Leak Detection of Gas Pipelines Based on Characteristics of Acoustic Leakage and Interfering Signals

When acoustic method is used in leak detection for natural gas pipelines,the external interferences including operation of compressor and valve,pipeline knocking,etc.,should be distinguished with acoustic leakage signals to improve the accuracy and reduce false alarms.In this paper,the technologies of extracting characteristics of acoustic signals were summarized.The acoustic leakage signals and interfering signals were measured by experiments and the characteristics of time-domain,frequency-domain and time-frequency domain were extracted.The main characteristics of time-domain are mean value,root mean square value,kurtosis,skewness and correlation function,etc.The features in frequency domain were obtained by frequency spectrum analysis and power spectrum density,while time-frequency analysis was accomplished by short time Fourier transform.The results show that the external interferences can be removed effectively by the characteristics of time domain,frequency domain and time-frequency domain.It can be drawn that the acoustic leak detection method can be applied to natural gas pipelines and the characteristics can help reduce false alarms and missing alarms.

Nonlinear Acoustic Shadow Method to Reduce Reverberation Artifact

A novel technique for reducing reverberation artifact in acoustic shadow imaging using nonlinear ultrasound interaction, called nonlinear acoustic shadow method, has been developed and experimentally studied. In this technique, the conventional acoustic shadow method is modified by using the secondary wave generated by nonlinear interaction of two primary sound waves emitted from parametric array. Either conventional or nonlinear acoustic shadow imaging is carried out for aluminum square cylinder and the size of the shadow is compared. The result shows that the nonlinear acoustic shadow method reduces reverberation artifact inside the square cylinder and has better accuracy in the size measurement than conventional acoustic shadow method.

温度、盐度和流体类型对圆柱周围湍流声学特性的影响研究

The effects of the temperature,salinity,and fluid type on the acoustic characteristics of turbulent flow around a circular cylinder were numerically investigated for the Reynolds numbers of 2.25×10^(4),4.5×10^(4),and 9.0×10^(4).Various hybrid methodsReynolds-averaged Navier-Stokes(BANS)with the Ffowcs Williams and Hawkings(FWH)model,detached-eddy simulation(DES)with FWH,and large-eddy simulation with FWH-were used for the acoustic analyses,and their performances were evaluated by comparing the predicted results with the experimental data.The DES-FWH hybrid method was found to be suitable for the aero-and hydro-acoustic analysis.The hydro-acoustic measurements were performed in a silent circulation channel for the Reynolds number of 2.25×10^(4).The results showed that the fluid temperature caused an increase in the overall sound pressure levels(OASPLs)and the maximum sound pressure levels(SPL_(T))for the air medium;however,it caused a decrease for the water medium.The salinity had smaller effects on the OASPL and SPLT compared to the temperature.Moreover,the main peak frequency increased with the air temperature but decreased with the water temperature,and it was nearly constant with the change in the salinity ratio.The SPLT and OASPL for the water medium were quite higher than those for the air medium.

Applications of physical methods in estimation of soil biota and soil organic matter

Soil biota is the living component of soil organic matter(SOM),and plays a key role in the decomposition of SOM.Both soil biota and SOM are indicators of soil fertility and soil quality.However,they both are sensitive to soil disturbance.Although researchers developed various technologies to detect soil biota and SOM,they are mostly destructive and cause disturbance to soil,which may not reflect the actual situation of soil biota and SOM.Therefore,here we mostly focused on the non-destructive physical methods for estimating soil biota and SOM and discussed their advantages and disadvantages.These methods include but not limited to acoustic detection,radio frequency identification,radioactive tagging,hyperspectral sensing and electron energy loss spectroscopy.In addition,we pointed out the current research problems and the potential research directions for applications of physical methods in estimation of soil biota and SOM.

1D Acoustic Velocity-Independent DOA Estimation Method with Arbitrary Arrays

The performance of conventional direction of arrival(DOA)method is greatly affected by the uncertainty of wave velocity in underwater environment.To solve this problem,an acoustic velocity-independent method is proposed to estimate the underwater DOA using two arbitrary intersecting uniform linear arrays in this study.By introducing the additional array compared to the conventional DOA methods,the proposed algorithm can make its performance independent of the acoustic velocity through the geometric relationship between those two arrays.The simulation results demonstrate that the proposed method is more accurate and robust than other methods in an unknown sound velocity.

Finite Element - Artificial Transmitting Boundary Method for Acoustical Field on Tapered Waveguide

In earlier approach, the 2-D acoustical field profiles on the substrate region are often calculated with BPM. In this paper, we present a new approach based on the finite element -artificial transmitting boundary method and calculate acoustical field on the substrate region.

Investigation on method for measuring dynamic shear modulus of underwater acoustic structure materials

A new method is described to measure the dynamic shear modulus of underwater acoustic structure materials in a small anechoic water tank by using a broadband parametric source, a precise coordinate installation and techniques of signal processing in the frequency range of 20 kHz - 100 kHz. The typical size of material samples is 500×500 mm2. Basic principles, experiment installation and measured results are also

Numerical study of the natural frequency and mode shape of prototype Francis turbine runner

The prediction of the dynamic behavior of the structure is a key to ensure the safe and stable operation of the unit.In this paper,the acoustic fluid-structure coupling method is used to study the natural frequency and the mode shape of the prototype Francis turbine runner.With an added mass,the natural frequency of the runner in the water is reduced.The added mass force mc is reduced under the cavitation,resulting in an increase of the natural frequency,but it is still much lower than the frequency in the air.As the order number of the runner mode increases,the added mass force increases,and the frequency reduction rate increases.From 0ND to 4ND,the nodal lines on the upper crown of the runner gradually disappear,and the mode shape becomes more complex.The modal displacement D*in the circumferential direction of the runner and the outlet edge of the blade are selected to compare the structural mode shapes under different operating conditions.The results show that the amplitude of D*in the circumferential direction of the runner gradually increases from the upper crown to the lower band of the runner,and the curve assumes a symmetrical distribution of sinusoidal waves,whose number is twice of that of the nodal lines of the runner.The D*value changes are caused by the added mass in the water,and it will further change under the cavitation conditions.It means that the vibration form of the structure has changed.These will cause damages to the runner under the resonance conditions at different positions and in different degrees.