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A limitation for Wind heeling moment calcuation

Version: 5.0-06 to All

When using HydroD 5 to calculate wind heeling moment from shape coefficient method, the structure in wind must have a roof to ensure closed volume.

For the structure without roof, for example an open-ended cylinder, wind heeling moment will end up with 2 times the normal value.

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Added mass for limiting frequencies

Please see the attached PDF for information on how this can be done from HydroD 4 and HydroD 6.

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COG, COB and compartment points printed in HydroD when trim/heel included

Center of gravity (COG), Center of buoyance (COB) and compartment points (COB and free surface point of each tank) printed in HydroD are given in the Input coordinate system.

When trim/heel angle is defined, what HydroD rotates is the global coordinate system. The structure and input coordinate system will remain their original position.

So all the points will be printed in the same original input coordinate system which is not being influenced by the trim/heel angle.

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Compartment Display

To change the transparency and labels, use the Modelling Draw Style option (right-click the compartment in the browser or in the graphics).

You can change these properties for one tank, or for all tanks. To change them for all tanks, the procedure should be to select all tanks (after opening the Modelling Draw Style menu?), then push the lower left button in the Draw Style menu.

Note that there are two occurrences of the tanks/compartments: one below the structure model in the browser and one in CompartmentContents in the Loading condition.

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Compartments and superelements

Can a superelement be mirrored in Presel and compartments/tanks still be used?

No. If a superelement is mirrored, the compartments will by default be defined across the space between the superelements, at least in Wadam. The centre of the compartment will be computed from the corners of the combined compartment's load case (from both the original and the mirrored superelement). This problem is that the same dummy load cases are defined in both superelements after the mirror operation. The solution is to mirror the superelement in GeniE, and renumber the compartment load cases, to create separate incidents of the superelements (e.g. T7.FEM and T8.FEM) to be assembled in Presel.

An exception is for a centre compartment with one half modelled in one superelement. When mirrored, this will make up the complete compartment.

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Coordinate systems for responses vs. load files (HydroD/Wadam)

The responses from Wadam is given in the Motion reference point (Results reference point). This point is by default in the origin of the global coordinate system in HydroD/Wadam. This origin is located in the still water line, directly above the origin of the Input (model) coordinate system.

The Motion reference point may be defined by the user in HydroD: WadamRun setup - Execution DIr. - Result files.

The load file (L#.FEM) is created in the superelement coordinate system of the structural model. Ln.FEM corresponds to Tn.FEM.

When the structural model is defined by one single superelement (one T#.FEM only), this is identical to the Input coordinate system.

If a superelement assembly is created, in Presel, and the superelements are translated/rotated/mirrored in Presel, the top level Input coordinate system may be different from the systems of the individual superelements. The load file will still use the Input coordinate system of the original superelement (T#.FEM).

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Damping Tutorial

This FAQ describes how to create and use a free surface mesh in HydroD and Wadam. A Sesam Manager zip file is attached.

HydroD 4.10, HydroMesh, Wadam and Postresp are used in this example. Create a new job in Sesam Manager and import the zip file. Open the HydroD_DampingTutorial.pdf file attached to the job and follow the instructions. NOTE: After importing the zip file make sure the HydroD version is 4.10.

There are two purposes of this tutorial:

  1. Show how to create free surface meshes (models) using HydroMesh
  2. Show how to use these models in Wadam for: a. Damping surfaces in moonpools or narrow gaps   b. Fixed lids for irregular frequency removal   c. Free surface meshes for any of the following uses   i. Second-order analysis   ii. Wave drift damping or forward speed analysis   iii. Offbody points

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Definition of a bilge keel (HydroD/Wadam)

Take care to define the bilge keel, in the roll damping model, within the boundaries of the strip model. Read the Wadam user manual carefully, also page 5-49 etc.

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Dummy hydro pressure on free surface (HydroD/Wadam)

If you want to do a second order QTF calculation in Wadam, then a free surface model is needed. This free surface model can be imported in LoadingCondition>New second order surface model.

Dummy hydro pressure must be defined on the free surface model but can be in both positive and negative Z-directions.

More information is found in Wadam_UM, section 2.1.10.

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For a sub-model, do I need to re-map the hydrodynamic loads to the sub-model (local model)? (HydroD/Wadam)

Yes, in normal cases you have to map the loads also to the local model. This is done by defining a new Wadam analysis in HydroD, where the global structural model is replaced by the local model. If you are not using the feature of internal compartments, you can still use the global structural model as a mass model (if this was used in the first place).

If compartments are included, special attention must be made to the definition of the total mass: As the local model does normally not have all compartments included, the total mass may be found from the global analysis and defined as a 'user specified' mass model.

If parts of compartments (i.e. not complete compartments) are included in the local model, the filling fraction cannot be handled properly by HydroD (total volume is needed). In this case the Compartment Points need to be defined in HydroD, giving the acceleration point at the centre of gravity for the compartment, and the zero pressure point at the free surface. Please see the attached document, HydroD_CompartmentPoints_Wadam_QS.pdf.

Please notice that it is required to rerun exactly the same wave periods and directions as in the global analysis. Everything should be identical except the structural model. A good way of doing this is to copy & paste the HydroModel inside HydroD, and replace the local model in the copy. Similar for the Wadam run.

If the panel model is big, using the restart option in the Advanced tab of the Wadam run setup will speed up the calculations (but this has to be done already when running the global analysis).

If the local model is very small, the local loads may in some cases be of less importance, as the bending action from the prescribed displacements on the edges will be governing for the results.

Please see the attached document HydroD_CompartmentPoints_QS.

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How can compartments be defined in a local model?

The versions of HydroD & Wadam (4.5-08 & 8.2-02) have a new feature on definition of an acceleration point and a zero pressure point for each compartment.

This means that the compartments do not anymore need to be modelled completely in the local model. Wadam will use these points instead of computing the points from the uncomplete compartments.

Please notice that special care must be taken if the local model includes part of a compartment above the free surface (filling fraction) of the compartment.

Wadam will by default put load to all wet elements in the tank. In normal cases the wet surface is removed by HydroD above the free surface, but not when a complete compartment is not included (closed volume).

Notice: From Wadam 9.3-06 Pressure is put 0 for elements above the free surface of tanks in quasi-static method. However, the previous situation is still present for Wasim.

More information is found in FAQs no. 4094 and 4095.

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How does Stability calculate wind exposed area?

This FAQ shows how HydroD Stability calculates wind exposed area when one structure is hidden behind another. For example, we have two beams, one is hidden behind another.

Two dimensions are defined first, by HydroD.

  • 'D_beams': Distance between two beams.
  • 'D_cell': Dimension of the structural model divided by “Search grid resolution”, which could be found in the dialog of “Define Heeling Moment Curve”.

When D_beams<D_cell

  • Exposed area for hidden beam will the projected area not be covered by the front beam.

When D_beams>D_cell

  •  Exposed area for hidden beam will be the whole beam projected area.

In both these two conditions, front beam and hidden beam are facing the same wind speed.

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How to add a point load to a structural analysis with wave loads from HydroD/Wadam

If you add a load manually in GeniE, the important issue is to define this load in a load case not conflicting with the wave load cases created by HydroD/Wadam.

If you have a Morison model included, and want to use the wave loads on the Morison model in the structural analysis, the only recommended option is to define the additional load in a load case following after all the resulting wave load cases. If you have for example 20 wave periods and 10 directions, and include the static load case from HydroD/Wadam, there will be 201 hydro load cases. The additional load case in GeniE should then be put into FEM load case no. 202, or higher. And, for sure, the load case name is not important; it is the FEM load case number that counts. This number may be adjusted by going into the properties of the load case (right-click). A picture from GeniE is attached

If you do not have a Morison model, and you do not need to run fatigue (ok for ULS), you can specify in HydroD that the wave load cases shall start at e.g. no. 5 (WadamRun - Exe. Dir - Result Files - Load Transfer). That means that the first (static?) load case from Wadam will be no. 5, and you can define the additional load in load case 2-4. The wet surface definition in load case 1 is a dummy load, but should not be used for the additional load. Load cases for compartments, if any, should be available for the additional load.

It is of course important (as always) to check the sum of loads in sestra.lis after the structural analysis has been run. The additional load case should be seen separated from the wave load cases.

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How to avoid breaking the limit of number of panels in a defined Correspondence (HydroD/Wadam)

When defining a Dual model for Wadam, a Correspondence between panels and Morison elements must be defined. There is a limitation of connecting max. 99 panels to one Morison element. To avoid breaking this limit, apart from changing the models, two main options exist:

  • Try to manually move some panels from one Morison element to another neighbouring element,
  • Split the Morison element into 'subelements', which may have a number of panels for each, max 99. The number of subelements for a Morison element is defined in the Morison Section property.

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How to explain the coupled stiffness/damping matrix for multi body analysis?

To explain the meaning of this 12*12 matrix, we take coupled stiffness matrix as an example.

We can divide this matrix into four parts with varying range for mode i (1-12, represents row) and j (1-12, represents column).

Cij (i=1-6; j=1-6) are stiffness for body number 1 in i mode due to unit motion of body number 1 in j mode;

Cij (i=7-12; j=7-12) are stiffness for body number 2 in i mode due to unit motion of body number 2 in j mode;

Cij (i=1-6; j=7-12) are stiffness for body number 1 in i mode due to unit motion of body number 2 in j mode;

Cij (i=7-12; j=1-6) are stiffness for body number 2 in i mode due to unit motion of body number 1 in j mode

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How to import DXF file to section model?

HydroD only supports POLYLINEs, not SPLINE entities.

Use a CAD program (e.g. Rhino) to export a DXF with POLYLINES only.

Set low accuracy of the exported lines. If the export accuracy is too high, the imported sections will contain too many points. (In that case you can use the pln editor tool to interpolate to a given number of points).

There is some information on this DXF file in the user manual for HydroD, section 5.3.8.

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How to include compartments when using multiple instances of the superelement in Presel?

It is not possible to reuse superelements with compartment definitions in HydroD. The only exception is if a compartment is actually split in two or more superelements, e.g. at the centre line of a vessel.

The reason for this is that the load case definitions for compartments must be unique in the 1st  level models. Reused superelements will have the same load case numbers as the original, modelled, superelements. Load combinations in Presel are not used for these dummy load cases. HydroD, Wadam and Wasim  will read the definitions as created in the 1st level model only.

The way to do this with superelements is to create more superelement T-files in GeniE, with specific load case numbers for the compartments in each; one superelement for each location in the complete model. Or, alternatively, not use the superelement technique this way.

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How to include mooring stiffness into the motion analysis?

The anchor stiffness is included by way of a Morison model. Given a Morison model, normally created in GeniE, mooring stiffness may be added by an anchor element or a TLP element and the corresponding anchor/tlp properties.

The Morison model may consist of one or more beams only, with their nodes giving positions for the mooring elements.

To include the mooring force into a load transfer analysis, the Morison model must normally be assembled with the shell structural model in a superelement assembly (using Presel).

Alternatively, a restoring matrix may be defined directly.

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How to include the damping force in sectional loads or load transfer? (HydroD/Wadam)

The only way to include damping forces in sectional loads or load transfer is to use Morison elements.

The drag coefficients should be tuned so that the resulting damping is similar to the case when using an additional (critical) damping matrix or the roll damping model.

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How to input non-linear damping coefficient in HydroD based on quadratic roll damping from model test (HydroD/Wadam)

From Wadam 9.3-06: If you have the quadratic roll damping B2 from tank test with SI unit Nms^2/rad^2, then the input quadratic roll damping coefficient b2 in HydroD under LoadingCondition>AdditionalMatrics>Define Non-linear Damping>Roll damping should be:

b2=B2/(2*M44*(180/pi))

In case B2 is following the unit Nms^2/deg^2, then input to HydroD will be:

b2=B2/(2*M44)

Where M44 is the dimensional mass inertia in roll which is measured in Wadam's global coordinate system. The non-dimensional value M44/(?VL*L) can be found in “MASS INERTIA COEFFICIENT MATRIX” in the Wadam.lis file.

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How to keep symmetry when balancing tanks

How to keep symmetry when balancing compartments in HydroD?

The system is made such that HydroD needs to adjust 3 tanks to reach a stable condition.  There is however an option for using groups of compartments, in the CompartmentContents property options.

See also the built-in user manual (F1, or Help), section 1.2.1.6.

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How to make sure Morison loads are included in the Sestra structural analysis?

How to use a composite model (Morison model plus shell model) in a HydroD/Wadam/Wasim load transfer analysis?

In order to use the anchor loads and any other loads from the Morison model in the structural analysis in Sestra, the Morison model has to be part of the structural model.

The recommended method is to use a “Single superelement composite model”. This means that the complete model can be created in one model, i.e. one superelement (one T#.FEM file), and this file can be read into HydroD as both a Morison model and the Structural model. In this method, all loads, both accelerations, surface pressures and Morison loads, will be part of the same load file (L#.FEM). More information is found in the Wadam user manual. The HydroD user manual and release notes (for HydroD 6 versions) can also be useful.

If the Morison model is a separate model (T#.FEM, e.g. T2.FEM), Wadam/Wasim will create a load file, e.g. L2.FEM, for the Morison loads, including anchor loads etc. Unless T2.FEM is also a part of the structural model, Sestra will not read the L2.FEM file. Only the L files matching the T files in the structural model will be used. In this case a superelement model assembled in Presel is required. This means that supernodes (special boundary conditions) need to be defined in the Morison model, e.g. T2.FEM. These need to match the supernodes for the connecting superelements (shell model). Then read T2.FEM into Presel together with the other superelements etc.

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How to make Wamit .out files with all needed results? (HydroD/Wadam)

Version: Up to 9.1-02

In Wadam version 9.2-03 and later versions, the Wamit.out file contains the complete results. The following work-around is thus not needed.

If you need results in Wamit format, e.g. for further mooring analysis in Simo etc., the option Save Wamit files has to be selected in the Advanced part of the Wadam setup in HydroD.

Some programs use the file .out, not the numerical results files. The .out file is created by the Wamit part of Wadam called Force, which is run twice in a normal Wadam calculation. The .out file is created by the first Force execution, then overwritten by the second Force execution. That means that you need to run one standard Wadam analysis and one where Wadam is stopped before second Force. This can be set up in HydroD - Wadam run - Advanced tab.

The first Force (i.e. stopped before second Force) will give:

  • Added mass and damping coefficients
  • Exciting forces

The second Force (i.e. without stopping) will give:

  • Global mass, damping, stiffness matrices - frequency independent
  • Motion RAOs
  • Offbody point results (pressure, velocities)
  • Drift forces

Please notice that the option Save Wamit files cannot be used together with the Wadam Restart option.

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How to open a .hyd file on another computer?

We do not recommend to use the .hyd file on another computer. The .hyd database file is not compatible between different versions of HydroD.

First, a .sat file is also required. Next, the compatibility may also be broken by setting an environment variable for memory usage (HydroD UM, section 4.7 Program Limitations.

Use a clean JS file to recreate a database on another computer. This file is created from the "File - Save clean JS" command in HydroD.

Remember to update or remove the path to any T#.FEM files in the JS file for panel models, mass models etc. No path means that the T#.FEM file will be read from the same folder as the JS file.

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How to recreate a workspace?

Use the logged js-file, or a 'clean' js -file (better), to recreate the workspace. A 'clean' js-file is created from 'File - Save clean js' inside HydroD. Update/remove path information for the T-files in the js-file prior to use.

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How to select filling fractions for sub model?

If the whole compartment in the sub model is fully wet or dry, then the filling fraction for that compartment can be defined to be 1 or 0.

If a compartment is not completely modelled in the sub model, and it is partly filled only, then some special technic is needed for filling fraction defined.

Go to GeniE first, using the global model and look at the interesting compartment. Carefully select the wetted/submerged internal compartment surface in the sub model, according to the filling fraction, assign them ‘wet surface’ property. Then apply the correct load case number.

Then run submod (the same as before).

Import into HydroD the modified sub model with only partly defined wetted internal surface.

Assign filling fraction for this compartment to be 1.

So the correct internal wet surface will be generated from HydroD and read into Wadam/Wasim.

Also remember to define the correct Compartment points, typically taken from the global analysis, from Wadam.lis or from HydroD information.

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How to solve wrong displacement and mass reported when transforming pln file while using symmetric function?

In HydroD, wrong displacement and mass will be reported when transforming pln file and at the same time using symmetric function. Use the below workaround get around this issue:

  1. Mesh the original pln file and get the T#.FEM files.
  2. T7320.FEM is the one with the whole mesh along the hull, so this T7320.FEM file will need to be mirrored to get the complete mesh model.
  3. Go to ‘Tools’>’Mirror/transform/scale FEM file’ to mirror the T7320.FEM file into a complete panel model.
  4. Define a new panel model with this new complete FEM file and translate it according to your interests.

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How to use (old) quasi-static load transfer option and local structure model with HydroD?

The calculation of static load inside a compartment may be difficult when the tank is not modelled completely.

When using the (old) quasi-static method, defining Compartment points in HydroD is required (in the Loading Condition) to give Wadam the correct position of the acceleration and zero pressure points. The correct position may typically be found from the compartment data for the global, complete, model. Right-click a compartment and select Information.

If the local model contains parts above the free surface of the compartment (but still not the complete comparment), HydroD cannot remove properly the wet part of the compartment above the actual free surface, as in normal cases.  

To avoid this problem, the best way is to remove the wet surface, or dummy hydro pressure, from the elements above the free surface. This must be done in the modeller, e.g. GeniE or Patran-Pre.

In some cases, simulating a high filling fraction (like almost full) may be done by defining a full tank with a reduced density.

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How to use file names for models in a Multibody analysis? (HydroD/Wadam)

Regarding the T#.FEM files in a multibody analysis, the panel models for different vessels must have a unique'superelement' number (e.g. T1.FEM and T2.FEM). They cannot be distinguished by a prefix in the file name, or by a different path, only.

The reason for this is that HydroD will strip off the path\prefix when copying these files into the Wadam run folder, thus making Wadam see only one of the files, if they both have names like <path\prefix>T1.FEM.

Please also remember that this superelement number in the file name needs to be defined in the model, like in GeniE (Edit - Rules - Meshing). Renaming the file from for example T1.FEM to T2.FEM will not work because this number is also given inside the file (in the first line).

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How to use new internal tank dynamics and local structure model with HydroD?

The calculation of static load inside a compartment may be difficult when the tank is not modelled completely. In that case HydroD cannot remove the wet part of the compartment above the actual free surface as in normal cases. For the new method of internal tank dynamics this is improved, but there still is some manual work:

Panel model shall take the global structural model in which all tank geometry has been defined. External hull can have symmetry property, whereas the tank geometry cannot have symmetry.

Structure model defined in HydroD shall also use the global structure model, so that the tank can be seen and tank properties can be defined. HOWEVER, after the WADAM1.FEM is generated by HydroD, one has to manually place the local structure model (T#.FEM) in the Wadam working folder, and change WADAMA8 card, so that the third field is corresponding to the superelement no. of local structure model (T#.FEM). Be aware that any coordinate transformation defined in HydroD may destroy the model settings.

Mass model defined by HydroD shall also be from the global structure model, the mass matrix without tank content will be found by HydroD and sent to WADAM later. Or, find the mass information from the global mass model, and add this as user specifed mass or as a mass matrix for the local analysis.

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How to use the characteristic length setting for model scale analysis?

If you use HydroD/Wadam to do a model scale analysis with a small dimensional model, then the setting for ‘Characteristic length’ should be paid attention to.

Usually, the number also needs to be scaled accordingly to a short characteristic length, so it can represent the real characteristic length of the model scale analysis.

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HydroD 4.x & Wasim: Torsethaugen wave spectrum cannot be used in an irregular sea state

A Torsethaugen wave spectrum cannot be used in an irregular sea state.

The Bretschneider and Jonswap spectra may be used.

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HydroD V5.x covers only stability - requires HYDROD__STAB license to start

HydroD V5.0 is a completely new version of HydroD, not only an upgrade of version 4. It is developed on  a new IT platform in accordance with DNV GL Software technology roadmap. Version 5.0 covers hydrostatic and stability calculations ONLY and may replace version 4 for this purpose.

Wave loads and motions analyses will be supported in a later upgrade of version 5. 

*This implies that for all other features than stability you still need to use HydroD 4.x *

To start HydroD 5.0 you will need a HYDROD__STAB license .

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When using overlapping panel model and Morison model in a Composite model in Wadam, the diameter of the overlapping Morison sections must be reduced, to avoid double buoyancy volume. Consequently, the drag coefficient for these Morison sections must be increased by the inverse factor, to keep the product of D*Cd correct. A normal procedure is to divide the diameter by a factor of 1000, and multiply the drag coefficient by 1000.

When using HydroD, this is done in the MorisonSections part of the HydroProperties in the browser. Just select Diameter and type the reduced value.

The added mass coefficient should not be changed. The added mass will be calculated from the panel model.

This is avoided altogether by defining the correspondence, for a Dual model, but then the consequence is that the load transfer will only give line loads and point loads for the Morison model, not pressure for any shell part.

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Is it possible to find the volume of compartments in HydroD?

Yes.

  • Right-click the compartments below the structure model in the browser and select Information. This will give volume, COG etc. for predefined filling fractions.
  • Right-click the Compartment contents in the Loading condition. This will give volume, COG etc. for all compartments using the assigned filling fractions.

This will also be available in the Stability Report from a hydrostatic/stability analysis.

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Is there a tool for creating a PLN file for HydroD?

No. The file is normally written directly in a text editor, or possibly by some 'personal' program, like Excel etc. It is possible to create a PLN file from a T#.FEM file in HydroD. There is even a separate tutorial for this, but it is not always an easy task.

The file format is given in the HydroD and Wasim user manuals.

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License error: invalid host when starting old Sesam programs (HydroD 4.10, Sestra 8.8, Profast)

License error: invalid host when starting old Sesam program (HydroD 4.10, Sestra 8.8, Profast) HydroD4.10, Sestra 8.8, Profast, and some other old Sesam programs, are not compatible with the latest dongle driver on some windows systems. The walkaround is to downgrade the dongle driver to 11.15.

  1. Delete the HASP folder in registry editor, as shown below. This will uninstall the license dongle driver.
  2. Install License dongle driver 11.15, which can be downloaded from (copy link if not working)

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Loading condition reference point

Q: What is the reference point for the definition of the water line in the loading condition? A: The origin of the model's coordinate system.

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Modelling compartments & superelements

A tank is defined in a single, dummy, load case, starting at #2 (#1 is external wet surface). Tanks split into several superelements must be modelled using the same load case number. Be careful with repeated superelements when using compartments, see the following FAQ:

HydroD Compartments and superelements

https://emea.salesforce.com/50120000000eHZa?srPos=0&srKp=501

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Morison model and beam element type (HydroD/Wadam)

Before Wadam version 9.7: Please note that the Morison model used in Wadam has to be created by using the standard 2 node beam element.

Beam elements meshed as second/higher order, 3 node, beam elements will be neglected by Wadam.

A typical message in the print file from Wadam, Wadam1.lis is, in section 2.2:

-  nn - ELEMENTS OF ILLEGAL TYPE ARE DETECTED AND DROPPED.

When creating the Morison model in GeniE, this element type is ensured by NOT selecting the option for use of second order elements in the Edit - Rules - Meshing dialogue.

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Out of virtual memory - For all versions prior to HydroD 5.0

The solution is described in the user manual for HydroD, section 4.7 Program Limitations:

Create an environment variable as follows:

4.7 Program Limitations

HydroD uses dynamic allocation of memory for all objects, meaning that there should be no limitations in the number of objects/sizes of objects. However, since HydroD employs a database called Objectstore, there is a limit on the maximum total size of the database. By default this limit is 128MB, but by defining an environment variable OS_PSE_AS_SIZE, the maximum size can be increased up to approximately 600 MB (OS_PSE_AS_SIZE = 600000000). If this environment variable is defined too large, the application will not start.

Also notice that the change above will make databases created prior to this change unreadable. To import such databases you must first set the variable back to the value it had when the database was created.

HydroD does also run Wadam and Wasim in the background, and these programs have some other limitations on the number of objects/sizes of objects. These can be found in the Wadam and Wasim user manuals.

NB: HydroD 4.10-01 can use a memory setting of up to 2 GB (2000000000).

This setting is defined in the System settings on the PC, normally accessed from the Control Panel - System - Advanced system settings.

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Postresp: How to define off body points for Postresp in a HydroD and Wadam analysis?

To use off body point results in Postresp, specific off body points must be defined in HydroD, using coordinates given in the Global coordinate system, i.e. having the origin in the still water line.

Further calculations can be done in Postresp on the results in these off body points.

The off body point grid is used for visualization & animation in Xtract only.

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Prefix of T#.FEM files (HydroD/Wadam)

When T#.FEM file are read into HydroD/Wadam, a prefix of the T file will automatically be neglected and only the characters after ‘T’ will be read by Wadam.

For example, ‘VesselT1.FEM’ and ‘ShipT1.FEM’ will have the same name in a Wadam run in HydroD, which is T1.FEM. This will cause trouble if more than one HydroModel exists in one workspace and different T files are read in different places, for example in a multibody analysis.

So T#.FEM files are needed to be assigned with different recognized numbers, like ‘VesselT1.FEM’ and ‘ShipT2.FEM’.

Please also remember that this superelement number in the file name needs to be defined in the model, like in GeniE (Edit - Rules - Meshing). Renaming the file from for example T1.FEM to T2.FEM will not work because this number is also given inside the file.

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Presel HydroD Xtract: Display of beam elements from Equipment vertical mass option

The display of beam elements from the equipment vertical mass option is different in Presel, HydroD and Xtract.

Presel and HydroD will show the "vertical mass" beam elements as beam 'tents', i.e. without eccentricities, in the same way as for the option "beams and mass" from equipments.

Xtract will show the vertical beam elements, i.e. with eccentricities, when the beam cross section is shown. In wireframe mode of beam elements, the eccentricities are not shown. The beam elements are shown in the same way as for the option "beams and mass" from equipments.

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Problem with reading T-file

Material and thickness must be properly defined in the T#.FEM files.

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Requires Wadam version no lower than 9.2

Version: 4.8-01 to All

HydroD version 4.8 (and later) requires Wadam version no lower than 9.2

Type: limitation

HydroD version 4.8 (and later) always writes WDDCUR card to Wadam1.fem file, which was started to be supported by Wadam from version 9.2. So HydroD version 4.8 must work together with Wadam version no lower than 9.2.

Always use latest versions of both HydroD 4.x and Wadam.

(from the HydroD status list)

(A possible, but not recommended, workaround is to delete the line starting with WDDCUR from the file Wadam1.FEM before starting the Wadam analysis itself.)

Typical error message in Wadam1.lis:

" Reference is zero or negative. IDGR:WDDCUR NREF: 1 IREF: 0

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Roll damping model bilge keel (HydroD 4.x/Wadam)

There is unfortunately a defect in HydroD 4 connected to the definition of the bilge keel angle within the roll damping strip model. This is listed in a separate entry in the HydroD status list.

It is important to know that the bilge angle actually being used in Wadam is listed in the Wadam1.lis print file, in section 3.1. As stated below the table of bilge keel data in this section, the angle PHI, initially given from HydroD, is the relative angle of the bilge keel from the line between (Yi,Zi) and the intersection of the centerline/waterline, seen from bow to stern.

PHI is given in HydroD relative to the input coordinate system. HydroD transforms this angle to the global coordinate systemand writes this to the Wadam input file, Wadam1.FEM.

The display defect in HydroD means that the correct angle to be used in Wadam may be displayed incorrectly in HydroD.

This issue is only relevant when the Integration option for the ITTC method is used (or the now old Tanaka/Kato method). When the Simplified option is used, the bilge keel angle is not relevant.

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Save/Restart option vs Save/Bypass of Wamit parts (HydroD/Wadam)

Two different options for saving and reusing Wadam results are available in HydroD.

  1. The Save/Restart option is the "Wadam way" of saving the potential solution, to avoid recalculating this when not needed. This is the recommended method for such time saving operations. The option for Save/Bypass/Stop of Wamit parts is included to help users knowing Wamit input/output files to obtain special results and features not available in the standard Wadam analysis. If the Wamit files are saved in the first run, the "bypass Poten" option will be similar to the Wadam Save/Restore option.
  2. To be able to reuse the potential solution, from Save/restart or Bypass, the wet part of the structure cannot be changed. This means that the panel model and the draught (displaced volume) cannot be changed. Because equilibrium of mass & buoyancy is needed, the mass cannot be changed either. The method of defining the mass may possibly be changed, though, as long as its resulting mass properties are not changed. The same wave periods must be used as well. Typical changes are variations of damping, and variations of output results like adding load transfer to a previous analysis.
  3. The Save/Bypass/Stop option makes it possible to edit intermediate Wamit files. There can be many reasons for wanting to change the Wamit files, like the need of special features not accounted for in a standard Wadam analysis. Knowledge in Wamit is of course required for this kind of editing. When Wadam is told to "Stop before Force", the input files will be made by Wadam. These may be edited, Force can be run independently of Wadam, before running Wadam again with "Bypass Force" selected. Some more information is found in the status list for Wadam (an example for a multi-body analysis is attached).
  4. To put it simply, the first Force execution will compute added mass, damping, excitation forces etc., while the last Force execution will compute e.g. off-body kinematics, drift forces etc. Handling of Morison effects (drag coefficients, added mass etc.) will be done in Wadam after the first Force.

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Sectional loads (HydroD/Wadam/Wasim)

When computing sectional loads for a vessel, we recommend to specify the side of the cross section with the smaller part of the vessel as the integration side. The integration side should be changed at midship to achieve the best results.

The numerical issues from integrating the pressure over all the panels may be fairly large. This will typically grow when the part of the model on the integrated side is large, and is one of the reasons for this recommendation.

The mesh size (discretization) may also affect the results; a finer panel mesh will be more accurate than a coarse mesh.

It must also be remembered that the total sectional load is the difference between the huge values of buoyancy and inertia. Small inaccuracies in these values may have a big consequence for the sectional load.

The end sections should be positioned to include all of the panel and mass model from the applicable side of integration, i.e. a bit on the outside of the model. This to include the complete horizontal pressure in the integration.

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Sesam Compartments with Dipole elements

How to create a compartment model including dipole elements in GeniE, and use them in HydroD?

Please see the document which is found in the attached zip file , together with model files.

Notice that there is also a tutorial in HydroD 6.2 and later versions on how to use dipole elements in the panel model and compartments for Wadam analyses, available from the Help menu.

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Settings for drift forces in HydroD

This document (link) describes several different settings for mean wave drift forces and second-order difference-frequency wave forces(full QTF).

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T-files created from meshing a .PLN file (HydroD/Wasim)

HydroD will create a number of T-files when meshing the section model (.pln file). The files are described as follows:

T7301.FEM - mesh of dry part of structure (above sea)

T7302.FEM - mesh of wet part of structure

T7303.FEM - mesh of sea

T7310.FEM - mesh of structure + sea (T7301+T7302+T7303)

T7320.FEM - mesh of structure (T7301+T7302), may be used as panel model

All these models are given in the input coordinate system (same as the section model).

T7310 includes mirror images in the case of symmetry. In addition, the model T7373.FEM is also mesh of the sea, but in the global coordinate system.

T7320.FEM does not contain symmetric parts. It is just the union of the wet and dry part. This superelement model can be used as panel model for Wadam for all loading conditions. This is what actually happens automatically when you import a section model, create the SectionHullMesh and refer to this HydroModel in a Wadam or hydrostatic analysis. The symmetry property is also automatically handled.

T7310 is used if you want to inspect the mesh in Xtract. It is not used for anything in connection with any type of HydroD analysis. Inspecting the mesh in Xtract was important in the old Wasim Manager which had limited graphical functionality, but it is not really needed with HydroD so this file is basically superfluous.

T7373.FEM - mesh of sea in Global coordinate system. May potentially be used as surface model in a Second order or a Wave Drift Damping Wadam analysis or alternatively as an offbody model for Wadam animations. In the last case it is however probable that in the case of symmetry you will want to create a model which includes symmetric parts.

With the possible exception of T7373 (and T7310 if you really want to use Xtract to inspect the mesh) the user should not really need to relate to any of these files. (As mentioned T7320 is automatically used as panel model without any need to specify this for the user).

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Very long wave and relavant water depth set up (HydroD/Wadam)

When very long waves are applied in HydroD/Wadam, the setup for ‘Water depth’ is important.

Different water depth will cause the vessel floating in shallow water, intermediate water or deep water condition for one fixed wave height and wave length.

Ranges of validity for various wave theories in relationship with the non-dimensional wave height and non-dimensional water depth are specified clearly in DNV-RP-C205, Figure 3-2 (look for Rules and standards in www.dnv.com).

User needs to have a proper water depth to make sure the floating structure is actually working within linear wave theory.

For example, if we have a long wave with amplitude =1m; period=180s, water depth needs to be at least around 48000m to make sure deep water condition is applied.

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What is the difference between a composite model and dual model? (HydroD/Wadam)

Version: All

The main difference is that in a load transfer analysis, the composite model will transfer panel pressure loads to the shell part of the structural model and Morison loads to the beam (Morison) part of the model. The use of a dual model will only transfer loads to a beam (Morison) model.

To change from a composite to a dual model, a correspondence between the panels and Morison elements has to be defined.

In a composite model, any Morison elements overlapping the panel model need to have a small diameter, with an increased drag coefficient. This is to ensure a correct calculation of the displaced volume and a correct drag calculation.

More information is available in the HydroD and Wadam user manuals.

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What to do when the Activity monitor says the data check is terminated while Wadam keeps on running?

In some cases the Activity monitor in HydroD will say the data check is terminated while Wadam keeps on running.

When an error like this is written from the HydroD datacheck to the Activity Monitor, there is normally a more detailed description in the Message tab at the bottom of the HydroD interface.

Some typical issues are:

  • when heel or trim angles are included in a loading condition, in conflict with symmetry options for the panel model
  • maybe defining cross sections for a user specified mass model
  • other settings in conflict with the Wadam ‘rules’.

The analysis may perhaps still be OK, but you need to check thoroughly. The Wadam.lis file should also be inspected closely.

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When and How to define a dual model?

The only situation when you really have to use a dual model is when you need to transfer all loads, both Morison and panel loads, to a beam structure model. 

The method is based on that the Morison model is defined for the complete structure model (FE model), while the panel model can cover a smaller part of the structure.

Also, making a correspondence between panel model and Morison model is necessary; all panels must be included in the correspondence.

Give the Morison model the real diameter in the property setting. This is very important for volume calculation during load transfer.

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When running load transfer with compartments, is it necessary to create a closed tank?

No. When using HydroD 4.5-08 (or later) and Wadam 8.2-02 (or later), the points for computation of acceleration in the tank/compartment and the point for zero pressure, at the top of the tank, can both be user defined.

The points are defined as Compartment Points within the loading condition.

This is very revelant for load transfer to a local structural model (e.g. for use in Submod), where the tank is not defined completely.

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Why can I not present the shear forces and bending moments in still water?

After having run a hydrostatic stability analysis, the graphs of sectional forces and moments in the Hydrostatic report are not always presented automatically.

This should be solved by right-clicking in the graph area and selecting "Zoom All".

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Why is there some times a problem in using a model from Patran-Pre?

If a material and thickness is not properly defined, the T#.FEM file from Patran-Pre will not be correct.

The thickness record (GELTH) is written to the T-file with zero thickness for shell elements that have no property defined in Patran-Pre.  Reading of this T-file by other programes (e.g. HydroD, Wadam or Sestra) will result in error termination.

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Workaround for phase angle set in deterministic calculation

When defining an array of phases within a phase set, HydroD writes WADAMD1 card into WADAM1.FEM file. In this card, the third value describes the number of phase input (NPHA). And then write out all the phase angles as users' input. If NPHA is larger than zero, Wadam will use the first entry as a starting value and the second entry as a phase step value. It subsequently ignores the others. WADAM thus interpreted phases in a wrong way and these wrong phases can be found in the output from WADAM.LIS.

There are two workarounds depending on users' input phase angles:

  1. If the users input phase angles has a constant phase step, then users can manually modify the second phase entry, i.e. the fifth value in WADAMD1 card as the phase step value.
  2. If the phase angles users input does not have a constant phase step, then users can modify the third value, i.e. NPHA=0 in WADAMD1 card. Thus WADAM will read the next 8 phase values and find out the total number of NPHA by counting non-zeros.

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