2. GHBMC M50 Occupant Model: Version and Mesh Configuration Check for a Frontal Impact Study

Why the Version and Mesh Baseline Must Be Fixed Before a Frontal Impact Study

The GHBMC M50 occupant model is distributed as a family of LS-DYNA keyword decks, and the two attributes that most strongly influence a frontal impact result are the model version and the mesh resolution. Version changes alter geometry, material definitions, contact thicknesses, and the seatbelt routing; mesh resolution changes element size, hourglass behavior, and the number of through-thickness solid elements in the thorax and abdomen. If either attribute is left implicit, two runs that appear identical in the deck name can produce thorax deflection differences of several millimetres and rib-strain differences large enough to flip an AIS prediction. The task here is therefore a verification and documentation task, not a simulation task: confirm that the selected deck matches the intended frontal loading and the injury metrics you plan to report, then freeze that configuration as the study baseline.

What "Version" and "Mesh Configuration" Actually Mean in the GHBMC M50 Deck

The GHBMC M50 (50th percentile male) occupant model is released in numbered versions (for example v4.x, v5.x, and later public releases), and each release ships with a documented change log covering geometry updates, material card revisions, belt and airbag interaction updates, and any changes to the validation matrix. Within a release, the model is typically offered in a coarse and a fine mesh variant. The practical differences that matter for a frontal impact are:

• Element size and count: the fine mesh resolves the rib cortical shell and the abdominal organs with more elements, which improves local strain resolution but raises the stable time step cost substantially.
• Through-thickness resolution: the fine thorax uses more solid elements through the rib and sternum, which changes bending stiffness and therefore chest deflection under belt loading.
• Contact and belt routing: belt segments, slip rings, and retractor definitions can differ between variants; a coarse deck may use simplified belt paths.
• Hourglass control and element formulation: coarse decks rely more heavily on hourglass control, so hourglass energy must be monitored and reported.

Because these differences propagate directly into the injury metrics you will report (chest deflection, VC, rib fracture risk, and head acceleration), the configuration must be chosen against the metric, not against convenience.

Decision Logic: Matching Configuration to Loading and Metrics

Use the following reasoning to select the configuration, then verify it against the deck contents rather than against the file name alone.

1. Define the reported metrics first. If the study reports only global kinematics and head acceleration, the coarse mesh is usually adequate. If it reports rib strain, localized chest deflection, or abdominal organ strain, the fine mesh is the defensible choice.
2. Check the loading path. A frontal impact with a diagonal belt and a driver airbag loads the thorax through the belt and the sternum. Fine mesh is preferred when belt–rib interaction and sternum deflection are part of the conclusion.
3. Check the time step budget. Fine mesh decks typically require a smaller stable time step; confirm the mass scaling and the resulting added mass are acceptable for the study, and record the added mass percentage.
4. Confirm the version against the validation matrix. Select the version whose published validation cases include frontal sled or frontal impact configurations comparable to your loading; do not select a version validated only for lateral loading.

Reading the Deck: Concrete Checks

The file name is not evidence. Open the keyword deck and confirm the following, recording each value in the baseline table. The exact card names below are standard LS-DYNA keywords and are stable across GHBMC releases; the specific values depend on the release you have.

*KEYWORD
*TITLE
GHBMC M50 occupant - frontal impact study baseline
*CONTROL_TERMINATION
       0.120     0.0       0.0       0.0       0.0
*CONTROL_TIMESTEP
       0.0  0.900000      0.0       0.0       0.0       0
*CONTROL_ENERGY
         2         2         2         1
*DATABASE_BINARY_D3PLOT
  0.000500
*DATABASE_GLSTAT
  0.000500
*DATABASE_MATSUM
  0.000500
*DATABASE_SLEOUT
  0.000500
*END

These control cards are the ones that most often drift between variants. A fine mesh deck that still carries the coarse variant's DT2MS mass-scaling value will produce an added-mass percentage that is no longer acceptable; a coarse deck run with a fine-variant time step wastes hours without improving accuracy. Confirm *CONTROL_ENERGY requests hourglass and sliding-interface energy so that the energy balance can be checked after the run.

Next, verify the part and material inventory against the release manifest. A quick and reliable check is to count the parts and materials and compare with the manifest shipped with the release:

grep -c "^\*PART"      ghbmc_m50_occ_frontal.k
grep -c "^\*MAT_"      ghbmc_m50_occ_frontal.k
grep -c "^\*ELEMENT_SOLID" ghbmc_m50_occ_frontal.k
grep -c "^\*ELEMENT_SHELL" ghbmc_m50_occ_frontal.k

If the solid-element count is close to the coarse manifest value while the deck is labelled fine, the deck has been mislabelled or partially replaced. This is the single most common configuration error in inherited study folders, and it is invisible in the simulation output until the chest deflection is compared against a reference.

Baseline Record

Freeze the verified configuration in a short, machine-readable record so that later runs, and later chapters of this study, can be traced to exactly one deck. The following is a complete, fillable example; the values shown are illustrative placeholders for a frontal impact study and must be replaced with the values read from your own deck.

Verification and Failure Symptoms

Run a short initialization-only or 5 ms trial and inspect the output before committing to the full study. The observable checks are:

• Added mass: read the added-mass percentage from glstat. If it exceeds the threshold you set for the study (commonly a few percent), the time step or mass scaling does not match the variant.
• Hourglass energy: if hourglass energy exceeds roughly 5–10% of internal energy in the thorax or abdomen, the coarse variant is being pushed beyond its intended use, or the fine variant has been run with an inappropriate element formulation.
• Initial penetration: check the contact initialization output for belt–torso and torso–seat penetrations; a mismatch between belt routing and mesh variant shows up here first.
• Element count mismatch: if the deck's solid and shell counts do not match the manifest for the declared variant, stop and resolve the labelling before running.

Typical failure symptoms and their causes: a run that terminates early with a negative-volume solid element usually indicates the fine thorax mesh was combined with a coarse-variant time step; a run that completes but shows implausibly low chest deflection usually indicates the coarse variant was used while the study claims rib-level metrics; a run with a large energy imbalance usually indicates hourglass control was disabled or the energy database was not requested. In each case the corrective action is to return to the deck, re-read the control and part cards, and re-record the baseline rather than to adjust the output.

Once the version, mesh variant, deck checksum, time step, and energy settings are confirmed and recorded, the configuration is frozen and the frontal impact study can proceed with a defensible, traceable baseline.