Highly Nonlinear Solitary Waves for Rail Buckling Prevention

One of the major structural problems in the railroads made of continuous welded rails is buckling in hot weather and breakage or pulling apart in cold weather. Buckling is usually caused by the high compressive stress due to thermal load or weak track conditions, and sometimes vehicle loads. The prevention of track buckling is related to the determination of the temperature, called rail neutral temperature, at which the net longitudinal force in the rail is zero. In the project presented in this thesis we investigated the capability of a novel sensing system to indirectly measure applied stress in rails and predict incipient buckling. This system consists of a simple and cost-effective transducer, recently developed at the University of Pittsburgh, which enables the generation and detection of highly nonlinear solitary waves (HNSWs), which are compact non-dispersive mechanical waves that can form and travel in highly nonlinear systems such as granular, layered, or porous materials, where they are conventionally generated by the mechanical impact of a striker. To prove the feasibility of this novel system to predict buckling temperature or measure applied stress, we investigated numerically and experimentally the interaction between solitary waves propagating along a chain of granular particles and slender beams of different shapes, lengths, and boundary conditions. We found that the geometric and mechanical properties of the beam or thermal stress applied to the beam alter certain features of the solitary waves. Overall, the work presented in this thesis was articulated in four main tasks: 1) literature review; 2) create a semi-analytical model; 3) design and test new transducers; and 4) conduct a series of experiments including a field test at the University of California, San Diego. This HNSWs approach does not require many electronic accessories and shows a good sensitivity to the properties of the material that is at the interface with the chain of particles. Moreover, it only observes the propagation of solitary waves within the transducer without the waves in the rail

Effects of channel cross-sectional geometry on long wave generation and propagation

Joint theoretical and experimental studies are carried out to investigate the effects of channel cross-sectional geometry on long wave generation and propagation in uniform shallow water channels. The existing channel Boussinesq and channel KdV equations are extended in the present study to include the effects of channel sidewall slope at the waterline in the first-order section-mean equations. Our theoretical results show that both the channel cross-sectional geometry below the unperturbed water surface (characterized by a shape factor kappa) and the channel sidewall slope at the waterline (represented by a slope factor gamma) affect the wavelength (lambda) and time period (Ts) of waves generated under resonant external forcing. A quantitative relationship between lambda, Ts, kappa, and gamma is given by our theory which predicts that, under the condition of equal mean water depth and equal mean wave amplitude, lambda and Ts increase with increasing kappa and gamma. To verify the theoretical results, experiments are conducted in two channels of different geometries, namely a rectangular channel with kappa[equivalent]1, gamma=0 and a trapezoidal channel with kappa=1.27, gamma=0.16, to measure the wavelength of free traveling solitary waves and the time period of wave generation by a towed vertical hydrofoil moving with critical speed. The experimental results are found to be in broad agreement with the theoretical predictions

Detecting the Presence of High Water-to-Cement Ratio in Concrete Surfaces Using Highly Nonlinear Solitary Waves

We describe a nondestructive evaluation (NDE) method based on the propagation of highly nonlinear solitary waves (HNSWs) to determine the excess of water on the surface of existing concrete structures. HNSWs are induced in a one-dimensional granular chain placed in contact with the concrete to be tested. The chain is part of a built-in transducer designed and assembled to exploit the dynamic interaction between the particles and the concrete. The hypothesis is that the interaction depends on the stiffness of the concrete and influences the time-of-flight of the solitary pulse reflected at the transducer/concrete interface. Two sets of experiments were conducted. In the first set, eighteen concrete cylinders with different water-to-cement (w/c) ratios were cast and tested in order to obtain baseline data to link the ratio to the time of flight. Then, sixteen short beams with fixed w/c ratio, but subject to water in excess at one surface, were cast. The novel NDE method was applied along with the conventional ultrasonic pulse velocity technique in order to determine advantages and limitations of the proposed approach. The results show that the time of flight detected the excess of water in the beams. In the future, the proposed method may be employed in the field to evaluate rapidly and reliably the condition of existing concrete structures and, in particular, concrete decks

On the Application of Highly Nonlinear Solitary Waves for Nondestructive Evaluation

Highly nonlinear solitary waves (HNSWs) are compact nondispersive waves that can form and propagate in slightly compacted 1D chains of identical particles. Such a 1D chain is a heterogeneous lattice, which holds nonlinearity due to geometry and periodicity. Depending on the dynamic excitation, the particles support linear, weakly nonlinear, or highly nonlinear waves. The latter are triggered when the excitation generates a dynamic force much higher than the initial precompression. Over the last decade, there has been a great effort to use HNSWs in engineering applications such as shock absorbers, energy harvesting, and nondestructive evaluation (NDE). For NDE application, many examples available in the literature show that the stiffness of the material/structure in contact with a chain of particles, where HNSWs are generated, affects the number, amplitude, and arrival time of the solitary waves. In this dissertation, the dynamic interaction between HNSW and structure is investigated for three NDE applications: (1) determination of the elastic modulus and ultimate strength of concrete material, (2) measurement of the internal pressure and bouncing characteristics of tennis balls, and (3) estimation of axial stress in beams and continuous welded rails (CWRs). In the concrete application, the aim is to study the effect of water-to-cement ratio on the entire mix and on the surface of fresh concrete (simulating the undesirable water added to the fresh concrete by rain) on the solitary wave features. An experimental setup including seven solitary wave transducers and a numerical analysis simulating concrete samples as semi-infinite material is conducted to prove the feasibility and accuracy of the proposed HNSW method

On the Processing of Highly Nonlinear Solitarywaves and Guided Ultrasonic Waves for Structural Health Monitoring and Nondestructive Evaluation

The in-situ measurement of thermal stress in civil and mechanical structures may prevent structural anomalies such as unexpected buckling. In the first half of the dissertation, we present a study where highly nonlinear solitary waves (HNSWs) were utilized to measure axial stress in slender beams. HNSWs are compact non-dispersive waves that can form and travel in nonlinear systems such as one-dimensional chains of particles. The effect of the axial stress acting in a beam on the propagation of HNSWs was studied. We found that certain features of the solitary waves enable the measurement of the stress. In general, most guided ultrasonic waves (GUWs)-based health monitoring approaches for structural waveguides are based on the comparison of testing data to baseline data. In the second half of the dissertation, we present a study where some baseline-free signal processing algorithms were presented and applied to numerical and experimental data for the structural health monitoring (SHM) of underwater or dry structures. The algorithms are based on one or more of the following: continuous wavelet transform, empirical mode decomposition, Hilbert transform, competitive optimization algorithm, probabilistic methods. Moreover, experimental data were also processed to extract some features from the time, frequency, and joint timefrequency domains. These features were then fed to a supervised learning algorithm based on artificial neural networks to classify the types of defect. The methods were validated using the numerical model of a plate and a pipe, and the experimental study of a plate in water. In experiment, the propagation of ultrasonic waves was induced by means of laser pulses or transducer and detected with an array of immersion transducers. The results demonstrated that the algorithms are effective, robust against noise, and able to localize and classify the damage

Acoustic and Elastic Waves: Recent Trends in Science and Engineering

The present Special Issue intends to explore new directions in the field of acoustics and ultrasonics. The interest includes, but is not limited to, the use of acoustic technology for condition monitoring of materials and structures. Topics of interest (among others): • Acoustic emission in materials and structures (without material limitation) • Innovative cases of ultrasonic inspection • Wave dispersion and waveguides • Monitoring of innovative materials • Seismic waves • Vibrations, damping and noise control • Combination of mechanical wave techniques with other types for structural health monitoring purposes. Experimental and numerical studies are welcome

Physical modeling of tsunamis generated by three-dimensional deformable granular landslides

Tsunamis are gravity water waves that are generated by impulsive disturbances such as submarine earthquakes, landslides, volcanic eruptions, underwater explosions or asteroid impacts. Submarine earthquakes are the primary tsunami source, but landslides may generate tsunamis exceeding tectonic tsunamis locally, in both wave and runup heights. The field data on landslide tsunami events are limited, in particular regarding submarine landslide dynamics and wave generation. Tsunamis generated by three-dimensional deformable granular landslides are physically modeled in the NEES (Network of Earthquake Engineering Simulation) 3D tsunami wave basin (TWB) at Oregon State University in Corvallis, Oregon. A novel pneumatic landslide tsunami generator is deployed to simulate natural landslide motion on a hill slope. The instrumentation consists of various underwater, above water and particle image velocimetry (PIV) cameras, numerous wave and runup gauges and a multi-transducer acoustic array (MTA). The subaerial landslide shape and kinematics on the hill slope and the surface elevation of the offshore propagating tsunami wave and runup on the hill slope are measured. The evolution of the landslide front velocity, maximum landslide thickness and width are obtained along the hill slope. The landslide surface velocity distribution is obtained from the PIV analysis of the subaerial landslide motion. The shape and the size of the submarine landslide deposit are measured with the MTA. Predictive equations are obtained for the tsunami wave amplitude, wave period and wavelength in terms of the non-dimensional landslide parameters. The generated 3D tsunami waves propagate away from the landslide source as radial wave fronts. The amplitudes of the leading tsunami waves decay away from the landslide source in radial and angular direction. The wave celerity of the leading tsunami wave may be approximated by the solitary wave speed while the trailing waves are slower due to the dispersion effects. The energy conversion rate between the landslide and the generated wave is estimated. The observed waves are weakly non-linear in nature and span from shallow water to deep water depth regime. The unique experimental data serves the validation and advancement of numerical models of tsunamis generated by landslides. The obtained predictive equations facilitate initial rapid tsunami hazard assessment and mitigation.Ph.D.Fritz, Herman

On the use of solitary waves for energy harvesting

In the last decade there has been an increasing attention on the use of highly- and weakly- nonlinear solitary waves in engineering and physics, such as shock mitigation, acoustic imaging and nondestructive evaluation. These waves can form and travel in nonlinear systems such as one-dimensional chains of particles. One engineering application of solitary waves is the fabrication of acoustic lenses. In this dissertation, an acoustic lens based on the propagation of highly nonlinear solitary waves is proposed. The lens is part of a novel energy harvester able to focus mechanical vibrations into a single point where a piezoelectric element converts the mechanical energy into electricity. The first step of this research was to investigate numerically and experimentally a novel acoustic lens composed by one-dimensional chains of spherical particles arranged to form a circle array in contact with a linear medium. The second step of the research was to incorporate the acoustic lens into an energy harvesting that includes a wafer-type lead zirconate titanate (PZT) transducer and an object tapping the array. The PZT transducer located at the designed focal point converts the mechanical energy carried by the stress waves into electricity to power a load resistor. The performance of the designed harvester was compared to a conventional non-optimized cantilever beam, and the results showed that the power generated with the nonlinear lens has the same order of magnitude of the beam. Moreover, the performance of the proposed harvester was compared to a similar system where the chains of particles were replaced by solid rods. The results demonstrated that the granular system generates more electricity. Moreover, some parametric studies were conducted to improve the harvesting performance of the proposed system. The materials and the geometry of the harvester were considered to enhance the power output of the harvester. Numerical models were built to predict the power output from harvesters designed with different materials and geometries. The design that produces the highest power output was selected as the best design. The best design was tested experimentally to validate the enhancement in energy harvesting capability as predicted in the previous numerical model

Advanced Sensors for Real-Time Monitoring Applications

It is impossible to imagine the modern world without sensors, or without real-time information about almost everything—from local temperature to material composition and health parameters. We sense, measure, and process data and act accordingly all the time. In fact, real-time monitoring and information is key to a successful business, an assistant in life-saving decisions that healthcare professionals make, and a tool in research that could revolutionize the future. To ensure that sensors address the rapidly developing needs of various areas of our lives and activities, scientists, researchers, manufacturers, and end-users have established an efficient dialogue so that the newest technological achievements in all aspects of real-time sensing can be implemented for the benefit of the wider community. This book documents some of the results of such a dialogue and reports on advances in sensors and sensor systems for existing and emerging real-time monitoring applications