Inverse models for ice-induced propeller moments on a polar vessel.

Thesis (PhD)--Stellenbosch University, 2021.ENGLISH ABSTRACT: It is necessary to quantify the loads experienced by the propellers of ice-going vessels.Knowledge of these loads will serve to improve propulsion design specifications and maintenance strategies for polar class ships. Recent developments include the inverse solutions of the external ice-induced propeller moments from indirect measurements on the propulsion shaft. These inverse solutions are performed using models that account for the dynamic influence of the shaft. Although torsional vibration calculations are required by design rules there is little information on the methodology external propeller moments as their use, in this context, is still relatively new. Full-scale propulsion shaft measurements were conducted on board the S.A. Agulhas II, in which the torque and angular velocity were captured, to be trans-formed into external propeller moments. Two inverse models of the propulsion shaft were investigated. The first is an existing model which represents the shaft as a combination of lumped masses. The inverse problem in this case is ill-posed and requires regularization. It was found that the assumptions made in the derivation of this model, that both the hydrodynamic and motor torques were constant, and its computational expense made it ill-suited for use in the inverse estimation of propeller moments. The second inverse model is newly developed and based on the superposition of the shaft modes, resulting in a well-posed problem. This model accounts for the modal inertia in the flexible modes of the shaft, as full-scale data indicated that this was important, and has increased accuracy and efficiency. To the author’s knowledge, this is the first model that has been efficiently applied to determine the inverse propeller moments from full-scale measurements for a complete voyage. The derivation of the corresponding estimated propeller load profiles is presented. The new model is suitable for the real-time monitoring of propeller loads, which can assist in ship operation.AFRIKAANSE OPSOMMING: Dit is nodig om die laste te kwantifiseer waaraan die skroewe van skepe onderhewig is ty-dens ysvaart. Kennis van hierdie laste dien om die spesifikasies en instandhoudingstrategieëvan aandrywingstelsels van ys-klas skepe toe te lig. Onlangse verwikkelinge sluit inverseoplossings van die eksterne in ys-geënduseerde skroefmomente in deur gebruik te maak vanindirekte metings op die dryfas. Hierdie inverse oplossings word uitgevoer met behulp vanmodelle wat die dinamiese invloed van die as in ag neem. Hoewel torsionele vibrasiebe-rekening deur ontwerpsreëls vereis word, is daar min inligting oor metodologie om inverseskroefmomente te bepaal, aangesien werk in die konteks nog relatief nuut is. Volskaalsedryfasmetings van wringkrag en hoeksnelheid is op die S.A. Agulhas II uitgevoer met diedoel om skroefmomente van hier af te bereken. Twee inverse modelle van die SA AghulhasII dryfas is ondersoek. Die eerste model is ’n bestaande model, wat die skag voorstel as’n kombinasie van gekonsentreerde massas. Die inverse probleem in hierdie geval is swakgestel en vereis regularisering. Verder word daar aangeneem dat beide die hidrodinamiese-en die motorwringkrag konstant is. Die berekeningsvereistes maak dit ongeskik vir gebruikin die inverse beraming van skroefmomente. ’n Tweede inverse model is nuut ontwikkel engebaseer op die superposisie van die modusse van die dryfas. Dit is meer akkuraat en doel-treffend en lei tot ’n volledig gestelde probleem. Dit sluit die modale traagheid van die as in,aangesien volskaalse data aandui dat dit belangrik is. Volgens die outeur is hierdie die eersteinverse model wat effektief aangewend is om invers-berekende skroefmomente vanaf volskaalmeetings te beraam vir ’n volledige vaart. Die afleiding van geskatte skroef lasprofiele wordaangebied. Die nuwe model is geskik vir intydse monitering van operasionele skroeflaste.Doctora

Development of an integrated numerical method for the fatigue analysis of railway bogies

Thesis (MEng)--Stellenbosch University, 2017.ENGLISH ABSTRACT: This study focuses on the creation of a numerical simulation process that can be used to determine the fatigue life of railway bogies, using the Commonwealth railway bogie of the class 5M train in South Africa as example. The numerical simulation is intended for use in future research on railway bogies. The research is supported and funded by the Passenger Rail Agency of South Africa (PRASA) Engineering Research Group at Stellenbosch University. A finite element (FE) model of the bogie has been created using an accurate three dimensional computer aided drawing (CAD) model, supplied by the PRASA Engineering Research Group. The FE model has been used to determine stress distributions due to unit loads applied at the primary and secondary suspension attachment points. Dynamic load cases have been determined through simulation of spring-mass-damper models representing the train and track systems. The load cases have been applied to the FE model stress distributions and superimposed to obtain stress histories. A script has been coded in Python to determine fatigue life from the stress histories. The process has been designed in such a way that each component can be altered and refined, allowing future research opportunities and refinements such as expanding the process to be applied to other bogies or allowing actual measured track data to be used as input for determining dynamic loads. Further research is required to validate and improve the numerical process.AFRIKAANSE OPSOMMING: Hierdie navorsing fokus op die daarstelling van ’n numeriese proses wat gebruik kan word om die vermoeidheidslewe van spoorlyn draaistelle te voorspel. Die "Commonwealth" spoorlyn draaistel van ’n Suid Afrikaans 5M trein word as voorbeeld gebruik. Die navorsing word ondersteun en befonds deur die "Passenger Rail Agency of South Africa (PRASA) Engineering Research Group" by Stellenbosch Universiteit. ’n Eindige element (EE) model van die draaistel was geskep deur die gebruik van ’n akkurate drie dimensionele rekenaargesteunde tekenprogram model, wat deur die PRASA Engineering Research Group verskaf is. Die EE model is gebruik om die verspreiding van die spanning in die draaistel te bereken as gevolg van eenheidslaste op die primêre en sekondêr veringstelsel punte. Dinamiese lasgevalle is deur die gebruik van ’n veer-massademper model van die trein en spoor sisteme bepaal. Die lasgevalle is op die EE model se spanningsvelde toegepas en gekombineer om die spanninggeskiedenis te bepaal. Die kode wat hierdie geskiedenis gebruik om die vermoeidheidslewe te voorspel, is in Python geskryf. Die hele proses is ontwerp so dat elke komponent op sy eie verfyn kan word. Dit skep verdere navorsingsgeleenthede soos studies op ander draaistelle of die gebruik van gemete spoor data as inset vir die dinamiese model. Verdere norvorsing is nodig om die proses te verbeter en geldig te maak