The aim of this study is to develop a sound transmission model that can be used to predict the vibration and noise levels of a submerged vessel. The noise transmitted from the mechanical vibrations of the hull of a submarine and the turbulent boundary layer excitation on the submarine are investigated. A simplified physical model of the submarine hull including the effects of bulkheads, end enclosures, ring stiffeners and fluid loading due to the interaction of the surrounding medium is presented in the study. An energy approach, i.e., Statistical Energy Analysis (SEA) is used for the analysis because the characterization of the hull of the structure can be done by a very large number of modes over the frequency range of interest and the deterministic analysis methods such as finite element and boundary element methods are limited to low frequency problems. The application consists of the determination of SEA subsystems and the parameters and the utilization of power balance equations to estimate the energy ratio levels of each subsystem to the directly excited subsystem. Through the implementation of SEA method, the sound pressure levels of the hull of the structure are obtained. In terms of military purposes, the sound levels of the submarine compartments are vital in the aspects of the preserving of submarine stealth.

This thesis introduces, for the first time, a novel 4-bit, metal-oxide-metal (MOM) digital capacitor switching array (MOMDCSA) which has been implemented into a wideband CMOS voltage controlled oscillator (VCO) for 5 GHz WiMAX/WLAN applications. The proposed MOMDCSA is added both in series and parallel to nMOS varactors. For further gain linearity, a wider tuning range and minor phase noise variations, this varactor bank is connected in parallel to four nMOS varactor pairs, each of which is biased at a different voltage. Thus, VCO tuning gain reduces and optimal phase noise variation is obtained across a wide range of frequencies. Based on this premise, a wideband VCO is achieved with low phase noise variation of less than 4.7 dBc/Hz. The proposed VCO has been designed using UMC 130 nm CMOS technology. It operates from 3.45 GHz to 6.23 GHz, with a phase noise of -133.80 dBc/Hz at a 1 MHz offset, a figure of merit (FoM) of -203.5 dBc/Hz. A novel microstrip low-phase noise oscillator is based on a left-handed (LH) metamaterial bandpass filter which is embedded in the feedback loop of the oscillator. The oscillator is designed at a complex quality factor Qsc peak frequency, to achieve excellent phase noise performance. At a centre frequency of 2.05 GHz, the reported oscillator demonstrates, experimentally, a phase noise of -126.7 dBc/Hz at a 100 kHz frequency offset and a FoM of -207.2 dBc/Hz at a 1 MHz frequency offset. The increasing demands have been placed on the electromagnetic compatibility performance of VCO devices is crucial. Therefore, this thesis extends the potential of highly flexible and conductive graphene laminate to the application of electromagnetic interference (EMI) shielding. Graphene nanoflake-based conductive ink is printed on paper, and then it is compressed to form graphene laminate with a conductivity of 0.43×105 S/m. Shielding effectiveness is experimentally measured at above 32 dB as being between 12GHz and 18GHz, even though the thickness of the graphene laminate is only 7.7µm. This result demonstrates that graphene has great potential for offering lightweight, low-cost, flexible and environmentally friendly shielding materials which can be extended to offering required shielding from electromagnetic interference (EMI), not only for VCO phase noise optimisation, but also for sensitive electronic devices.

This master’s thesis deals with the determination of the transmission error in spiral bevel gears and its minimization using tooth profile modification in order to reduce vibrations and noise of transmission systems. Gears are the primary source of vibrations transmitted through the shaft and bearings to the gearbox housing and adjacent surfaces that emit noise into the surrounding space. In order to increase the level of comfort and due to the legislative requirements, increasing emphasis is being placed on reducing the noise and vibrations of machine components, including transmission systems. This leads to the need to identify noise sources and evaluate them in terms of expected acoustic performance. The quality of the gear meshing can be judged by transmission error that is closely related to the noise and vibrations. To evaluate the quality of gears based on transmission error, experimental measurements are used that are costly and require quality equipment. Therefore, it is efficient to determine the expected transmission error already at the design stage using numerical methods. In this work a parametric model of bevel gear geometry and a numerical model for the simulation of gear meshing using FEM software Ansys Mechanical are created in order to determine the transmission error. Based on the transmission error, various load cases and gear modifications designed for transmission error reduction are compared.

This master’s thesis is focused on the compilation of a computational modelling of gear mesh engagement dynamics of a spur gear by MBS approach. The user input is the specific geometry of gears, the operating speed, and the load torque. The output are the forces in the gear engagement and the reaction of the forces in the wheel bearings depending on the change in the stiffness of the gear due to the changing number of teeth in the engagement and the change in the axial distance. This model is characterized by a fast and relatively accurate calculation in the time domain. This means that it can react to changes in parameters during simulation such as axial distance, speed, and torque.