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Can Wajac print Summary of Minimum Base Shear and Minimum Overturning Moment, in addition to max value?

Question:  

Can Wajac print Summary of Minimum Base Shear and Minimum Overturning Moment, in addition to max value?

Answer:

By default, summary of maximum base shear and overturning moment of all sea states will be printed in the Wajac listing file. But if the design load is defined as MinBaseShear, MinOMoment or MinBothLoads, then the summary of minimum base shear and minimum overturning moment will be printed in the listing file.

It should be paid more attention to that the summary of minimum base shear and overturning moment only relates to the sea states have been defined with Minimum.

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Error in Dean Stream function seastate parameters

Version: 6.2-01 from All

For Dean Stream function theory to be used for computation of wave kinematics, the three errors which are computed should sum up to higher than 0.0001, if less than 0.0001 then we get error for this wave theory. Below is a link which has a flash window for inputting the sea state parameters. After you click on 'calculate', the errors are listed to the left side in a window, the three errors are

Wave Height Error: Mean Sea Level Error: Bernoulli RMS Error:

Sum of these three errors should be higher than 0.0001.

http://www.coastal.udel.edu/faculty/rad/streamless.html

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GeniE MorisonConstant to Wajac

Question

The defined MorisonConstant is assigned to beams. But it is not written into Wajac input file. Where does GeniE write it and how to check the applied Morison coefficients used in wave load calculations?   Answer

In a GeniE workspace, after the defined MorisonConstant is assigned to beams, it is written on SPROHYDR card in the T1.FEM file during the analysis. The **SPROHYDR **card is as below.

SPROHYDR  1.50000000E+01  2.00000000E+00  6.00000000E+00  5.01000000E+02
          0.00000000E+00  5.02000000E+02  1.14999998E+00  5.03000000E+02
          1.14999998E+00  5.04000000E+02  0.00000000E+00  5.05000000E+02
          1.35000002E+00  5.06000000E+02  1.35000002E+00

Please refer to the document Input Interface Format - Finite Element Model and Load Data Types for detail explanations of this card (available from the Sesam Input Interface Format/download/public/sesam/user-documentation/knowledge-articles-files/ACCEL.pdf){target="_blank" rel="noreferrer nofollow"}

User can include the command MPRT into the Wajac input file to make Wajac print out the Morison Coefficients used in wave load calculations for the selected waves and the selected elements.

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Height of breaking wave

Version: 6.2-01 from All

print in Wajac .lis file:

Error: The wave height is exceeding the breaking wave height

Height of breaking wave is computed using the following equation:

Hb = 0.142 * L where L is the wave length and Hb is height of breaking wave

L = (g* T^2)/(2*pi);

If you are using any other theory than Airy wave theory, Wajac will still consider wavelength computed by Airy wave theory. Rest of the calculations will be based on actual wave-length computed by relevant selected wave theory but only the comparison for height of breaking wave is done on the basis of airy wave theory wave-length. This will be corrected in the future Versions.

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How to output a text file of the wave kinematics in Wajac

There are two ways to print the wave kinematics in Wajac.

  • KPRT – this command can be used to print out fluid kinematics at a specified point.
  • The coordinate of this point is specified relative to the origin of the global coordinate system except for the Z coordinate which is relative to the mudline.
  • The fluid velocity and acceleration are printed in wajac.lis file.
  • Maximum 100 points may be specified
  • The command is only applicable for deterministic wave load calculation.
  • OPT9 in OPTI card – OPT9 can be set to 1.0 2.0 to print the local data from member load generation.
  • OPT9 = 1.0, then fort.number files will be generated. 
  • OPT9 = 2.0, then prefix_LocalData_.lis file will be generated.
  • The command can be used for deterministic wave load calculation and irregular wave load calculation.
  • Below is an example in the _LocalData_6.lis file. The file contains the fluid velocity, acceleration, Morison load intensity value of each member.

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Hydrodynamic added mass in eigenvalue analysis run

Version: All

Create a dummy loadcase with fem loadcase number 11. Now create dummy waveload condition and add wajac activity to the analysis. Select Added mass and dampling tab for calculation and click Apply. Now waveload case has fem number 12. 1 to 10 are the eigenmodes.

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Hydrodynamic coefficients have not been specified by the Wajac analysis control data.

Wajac can give the following Warning saying that hydrodynamic coefficients have not been specified by the Wajac analysis control data. 

    *** WARNING: HYDRODYNAMIC COEFFICIENTS HAVE NOT BEEN SPECIFIED BY THE WAJAC ANALYSIS

        CONTROL DATA. ENSURE THAT THE COEFFICIENTS ARE SPECIFIED ON THE SESAM INTERFACE FILE ***

This warning means that you did not specify a hydrodynamic coefficient in the Wajac input file manually. However, an easier way in most cases is to specify those coefficients directly in GeniE, so that hydro coefficients are included in the *T.FEM file.

Both ways are correct, but if you choose to use GeniE to specify coefficients, it will give you the warning mentioned above.

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Marine Growth Weight and Buoyancy always on

Version: All

When defining a loadcase with sea water level and Marine Growth, the vertical load due to Marine Growth is always the vectorial sum of its weight and buoyancy. This is independent of turning on or off the buoyancy calculation and only applies to the amount of Marine Growth that is submerged. All other Marine Growth is neglected.

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Wajac (All Versions) Hydrodynamic results file generations takes too long

If you are running wajac and it takes hours in finishing while generating hydrodynamic results file G1.SIU then please check as follows,

There may be a wrong entry on OPTI card. If you change OPT3 option from 3 to 2 then it will work fine. Please make sure that all the entries are at correct positions. For spacings, please see user manual. 

OPTI 0. 0. 2. 0. 0. 0. 0. 0.

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Waveloads and Buoyancy including eccentricities

Version: All

The OPT8 under the OPTI command governs the consideration of element eccentricities in load calculation. It applie to both wave and buoyancy calculation. If OPT8 = 0 or blank, eccentricities will be taken into account for calculations of both wave & buoyancy load, and if OPT8 = 1, eccentricities will not be considered in both wave and buoyancy calculations.

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What are ILLEGAL ELEMENTS

Question: When running the model, WAJAC produces the warning below. How to identify the illegal elements so that you can decide whether this issue needs corrected

Answers:

This warning indicates that there are illegal elements in the model, which will lead to the reported structure mass in " W E I G H T   A N D   B U O Y A N C Y   S U M M A R Y" is incorrect as they are not counted in the mass calculation.

Please notice that only beam type BEAS is supported by Wajac. So any other beam type like truss elements (TESS), second order beam elements (BTSS) will be issued as illegal elements.

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Why is there a mismatch between the loads reported in Wajac.lis and Sestra.lis?

In some cases, the wave loads reported in Wajac.lis might not match those in Sestra.lis. An obvious reason can be errors in the load transfer, but another reason which is not related to an error is the following.

The cause of the difference between Wajac and Sestra can be due to non-zero Cdx and/or Cmx components (drag and inertia coefficient along the member) specified in the Morison coefficients in the model.

Wajac will use the Cdx and Cmx components to calculate the loading on the model, and will find the overturning moment and base shear including these loads. However, the loads are only used by Wajac to compute the overturning moment and base shear. As such, these values are correct and the correct phase angle is found for the wave loads. The wave loads for those phase angles are then used in Sestra, but without the Cdx and Cmx components of the load. These are only used to find the overturning moment and base shear and will not be used in the structural analysis afterwards. If the Cdx and Cmx components of the Morison coefficients are set to zero, the values in Wajac.lis and Sestra.lis will be the same. Otherwise, the values in Wajac will be different due to the added Cdx and Cmx component used for the Wajac determination of the phase angles of maximum overturning moment and base shear.

Hence, adjusting the Cdx and Cmx values to 0, which is how Sestra gets the loads from Wajac, makes Wajac and Sestra report the same. Note that the main difference is that in the case the Cdx and Cmx are not equal to zero, the phase angle found at which the maximum base shear occurs may change compared to when Cdx=0 and Cmx=0.

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Wind loads without wave loads

Version: All

If you want to compute only wind loads on the structure then you have to use a dummy wave load condition with it in GeniE. This is a limitation. Dummy wave load condition might have calm sea condition, buoyancy may optionally be switched off.

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