This thesis describes how to evaluate a first-order approximation of the vibration induced on a beam that is vertically curved and experiences a moving load of non-constant velocity. The curved beam is applicable in the example of a roller coaster. The present research in the field does not consider a curved beam nor can similar research be applied to such a beam. The complexity of the vibration of a curved beam lies primarily in the description of the variable magnitude of the moving load applied. Furthermore, this motion is also variable. This thesis will present how this beam will displace in response to the moving load. The model presented can be easily manipulated as it considers most variables to be functions of time or space. The model will be compared to existing research on linear beams to ensure the unique response of a curved beam.

Resonance frequency detuning (RFD) is a piezoelectric-based vibration reduction approach that applies to systems experiencing transient excitation through the system*s resonance—for example, turbomachinery experiencing changes in rotation speed, such as on spool-up and spool-down. This technique relies on the inclusion of piezoelectric material and manipulation of its electrical boundary conditions, which control the stiffness of the piezoelectric material. Resonance frequency detuning exploits this effect by intelligently switching between the open-circuit (high stiffness) and short-circuit (low stiffness) conditions as the excitation approaches resonance, subsequently shifting the natural frequency to avoid this resonance crossing and limit the response. The peak response dynamics are then determined by the system*s sweep rate, modal damping ratio, electromechanical coupling coefficient, and, most importantly, the trigger (represented here in terms of excitation frequency) that initiates the stiffness state switch. This thesis identifies the optimal frequency-based switch trigger over a range of sweep rates, damping ratios, and electromechanical coupling coefficients. With perfect knowledge of the system, the optimal frequency-based switch trigger decreases approximately linearly with the square of the coupling coefficient. Furthermore, phase of vibration at the time of the switch has a very small effect; switching on peak strain energy is marginally optimal. In practice, perfect knowledge is unrealistic and an alternate switch trigger based on an easily measurable parameter is necessary. As such, this thesis also investigates potential methods using the open-circuit piezoelectric voltage response envelope and its derivatives. The optimal switch triggers collapse to a near linear trend when measured against the response envelope derivatives and, subsequently, an empirical control law is extracted. This control law agrees well with and produces a comparable response to that of the optimal control determined using perfect and complete knowledge of the system.

Light and rapid constructions as well as considerations such as improved line of sight and increased capacity for modern stadium structures make them vulnerable for vibration serviceability problems. These problems are also observed at convention centers, large shopping malls, concert halls and ballrooms. Especially when the individuals in a crowd are involved in some sort of coordinated motion, this type of loading creates the most potential for high levels of vibration. In order to understand the causes of vibration, vibration levels, service and safety levels, Structural Health Monitoring (SHM) can be implemented to track and evaluate performance of a structure during events such as games at football stadia. SHM becomes a critical need especially when decisions such as repair and retrofit are to be made for the structure. The main objectives of this study are a) to determine the impact of vibration to human comfort levels; b) to identify dynamic loading for the coordinated motion; c) to determine the structural performance by means of a detailed model validated using experimental data. In order to achieve these objectives, a football stadium was monitored for three years to establish the vibration levels during different games and different events in each game such as goals, interceptions, playing a particular song. It is seen that certain events and long periods of playing particular songs induced vibration levels that are at the threshold of human comfort based on the design codes. To simulate the crowd motion due to this song, a laboratory study was designed and conducted to experimentally determine the forcing functions due to jumping with the rhythm of the song. The spectral analysis of the stadium data and the song also revealed that the first mode frequency of the stadium and the dominant frequency of the music are very close, creating iv resonance conditions. Further investigative studies were conducted by developing a finite element (FE) model of the stadium, which was validated using the results of the modal analysis from the ambient vibration data. Subsequently, the FE model was employed to simulate forcing functions obtained from the laboratory studies to explore the vibration levels, dynamic response as well as the response of the structure when it is retrofitted by additional elements. In addition, different aspects of model development, with respect to the physical model of the stadium were outlined in terms of design considerations, instrumentation, finite element modeling, and simulating dynamic effect of spectators. Finally, the effectiveness of the retrofit by adding elements to the steel structure of the stadium was explored by simulating the crowd motion with the FE model.

The following thesis document researches into creating a model to represent the behavior of a wind turbine gearbox. This model is developed based on the overall parameters of a NORDEX N90 2.5MW wind turbine developed by a German company Nordex SE. This research focuses on the combination of a flexible body and a multibody dynamics analysis software. This is done through the usage of MSC ADAMS, a multibody dynamic analysis program, and MSC Patran/Nastran, a finite element analysis software, and its associated solver. The model is created to show the vibration patterns of a healthy gearbox with rigid bodies, with a flexible body, and with a defect applied on a particular gear in the planetary gear systems that is representative of the N90 wind turbine. The flexible body incorporation allows for stress analysis of different gear teeth at different locations. Using this model a vibration signature is generated for a specific type of defect.

Impact strength is one of the most important structural properties for a designer to consider, but it is often the most difficult to quantify or measure. A major concern for composite structures in the field is the effect of foreign objects striking composites because the damage is often undetectable by visual inspection. The objective for this study was to determine the effectiveness of using dynamic testing to identify the existence of damage in a small scale composite wing design. Four different impact locations were tested with three specimens per location for a total of 12 wings manufactured. The different impact locations were over the skin, directly over the rib/spar intersection at the mid-span of the wing, directly over the middle rib, and directly over the leading edge spar. The results will be compared to a control group of wings that sustain no damage. The wing design was based on an existing model located in the Cal Poly Aerospace Composites/Structures lab. The airfoil selected was a NACA 2412 airfoil profile with a chord length of 3 inches and a wingspan of just over 8 inches. All parts cured for 7 hours at 148°F and 70 psi. The wings were each tested on a shaker-table in a cantilever position undergoing 1g (ft/s2) acceleration sinusoidal frequency sweep from 10-2000 Hz. The 1st bending mode was excited at 190 Hz and the 2nd bending mode was excited at 900 Hz. After the pre-impact vibrational testing each wing was impacted, excluding the control group. To verify the experimental results, a finite element model of the wing was created in ABAQUS. The frequency and impact numerical results and the experimental results were in good agreement with a percent error for both the 1st and 2nd mode at around 10%.

Low back pain is a leading cause of disability and is associated with whole-body vibration exposure in industrial workers and military personnel. The pathophysiological mechanisms by which whole-body vibration causes low back pain have been studied in vivo, but there is little data that improve diagnosis of low back pain. The overall objective of this research was to elucidate diagnostic biomarkers associated with whole-body vibration. Hence, a rat model for vibration-induced inflammatory responses was developed. Von Frey filaments were used to determine the withdrawal threshold of the hind paw as a surrogate behavioral marker for pain. The concentration of nerve growth factor in the serum was measured every four days using an assay as a potential diagnostic biomarker for low back pain. In the first study, whole-body vibration was applied using a modified commercially available device at 8 or 12 Hz every other day for two weeks, following which animals recovered for one week. At the conclusion of the study, intervertebral discs were graded histologically for degeneration. The nerve growth factor concentration increased threefold in the 8 Hz group and twofold in the 12 Hz group and returned to baseline by the end of the recovery period for 12 Hz, but not 8 Hz. Mechanical sensitivity appeared to change over time due to habituation and not any effect of vibration and was inconclusive. There was no difference in intervertebral disc degeneration scores between groups. In the second study, rats were vibrated at 8 Hz every other day for two or four weeks. The concentrations of nine cytokines were determined in the longissimus muscle, spleen, and thymus using a multiplex assay. These cytokines were ranked according to their ability to differentiate vibrated and non-vibrated animals, and classification models were compared. Nerve growth factor serum concentration peaked on day 13, then returned to baseline on day 17. The withdrawal threshold in vibrated animals decreased throughout the study indicating greater sensitivity to the stimulus, a surrogate for increased pain. Several longissimus muscle and spleen cytokines were important in distinguishing vibrated animals from non-vibrated, while thymus cytokines and weeks of exposure were not significant.

<p>An investigation of the steady state response of a non-linear system provided with an impact vibration absorber is made. The term non-linear in the present case refers to a system in which the spring restoring force is bi-linear./p><p> The effect of two main parameters viz. clearance d o (i.e. the free path of travel of the mass particle) and mass ratio μ = m/M (i.e. mass ratio between the mass particle and the primary system) on amplitude of vibration of the system has been investigated experimentally over a range of frequency.</p> <p>A numerical analysis of the problem is made with the aid of a digital computer to supplement the experimental results.</p> <p> It has been found that with proper choice of parameters an impact vibration absorber is effective in reducing vibration level of a nonlinear system undergoing sinusoidal excitation.</p> / Thesis / Master of Engineering (MEngr)

<p> Vibration Analysis (VA) is a key technique used for maintenance and fault detection of vibrating machinery. The purpose of maintenance is to analyze how well the machinery is operating within its target parameters, while fault detection is done to diagnose and locate a fault that might be developing on the machinery.</p> <p> If we consider s(n) to be the true signal from a rotating system and e(n) to be the additive noise corrupting the signal, then the observed signal is x(n) = s(n) + e(n). If s(n) is composed of a main driving frequency sm(n) and summed fault frequencies sf(n), then fault detection is the study of sf(n). In fault detection, we eliminate e(n) as much as possible so that sf(n) can be isolated and studied.</p> <p> This thesis presents a technique based on cross-correlation, utilizing a network of sensors, to eliminate e(n) from the measurements, preserving just the correlated frequency content. This is extended to provide a means of localizing the source of the frequency content, based on the relative strengths of the members of the complete set of cross-correlations between all sensors. This technique has been shown to be able to extract a signal buried by noise, in situations where the traditional FFT fails.</p> <p> To enable this, a new VA system has been developed. This introduces new wireless vibration sensors as well as a data capture unit capable of providing real-time VA data to technicians. The system can simultaneously capture data from eight sensors, so the data can be used not only for traditional VA techniques, but also in conjunction with the cross-correlation technique described above. This system is now commercially available and in use by dozens of technicians around the world. </p> / Thesis / Doctor of Philosophy (PhD)

<p> Inflatable structures have attracted much interest in space applications. The three main components of inflatable satellites are inflatable struts, an inflatable torus as the structural support component, and some sort of lens, aperture, or array housed inside the boundary of the torus. This project is devoted towards understanding the dynamic characteristics of an inflated torus with a focus on the self-rigidizing torus, SRT, developed by United Applied Technologies.</p> <p> The self-rigidizing torus is manufactured from flat sheets of Kapton® that are formed into curved films with the regular pattern of hexagonal domes. The inflated torus can support its structural shape even when there is no internal pressure.</p> <p> Modal testing is used to determine the dynamic properties of the structure for comparison with the numerical model. The feasibility of using a non-contact in-house fabricated electromagnetic excitation is investigated. The first four, in-plane and out-of-plane, damped natural frequencies and their corresponding damping ratios and modes shapes are extracted and compared with prior experimental studies. A preliminary finite element modal analysis is carried out for a torus made of flat film and the results are compared with prior studies. Kapton 300JP®'s frequency-dependent modulus of elasticity is determined.</p> <p> Owing to the large number of hexagonal domes in the self-rigidizing torus, a simplified sub-structuring technique is used. Each hexagonal dome is replaced with a statically equivalent flat hexagon with the same mass and stiffness as the hexagonal dome. Then the finite element modal analysis of the self-rigidizing torus is carried out for an equivalent torus made of flat film. The geometric nonlinearity and the effect of the follower load on the stiffness are included in this analysis. The methodology is verified through the correlation between the analytical and modal test results of the self-rigidizing torus.</p> / Thesis / Doctor of Philosophy (PhD)

Within the era of the fourth industrial revolution the steel production industry is faced with demands of lower environmental impact and more cost-effective production are some of the challenges faced. To achieve more sustainable and efficient manufacturing processes companies try to digitalize and automate their production to a greater extent. Creating more robust, energy-efficient and adaptable solutions to increase the competitiveness of their company. This master thesis is about reverse engineering an existing solution for vibration measurements used at Alleima Strip. The goal was to create a new in-house solution for vibration measurements according to local programming standards using an ABB AC500v2 CPU paired with a FM502-CMS module. Using vibration measurements as a health indicator Alleima Strip hopes to progress their way of working with maintenance towards being more condition based. The result is a solution for vibration measurements customized for Alleima Strip. The report contains suggestions for improvements of the developed solution as well as ideas for future work.