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    Fatigue Analysis For Fixed Platforms PDF

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    m_ilahi9296
    This document outlines a 5-step process for fatigue analysis: 1) Create a superelement model. 2) Perform an eigenvalue analysis to determine natural frequencies. 3) Generate a static transfer function. 4) Generate a dynamic transfer function. 5) Perform the fatigue analysis using the generated inputs and outputs from the previous steps.

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    Fatigue Analysis For Fixed Platforms PDF

    Uploaded by

    m_ilahi9296
    145 views13 pages
    This document outlines a 5-step process for fatigue analysis: 1) Create a superelement model. 2) Perform an eigenvalue analysis to determine natural frequencies. 3) Generate a static transfer function. 4) Generate a dynamic transfer function. 5) Perform the fatigue analysis using the generated inputs and outputs from the previous steps.

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    This document outlines a 5-step process for fatigue analysis: 1) Create a superelement model. 2) Perform an eigenvalue analysis to determine natural frequencies. 3) Generate a static transfer function. 4) Generate a dynamic transfer function. 5) Perform the fatigue analysis using the generated inputs and outputs from the previous steps.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    145 views13 pages

    Fatigue Analysis For Fixed Platforms PDF

    Uploaded by

    m_ilahi9296
    This document outlines a 5-step process for fatigue analysis: 1) Create a superelement model. 2) Perform an eigenvalue analysis to determine natural frequencies. 3) Generate a static transfer function. 4) Generate a dynamic transfer function. 5) Perform the fatigue analysis using the generated inputs and outputs from the previous steps.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 13

    FATIGUE ANALYSIS

    - Fatigue analysis consist of 5 steps


    i- Superelement
    ii- Eigenvalue
    iii- Static Transfer Function
    iv- Dynamic Transfer Function
    v- Fatigue
    Step 1 (Superelement)
    Input files required

    a) SACINP
    b) PSIINP

    1. Using spreadsheet, calculate center of damage based on wave statistics provided by metocean report.
    2. In sacinp, define load combinations for orthogonal directions. Each load combinations consist of dead loads, live loads, wave (center of damage
    values) and crane moment.
    3. Options - Add the superelement creation options.
    4. Load Case Selection - Add the load combinations defined in step a.

    Superelement Creation

    Load Case Selection


    5. Edit psiinp file (from in-place analysis) as following
    a- In the pile superelement creation (PILSUP) command, insert all the load combinations defined in the sacinp step a.

    Pile super element creation


    Step 2 (Eigenvalue)
    Input files required

    1) SACINP
    2) DYNINP
    3) DYNSEF (output from step 1)

    1. In sacinp, select load case that represent gravity load only (e.g. structural appurtenances, instrument, piping, live loads). Remove any self-weight
    and buoyancy loads generated by SACS. Choose dynamic options by selecting “DY” in front of each line after “LCSEL”.
    2. For each of the load case selected above, put the factor according to the preload combination. Also, choose dynamic options by selecting “DY” in
    front of each line after “LCFAC”.
    3. Select super element input in options
    4. Increase density for each group member by multiplying with contingencies (e.g. 7.85 x 1.05 = 8.2425)

    Super element Input

    Load Case Selection

    Load Case Factor

    Increase density
    5. Open sacinp in precede, change fixity at main joint (jacket leg, topside column connected to jacket leg, x braces at jacket) to “222000”
    6. For dynamic input, change input to suit respective platform conditions
    a- Dynpac options - Check water depth
    - Check density contingencies (e.g. 7.85 x 1.05 = 8.2425)

    b- Member group override - Pile member group in sacsinp, set the “effective OD for added mass calculation” to 0.001. Density of the pile
    member group is factored (same as in the dynpac options).

    - Wishbone member group in sacinp, set the “effective OD for added mass calculation” to 0.001. Density of the
    member group is 0.001.

    Density
    Water depth

    effective
    OD for
    added
    mass
    calculation

    Density

    Group
    member
    NOTE: After completing the 2 steps, vary the live load as per PTS and repeat the first 2 steps.

    Vary open area live loads (eg %, 50%,


    70%)
    Step 3 (Static Transfer Function)
    Input files required

    1) SACINP
    2) SEAINP

    1. Using spreadsheet, generate seainp by determine the wave period and wave height. Sacinp can be used from previous step. Run analysis for 0, 45
    and 90 degree direction.
    2. From output, open the base shear vs frequency graph. Create vertical line where the natural frequency of the platform is located (from 2nd step) for
    0, 45 and 90 degree wave direction. Select live load variations based on which direction the platform is most sensitive. (if x-direction, 0 degree graph
    is referred). Select where the 1st mode is located at the peak of the graph.
    Step 4 (Dynamic Transfer Function)
    Input files required

    1) SACINP
    2) SEAINP
    3) WVRINP
    4) DYNMAS (output from step 2)
    5) DYNMOD (output from step 2)

    1. For seainp, additional frequency is added based on selected live load variations. Sacinp from step 2 can be used.
    2. For wvrinp, follow the below input. Run for 8 directions.
    No of mode defined in step 2

    Wave period and wave height No of load case defined in


    input seainp
    Step 5 (Fatigue)
    Input files required
    Taken from step 4. Include all
    1) FTGINP 8 directions.
    2) CSF file
    3) SEAINP

    1. For ftginp, input is generated by using excel (same spreadsheet that calculate center of damage for step 1).

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