# Compile FAST to model distributed spring model for monopile.

**URL:** <https://forums.nlr.gov/t/compile-fast-to-model-distributed-spring-model-for-monopile/768>\
**Category:** Structural Analysis\
**Created:** [September 20, 2013, 5:14pm UTC](https://forums.nlr.gov/t/compile-fast-to-model-distributed-spring-model-for-monopile/768 "2013-09-20T17:14:36Z")\
**Posts on this page:** 1\
**Showing post:** 1

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**Author:** ![Lingling.Yin](https://avatars.discourse-cdn.com/v4/letter/l/cab0a1/32.png) [@Lingling.Yin](https://forums.nlr.gov/u/Lingling.Yin)\
**Post date:** [September 20, 2013, 5:14pm UTC](https://forums.nlr.gov/t/compile-fast-to-model-distributed-spring-model-for-monopile/768/1 "2013-09-20T17:14:36Z")

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Dear FAST programmer,

I am trying to model the equivalent distributed spring model for monopile foundation. What I have done is following:

1. I downloaded the UserTwrLd\_DS.f90 file from [Turbine-soil interaction. Influence on the mode shapes.](http://forums.nlr.gov/t/turbine-soil-interaction-influence-on-the-mode-shapes/481/1). And I modified the input with my pile and spring value.

2. Copy the UserTwrLd\_DS.f90 file to the folder where other FAST source files are located.

3. Modify Compile\_FAST.bat file according to [wind.nrel.gov/public/bjonkman/De … ctions.pdf](http://wind.nrel.gov/public/bjonkman/DesignCodes/FASTCompilingInstructions.pdf)

The questions are

1. I don’t know what is the syntax to add UserTwrLd\_DS.f90 in Compile\_FAST.bat file.
2. How do you know whether you correctly include the soil-pile interaction model (distributed spring model in my case)?

Since I did not know how to add UserTwrLd\_DS.f90 in Compile\_FAST.bat. I just run the Compile\_FAST.bat in the attachment with UserTwrLd\_DS.f90 locating in FAST source folder but without any syntax to add it. Then I used the generated FAST source file to run my model. The natural frequencies I got are very close to what I got from BModes distributed spring model but without any spring constant inputs (i.e. a cantilever beam without soil-pile interaction). I believe my FAST.exe did not include correctly the distributed spring model.

Can somebody with such experience help me with my issue?

Really appreciate.

Best regards,  
Lingling

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