Three types of lies; lies, damn lies and … simulations? 

 

The title of this paper is “Three types of lies which should not apply to simulations” is intended to be an 

apologetic report on behalf of all scrupulous modelers of physical events or simulators. 

This short commentary is intended to blow the whistle on litigation settlement by insurance companies 

based upon faulty simulations modeling and results from attorneys on behalf of their clients; whether 

inadvertently or  intentional.   The case presented  in this paper had been  in my mind  for fourteen  (14) 

years. When I first saw the article in the May 2000 issue of ASME I had waited to see whether there would 

be any objections to its claims.  To my knowledge none has been made. 

Here  is my  perplexity  of  this  case;  I  have  a MSME  from  Tufts  University,  1984 with  computational 

mechanics (simulations) core courses of study. As of this year, 2014, I have been creating and evaluating 

thermo‐structural simulations for 30 continuous years and have never seen a credible simulation without 

classical  hand  calculations  to  establish  the  boundaries  of  the  proverbial,  “Ball  Park”.  The  case  I  am 

presenting has many obvious flaws but to my surprise, even the ASME (American Society of Mechanical 

Engineers) published the flawed‐simulation perpetuating the offense to investigators of physical events 

via numerical simulation”. 

I propose that the readers of this white paper will take it upon themselves to prove whether or not my 

claims of inadequate simulation are true. 

 

Like the Phoenix rising from the remaining ashes after a fire, it is my hope that students of simulations 

methodology and practicing engineers would take this case as a benchmark of “erroneous zones” to be 

understood and avoided in their own practice. 

Having watched on TV two (2) separate beauty contestants fall on their posterior, without a “cushioned 

seat” from full height without damage to their spines, then reading the article that a man falls two (2) 

inches  on  a  “cushioned  seat” with  consequential  damages worthy  of  a  law  suit  and  the  subsequent 

publication of such a “Heroic simulation” in the ASME simply infuriated me that after fourteen (14) yeas 

of contemplation decided to publish this white paper. Due to this misuse of simulation, I shall endeavor 

to participate  in any event that  I can  find  in which simulations are being misused for financial gain by 

attorneys and  their clients. This area of simulation pertains  to “Forensic Examination of Biomechanics 

Claims of Bodily Damage Litigations”. The average weight, and height of a feminine beauty contestant is 

120 lb (10 pounds lower than the average woman of the same height), and 5 feet 6 inches (66 inches) in 

height, respectively.   The following  image can be used to establish an estimate of the height from the 

ground to the bottom of the spinal cord 

 

 

Reference: NASA‐STD‐3000, Vol. 1, Man‐Systems Integration Standards, page 3‐11 (81 of 801 in the PDF 

file). 

The height in inches corresponding to the bottoms of the buttock, 973 mm, is found by the linear ratio, 

x/66” = 605 mm/ 973 mm. That is, x = 66” x (605/973) = 41.0”. Using this height for “Miss Beauty” and 

multiplying it by the weight of 120 lb we get the potential energy (PE) at the time of being standing: 

PE1 = w1 x h1 = 120 lbf x 41 inches = 4920 lbf‐in 

The operator who claim that he was injured from a 2 inch fall while seating on a cushioned seat is 288 lbf 

x 2  inches = 576  lbf‐in.   The ratio of energy at  the  time of  impact of “Miss Beauty” and “unfortunate 

operator”  is 4950/576 = 8.6.   That  is to say, “Miss Beauties had experienced an  impact force 8.6 time 

greater than that of the ‘unfortunate operator’ but did not report any injuries due to such a fall”. 

My conclusion is that either the two (2) “Miss Beauty” contestants are actually “Bionic women” or the 

man had a “pre‐existing condition such as herniated disc”. See detailed calculations starting on the next 

page. 

Let us think of the scenario where the “unfortunate operator” claim that he had his head resting on some 

support system that failed and his head impacted the ground from a height of 2 inches; would anyone 

believe him? How would one not believe the damage caused by a 2 inch drop of a person’s head onto a 

rigid foundation while readily and implicitly admitting that the normal curvature of the snail cord would 

not absolve most of the impact energy by means of the flexibility of spinal cartilage discs?  

The only condition under which  I would accept an  injury claim from a 2‐inch fall  is  if the “unfortunate 

operator” was “operating a rocket during take‐off and the seat broke at such an instant”. 

The advices that apply to this case are extracted from the article published in BENCHmark magazine on 

April 2001, page 11: 

Don't apply any model until the simplifying assumptions on which it is based are, fully understood 

and the assumptions can be tested for applicability, 

Don't believe that the model is reality. A simulation no matter how complex is always subject to the GIGO (garbage in, garbage out) rule. GIGO rule means that regardless of how accurate the simulations model is, the output quality of the simulation results is ultimately governed by the quality of the input data. 

Don't distort reality to fit the model. The model only represents results for the analyst to determine correctness. 

Don't believe the second order consequences of a first-order model 

I believe the model is flowed with subsequent erroneous results and conclusions due to being: 

Not having classical hand calculations to establish the  limiting results such as potential energy 

estimate. That is KE (Kinetic Energy) at time of impact equals the PE (Potential Energy) at the start 

of the free fall. 

Not modeling  the  curvature of  the  spinal  cord which would have  required  “beam  elements” 

instead of “truss elements”. The model simulates a “first‐order” phenomenon but the author used 

such results to make a conclusion requiring “Second‐order simulation”. 

 

SUMMARY:   A computer model of a physical event  is only good as the assumed governing equations, 

constraint  and  input  data.  The  model  case  being  presented  in  this  paper  should  be  consider  a 

“benchmark” to avoid similar errors in our own digital simulation models. 

 

CONCLUSION:  The insurance companies should establish a forum where simulations analysts can be given 

an  opportunity  to  evaluate models  submitted  for  claims  keeping  the  litigants  anonymously  by  not 

mentioning  their  cases  as  either pending or  resolved nor  any  identification of  the  litigants  and  their 

attorneys. Group sourcing would enhance the discipline of simulations by allowing contributors to both 

learn and teach the arts and sciences of simulations. 

A 2-inch drop impact energy should cause negligible biomechanical damage.mcdx

This paper will derive the equations necessary to demonstrate that the impact energy due to a 2-inch drop would cause negligible biomechanical damage.

Determine the impact velocity of a free-fall object released from a given height, h

Conservation of Energy:

＝KE PE ((1))

＝⋅⋅―1

2m V

2⋅w h ((2))

＝w ⋅m g ((3))

Substitute Eq. 3 into Eq. 2

＝⋅⋅―1

2m V

2⋅(( ⋅m g)) h ((4))

Solve for V2

＝V2

⋅⋅2 g h ((5))

Equation 5 is useful in obtaining ratios of impact velocities for given heights. For instance, given two (2) release heights, h1, and h2, one can determine the ratio of velocitis as

＝⎛⎜⎜⎝

―

V2

V1

⎞⎟⎟⎠

2 ⎛⎜⎜⎝

―

h2

h1

⎞⎟⎟⎠

((6))

Obtain the ratio of the impact velocities by taking the square root of boths sides of Eq. 6

＝⎛⎜⎜⎝

―

V2

V1

⎞⎟⎟⎠

‾‾‾

―

h2

h1

((7))

The ratio of the kinetic energies of two objects given their corresponding heights is

＝⎛⎜⎜⎝

――

KE2

KE1

⎞⎟⎟⎠

⋅⎛⎜⎜⎝

――

m2

m1

⎞⎟⎟⎠

⎛⎜⎜⎝

―

V2

V1

⎞⎟⎟⎠

2

((8))

Yo Creo Page 1 of 2

A 2-inch drop impact energy should cause negligible biomechanical damage.mcdx

Substitute equations and 6 into Eq. 8

＝⎛⎜⎜⎝

――

KE2

KE1

⎞⎟⎟⎠

⋅⎛⎜⎜⎝

―

w2

w1

⎞⎟⎟⎠

⎛⎜⎜⎝

―

h2

h1

⎞⎟⎟⎠

((9))

ExampleTwo persons fall from different heights. Person one (1) has a weight of 288 lbf and falls a distance of 2 inches and claim to have been "critically injured" filing, therefore, a lawsuit. Person two (2) weights 120 lbf and falls 41 inches without any physiological damage.

Calculate the impact velocities and corresponding kinetic energy due to free fall from the given heights.

Weight Height

Person one (1): ≔w1

⋅288 lbflbflbflbf ≔h1

⋅2 inininin

Person one (2): ≔w2

⋅120 lbflbflbflbf ≔h2

⋅41 inininin

Solution

Velocity ratio (Eq. 7): ≔RatioV =

‾‾‾

―

h2

h1

4.5

Kinetic Energy ratio (Eq. 9): ≔RatioK =⋅⎛⎜⎜⎝

―

w2

w1

⎞⎟⎟⎠

⎛⎜⎜⎝

―

h2

h1

⎞⎟⎟⎠

8.5

ResultsThe second person falling 41 inches experiences an impact velocity and kinetic energy, 4.5 and 8.5 times as large as that experienced by the first person falling 2 inches.

Conclusion

The claim of injury from the 2 inch free fall of person one (1) can be attributed to a pre-existing condition such as herniated disc or discs and not by the amount of energy transmitted to the spinal cord by the impact.

Yo Creo Page 2 of 2

A Few Words From The Dark Side.,.1~ ~5",;1£5 of 1:-"" L j J ." GOOC!L /vlof..Wv

d"" VOo-} 0J'1P'1 r\J

" siome form of reality, chel c~ ShOUlld vhalue Of

l a resllJdlt anwd its, relevance kto _. Don't believe ttiat the model is ~

~ a ways accompany slmu atlons. n t e rea wor. e a ways ma e reality. A simulation no matter how \S many instances, these may relatively exception to general rules and if complex is always subject to the ~ t

~'_. easy to perform. However, as analyses pushed exceptions to the exceptions. )"garbage in, garbage out" rule. ,..!i- \ '0t . become more complex and include Simulations, no matter how generic, are '- G~IJ t.) ~

more non-linear effects, simple checks always conditioned to behave by a set ' • Don't distort reality to fit the model. and verification methods often become of rules. Will a complex simulati,on \ The d~nkey an? tail syndrome, the ~ ') impractical. In these situations it is perform well for only one set of specific \=model IS R9'rQr RSAt • .J.t..enly presents·~ ;2

V) important to understand the limitations initial conditions and give poor and suits for the user to determine ~ '~ ,,\J of an analysis before, during and after unusable results when subjected to co ~ss. ~ . ..".;) it has been carried out. "To my mind, slightly different initial conditions? How _ I D ' I b d h 'i. r.

~ the reality check is best summed up in stable is the solution? V· on t extrapo ate eyon t e r':~ ~ the form of a paper presented several ~ v..-cL9~ region of fit. This can lead to violation,~

"'_\:,' years ago by an engineer of the 'Relying solely on the opinions of of th~ rules, that were used to perform :::s ~ ~ Chrysler Corp.oration (1)" Jacob says. experts can, be risky. The simulation the Simulation. ~~

"" The con.cl USI on s of the paper are. of a~ event IS th7 c?~sequence of the • Don't believe the second order '" J. ~ threefold. IA !'IV- ?f. the tndlvldu,als who, base consequences of a first-order model. ~;b

, , ~ -M=tese opinions on their experience There is a limit to the resolution at which () ~ Human cognitive skills are always gained in addressing similar cases. results become meaningless. . ~

i greater than those of a simulation When required to explain their choices, J ~ model, but the model's complexity (the metaphoric reasoning and imprecise • Don't fall in love with the model i

It shear number of calculations) is greater models of the system response are /" ro

~~ th th h . d d I 'th V. Don't retain a discredited model ~ an e uman min can ea WI. often used. .~

This means th~t the use of very • Don't expect that by having named ~~

~ complex models IS balanced not only From these realities emerge several , , --. b't th t' II' 't t' 'b t b th cautionary points that need to be a demon within a model that you have V" . ~ I S eore Ica Iml a. Ion s u y e ~ ed it ,-~r~ ...L ~ ~ mind of the analyst. remembered: y ~ e/ 1 /} ~ ~ Thankfully many engineers realize his ~ ~

~. Second, if one tortures the data long • Don't apply any model until the and are aware the above. ~)

enough, it will confess. Rational and simplifying assumptions on which it is C. ~ I 'bl I ' b d f II d t d d th (1) "Beware the Dark Side of Simulations" Guy <V p ausl e exp anatlons can always be ase are, u y un ers 00 an e ~_

Nucholtz, Proceedings of the 6th International t 1

'.

. found for an.alysis resu. Its from complex a. ss~m PtIO. ns can be tested for Madymo User Meeting 1-2 April 1996, \J

. models. The trick is to determine the applicability, Amsterdam, Holland,

;¥ 62(.(. ~ t-ry (if ~ 'b-vtfwl- ¢dfa. BENCHmark April 2001 Page 11

Reprinted with permission from MECHANICAL ENGINEERING Magazine, 6/2000 © ASME International

• orenSIC • exa Ina on

Engineering software backs the plaintiff's case In a product la\Vsuit.

IT STARTED OUT as an ordinary day at the TU Electric Oak Hill strip mine near Tatum,

Texas. It became less than ordi­nary when the excavating ma­chine's seat pedestal collapsed. It became serious when the excavator operator reported that the accident had inj ured his lower back.

excavator seat pedestal of the same part number. Mark Mann, the lawyer who handled the case, raised a new question that sent Giesen seeking a solution: What was the impact suffered by the operator's lower spinal column when his seat collapsed?

A VARIED BACKGROUI\ID

Giesen was associated with the U.S. Air Force for 15 years, then became involved in the private sector aerospace industry. His consulting business has given him extensive experience in forensic

The strip mine's insurance company brought a faulty­product lawsuit against the manufacturer of the excavator. So it eventually became the task of the Henderson, Texas, law firm of Wellborn, Hous­ton, Adkinson, Mann, Sadler &

Hill LLP to prove that the me­

A close-up of the excavating machine's seat is shown with its engineering, along with a long supporting pedestal. The suit arose when the pedestal failed. history of systems engineering

chanical failure of the seat caused the operator's lower back injury.

RAISING A NEW QUESTIOI\I

When it took over the case, the firm contacted Herman M. Giesen, a Dallas professional engineer and engineer­ing consultant who had been researching the cause of the failure. Giesen had been working first for the insurance company itself, and then for a lawyer who had taken the case before it came to Wellborn, Houston.

By that time, Giesen, an ASME member, had reviewed design drawings and conducted a destructive test of an

This article was prepared by staff writers in collaboration with outside contributors.

and mechanical systems design. Pursuing an answer to Mann's question led Giesen to

his first practical experience with finite element analysis. He eventually would use Mechanical Event Simulation software from Algor Inc. to calculate and present a visual reconstruction of impact forces, stresses, and oscillating movement.

Giesen's research into the cause of the failure focused on the seat's pedestal assembly, based on a witness's report that the seat had apparently failed in the area of the tor­sion assembly axle. The seat of the excavator rests on a pedestal assembly that includes an adjustable torsion spring scissors mechanism. This mechanism lets the op­erator adjust the seat to a proper height to reach two pedals and a hand manipulator comfortably.

Giesen was unable to study the seat pedestal actually

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This Mechanical Event Simulation model replicated the seat's dead-drop onto a stiff floor, showing the motion, flexing, and stresses involved in the impact.

involved in the accident, although he tried to recover the seat at the mine site. He thought that it was buried there, but it had been discarded, and a search of the site failed to recover it.

Thus, instead of the original, Giesen decided to ac­quire two seat pedestals of the same model and the seat pedestal design drawings through the legal discov-ery process.

By reviewing the design drawings, Giesen detected two important facts about the design: The bearings that sup­port the axles overhang the axle roots, and there are no fillets at the roots of the axles. The effect of the first fact is to create a significantly overhung load, which stresses the root heavily under a bending load. This stress con­centration at the root is further amplified by the second fact-the absence of root fillets.

"Failure to provide axle root fillets was a design flaw and was the root cause of the failure and the operator's injury," Giesen wrote in his final

port the axle was tapered and ragged, possibly because the hole was punched in manufacturing.

"The tapered axle hole would have allowed for an axle root fillet radius of approximately 0.02 inch," Giesen wrote. "A fillet of that size would have signifi­cantly reduced the stress concentration factor and, hence, the likelihood of the failure. Alternatively, a non-tapered hole would have better supported the axle root as machined. Either way, it was unambiguously clear that no relief had been specified in the machining of the axle root."

By studying the drawings and by a destructive test of one of his samples, Giesen became convinced that de­sign and manufacturing flaws were causal factors in the failure of the seat pedestal. When Mann came onto the scene, he asked how much force was actually involved in the impact.

"Simple question," Giesen said, "tough answer."

SEEKING ANSWERS report. "Had appropriate fillets been provided, the event most probably would not have oc­curred. Given these design flaws, chronic cyclical and vibrational stress are likely to cause fatigue cracks to develop, propagate, and cause failure."

As Giesen moved forward with the destructive disassembly and ex­amination of the sample seat pedestal to confirm that there were no fillets at the axle roots as manu­factured, he also discovered that a hole called for in the plans to sup-

Design and lllanufacturing

flaws were cited as causal factors in the

failure of the

In search of a practical method to obtain the answer, Giesen talked to a number of colleagues, who all agreed that it was a tough problem and, no, they didn't have any sug­gestions to offer.

"Since I am not an expert in me­chanical analysis of this sort, I sought the counsel of mechanical analysis experts I respect," Giesen said. "From them I learned that quantifying an impact force defies traditional methods provided by handbooks and calculations in

seat pedestal.

practical terms. You just can't do it."

Giesen happened to notice an advertisement for Algor's Accupak/ VE Mechanical Event Simu­lation software, which simulates motion and flexing in mechanical events, and computes stresses.

the operator, 360 pounds, was discounted by 20 per­cent to account for the par­tial support from his feet on the pedals and his hands on the controls.

Boundary conditions fixed the hands where they would grasp the manipula­tor and the feet where the heels would rest on the floor. Beam and contact elements represented the knee and shoulder joints. The spine consisted of truss elements.

Although Giesen had extensive experience in mechanical and electro­mechanical design and systems engineering, he didn't have any hands-on experience with finite el­ement analysis and simu­lation. So he went to Al­gor's Pittsburgh head­

In the assembled seat pedestal (top right), the axle is in the upper right corner of the mechanism. The axle close-up at lower left shows no fillet at the axle root.

Although the human spine naturally has a curved shape, the spine was modeled straight to simplify the issue of im­

quarters to work with an applications engineer to devel­op an impact model, over the course of three days.

Giesen used another Algor product, Superdraw III, to develop the model following the manufacturer's design drawings. He incorporated information about the oper­ator as provided by the lawyer. Where numerical values were not available, Giesen used conservative estimates and varied them over several iterations.

The seat assembly was modeled in an upright position us­ing three-dimensional beam, plate/shell, and solid brick el­ements. The beam and plate/shell elements were used to represent the steel base of the seat and were defined using the material properties of steel from the software's Material Library Manager.

The seat cushions were modeled using solid brick ele­ments and were defined using a custom material. The density of custom material was defined so that the seat assembly would weigh a total of 120 pounds. Giesen re­searched common material property values of poly­urethane foams at the University of Pittsburgh's engi­neering library to establish a reasonable range of Young's moduli for the cushions. The Young's modulus of the seat cushioning was one of the variables that would be altered over a series of iterations.

Although the seat in the accident dropped 3 to 5 inch­es, Giesen decided to model conservatively and so assumed a 2-inch dead drop onto a stiff floor. The con­tact between the seat and the floor was modeled using Algor's proprietary contact elements, which enable engi­neers to model how parts of a mechanism behave when they come into contact.

SUDDEN IMPACT

A representation of the operator in an upright posture­perched on the seat to reach the excavator's controls-was then added to the seat assembly. The arms, legs, body, and head were modeled using solid brick elements with a den­sity so that the weight totaled 288 pounds. The weight of

pact force. If the backbone had been curved, it would have deflected in the analysis, thus absorbing much of the force, rather than calculating a total impact force as was intended. The Young's moduli for the body parts was based on biomechanical information resources, in­cluding a telephone call from Algor's offices to an expert in the field, and were varied over a series of iterations .

STANDARD GRAVITY LOADING

The complete model was subjected to a standard gravity loading for the duration of one second, analyzed in 100 time steps. Giesen could watch the event unfold as it was processed.

The software displays the movement of the mecha­nism and stresses as they occur over time. Thus, Giesen was able to vary the stiffness of the seat cushions and body based on the behavior of the model.

He evaluated the results at the moment of impact in gs, for force amplification factor, which is a factor of how much a subject's body weighs at the time of im­pact. Depending on the input variables, including height, some of Giesen's models yielded an impact force of as much as 5 and 6 gs. However, Giesen's final, optimized model, with the 2-inch fall, yielded 2 .24 gs. Multiplying the estimated 288 pounds by the g force gave the operator an effective weight of 645.12 pounds at the moment of impact-a considerable load for the human spine to bear.

Giesen followed the event step by step on his com­puter screen and watched the force operating at points on the body in real time. "It was remarkable to see the reverberation in very high mechanical frequency rip­pling up and down the backbone," he said.

There was no need for Giesen to swear in and tell a jury of his results. The report of his destructive exami­nation and Mechanical Event Simulation results was one of many considerations in the subsequent settle­ment of the lawsuit. _