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
