining pressure experiments. We indicate that AE signal decreases significantly in the elastic stage, and the relatively quiet period of AE before the specimens failure is not obvious under confining pressure. The AE amplitude distribution with time and its envelope line can indirectly reflect the trend of stress. The AE events peak stress and elastic modulus decrease with the temperature increase, and the value of m which reflects the cumulative distribution of amplitude increases as the confining pressure rises. The results also show that the AE frequency distributes in three frequency domains, and the proportions of dominant frequency significantly increase while the specimens are broken.     

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.     

Analysis and Simulation of the Highway Tunnel Fire Contamination

A one-dimensional contamination diffusion model for tunnel fire is presented. Based on this model, a highway tunnel fire within a short time course was simulated and analyzed. Compared to the test results, the simulation result demonstrates that the model is feasible. In the end, it suggests a formula for highway tunnel fire contamination. The author hopes that this analysis will be available as the foundation of highway tunnel fire control.     

Finite Element Analysis on Interaction of Neighboring Highway Tunnels under Construction

Recently, the construction of neighboring highway tunnels with small interval gets more and more in China. The construction of such tunnels proceeds usually by excavating one after another. The second tunnel is constructed with the surrounding rock disturbed by the first one. And the construction of second tunnel also has effect on the first excavated one. For revealing the interaction laws of such tunnel construction in combination with the engineering practice of Lanfeng tunnel at Jinshan Road in Chongqing, The FE numerical simulation analysis was used to study the characters of surrounding rock deformation, stress field, and plastic zone of the tunnel. From this analysis, it clearly shows that the excavation of second tunnel has significant influence on the first one. This study provides a scientific basis for design and excavation of neighboring highway tunnels.     

MODEL TEST RESEARCH ON A COMPOSITE LINING OF UNDERGROUND ENGINEERING IN JOINTED ROCK

Combined with thedesign precept of Cai-Yuan highway tunnel 2 in Chongqing,stress state,time ffectiveness and rupture mechanism of rock near the bounda-ries of the tunnel and the second lining in jointed rock mass arc studied with model tests.The results show that shotcretc-bolt support betters mechanical properties of the periphey rock of the tunnel,and increases the capacity of anti-deformation.The second lining also has the action of supporting structure.     

Reasons of Tunnel Disease and Disease Management on Highway

Based According to the on the careful investigation in site of highway tunnel, the classification of tunnel disease is obtained. , design and construction of tunnel, in relation to the distribution of stress and loading of tunnel by numerical analysis and back analysis, the existing condition and reasons of tunnel diseases are carefully analyzed. At the same time, the disease management methods are provided, which are important to guide similar tur/nel to search diseases reasons and manage diseases.     

Mechanical and Deformation Characteristicson Shield Tunnel Segment with Cracks

The 3D Goodman element is used to simulate segments' cracks in one section of shield tunnel in Guangzhou. Mechanical and deformation characteristics of segment structure responded to varied depth of cracks is analyzed in this paper. Meanwhile, research on coefficient of lateral earth pressure, soil coefficient and ground water level on mechanical and deformation characteristics is carried out. The research result shows that along with the increase of cracks' depth, the tensile stress, pressure stress reach the maximum value while the increment is not too much. However, when the depth equals to the thickness of segment, the reinforcements' tensile stress has increase sharply, even exceeded the allowable value. Moreover, the maximum number of tensile stress, horizontal and vertical convergent value of shield tunnel segment with cracks increase with the reduction of the coefficient of lateral earth pressure and soil coefficient, and increase with the increase of ground water level as well. Specific repair measure has been taken to segments' cracks in this section of shield tunnel based on the conclusions. In general, this section of shield tunnel is stable and safe now, and there is no longer new cracks appeared.     

Modal Analysis and Vibration Control of Benfield Frame

There is a low frequency and great amplitude on Benfield frame of Jianfeng chemical plant. With finite element modal, the reasons and mechanism of the vibration on Benfield frame are analyzed and confirmed. And a method of vibration control about the main vibration resource (100V10) is proposed to reduce the amplitude of Benfield frame vibration.     

Low Voltage Power Line Communication Based on MSK

For that the characteristics of low voltage power line channel are complicated and variable, how to use low voltage power line to realize reliable and high speed communication has always been the hottest question in power line communication field. This article introduces how to apply MSK to the low voltage power line communication. It analyses the application elements of MSK and structures the model of low voltage power line communication based on MSK. simulation result indicates that MSK modulation technology can satisfy the characteristics that the bandwidth of power line communication channel is narrow and the attenuation to the amplitude of signal is time variable and frequency selected. Also, it makes better use of the spectrum.     

Least-square-based Optimization of Frequency Response Function Estimation in Modal Parameters Identification

The accuracy of modal parameters identification has the influence on the quality of dynamic characteristics analysis of mechanical structure directly. And the precision of the frequency response function estimation has the great influence on the accuracy of modal parameters identification. In the engineering the frequency response function can be estimated by the average power spectrum and cross-power spectrum with the hel Pof FFT. As the result of limited frequency resolution in the course of FFT and the noise, the accuracy of modal parameters identification is influenced by the frequency response function estimation. This paper has put forward a least-square-based optimization of frequency response function estimation in modal parameters identification. According to the optimized frequency response function, the peak value can be searched to identify the damped natural frequencies and damping ratio directly. An experiment has been made to validate the proposed method. The result indicates that the damped natural frequencies and damping ratio identified by the optimized frequency response function are closer to the true results than which without the optimized frequency response function. So the accuracy of modal parameters identification can be improved by adopting the proposed method.     

Rock Deformation, Stability Monitor Active Control About Excavation of Super-span Tunnel

According to the measurement during excavation of Jinzhou tunnel with four lanes in one cave which lies on the rebuilt highway from Shenyang to Dalian, this paper analyzes the rock deformation rule, discusses the reason of instability after a highway tunnel was excavated, emphasizes the necessity of the construction stability monitor and active control. The importance of support is Fresented with bolts and shotcrete to improve and enhance the carrying capability of the rock. It is necessary to insist on the rule of measurement and active control to ensure the safety and quality of tunnel construction.     

Modal parameters identification for short data sequences based on stratified sampling and optimism complex Morlet wavelet

A novel modal parameter identification method based on stratified sampling and optimism complex Morlet wavelet is proposed for short data sequences. Stratified sampling is applied to divide the structure response signal into different layers which called sub samples with different thresholds, and then free decrement response signal of each layer is extracted by random decrement technique. The optimism complex Morlet wavelet transform is applied to identify modal parameter of each layer, and the weight of the layer is also determined based on the sample standard deviation. The modal parameter of the structure can be obtained by weighted calculation.The engineering application shows that the proposed method has the ability to identify modal parameter accurately, decouple low frequency intensive modal composition and restrain high frequency fake modal effectively.     

Influence of Location and Form of HE-charges on the Air Blast Pressure Inside the Tunnel

In order to understand clearly to the influence of location and form of HE-charges on the air blast pressure inside the tunnel, based on Hopkinson scaling law, attenuation of air blast peak pressures in long tunnels due to HE-detonations in the case of different location and form at the tunnel entrance is simulated with the dynamic finite element software of LS-DYNA. The results are compared with other experimental methods. The results indicate that the influence of location and form of HE-charges is significant near the HE-charges. As the distance from the HE-charges larger and larger, the influence of location of HE-charges is smaller and smaller, but the influence of form of HE-charges is larger and larger. The methods and data presented can be refereed in similar engineering and determination of loadings upon protective doors.     

Topology optimization for constrained layerdamping material in structures using ESO method

Topology optimization for constrained damping material in structures is investigated in order to suppress structural vibration through the optimal placement of constrained damping material in structure. A mathematical model to describe the topology optimization problem is established. In the topology optimization approach, structural modal damping ratio is designed as objection function, while constrained damping material consumption is considered as constraint condition. The sensitivity of modal damping ratio to the place is analyzed. An evolutionary criterion for placement of constrained damping material in a structure is presented. The formula of sensitivity is derived and used to determine the optimized placement of constrained damping material in structure. The topology optimization problem is further solved by evolutionary structural optimization (ESO) method. The numerical examples are given. The results show that a stable and dramatic increase of the modal damping ratio during the course of iterations can be observed. Therefore, an optimal layout of constrained damping material in structure is obtained. The comparison of amplitude frequency characteristics with the optimal and fully covered layout validates the effectiveness of proposed topology optimized approach.     

The Method on Surrounding Rock Classification for Highway Tunnel Construction Period in The Karst Areas of South China

Through the statistical analysis of analyzed the particularity of karst surrounding rock classification, finally obtained the rock classification index system of south karst highway tunnel construction based on rock strength, rock complete coefficient ,groundwater state, structural plane state the structural plane strike to tunnel influence, karst development to tunnel influence. And the model is applied to tianshengqiao tunnel and guanshang 2 tunnel with the example verification, and compared with the classification results and experts judgment to get the accuracy is 93.3%.     

Probe microphone instrumentation for determining soil physical properties: testing in model porous materials

An acoustic technique for evaluating soil physical properties is described and tested in model porous materials. A probe microphone is used to measure the acoustic signal attenuation and phase speed. Emphasis is on the probe construction, insertion in soils and reduction of acoustic data to predict tortuosity and an effective air-flow resistivity of the soil. Well-known capillary-tube models of porous materials which incorporate these two porous material properties are used to invert the acoustic data. The probe microphone, associated hardware, data acquisition and analyses are implemented on a personal computer. The system can provide real time prediction of the soil properties in the field. Measurements in three materials: glass beads, washed sand and loess soil are analyzed and discussed. The instrumentation works well in the glass beads and washed sand tested; however, in the loess soil tested some restrictions occur.     

Assessment Method of Buildings Damage Induced by Underground Construction

With increased urban highway tunnel construction in P.R. China,there are more shallow cover tunnels passing under buildings.Finding a means to appraise buildings' degree of damage is one of the most important preconditions so that tunnels can safely pass under buildings.First,the instance of damage should be confirmed according to the buildings' actual settlement.Then, referring to the buildings damage evaluation criteria,the buildings' control damage rank and critical distortion value can be determined.The permissible distortion value can be drawn from the difference of buildings' critical distortion value and distortion value corresponding to its damage ranking.Finally,a three-stage appraisement is carried out to assess the degree of buildings' damage induced by tunnel construction.If every stage's calculated result of this appraisement exceeds buildings' permissible distortion value,the buildings should be reinforced to assure that the tunnels could pass through safely.At the same time, the calculation method has important reference value for the similar projects.     

Brief Study on Physiological Effects of Sound Field on Actinidia Chinensis Callus

Insight into the relationship between plant cell (tissue) and physical stimulation is a focus of biomechanics. In this study, several important plant physiological indexes of Actinidia chinensis callus in sound field including the content of soluble proteins, the activity of SOD, the activity of IAA oxidase and the penetrability of cell membrane, were measured. Some information is got about stress effect through the study and try to explore its mechanism. From the result of experiment,we found that there were a great similarity of stress effect on sound field between Actinidia chinensis and Gerbera Jamesonii acrocarpous , a kind of herbage plant, which had been studied in our lab before. That is to say, the sound field also has dual effect on woody plant. It can enhance or inhibit the growth and development of Actinidia chinensis callus along with the sound field frequency ,and the moderate frequency of sound field acting on the callus could promote callus growth. A conclusion is drawn that the optimal stimulation of sound field are 100 dB and 1 000 Hz. Under the conditions, the sound field can distinctly enhance the growth of Actinidia chinensis callus Whereas, it is not very easy to explore the detail mechanism of environmental stress effects on plant. This paper discussed the mechanism of sound field stress on plant from the level of cell and molecule.     

基于西瓜声学特性测定其成熟度

为达无损检测西瓜糖度目的,本研究在自主搭建的声学检测台上采集西瓜声学信号,提取声振动从敲击点传到接收点过程中声透过率参数(δ)。利用Matlab软件中的线性回归函数,将δ与西瓜糖度分别做线性回归,得到1 024个相关系数。从中选取相关系数前20位的声透过率值,借助软件中多元线性回归函数建立多元线性回归方程。研究比较不同敲击点和信号接收点组合所建模型的预测值和实测值相关系数(R),最高可达0.884 2。试验结果表明,敲击点和接收点位于赤道部位能获得较好的测定模型。