Correct OWC piston-force path and simulation step

OWC/OrificeModel/README.md

@@ -19,6 +19,25 @@ file with the _clean suffix.
 Run wecSimMCR for orifice area study in mcrOrifice.mat which will work with the
 userDefinedFunctions.m
 
+## Flexible-body piston force
+
+In `OWC_GBM.slx`, the orifice piston force and wave excitation are summed before
+the generalized-body-mode state-space input. The piston force was already
+included in the reported flexible-body acceleration, but its previous direct
+excitation-only connection to the state-space path left the force out of the
+integrated flexible-body motion. The state-space block retains the existing
+flexible stiffness and damping terms.
+The corrected model is saved in the original R2023b Simulink format.
+
+The 130 s irregular-wave case in `wecSimInputFile.m` uses `ode23t`, a
+0.00015625 s simulation step, and 0.005 s output sampling. WEC-Sim
+initialization sets the model's maximum solver step from `simu.dt`, so the
+simulation step must be specified in the input file. The radiation convolution,
+nonlinear-force, and Morison-force sample times remain explicitly at their
+original 0.005 s setting. An audit with the old 0.005 s solver step found up
+to 1.687 m difference in surge and 1.62% difference in pneumatic work against
+a refined solver run with identical waves and no Mach-limit warnings.
+
 **Relevant Citation(s)**
 
 Add relevant citaions. 

OWC/OrificeModel/wecSimInputFile.m

@@ -8,7 +8,11 @@
 simu.endTime = 130;                     % Simulation End Time [s]
 % simu.solver = 'ode45';                  % simu.solver = 'ode4' for fixed step & simu.solver = 'ode45' for variable step 
 simu.solver = 'ode23t';                 % simu.solver = 'ode4' for fixed step & simu.solver = 'ode45' for variable step 
-simu.dt = 0.005; 						% Simulation time-step [s]
+simu.dt = 0.00015625;               % Simulation and maximum solver step [s]
+simu.dtOut = 0.005;                 % Output sampling step [s]
+simu.cicDt = 0.005;                 % Radiation convolution sampling step [s]
+simu.nonlinearDt = 0.005;           % Nonlinear-force sampling step [s]
+simu.morisonDt = 0.005;             % Morison-force sampling step [s]
 simu.cicEndTime = 15;
 simu.mcrMatFile = 'mcrOrifice.mat';