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Design Variables

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Rick Fenrich edited this page Dec 16, 2016 · 4 revisions

Design variables are defined using the DV_LIST keyword. The filename of the input file containing the values of design variables is set using the INPUT_DV_NAME keyword. The order of design variables listed in DV_LIST corresponds to the order of values listed in the input file. When the nozzle setup is invoked, any values of design variables provided in the input file will overwrite any values provided in the config file. An example design variable setup is:

DV_LIST= (WALL, 21, THERMAL_LAYER, 20, AIR_GAP_THICKNESS, 1, LOAD_LAYER_INSIDE, 20, LOAD_LAYER_MIDDLE, 20, LOAD_LAYER_OUTSIDE, 20, BAFFLES, 10, STRINGERS_THICKNESS_VALUES, 6)
INPUT_DV_NAME= inputDV.in

where the number given on the right of each keyword in the list is the number of design variables corresponding to the keyword. For example the WALL parameterization is associated with 21 design variables and the THERMAL_LAYER parameterization is associated with 20 design variables. Note that the layer name is used (i.e. THERMAL_LAYER not LAYER1) to refer to the design variables.

What can be defined as a design variable?

Any geometric parameter, material property, inlet fluid or atmospheric parameter, or heat transfer parameter can be defined and used a design variable by appending a keyword and quantity to the DV_LIST:

  • A whole geometric parameterization for a component can be referenced by appending the component's name. For example: WALL or THERMAL_LAYER. The COMPONENT-NAME_DV vector is used to specify which parameters correspond to design variables. See Geometric Design Variables below.
  • A part of a geometric parameterization for a component can be referenced by appending the keyword for that part. For example: STRINGERS_THICKNESS_VALUES or AIR_GAP_THICKNESS
  • Material properties are best referenced by appending MATERIAL-NAME_MATERIAL-PROPERTY. For example: CMC_DENSITY, CMC_ELASTIC_MODULUS etc.
  • Inlet fluid properties are referenced by appending INLET_PSTAG or INLET_TSTAG.
  • Atmospheric properties are referenced by appending ATM_PRES or ATM_TEMP.
  • The heat transfer coefficient to the environment is referenced by appending HEAT_XFER_COEF_TO_ENV.

Geometric Design Variables

A nozzle component is associated with a certain geometry definition, however not all parameters of the geometry definition may be design variables. For example, the inner wall of the nozzle is parameterized with a B-spline, but not all B-spline coefficient coordinates are design variables, and some B-spline coefficient coordinates must be the same, i.e. they must map to the same design variable. This is the purpose of specifying a DV vector. Each element in the DV vector corresponds to an element in that component's geometry definition. The value of the n-th element in the DV vector is the number (1-based) of the design variable associated with the n-th parameter in that component's geometry definition. A value of 0 denotes the parameter is not associated with a design variable. Duplicate values denote several parameters map to one design variable.

B-spline Geometries

For example, the wall parameterization requires a WALL_COEFS vector and associated WALL_DV vector if the coordinates of the inner wall B-spline coefficients are to be used as design variables:

WALL_COEFS= (0.0000, 0.0000, 0.1500, 0.1700, 0.1900, 0.2124, 0.2269, 0.2734, 0.3218, 0.3218, 0.3230, 0.3343, 0.3474, 0.4392, 0.4828, 0.5673, 0.6700, 0.6700, 0.3255, 0.3255, 0.3255, 0.3255, 0.3255, 0.3238, 0.2981, 0.2817, 0.2787, 0.2787, 0.2787, 0.2797, 0.2807, 0.2936, 0.2978, 0.3049, 0.3048, 0.3048)
WALL_DV= (0, 0, 0, 0, 0, 1, 2, 3, 4, 4, 5, 6, 7, 8, 9, 10, 11, 11, 0, 0, 0, 0, 0, 12, 13, 14, 15, 15, 15, 16, 17, 18, 19, 20, 21, 21)

In the example above, there are 18 B-spline coefficients listed in the WALL_COEFS vector x-coordinates first, then r-coordinates, for a vector of length 36. The length of WALL_COEFS_DV is also 36. Looking at WALL_COEFS_DV, it can be seen the first 5 B-spline coefficient x-coordinates are not design variables and that the 6th coefficient x-coordinate corresponds to design variable 1. The 9th and 10th B-spline coefficient x-coordinates are both controlled by design variable 4. Again the 17th and 18th B-spline coefficient x-coordinates are controlled by design variable 11, and so on.

Piecewise Linear Geometries

Wall layer piecewise linear geometries also use a DV vector. The first N components of the vector correspond to the elements in the LAYER#_THICKNESS_LOCATIONS vector and the last N components correspond to the elements in the LAYER#_THICKNESS_VALUES vector. For example:

LAYER3_THICKNESS_LOCATIONS= (0, 0.3, 0.6, 1.0)
LAYER3_THICKNESS_VALUES= (0.002, 0.002, 0.002, 0.002)
LAYER3_DV= (0, 1, 2, 0, 3, 4, 5, 6)

In the above example, the first and last thickness locations (0 and 1) are not design variables, but the second and third are. All layer thickness values are design variables.

Baffle Design Variables

The BAFFLES_DV keyword is a vector of length 3*N where N is the number of baffles. The first N elements map the BAFFLES_LOCATION parameters to design variables, the next N elements map the BAFFLES_THICKNESS parameters and the last N elements map the BAFFLES_HEIGHT parameters.

Stringer Design Variables

The STRINGERS_DV keyword is a vector of length 3*N where N is the number of break locations. The first N elements map the STRINGERS_BREAK_LOCATIONS parameters to design variables, the next N elements map the STRINGERS_HEIGHT_VALUES, and the last N elements map the STRINGERS_THICKNESS_VALUES parameters.

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