An approximate theoretical validation of the measured variation of ultrasound velocity with porosity of dry and saturated cement paste is proposed using finite element analysis of cement paste assuming as a multiphase composite. Cement paste is a multiphase composite consisting of solid cement and microscopic voids filled either with air or water. e void content in cement paste is directly related to strength and durability. Experimental tests showed that ultrasound wave velocity is decreased with the increase in porosity of cement paste, where pore sizes are similar in dimension to the wavelength of the sound enabling ultrasound to be used as a potential condition assessment technique. However, the variation of ultrasound wave velocity also depends on the fluid in the voids. Several finite element simulations using two commercially available software packages were performed for both fully saturated and dry blocks of cement paste with different porosities. en back-calculated elastic moduli values from finite element simulations were used to compute the wave velocities of both fully saturated and dry cement paste with different porosities. e predicted ultrasound velocities with porosity for both dry and saturated cement paste are compared well with the laboratory measurements.

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The hydraulic fracturing or fracking and extraction of shale gas is vital to the continued success of the human race to provide a relatively clean energy source. However, there are several environmental issues that must be solved in order to make fracking environmentally acceptable. Once these issues are resolved, it could lead to a brighter future by allowing shale gas to act as a bridge to clean energy, while providing energy independence for the United States. To achieve these goals, there is a need to find suitable solutions to the following problems: methane gas leaks while fracking and during production, trigger of earthquakes due to fracking, and the disposal of the wastewater (largely comprised of fracking fluid) after the completion of fracking. To investigate the aforementioned environmental impacts, comprehensive research was performed using data for the Marcella formation. Although it is clear that additional research must be performed to fully deal with all the issues, the following strategies have been found to solve or mitigate the problems. To prevent the impact of methane gas leaks, well workers must be properly trained and supervised. As another precaution to prevent the methane from contaminating groundwater, groundwater wells must be a minimum of 1 km away from the vertical section of fracking wells. To lessen the intensity and frequency of earthquakes caused by fracking, a regulation should be set in place that prevents disposal of wastewater by groundwater injection wells. In addition, the site should be checked for possible active and inactive faults before the approval of fracking. Finally, fracking companies must be required to withdraw most fluids from wells and to treat them according to state regulations and reuse or surface disposal as treated water. If all of these suggestions are implemented, fracking can be made much more environmentally viable and safe.

In this paper, nonlinearity associated with intense ultrasound is studied by using the one-dimensional motion of nonlinear shock wave in an ideal fluid. In nonlinear acoustics, the wave speed of different segments of a waveform is different, which causes distortion in the waveform and can result in the formation of a shock (discontinuity). Acoustic pressure of high-intensity waves causes particles in the ideal fluid to vibrate forward and backward, and this disturbance is of relatively large magnitude due to high-intensities, which leads to nonlinearity in the waveform. In this research, this vibration of fluid due to the intense ultrasonic wave is modeled as a fluid pushed by one complete cycle of piston. In a piston cycle, as it moves forward, it causes fluid particles to compress, which may lead to the formation of a shock (discontinuity). Then as the piston retracts, a forward-moving rarefaction, a smooth fan zone of continuously changing pressure, density, and velocity is generated. When the piston stops at the end of the cycle, another shock is sent forward into the medium. The variation in wave speed over the entire waveform is calculated by solving a Riemann problem. This study examined the interaction of shocks with a rarefaction. The flow field resulting from these interactions shows that the shock waves are attenuated to a Mach wave, and the pressure distribution within the flow field shows the initial wave is dissipated. The developed theory is applied to waves generated by 20 KHz, 500 KHz, and 2 MHz transducers with 50, 150, 500, and 1500 W power levels to explore the effect of frequency and power on the generation and decay of shock waves. This work enhances the understanding of the interactions of high-intensity ultrasonic waves with fluids.

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