This study investigated the effect of sensor mass, sensor location, and delamination location of different composite structures under dynamic loading. The study pertains to research of the use of accelerometers and dynamic response as a cost-effective and reliable method of structural health monitoring in composite structures. The composite structures in this research included carbon fiber plates, carbon fiber-foam sandwich panels, and carbon-fiber honeycomb sandwich panels. The composite structures were manufactured with the use of a Tetrahedron MTP-8 heat press. All work was conducted in the Cal Poly Aerospace Structures/Composites Laboratory. Initial delaminations were placed at several locations along the specimen, including the bending mode node line locations. The free vibration of the composite structure was forced through a harmonic horizontal vibration test using an Unholtz-Dickie shake system. A sinusoidal sweep input was considered for the test. The dynamic response of the composite test specimens were measured using piezoelectric accelerometers. Measurements were taken along horizontal and vertical locations on the surfaces of the composite structures. Square inch grids were marked on the surfaces to create a meshed grid system. Accelerometer measurements were taken at the center of the grids. The VIP Sensors 1011A piezoelectric accelerometer was used to measure vibration response. The measurements were then compared to response measurements taken from a PCB Piezotronics 353B04 single access accelerometer to determine the effects of sensor mass. Deviations in bending mode natural frequency and differences in mode shape amplitude became the criteria for evaluating the effect of sensor mass, sensor location, and delamination location. Changes in damping of the time response were also studied. The experimental results were compared to numerical models created using a finite element method. The experimental results and numerical values were shown to be in good agreement. The sensor mass greatly affected the accuracy and precision of vibration response measurements in the composites structures. The smaller weight and area of the VIP accelerometer helped to minimize the decrease in accuracy and precision due to sensor mass. The effect of sensor location was found to be coupled with the effect of sensor mass and the bending mode shape. The sensor location did not affect the vibration response measurements when the sensor mass was minimized. Off-center horizontal sensor placement showed the possibility of measuring vibration torsion modes. The effect of delamination changed the bending mode shape of the composite structure, which corresponded to a change in natural frequency. The greatest effect of the delamination was seen at the bending mode node lines, where the bending mode shape was most significantly affected. The effect of delamination was also dependent on the location of the delamination and the composite structure type. The results of this study provided considerations for future research of an active structural health monitoring system of composite structures using dynamic response measurements. The considerations included sensor mass reduction, sensor placement at constraints and bond areas and the presence of damping material.

Existing methods of evaluating the structural system of a building after a seismic event consist of removing architectural elements such as drywall, cladding, insulation, and fireproofing. This method is destructive and costly in terms of downtime and repairs. This research focuses on removing the guesswork by using forced vibration testing (FVT) to experimentally determine the health of a building. The experimental structure is a one-story, steel, bridge-like structure with removable braces. An engaged brace represents a nominal and undamaged condition; a dis-engaged brace represents a brace that has ruptured thus changing the stiffness of the building. By testing a variety of brace configurations, a set of experimental data is collected that represents potential damage to the building after an earthquake. Additionally, several unknown parameters of the building’s substructure, lateral-force-resisting-system, and roof diaphragm are determined through FVT. A suite of computer models with different levels of damage are then developed. A quantitative analysis procedure compares experimental results to the computer models. Models that show high levels of correlation to experimental brace configurations identify the extent of damage in the experimental structure. No testing or instrumentation of the building is necessary before an earthquake to identify if, and where, damage has occurred.

The suspension system in vehicles supports the vehicle's road stability and ride quality by scaling down the vibration responses resulting from road surface's roughness. This research focuses on fatigue life analysis of coil spring component. Static linear analysis is conducted on the 3D model of helical coil spring to investigate deformation and stress responses. Modal analysis evaluates the characteristics of vibration, i.e. natural resonance frequencies and corresponding mode shapes. The stress frequency response is generated after performing the harmonic analysis on the spring. Dynamics and performance of spring are analyzed over practical frequency range of 0 Hz to 200 Hz. Fatigue life estimation of vehicle suspension spring is performed using the stress data obtained from frequency response analysis. The stress-life (S-N) approach is utilized for fatigue life assessment of suspension spring. This durability analysis technique can be utilized in the automotive industry to improve reliability of vehicles. The outcome of this research can contribute in analysis and design of modern smart vehicles. / Master of Science / The suspension system in vehicles supports the vehicle's road stability and ride quality by scaling down the vibration responses resulting from road surface's roughness. This research focuses on the fatigue life analysis of suspension spring component. Initial phase of analysis is conducted to investigate the deformation and stress in 3D model of spring. Dynamics and performance of spring are analyzed over applicable frequency range of 0 Hz to 200 Hz. Fatigue life of vehicle suspension spring is evaluated using stress data from frequency response analysis. This durability analysis technique can be utilized in the automotive industry to improve reliability of vehicles. The outcome of this research can contribute in analysis and design of modern smart vehicles.

Studying the dynamic characteristics and evolution laws of the ballast bed under low-temperature, rain and snow environments has practical significance for the driving stability of railways in alpine. In this paper, a full-scale ballasted track model was constructed in a programmable temperature control laboratory, and the frequency response function (FRF) curves of the ballast bed under different temperature and humidity conditions were measured. Then the vibration characteristics and the evolution laws of the ballast bed under different conditions were analyzed. The longitudinal transfer behavior and the dissipation of the vibration energy in the ballast bed under different humidity and temperature environments were discussed combined with the finite element method. The results show that the influence of temperature on the vibration characteristics of the ballast bed is not significant in the dry and water-rich environments, but the vibration characteristics of the ballast bed in the frozen environment change dramatically with the decrease of temperature. The vibration energy is harder to dissipate in the frozen ballast bed than in the dry and water-rich ballast beds, and the frozen ballast bed is more prone to be sudden damaged when a train passes due to the significant increase in its stiffness. Thus, the performance monitoring and emergency maintenance of the ballast bed in those environments should be strengthened.

Диссертация посвящена проблеме возникновения шума и вибрации от трубопроводных систем многоэтажных зданий. Предложен способ определения вероятности возникновения повышенных вибраций с помощью модального анализа в программном комплексеANSYS Workbench. Представлены результаты численного анализа влияния длины, диаметра и толщины стенки участка трубопровода на изменение значений частот его собственных колебаний с целью прогноза риска возможных резонансных режимов. Выполнены статистический и регрессионный анализы. / The dissertation discusses the occurrence of noise and vibration from the piping systems of multi-storey buildings. A method for determining the probability of excessive vibrations using modal analysis software complex ANSYS Workbench. The results of the digital analysis of influence of length, diameter and thickness of a wall of the pipeline’s section on change of values of frequencies of its natural oscillations are provided. Statistical and regression analyses are made.

Träbyggandet har ökat drastiskt sedan år 1994 då den Europeiska unionen (EU) införskaffade ett byggproduktdirektiv, idag numera ersatt med byggproduktförordningen CPR, Construction Products Regulation. Från att träbyggandet tidigare främst inkluderat bostadsbyggande kan nu även föreskrivna funktioner godkännas för högre byggnader. Trämaterialets förmåga att binda koldioxid och utveckling av korslimmat trä, förkortat KL-trä, är två bidragande faktorer till att trä idag är ett uppmärksammat byggmaterial. Mer användning av trä i höga byggnader kan dock, på grund av dess låga vikt och styvhet, medföra känsligheter mot dynamisk vindpåverkan vilket kan vara en avgörande faktor vid dimensionering. Förhöjda accelerationsnivåer är en konsekvens av de dynamiska lasterna vilket som påföljd kan ha en negativ effekt på brukarna av byggnaden. I följande examensarbete studeras denna problematik för en standardiserad byggnad. Syftet med examensarbete är att undersöka hur implementering och användning av trä i en hög byggnad påverkar byggnadens dynamiska respons och koldioxidutsläpp. Studien fokuserar på att undersöka hur accelerationsnivåerna ser ut vid användning av konstruktionssystem som är helt eller delvis av trä samt vilket förändrat klimatavtryck detta medför jämfört med en standardiserad betongbyggnad. I första delen av fallstudien studeras accelerationsnivåerna för olika alternativa konstruktionssystem där majoriteten av stabiliseringen nyttjas genom stabiliserande skivor internt och externt i byggnaden. I fallstudiens andra del används resultaten från första delen för att iterativt skapa en modell med lägst möjliga koldioxidavtryck och som samtidigt uppfyller acceptabla accelerationsnivåer enligt ISO 10137. De studerade strukturerna modelleras upp i Finita Element programvaran FEM-Design 20 utifrån en framtagen grundmodell baserad på tidigare litteraturstudie. I programvaran utförs en modalanalys för att erhålla egenfrekvenser och svängningsmoder för de studerade strukturerna. Med dessa ingångsvärden beräknas accelerationsnivåerna för samtliga strukturer enligt riktlinjer i EKS11 och SS-EN 1991-1-4 samt jämförs med acceptabla accelerationsnivåer i ISO 10137. Med erhållna resultat används en iterativ process för att ta fram en struktur med minsta möjliga koldioxidavtryck. Klimatavtrycket jämförs med den standardiserade betongbyggnaden genom att beräkna och jämföra mängden koldioxidekvivalenter.  Resultatet visar att det är mest fördelaktigt att nyttja intern stabilisering för att erhålla högre egenfrekvenser och lägre accelerationsnivåer. Strukturer som nyttjar extern stabilisering visar förhöjda accelerationsnivåer med   jämfört med intern stabilisering. Dock visar användning av intern stabilisering att det är större sannolikhet att erhålla roterande svängningar som första svängningsmod, detta innebär att de stabiliserande väggarna bör adderas till strukturen med försiktighet. Användning av kombinerad intern- och extern stabilisering visar ingen påtaglig fördel, dock visar resultatet att sammanhängande skivor som bildar en stabiliserande kärna bidrar till en markant ökning i byggnadens styvhet. Den modell som tagits fram med minst klimatavtryck har ett pelar-balksystem i limträ med KL-träskivor i bjälklag och som stabilisering i byggnadens centrala delar. Beräkning av byggnadernas koldioxidavtryck visar en reduktion på  , störst reduktion fås för bjälklagen. / Since year 1994, timber construction has increased dramatically due to that the European Union (EU) acquired a construction product directive, later replaced by the Construction Products Regulation (CPR). Timber construction has previously mainly included housing construction but is nowadays also used for high-rise buildings, this due to that the prescribed properties now can be approved for taller buildings. Two contributing factors to making timber a popular building material is its ability to bind carbon dioxide and the development of cross-laminated timber. On the other hand, using more timber in high-rise buildings can lead to sensitivities to dynamic wind loading due to its low weight and stiffness. This can be a decisive factor during design. Increased acceleration levels are a consequence of the dynamic loading which can have a negative effect on the users of the building. In following thesis this problem is studied for a standardized building. The purpose of the thesis is to investigate how implementation and the use of timber in high-rise buildings affects the building’s dynamic response and carbon dioxide emissions. The main focus is to study how the acceleration levels vary when using construction systems entirely or partly of timber and what carbon footprint this entails, compared to a standardized concrete building. In the first part of the case study, the acceleration levels for different construction systems are studied, where the majority of the stabilization is used internally and externally in the building. In the second part of the case study, the results from the first part are used to iteratively produce a model that have the lowest possible carbon footprint, as well as acceptable requirements regarding acceleration levels is achieved according to ISO 10137. The studied structures are modeled in the Finite Element software FEM-Design 20 based on a base model from a literature study. A modal analysis is performed in the software to obtain natural frequencies and mode shapes for the studied structures. With these input values, the acceleration levels can be calculated according to the guidelines in EKS 11 and SS-EN 1991-1-4, and then compared with acceptable acceleration levels in ISO 10137. With the results obtained, an iterative process is used to make a model with lowest possible carbon footprint. Lastly, the carbon footprint is compared with the standardized concrete building by calculating and comparing the amount of carbon dioxide equivalents.  The results show that it is most beneficial to use internal stabilization in order to obtain higher natural frequencies and lower acceleration levels. Structures using external stabilization show increased acceleration levels by   compared to internal stabilization. However, the use of internal stabilization shows that rotational mode shapes are more likely to be obtained as the first mode shape, this means that the stabilizing walls should be added to the structure with caution. The use of a combination of both internal and external stabilization shows no significant improvements. However, the results show that continuous walls forming a central core contributes to a significant increased stiffness for the structure, compared to separately placed walls. The final model with the lowest possible carbon footprint has a column-beam system in glulam with cross-laminated timber in the floors, and as stabilization in the central parts of the building (core). Calculation of the building’s carbon footprint shows a reduction of  , the largest reduction is achieved in the floors.

This work is focusing to study the structural behavior of Composite Overwrapped Pressure Vessels (COPVs). These COPVs are found in many engineering applications. In the aerospace field, they are installed onto spaceships and aid the reorientation of the spacecraft in very far and airless, therefore frictionless, orbits to save energy and fuel. The intent of this research is to analyze the difference in performance of both perfectly intact and purposely damaged tanks. Understanding both the source and location of a structural fault will help NASA engineers predict the performance of COPVs subject to similar conditions, which could prevent failures of important missions. The structural behavior of six tanks is investigated by means of experimental modal analysis. Knowledge of statistical signal processing methods allows to sort out and extract meaningful features from the data as to gain understanding of the performance of the structures. Structural identification is carried out using Narrow Band and Broad Band algorithms. A comparison through correlation tables and figures presents the differences in natural frequencies, mode shapes and damping ratios of all structures. A careful analysis displays the deviation of these modal parameters in the damaged tanks, highlighting the evident structural defects.

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Utilization of power electronics based controllable systems (or devices) in transmission systems has opened new opportunities for the power industry to optimize utilization of the existing transmission systems, and at the same time to keep high system reliability and security. As a member of these controllable systems, Voltage Source Converters-based High Voltage direct current (VSC-HVdc) systems have the ability to rapidly control the transmitted active power, and also to independently exchange reactive power with transmissions systems. Therefore, VSC-HVdcs with a suitable control scheme can offer an alternative means to enhance transient stability, to improve power oscillations damping, and to provide voltage support. An interesting application of this system is the analysis of a power system when a VSC-HVdc is connected in parallel with ac transmission lines. This thesis presents the derivation of control strategies to damp power oscillations, to enhance the transient stability and to provide voltage support for a VSC-HVdc. The thesis also formulates a multichoice control strategy and its application when the VSC-HVdc is connected in a synchronous system. The control strategy for enhancing transient stability is based on the theory of Control Lyapunov Function. The control strategy for increasing the damping is based on Linear Analysis. A very effective well known way to increase damping in the system is modulating the active power through the HVdc. However, besides the control of active power, the thesis explores an alternative way to mitigate power oscillations by controlling the reactive power. This condition might be very useful when the dc link in the VSC-HVdc system is out of service, but the converter stations are in operating conditions. A simple model of VSC-HVdc is considered in order to test the control strategy. The model represents the VSC-HVdc as an element in the power system that provides adequate interaction with other systems elements. The model is intended for analysis of power flows and electromechanical transients. It is then sufficient to consider the power frequency components of voltages and currents represented by phasors that vary with time during transients. The model is valid for symmetrical conditions, i.e. positive sequence phasors are used for the representation of the electrical state. / QC 20101117