SIMULASI GETARAN PADA RODA DAYA YANG DIDUKUNG BANTALAN MAGNET PERMANEN

Object such as Fly Wheel, it is bound to have natural frequency as one of it is vibration parameter. If excitation is applied at the same frequency as natural frequency, then resonance will occur. As the result, excess deformation on the structure can occur. In this research, the natural frequency from the Fly Wheel was calculated. The calculation was conducted with the help of Finite Element on a software. Followed with the calculation of the working frequency range and structure deformation as a result of the vibration that occurred. The deformation calculation was conducted because deformation will effect the size (dimension) between the wheel and the housing.  However, the simulation that was conducted only on the first five vibration mode. This Research is consisted of four stages. The four stages are literature study, fn analysis of a basic road, preliminary measurement mechanical battery and fn analysis of the mechanical battery. Preliminary measurement was conducted because the mechanical battery that was analysed is already constructed in Construction Laboratory, Department of Mechanical Engineering, University of Sam Ratulangi.The Result of the simulation indicated that five vibration mode occurred on these spinning frequency are 32.21 Hz, 88.71 Hz, 173.93 Hz, 287.48 Hz, and 429.32 Hz. Followed, the biggest working range are between vibration mode two to three. Finally, deformation that effected the size between Fly Wheel and housing bearing it is on two, three and five.Key Words: Fly Wheel, Natural Frequency, Vibration Simulation with Software

Low frequency structural and acoustic responses of a submarine hull under eccentric axial excitation from the propulsion system

A model to describe the low frequency dynamic and acoustic responses of a submarine hull subject to an eccentric harmonic propeller shaft excitation is presented. The submarine is modelled as a fluid-loaded, ring stiffened cylindri-cal shell with internal bulkheads and conical end caps. The stiffeners are introduced using a smeared approach. A harmonic axial force is introduced by the propeller and is transmitted to the hull through the shaft. It results in excita-tion of the accordion modes only if the force is symmetrically distributed to the structure. Otherwise the excitation can be modelled as the sum of a distributed load and a moment applied to the edge of the hull. This leads to excitation of the higher order circumferential modes that can result in high noise signature. Structural and acoustic responses are presented in terms of deformation shapes and directivity patterns for the radiated sound pressure. Results for the case of purely axisymmetric excitation and the case in which an eccentricity is introduced are compared

What really caused the ROKS Cheonan warship sinking?

This paper is concerned with the sinking of the Korean naval warship (ROKS Cheonan) and the reported spectra of the seismic signals recorded at the time of the incident. The spectra of seismic signals show prominently amplitude peaks at around 8.5 Hz and its harmonics. These frequencies were explained with the vibrations of a water column due to an underwater explosion. This explanation is highly doubtful and concerns about its validity have already been raised in the scientific community. In this work an alternative explanation is presented: it is shown that the recorded seismic spectra are consistent with the natural frequencies of vibrations of a large submarine with a length of around 113 m. This finding raises the possibility that the ROKS Cheonan sunk because of the collision with a large submarine rather than the explosion of a torpedo or an underwater mine.Peer Reviewe

Acoustic signature of a submarine hull

A model to predict the acoustic signature of a submarine resulting from the radial vibration of the hull under axial excitation is presented. The simplified physical model of the submarine hull includes complicating effects such the presence of bulkheads, end enclosures, ring stiffeners and fluid loading due to the interaction with the surrounding medium. Under an axial symmetric force, only the ‘breathing’ modes of the cylinder corresponding to the n=0 circumferential modes are excited. To show the sound radiation due to the higher order n≥1 modes, a point axial force acting at one end of the shell has been considered. At low frequencies, the structural wavenumbers are generally subsonic. However, due to the finite cylinder, the wavenumber spectrum is a convolution of the spectrum of an infinite structure and a window generating radiation by means of the presence of supersonic components. The effect of the bulkheads on the structural and acoustic responses of the hull is also presented

) Australian Nuclear Science and Technology Organisation (ANSTO)

ABSTRACT The aim of this work is to model the vibrational behaviour of thin plates joined to a stiff orthogonal side plate using the technique of 'roll swaging'. Swage joints are typically found in plate-type fuel assemblies for nuclear reactors. Since they are potentially liable to flow-induced vibrations, it is crucial to be able to predict their dynamic characteristics. It is shown that the contact between the plates resulting from the swage can be modelled assuming a perfect clamp of all the degrees of freedom but the rotational around the axis parallel to the swage. A modal analysis was performed on different specimens and the values of the first natural frequencies are used to find the equivalent torsional spring stiffness, by matching these frequencies with the results obtained from a finite element model (FEM)

Gallium Nitride (GaN) specific mechanical phenomena and their influence on reliability in power HEMT operation

In den letzten Jahren ist Gallium Nitride (GaN) auf dem Markt für Leistungsbauelemente in größerem Maßstab angekommen, wodurch die Notwendigkeit eines tieferen Verständnisses der grundlegenden Interaktionen im Chip notwendig geworden ist. Umfangreiche Forschung wurde auf dem Gebiet der elektrischen Effekte durchgeführt, da dort die wichtigsten Unterschiede gegenüber Silicon (Si) liegen. Im Gegensatz zur generellen Forschungsrichtung fokussiert sich diese Arbeit auf neue mechanische und thermo-mechanische Phänomene, die bisher in Si Bauteilen nicht vorhanden waren. In Kapitel 3 wird die Wechselwirkung von mechanischer Spannung, Temperatur und elektrischem Feld besprochen. Die physikalischen Effekte, die diese Zustandsgrößen verbinden, werden im Detail erklärt und es wird gezeigt, welche Effekte aufgrund ihrer Größe sicher vernachlässigt werden können und welche einer näheren Untersuchung bedürfen. In Kapitel 4 werden die thermischen Fähigkeiten bei massiver thermischer Überlastung, die durch einen Kurschluss verursacht wird, diskutiert. Der Testaufbau, auf dem die Chips bis zum Ausfall gestresst werden, wird vorgestellt. Anschließend werden die ausgefallenen Bauelemente analysiert und die Grundursache mit Hilfe von der Finite Element Analysis (FEA) und einer umfassenden, detaillierten physikalischen Fehleranalyse erklärt. Zusätzliche Vorschläge für Verbesserungen in diesem speziellen Versagensmodus werden am Ende gegeben. Kapitel 5 gibt Einblicke in die Resonanzphänomene bei GaN. Da GaN piezoelektrisch ist kann es als Aktuator fungieren, um den gesamte Chip in Resonanz zu bringen. Dieses Phänomen ist vermessen worden und wird anschließend durch FEA simuliert. Die Simulation wird dann gegen die Messung validiert, um die Richtigkeit der Simulation sicherzustellen. Aus diesen Simulationen werden Schlussfolgerungen bezüglich der Zuverlässigkeit der beiden am meisten gefährdeten Schichten, der GaN Schicht und Chip Verbindungsschicht, gezogen. Zusätzlich werden am Ende Extremfälle diskutiert, die einen Ausblick auf kommende Chipgehäuse geben sollen.In recent years Gallium Nitride (GaN) has entered the market for power devices on a broader scale, increasing the need for a deeper understanding of fundamental interactions within such devices. Extensive research has been conducted in the field of electric effects since the main differences of GaN over Silicon (Si) lie there. In contrast to this, this thesis will focus on new mechanical and thermo-mechanical phenomena, previously not occurring in Si devices. Chapter 3 will introduce the interactions of the mechanical stress, the temperature and the electric field. The effects connecting these state variables are explained in detail and it will be shown which effects can be neglected and which ones need closer investigations. In Chapter 4 the thermal capabilities under massive thermal overload, caused by a short circuit pulse, are discussed. The setup, which is used to stress the chips until failure, is presented. Failed devices are analyzed extensively by in depth physical failure inspection methods. Root cause analysis is done by means of Finite Element Analysis (FEA) and in depth physical failure analysis, finally enabling to provide suggestions for improvements in this particular failure mode. Chapter 5 will elaborate on resonance phenomena in GaN. Since GaN is piezoelectric it can act as an actuator to resonate the whole chip assembly. This phenomenon is measured in two steps and subsequently investigated by FEA. The Finite Element (FE) simulation results are validated against the measurements to ensure the correctness of the FE model. From these simulations conclusions regarding the reliability of the two most failure prone layers, namely the GaN stack and the die attach layer, are drawn. Additionally extreme cases are discussed giving an outlook on this issue in advanced package assemblies

Configuración óptima de transductores piezoeléctricos para control activo de vibraciones en estructuras delgadas utilizando el método de optimización topológica

En esta tesis, una técnica de optimización novedosa; llamada Método de Optimización Topológica (MOT), es utilizada para proponer una solución a problemas de vibración estructural. Un conjunto de transductores piezoeléctricos en configuración de sensores y actuadores se modelan usando el Método de los Elementos Finitos (MEF). Para esto, se desarrolló un software de simulación que permite realizar análisis estáticos, modales y armónicos con elementos finitos hexaédricos de segundo orden tipo Brick-3D de 20 nodos, con cuatro grados de libertad por nodo, tres de ellos de desplazamientos y uno de voltaje. A partir del modelo numérico, se genera un modelo de control en variables de espacios de estado mediante un conversión matemática que reorganiza los grados de libertad en conjuntos de matrices de estado que relacionan la estructura con los actuadores y sensores. Adicionalmente, se realiza durante la conversión del modelo una reducción modal truncada del sistema a través de un cambio de coordenadas cartesianas a coordenadas modales usando sus vectores propios. Este modelo de espacios de estado es utilizado para formular un problema de optimización que encuentra una distribución topológica óptima de transductores piezoeléctricos sobre la estructura elástica, usando dos funciones objetivo evaluadas paralelamente, que calculan la maximización de la traza del gramiano de controlabilidad y del gramiano de observabilidad. En la solución del problema de optimización se usa un modelo de interpolación de material SIMP (Solid Isotropic Material with Penalization), se definen límites móviles filtrados para resolver el problema con el método de Programación Lineal Secuencial (PLS), y se realiza un análisis de sensibilidad por un método numérico de diferencias finitas de ambas funciones objetivo. Finalmente, un controlador óptimo LQG (Linear-Quadratic Gaussian Regulator) es implementado para verificar el rendimiento del sistema optimizado para un caso de estudio de una viga en cantilever sometida a vibración. Los resultados de simulación con el MEF son verificados por comparación directa con el software comercial ANSYS®, y los resultados de optimización son verificados con análisis energéticos del control, la salida del sensor, y el coeficiente de amortiguamiento del sistema planta-controlador.Abstract: In this thesis, a novel optimization technique; called the Topology Optimization Method (TOM), is used to propose a solution to structural vibration problems. A set of piezoelectric transducers as sensors and actuators are modeled using the Finite Element Method (FEM). To do this, a software was developed that allows simulations of static, modal and harmonic analysis with second-order hexahedral Brick-3D finite elements of 20 nodes, with four degrees of freedom per node, three of them for displacements and one for voltage. From the numerical model, a control model is generated in state-space variables through a mathematical conversion that reorganizes the degrees of freedom in sets of state matrices that relate the structure to the actuators and sensors. Additionally, a truncated modal reduction of the system is carried out during the conversion of the model through a change of cartesian coordinates to modal coordinates using its eigenvectors. This model of state-space is used to formulate an optimization problem that finds an optimal topology distribution of piezoelectric transducers over an elastic structure, using two objective functions evaluated in parallel, which calculate the maximization of the trace of the gramians of controllability and observability. In the solution of the optimization problem, a Solid Isotropic Material with penalization (SIMP) material interpolation model is used, filtered mobile limits are defined to solve the problem with the Sequential Linear Programming (SLP) method, and an analysis of sensitivity with a numerical method of finite differences of both objective functions is performed. Finally, a Linear-Quadratic Gaussian Regulator (LQG) controller is implemented to verify the performance of the optimized system for a study case of a cantilever beam subject to vibration. The results of the simulation with the FEM are verified by direct comparison with the commercial software ANSYS®, and the optimization results are verified with an energy analysis of the control, the sensor output, and the damping coefficient of the plant-controller system.Maestrí

Real-Time Implementation of Time-Varying Surface Prediction and Projection

Spatial augmented reality makes use of projectors to transform an object into a display surface. However, for time-varying, non-rigid surfaces this can prove to be difficult, and often leads to image distortion. In order to avoid this highly accurate measurements of the surface are required. Traditional methods of measuring surface deformations are inadequate due to noise as well as potential sources of time delay, such as projector lag. To get more accurate results, a mass spring model can be used to simulate the dynamics of the time-varying surface. This model can be put into a nonlinear state space form to get a first order differential equation. Numerical integration techniques can then be used to solve the differential equation presented. In order to reduce uncertainty in the model generated a filtering algorithm can be used. Both, the extended Kalman filter (EKF) and the cubature Kalman filter (CKF) are evaluated as potential candidates. To be able to run these filters in real time a reduced order model is developed. This enables the use of fewer mass nodes in the model, allowing for faster compute times. Additionally, to reduce visual error, an optimal node placement algorithm is used. This ensures that the surface generated by the mass spring mesh closely matches the real, curved surface of the system, minimizing error. The EKF and CKF algorithms are implemented onto a hanging cloth system perturbed by an oscillating fan. A parameter identification technique is used to create a model that accurately represents this hanging cloth system. Additionally, noise parameters of the EKF and CKF are adjusted to compensate for modeling errors and sensor noise. Finally, The mean squared error of the EKF and CKF algorithms are compared to evaluate their effectiveness. Both algorithms provide satisfactory results for use in spatial augmented reality applications. However, in all cases tested the CKF is shown to have significantly lower error values. Although the CKF algorithm is shown to be more accurate than its EKF counterpart, its computation time is much larger. However, the computation time required is still within the threshold of being able to perform real-time estimation at up to 100Hz. Furthermore, due to the nature of the construction of the CKF, it can be applied as a multi-threaded workload to significantly reduce computation time. Therefore, the implementation of a CKF algorithm can be used to accurately estimate the positions of a measured surface for use in spatial augmented reality