def _createMeshName(mesh, outputDir='./output', index=None):
    """
    Returns a string - "outputDir/Mesh_res_time.h5"

    """
    if not index == None:
        if not isinstance(index, int):
            ValueError("'index' must be None or type int")
    tmp = map(str, mesh.elementRes)
    st = ''
    for x in tmp:
        st += str(x) + 'x'
    st = st[:-1]
    if index == None:
        return '{0}/Mesh_{1}.h5'.format(outputDir, st)
    else:
        return '{0}/Mesh_{1}.{2}.h5'.format(outputDir, st, index)
