Calculation Settings

Overview

Several injury metric calculations can be modified by editing fields in the “Calculation Settings” window. This window can be accessed from the top menu bar under Settings → Calculation Settings.

Head

HIC

Downsample Ratio:

When simulations are performed with high sampling frequencies (i.e. the GHBMC default 10 kHz), HIC can become a slow computation that takes several seconds. HIC values can be negligibly different, but calculated much faster when the data has first been resampled to a lower frequency.

The downsample ratio parameter specifies the ratio of the original sampling frequency to the downsampled frequency. For instance, if the original sampling frequency of the nodal output data in the simulation was 10 kHZ, and the downsample ratio parameter is set to 10, then the HIC calculation downsamples the resultant head acceleration data to 1 kHz before performing the HIC calculation and reporting the HIC value.

Default value is set to 1.

BrIC

Calculation Method:

Two studies have proposed different sets of critical values and injury risk curves for use with the BrIC injury metric. Refer to the BrIC injury metric page calculation methods for a summary of differences between the Takhounts and Laituri calculations.

Default calculation method is Takhounts et al.

CSDM

Strain Threshold:

CSDM corresponds to the volume fraction of the brain above a maximum principal strain threshold. This setting overrides the default strain threshold for CSDM calculations.

Default strain threshold is 0.25.

Thorax

Deterministic Rib Fracture

Contiguous Elements:

Deterministic rib fractures are reported when N contiguous elements are deleted from the rib cage during the simulation. This setting allows the user to override the default number of contiguous elements required to define a rib fracture.

Default value is 5.

Probabilistic Rib Fracture

Model Age:

The probabilistic rib fracture algorithm is capable of accounting for the age of the subject.

The default model age is 65 years old.

Strain Averaging:

The probabilistic rib fracture algorithm can use peak strain data from individual elements or average the strains of an element and its immediately contiguous neighboring (2 shared nodes) elements.

Default behavior is strain averaging “On”.

Lateral Rib Deflections

Model Age:

The probabilistic rib fracture algorithm is capable of accounting for the age of the subject.

The default model age is 65 years old.

Strain Averaging:

The probabilistic rib fracture algorithm can use peak strain data from individual elements or average the strains of an element and its immediately contiguous neighboring (2 shared nodes) elements.

Default behavior is strain averaging “On”.

Thoracic Spine (T-Spine) Kinetics

Default Outputs:

The T-Spine kinetics tool is currently (v0.3) capable of reporting cross-sectional forces and moments for each vertebral level. However, the default outputs display by the tool will be limited to T1, T6, T9, and T12 unless overridden by this setting or by manually changing the outputs in the GUI. Modifying this setting is the recommended method to change the T-Spine outputs when running Metriks from the command line. (See Calculation Settings file description below).

Default is T1, T6, T9, T12.

Abdomen

Organ Strain Energy Density (SED)

The SED threshold modifies where the horizontal line is drawn on the SED history signal plots for abdominal soft tissue organs.

Lumbar Spine (L-Spine) Kinetics

Default Outputs:

The L-Spine kinetics tool is currently capable of reporting cross-sectional forces and moments for each vertebral level. However, the default outputs display by the tool will be limited to L1 and L5 unless overridden by this setting or by manually changing the outputs in the GUI. Modifying this setting is the recommended method to change the L-Spine outputs when running Metriks from the command line. (See Calculation Settings file description below)

Default is L1, L5.

PLEX

Tibia Kinetics

Lower Leg Cross-Section:

For models in the GHBMC family, two cross-section load cells are defined in each lower leg. The user can select to report tibia kinetics as either the load cell for just the tibia, or for the combined tibia and fibula cross section.

Default output is the combined tibia-fibula load cell.

Tibia Index Method:

Two forms of the tibia index calculation have been used historically. As described in the Tibia Index help page, the difference between “Tibia Index” and “Revised Tibia Index” is the critical values in the calculation.

Default is “Revised Tibia Index”

Filtering Settings

The default filtering frequency settings can be overridden on the respective body region tab within the Calculation Settings window. Default filtering frequencies are defined by SAE J211 filtering specifications.

Restore Defaults

All calculation settings can be restored to the default installation state by clicking the “Restore Defaults” button in the bottom left corner of the Calculation Settings window.

Calculation Settings Files

Calculation setting preferences can be loaded and saved to ASCII text-based, YAML-formatted files with the extension “.calc”

Note: Calculation settings file formatting is subject to change during beta versions before the release of Metriks v1.0.

“Save Settings”…

Export the current calculation settings to a file on local storage system as a “.calc” file.

“Load Settings”…

Import the calculation settings from a “.calc” file on local storage system.

Modifying the “.calc” settings file

The current format of the “.calc” settings file is based on YAML. It has two main sections/headings, “Calculation Settings” and “Filter Settings”.

Each calculation setting should be indented a level from Each calculation setting “name” is defined as a python/tuple and can contain multiple lines (i.e. lines 2-5 below). The setting value is delineated using a colon followed by a space, i.e. line 6 below. The text following this colon can be edited in a text editor to change the setting value.

For calculation settings that correspond to dropdown selections in the calculation settings window, the entire name of the setting is not written to the calculation settings file. Instead, just the index (zero-based) is written out. For instance, in the example below, “0” in the calculation settings file corresponds to “NHTSA (Takhounts, 2013)” in the BrIC calculation methods setting dropdown, while “1” would correspond to the “NASA (Laituri, 2016).

The filtering settings are formatted similarly to the calculation settings but separated into their own section.