Vita. / Digitized by Kansas Correctional Industries

Exposure to whole body vibration has been identified as a risk factor for the development of low back problems and exposure to frequent vertical impacts has been identified as a risk factor for both acute and chronic back injury. While there have been many prior studies into human response to both vibration and impacts, these studies have only examined them in isolation from one another, i.e. only sinusoidal vibration or impacts with no concurrent vibration. This does not reflect the environments in which occupational exposures take place and limits our ability to generalize these findings to the real world. The first obstacle in examining the interaction between vibration and impacts is the lack of any quantitative definition of what constitutes an impact within a vibrating environment. To take the first steps toward creating this quantitative definition of an impact, we examined acceleration, posture, and erector spinae electromyography (EMG) data from farm vehicle operators as they completed routine farm tasks. We created several novel impact detection methods based upon our current understanding of human muscle response to impacts that analyze acceleration data and return the locations in the data at which an impact is believed to have occurred. These novel impact detection methods are the Thump, Womp, and Wiggle Methods. We compared their relative successes in predicting a substantial change in EMG activity immediately following an identified impact to that of a method that randomly selected points in the data, as determined by a novel locally-normalized muscle response evaluation method. We then created a series of generalized linear mixed models that included posture and subject-specific data to compare how the odds ratios between the quartiles of each predictor align with we would expect these predictors to affect the likelihood of an impact to trigger a muscle response. We found that none of our novel impact detection methods predicted muscle response at an appreciably different rate than the random method. However, when posture and subject-specific predictors are introduced into generalized linear mixed models, we see statistical significance in how increases in the chest and lumbar angles affect the likelihood of a muscle response in impacts identified by the Thump Method (p<0.001). We also see statistical significance in how increases in the magnitude of the impact metric in impacts identified by the Wiggle Method increase the likelihood of an observed muscle response being observed (p<0.05). We believe that the Thump and Wiggle Methods of impact identification described within this thesis together provide a foundation for the development of an ideal impact identification method for future studies into impacts within vibrating environments.

Vibration-based damage detection methods are used in structural applications to identify the global dynamic response of the system. The purpose of the work presented is to exhibit a vibration-based damage detection algorithm that localizes the sensor arrangements such that irregularities within the structural system can be detected, located, and quantified. Damage can occur in a structure either within the material or at a connection between segments; therefore two different types of specimens, a plate specimen and a connection specimen, were analyzed with the algorithm. Numerical and experimental analyses were completed for each of the specimen types, and the results prove that damage can be detected, located and quantified in each scenario. It is noted that the quantification of the damage is based on a supervised learning method (original and damaged states are known) and that the accuracy in which the damage is quantified within the scope of this work might have difficulty in unsupervised learning methods (only current state is known). This work will extend to be applied on a highway bridge as a basis for a structural health monitoring system, as preliminary results suggest that further refinement is needed.

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This thesis is concerned with the prediction of the vibro-acoustic response of structures with uncertain properties in the mid frequency region. The motivation for this research is the growing need of engineers to understand the responses of a group of similar structures ranging from vehicles, aircraft and aerospace structures, to household whitegood appliances. These structures are complex in geometry and may possess variability in their material or geometric properties, as well as variation arising from the assembly and manufacturing processes. Small variations can have a significant effect on a dynamic response of a structure, and the effect of structural uncertainties increases as the frequency increases. Deterministic modelling techniques such as finite element analysis are only suitable to model complex structures at low frequencies. Furthermore, FEA cannot easily account for uncertainty or randomness in structural parameters. High frequency dynamic predictive techniques such as Statistical Energy Analysis can account for structural uncertainty but is limited to structures with high modal density. There exists a frequency range between the two methods in which neither technique can be applied with great confidence. The objective of this thesis is to investigate predictive techniques for mid frequency vibration analysis of dynamic systems with structural uncertainties. The first part of this work is to numerically characterise the effect of a range of uncertainties on the modal statistics of structures. The degree of uncertainty required to achieve universality of the statistical properties is investigated. This is achieved by examining the modal statistics of dynamic systems with a range of uncertainty, corresponding to uncertainty due to mass and stiffness perturbations, uncertainty at the boundaries of a structure, uncertainty in the coupling between structures, uncertainty in the material properties of a structure and uncertainty in the geometry of a structure. Several structures are examined corresponding to a plate with masses and/or linear springs added at random locations, a plate with torsional springs attached at random locations along its boundary edges, two plates coupled by linear springs at random locations, a mass-loaded coupled L-shaped plate, a mass-loaded frame-plate structure, and a plate with varying Young's modulus, density and thickness. The natural frequencies of the aforementioned structures have been derived using either the Lagrange-Rayleigh-Ritz technique, finite element analysis, or the use of interval analysis in conjunction with FEA. The natural frequency statistics of structures with uncertain properties are observed using two statistical measures; the statistical overlap factor and the probability density function of the spacing between successive natural frequencies. The statistical overlap factor is defined by the variation in a natural frequency from its mean value measured across an ensemble of nominally identical structures with uncertainty. For a single ensemble member, the probability density function of the spacing between successive natural frequencies is compared to a Rayleigh distribution of the mean frequency spacing. A Rayleigh distribution of modal spacings is a feature of the universality exhibited by structures with uncertainty. To further investigate the effect of structural uncertainty on the vibrational characteristics of structures, the interval analysis is applied to finite element models of a plate with uncertainty in its material properties and dimensions. Using this method, the Young's modulus, density and thickness of a rectangular plate were set to vary by a small amount within predefined bounds. Using finite element equations, the natural frequencies and modeshapes of the structure were then determined in terms of the Young's modulus, density and plate thickness. For the mass and spring loaded plates, the springs were shown to affect the lower order modes while the masses had a significant effect on the higher order modes. As the frequency increased, only a small amount of perturbation was sufficient to affect the natural frequencies of a structure. Using the interval analysis method, the variation of the natural frequencies from their deterministic value increased as the frequency increased. An ergodic hypothesis was used to examine the responses statistics of structures with uncertainty. Three structures have been computationally studied corresponding to two plates coupled by springs, an L-shaped plate and a frame plate structure. Uncertainty has been generated for the two coupled plates by locating the springs randomly across the surface of the two plates. For the L-shaped plate and a frame plate structure, uncertainty was generated by randomly positioning small masses across the plates. Using the ergodic hypothesis, the frequency averaged response on one member of an ensemble is compare with the ensemble averaged response. It was found that the ensemble averaged response was well predicted by a frequency averaged response of a single ensemble member. The width of the frequency averaging band was shown to have a large influence on the quality of the match between the frequency and ensemble averaged responses. Results were significantly improved using a frequency averaging bandwidth which varies proportionally to frequency. Finally, experiments have been conducted on an L-shaped plate, a frame plate structure and a vehicle to validate the computational results for the natural frequency and response statistics.

The use of vibration as an exercise intervention offers new possibilities for coaches, clinicians, and strength and conditioning practitioners. It appears that muscle activation by means of vibration may induce improvements in strength and power similar to those observed with conventional strength training. Furthermore, vibration is thought to affect the neuromuscular functions that regulate muscle stiffness. There has been preponderance in the literature to assume that the stiffness properties of the muscle affect muscle function, which in turn affects functional performance. Improving functional performance is a major goal for recreational to elite athletes. However, improving the performance of well-trained athletes, especially whilst engaged in in-season training, is challenging, as the training status of such athletes is near optimal. Furthermore, training and playing schedules usually do not allow for adequate training frequencies. Therefore, the application of in-season vibration training may offer a means by which substantial loading can be placed upon the athlete with minimal interference to the weekly schedule. Consequently, the aims of this thesis were to: 1) determine the reliability of a new method to measure the stiffness of the knee extensor muscles; 2) investigate the relationship between knee extensor stiffness, strength, power, and speed; and 3) examine the effect six weeks of squat training with and without whole body vibration (WBV) has on knee extensor stiffness, strength, power, and speed.The reliability of a new method to measure the stiffness of the knee extensors was assessed. The within trial variation (coefficient of variation [CV] - 5.41-7.45%) for all five loads (30, 40, 50, 60, and 70% one-repetition-maximum [1RM]) and test-retest reliability (intra-class correlation coefficients [ICC] - 0.92-0.96) were deemed acceptable. Thirty semi-elite male rugby union players were assessed on sprint speed, squat strength, countermovement-jump (CMJ), and drop-jump (DJ) performance to investigate their relationships to knee extensor stiffness. Knee extensor stiffness was found to have no significant relationship to any of the functional performance measures (r = -0.16-0.17). On the basis of these findings it was suggested that the relationship of the knee extensor stiffness to functional performance was not significant (P>0.05). It was suggested that either the postural requirements of the test were inappropriate, or the knee extensor muscles were not the most suitable muscle group to measure.Immediately after the testing session described above, subjects began a six-week intervention of squat training with or without WBV. The percentage change over the six-week intervention for the stiffness and performance data were calculated and compared to determine if differences between training interventions were significant (P<0.05). The mean percentage change in knee extensor stiffness (average load of 30, 40, 50, 60, and 70% 1RM) for the squat only and squat vibration group were -4.18% and -6.59%, respectively. Non-significant mean percentage changes in squat strength (1.32 and -0.50%), CMJ height (-7.92 and -1.47%), DJ reactivity co-efficient (1.25 and -3.54%), and sprint times over 5, 10, and 20 m (range = -0.86 to -1.16% and 0.54 to -1.88%) were observed for the squat only and squat vibration groups, respectively. Squat training with and without WBV was capable of maintaining, but not improving knee extensor stiffness, strength, power, and speed during a six-week in-season training cycle.

Whole body vibration (WBV) is a mode of exercise by which an individual stands on a vibration platform that may be oscillating and therefore creating vertical displacement which affects gravitational forces acting upon the whole body. Manipulations of platform amplitude or frequency can affect the rate of change of the WBV (i.e. acceleration) acting upon an individual. The specific influences of frequency or amplitude, however, are unknown. The aim of the study, therefore, was two fold; (1) to identify chronic WBV effects of neuromuscular performance within a community dwelling older adult sample, and; (2) to identify WBV methods that would elicit chronic neuromuscular performance changes within such a sample. The study incorporated a randomised controlled experimental design to examine the aim. Seventy-three community dwelling older adults freely consented to the requirements of the study (mean age = 72.0 years). Neuromuscular performance was quantified with the 5-Chair Stands test, the Timed Up and Go (TUG) test and the Tinetti test. Health Related Quality of Life (HRQOL) was qualified with the SF-36 Health Survey. A six week WBV intervention significantly changed the quantifiers of neuromuscular performance in a community dwelling older adult sample. The WBV intervention significantly reduced time taken to complete the 5-Chair Stands test (p <.05) and the TUG test (p <.05). The six week WBV intervention significantly improved Tinetti test scores (p <.05). The six week WBV intervention significantly improved all components of HRQOL. For the 5-Chair Stands test, a three WBV sessions per week intervention elicited significantly larger (p <.05) neuromuscular performance gains than a two WBV sessions per week intervention in the target sample. For the TUG test, a three WBV sessions per week intervention elicited significantly larger (p <.05) neuromuscular performance gains than a zero and one WBV session per week intervention in the target sample. A significant difference (p <.05) was found between pre-test and post-test Tinetti test scores for all WBV intervention groups. There was an insignificant difference (p >.05) found within the control group of community dwelling older adults for the Tinetti test. Detraining effects were observed three weeks after the cessation of the six week WBV intervention for the three WBV sessions per week group. Neuromuscular performance reduced after the detraining period. Vibration platform dynamics (manipulated frequency and controlled amplitude) showed that gravitational forces created by the WBV were safe since no injuries were associated with the intervention and since participant compliance was 100% during the six week WBV intervention. The methods of this study showed a chronic WBV intervention to be a safe and easily administered exercise to improve neuromuscular performance and HRQOL of a community dwelling older adult sample. Specifically, WBV could be used as a safe and effective tool to improve aspects of normal daily function such as body balance and gait speed.

This thesis documents a PhD level research program, undertaken at the Industrial Institute Swinburne, Swinburne University of Technology between the years of 1997 and 2000. The research program investigated electromagnetic energy regenerative vibration damping; the process of recovering energy from damped, vibrating systems. More specifically, the main research objective was to determine the performance of regenerative damping for the application of vehicle suspension systems. This question emerged due to the need for continuous improvement of vehicle efficiency and the potential benefits possible from the development of regenerative vehicle suspension. It was noted, at the outset of this research, that previous authors had undertaken research on particular aspects of regenerative damping systems. However in this research, the objective was to undertake a broader investigation which would serve to provide a deeper understanding of the key factors. The evaluation of regenerative vibration damping performance was achieved by developing a structured research methodology that began with analysing the overall requirements of regenerative damping and, based on these requirements, investigated several important design aspects of the system. The specific design aspects included an investigation of electromagnetic machines for use as regenerative damping devices. This analysis concentrated on determining the most promising electromagnetic device construction based on its damping and regeneration properties. The investigation then proceeded to develop an 'impedance-matching' regenerative interface, in order to control the energy flows in the system. This form of device had not been previously developed for electromagnetic vibration damping, and provided a significant advantage in maximising energy regeneration while maintaining damping control. The results from this analysis, when combined with the issues of integrating such a system in vehicle suspension, were then used to estimate the overall performance of regenerative damping for vehicle suspension systems. The methodology and findings in this research program provided a number of contributing elements to the field, and provided an insight into the development of regenerative vehicle systems. The findings revealed that electromagnetic regenerative vibration damping may be feasible for applications such as electric vehicles in which energy efficiency is a primary concern, and may have other applications in similar vibrating systems.