Evaluation Methods for Components of Forces and Moments Sample Clauses

Evaluation Methods for Components of Forces and Moments. The terms of the equation system (16)-(18) can be defined with different methods: empirical formulae, numerical methods or model experiments. The methods that can be applied are described in Table 8. Table 8. Methods for evaluation of components in Comprehensive Assessment procedure Elements Components Model Tests Numerical Methods Empirical Methods Calm-water X, Y, N steady-drift tests towing double-body steady-drift CFD simulations empirical formulae Time-average forces wave X,Y,N drift forces in regular waves at different speeds and headings potential methods, CFD for drift forces in regular waves empirical formulae Wind forces X,Y,N static wind tunnel tests CFD for static wind forces empirical formulae Rudder forces X,Y steady towing tests with working propeller CFD simulations rotating propeller with empirical methods Open-water propeller characteristics T, J, nP , PD open-water tests propeller potential methods, CFD for open-water propeller simulations propeller series Engine Pav static model (engine diagram) Because the proposed assessment procedure allows definition of different forces separately, using different (experimental, numerical or empirical) methods, an important question is how much freedom we have in the definition of each force component. Table 9 shows the percentage of the change of the required installed power to fulfil propulsion and steering ability requirements due to changes of each force or moment component in turn by 10% at significant wave height of 5.5 m, obtained with the Comprehensive Assessment (maximum values over several ships of different types are shown). The figures mean, for example, the following: a change of the x-calm water force by 10% changes the required installed power by 3.0%. The table shows that the most important contributors (bold) are the time-average x- (added resistance) and y-forces, calm-water x- and y- forces and z-moment and lateral rudder force. For these forces, the error of about 15% leads to the error in the definition of the required power of 5%.