Equipped with advanced field instruments in the past few decades, oceanographers have been able to comprehend some characteristics of the internal waves(IWs), such as the generation, propagation and energy dissipation, as well as to promote understanding in oceanography and marine ecology affected by IWs in the world ocean. Although surface gravity wave and internal wave are two of the most common natural phenomena in the ocean, the interaction between them has not been fully investigated, despite limited theoretical derivations in the literature, nor using laboratory experiments to verify the theory. A series of laboratory experiments were conducted at the National Sun Yen-sen University to study the waveform evolution of continuous IWs propagation on the flat bottom and across a trapezoidal obstacle. Surface waves were generated on a density stratified fluid system in a wave flume, from which IWs were induced indirectly to investigate their wave properties associated with their propagation . The experimental results are then used to determine the maximum depth which could be affected by surface waves in different wave conditions(wave height and period), as well as the amplitude of the IWs induced. The relationship between them are then presented in graphic form. Experiments were also conducted in uniform density and stratified fluid system with a trapezoidal obstacle. The results reveal that (1)long-period surface waves were susceptible to the interaction with the IWs in a stratified system, thus rendering wave height reduction, and (2)short-period surface waves interactions with their IWs counterparts was insignificant, hence yielded wave height similar to that in uniform density fluid system. Moreover, experiments were also conducted to study for long and short period IW propagated over pseudo slope-shelf(using trapezoidal obstacle). The results show that the variation in the IWs significantly affected the strength of internal hydraulic jump and vortices on the front slope and subsequent waveform inversion on the horizontal plateau. For IWs with short period, the horizontal distance on the plateau affected by the IWs was shirter and the total time of wave-topography interaction decreased.

The main aim of this research project is to extend theories of four-wheel-steering as developed by J. Ackermann to include an individually steered four-wheel steering system for passenger vehicles. Ackermann’s theories, including theories available in this subject area, dwell much on vehicle system dynamics developed from what is called single track model and some call it a bicycle model. In the bicycle model, the front two wheels are bundled together. Similarly, the rear wheels are bundled together. The problem with this is that it assumes two front wheels or two rear wheels to be under the same road, vehicle and operating conditions. The reality on the ground and experiments that are conducted are to the contrary. Therefore this study discusses vehicle disturbance rejection through robust decoupling of yaw and lateral motions of the passenger vehicle. A mathematical model was developed and simulated using Matlab R2008b. The model was developed in such a way that conditions can be easily changed and simulated. The model responded well to variations in road and vehicle conditions. Focus was in the ability of the vehicle to reject external disturbances. To generate yaw moment during braking, the brake on the left front wheel was disconnected. This was done because lateral wind generators, as used by Ackermann, were not available. The results from both simulations and experiments show disturbance rejection in the steady state. Copyright / Dissertation (MSc)--University of Pretoria, 2010. / Mechanical and Aeronautical Engineering / unrestricted

Internal waves (IWs) owe their existence to the stratification in the medium. These waves affect acoustic transmission greatly. Impact of these waves on acoustic transmission in deep water is fairly well understood due to better performance of well-celebrated Garrett-Munk (GM) model. However, in shallow waters, predicting these waves is not as easy, because of interactions with the bottom and surface. Hence two experiments, one during October 2002 and the other during October 2004 were conducted to characterize IWs in the shallow waters of northeastern Arabian Sea. The first experiment was carried out during October 2002 south of Gulf of Kutch (GOK) and the second experiment during October 2004 both south and north of GOK. During these experiments CTD moorings were deployed and temperature and salinity (TS) data were collected at 5 seconds interval. CTD Yo-Yo collected vertical profiles of TS at a sampling interval of 2.5 minutes for 3.5 hours during October 2002 and 1 hour during October 2004 experiment. In addition, during the first experiment, currents were measured using a vessel mounted Acoustic Doppler Current Profiler (ADCP), and in both experiments CTD TS profiles were taken from the ship. This data set has been used for characterizing internal waves in the northeastern Arabian Sea. Experiment conducted during October 2002, south of GOK has revealed large tidal ranges. The barotropic tidal range at the experimental site was 1.5m. Current observations made using the vessel mounted ADCP, along the shore and across the shore, showed signs of first mode (baroclinic) oscillations; currents in the top and bottom layers were in opposing directions. They were found to be southwesterly in the top layer and northeasterly in the bottom layer. Time - depth sections of TS profiles from CTD yo-yo data, revealed the presence of high frequency internal waves and solitons overriding on low frequency trend. Moored CTD time series of temperature records showed the presence of internal solitons, which caused a vertical displacement of about 8m in the isotherms, which is equivalent to 3OC change in temperature, in less than 10 minutes. Passage of internal solitons induced vertical mixing causing the mixed layer to deepen by about 10m and current speed increased by about 0.1 m/s. Internal solitons were traveling towards northwest and current vectors suggest that they were generated when the internal tide is reflected from the bottom. Vertical displacement spectra agreed well with GM spectra when solitons were not present. However, when the solitons were present the displacement spectra had higher energy levels compared to the GM spectra. Another experiment was done in October 2004, mainly aimed at characterizing internal solitons and to verify the consistency of the results obtained during October 2002 experiment. This experiment also showed that IWs of both high and low frequency along with internal solitons were present at the experimental site. It was found that internal solitons were more energetic during spring tide than the neap. The observed amplitudes of these solitons were around 12m and were not rank ordered suggesting that the experimental site is close to the generation point. It is believed that, generally, solitons get phase locked to the barotropic tide’s trough and travel. Such phase locking was not observed at the experimental site. They were observed riding on both troughs and crests of barotropic tide. One of the aims of this thesis is to develop a simulation model based on Garrett-Munk steady state internal wave spectrum. Hence, an internal wave model IWAVE was developed to simulate the sound speed structure due to internal waves. Sound speed structure is simulated instead of TS structure, because of their direct utility in sonar range prediction models. Since the GM model is a deep-water and mid-latitude model, it was calibrated to suite shallow-water tropical environment by incorporating the site and region specific parameters. EOFs and Dynamical modes estimated using TS profiles were used to identify the site-specific parameters of the GM model. Values for characteristic mode number and spectral slope used in the GM model are 3 and 2 respectively. However, it was found that they are different in the northeastern Arabian Sea. At this site, the characteristic mode number was found to be 1 and the spectral slope was found to be 3. The modified model was validated against the measured sound speed profiles. In the first case, the first sound speed profile (TS) of the CTD yo-yo data (20 October 2002) was used for predicting the remaining profiles and compared them with observations. This was done to verify the model’s ability to predict high frequency case (TS profiles are measured at every 2.5min.). In the second case, during October 2004, TS profiles collected at every one-hour for 24 hours were used. This gives an idea of the model’s performance for the low frequency case. The variances of the measured and simulated sound speed profiles matched well in both cases with the modified GM model.