Postresp_Workshop1_Semisub

SESAM

Postresp

SESAM User Course in Hydrodynamics Postresp Workshop Basic part - Semi-submersible

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Postresp will be run in two separate workshops:  Basic part: part: Calculation of short term statistics for a few global responses of the

structure  ‘Advanced’ part: Calculation of long term extreme for air gap in the semi-submersible

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This basic workshop assumes that the models mo dels needed for the analyses are prepared in advance. The skills needed for this preparation is covered by the basic Sesam and Wadam course.

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From the data on a Gn.SIF file, produced by Wadam, a combined response variable shall be created and the transfer function shall be displayed. Next short term response and short term statistics shall be computed.

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The following tasks are to be performed:  1. Open the HydroD workspace used in the HydroD workshop.  2. Display the response variables for the motions, e.g. heave and roll  3. Create a combined response variable for the necessary force in y direction needed to

keep a unit mass in place at the point (20,10,20.5), see slide 28 in the presentation  4. Display the transfer function for this response variable for wave headings 45º and 90º.  5. Find relevant response variables for wave elevation (ELEV#)

change in air gap at the specific point (27, 0,12.5). Results  6. Create and display the change from using the incoming wave only and results from using the total wave, ELEV2, shall be compared.  7. Create and display the change in submergence of pontoons at the point (0, 27, -13).

Results from using the incoming wave only and results from using the total wave, ELEV3, shall be compared.

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In the remaining tasks the wave heading shall be 90º. Use only results based on total wave elevation.  8. Find the most probable largest value for the variables created in points 3, 6 and 7 in a

sea state given by a PM spectrum with Hs=8m and Tz=10s with a duration of 3. Use the Rayleigh Rayleigh distribution. d istribution.  9. Compare most probable largest response for different durations with the extreme

response for a given duration and different probability levels. l evels.  10. Find the response levels corresponding to a sequence of 5 probabilities from 0.01 to

0.0001 in the same same sea state. state. Print this to a file.  11. Create and display the short term response for the three response variables in PM-

spectra for Tz in the range 10s to 20s with a step of 0.5s. Print this to a file.

DNV Software - Postresp Workshop 1 Semi Revised 1 March 2012

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Postresp

Detailed procedure Step 1: Start Postresp • •

Open the HydroD workspace used in the HydroD workshop. File – Recent Workspaces …  Select Start Postresp from the Right Mouse Button (RMB) menu on the Wadam run.

Now Postresp is started and the G-file created by Wadam is read automatically.


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GUI of Postresp


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Task 2: Define Presentation Option •

Change the variables for the axis of the graphs

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Define - Presentation Option  Abscissa Axis: Select Period  Ordinate Units: Select Degrees

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Click OK


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Step 2: Display Response Variables, cont. • •

Display the response variables for the motions, e.g. heave and roll Display – Response Variable …  Select Heave and all wave directions (click & drag)  Click Apply

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The resulting display is shown on the next page


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Step 2: Display Response Variables, cont.


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Step 3: Create Specific Point • •

Create a point where the acceleration shall be calculated Create – Specific Point ...  Define point P1 at [20, 10, 20.5]  Give a description, e.g. ‘Point where mass is to be kept in place’


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Step 3: Create Response Variables • •

Create a response variable for the acceleration at the point P1, see slide 28 in the presentation. Create – Response Variable – Combined Motion – Absolute …

Z Z'

P1

yacc

-gsin(phi)

Y'

g

phi

Y

 Give a name, YACCP1, and description  Select Combined Motion  Select Acceleration  Absolute Y direction  Select point P1  Select all motions

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Click Apply to keep the menu available for the next operation (OK will close the menu)


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Step 3: Create Response Variables, cont. •

Create a combined response variable for the necessary force in y direction needed to keep a unit mass in place at the point P1, see slide 28 in the presentation.

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Create – Response Variable – General Combination …

Z Z'

P1

yacc

-gsin(phi)

Y'

g

phi

Y

 Give a name, FY, and description  Select General Combination  Type the wanted responses to be included

with their factor. Click Include for each pair

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»

YACCP1

1.0

»

ROLL

9.81 (gravity)

This time click OK to perform the operation and close the menu


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Step 4: Display Response Variables • •

Display the transfer function for this response variable Display – Response Variable …  Select the new response variable FY and wave directions 45º and 90º (click &

ctrl-click)  Click OK

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The resulting display is shown below


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Step 5: Find existing Response Variables • •

Find relevant response variables for wave elevation (ELEV#) Print – Overview – Response Variable  This will show all existing response variables, including any user defined variables

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Print – Specific Point …  This will show information of the existing points, both from offbody points in

HydroD/Wadam and points defined in Postresp

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The resulting print is by default shown in a print window on screen, as displayed on the next page. We will show later how to direct this print to a text file.


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Step 5: Find existing Response Variables, cont.


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Step 6: Calculate relative motion 1 •

Create and display the relative motion at the specific point [27, 0, 12.5]. Results from using the incoming wave only and results from using the total wave, ELEV2 (computed by Wadam), shall be compared.

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Create – Specific Point ...  Create point PF at [27 0 12.5], as in step 3

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1. Create – Response Variable – Combined Motion – Relative Displacement Z …  Define name & description: AG1 – ‘Air gap based on incoming wave alone’  Select point PF and all motions

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2. Create – Response Variable – Combined Motion – Absolute Displacement Z …  Define name & description: MOT1 – ‘Vertical motion at PF’  Select point PF and all motions

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3. Create – Response Variable – General Combination …  Define name & description: AG2 – ‘Air gap based on total wave’  Give MOT1 1.0 & ELEV2 -1.0  ELEV2 is the wave elevation computed by Wadam (disturbed wave)

1 2 3


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Step 6: Calculate relative motion 1, cont. • •

Display the response variables for the motions Display – Response Variable …  Select the new response variables AG1 & AG2 and wave directions 45º and 90º

(click & ctrl-click)


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Step 7: Calculate relative motion 2 •

Create and display the relative motion at the specific point [0, 27, -13]. Results from using the incoming wave only and results from using the total wave, ELEV3 (computed by Wadam), shall be compared.

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Create – Specific Point ...  Create point PS at [0 27 -13], as in step 3

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1. Create – Response Variable – Combined Motion – Relative Displacement Z …  Define name & description: SUB1 – ‘Submergence based on incoming wave only’  Select point PS and all motions

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2. Create – Response Variable – Combined Motion – Absolute Displacement Z …  Define name & description: MOT2 – ‘Motion on top of pontoon’  Select point PS and all motions

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3. Create – Response Variable – General Combination …  Define name & description: SUB2 – ‘Submergence based on total wave’  Give MOT2 -1.0 & ELEV3 1.0  ELEV3 is the wave elevation computed by Wadam (disturbed wave)

1 2 3


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Step 7: Calculate relative motion 2, cont. • •

Display the response variables for the motions Display – Response Variable …  Select the new response variables SUB1 & SUB2 and wave directions 45º and 90º

(click & ctrl-click)


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Step 8: Statistics – Response Spectrum • •

In the remaining tasks the wave heading shall be 90º

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Create – Wave Spectrum …

Find the expected extreme value in a sea state given by a PM wave spectrum with Hs=8m and Tz=10s  Define name & description: PMSINGLE – ‘Hs=8m,

Tz=10s’  Select Pierson Moskowitz Single  Give Hs=8 and Tz=10

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Create Response Spectrum for the interesting response variables

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Create – Response Spectrum  Select AG2, FY and SUB2  Select Wave direction 90º  Select Wave spectrum PMSINGLE


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Step 8: Statistics – Short Term Statistics I •

The PM spectrum is defined and the corresponding response spectrum is defined.

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Now find the expected extreme value in a sea state with a duration of 3 hours and the corresponding probability of exceedance. Use the Rayleigh distribution.

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Print – Overview – Response Spectrum …

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Print – Short Term Statistics  Select Sea State Duration  Give 10800 s (3 hours)  Select Response Spectra 1, 2, 3

Overview


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Step 9: Statistics – Short Term Statistics II •

The purpose of this task is to compare the results for duration (i.e. most probable largest with results for combining duration and probability.

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Print – Short Term Statistics  Select Sea state duration  Give durations

10800 108000 1080000 Click Include for each value  Select Response Spectrum 1  Press Apply  Select Sea state duration and Probability of Exceedance  Give duration 10800 and the probabilities

0.63 0.1 0.01 Click Include for each combination of duration and probability  Select Response Spectrum 1  Press Apply

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Compare the results


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Step 10: Statistics – Short Term Statistics III •

Find the response levels corresponding to a sequence of 5 probabilities from 0.01 to 0.0001 in the same sea state. Print this to a file.

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Set – Print – Destination …  Select File  Give Prefix: st

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Print – Overview – Response Spectrum  As in the previous page

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Print – Short Term Statistics  Select Probability of Exceedance  Give probabilities

0.01 0.005 0.001 0.0005 0.0001 Click Include for each value  Select Response Spectra 1, 2, 3

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This will produce a text file called stPOSTRESP.LIS, located in the project directory


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Step 11: Statistics – Short Term Response I •

Create and display the short term response for the responses using PM-spectra for Tz in the range 10s to 20s with a step of 0.5s. Print this to a file.

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Create – Wave Spectrum …  Define name & description: PM – ‘Range from Tz=10 to

Tz=20’  Select Pierson Moskowitz Full Range  Give min. Tz=10, max. Tz=20  Give Increment = 0.5


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Step 11: Statistics – Short Term Response II •

Create Short Term Response for the interesting response variables

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Create – Short Term Response  Select AG2, FY and SUB2 (click & ctrl click)  Select Wave direction 90º  Give Wave spectrum

prefix = PM  Give Min/Max sequence

= 1 – 21

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Print an overview of the short term responses to the file

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Print – Overview – Short Term Response

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Print the short term responses to the file Print – Short Term Response  Select Responses 1, 2, 3

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The results will be added to the current file, stPOSTRESP.LIS. This file can be printed or read by a standard text editor


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Step 10: Display Short Term Response • •

Display the results Display – Short Term Response …  Select responses 1, 2 and 3


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Postresp_Workshop1_Semisub

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