The concept of using dynamic excitation to enhance fluid flow in a porous medium began to arise in the mid-twentieth century. The initial spark of interest in the subject spurred numerous laboratory investigations throughout the latter half of the twentieth century to identify the mechanisms at work, and to develop field techniques for practical application of the technology. Several prominent laboratory and field studies have been published; however, there are some deficiencies that facilitate the need for further investigation. Groundwater flow and soil dynamics are two distinct areas of research. There is little in common between the two subjects and there is no consideration of soil dynamic properties in any of the reviewed papers. This study will attempt to bridge the gap between these two areas of research. The objective of this research is to attempt to determine how dynamic excitation of a soil matrix affects saturated single-phase fluid flow. This question is investigated through an extensive literature review of previous studies conducted on this topic, as well as through experimentation designed to replicate the mechanisms responsible for this phenomenon. Experimentation on coarse soil samples is conducted using a modified Stokoe-type resonant column device that allows a quantification of the effects of torsional and axial excitation, frequency of vibration, and strain level. This type of testing in the both the torsional and axial mode has never been conducted before using a resonant column; the Poisson ratios computed using the complimentary data has never been published in the literature.

The concept of using dynamic excitation to enhance fluid flow in a porous medium began to arise in the mid-twentieth century. The initial spark of interest in the subject spurred numerous laboratory investigations throughout the latter half of the twentieth century to identify the mechanisms at work, and to develop field techniques for practical application of the technology. Several prominent laboratory and field studies have been published; however, there are some deficiencies that facilitate the need for further investigation. Groundwater flow and soil dynamics are two distinct areas of research. There is little in common between the two subjects and there is no consideration of soil dynamic properties in any of the reviewed papers. This study will attempt to bridge the gap between these two areas of research. The objective of this research is to attempt to determine how dynamic excitation of a soil matrix affects saturated single-phase fluid flow. This question is investigated through an extensive literature review of previous studies conducted on this topic, as well as through experimentation designed to replicate the mechanisms responsible for this phenomenon. Experimentation on coarse soil samples is conducted using a modified Stokoe-type resonant column device that allows a quantification of the effects of torsional and axial excitation, frequency of vibration, and strain level. This type of testing in the both the torsional and axial mode has never been conducted before using a resonant column; the Poisson ratios computed using the complimentary data has never been published in the literature.

Vibration-based damage detection (VBDD) methods are structural health monitoring techniques that utilize changes to the dynamic characteristics of a structure (i.e. its natural frequencies, mode shapes, and damping properties) as indicators of damage. While conceptually simple, considerable research is still required before VBDD methods can be applied reliably to complex structures such as bridges. VBDD methods require reliable estimates of modal parameters (notably natural frequencies and mode shapes) in order to assess changes in the condition of a structure. This thesis presents the results of experimental and numerical studies investigating a number of issues related to the potential use of VBDD techniques in the structural health monitoring of bridges, the primary issue being the influence of the excitation source.<p> Two bridges were investigated as part of this study. One is located on Provincial Highway No. 9 over the Red Deer River south of Hudson Bay, Saskatchewan. The other is located near the Town of Broadview, Saskatchewan, off Trans-Canada Highway No. 1, 150 km east of the City of Regina. Field tests and numerical simulations were conducted using different types of excitation to evaluate the quality of the modal properties (natural frequencies and mode shapes) calculated using these excitation types, and thus to evaluate the performance of VBDD techniques implemented using the resulting modal data. Field tests were conducted using different sources of dynamic excitation: ambient, traffic excitation, and impact excitation. The purpose of field testing was to study the characteristics and repeatability of the modal parameters derived using the different types of dynamic excitation, and to acquire data that could be used to update a FE model for further numerical simulation.<p> A FE model of the Red Deer River bridge, calibrated to match the field measured dynamic properties, was subjected to different types of numerically simulated dynamic excitation with different noise (random variations) levels added to them. The types of dynamic excitation considered included harmonic forced excitation, random forced excitation and the subsequent free vibration decay, impact excitation, and different models of truck excitation. The bridge model was subjected to four different damage scenarios; in addition, six VBDD methods were implemented to evaluate their ability to identify and localize damage. The effects of uncertainty in the definition of controlled-force excitation sources and variation in measurement of the bridge response were also investigated.<p> Field tests on the Hudson Bay bridge showed that excitation induced by large trucks generally produced more reliable data than that of smaller vehicles due to higher signal-to-noise ratios in the measured response. It was also found that considering only the free vibration phase of the response after the vehicle left the bridge gave more reliable data. Impact excitation implemented the on Hudson Bay bridge using a spring-hammer yielded repeatable and high quality results, while using a heavy weight delectometer for impact excitation on the Broadview bridge produced results of lesser quality due to the occurrence of multiple strikes of the impact hammer. In general, wind induced vibration measurements taken from both bridges were less effective for defining modal properties than large vehicle loading or impact excitation. All of the VBDD methods examined in this study could detect damage if the comparison was made between modal parameters acquired by eigenvalue analyses of two FE models of the bridge, before and after damage. However, the performance of VBDD methods declined when the dynamic properties were calculated from response time histories and noise was introduced. In general, the damage index method performed better than other damage detection methods considered.<p> Numerical simulation results showed that harmonic excitation, impact excitation, and the free decay phase after random excitation yielded results that were consistent enough to be used for the identification of damage. The reliability of VBDD methods in detecting damage dropped once noise was introduced. Noise superimposed on the excitation force had little effect on the estimated modal properties and the performance of VBDD methods. On the other hand, noise superimposed on the measured dynamic response had a pronounced negative influence on the performance of the VBDD methods.

This thesis utilized pulse shaping technology to study chirp response of SSBR and attempt to analyze contribution of SSBR in mode-locked process. A home-made pulse shaping system (based on 4f scheme) with Freezing algorithm and Gerchberg-Saton algorithm was demonstrated. A normal dispersion at nonabsorbable wavelength and an anomalous dispersion around absorbable wavelength region in SSBR were obtained. Meanwhile, a Kramers-Kronig relation like behavior of pulse depression/broadening ratio in the strained multiple quantum well was observed and also refer to that pulse starting force is stronger at short wavelength. Decrease of pulse compression with increasing power of negative chirp incident pulse was characterized. Unclear power dependence for positive chirp case was also performed. These could be due to competition of band-filling and pump dump process. In addition, higher reflectivity and tendency of lower saturation fluence of SSBR for negative chirp incident pulse were observed.

No description available.

We study the optical properties of InGaN/GaN multiple quantum wells grown on silicon (111) substrate with different buffer layers. Because of the lattice mismatch and mismatch in thermal expansion coefficient, there exists stresses in the nitride sample grown on silicon substrates, which influence the growth properties and optical properties. A set of buffer layers was proposed in order to reduce the stress in our samples. The influence on optical properties is investigated in our work. In Raman spectra, we observed the characteristic phonon mode of GaN. According to the variation of E2 mode, the stress can be estimated. From our results, growing buffer layers can effectively reduce the stress in the sample. From temperature dependent and power dependent photoluminescence¡]PL) measurement, we found that appropriate buffer layers bring about less stress and better efficiency of luminescence. There are absorption of GaN and some vibrational behaviors in PLE spectra. According to the stokes shift calculated from temperature dependence PL and PLE spectra, we infer that the mechanism of recombination is not only carrier localization. The recombination is involved with the interaction of carriers and longitudinal optical phonons, and the stokes shift is independence on temperature.

The fundamental character of excitation system is to provide the direct-current power for field windings for synchronous generators. Excitation control system controls the generator output voltage and reactive power by varying the field winding¡¦s currents. Therefore, it can improve the transient stability of power system. The thesis proposed a process for modeling and simulation on a brushless coal-fired unit, since the 40 years-old magnetic amplifier (Type WMA MAG-A-STAT) Automatic Voltage Regulator (AVR) was replaced by a Programmable Logical Controller based digital redundancy system, for the purpose to verify the excitation system model and dynamic response gains in the future power system study. To establish the generator excitation system and simulations on a popular software program MATLAB/SIMULINK, we wish to manipulate the effective and precise simulation test on a personal-computer and apply Particle Swarm Optimization (PSO) to find the global optimal solution for AVR controller settings. This thesis contributes in building a reliable excitation system model with dynamic response figures for power system network planning and dispatch.

Thèse doctorat : Physique Théorique : Strasbourg 1 : 2006. / Titre provenant de l'écran-titre. Bibliogr. 10 p.

Thesis--Rijksuniversiteit te Leiden. / Summary also in Dutch. eContent provider-neutral record in process. Description based on print version record. Includes bibliographies.

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