ELEMENT_DATA
Preprocess data for DISPLAY4

ELEMENT_DATA is a FORTRAN90 program which preprocesses simple element-based data on a grid into a form that the DISPLAY4 program can handle.

A set of nodes are specified in a region, and groups of 4 nodes comprise elements. At each node, a set of physical quantities is given, in particular, the X and Y coordinates, the fluid pressure P, and the horizontal and vertical flow velocity components U and V. This information has been written into a file. That information must be reformatted to work with DISPLAY4.

Specifically, for each node, there is at least one line of the form:

        X  Y  P  PSI  U  V  W

where PSI (presumably the stream function) and W (the magnitude of (U,V)) are not of interest to us.

Each element is represented by listing the nodes that comprise it, with the initial node repeated at then end, followed by a blank line. All elements in the current data set comprise 4 nodes. Thus, the information defining one element would be the central lines of the following:

         (previous element just finishing up)
         X1  Y1  P1  PSI1  U1  V1  W1

         X1  Y1  P1  PSI1  U1  V1  W1
         X2  Y2  P2  PSI2  U2  V2  W2
         X3  Y3  P3  PSI3  U3  V3  W3
         X4  Y4  P4  PSI4  U4  V4  W4
         X1  Y1  P1  PSI1  U1  V1  W1

         X1  Y1  P1 PSI1 U1 V1 W1
         (New element being defined)

DISPLAY4, on the other hand, expects two data files, a node data file, which lists each node once, and the properties U, V, and P:

        X Y U V P

which implicitly assigns an index to each node, and an element data file, which lists the number of elements, the number of nodes per element, and then, for each element, the node indices related to the element:

        1024
        4
        N1 N2 N3 N4
        N1 N2 N3 N4
        ...
        ...(1024 records like this)
        ...
        N1 N2 N3 N4

ELEMENT_DATA reads the old data, counts items, discards duplicate node information, and writes out the two data files needed by DISPLAY4.

Usage:

The name of the input file is usually specified on the command line:

element_data input_file

reads input_file and creates two files, whose names are always element.txt and node.txt.

Licensing:

The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.

Related Data and Programs:

DISPLAY4, a FORTRAN90 program which displays graphics from the flow data computed by FLOW3, FLOW5 or FLOW7. This program used to work, but it is very out of date;

ELEMENT_DATA is available in a FORTRAN77 version and a FORTRAN90 version.

Source Code:

element_data.f90, the F90 source code;
element_data.csh, commands to compile and load the source code;

Examples and Tests:

A first set of test data:

values1.txt, an input data file read by the program;
node1.txt, the node data file created by the program. An internal flag was set so that pressures were copied.
element1.txt, the element data file created by the program.

A second set of test data:

values2.txt, an second example input data file;
node2.txt, the node data file created by the program. An internal flag was set so that PSI (stream function) was copied into the nominal P (pressure) slot.
element2.txt, the element data file created by the program.

List of Routines:

ELEMENT_DATA organizes data on a rectangular grid into finite element data.
CH_CAP capitalizes a single character.
CH_EQI is a case insensitive comparison of two characters for equality.
CH_TO_DIGIT returns the integer value of a base 10 digit.
FILE_COLUMN_COUNT counts the number of columns in the first line of a file.
FILE_LINE_COUNT counts the number of lines in a file.
GET_UNIT returns a free FORTRAN unit number.
R_NEXT "reads" real numbers from a string, one at a time.
READ_ELEMENTS reads Niyazi Sahin's file and constructs the elements.
RRVEC_COMPARE compares two RR vectors.
RRVEC_INDEX_SEARCH searches for an RR value in an indexed sorted list.
RRVEC_INDEX_INSERT_UNIQUE inserts a unique RR value in an indexed sorted list.
S_TO_R reads a real number from a string.
TIMESTAMP prints the current YMDHMS date as a time stamp.
WORD_COUNT counts the number of "words" in a string.
WRITE_ELEMENT writes an element data file.
WRITE_NODE writes a node data file.

You can go up one level to the FORTRAN90 source codes.

Last revised on 18 January 2007.