Brief Description

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BsaLib, a Modern Fortran Library for the Bispectral Stochastic Analysis of structures under non-Gaussian stationary random actions.

NOTE: currently, only wind action is included in the library, but other phenomena (waves for instance) can be easily integrated. See further developments.

Build system

BsaLib uses CMake as a build system generator.

Documentation

BsaLib documentation is generated using FORD.

License

BsaLib is release under the GNU Lesser General Public License v3.0. Visit the GPL official website for more information.

Code structure

There are two parts in this repository:

1. BsaLib, the core library;
2. BSA, the built-in executable program.

BsaLib: core library

BsaLib is the main core of this repository. It consists of the main library and its API to which anyone could link to and interact with. To use BsaLib, simply import the main BsaLib API module:

program test
    use, non_intrinsic :: BsaLib
    implicit none (type, external)
    ! your declarations here

    ! your logic here

    ! initialise BsaLib
    call bsa_Init()

    ! set BsaLib internal state through its API procedures

    ! once done, run BsaLib
    call bsa_Run( ... args ... )

    ! finally, release BsaLib memory
    call bsa_Finalise()
end program

Being designed as a plug-in library, it needs the hosting program/library to provide some data needed by BsaLib in order to function properly. For more details on the public API, visit the main documentation page.

BSA: executable program

As a side project package, a single-source executable file is provided under ./app/. It emulates what one would normally do when using BsaLib as a plug-in for its own library/program. On the other hand, this program is thought and provided for all those interested in using BsaLib but not having any hosting library/program. Nonetheless, even if this program is provided, the user would yet need to provide the data for BsaLib to function properly. If any of this data is not provided, the BsaLib runtime check would detect it and abort correct logic flow.

For that, the provided executable program relies on reading two input files:

1. BsaLib related settings (formatted file, named bsa.bsadata). For details, read the dedicated section.
2. External data file (named bsa.extdata), in binary format, containing 8-byte floating point records (real64 of the iso_fortran_env compiler intrinsic module). For full details, read the external data section.

Cross-platform support

BsaLib strives to be as cross-platform as possible, so that any user can use it regardless of the tooling availability. Currently, the code has been compiled and tested under three different OS-compiler configurations:

1. Windows OS Build 10.0.19045 - Intel Fortran Compilers (ifort 2021.7.1-20221019_000000, ifx 2022.2.1-20221101)
2. MacOS - GFortran 13.2
3. Linux Centos Fedora 8.7 - Intel Fortran Compilers (ifort 2021.10.0-20230609, ifx 2023.2.0-20230721)

For the Proper Orthogonal Decomposition (POD) problem, two approaches have been tested, for configurations 1 and 3:

• Linkage to proprietary Intel MKL (Math Kernel Libraries)
• Linkage to LAPACK native implementation (NOTE: from direct source build in configuration 1)

What's missing? Further developments

Mathematical:

• Integrate models for other non-Gaussian actions (waves, for instance)
• Extend to non-diagonal modal Frequency Response Function (FRF) models
• Extend to frequency-dependent modal matrices (e.g. aeroelastic phenomena in Wind Engineering)
• Add library core to generate spectra (PSDs and Bispectra) from time series

Numerical:

• Adapt Classic approach to dump BFM info as in Mesher (easy)
• Improve internal policy mechanism and integration (WIP)
• Provide a general API for user defined models integration
• Complete full support for spatial (in-plane) symmetries of a real-valued bispectrum
• Compute nodal correlation internally (don't require it as user data)
• Add support for Mesher zones' interest modes
• Add a local caching system
• Add MPI support (for running BsaLib on multi-node clusters)
• Improve and extend GPU offloading capabilities
• Provide automation service to convert user-level model function into GPU-kernel code
• Enhance the mechanism that lets the user provide its own desired exporting function, so that BsaLib is not tight to any specific exporting format.
• Integrate a built-in bispectrum post-processing Visualiser (using Vulkan, for optimal performances)

Known Issues

There is one main known issue in the current version.

Using OpenMP parallelisation in the second Post-meshing phase, execution time is higher compared to serialised version. This is due to the necessary synchronisation between threads when accessing shared file I/O when reading each zone's dumped data, causing the critical section to be the main bottleneck in this part. For a proper use of OpenMP parallelisation in Post-meshing phase, a fundamental rethinking of the algorithmic structure needs to be done. A first, temporary, possible solution, could be the usage of thread-level private I/O with dedicated units, avoiding the need to synchronise when reading back information in post-meshing phase. However, this might soon become inelegant solution when the number of threads would start increasing considerably. For this, as a temporary solution, a conditional compilation flag (BSA_USE_POST_MESH_OMP) can be used to control effective use of OpenMP parallelisation in Post-meshing phase, disabled by default.

Related Scientific Publications

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1. Non-Gaussian buffeting analysis of large structures by means of a Proper Orthogonal Decomposition
2. A multiple timescale approach of bispectral correlation
3. On the background and biresonant components of the random response of single degree-of-freedom systems under non-Gaussian random loading