Nonlinear damper parameter sweep problem

I’m simulating a multibody vehicle model. Within this model I’m using nonlinear dampers – damper subsystem reads the damper velocity vector and damper force vector from base workspace. Force and velocity vectors are defined via live script which uses base workspace variables for “low speed” compression damping, “high speed” compression damping, blow off velocity (damper velocity at which it “switches” to “high speed” damping curve etc.

%Variables that I want to change/sweep in an automated design stady
fdlb; % Bump/Compression Low speed damping rate 
fdhb; % Bump/Compression High speed damping rate 
fdlr; % Rebound Low speed damping rate 
fdhr; % Rebound High speed damping rate 
fkb; % Bump/Compression High/Low speed cutoff coefficient (number of velocity vector component)
fkr; % Rebound High/Low speed cutoff coefficient 

fvb=0:0.025:0.3; % Bump/Compression velocity (positive) vector
fvr=-0.3:0.025:0; % Rebound velocity (negative) vector

fvhb=fvb(fkb:end); % Bump/Compression High Speed velocity vector 
fvlr=fvr(fkr:end); % Rebound Low Speed velocity vector
fvhr=fvr(1:fkr); % Rebound High Speed velocity vector

fDbl=fvlb*fdlb; % Bump/Compression Low Speed damping forces
fDbhi=fvhb*fdhb; % Bump/Compression High Speed damping forces (starting from zero)
fDeltab=fDbl(end)-fDbhi(1);  % Delta at kb (cutoff velocity) 
fDbh=fvhb*fdhb+fDeltab; % Bump/Compression High Speed damping forces

fDrl=fvlr*fdlr; % Rebound Low Speed damping forces
fDrhi=fvhr*fdhr; % Rebound High Speed damping forces (starting from zero)
fDeltar=fDrl(1)-fDrhi(end);  % Delta at kr (cutoff velocity) 
fDrh=fvhr*fdhr+fDeltar; % Rebound High Speed damping forces

% Front Damper force and velocity vectors
F_vDamper=[fvr,fvb(2:end)]
F_fDamper=[fDrh,fDrl(2:end),fDbl(2:end),fDbh(2:end)]


 % assigning vectors to workspace variables that simulink non linear
 % damper will use for velocity and force vectors
Damper.NonLinear.Faxle.vDamper.Value=F_vDamper; 
Damper.NonLinear.Faxle.fDamper.Value=F_fDamper;  

In the Model Callbacks (InitFcn) I call this above-mentioned Live script to update damping force and velocity vectors according to current values (base workspace) of above-mentioned variables.

My problem is that I can’t figure out how I can do damping parameter sweeps… i.e. how can I set up the model so that it runs multiple simulations and changes damping related variables (base workspace) according to some predefined list. It works fine if I would be changing/sweeping any of model block parameters or variables that are mentioned within block. In this particular case it’s an array with values calculated via script. If I setup design study from multiple simulations panel – it doesn’t effect variables in base workspace that would effect the script that calculates required vectors.

I’ve tried to use matlab function that would use this script to create required vectors and assign it to base (or model) workspace but it doesn’t work or better say I don’t know how to do it properly.

Any suggestions would be very highly appreciated.

Thank you.

Ted

Answer 1

[Steve Miller]

Hi Tudor,

Two things to try:

1. Make sure the fields where you have defined the parameter are configured to be run-time parameters. The setting is shown below.
2. To reduce the complexity a bit, try storing the values you are sweeping in a separate MATLAB variable, just to see if that works. Enter F_vDamper and F_fDamper directly in the fields. This is not required, but it eliminates some complexity to figure out what is not working.

--Steve

[Tudor Miron]

Hi Steve,

Many thanks for your reply. Problem is that it doesn't change anything. If I run simulations from multiple simulations panel where I assign base workspace variables to be changed - it doesn't change those variables and thus the script (initial question above) runs with non changed fdlb,fdlh,fdlr etc. variables and resultant F_vDamper,F_fDamper stays unchanged. As far as I understand values don't effect variables in base workspace.

I think that I could overcome it by setting up simulations via SimulationInput object but I can't figure out how should I setup For Loop if I want to change more than one variable.

Thank you,

Ted

[Steve Miller]

In the attached small example you will see how it can be applied to the nonlinear damper. Things to watch out for in your example:

1. Make sure the values modified by your simInput are used in the model.
2. Make sure that the simulation is reaching the range of behavior you have changed. If your nonlinear damper is only exercised at low compression rates, you may not see the difference even if a new parameter set is used.

--Steve

[Tudor Miron]

Many thanks Steve,

Your model works perfectly.

I don't want to sound as ungrateful scum but is there anyway to be able to assign "low speed" damping/"high speed" damping and "knee" velocity (damper velocity where "low speed" damping is substituted by "high speed" damping (like it was done in the code in initial question above)?

Thank you,

Ted

[Steve Miller]

There certainly is. I would have used your code but it doesn't run because many of the values at the start are unassigned. The code you provided should from line fvhb=fvb(fkb:end); should appear in the for-loop that creates the simInput object. As long as the for-loop indexes through the variables you wish to modify and the calculated force and velocity vectors are assigned to the simInput object using setVariable, it will work.

If you are going to vary multiple parameters, you will need nested for loops.

I recommend you set up the code that generates the force-velocity relationships for nonlinear damping all set up first, and plot the damper curves on top of another to make sure your parameterization is set up correctly before trying to run the sweep. If you get that code set up so that it plots all the damper curves, I can help you set up the sweep.

--Steve

[Tudor Miron]

Let me once again say: Thank you for your help!

Here's a code that seem to be working (it does plot expected damper curves).

fdlb=18000; % Bump/Compression Low speed damping coefficient 
fdhb=8000; % Bump/Compression High speed damping coefficient
fdlr=12000; % Rebound Low speed damping coefficient
fdhr=5000; % Rebound High speed damping coefficient

fvb=0:0.025:0.3; % Bump/Compression velocity (positive) vector
fvr=-0.3:0.025:0; % Rebound velocity (negative) vector
fkb=4; % Bump/Compression High/Low speed cutoff coefficient (number of velocity vector component)
fkr=10; % Rebound High/Low speed cutoff coefficient 

fkb_sweep=[4 5 6];


for i = 1:length(fkb_sweep)
  fvlb=fvb(1:fkb_sweep(i)); % Bump/Compression Low Speed velocity vector
  fvhb=fvb(fkb_sweep(i):end); % Bump/Compression High Speed velocity vector
  fvlr=fvr(fkr:end); % Rebound Low Speed velocity vector
  fvhr=fvr(1:fkr); % Rebound High Speed velocity vector

  fDbl=fvlb*fdlb; % Bump/Compression Low Speed damping forces
  fDbhi=fvhb*fdhb; % Bump/Compression High Speed damping forces (starting from zero)

  fDeltab=fDbl(end)-fDbhi(1);  % Delta at kb (cutoff velocity) 
  fDbh=fvhb*fdhb+fDeltab; % Bump/Compression High Speed damping forces
 
  fDrl=fvlr*fdlr; % Rebound Low Speed damping forces
  fDrhi=fvhr*fdhr; % Rebound High Speed damping forces (starting from zero)
  fDeltar=fDrl(1)-fDrhi(end);  % Delta at kr (cutoff velocity) 
  fDrh=fvhr*fdhr+fDeltar; % Rebound High Speed damping forces
  F_vDamper=[fvr,fvb(2:end)];
  F_fDamper=[fDrh,fDrl(2:end),fDbl(2:end),fDbh(2:end)];
  
  plot(F_vDamper,F_fDamper)
  hold on
  grid on
  xlim([-0.3 0.3])
  ylim([-4000 4000])
  xlabel('Velocity [m/s]')
  ylabel('Force [N]')
  title('Front Force vs Velocity')
end

hold off

Below is the code where I want to alter 2 variables (fkb and fkr for example).

fdlb=18000; % Bump/Compression Low speed damping coefficient 
fdhb=8000; % Bump/Compression High speed damping coefficient
fdlr=12000; % Rebound Low speed damping coefficient
fdhr=5000; % Rebound High speed damping coefficient

fvb=0:0.025:0.3; % Bump/Compression velocity (positive) vector
fvr=-0.3:0.025:0; % Rebound velocity (negative) vector
fkb=4; % Bump/Compression High/Low speed cutoff coefficient (number of velocity vector component)
fkr=10; % Rebound High/Low speed cutoff coefficient 

fkb_sweep=[4 5 6];
fkr_sweep=[8 9 10];
% Store simulation inputs

for i = 1:length(fkb_sweep)
    for idx=1:length(fkr_sweep)
    fvlb=fvb(1:fkb_sweep(i)); % Bump/Compression Low Speed velocity vector
    fvhb=fvb(fkb_sweep(i):end); % Bump/Compression High Speed velocity vector 
    fvlr=fvr(fkr_sweep(idx):end); % Rebound Low Speed velocity vector
    fvhr=fvr(1:fkr_sweep(idx)); % Rebound High Speed velocity vector

    fDbl=fvlb*fdlb; % Bump/Compression Low Speed damping forces
    fDbhi=fvhb*fdhb; % Bump/Compression High Speed damping forces (starting from zero)

    fDeltab=fDbl(end)-fDbhi(1);  % Delta at kb (cutoff velocity) 
    fDbh=fvhb*fdhb+fDeltab; % Bump/Compression High Speed damping forces
 
    fDrl=fvlr*fdlr; % Rebound Low Speed damping forces
    fDrhi=fvhr*fdhr; % Rebound High Speed damping forces (starting from zero)
    fDeltar=fDrl(1)-fDrhi(end);  % Delta at kr (cutoff velocity) 
    fDrh=fvhr*fdhr+fDeltar; % Rebound High Speed damping forces
    F_vDamper=[fvr,fvb(2:end)];
    F_fDamper=[fDrh,fDrl(2:end),fDbl(2:end),fDbh(2:end)]
    plot(F_vDamper,F_fDamper)
    end

    
hold on
grid on
xlim([-0.3 0.3])
ylim([-4000 4000])
xlabel('Velocity [m/s]')
ylabel('Force [N]')
title('Front Force vs Velocity')
end

F_fDamper = 1×25

1.0e+03 * -2.3750 -2.2500 -2.1250 -2.0000 -1.8750 -1.7500 -1.6250 -1.5000 -1.2000 -0.9000 -0.6000 -0.3000 0 0.4500 0.9000 1.3500 1.5500 1.7500 1.9500 2.1500 2.3500 2.5500 2.7500 2.9500 3.1500

F_fDamper = 1×25

1.0e+03 * -2.2000 -2.0750 -1.9500 -1.8250 -1.7000 -1.5750 -1.4500 -1.3250 -1.2000 -0.9000 -0.6000 -0.3000 0 0.4500 0.9000 1.3500 1.5500 1.7500 1.9500 2.1500 2.3500 2.5500 2.7500 2.9500 3.1500

F_fDamper = 1×25

1.0e+03 * -2.0250 -1.9000 -1.7750 -1.6500 -1.5250 -1.4000 -1.2750 -1.1500 -1.0250 -0.9000 -0.6000 -0.3000 0 0.4500 0.9000 1.3500 1.5500 1.7500 1.9500 2.1500 2.3500 2.5500 2.7500 2.9500 3.1500

F_fDamper = 1×25

1.0e+03 * -2.3750 -2.2500 -2.1250 -2.0000 -1.8750 -1.7500 -1.6250 -1.5000 -1.2000 -0.9000 -0.6000 -0.3000 0 0.4500 0.9000 1.3500 1.8000 2.0000 2.2000 2.4000 2.6000 2.8000 3.0000 3.2000 3.4000

F_fDamper = 1×25

1.0e+03 * -2.2000 -2.0750 -1.9500 -1.8250 -1.7000 -1.5750 -1.4500 -1.3250 -1.2000 -0.9000 -0.6000 -0.3000 0 0.4500 0.9000 1.3500 1.8000 2.0000 2.2000 2.4000 2.6000 2.8000 3.0000 3.2000 3.4000

F_fDamper = 1×25

1.0e+03 * -2.0250 -1.9000 -1.7750 -1.6500 -1.5250 -1.4000 -1.2750 -1.1500 -1.0250 -0.9000 -0.6000 -0.3000 0 0.4500 0.9000 1.3500 1.8000 2.0000 2.2000 2.4000 2.6000 2.8000 3.0000 3.2000 3.4000

F_fDamper = 1×25

1.0e+03 * -2.3750 -2.2500 -2.1250 -2.0000 -1.8750 -1.7500 -1.6250 -1.5000 -1.2000 -0.9000 -0.6000 -0.3000 0 0.4500 0.9000 1.3500 1.8000 2.2500 2.4500 2.6500 2.8500 3.0500 3.2500 3.4500 3.6500

F_fDamper = 1×25

1.0e+03 * -2.2000 -2.0750 -1.9500 -1.8250 -1.7000 -1.5750 -1.4500 -1.3250 -1.2000 -0.9000 -0.6000 -0.3000 0 0.4500 0.9000 1.3500 1.8000 2.2500 2.4500 2.6500 2.8500 3.0500 3.2500 3.4500 3.6500

F_fDamper = 1×25

1.0e+03 * -2.0250 -1.9000 -1.7750 -1.6500 -1.5250 -1.4000 -1.2750 -1.1500 -1.0250 -0.9000 -0.6000 -0.3000 0 0.4500 0.9000 1.3500 1.8000 2.2500 2.4500 2.6500 2.8500 3.0500 3.2500 3.4500 3.6500

hold off

It would be extremely helpful if you could help me setup the sweep properly.

Thank you,

Ted

Answer 2

[Tudor Miron]

I have no problem creating Simulation Input object if I want to sweep 1 variable (code from the 1st half of the above post/comment):

fdlb=18000; % Bump/Compression Low speed damping coefficient 
fdhb=8000; % Bump/Compression High speed damping coefficient
fdlr=12000; % Rebound Low speed damping coefficient
fdhr=5000; % Rebound High speed damping coefficient

fvb=0:0.025:0.3; % Bump/Compression velocity (positive) vector
fvr=-0.3:0.025:0; % Rebound velocity (negative) vector
fkb=4; % Bump/Compression High/Low speed cutoff coefficient (number of velocity vector component)
fkr=10; % Rebound High/Low speed cutoff coefficient 

fkb_sweep=[4 5 6];
mdl = 'FullVehicleAssembly_v3_6_1';

clear simIn

for i = 1:length(fkb_sweep)
    simIn(i) = Simulink.SimulationInput(mdl);
  fvlb=fvb(1:fkb_sweep(i)); % Bump/Compression Low Speed velocity vector
  fvhb=fvb(fkb_sweep(i):end); % Bump/Compression High Speed velocity vector
  fvlr=fvr(fkr:end); % Rebound Low Speed velocity vector
  fvhr=fvr(1:fkr); % Rebound High Speed velocity vector

  fDbl=fvlb*fdlb; % Bump/Compression Low Speed damping forces
  fDbhi=fvhb*fdhb; % Bump/Compression High Speed damping forces (starting from zero)

  fDeltab=fDbl(end)-fDbhi(1);  % Delta at kb (cutoff velocity) 
  fDbh=fvhb*fdhb+fDeltab; % Bump/Compression High Speed damping forces
 
  fDrl=fvlr*fdlr; % Rebound Low Speed damping forces
  fDrhi=fvhr*fdhr; % Rebound High Speed damping forces (starting from zero)
  fDeltar=fDrl(1)-fDrhi(end);  % Delta at kr (cutoff velocity) 
  fDrh=fvhr*fdhr+fDeltar; % Rebound High Speed damping forces
  F_vDamper=[fvr,fvb(2:end)];
  F_fDamper=[fDrh,fDrl(2:end),fDbl(2:end),fDbh(2:end)];
  
  simIn(i) = simIn(i).setVariable('F_vDamper',F_vDamper);
  simIn(i) = simIn(i).setVariable('F_fDamper',F_fDamper);
    plot(F_vDamper,F_fDamper)
hold on
grid on
xlim([-0.3 0.3])
ylim([-4000 4000])
xlabel('Velocity [m/s]')
ylabel('Force [N]')
title('Front Force vs Velocity')
end
hold off


simOut = [];
simOut = sim(simIn,'ShowProgress','off','UseFastRestart','on');

It does output 1X3 SimulationInput object. When I check it out - each (1,1;1,2 etc) simIn has proper F_fDamper value. Model runs fine. BUT when I check the results - damper forces are unchanged. I run the model over 50mm bump to make sure that high damper velocities are produced. It does use Simin(1,1) variable thought as can be seen from scatter plot (force vs velocity). Both velocity and force vector of nonlinear damper are set as "Run-time". I'm really lost what may go wrong... May I ask if can suggest what may be wrong?

And I can't figure out how can I create 1X9 SimulationInput object - code from 2nd half of the above post/comment.

Thank you,

Ted

[Tudor Miron]

Interestingly enough removing 'UseFastRestart' solved the problem and now it does iterate through damping settings variants that are created in SimulationInput object.

Now if I could figure out how do I properly setup nested for loop when I want to alter more than one variable...