NCHRP Project Development of Verification and Validation Procedures for Computer Simulation use in Roadside Safety Applications SURVEY OF PRACTITIONERS

INTENT  A survey was sent out to practitioners who use LS-DYNA in roadside safety analysis  To assimilate useful and practical information for the project team  To determine state of the art practices for building, verifying and validating FEM  Increase likelihood of developing models that run without errors

APPLICATION  Practitioners were asked about what types of techniques they use and what range of variation they considered acceptable when performing typical roadside safety simulations.  A total of 41 questions asked to practitioners in following topics: 1.Background information on practitioners 2.Details about model building 3.Model verification 4.Model validation

RESPONSE TO SURVEY Background Information  33 practitioners out of 45 identified responded to survey  Average LS-DYNA experience 8.5 years  Average years of experience in roadside safety also 8.5 years  Approximate number of LS-DYNA projects used to evaluate roadside hardware 23.

RESPONSE TO SURVEY Details about Model Building

Source was used Primary Source

RESPONSE TO SURVEY Details about Model Building Where do you generally obtain your vehicle models:

RESPONSE TO SURVEY Details about Model Building

Rate the importance of the following model features for Roadside Safety Analysis

RESPONSE TO SURVEY Details about Model Building Rate the importance of the following model features for Roadside Safety Analysis lowest highest

RESPONSE TO SURVEY Details about Model Building Continued at next page

RESPONSE TO SURVEY Details about Model Building Continued at next page Which of the following NCAC Vehicle Models have you used?

RESPONSE TO SURVEY Details about Model Building

Which of the following do you model in detail and which are modeled using approximate techniques?

RESPONSE TO SURVEY Details about Model Building

Sources for Material Properties

RESPONSE TO SURVEY Details about Model Building

How are Welded Connections Modeled?

RESPONSE TO SURVEY Details about Model Building

How do you model post-soil interaction?

RESPONSE TO SURVEY Model Verification

Comments on the definition:  The ASME definition can be more generic: “The process of determining that a model implementation correctly represents the modeler’s conceptual description of the model and the solution to the model.”  The verification checks should ensure that the model is build correctly. It should include more than that the simulation should run. The verifications would include the material model selection and properties, element formulation selection and properties, mesh quality and geometry, contacts and friction coefficients, boundary and initial conditions, and connections. I think all verifications checks could be made before running the simulation to ensure the model is free of error and is a correct representation of actual structure. Validations are performed by running the simulation and comparing to test data (iterative).  Somewhat Agree with the above statement, but is not sufficient. Model verification is building the model RIGHT. The verification process should deal with accuracy assessments that ensure correct models are created which are free of errors and provide adequate representation of the actual systems.  "Verification" is usually understood as a demonstration that the model behaves according to the theory. "Validation" is usually understood as a demonstration that the model behaves as the physical reality.  I would add that the models do NOT produce non-physical behaviors aside from numerical instabilities.  Verification of a model should also include checking that the results are reasonable.  We propose that this item, rather than "Verification", is called "Computational Verification", in order to make clearer that it deals with problems related to the mathematical implementation and calculation of the problem.  I agree more closely with the DoD/AiAA statement. For developing material models, verification is a check on the coding of the material model - making sure it was implemented according to the theory that was intended to be implemented.

RESPONSE TO SURVEY Model Verification Comments on the definition:  There is no need to create a specific definition for roadside safety simulations. More general definition can be used such as: “Verification evaluates the accuracy with which the computational (FE, discrete) model depicts the mathematical model”. The mathematI share the ASME definition (Check Len Schwer committee) "Verification is the process of determining that a computational model accurately represents the underlying mathematical model and its solution." This puts the responsibility of verification on the code developers, except for user's verification activities like mesh sensitivity and convergence of solution.  ….What you want to know is whether or not the model simulates real life conditions. Verification, in my opinion, should read model Validation. The simulated results should be correlated with testing to verify the model….  ……I had not considered this attempt to distinguish between verification and validation before. Assuming that it is a sensible distinction (of which I am not fully convinced), there appear to be two different statements offered. I assume that a polished statement should amount to the model including all the relevant parts of the system modeled in a way that satisfactorily deploys the capabilities of the simulation code. Verification is about the model "working" in the intended way, and validation about the accuracy of its representation of reality. (This is YOUR project - you sort it out!)  I would NOT limit it to the collective experience of the roadside safety simulation community

RESPONSE TO SURVEY Model Verification Chuck’s comment: Another factor in determining appropriate element size is the deformed curvature of the element or angle between elements. Required element size will be different for 12 gauge sheet metal compared to 1/2 –inch plate steel

RESPONSE TO SURVEY Model Verification 23 mm 44 mm 93 mm Mesh Sensitivity and Quality Determination: What is the largest shell element size used for steel parts that:

RESPONSE TO SURVEY Model Verification

RESPONSE TO SURVEY Model Verification mm 33 mm 56 mm Mesh Sensitivity and Quality Determination: What is the largest solid element size used for wood posts where:

RESPONSE TO SURVEY Model Verification

Analysis time step is controlled by:

RESPONSE TO SURVEY Model Verification

In general, what is the maximum warpage angle that you try to limit the elements to in your models: 48.3% 13.8% 3.4% 20.7%

RESPONSE TO SURVEY Model Verification

I generally keep the aspect ratio of my mesh smaller than: 19.4% 45.2% 22.6% 12.4%

RESPONSE TO SURVEY Model Validation

Rank the following statements in order of importance in validating a finite element simulation with physical test (1=least important, 5 = most important):

RESPONSE TO SURVEY Model Validation

Which qualitative comparisons do you use to compare your simulation to the physical tests?

RESPONSE TO SURVEY Model Validation

Which quantitative time history comparisons do you use to compare your simulation to the physical tests?

RESPONSE TO SURVEY Model Validation

Which of the following parameters or metrics do you use to compare your simulation results with experimental results?

RESPONSE TO SURVEY Model Validation

Summary  The survey provided information regarding the current state of the art practices for building, verifying and validating FEM  This information will provide some practical guidance for the project team when developing V&V procedures  The information could also be synthesized into a “Best Practices” document.  BUT, probably doesn’t provide enough information to do one justice  May be out of scope for this project

LIST OF PRACTITIONERS RESPONDED