|
Vessel results |
|
|
Vessel results |
For general information on selecting and producing results, see the producing results topic.
The names of the vessel results follow the convention that lower case letters x,y,z indicate components in the vessel axes directions $\Vxyz$, whereas upper case letters X,Y,Z indicate components in the global axes directions $\GXYZ$.
All the position and motion results report the motion at a user-defined point $\vec{p}$ on the vessel whose position is given on the results form. The position of $\vec{p}$ is given in the vessel local frame, so is relative to the vessel origin: if $\vec{p} = (0,0,0)$ then the results reported are for the vessel origin.
Vessel motion can include both primary and superimposed motions. The position and orientation results are available for each of these contributions separately, as well as for the total combined vessel motion.
In addition, if the vessel primary motion is treated as being both low frequency and wave frequency then the low frequency (LF) and wave frequency (WF) parts of the primary motion are available separately:
The velocity, acceleration and other results are only available for the total combined motion of the point $\vec{p}$. The velocity and acceleration results are obtained from logged values of the velocity and acceleration of the vessel. So, unlike line velocity results, the vessel velocity and acceleration results do not have possible inaccuracy due to numerical differentiation of logged position values.
$X, Y, Z$ are the global axes coordinates of the position of the user-defined point $\vec{p}$ on the vessel, due to the total combined primary and superimposed motion.
Rotation 1, 2 and 3 define the orientation of the vessel, due to both primary and superimposed motion, relative to global axes. The three rotations (called Euler angles) are successive rotations that take the global axes directions to the vessel axes directions.
Rotation 2 is in the range -90° to +90°. Range jump suppression is applied to the rotation 1 and rotation 3 angles, so values outside the range -360° to +360° might be reported.
The position of the user-defined point $\vec{p}$ on the vessel, relative to the static position of $\vec{p}$, and with respect to the static orientation of the vessel. By static position and static orientation we mean the position and orientation in the model's static state. So, if $\vec{p}_\textrm{inst}$ is the instantaneous position, and $\vec{p}_\textrm{static}$ is the static position, then these results report $\vec{p}_\textrm{inst} - \vec{p}_\textrm{static}$ with respect to the vessel's static axis directions.
The orientation of the vessel relative to its static orientation. Considered as a vector, $\vec{R} = (Rx, Ry, Rz)$ defines the rotation from the static orientation to the instantaneous orientation. The rotation is about the direction of the vector $\vec{R}$, and has magnitude $\lvert\vec{R}\rvert$.
The magnitude and components, in the global axes directions, of the velocity of the vessel at the user-defined point $\vec{p}$, due to the total combined primary and superimposed motion.
The components, in the vessel axes directions, of the velocity of the vessel at the user-defined point $\vec{p}$, due to the total combined primary and superimposed motion.
The magnitude and components, in vessel axes directions, of the angular velocity of the vessel, due to the total combined primary and superimposed motion.
The magnitude and components, in the global axes directions, of the acceleration of the user-defined point $\vec{p}$ on the vessel, relative to earth. The acceleration is that of the point $\vec{p}$, relative to earth, due to the total combined primary and superimposed motion of the vessel.
The components, in the vessel axes directions, of the acceleration of the user-defined point $\vec{p}$ on the vessel, relative to earth. The acceleration is that of the point $\vec{p}$, relative to earth, due to the total combined primary and superimposed motion of the vessel.
The magnitude and components, in vessel axes directions, of the acceleration of the user-defined point $\vec{p}$ on the vessel, relative to the vertically downwards acceleration due to gravity.
The acceleration vector is that of the point $\vec{p}$ due to the combination of both primary and superimposed motion of the vessel, expressed relative to the (downwards) acceleration due to gravity.
This relative acceleration can be thought of as the acceleration of the point $\vec{p}$ relative to the free-falling state, and corresponds to the acceleration which would be reported by an accelerometer attached to the vessel at $\vec{p}$ (since an accelerometer reading of zero corresponds to free-falling), with its measurement directions aligned with the vessel local axes directions.
The magnitude and components, in vessel axes directions, of the angular acceleration of the vessel, due to the total combined primary and superimposed motion.
The sea state results are reported at the user-defined point $\vec{p}$ on the vessel, which moves according to the total combined primary and superimposed motion.
The global Z coordinate of the sea surface directly above or below $\vec{p}$.
The vertical clearance of $\vec{p}$ above the instantaneous sea surface. A positive value means that $\vec{p}$ is above the sea surface.
The magnitude and global $X$, $Y$ and $Z$ components of the water particle velocity (due to current and waves) and acceleration (due to waves) at $\vec{p}$. If $\vec{p}$ is above the water surface then the value at the water surface is reported.
These are directly analogous to their undisturbed equivalents, but take into account any sea state disturbance associated with the vessel.
| Note: | If the sea state RAO interpolation method is set to direction and period only, then the sea state RAOs used will be those at the position closest to $\vec{p}$ at the start of the simulation. This is consistent with how OrcaFlex computes the sea state for other model objects that experience the disturbed wave field generated by the vessel. |
The vertical clearance of $\vec{p}$ above a scaled instantaneous sea surface. In addition to providing coordinates for point $\vec{p}$, you also provide a sea surface scaling factor, $f$. Air gap is calculated as \begin{equation} Z_r - \{Z_\textrm{MWL} + f (Z_s - Z_\textrm{MWL})\} \end{equation} where
$Z_r$ is the instantaneous global Z coordinate of reporting point $\vec{p}$
$Z_\textrm{MWL}$ is the global Z coordinate of the mean water level
$Z_s$ is the sea surface elevation, sampled from the environment at the global XY position of point $\vec{p}$
Should the vessel type have sea state RAOs specified, then air gap results will automatically use the disturbed sea surface elevation.
For convenience, vessels can specify a set of air gap reporting points and a summary report of minimum clearance for those points is available.
Primary X, primary Y and primary Z are the global axes coordinates of the user-defined point $\vec{p}$ on the vessel, due to the vessel primary motion only.
Primary rotation 1, primary rotation 2 and primary rotation 3 are the rotation angles of the orientation of the vessel relative to global axes, due to the vessel primary motion only.
Primary rotation 2 is in the range -90° to +90°. Range jump suppression is applied to primary rotation 1 and primary rotation 3, so values outside the range -360° to +360° might be reported.
These results are analogous to the primary X, Y, Z and primary rotation 1, 2, 3 results described above, but for only the low frequency (LF) component of the vessel primary motion. They report the components in the global axes directions of the position of point $\vec{p}$ due to only this low frequency primary motion.
The wave frequency component of the primary motion of the user-defined point $\vec{p}$ on the vessel. They therefore represent the total primary motion position and orientation of the point $\vec{p}$, relative to its position and orientation after only the low frequency part of the primary motion has been applied. The components are, similarly, in the directions of the vessel axes after only the low frequency part of the primary motion has been applied.
Primary WF pitch is in the range -90° to +90°. Range jump suppression is applied to primary WF roll and primary WF yaw, so values outside the range -360° to +360° might be reported.
The position and orientation of the vessel due to superimposed motion, relative to the primary position of the vessel. These are typically the wave-generated part of the motion.
Surge, sway and heave are the superimposed translational displacement components, in the primary vessel axes directions, of the user-defined point $\vec{p}$ on the vessel, relative to its primary motion position.
Roll, pitch and yaw are the superimposed rotation angles, relative to the primary vessel axes directions, due to the superimposed motion.
Pitch is in the range -90° to +90°. Range jump suppression is applied to the roll and yaw angles, so values outside the range -360° to +360° might be reported.
Force and moment results are available for the total load on the vessel, and also separately for the various individual loads on the vessel that are in the vessel's included effects. If a load is not included, then it will not be calculated, will not appear in the list of available results, and will not be included in the total load results.
For each of these loads the results available are the magnitudes of the force and moment vectors, and the components $(Lx,Ly,Lz)$ of those vectors in the vessel axes directions $\Vxyz$.
In all cases the moments given are those about the vessel origin.
The magnitude and components (in vessel axes directions) of the sum of the constituent loads on the vessel which are included in the calculation.
The sum of the loads from all connected lines, links, winches, shapes, etc. Note that the connections loads reported include the structural inertia loads and added inertia loads on the objects connected to the vessel due to the translational and rotational acceleration of their points of connection.
For convenience, the components of connection force and moment are also available as components $(GX,GY,GZ)$ in global axes directions $\GXYZ$. Details of the loads exerted by each individual connected object are available as summary results, and can also be found under the results for each object itself.
The sum of all the local and global applied loads. Available only if applied loads is in the vessel's included effects.
The hydrostatic stiffness force and moment on the vessel.
The force and moment on the vessel due to the wave load RAOs. Available only if wave load (1st order) is in the vessel's included effects.
The wave drift force and moment exerted on the vessel. If wave drift damping is also included, then its effect will be accounted for in this wave drift load (2nd order) result. These results are available only if wave drift load (2nd order) is in the vessel's included effects. For frequency domain analyses, these results are available only for the free degrees of freedom of the vessel.
The sum frequency wave force and moment exerted on the vessel. These results are available only if sum frequency load (2nd order) is in the vessel's included effects.
| Notes: | The content of second order wave drift and sum frequency loads from dynamic simulation changes depending on the choice of vessel calculation mode. |
| If vessel calculation mode is set to QTF modification, these results no longer contain contributions from common second order loads, because such loads are subtracted from the input QTF data before dynamic simulation. The contributions to these results are therefore dependent on vessel included effects in this case. |
The sum of the forces and moments on the vessel due to added mass and damping. Available only if added mass and damping is in the vessel's included effects.
| Note: | If vessel calculation mode is set to QTF modification, the first order hydrostatic stiffness load, wave RAO load, added mass and damping loads, second order wave drift load and sum frequency load are all applied with respect to diffraction frame axes, but their load results are reported with respect to vessel axes. In most cases there will be little difference between the two frames of reference, but in some cases large values of datum heel and trim or superimposed motion may have a significant effect on these results. |
The manoeuvring load on the vessel. Available only if manoeuvring load is in the vessel's included effects.
The force and moment due to the specified other damping on the vessel. Available only if other damping is in the vessel's included effects.
The current drag force and moment on the vessel, plus any load from low frequency yaw rate drag. Available only if current load is in the vessel's included effects.
The wind drag force and moment on the vessel. Available only if wind load is in the vessel's included effects and wind loads on vessels are included.
Morison element results are available for the vessel if it has one or more Morison elements. The results (other than the summed results) are specific to an individual element, chosen by its number. Segment results are reported at a user-specified arc length.
The magnitude and components (in vessel axes directions and at the vessel origin) of the sum of the loads on the vessel due to all of its Morison elements.
The magnitude and components (in vessel axes directions) of the total drag force on an individual Morison element.
The magnitude and components (in vessel axes directions) of the total fluid inertia force on an individual Morison element.
The proportion of a Morison element segment that is submerged in the sea. The value is in the range 0 to 1, a value of 0 meaning no submersion and 1 meaning completely submerged.
The magnitude and components (in element axes directions) of the relative fluid velocity for a Morison element segment.
The components (in element axes directions) of the drag coefficient for a Morison element segment.
The magnitude and components (in element axes directions) of the drag force, per unit length, applied to a Morison element segment.
The magnitude and components (in element axes directions) of the fluid inertia force, per unit length, applied to a Morison element segment.
Support results are available for the vessel if it has one or more supports. The results (other than the summed results) are specific to an individual support, chosen by its number. The support contact clearance, support contact arc length, support lift out and support off end contact distance results also allow a supported line to be selected, in which case the result is specific to that supported line; alternatively for those results, (all supported lines) may be selected to report the result across all lines supported by the vessel.
The magnitude and components (in support axes directions) of the reaction load on the support due to contact between the support and the supported line(s).
The minimum distance between the contact surfaces of the support cylinders and the supported line spline. If (all supported lines) is chosen, then the minimum contact clearance across all supported lines is reported. If the result is negative it means one or more of the supported lines has penetrated one or more of the support cylinders and the result represents the greatest penetration. If the point of closest approach on the supported line spline(s) falls more than one support cylinder radius beyond either end of the supported line(s), this result is not available: see the support off end contact distance result.
The arc length along the selected supported line at which contact with the support occurs. For a support that has more than one support cylinder, it is the arc length of the point of contact with the smallest support contact clearance. A negative value indicates that the support cylinder is beyond the end of the supported line, but by less than the support cylinder radius. If the point(s) of closest approach on the supported line spline are beyond the end of the supported line by more than one support cylinder radius, then there is no contact and this result is not available.
A supported line must be specified to obtain values for this result – contact arc length for (all supported lines) is not available.
The maximum distance, in the support z direction, from the support position to the point of closest approach on the supported line(s) spline axis. If (all supported lines) is selected, the maximum lift out over all supported lines is reported. If the point of closest approach on the supported line spline fall beyond the end of the supported line by more than one support cylinder radius, this result is not available.
Essentially this result gives the distance, in the support $z$ axis direction, by which the supported line axis has lifted away from the support position.
The maximum support lift out across all of the vessel's supports.
If the supported line is in contact with a support cylinder at a point beyond the support cylinder's ends this result reports the distance from the end of the support cylinder to the point of closest approach on the axis of the support cylinder. If the support has multiple support cylinders, and more than one of them is in contact with the supported line, then the maximum off-end contact distance across all these cylinders is reported. If (all supported lines) is specified, then the maximum off-end contact distance over all supported lines is reported. If none of the support cylinders and specified supported line(s) are in contact, or all the points of contact on the support cylinders are within the length of the support cylinders, this result is zero.
This enables you to check for the potential escape of support lines from their supports; the support cylinders are drawn with finite length but for the purpose of contact they are assumed to have infinite axial extent, so it is possible that the supported line is being contained by a non-physical part of the support.
The maximum support off end contact distance across all of the vessel's supports.
The magnitude and components (in vessel axes directions) of the sum of reaction loads on all the vessel's supports.
The magnitude and components (in vessel axes directions) of the sum of the connections loads and all of the supports reaction loads.