Phase Function Initialization Method#

Phase Function Initialization Method = {method_name} {parameter list}

Description / Usage#

This card specifies the means by which the phase functions are initialized. After the initial instance, subsequent instances of {model_name} {parameter_list} are used to describe initializations of phase fields 2 through 5. This card constructs from a representation of the starting interface shape, a value for the distance function at every node in the mesh. The syntax of the card is as follows:

{method_name}

A character string which identifies the initialization option desired. Choices for this string are: Projection, Exodus, Nodeset, Surfaces, SM_object.

{parameter list}

This is a variable parameter list specific to each option. The nature of it for each method is detailed in the syntax descriptions below.

Below are the exact syntax used for each initialization method, a brief description of the method and a specification of any additional required parameters.

Projection

This method computes the initial phase function field by calling a user-specified routine which returns the signed distance function for a given point. It has no parameter list after its name.

Exodus

Using this card indicates that the initial phase function field is to be read from the exodus file specified earlier (see FEM file and Initial Guess cards for ** read_exoII** option). This card has no parameter list after its name.

Nodeset <integer1> EB <integer2>

This method establishes the initial location of the interface as the boundary between two element blocks. The value <integer1> is the nodeset identification number for an internal nodeset defined to exist at the interface between the two element blocks. The character string EB is required. The integer <integer2> is the element block id number to which positive values of phase function function is going to be assigned.

Surfaces <integer>

This card establishes the initial phase function function by referring to a set of primitive geometric objects. It is the easiest to use and the most general. The integer value <integer> is the number of surface objects that are used to construct the initial interface. This number of SURF object cards must follow this card. This is the syntax of the SURF object card:

SURF = {object_name} {float list}

{object_name}: a character string identifying the type of geometric object. Options are: PLANE, CIRCLE, SPHERE, SS, USER.

{float list}: geometric parameters associated with each object as float values.

The following is the syntax and description for each geometric object option, i.e., the “{object_name} {float list}” part of SURF

PLANE <nx. <ny> <nz> <d>

This card constructs a planar interface surface.The float values <nx>, <ny>, <nz> define a vector normal to this plane with the restriction that the sign of the vector must be such that it points from the negative side of the interface to the positive side of the interface. The float value <d> effectively represents the distance of the plane from the origin. Its value must be set, however, so that the dot product of any position vector to a point on the desired plane and the vector (nx,ny,nz) must be equal to <d> (it is a property of planes that this number is independent of the point on the plane that is chosen).

CIRCLE <cx> <cy> <radius>

This card constructs a circular interface surface in a two-dimensional domain. The float values <cx> <cy> identify the coordinates of the center of the circle. The float value <radius> establishes the radius of the curve. By definition, points interior to the circle are assigned negative phase function function values.

SPHERE <cx> <cy> <cz> <radius>

This card constructs a spherical interface surface in a three-dimensional domain. The float values <cx> <cy> <cz> identify the coordinates of the center of the circle. The float value <radius> establishes the radius of the sphere. By definition, points interior to the sphere are assigned negative phase function function values.

SS {ss_id}

This card uses an existing sideset in the problem as a defined geometric object for construction of an interface. The parameter <ss_id> identifies this sideset.

USER {user-defined float list}

This card indicates the user has defined an object function using the supplied parameter float list that returns a signed distance value when supplied with the coordinates of a point in space. This object function should appear in the function call user_init_object * in the file **user_pre.c.*

SM_object {object_type} {object_name}

This card allows the user to initialize the phase function location by using a piece of solid model geometry. The solid model object_type can be either FACE or ** BODY.** A 2D initialization uses the boundary of the specified FACE (or surface) as the 0 phase function. A 3D initialization uses the boundary of the specified BODY (or volume) as the 0 phase function.

Examples#

Three examples of initialization methods for a single phase function are provide below:

Phase Function Initialization Method = Nodeset 20 EB 1

Phase Function Initialization Method = Surfaces 3
        SURF = PLANE -1. 0. 0. -3.
        SURF = CIRCLE -2 0 1
        SURF = CIRCLE -3 0 0.5

Phase Function Initialization Method = SM_object BODY my_blob

Technical Discussion#

Please consult Level Set Initialization Method card for discussion.

References#

GT-020.1: Tutorial on Level Set Interface Tracking in GOMA, February 27, 2001, T.A. Baer