Extrapolated and Stretched Airy Wave Theory

Dear Sir

I am curious about Airy wave theory using in SACS.

Refer to 'Seastate manual',

AIRY in WAVE card means that kinematic will be calculated at wave crest and trough.

AIRC in WAVE card means that kinematic will be calculated at water line (No crest and trough).

Both options are clear.

However, I am curious about 'Extrapolated Airy Wave Theory' and 'Wheeler Stretching Airy Wave Theory' as shown in the figure below.

My question is 

1) Do we have 'Extrapolated Airy Wave Theory' in Seastate software ? If not, can we have in the future SACS version ?

2) Do we have 'Wheeler Stretching Airy Wave Theory' in Seastate software ? If not, can we have in the future SACS version ?

3) Is 'Extrapolated Airy Wave Theory' equivalent to 'VS' option in WAVTIM command in Wave response module ?

4) Is 'Wheeler Stretching  Airy Wave Theory' equivalent to 'WH' option in WAVTIM command in Wave response module ?

5) Is 'AIRY' in Seastate module equivalent to 'ST' option in WAVTIM command in Wave response module ?

6) Is 'AIRC' in Seastate module equivalent to 'CA' option in WAVTIM command in Wave response module ?

Regards,

Kasiphon

  • Kasiphon,

    1) Do we have 'Extrapolated Airy Wave Theory' in Seastate software ? If not, can we have in the future SACS version ?

    Seastate doesn't support Extrapolated Airy Wave Theory yet, only in Wave Response. I will  put in an enhancement request.

    2) Do we have 'Wheeler Stretching Airy Wave Theory' in Seastate software ? If not, can we have in the future SACS version ?

    Seastate doesn't support Wheeler Stretching Airy Wave Theory yet, only in Wave Response. I will  put in an enhancement request.

    3) Is 'Extrapolated Airy Wave Theory' equivalent to 'VS' option in WAVTIM command in Wave response module ?

    Yes

    4) Is 'Wheeler Stretching  Airy Wave Theory' equivalent to 'WH' option in WAVTIM command in Wave response module ?

    Yes

    5) Is 'AIRY' in Seastate module equivalent to 'ST' option in WAVTIM command in Wave response module ?

    Yes

    6) Is 'AIRC' in Seastate module equivalent to 'CA' option in WAVTIM command in Wave response module ?

    Yes

    Regards,

    Geoff

    Answer Verified By: Kasiphon Kurojjanawong 

  • Hi,

    I stumbled upon this thread and I have some question about it. What stretching method does the AIRY wave theory in SEASTATE module use? Because from what I understand, AIRY waves are based on linear theory, meaning that the free surface is approximated in mean water level (so does the wave particle). But, when I tried to look into the kinematic that AIRY module generate, it generates up to the crest and trough. And in SEASTATE manual, it does not say anything about it. Can you clarify this? 

    Best Regards, 

    Mukhlas 

  • Hi, 

    In addition, I have tried to make comparison of Horizontal particle velocity (m/s) between AIRY, AIRC and STOK5th. I generated the kinematic profile through wave print options number 3 ('VA'). The generated profiles for all theory look "similar", the discrepancies occur only in the elevation height where they stop (AIRC at MSL, AIRY at linear free surface, and STOKES 5th at its free surface). It seems not correct, since AIRY and STOKES 5th kinematic profile should be different. Can you also clarify about this? Maybe I made mistake in some steps throughout the process ? 

    Best Regards,

    Mukhlas

  • As I am confusing about this before. 

    What I understand is 

    'AIRY (in SACS)', SACS keep using exponential term in calculation i.e. exp(kz) to the crest height

    'AIRC (in SACS)', SACS ignore exponential term in calculation i.e. exp(kz) and stop calculation at water depth.

    Then, AIRY option is always used by most of engineer, i understand that it creates higher load than other stretching technique.

    Please, note that you can not use stretching option in seastate. To use those option, you need to go to wave response module.

    To be honest, I would like to beg Bentley to create 'Theory manual' similar to other software. The explanation in user manual is not good enough to understand it. Most of the time, i need to spend my time to do hand calculation to understand SACS option

    Regards,

    Kasiphon

  • Dear Kasiphon,

    Thank you for the explanation, and now I understand. Hence for high wave height, AIRY will give more conservative drag force results.

    But how about the Stokes 5th? as per my post in https://communities.bentley.com/products/offshore/f/maxsurf-moses-sacs-forum/158097/clarification-of-wave-kinematics-in-sacs-seastate-module, you can see that I got similar kinematic profile with AIRY and AIRC, the only different is the crest height. I do not think it would be the same, as the wave potential used to derive the kinematic profile for Stokes 5th order theory use up to 5th order (according to pertubation series approach).

    Regards,

    Mukhlas