.. _auto_curve_vpi_displacement:

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

Computes the Vehicle Pulse Index (VPI) time-history from a vehicle displacement curve using a lumped mass-spring model with configurable slack, stiffness, and mass parameters. Use this worker to derive the VPI signal as part of crash pulse characterisation or occupant-environment interaction analysis.

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

Classification: **process**.

Tagged: ``crash_pulse``, ``displacement``, ``lumped_mass_spring``, ``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 Displacement
     - vehicle_displacement
     - vector
     - —
     - 
     - Vehicle displacement time-history curve (time vs. displacement, typically in ms and mm from a crash simulation or physical test); the first channel of this vector is used as the input signal.
   * - Slack
     - slack
     - scalar
     - 1
     - 
     - Free-play / slack distance in the lumped model (same length units as the displacement curve, e.g. mm); leave at default of 1 if no slack is present.
   * - Stiffness
     - stiffness
     - scalar
     - 1
     - 
     - Spring stiffness of the lumped mass-spring model (force/length units consistent with mass and displacement, e.g. N/mm); leave at default of 1 for a unit-stiffness baseline.
   * - Mass
     - mass
     - scalar
     - 1
     - 
     - Lumped mass value used in the VPI computation (kg or consistent mass unit); leave at default of 1 for a normalised, unit-mass result.

Outputs
-------

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

   * - Label
     - ID
     - Type
     - Description
   * - curve_vpi_displacement_output_1
     - curve_vpi_displacement_output_1
     - scalar
     - Computed VPI time-history scalar output derived from the vehicle displacement curve using the specified slack, stiffness, and mass parameters; represents the Vehicle Pulse Index signal over time.

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

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

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

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

.. raw:: html

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   Auto-generated from <code>transformation</code> schema. Worker id: <code>curve_vpi_displacement</code>. Schema hash: <code>951a7e8e48ae</code>. Hand-curated docs in <code>workerexamples/</code> override this page when present.
   </p>