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Measurements and predictions of railway-induced vibrations are becoming a necessity in today’s society where land scarcity causes buildings to be put close to railway traffic. The short distances mean an increased risk of the indoor vibration and noise disturbances experienced by residents. In short, the scope of the project is to investigate the transmission loss and vibration level decrease across various junction geometries. The junctions are modelled in both the Finite Element Method (FEM) and the Dynamic Stiffness Method (DSM). Resonances are avoided when possible by using semi-infinite building components. A two-dimensional model that included Timoshenko beams was set up by Wijkmark [1] and solved using the variational formulation of the DSM by Finnveden [2]. The model is efficient and user-friendly but there is no easy way to adjust the junction geometry since the depths of the walls and the floor slabs are the same. From that study, the current topic was formulated. The results presented in this paper indicate that both the Euler-Bernoulli DS model and the three-dimensional FE model have good potential in describing the vibration transmission across the different junction geometries. The two modelling types show more similar results in the analyses of the bending wave attenuation than in the analyses of the quasilongitudinal wave attenuation. One of the probable causes is that the set length of the Perfectly Matched Layers (PML) is not sufficient at such low frequencies. Larger PMLs require bigger geometries that lead to an increase of the computational time. The other proposed reason is the fact that bending waves are created above the asymmetrical junction when the lower beam is excited by a vertical harmonic force. The flexural displacements are neglected in those cases. The results however, were good enough to be satisfactory. Three junction models were investigated and the attenuation is the highest for both wave types in the case with a beam pair attached to the “middle” of an infinite plate. The attenuation is the second highest across the edge of a semi-infinite plate and the lowest across a junction corner of a semi-infinite plate. As part of the suggested future work, the wave transmission between beam and plate needs to be investigated when Timoshenko beams are included in the DS model. In the Euler-Bernoulli beam theory the cross-section remains perpendicular to the beam axis, which is different to the behaviour of solid elements in FEM.

Structure borne sound can travel multiple paths from one office to another and choosing to sound insulate a specific building element can be difficult since all the building elements are connected together and form a coupled system. The current approach by engineers when investigating transmission paths between spaces in a building is using a computer model and assuming that the junctions are firmly clamped or free. Standardized measuring methods includes a large amount of measuring points on each side of a junction and excitation over large areas. This study intends to investigate if it is possible to gain valuable information with a small amount of measuring points in a field measurement by comparing the data with an analytical model and a finite element model. The field measurement consisted of excitation from an impulse hammer from two excitation points and three accelerometers placed on each side of the junctions and on both sides of the separating wall. The measurement took place in a office building, with no information about the structure other than length, width and thickness of the elements.The reduction over the junctions varied with frequency and no general conclusion could be made about the transmission paths. The results showed high vibration reduction over the junction in low frequencies which then decreased in higher frequencies. Measurement results in low frequencies coincided with the analytical model, that vibration reduction is high over a junction for lighter separating walls in low frequencies and decrease quickly as frequency increases. Different results over each junction was obtained depending on excitation point, which indicates that there is flanking transmission along with the fact that it is a complex coupled system. / Strukturburet ljud kan färdas flera olika vägar från ett kontor till ett annat och att ljudisolera en specifik vägg kan vara svårt då alla byggnadselement är ihopkopplade och skapar ett kopplat system. Den nuvarande metoden ingenjörer använder för att undersöka transmissionsvägar mellan rum är att skapa modeller i datorprogram där antaganden att byggnadselementen är fast inspända eller fritt upplagda är gjorda. Standardiserade mätmetoder använder sig av en stor mängd mätpunkter på båda sidor om knutpunkterna och excitationer över stora ytor. Den här studien avser att undersöka möjligheten att erhålla värdefull information med ett fåtal mätpunkter i en fältmätning genom att jämföra den samlade mätdatan med en analytisk modell och en FEM modell. Fältmätningen består av excitation med en impulshammare i två excitationspunkter och tre accelerometrar på vardera sida om knutpunkterna och båda sidor om skiljeväggen. Mätningen utfördes i en kontorsbyggnad, utan någon information om strukturen förutom längd, bredd och tjocklek på byggnadselementen.Reduktionen över knutpunkterna varierade i frekvens och inga generella slutsatser kunde göras angående transmissionsvägar. Resultaten visade hög reduktion i vibrationsskillnad över knutpunkterna i låga frekvenser vilket minskade med ökad frekvens. Mätningsresultaten stämde överens med den analytiska modellen i låga frekvenser, med avseende på att reduktionen över knutpunkter med lätt skiljevägg är hög i låga frekvenser och avtar med ökad frekvens. Resultaten över knutpunkterna var beroende på val av excitationspunkt vilket indikerar att mätresultaten innehåller flankerande transmissioner och att det är ett komplext kopplat system.

As human dependence on electronic devices grows, there is an emerging need on finding sustainable power sources for low power electronics and sensors. One of the promising possibilities in this space is the human body itself. Harvesting significant power from daily human activities will have a transformative effect on wearables and implantables. One of the main challenges in harvesting mechanical energy from human actions is to ensure that there is no effect on the body itself. For this reason, any intrusive mechanism will not have practical relevance. In this dissertation, novel non-intrusive energy harvesting technologies are investigated that can capture available energy from body, motion, and surroundings. Energy harvesting from the body is explored by developing a wrist-based thermoelectric harvester that can operate at low-temperature gradients. Energy harvesting from motion is investigated by creating a backpack and shoe sole. These devices passively store kinetic energy in a spring that is later released to a generator when it is not intrusive to the user kinematics. Lastly, energy harvesting from immediate surroundings is investigated by designing a two degree of freedom vibration absorber that is excited by electromagnetic fields found in common household appliances. These novel solutions are shown to provide consistent electrical power from wasted energy. Harvester designs are extensively modeled and optimized device architectures are manufactured and tested to quantify the relevant parameters such as output voltage and power density. / Doctor of Philosophy / Energy harvesting is the action to transform energy in the form of heat, relative motion, light, etc. into useful electrical energy. An example of an energy harvester is a solar cell which converts energy in the form of light to electricity. Our body consumes a considerable amount of energy to maintain our body temperature and achieve everyday movements, i.e., walking, jumping, etc. The purpose of this research was to fabricate, model and test wearable energy harvesters in the form of a backpack, a shoe sole, a watch, and a cantilever beam to charge mobile electronics on the go. Electrical energy is harvested from human motion by using the relative displacement between the human torso and a payload. Similarly, the ankle joint is used to produce electricity by using the relative rotation between the foot and shank. The difference in temperature between the ambient air and the human body is used to generate enough electricity to power a wrist watch. Finally, energy is harvested from everyday surroundings by using a cantilever beam which absorbs magnetic fields coming from power cords and able to power sensors.

This work addresses two primary topics related to vibrations in structures. The first topic is the use of a spatially distributed sensor network for localization of vibration events. I use a received signal strength (RSS) framework that presumes exponential energy decay with distance to the source. I derive the Cramér-Rao bound (CRB) for this parameter estimation problem, with the unknown parameters being source location, source intensity, and the energy dissipation rate. In this framework, I show that the CRB matches the variance of maximum likelihood estimators (MLEs) in more computationally expensive Monte Carlo trials. I also compare the CRB to the results of physical experiments to test the power of the CRB to predict spatial areas where MLEs show practical evidence of being ill-conditioned. Supported by this evidence, I recommend the CRB as a simple measure of localization accuracy, which may be used to optimize sensor layouts before installation. I demonstrate how this numerical optimization may be performed for some regions of interest with simple geometries. The second topic investigates modal vibrations of multi-body structures built from simple one-dimensional elements, with networks of elastic strings as the primary example. I introduce a method of using a nonlinear eigenvalue problem (NLEVP) to express boundary conditions of the vibrating elements so that the (infinitely many) eigenvalues of the full structure are the eigenvalues of the finite-dimensional NLEVP. The mode shapes of the structure can then be recovered in analytic form (not as a discretization) from the corresponding eigenvectors of the NLEVP. I show some advantages of this method over dynamic stiffness matrices, which is another NLEVP framework for modal analysis. In numerical experiments, I test several contour integration solvers for NLEVPs on sample problems generated from string networks. / Doctor of Philosophy / This work deals with two primary topics related to vibrations in structures. The first topic is the use of vibration sensors to detect movement or impact and to estimate the location of the detected event. Sensors that are close to the event will record a larger amount of energy than the sensors that are farther away, so comparing the signals of several sensors can approximately establish the event location. In this way, vibration sensors might be used to monitor activity in a building without the use of intrusive cameras. The accuracy of location estimates can be greatly affected by the relative positions of the sensors and the event. Generally, location estimates tend to be most accurate if the sensors closely surround the event, and less accurate if the event is outside of the sensor zone. These principles are useful, but not precise. Given a framework for how event energy and noise are picked up by the sensors, the Cramér-Rao bound (CRB) is a formula for the achievable accuracy of location estimates. I demonstrate that the CRB is usefully similar to the location estimate accuracy from experimental data collected from a volunteer walking through a sensor-rigged hallway. I then show how CRB computations may be used to find an optimal arrangement of sensors. The match between the CRB and the accuracy of the experiments suggests that the sensor layout that optimizes the CRB will also provide accurate location estimates in a real building. The other main topic is how the vibrations of a structure can be understood through the structure's natural vibration frequencies and corresponding vibration shapes, called the "modes" of the structure. I connect vibration modes to the abstract framework of "nonlinear eigenvalue problems" (NLEVPs). An NLEVP is a square matrix-valued function for which one wants to find the inputs that make the matrix singular. But these singular matrices are usually isolated---% distributed among the infinitely many matrices of the NLEVP in places that are difficult to predict. After discussing NLEVPs in general and some methods for solving them, I show how the vibration modes of certain structures can be represented by the solutions of NLEVPs. The structures I analyze are multi-body structures that are made of simple interconnected pieces, such as elastic strings strung together into a spider web. Once a multi-body structure has been cast into the NLEVP form, an NLEVP solver can be used to find the vibration modes. Finally, I demonstrate that this method can be computationally faster than many traditional modal analysis techniques.

Hand transmitted vibration (HTV) is one of the most common hazards faced by workers in the construction industry. A major source of HTV is hand held percussion tools, such as pneumatically driven chipping hammers and rock drills. This thesis presents a new approach to measuring the vibration from these tools using an experimental hand arm model to which the tools are attached. The experimental hand-arm model has been designed to have similar dynamic characteristics to that of a human hand-arm system. This approach addresses the issue of repeatability as HTV measurements suffer from variability between cases. The measured acceleration of the hand-arm system is in range or close to range of the measured accelerations of the test subjects with superior repeatability. Further, the thesis presents a nonlinear numerical model of a pneumatic impact hammer. Fundamentally, the numerical model was made up of two different sub-models, 1) a fluid flow model and 2) a structural dynamic model. The fluid flow model was based on the equations for mass flow rate of air though a bleed orifice assuming an isentropic process. The second sub-model deals with modeling the structural components of the impact hammer consisting of the major hammer like the center body, handle, piston and chisel as well as the human hand and the ground. Time domain simulations of the hammer were carried out by using a state space formulation to get displacements, velocities and accelerations of the each component as well as the exhaust jet velocities. Experiments were carried out to measure the handle response and exhaust jet velocities as well as pressure profiles. The results obtained from the numerical model were then validated using these experimental results. Finally, a parametric study using the numerical model was carried out to explore different vibration control techniques. / Master of Science

Tesis por compendio / Real Herráiz, JI. (2015). CONTRIBUTION TO THE MODELIZATION, ANALYTICAL AND NUMERICAL, OF GENERATION AND PROPAGATION OF VIBRATIONS ORIGINATED BY RAILWAY TRAFFIC. ANALYSIS OF MITIGATION PROPOSALS [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/52247 / Compendio