# TRACE_PARAMETERS

Specifies parameters controlling the computation of the particle path.

## Type

AcuTrace Command

## Syntax

TRACE_PARAMETERS {parameters}

## Qualifier

This command has no qualifier.

## Parameters

- element_crossing or elem_cross (boolean) [=off]
- Specifies whether or not a single particle trace segment can cross an element boundary.
- max_segment_length or max_seglen (real) >= 0 [=0]
- Maximum length of a segment. If 0, this value imposes no maximum.
- max_segment_coordinate_increment or max_coord_inc (real) >=0 [=0.5]
- Maximum local coordinate segment length allowed (segment length as a fraction of the size of the element.) If 0, this value imposes no maximum.
- max_segment_time_increment or max_dt (real) >=0 [=0.0]
- Maximum time step per segment. If 0, this value imposes no maximum.
- max_turning_angle or max_angle (real) >=0 [=15]
- Maximum turn angle in degrees of the particle velocity from the previous segment. If 0, this value imposes no maximum.
- turbulence_trace or turb (boolean) [=off]
- Specifies whether or not the particle integration accounts for the effects of turbulence.

## Description

The TRACE_PARAMETERS command specifies parameters controlling the computation of the particle path.

Particle traces are computed by AcuTrace as a series of segments using fifth-order time-discontinuous Galerkin (TDG) with error control. In the absence of any other restrictions, the end point of single particle segment can be anywhere in the element containing the segment start point or anywhere in any of the neighboring elements sharing a face with the element of origin. There are four such neighbors for tetrahedral elements, five for pyramidal and wedge elements, and six for hexahedral elements. This restriction in effect imposes a time increment restriction on the particle advance similar to a CFL=1 condition on the flow solver. max_segment_time_increment is the maximum value this time increment can have. The values of the max_segment_length, max_segment_coordinate_increment, and max_turning_angle parameters further restrict the time increment of a single particle segment.

A value of off for element_crossing further restricts the time step by forcing the particle segment endpoint to be in the element, or on the element face of the element, containing the segment starting point. The particle trace is computed more accurately if element_crossing is off, but the computation time will be about 50 percent greater than if element_crossing is on.

If turbulence_trace equals on, the effect of turbulence is modeled by randomly perturbing the particle velocity as a function of the local eddy viscosity. The result is a statistically correct lateral diffusion of the particle paths from the path given by the unperturbed flow velocity field alone. This process is repeatable, that is, successive runs of AcuTrace will yield the same trajectories.