This system computes forces and moments due to the hull's interaction with water, both hydrostatic and hydrodynamic, with respect to the hydrodynamic reference point (HRP). The coordinate frame used to define the forces and moments is similar to the body frame but is always aligned with the water surface (which is assumed to be horizontal). Forces can also be defined in a "wind" frame. The forces are split into the channels: - Fbx - body forward. - Fby - body right. - Fbz - local up (the same as -Z in the local frame). - Drag - opposing the relative water flow. - Side - 90 degrees right from the relative water flow in the surface plane. The moments are split into the hydrodynamic body frame channels (with the same sense as the normal body frame moments): - Pitch - Yaw - Roll The properties determining the location and orientation of the hull w.r.t the the water surface and stream are: - hydro/height-agl-ft - Height of the hydrodynamic reference point over the water surface. - hydro/beta-deg - angle between the hull's velocity vector throught the water and its longitudal axis. Analogous to aerodynamics/beta-deg. - hydro/pitch-deg - angle between the hull longitudal axis and the water surface (ground plane). - hydro/roll-deg - angle between the hull traverse axis and the water surface (ground plane). - hydro/v-fps - The hull's total speed relative the water. Usage: Include this system in your aircraft. Define the following properties in a system of your aircraft: - Hydrodynamics reference point: metrics/hydro-rp-x-in metrics/hydro-rp-y-in metrics/hydro-rp-z-in - Functions computing the forces in the hydrodynamic body frame - hydro/fbx-lbs - hydro/fby-lbs - hydro/fbz-lbs Alternative force inputs in the water frame - hydro/fdrag-lbs - hydro/fside-lbs Unused properties also have to be declared (and set to zero). - Functions computing the moments in the hydrodynamic body frame. FIXME: Yaw is applied in the standard body frame. - hydro/yaw-moment-lbsft - hydro/pitch-moment-lbsft - hydro/roll-moment-lbsft Define the following external forces in the main FDM file of your aircraft: { HRP } 1.0 0.0 0.0 { HRP } 0.0 1.0 0.0 { HRP } 0.0 0.0 -1.0 HRP X - 0.3048 HRP Y HRP Z 0.0 0.0 -1.0 HRP X + 0.3048 HRP Y HRP Z 0.0 0.0 -1.0 HRP X HRP Y - 0.3048 HRP Z 1.0 0.0 0.0 HRP X HRP Y + 0.3048 HRP Z 1.0 0.0 0.0 HRP X HRP Y - 0.3048 HRP Z 0.0 0.0 -1.0 HRP X HRP Y + 0.3048 HRP Z 0.0 0.0 -1.0 hydro/environment/water-level-ft hydro/environment/rho-slug_ft3 hydro/environment/current-from-north-fps hydro/environment/current-from-east-fps hydro/environment/waves-from-deg hydro/environment/wave-amplitude-ft hydro/environment/wave-length-ft 32.174049 hydro/environment/rho-slug_ft3 inertia/weight-lbs inertia/mass-slugs The difference in heading between the hull and the wave. 3.1415927 0.017453293 hydro/environment/waves-from-deg attitude/psi-rad The result of dot(Dwave, (1,0)), i.e. the cosine of the angle between the wave heading and the hull heading. hydro/environment/wave/relative-heading-rad The result of dot(Dwave, (0,1)), i.e. the sine of the angle between the wave heading and the hull heading. hydro/environment/wave/relative-heading-rad Hull speed in the wave's direction expressed in the wave's angular frequency. 6.2831853 hydro/vbx-fps hydro/environment/wave/hull-x-factor hydro/vby-fps hydro/environment/wave/hull-y-factor 0.001 hydro/environment/wave-length-ft The hull's angular offset at its present position. hydro/environment/wave/hull-angular-frequency-rad_sec 1.0 The angular frequency of the wave. -1.0 6.2831853 hydro/environment/gravity-ft_sec2 0.001 hydro/environment/wave-length-ft 0.5 hydro/environment/wave/hull-angular-offset-rad simulation/sim-time-sec The wave number of the wave. 6.2831853 0.001 hydro/environment/wave-length-ft The water level change due to the waves. Guessed. Integrated over -0.5 * hydro-length-ft to 0.5 * hydro-length-ft. hydro/environment/wave-amplitude-ft 0.5 metrics/hydro-length-ft hydro/environment/wave/hull-x-factor hydro/environment/wave/wave-number-rad_ft hydro/environment/wave/angular-frequency-rad_sec simulation/sim-time-sec hydro/environment/wave-amplitude-ft -0.5 metrics/hydro-length-ft hydro/environment/wave/hull-x-factor hydro/environment/wave/wave-number-rad_ft hydro/environment/wave/angular-frequency-rad_sec simulation/sim-time-sec hydro/environment/wave/hull-x-factor hydro/environment/wave/wave-number-rad_ft hydro/hull-length-ft The water level change at the HRP location. For debugging. hydro/environment/wave-amplitude-ft hydro/environment/wave/angular-frequency-rad_sec simulation/sim-time-sec The water level change at 0.5 * metrics/hydro-length-ft forward of the HRP location. hydro/environment/wave-amplitude-ft 0.5 metrics/hydro-length-ft hydro/environment/wave/hull-x-factor hydro/environment/wave/wave-number-rad_ft hydro/environment/wave/angular-frequency-rad_sec simulation/sim-time-sec The water level change at 0.5 * metrics/hydro-length-ft aft of the HRP location. hydro/environment/wave-amplitude-ft -0.5 metrics/hydro-length-ft hydro/environment/wave/hull-x-factor hydro/environment/wave/wave-number-rad_ft hydro/environment/wave/angular-frequency-rad_sec simulation/sim-time-sec The pitch trim change due to the waves. Guessed. 57.29578 hydro/environment/wave/level-fwd-ft hydro/environment/wave/level-aft-ft metrics/hydro-length-ft The roll trim change due to the waves. Guessed. 57.29578 hydro/environment/wave-amplitude-ft -0.5 metrics/hydro-beam-ft hydro/environment/wave/hull-y-factor hydro/environment/wave/wave-number-rad_ft hydro/environment/wave/angular-frequency-rad_sec simulation/sim-time-sec hydro/environment/wave-amplitude-ft 0.5 metrics/hydro-beam-ft hydro/environment/wave/hull-y-factor hydro/environment/wave/wave-number-rad_ft hydro/environment/wave/angular-frequency-rad_sec simulation/sim-time-sec metrics/hydro-beam-ft Distance between the hydrodynamic reference point and the water surface. Not completely correctly computed yet. position/h-sl-ft -0.083333333 metrics/hydro-rp-x-in inertia/cg-x-in attitude/pitch-rad 0.083333333 metrics/hydro-rp-z-in inertia/cg-z-in attitude/pitch-rad hydro/environment/water-level-ft velocities/v-east-fps hydro/environment/current-from-east-fps velocities/v-north-fps hydro/environment/current-from-north-fps 57.29578 hydro/true-course-rad 57.29578 attitude/pitch-rad 57.29578 attitude/roll-rad attitude/pitch-rad velocities/v-down-fps hydro/v-fps 57.29578 hydro/alpha-rad hydro/true-course-rad attitude/psi-rad hydro/tmp/beta-rad hydro/tmp/beta-rad -3.1415927 6.2831853 hydro/tmp/beta-rad 3.1415927 -6.2831853 57.29578 hydro/beta-rad velocities/v-north-fps hydro/environment/current-from-north-fps 2.0 velocities/v-east-fps hydro/environment/current-from-east-fps 2.0 0.5 0.5924838 hydro/v-fps hydro/beta-rad hydro/v-fps hydro/beta-rad hydro/v-fps 0.50 hydro/environment/rho-slug_ft3 hydro/v-fps hydro/v-fps 0.50 hydro/environment/rho-slug_ft3 hydro/vbx-fps hydro/vbx-fps 0.50 hydro/environment/rho-slug_ft3 hydro/vby-fps hydro/vby-fps attitude/psi-rad hydro/fbx-lbs attitude/psi-rad hydro/fby-lbs -1.0 hydro/true-course-rad hydro/fdrag-lbs -1.0 hydro/true-course-rad hydro/fside-lbs

external_reactions/hydro-X/magnitude

attitude/psi-rad hydro/fbx-lbs attitude/psi-rad hydro/fby-lbs -1.0 hydro/true-course-rad hydro/fdrag-lbs hydro/true-course-rad hydro/fside-lbs

external_reactions/hydro-Y/magnitude

hydro/fbz-lbs

external_reactions/hydro-Z/magnitude

hydro/pitch-moment-lbsft 0.5

external_reactions/hydro-pitch[0]/magnitude

hydro/pitch-moment-lbsft -0.5

external_reactions/hydro-pitch[1]/magnitude

hydro/roll-moment-lbsft 0.5

external_reactions/hydro-roll[0]/magnitude

hydro/roll-moment-lbsft -0.5

external_reactions/hydro-roll[1]/magnitude

hydro/yaw-moment-lbsft 0.5

external_reactions/hydro-yaw[0]/magnitude

hydro/yaw-moment-lbsft -0.5

external_reactions/hydro-yaw[1]/magnitude