Functionally Determined Constraint Level - User Interface

Everything that you wanted to know about Functionally Determined Constraint Levels but were afraid to ask.

In SpringSys, a FDCL can be the value of an independent (p) or dependent (x) variable or a floating point constant (d). It cannot be a string constant (ds), an integer constant (di) or any kind of "freeform" expression.

The FREE command is used to remove a FDCL.

In order to impose a FDCL in SpringSys, use the CHANGE command with a valid (variable or constant) name where a simple value might otherwise appear.
Example:
CHANGE Stress_Hook MAX Stress_Lim_Bend

In SpringSys, when an FDCL is established, the LIST command STATUS column (might show "FIXED") will show "FUNCTION". The CONSTRAINT LEVELS MIN and MAX columns will show the current numerical value of the associated FDCL. For example, in this SpringSys extension spring output the quantity Stress_Initial is constrained to be a MIN of Stress_Init_Lo and a MAX of Stress_Init_Hi.

DEPENDENT VARIABLES                                       CONSTRAINT LEVELS
                                           STATUS         MIN           MAX
ID_FREE         =        0.8890  INCHES                   0.1000
COILS_A         =       10.4000  COILS                    1.0000       50.0000
RATE            =       17.4088  LB/IN           
DEFLECT_1       =        0.2298  INCHES          
DEFLECT_2       =        1.9530  INCHES          
L_FREE_(W/ENDS) =        2.9385  INCHES          
L_1             =        3.1683  INCHES          
L_2             =        4.8915  INCHES          
L_STROKE        =        1.7233  INCHES                   0.0500
WEIGHT          =        0.0931  POUNDS          
SPRING_INDEX    =        9.4265  RATIO           
STRESS_INITIAL  =    12940.1300  PSI     FUNCTION     10183.3700    16724.5100
STRESS_2        =    99574.0100  PSI             
STRESS_HOOK     =   191924.3000  PSI             
FS_2            =        1.3127  RATIO                    1.1000        1.6000
FS_CYCLE_LIFE   =        1.2703  RATIO           
FS_HOOK         =        1.0216  RATIO           
CYCLE_LIFE      =   794230.0000  CYCLES          
STRESS_INIT_LO  =    10183.3700  PSI             
STRESS_INIT_HI  =    16724.5100  PSI

The SpringSys LIST LEVELS command will report the existing status:

FUNCTIONALLY DETERMINED CONSTRAINT LEVELS:
(REFER TO DOCUMENTATION SECTION  "FUNCTION".)

CONSTRAINT ON:           IS CURRENT VALUE OF:
----------------         -------------------
FORCE_1            MIN   INITIAL_TENSION
STRESS_INITIAL     MIN   STRESS_INIT_LO
STRESS_INITIAL     MAX   STRESS_INIT_HI

Extension spring FDCLs:

Extension springs have three FDCLs configured in the default startup file.

Constraint on: Is current value of:

Force_1 MIN Initial_Tension
Stress_Initial MIN Stress_Init_Lo
Stress_Initial MAX Stress_Init_Hi

One additional FDCL may be routinely configured by the user:

Constraint on: Is current value of:

Stress_Hook MAX Stress_Lim_Bend

GitHub issue #179 "Investigate Rectangular Solid handling of "Girth" " describes how implementing FDCL might be useful for the Rectangular Solid design type.

User interface alternatives for configuring FDCL in ODOP

Have the user to enter variable names into the constraint fields.

I don't think that this is the best approach. It is more consistent to select from a list.

Invoke the FDCL configuration process from a menu item that uses a pop-up dialog. Most of the details including status indication could be as described below.

I think that #3 is a better alternative.

Invoke the FDCL configuration process by clicking in a constraint's value field.

This alternative would produce a modal dialog (or pop-up / pop-over) that offers an entry field for entering constant values plus a selection list containing the names of all available variables. Perhaps a radio button is necessary to designate whether the constant value or the variable name is active.

In order for the user to view / confirm the currently established FDCL configuration, a tooltip can be provided.

It is likely desirable to add a property to those names in initialState that are configurable to have a FDCL. The new property can specify the set of variable names that are eligible for selection. To be consistent with "cmin" and "max" (the internal variable names for constraint levels), the set of eligible names can be "cminchoices" and "cmaxchoices". Thus, the new property to be added to the Force_1 entry in initialState might look like:

    "cminchoices": { "Initial_Tension" }

If necessary in addition to the tooltip, the fact that an FDCL is active might also be indicated by color:

of the check mark ?
of the check box perimeter ?
of the checkbox cell background ?
of the checkbox cell perimeter ?
of the constraint value background ?

Note:
Color of constraint text and color of the perimeter of constraint box are already utilized. The color of the constraint value background has been mentioned for use in Demo & Tutor sessions as a way to bring user attention to the subject of the discussion.

Color choices mentioned in conversation are dark gray, black and dark blue. If available, a dark violet might be a reasonable choice.

While it is also possible to show that FDCL is active by adding an icon, likely adjacent to the checkbox, this approach is less desirable because it requires extra screen real estate.

Perhaps the best approach is to change the color of the perimeter of the checkbox cell.

More Notes
While the approach described in alternative #3 above might work well for Independent Variables, the process of imposing FIXed status on Dependent Variables will introduce additional complexity. The consequences are not fully thought through at this time.

While the current development direction is to hand code the available choices in initialState, the idea of automatically forming the list based on variables with identical units was discussed.

The alternative of using left click in the constraint value field to supply constant values and using right click to invoke the FDCL configuration dialog was discussed and rejected.