The response to ship induced motions has been predicted for four towed underwater vehicles. The purpose of the study is to determine the suitability of these vehicles for their use as oceanic microstructure sensor carrying platforms. All have been used in the past for oceanic studies, and these four vehicles show the most promise for microstructure work. Transfer functions which describe the response of a towed vehicle have been determined, for longitudinal motions. Also, the motion spectra of the vehicles have been predicted for the longitudinal mode as a result of being towed by a typical research vessel in a sea state three. / M.S.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The hydrodynamic characteristics of three typical ship-like hull sections, in different motions, are numerically investigated using FLUENT, 2009. These simple shapes, namely a v-bottom (triangle) hull, a at-bottom (square) hull and a round-bottom (semi-circle) hull, are investigated in uncoupled heave, sway and roll. The problem is described in two dimensions. A combination of numerical methods and models, found in literature, are used to conduct this investigation. Hull characterisation is achieved through the use of hull mass and damping coe cients. These numerically determined coe cients are compared to experimental work conducted by Vugts (1968). A good correlation between the numerical and experimental results exists for the heave and sway cases. By normalising the coe cients, different hulls are comparable to one another. The numerical models used are validated and veri ed. Roll motion remains largely unsolved for very large angles of roll (in excess of 11°). Different uid ow phenomena occurring around the hull sections have varying degrees of in uence on the motions of a hull. It is found that not one of the turbulence models investigated can be employed to globally solve each type of hull-motion case. Also, forced oscillations in computational simulations require considerably more computational time than free-decay oscillating hull simulations. / AFRIKAANSE OPSOMMING: Die hidrodinamiese karakteristieke van verskillende skeepsrompvorms, in verskeie bewegingswieë, is numeries ondersoek met behulp van FLUENT, 2009. Drie eenvoudige vorms ('n v-bodem (driehoek), plat-bodem (reghoek) en rondebodem (semi-sirkel) romp) is onderskeidelik ondersoek in opwieg, dwarswieg en rol. Die probleem is twee-dimensioneel. Daar is gebruik gemaak van 'n kombinasie van numeriese metodes en modelle, uit die literatuur, om die ondersoek uit te voer. Die rompe is gekarakteriseer met behulp van massa- en dempingskoëffi siënte. Hierdie numeries bepaalde koë ffisiënte is vergelyk met die eksperimentele werk van Vugts (1968). Daar bestaan 'n goeie korrelasie tussen die numeriese en eksperimentele resultate vir die opwieg en dwarswieg gevalle. Die koë ffisiënte is genormaliseer om die verskeie rompvorms te vergelyk. Die numeriese modelle is geverifi eer en valideer. Rolbewegings is onopgelos vir groot rolhoeke (groter as 11°). Die mate waartoe die romp se beweging beïnvloed word deur die verskillende vloei verskynsels wat om die rompe ontstaan, verskil. Daar is bevind dat geen van die turbulensie modelle gebruik kan word om alle skeepsbeweging-gevalle op te los nie. Gedwonge-ossilasie numeriese simulasies benodig meer berekeningstyd as vrye-verval ossilasie gevalle.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2008. / This study investigates practical passive methods to improve the seakeeping of a Hydrofoil Supported Catamaran (Hysucat). The Hysucat is a hybrid vessel combining hydrofoil efficiency with the stability of catamarans. The seakeeping of the Hysucat was initially investigated experimentally to determine what seakeeping improvements are inherent to the Hysucat design. The results showed that the seakeeping is improved by 5-30%. A passive suspension system for the main hydrofoil of the Hysucat was designed and tested. A concept development strategy was followed for the design of the suspension system as such a system had never been investigated previously. Detailed specifications for the design were developed and concepts that could satisfy the customer and engineering requirements were generated. Numerical simulation models for the Hysucat and the final concepts were derived assuming a simplified 2nd order system to describe the seakeeping dynamics of the demi-hulls. Unknown parameters were determined using parameter estimation techniques. Representative parameter values were calculated from multiple towing tank experiments. Theory describing the motion of a hydrofoil in an orbital velocity wave field was combined with the hull model to simulate the Hysucat as well as the suspension system concepts. The models indicated that the concept where the main hydrofoil was attached to a spring loaded arm, that was free to pivot in response to orbital waves, was the most feasible in damping out vertical transmitted accelerations. Experimental tests indicated that little improvement was achieved with the suspension system at low frequencies. At resonance the suspension system was effective in decreasing the heave of the vessel by up to 27%. The pitch and acceleration response results showed improvements at the higher encounter frequencies of up to 50%. The calm water resistance of the vessel increased by 10% over the Hysucat with rigidly attached hydrofoils; however was still 24% less than the hull without foils.

Thesis (PhD)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: This work is concerned with the hydrodynamic design of hydrofoil-assisted catamarans. Focus is placed on the development of new and suitable design methods and application of these to identify the most important geometric parameters of catamaran hulls and hydrofoil configurations that influence efficiency and performance. These goals are pursued by firstly gaining a thorough understanding of the governing hydrodynamic principles involved in the design process. This knowledge is then applied to develop new and improved experimental techniques and theoretical methods needed for design. Both are improved to the extent where they can be applied as design tools covering the important semi-displacement and semi-planing speeds, which are the focus of this study. The operational speed range of hydrofoil-assisted catamarans is shown to consist of three distinct hydrodynamic phases (displacement, transition and planing) and that different hydrodynamic principles govern vessel performance in each phase. The hydrodynamics are found to differ substantially from that of conventional high-speed craft, primarily due to the interaction between the hull and the hydrofoils, which is found to vary with speed and results in the need for more complex experimental procedures to be followed if accurate predictions of resistance are to be made. Experimental predictions based on scaled model tests of relatively small hydrofoilassisted catamaran models are found to be less accurate than that achievable for conventional ships because of the inability to correct for all scaling errors encountered during model testing. With larger models scaling errors are encountered to a lesser degree. The most important scale effect is found to be due to the lower Reynolds number of the flow over the scaled foils. The lower Reynolds number results in higher drag and lower lift coefficients for hydrofoils compared with those achieved at full scale. This effect can only be partially corrected for in the scaling procedure using the available theoretical scaling methods. Presently available theoretical methods commonly used for the design of conventional ships were found to be ill adapted for modeling the complex hydrodynamics of hydrofoil-assisted catamarans and required further development. Vortex lattice theory was chosen to model the flow around hydrofoil-assisted catamarans as vortex theory models the flow around lifting surfaces in the most natural way. The commercial code AUTOWING is further developed and generalized to be able to model the complex hull-hydrofoil interactions that change with speed. The method is shown to make good predictions of all hydrodynamic quantities with accuracies at least as good as that achievable through model testing and therefore fulfills the requirements for a suitable theoretical design tool. The developed theoretical and experimental design tools are used to investigate the design of hydrofoils for hydrofoil-assisted catamarans. It is found that the main parameter needing consideration in the hydrofoil design is selection of a suitable hydrofoil lift fraction. A foil lift fraction in the order of 20-30% of the displacement weight is needed if resistance improvements using hydrofoil assistance are to be obtained over the hull without foils. It is often more favorable to use higher foil lift fractions (50%+) as the resistance improvements are better, although careful attention should then be given to directional and pitch-heave instabilities. The Hysuwac hydrofoil system patented by the University of Stellenbosch is found to be hydrodynamically optimal for most hullforms. The hullform and in particular the curvature of the aft buttock lines of the hull are found to have an important influence on the achievable resistance improvements and behaviour of the hydrofoil-assisted hull at speed. Hull curvature is detrimental to hydrodynamic performance as the suction pressures resulting from the flow over the curved hull counter the hydrofoil lift. The hullform best suited to hydrofoil assistance is found to be one with relatively straight lines and hard chine deep- V sections. The main conclusion drawn from this study is that hydrofoil-assistance is indeed suitable for improving the performance and efficiency of catamarans. The design and optimization of such vessels nevertheless requires careful consideration of the various resistance components and hull-foil interactions and in particular, how these change with speed. The evaluation of resistance for design purposes requires some discipline between theoretical analysis and experimental measurements as the complexity of the hydrodynamics reduce the accuracies of both. Consideration of these factors allows hulls and hydrofoils to be designed that are efficient and also free of dynamic instabilities. / AFRIKAANSE OPSOMMING: Hierdie studie is gerig op die hidrodinamiese ontwerp van hidrovleuel-gesteunde katamarans. Daar word gefokus op die ontwikkeling van nuwe en geskikte ontwerpmetodes, asook die toepassing van hierdie metodes om die belangrikste geometriese parameters van katamaranrompe en hidrovleuel-konfigurasies wat 'n invloed op doeltreffendheid en werkverrigting het, te identifiseer. As aanloop tot die studie is 'n deeglike begrip van die onderliggende hidrodinamiese beginsels bekom. Hierdie kennis is toegepas om nuwe en verbeterde eksperimentele en teoretiese tegnieke te ontwikkel wat nodig is vir die ontwerp van hidrovleuel-gesteunde katamarans in die belangrike deels-verplasing en deels-planering spoedbereike. Daar word getoon dat die bedryfspoedbereik van 'n hidrovleuel-gesteunde katamaran uit drie onderskeibare hidrodinamiese fases bestaan, naamlik verplasing, oorgang en planering, en dat verskillende hidrodinamiese beginsels die vaartuig se werkverrigting in elke fase bepaal. Daar is ook gevind dat die hidrodinamika wesentlik verskil van dié van konvensionele hoëspoed-vaartuie, hoofsaaklik as gevolg van die interaksie tussen die romp en die hidrovleuels wat wissel na gelang van die spoed. Hierdie interaksies moet in ag geneem word gedurende die ontwerpproses en beide eksperimentele en teoretiese metodes is nuttig om die omvang daarvan te bepaal. Daar is gevind dat die eksperimentele voorspellings gebaseer op toetse met relatief klein skaalmodelle van hidrovleuelgesteunde katamarans minder akkuraat is as dié wat bereik kan word met konvensionele skepe. Dit is omdat al die skaalfoute wat tydens die toetsing met die model ontstaan, nie gekorrigeer kan word nie. Die belangrikste skaaleffek is as gevolg van die laer Reynoldsgetal van die vloei oor die afgeskaalde vleuels. Groter modele Die laer Reynoldsgetal lei tot hoër sleur- en hefkoëffisiënte in vergelyking met dié vir die volskaal-hidrovleuels. Wanneer die beskikbare teoretiese metodes gebruik word, kan daar slegs gedeeltelik vir hierdie effek in die skaalprosedure gekorrigeer word. Daar is ook vasgestel dat die skaaleffekte op die Reynoldsgetal verminder word wanneer die hidrovleuels baie nabyaan die vrye oppervlakte is. Dit lei daartoe dat eksperimentele voorspellings van werkverrigting meer akkuraat is vir die ontwerpe waar die hidrovleuels nie so diep onder die water is nie. Daar is gevind dat die teoretiese metodes wat tans beskikbaar is en algemeen vir die ontwerp van konvensionele skepe gebruik word nie die komplekse hidrodinamika van hidrovleuel-gesteunde katamarans kan modelleer nie. Die werwelroosterteorie is gekies om die vloei om hidrovleuel-gesteunde katamarans te modelleer aangesien dié teorie die vloei om hefvlakke op die natuurlikste manier weergee. Die kommersiële kode AUTOWING is verder ontwikkel en veralgemeen om ook die komplekse spoed-afhanklike interaksies van die romp en hidrovleuel te kan modelleer. Hierdie metode lewer goeie voorspellings van al die hidrodinamiese maatstawwe met akkuraathede wat ten minste so goed is soos di wat met modeltoetsing bereik word en voldoen daarom aan die vereistes vir 'n geskikte teoretiese ontwerpmetode. Die teoretiese en eksperimentele ontwerpmetode wat ontwikkel is, word gebruik om die ontwerp van hidrovleuels vir hidrovleuel-gesteunde katamarans te ondersoek. Daar is gevind dat die belangrikste parameter wat in die hidrovleuel-ontwerp in ag geneem moet word, die keuse van 'n geskikte hidrovleuelhefverhouding is. Om in rompe met hidrovleuelsteun verbeterings in die weerstand te kry in vergelyking met rompe sonder vleuels, is 'n vleuel-hef-verhouding van 20-30 persent van die verplasingsgewig nodig. Dit is dikwels beter om hoër vleuel-hef-verhoudings (van 50 persent of meer) te gebruik omdat die verbetering in weerstand dan groter is. Daar moet dan egter gewaak word teen rigtings- en hei-hef-onstabiliteite. Daar is gevind dat die Hysuwachidrovleuel- stelsel wat deur die Universiteit van Stellenbosch gepatenteer is, hidrodinamies optimaal is vir die meeste rompvorms. Daar is gevind dat die vorm van die romp en veral die kromming van die lyne gevorm deur vertikale snitte deur die romp (Engels: "aft buttock lines") van die romp 'n belangrike invloed het op die bereikbare weerstandsverbeterings en die gedrag van die hidrovleuel-gesteunde romp wat op spoed is. Die kromming van die romp is nadelig vir die hidrodinamiese werksverrigting aangesien die suigdruk as gevolg van die vloei oor die gekromde romp die hefkrag van die hidrovleuels teenwerk. Die rompvorm wat die geskikste is vir hidrovleuel-ondersteuning is 'n romp met relatiewe reguit lyne en skerp hoekige diep- V seksies. Die belangrikste gevolgtrekking waartoe tydens die studie gekom is, is dat hidrovleuelondersteuning wel geskik is vir die verbetering van die werkverrigting en die doeltreffendheid van katamarans. Die ontwerp en optimering van sodanige vaartuie verg nogtans die noukeurige oorweging van die verskeie weerstandskomponente en rompvleuel- interaksies en veral hoe hierdie interaksies verander met spoed. Die evaluering van die weerstand vir die doeleindes van ontwerp verg dissipline tussen die teoretiese analise en die eksperimentele metings aangesien die kompleksiteit van die hidrodinamika die akkuraatheid van die algemeen-gebruikte teoretiese en eksperimentele metodes vir die hidrodinamiese ontwerp verminder. As hierdie faktore in ag geneem word, kan rompe en hidrovleuels ontwerp word wat doeltreffend is en ook vry is van dinamiese onstabiliteite.

Numerical simulations of waterjet inlets have been conducted in order to understand inlet performance during ship turning maneuvers. During turning maneuvers waterjet systems may experience low efficiency, cavitation, vibration, and noise. This study found that during turns less energy arrived at the waterjet pump relative to operating straight ahead, and that the flow field at the entrance of the waterjet pump exhibited a region of both low pressure and low axial velocity. The primary reason for the change in pump inflow uniformity is due to a streamwise vortex. In oblique inflow the hull boundary layer separates when entering the inlet and wraps up forming the streamwise vortex. These changes in pump inflow during turning maneuvers will result in increased unsteady loading of the pump rotor and early onset of pump rotor cavitation. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2015. / FAU Electronic Theses and Dissertations Collection

Thesis: M.S., Massachusetts Institute of Technology, Department of Ocean Engineering, 1978 / Includes bibliographical references. / M.S. / M.S. Massachusetts Institute of Technology, Department of Ocean Engineering

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2006. / This thesis investigates practical methods of modelling and control of the vertical motions of a hydrofoil assisted catamaran, the HYSUCAT. The aim of the control application is to reduce the motions, and consequently the motion sickness of the passengers. First, a potential flowcommercial program, POWERSEA,was used to model the system. This uses 2-D strip methods to model the planing hull-form of the vessel, and the Peter du Cane hydrofoil theory for modelling of the foils. These simulations are compared to experimental towing tank results, with fair agreement at lower speeds, but limited applicability at high speeds. Thus for the control design the agreement was insufficient. As an alternative, a simple coupled 2 degree-of-freedom spring - mass - damper model is proposed, for which the equations of motion are derived. This has 9 unknown parameters; three of these aremeasured directly, two are modelled, and the remaining four were identified using an experimental parameter estimation technique. Representative parameter values were calculated frommultiple experiments for application in the control design. The design of a control system was based on the above model. First, an output-weighted Linear Quadratic Regulator (LQR) was designed to obtain the full state feedback gains. A non-linear ’bang-bang’ control design was then implemented to try and speed up the response of the system. These control strategies, as well as no control, were applied in the towing tank in regular waves, with good results at low and medium frequencies. At the design point, 32% and 65% reductions in rms motions were achieved for pitch and heave, respectively. At high frequencies, though, not much improvement was achieved due to the bandwidth limitation of the control system. The LQR results were better overall (reduced motions) across the frequency range than the bang-bang controller, as well as having a lower added resistance in waves. The control design of the output-weighted LQR was then revised to be based on alternative outputs, as a possible improvement. However, a further two controller designs did not yield any noticeable improvement and were not developed further.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: When a sailing ship passes a moored ship the moored ship experiences forces and moments. These forces and moments cause the moored ship to move. The resulting ship motions due to the passing ship can sometimes be more severe than the ship motions due to ocean waves and can cause serious accidents at moorings such as the failing of mooring lines or even the total break away of the ship from the berth. Since bulk carriers and tankers were traditionally the largest seafaring ships, passing ship studies have focused mainly on these vessels, but recently container ships have grown to a comparable size. In this study an existing numerical model “Passcat” is validated with physical model measurements for a Post Panamax container ship passing a Panamax bulk carrier. Other existing mathematical formulae are also evaluated by comparison with these model tests. In the physical model tests the passing speed (V), passing distance (G), depth draft ratio (d/D) and the presence of walls and channels were varied. It was found that the passing ship forces are proportional to the passing speed to the power of 2.32. This is slightly higher than the generally accepted quadratic relationship for passing ship induced forces. Similar relationships were found for the other variables. The numerical model results were compared to the physical model measurements by determining agreement ratios. A perfect agreement between the numerical and physical models would result in an agreement ratio of 1. Agreement ratio boundaries, wherein agreement would be regarded as good, were drawn between 0.7 and 1.3. The numerical model, Passcat, was found to under predict the passing ship forces. It was found that Passcat is valid for a wide range of sensitivities and remains within the agreement ratio limits as long as passing speed is limited to 10 knots (kt), depth draft ratio to more than 1.164, passing distance to less than four times the moored ship beam (Bm) for surge and sway estimation and passing distance to less than three times the moored ship beam for yaw estimations. These limits are true for no structures in the water. For structures in the water only the passing speed limits are different. When quay walls are present, the surge and sway forces will only provide acceptable answers at passing speeds below 9kt. When 9Bm or 12Bm channels are present, the sway force will only provide acceptable answers at passing speeds below 7kt. When a 6Bm channel is present, the yaw moments will only provide acceptable answers at passing speeds below 6kt. From the mathematical model evaluation study it was found that empirical or semi empirical methods can not provide answers with good agreement to the physical model when walls or channels are present. For the open water case, it is only the Flory method that can provide answers with good agreement to the physical model for surge, sway and yaw forces. The Flory method can provide answers with acceptable agreement within narrow boundaries of passing distance (1 to 2 times the beam of the moored ship), passing speed (4 kt to 14 kt) and depth draft ratio (less than 1.7). The numerical model, Passcat can be used with little effort to provide answers with better agreement to the physical model for a larger range of variables. / AFRIKAANSE OPSOMMING: Wanneer ’n skip verby ‘n vasgemeerde skip vaar, ondervind die vasgemeerde skip kragte en momente. Hierdie kragte induseer beweging van die vasgemeerde skip. Die beweging kan soms groter wees as die effek van wind of golwe. Indien die bewegings groot genoeg is kan dit van die vasmeer lyne van die skip laat breek, of al die lyne laat breek sodat die skip vry in die hawe ronddryf. Aangesien erts skepe en tenk skepe vir jare die grootste skepe in the wêreld was, het die meeste van die skip interaksie studies op daardie skepe gefokus. Die grootte van behouering skepe het egter in die onlangse tye gegroei om dimensies soortgelyk aan die van erts en tenk skepe te hê. In hierdie studie word ’n bestaande numeriese model “Passcat” gestaaf met fisiese model metings op ’n Post Panamax behoueringskip wat verby ‘n Panamax erts skip vaar. Bestaande wiskundige formules is ook getoets deur dit met dieselfde fisiese model metings te vergelyk. In die fisiese model studie is die spoed van die skip (V), tussenafstand (G), diepte diepgang verhouding (d/D) en die teenwoordigheid van kaai mure en kanale in die water getoets. Daar is gevind dat die kragte op die vasgemeerde skip direk eweredig is aan die spoed van die skip tot die mag 2.32. Dit is effens meer as die algemeen aanvaarde kwadratiese verhouding tussen vloeistof sleurkrag en vloeisnelheid asook tussen skip interaksie kragte en vaar snelheid. Soortgelyke verhoudings is vir al die veranderlikes bereken. Numeriese model resultate is vergelyk met die fisiese model om die verhouding van ooreenstemming te bepaal. ’n Perfekte ooreenstemming word voorgestel deur ’n verhouding van ooreenstemming van 1. Grense waarbinne die verhouding van ooreenstemming as goed beskou word is getrek tussen 0.7 en 1.3. Daar is gevind dat die numeriese model, Passcat, kragte oor die algemeen onderskat. Passcat is geldig vir 'n breë reeks van veranderlikes en sal geldig bly solank die skip spoed tot 10 knope, diepte diepgang verhouding tot meer as 1.164, tussenafstand tot minder as vier skipwydtes (Bm) vir 'surge' en 'sway' kragte en tot minder as drie skipwydtes vir 'yaw' momente beperk word. Hierdie grense is opgestel vir geen strukture in die water. Vir strukture in die water word slegs die skip spoed aangepas. Wanneer daar mure in die water is sal 'surge' en 'sway' slegs geskikte antwoorde gee as die skip spoed tot 9 knope beperk word. Vir 9Bm of 12Bm kanale sal geskikte antwoorde vir 'sway' kragte slegs voorkom met 'n skip spoed minder as 7 knope. Vir 6Bm kanale sal geskikte antwoorde vir 'yaw' momente slegs voorkom met 'n skip spoed van minder as 6 knope. Van die wiskundige model evaluasie studie is gevind dat empiriese of semi empiriese metodes nie resultate met goeie ooreenstemming tot the fisiese model metings kan gee, wanneer daar kaai of kanaal mure in die water is nie. Vir die oopwater geval is dit slegs die Flory metode wat antwoorde kan voorsien wat goed ooreenstem met die fisiese model vir 'surge', 'sway', en 'yaw' kragte. Die Flory metode voorsien hierdie resultate binne noue grense vir tussenafstand (1 tot 2 wydtes van die vasgemeerde skip), verbyvaar spoed (4 knope tot 14 knope) en diepte diepgang verhouding (minder as 1.7). Die numeriese model, Passcat, kan met min moeite antwoorde bereken wat beter ooreenstemming vir 'n groter reeks veranderlikes gee.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science; and, (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING / Includes bibliographical references. / by Marc Bodson. / M.S.

Modeling the free surface flows is important in order to estimate the total drag of the sea Vessels. It is also necessary to study the effects of various maritime maneuvers. In this work, different ways of approximating an unstructured free surface grid with a B-spline surface are investigated. The Least squares and Galerkin approaches are studied in this regard. B-spline nite element method (BSPFEM) is studied for the solution of the steady-state kinematic free surface equation. The volume grid has to be moved in order to match the free boundary when the surface-tracking approach is adopted for the solution of free surface problem. Inherent smoothness of the B-spline representation of the free surface aids this process. B-spline representation of the free surface aids in building viscous volume grids hose boundaries closely match the steady state free surface. The B-spline approximation algorithm and BSPFEM solution of free surface equation have been tested with hypothetical algebraic testcases and real cases such as Gbody, Wigley hull and David Taylor Model Basin(DTMB) 5415 hull series.