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Thread: Useful simulations

  1. #1

    Useful simulations

    Does the simulation software that you created help you to make a better car? If so how and how quickly?

    I wanted to share this perspective about simulation software created and/or used by students for a while. The last design judging and conversations I had with students at FSAE Michigan convinced me I had to do it sooner than later.

    I see some OK lap time prediction, vehicle dynamics, CFD, FEA etc.… software that decently simulate the car aerodynamics, handling, stiffness etc… but when I ask how a particular piece of software helps the students to design a better car I have little or no answer.

    Two examples
    1. A software that makes weight transfer calculations. I ask the student to change the springs stiffness in his simulation. To do so he had to scroll down several pages on his laptop screen to change spring stiffness number in his codes. Not nice. I would have like to see some sort of input graphical interface. I then asked him to overlay the weight transfer results, ideally Vs lateral acceleration (in case of nonlinear stiffness) with the new and old springs stiffness. He couldn’t. No output graphical representation.
    What we need is at least some batch rum where the front and rear springs can be change from value X N/mm to value Y N/mm with steps of Z N/mm or a given number of steps.
    When I asked the students how this software help him to decide what springs he wanted to put on the car he had no answers. When I asked him, what were the criteria he used to decide his spring stiffness, he did not have any either. He was just happy to show me a software that works. It painfully worked but it had absolutely no relevance
    2. A software that shows how much the camber or the bump steer will change if a suspension point coordinates is changed. Good. But when I asked which bump steer is needed and which roll center movement he wants and why he could not give me any answer. What was the point of creating such software?

    Students need to create software that are useful, relevant and easily usable. Practically that means: input and output graphical interface, automated batch run, trends, slope and tendencies. Ideally use tools such as heat map, parallel axis chart, scatter plot metrics..
    Examples
    1. if I raise the front roll center x mm how much do I want to raise my rear one to keep the same TLLTD. Is this relationship linear? How much do I need to soften my front and rear ARB if, after raising my front and rear roll centers, I want to keep the same roll gradient and the same TLTTD.
    2. If I change the caster angle by changing the x coordinates of my front (or rear) top wishbone inboard pickup points does my bump steer change and if so how much do I need move vertically my outboard toe link rod end to keep the initial bumpsteer value? Show the result in a XY (X front roll center or froth ARB, Y rear roll center or rear ARB) graph of isolines bump steer values.
    3. Show the aerobalance and the dynamic front and rear ride height Vs speed for front springs Kf1 and Kf2 and rear spring Kr1 and Kr2 rear or static front ride height of 20 and 25 mm and static rear ride height of 40 and 45 mm

    Also make software that are relevant.
    - A few years ago I judged a team of which one student crated an amazing virtual 7 post rig. When I asked him how he used it to define his dampers he told me he did not have the time. If the competition would have been about a 7 post rig simulation he would have scored close to a maximum of points but here I was judging the car design not the car simulation software design.
    - Recently a student showed me a CFD study of his car - Formula One style, really amazing- but when I asked him what the tire coefficient of friction was he had no ideas. He told me his job was to create downforce not grip. Well, he is really ready for the hyper specialization of Formula One.
    - This year at FSAE Michigan a student showed me his own vehicle dynamics / lap time simulation software and I thought we were going to have a interesting conversation but he could not define understeer and oversteer, neither control or stability. Let's be serious.

    I think the problems occur because students spend too much time designing and manufacturing their car and not testing it. But I have been singing that song for a while....
    Claude Rouelle
    OptimumG president
    Vehicle Dynamics & Race Car Engineering
    Training / Consulting / Simulation Software
    FS & FSAE design judge USA / Canada / UK / Germany / Spain / Italy / China / Brazil / Australia
    [url]www.optimumg.com[/u

  2. #2
    I'll second Claude's thoughts, and add a few more based on my own judging experience.

    Whether you write your own code or use third-party software it is important to validate (correlate) your results. Very few students/teams have shown me any kind of measured data which they then compared against simulation results. Of course, the measured data will not match the simulation output, but why? How did you tune your simulation parameters to achieve a more realistic result? What model assumptions limit its accuracy? What variables are uncontrolled or unaccounted for on the real car? Then, after the correlation exercise, how does your simulation help you increase your knowledge and compete with a better car? An easy way to impress design judges is to close the loop by measuring some data, comparing it to your software/calculations and understanding the discrepancies. Few teams do this well.

    Also, if you use third-party software you should have an idea how it does what it does and what limitations apply. All models make assumptions--what are they? What parameters are important and which are ignored? For example, I spoke with more than one team at Michigan this year who used a third-party software tool to calculate lateral load transfer distribution. When I asked if the calculations included any suspension geometry they said they weren't sure. When I asked if it should or shouldn't include suspension geometry I got the same answer. Disappointing. A third-party tool is not a substitute for your own knowledge and understanding. Without understanding the problem/calculation you will not be a good user of a pre-programmed tool.

    Having/using a simulation is not enough. Engineers did this kind of work for a long time without computer simulations. They're a tool. It's the knowledge and understanding that counts.
    Dr. Edward M. Kasprzak
    President: EMK Vehicle Dynamics, LLC
    Associate: Milliken Research Associates, Inc.
    Co-Director: FSAE Tire Test Consortium
    Lecturer: SAE Industrial Lecture Program
    FSAE Design Judge

  3. #3
    Senior Member
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    Sounds like it is time for a '5 Whys'!

    Why do students spend so much time and effort to build their own simulations if those simulations do not improve performance?

    Or

    Why do students spend so much time designing and manufacturing their car and not testing it?

    -William

  4. #4
    Hey Guys,

    A most interesting discussion point. Given I've been developing and more importantly using simulation for a while let me add my two cents worth.

    The best way of using simulation is a three stage process
    *Hand calculations to get a feel for the numbers.
    *Simulation validation so you know the beast you are dealing with.
    *Using this in the design/race engineering of the car.

    Where Junior engineers/undergrads get into trouble is with all three steps. Let me break this all down.

    In a lot of cases there is the view we don't need hand calculations because of CAE tools. This is actually one of the greatest suck you ins of the modern engineering world. What hand calcs do is give you a sixth sense of the numbers. This ensures you don't get led up the garden path when you use your CAE tools.

    The biggest tripping point is correlation and what tends to happen here is you get so obsessed on perfect correlation you waste months on it. As a case in point with lap time simulation I see students and race teams get so obsessed on this they never use simulation in anger. You will never achieve perfect correlation. Rather you need to be focused on at equivalent speeds do the damper compressions match up, or at equivalent g what are the dampers are doing. If you are focused on that the correlation has this funny habit of looking after itself. I also can not stress enough always validate to race data. Also when things don't match up the simulator is trying to tell you something.

    Lastly there is using simulation to maximum effect. When you look at simulated data you need to look at it with slightly different eyes to race data. This is an excellent case in point,

    https://youtu.be/5kb3cJGuXq0

    Also let me pass on two final bits of advice. Firstly simulation does not replace running the car and running the car alone does not replace simulation. When you use them in concert with one another they immeasurably add to each other. Also get going. Your not going to win races/events by reading about it. It's time for the rubber to meet the road. I hope this helps.

    All the Best


    Danny Nowlan
    Director
    ChassisSim Technologies

  5. #5
    Good post Claude, I think this is on the right track. We need to be more “results oriented” not “fancy tools oriented”. You and I both work in Consulting – granted yours is about racecars, mine is about making companies more profitable – and we both are asked to deliver answers, not tools. So yes, this makes perfectly sense to me for “real world application”. However, I think you are mixing a couple of points I would like to raise.

    1) It is always dangerous to use 3-4 examples as a problem for all FSAE teams. Yes there are some teams out there that use like a lot of fancy stuff that does not make the car faster. The vast majority of the teams however does not use the tools at all and just plays around. That is even more concerning. I fully agree with you that those guys in your examples probably had the wrong focus and they were just thrown into the Design event because the software was cool and the team did not think about that. What would have happened if they would just have stayed out? Nobody would complain…
    2) In “real life” you are either the guy that builds a tool or the guy that uses a tool. There is no big car company or what ever where one guy does it all. So I think it is actually okay-ish training in the end
    3) FSAE is just too time constraint to do it all. There is a steep learning curve in teams. For example in Zurich we started with our own LapSim in 2012. Probably if you came to us at FS UK 2012 we would not have the perfect answers to questions on “how did the LapSim influence your car design” and we might have ended up in your post here. And there was no user interface but a bearded guy hacking in Matlab… Starting in September 2012 we had that LapSim however and build the first 4WD car due to this. Half a year later we had a proper interface and even illiterates like myself could use it. This is just progress and we need to respect that. I am quite sure that the example with the 7 post rig is –hopefully- the same. They will start to use it as a team next year and it will help them for a long time.
    4) Come on, you really expect an Aero guy to know the tire friction? In Zurich, we taught everyone in Design the super basics of all car elements so that they can answer “the first question” before handing over the experts but I think this is too much to ask. Next time you want everyone in the team to know the Young’s modulus of our brake pads (remember judging us in 2011? ) I mean yes students should not be hyper specialized in one area but you are so super time constraint and you just don’t care about the tire coefficient when you are working on Aero. You need to set clear boundaries to be efficient and I think this is the right way to do so.
    5) I am convinced that “testing more” is the right way to go to be successful and in the end this is the “goal” of the competition for most teams. Not the fastest car, not the fanciest tools but the most points in the event. But it is just not as easy as we think from the outside. There are some time constraints in the development and therefore we cannot test too much. I rather have the young guys trying out new designs instead of keeping 90% of last years car, rebuilding it and test just 4-5 months. This is not where most of the guys will end up working later on. This should not be the total focus in my opinion…
    -------------------------------------------
    Alumnus
    AMZ Racing
    ETH Zürich

    2010-2011: Suspension
    2012: Aerodynamics
    2013: Technical Lead

    2014: FSA Engineering Design Judge

  6. #6
    OK I see I am not the only one so I will be continuing the ranting

    Chassis torsion stiffness calculated from torque acting on rear bulkhead and front bulkhead virtually attached to the ground, totally ignoring tire forces load path from tire contact patches to suspension pick up points.

    Teams' students who do not have any idea of their tire temperature because they NEVER measured it.

    Teams' students having no idea of their CFD simulation is 5 % or 50 % close to the real aerodynamic forces and moments

    Team's student's having no idea of what the bump steer (simulated - with or without compliance - or measured - with or without compliance) is

    A winning team that stated in their design report that the low speed bump was at 70% of the critical damping but no one of the students could define critical damping. That car was quick because it was a good car, well thought, well manufactured with very good drivers but the knowledge of previous year students wasn't transmitted.
    The car was quick but no one could explain why. And you wonder why some design judges push to increase the number of points in static and decrease it in dynamic events...

    Team that have suspension linear potentiometers but have not idea what the range of their damper speed of their car on the track is and how to relate them to force Vs speed graphs from damper manufacturers and/or their dampers dyno test data

    Design report: "....the suspension kinematics has been defined to give each tire the ideal contact patch...." but no one of that team students could define what the "ideal contact patch" was.

    Some students couldn't even tell me any suspension adjustment numbers:
    - how many shims do they need to add or remove to change the camber by an x amount
    - how many pushrod or toe link shims (or turn buckle turns) were necessary to change the ride height or the toe.
    - Some of them did not even know their hot and cold tire pressure target was

    A few years ago a team declared itself as the king of data acquisition and data analysis but when asked by a judge how if they were able to zoom or change a color trace in their MoTeC i2 software... they couldn't. Not very encouraging. Can help to wonder if the team wasn't the king of…. BS.

    Another judge, last year if I remember well, ask all the design finalists their car setup sheet. No one could! Not one!!! How could you go testing without a paper or electronic trace of your car beginning, end and ideally evolving setup?

    Last year one specific UK university that claims their school is the indispensable gate to a Formula One job had students who could not define understeer, oversteer, control and stability. But they told me they had superior vehicle dynamic courses.

    And do not tell me they can't find such info. Just Google it; most of it, at least the basic is there!

    Can't help to see Z coming here soon: "......education going down the drain....." and after some depressing times like the ones I had after Michigan Design Finals I could sometimes be right.
    Claude Rouelle
    OptimumG president
    Vehicle Dynamics & Race Car Engineering
    Training / Consulting / Simulation Software
    FS & FSAE design judge USA / Canada / UK / Germany / Spain / Italy / China / Brazil / Australia
    [url]www.optimumg.com[/u

  7. #7
    Ok. So we covered that most students are pretty bad in their design discussions. I had similar experiences - agree totally.

    So what are we going to do about this?

    There is the Z-way: Kill design, let them race and learn from the hillbillys at the drag strip and teach them via this way.
    There is your proposal: Reduce designing time make more testing time
    Or go extreme: Calling them out on their BS, give them crazy bad scorings, call them out personally... don't do these shady design feedback forms. Just go to the guy after every session and tell him what he was screwing up.

    I don't know what we want to achieve here. We will never have perfect race car engineers in all teams. There is no time to learn all this in one year while studying and designing parts. We have to acknowledge that as well.

    I just had the best experience project managing that whole thing which in the end landed me my job a first class MBA position and so on. All that thanks to FSAE. I want to give the next generations the same experience.
    And I don't want to see cars that are on the level as our first Electric Car in 2010 presented to me as "lightweight awesomeness"...
    -------------------------------------------
    Alumnus
    AMZ Racing
    ETH Zürich

    2010-2011: Suspension
    2012: Aerodynamics
    2013: Technical Lead

    2014: FSA Engineering Design Judge

  8. #8
    Quote Originally Posted by Claude Rouelle View Post

    Some students couldn't even tell me any suspension adjustment numbers:
    - how many shims do they need to add or remove to change the camber by an x amount
    - how many pushrod or toe link shims (or turn buckle turns) were necessary to change the ride height or the toe.
    - Some of them did not even know their hot and cold tire pressure target was
    I wouldn't say that knowing the exact shimming amount to change camber is an accurate indication of whether or not team members understand how to adjust/tune the suspension. Personally due to the reality of student manufacturing, I am well aware that our uprights and shims are not all exactly the same. At best you might have 1 person who has memorized the odd combinations of different shims that each individual upright needs to reach a rough target number. As much as we would like to be one, we don't have the professionalism of a pro team. We will have to deal with remeasuring/readjusting in random increments to get desired toe/camber/ride height. We make due with what we have.

  9. #9
    I'm not entirely sure how to make shims that give random adjustment - normally they're cut from sheet metal, which is rolled to a tightly controlled thickness. If it's undergauge you get your money back from the mill, if it's overgauge the mill is giving metal away. If you're stuck cutting out shims with tinsnips, and the design doesn't let you cut them flat, mashing them with a big hammer against the end of a heavy bar should result in shims of constant thickness within .05 mm or so.
    Last edited by Charles Kaneb; 05-24-2017 at 11:32 PM.
    Charles Kaneb
    Magna International
    FSAE Lincoln Design Judge - Frame/Body/Link judging area. Not a professional vehicle dynamicist.

  10. #10
    Noah, Charles,

    Unless I misunderstood your comments what I am trying to say is that if, for example, your static camber is -1.8 deg. and you want - 2.2 deg. you need to remove 2.6 mm of shims. Boom; you get it right first time out, not need for successive approximations. That is also what engineering a car means.

    Similarly if you want to raise the rear right height 5.2 mm and you want to add 1.5 Kg on the static LF load and remove 2 kg on the RF static load you know you have to add 8.2 mm of pushrod shims on the RR pushrod and 6.8 mm of shims on the LR pushrod
    By the way many students can't tell me where the reference points of the LF, RF, LR and RR ride heights measurements are on their car. You wonder if these measurements were ever made.....

    These are the kind of measurements that need to be simulated and validated with workshop measurements on the setup pad (little advice; if yo do so do it with all dampers bump and rebound setting at the minimum to avoid dampers residual friction - do not forget the put your dampers setting back after the setup procedure).

    Students made a business case showing they want to build and sell x cars. I guess each car should come with a user manual. Where is the user manual?

    Even with no planned sales the engineer who setup the car should know these numbers ahead of time. I have seen teams changing the caster and keeping the same bumpsteer in less than 5 minutes while other were doing it in 2 hours with successive approximations. Precious track time lost.
    Last edited by Claude Rouelle; 05-25-2017 at 12:57 AM.
    Claude Rouelle
    OptimumG president
    Vehicle Dynamics & Race Car Engineering
    Training / Consulting / Simulation Software
    FS & FSAE design judge USA / Canada / UK / Germany / Spain / Italy / China / Brazil / Australia
    [url]www.optimumg.com[/u

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