.. _auto_curve_vpi_acceleration:

*COMPUTE THE VDI TIME-HISTORY FROM ACCELERATION*
================================================

Computes the Vehicle Pulse Index (VPI) time-history from a vehicle acceleration signal using a lumped spring-mass model parameterised by slack, stiffness, and mass. Use this worker to evaluate VPI as a crash pulse quality / occupant-loading metric derived directly from measured or simulated vehicle acceleration.

When to use
-----------

Classification: **process**.

Tagged: ``acceleration``, ``crash_pulse``, ``occupant_loading``, ``spring_mass``, ``time_history``, ``vehicle_pulse_index``, ``vpi``.

Inputs
------

.. list-table::
   :header-rows: 1
   :widths: 20 20 20 20 20 20

   * - Label
     - ID
     - Type
     - Default
     - Required
     - Description
   * - Vehicle Acceleration
     - vehicle_acceleration
     - vector
     - —
     - 
     - Vehicle acceleration time-history curve (time vs. acceleration, typically in g or m/s²) used as the excitation signal for the VPI lumped-model integration.
   * - Slack
     - slack
     - scalar
     - 1
     - 
     - Free-play / slack distance (length units consistent with stiffness) in the lumped spring-mass model before contact force is engaged; defaults to 1.
   * - Stiffness
     - stiffness
     - scalar
     - 1
     - 
     - Spring stiffness of the lumped occupant-restraint model (force/length units); controls the rate at which load builds after slack is consumed; defaults to 1.
   * - Mass
     - mass
     - scalar
     - 1
     - 
     - Lumped occupant mass (kg or consistent mass unit) used to scale the inertial response in the VPI model; defaults to 1.

Outputs
-------

.. list-table::
   :header-rows: 1
   :widths: 20 20 20 20

   * - Label
     - ID
     - Type
     - Description
   * - curve_vpi_acceleration_output_1
     - curve_vpi_acceleration_output_1
     - scalar
     - Computed VPI scalar or time-history value derived from integrating the spring-mass model against the input vehicle acceleration; represents the Vehicle Pulse Index metric for crash pulse assessment.

Disciplines
-----------

- data.curve.transform
- engineering.crash.dynamics
- engineering.crash.occupant_safety

Runnable example
----------------

A runnable example is registered for this worker. Open the example workflow on the d3VIEW canvas: `/api/workflow/example?id=curve_vpi_acceleration <https://www.d3view.com/api/workflow/example?id=curve_vpi_acceleration>`_

.. raw:: html

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   Auto-generated from <code>transformation</code> schema. Worker id: <code>curve_vpi_acceleration</code>. Schema hash: <code>475367e4db32</code>. Hand-curated docs in <code>workerexamples/</code> override this page when present.
   </p>