Abstract
The theoretical investigation of acoustical wave propagation in cylindrical layered media is the main interest of our research. The propagation of wire break or slip related acoustical signal in the buried water-filled Prestressed Concrete Cylinder Pipe (PCCP) is taken as a specific application. The PCCPs are widely used for potable-and waste-water distribution and transmission systems, which are generally located below the surface ground. Therefore, it is difficult to inspect or detect the damage caused by the wire-break or slip related events in the pipeline. In current practice, the acoustic emission (AE) monitoring system is used for random examination of prestressing wires by excavating or internal inspecting of the pipe walls, which is based on field data analysis. This gives only the localized knowledge of wire break or slip, which can be misleading, underestimated of the extent of corroded areas, deterioration of wire failure, due to the system resonance, acoustoelasic effect, loading effect, etc. There is no systematic theoretical analysis from the acoustic signal generation to propagation related to these effects, and hence, a common problem in AD technology is to extract the physical features of the ideal events, so as to detect the similar signals. The theoretical analysis is important to understand how the AE signal is generated by the leak, wire break or slip related events and how the path characteristics, excitation frequency, and modes of propagation physically affect the signal propagation. For this purpose, and acoustical model is developed from the Navier's equation of motion. This can simulate vibrating AE signal propagation through the fluid-filled PCCP. The interaction of this propagation with the pipe structure is modeled by using Newton's law of motion in equilibrium. The principle of virtual work is used to develop the fluid-structure interaction. In this work, the impact of the path on the spectral profiles of the vibrating AE signals in different locations throughout the pipes were investigated for low and high frequency excitation signals. At low frequency, there is only plane wave propagation, therefore the stoneley or tube mode analysis is used for this purpose. The tube wave effects on the acoustical wave propagation were observed from this analysis. At high frequencies, there also exist rayleigh or shear modes which exhibit oscillatory amplitudes in the fluid and a decaying amplitude in the pipe and the surrounding medium. The eigenfrequency and the modal analysis is used in this case. From the analyses, the phase velocity, group velocity, tube wave velocity, system resonance frequencies, cut-off frequencies were observed. The high frequency analysis has some special advantage over low frequency signal. This can provide an earlier indication of incipient faults, which is important to detect the AE event in early stage of pipe deterioration. Moreover, it was established that the frequency of propagating AE signal in the pressurizing fluid medium ranges up to 30kHz. Therefore, it is important to investigate the wave propagation of AE signal propagation through the fluid column inside the pipe within the range of sonic/ultrasonic frequency. The acoustic wave propagation in fluid-filled PCCP of various radius, stiffness and thickness of the pipe as well as different types of surrounding medium, is obtained by applying a numerical Finite Element Method (FEM). Finally, the results are compared with available analytical solutions. The proposed model is independent of sources, dimensions and medium characteristics. Therefore, it can be used for the analysis of acoustic wave propagation through any type of cylindrical shells immersed or surrounded by different types of medium. The current analysis, therefore, has fundamental importance in many applications.
Highlights
In 1942, the first prestressed concrete Lined Cylinder Pipe (LCP) was introduced, where a concrete lined steel cylinder was wrapped with a helix of highly stressed steel wire and coated with a dense cement mortar to protect the wire
Later in 1950, a second type of prestressed concrete Embedded Cylinder Pipe (ECP) was developed, where the steel cylinder is embedded in the concrete core after that stressed steel wire helix is wounded, so that the wire is in contact with concrete rather than with the steel cylinder
Different dimensions and stiffness of the layered media were investigated. This illustrates the effect of pipe profiling on the tube mode propagation of acoustic emission (AE) signal through water-filled elastic pipe (PCCP)
Summary
Said as a pipe, should be impervious against leakage of liquid from the inside to the outside and against the ingression of external materials inside. The acoustic signals are generated through the breakage or sliding of steel wires that are prestressed to structurally enforce the pipes These signals feature certain frequency spectral characteristics that are close to the eigenfrequency of the piping system. The frequency domain numerical analysis of the acoustical model is carried out to determine the eigenfrequency, modes of propagation, cut-off frequency, and phase speed of acoustic wave in elastic pipes with a range of radii, stiffness and thickness of pipe and surrounding medium. We present the numerical investigation of this problem The time domain acoustical model is used to explore the impact of the impulse response of the pipe and the surrounding medium on the spectral profile of the high frequency excitation signal.
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