▪ Version 3 of the co-simulation interface for fluid-structure-interaction (FSI) has been implemented into the LS-DYNA user-subroutine dyn21.f/loadud. This interface permits the coupled simulation of explosively loaded structures with LS-DYNA and the APOLLO Blastsimulator V2024.2.

▪ LS-DYNA models can be used for a coupled LS-DYNA/APOLLO simulation without any formal modifications. The interface implemented in dyn21.f/loadud provides an automatic identification of the free surfaces of the LS-DYNA model (coupling surfaces) and automatically updates the topology of the coupling surfaces if element erosion occurs.

▪ Compiled object files of dyn21.f and readily linked versions of LS-DYNA are provided for Windows and Linux together with the APOLLO Blastsimulator software (LSDYNA license must be available for using the provided LS-DYNA executables).

Further Information is provided in the downloadable PDF.

FSI Co-Simulation Interface
▪ The co-simulation interface has been updated and is now available as version 3. This version offers an optional inclusion of the local fluid impedances to the data send from APOLLO to the coupled structural dynamics code. The impedances are optionally used for the pressure extrapolation when the structural solver performs sub-cycles. Thereby, the stability of the coupling process is significantly improved particularly for UNDEX.
▪ The optional inclusion of particles in the coupling process was already implemented in version 2 and is further available in version 3. Versions 1 and 2 of the interfaces are still available in the current APOLLO version (2024.2).
▪ New versions of LS-DYNA executables which are equipped with the co-simulation interface v3 have been compiled for Linux and Windows (download package LSDYNA 2024.2 from https://apollo-blastsimulator.de). The new version can optionally use the fluid-impedances provided by APOLLO for extrapolation of the pressure applied during sub-cycling. Furthermore, the impulse transferred upon impact of APOLLO particles onto the coupling surface is now included in LS-DYNA. The specification of parameters for LS-DYNA with co-simulation interface v3 in LSDYNA-FSI_INPUT.txt has been simplified (see section FILE FORMATS in this manual). The interface versions 1 and 2 are no longer supported in our LS-DYNA executables.
▪ A new history file PROJECT_fsi is now generated if the co-simulation interface is used. The file contains relevant time-dependent parameter values related to the coupling process.

Memory Update Mode
▪ APOLLO-B3d has a dynamic memory management associated with the dynamic mesh adaption. While memory updates hitherto employed temporary scratch files in the project folder or the tmp-directory, the preferred method now temporarily stores data in the RAM-memory. This allows a faster processing of memory updates. See section B3D for details.

DMA
▪ The functionalities which permit a user-defined setting of resolution levels (Zoom, Degrading, Part Specific Levels) can be applied in combination and may address overlapping regions.
What’s new in Version 2024.2
Therefore, a sensible priority order is required for cases of overlapping regions. This priority order has been improved – see section DMA for details.
▪ The definition of the undegraded region in the input for the Degrading functionality is now specified in terms of the xyz-position of the minimum corner and the size of the box-shaped region in xyz-directions (formerly the position of the maximum corner was specified). The input scheme is thus consistent now with other specifications related to box-shaped region.

Options affecting robustness
▪ In rare cases problems such as an ever decreasing time step size may occur under extreme flow conditions. As a treatment for such cases some specific options affecting the robustness can now be selected for APOLLO-B3D (see section B3D for details).

Alternative Linux executables
▪ We now provide two versions of executables for Linux: one version has been linked on ROCKY Linux 9.3, the other on CentOS 7. See manual chapter Executable Modules for more information.

• The new Graphical User-Interface (GUI) has been in the field for some months. Thanks to users feedback several improvements and bug fixes could be implemented.
• The Friedlander blast-wave model (“TNTAir”) offered as an option within the Off-site-blast functionality has been improved: the correlations for peak overpressure, positive duration, wave-shape (factor in the exponential term) and time of arrival have been revised to better match the APOLLO predictions for airblast waves. Particularly the modelling of the negative phase has been improved, which suffered from insufficient accuracy before. As a result, the perturbations generated at feed-in boundaries due to discrepancies between APOLLO predictions and the Friedlander model were (in most cases) reduced.
• An alternative EOS parameter set for Air is offered in apollo-eos.dat (“Air2”), which provides an improved sound speed value at ambient state. This model is recommended to be used with the TNTAir model in Off-Site-Blast.
• The numerical methods applied for the simulation of jet blow-down have been revised and improved, leading to better comparisons with available test data.
• A new output file NAME_eos is now generated when a non-default version of apollo-eos.dat is used in a simulation (see section EOSFILE). This file saves a copy of the parameter sets loaded from the selected apollo-eos.dat file. Thereby the parameter values actually used for a simulation are documented together with the simulation results and can be looked up, even if changes have been made in the apollo-eos.dat file.
• A new, extended version of the KAB model (KABX) has been implemented which covers both gaseous afterburning and the finite rate particle combustion which occurs in metallized explosives. The model has recently been successfully calibrated and applied for an aluminized explosive (not included in apollo-eos.dat). A calibration of the KABX model for TNT (w/o the optional particle combustion) is included in apollo-eos.dat. Tests with that model have shown improved accuracy compared to the original KAB model.
• An error in the implementation of the original KAB model in the 2023 versions has been found and corrected. Due to a miscalculation of the fireball volumes in these versions, the afterburning may have been underestimated in these versions. This has been corrected in the current version.
• The keyword “Charge” for the respective option of the zoom-functionality has been changed into “Charge-Airblast” to make clear that the settings selected thereby are tuned for explosions in air. For the same reason the meshing option “Auto” in DOMAIN-B1D has been renamed to “Auto-Airblast”. In the next update complementary settings for UNDEX will be implemented.
• Initiation positions Tail, Head and Booster selectable in CHARGES are automatically shifted about a small length into the charge to ensure successful initiation. While a fraction of charge length was used for this shift before, this has been changed to a fraction of a grid cell now.