convert_nastran_to_gmsh.py

def read_nastran_mesh(file_path):
    nodes = {}
    elements = {}
    element_tags = {}
    physical_names = {}
    physical_names_dim = {}

    with open(file_path, "r") as file:
        lines = file.readlines()

        # Flag variables to determine whether to read nodes or elements
        reading_nodes = False
        reading_elements = False
        reading_physical_names = False

        num_nodes = 0
        num_elements = 0
        num_physical_names = 0
        physical_name = ""

        records = []
        current_record = ""
        # first check for continuation lines, these need to be combined
        for line in lines:
            line = line.rstrip('\n')
            if line.startswith('+'):
                # Lines that start with plus belong to the previous line,
                # remove the + and concatenate
                current_record = current_record.rstrip('+')
                # remove the first 8 character record, this includes the +
                current_record += line[8:]
            else:
                if current_record:
                    records.append(current_record)
                current_record = line

        if current_record:
            records.append(current_record)

        # operate on the concatenated file
        for line in records:
            if line.startswith("$ Node cards"):
                reading_nodes = True
                reading_elements = False
                reading_physical_names = False
                continue
            elif line.startswith("$ Element cards"):
                reading_elements = True
                reading_nodes = False
                reading_physical_names = False
                continue
            elif line.startswith("$ Property cards"):
                reading_elements = False
                reading_nodes = False
                reading_physical_names = True
                continue
            elif line.startswith("$ Material cards"):
                reading_elements = False
                reading_nodes = False
                reading_physical_names = False
                continue

            def read_line(line, field_length=8):
                fields = [line[i:i+field_length] for i in range(0,len(line), field_length)]
                return fields

            if reading_nodes:
                if line.startswith("GRID"):
                    parts = read_line(line)
                    num_fields = len(line)/8
                    node_id = int(parts[1])
                    scale = 1.
                    scale = 0.001
                    x = float(parts[3])*scale
                    y = float(parts[4])*scale
                    z = float(parts[5])*scale if len(parts) > 5 else 0.0
                    nodes[node_id] = (x, y, z)
            elif reading_elements:
                if line.startswith("CQUAD") or\
                   line.startswith("CHEX") or\
                   line.startswith("CROD"):
                    parts = read_line(line)
                    element_id = int(parts[1])
                    element_nodes = [int(parts[i]) for i in range(3, len(parts))]
                    elements[element_id] = element_nodes
                    if element_id in element_tags:
                        element_tags[element_id].append(int(parts[2]))
                    else:
                        element_tags[element_id] = [int(parts[2])]
            elif reading_physical_names:
                if line.startswith("$ Name:"):
                    num_physical_names += 1
                    parts = line.split()
                    physical_name = parts[2]
                    #physical_names[num_physical_names] = physical_name

                if line.startswith("PROD"):
                    pdim = 1
                    #parts = line.split()
                    parts = read_line(line)
                    physical_id = int(parts[1])
                    physical_names_dim[physical_id] = pdim
                    physical_names[physical_id] = physical_name
                elif line.startswith("PSHELL"):
                    pdim = 2
                    #parts = line.split()
                    parts = read_line(line)
                    physical_id = int(parts[1])
                    physical_names_dim[physical_id] = pdim
                    physical_names[physical_id] = physical_name
                elif line.startswith("PSOLID"):
                    pdim = 3
                    #parts = line.split()
                    parts = read_line(line)
                    physical_id = int(parts[1])
                    physical_names_dim[physical_id] = pdim
                    physical_names[physical_id] = physical_name

    # sort the nodes
    sorted_nodes = dict(sorted(nodes.items()))
    sorted_elements = dict(sorted(elements.items()))


    return sorted_nodes, sorted_elements, element_tags, physical_names, physical_names_dim