MHKiT WEC-Sim Example

This example loads simulated data from a WEC-Sim run for a two-body point absorber (Reference Model 3) and demonstrates the application of the MHKiT wave module to interact with the simulated data. The analysis is broken down into three parts:

1. Load WEC-Sim Simulated Data

2. WEC-Sim Simulated Data

Wave Class Data
Body Class Data
PTO Class Data
Constraint Class Data
Mooring Class Data

3. Apply MHKiT Wave Module

1. Load WEC-Sim Simulated Data

WEC-Sim saves output data as a MATLAB structure, generated by WEC-Sim's Response Class. The WEC-Sim structure contains data for Wave, Bodies, PTOs, Constraints, Mooring, MoorDyn, and PTOSim classes.

% Relative location and filename of simulated WEC-Sim data (run with mooring)
filename = './data/RM3MooringMatrix_matlabWorkspace.mat'
filename = './data/RM3MooringMatrix_matlabWorkspace.mat'
load(filename, 'output');

2. WEC-Sim Simulated Data

Wave Class Data Data from WEC-Sim's Wave Class includes information about the wave input, including the wave type and wave elevation as a function of time.

Store WEC-Sim output from the Wave Class

wave_data = output.wave;

Display the wave type from the WEC-Sim Wave Class

fprintf('WEC-Sim wave type: %s\n', wave_data.type);
WEC-Sim wave type: etaImport

Plot Wave Elevation Data

figure('Position', [100, 100, 1600, 600]);

plot(wave_data.time, wave_data.elevation);

xlabel('Time [s]');

ylabel('Wave Surface Elevation [m]');

title('Wave Elevation');

Body Class Data

Data from WEC-Sim's Body Class includes information about each body, including position, velocity, acceleration, forces, and body name.

Store WEC-Sim output from the Body Class

bodies = output.bodies;

Body Class Data for Body 1

body1 = bodies(1);
fprintf('Name of Body 1: %s\n', body1.name);
Name of Body 1: float

Plot heave position data for Body 1

figure('Position', [100, 100, 1600, 600]);

plot(body1.time, body1.position(:,3));

xlabel('Time [s]');

ylabel('Heave Position [m]');

title('Body 1 Heave Position');

Calculate and display max/min heave position

fprintf('Body 1 max heave position = %.4f [m]\n', max(body1.position(:,3)));
Body 1 max heave position = -0.0975 [m]
fprintf('Body 1 min heave position = %.4f [m]\n', min(body1.position(:,3)));
Body 1 min heave position = -1.3264 [m]

Plot Body 1 position data for all DOFs

figure('Position', [100, 100, 1600, 600]);

plot(body1.time, body1.position);

xlabel('Time [s]');

ylabel('Position [m or rad]');

title('Body 1 Position - All DOFs');

legend('DOF1', 'DOF2', 'DOF3', 'DOF4', 'DOF5', 'DOF6', 'Location', 'eastoutside');

Body Class Data for Body 2

body2 = bodies(2);
fprintf('Name of Body 2: %s\n', body2.name);
Name of Body 2: spar
body2
body2 = struct with fields:
                       name: 'spar'
                       time: [40001×1 double]
                   position: [40001×6 double]
                   velocity: [40001×6 double]
               acceleration: [40001×6 double]
                 forceTotal: [40001×6 double]
            forceExcitation: [40001×6 double]
      forceRadiationDamping: [40001×6 double]
             forceAddedMass: [40001×6 double]
             forceRestoring: [40001×6 double]
    forceMorrisonAndViscous: [40001×6 double]
         forceLinearDamping: [40001×6 double]

PTO Class Data

Data from WEC-Sim's PTO Class includes information about each PTO, including position, velocity, acceleration, forces, and PTO name.

Store WEC-Sim output from the PTO Class

ptos = output.ptos;
fprintf('Name of PTO: %s\n', ptos.name);
Name of PTO: PTO1

Plot PTO power

figure('Position', [100, 100, 1600, 600]);

plot(ptos.time, -1 * ptos.powerInternalMechanics(:,3) / 1000);

xlabel('Time [s]');

ylabel('Power Generated [kW]');

title('PTO Power');

Constraint Class Data

Data from WEC-Sim's Constraint Class includes information about each constraint, including position, velocity, acceleration, forces, and constraint name.

constraints = output.constraints;
fprintf('Name of Constraint: %s\n', constraints.name);
Name of Constraint: Constraint1
constraints
constraints = struct with fields:
               name: 'Constraint1'
               time: [40001×1 double]
           position: [40001×6 double]
           velocity: [40001×6 double]
       acceleration: [40001×6 double]
    forceConstraint: [40001×6 double]

Mooring Class Data

Data from WEC-Sim's Mooring Class includes information about the mooring, including position, velocity, mooring force, and mooring name.

mooring = output.mooring;
mooring
mooring = struct with fields:
            name: 'mooring'
            time: [40001×1 double]
        position: [40001×6 double]
        velocity: [40001×6 double]
    forceMooring: [40001×6 double]

3. Apply MHKiT Wave Module

Calculate spectrum from the WEC-Sim wave elevation timeseries data using the MHKiT elevation_spectrum function.

Calculate wave spectrum

sample_rate = 60;
nnft = 1000;  % Number of bins in the Fast Fourier Transform
ws_spectrum = elevation_spectrum(wave_data.elevation, sample_rate, nnft, wave_data.time);

Plot calculated wave spectrum

figure('Position', [100, 100, 1600, 600]);

plot_spectrum(ws_spectrum);

xlim([0, 4]);

Calculate Wave Statistics using MHKiT wave module functions

Hm0 = significant_wave_height(ws_spectrum);
Tp = peak_period(ws_spectrum);
Te = energy_period(ws_spectrum);
 
wave_statistics_data = {
    % Parameter, Value, Units
    'Significant Wave Height, Hm0', Hm0, 'm';
    'Peak Wave Period, Tp', Tp, 's';
    'Energy Period, Te', Te, 's';
};
 
wave_statistics_table = cell2table(wave_statistics_data, 'VariableNames', {'Parameter', 'Value', 'Units'});
wave_statistics_table.Value = round(wave_statistics_table.Value, 4);
wave_statistics_table
wave_statistics_table = 3×3 table 
 ParameterValueUnits
1'Significant Wave Height, Hm0'1.7857'm'
2'Peak Wave Period, Tp'8.3333's'
3'Energy Period, Te'11.4778's'

	Parameter	Value	Units
1	'Significant Wave Height, Hm0'	1.7857	'm'
2	'Peak Wave Period, Tp'	8.3333	's'
3	'Energy Period, Te'	11.4778	's'