**6.1. Crash simulations of the vehicles**

The studies about the crash worthiness and impact scenarios as explained in the previous section are based on the explicit dynamics solution technique resulting with the satisfactory approximations. Some of the commercial codes for the explicit dynamics simulations are embedded inside the multidiscipline FEA programs such as ABAQUS, ANSYS, and MSC softwares, even though some of them working alone for just these types of applications as LSDYNA, PAMCRASH, etc. As it was mentioned, before these softwares are auxiliary engineering applications for solving the problems with the numerical methods. The most important task is the prediction of the failures of the system or structure of the vehicle and the problems that occupants can be faced. When the prediction of the simulations is validated, it can be said that FEM code has done its job properly.

To comprehend the validation of the simulations with the real crash tests, numerous topics should be investigated before, during or after the simulations. We can simply name these steps like: before the process is pre-processing, during is processing or simulation, and after the processing is post-processing.

Pre-process section is dealing with the creation of the finite element model, starting from the Computer-Aided Design (CAD) of the structure or the system, material descriptions or modelling, element selections, defining the boundary conditions (describing the loads, displacements and support properties, etc.) and initial values like velocities, adjusting the contact algorithms, total time and timestep size definition. For more elaboration, mass scaling factor and/or hourglass controls can be adjusted. Considering the information given, the geometry should be meshed as smooth shapes as possible. During the mesh generation element, sizes are so prominent, will affect the simulation time, according to the number of the elements. If the mesh is coarse, there will be a weak approximation and short period of processing time, notwithstanding if there is a finer meshed model exists, the convergence rate will be better, while the processing time is prolonged. Thus, there should be an optimum mesh size for the common structure; however, the significant zones are meshed with finer elements to increase the stability and for the better result.

When the simulation is processed, the finite element model is ready for the post-processing. The most considerable issue for the impact is absorb or get rid of the shock energy by different methods like geometrical change of the structure, material selection, and application. The second problem is the large deformation of the structural components. Additionally, changing the parameters of the simulation model will affect the results widely depending on the experience of the analyst. Because of dealing with the highly plastic problems and non-linearity during collisions, the analyst needs to possess deep knowledge about nonlinear finite element analysis for continuum mechanics [20–22]. It should be stated that the analyst can be faced with the geometrically nonlinear problems or material nonlinearities which is imported to be expressed.

**Figure 7.** The vehicle crash test and simulation.

Considering the LSDYNA, the widely known commercial explicit solver, the procedure for

When *t* = 0, it will be the beginning of the solution loop or cycle. Whereupon, the displacement will be updated at Eq. (10), while the velocity is also updated at Eq. (13). Then, the internal forces (strain rate, strain, stress, and force magnitude) will be computed looping over the elements. Subsequently, external forces will be calculated to reach the computation of the accelerations at Eq. (14) which is finalizing the initial loop. Thereafter, following loops will go

For the robust design, stress wave propagation, timestep adjustment, critical element length and finally, the mesh size and quality are the factors, will be considered carefully to affect the

Due to the reliable side of the explicit dynamics solution methodology, we indicated the differences between the implicit and explicit solver for the approximation of the vehicle crash simulations and safety of the occupants and vehicles. We can possibly say that, for the collision of the regular or autonomous vehicles the accident results will be similar that should be taken

The studies about the crash worthiness and impact scenarios as explained in the previous section are based on the explicit dynamics solution technique resulting with the satisfactory approximations. Some of the commercial codes for the explicit dynamics simulations are embedded inside the multidiscipline FEA programs such as ABAQUS, ANSYS, and MSC softwares, even though some of them working alone for just these types of applications as LSDYNA, PAMCRASH, etc. As it was mentioned, before these softwares are auxiliary engineering applications for solving the problems with the numerical methods. The most important task is the prediction of the failures of the system or structure of the vehicle and the problems that occupants can be faced. When the prediction of the simulations is validated, it

To comprehend the validation of the simulations with the real crash tests, numerous topics should be investigated before, during or after the simulations. We can simply name these steps like: before the process is pre-processing, during is processing or simulation, and after the

Pre-process section is dealing with the creation of the finite element model, starting from the Computer-Aided Design (CAD) of the structure or the system, material descriptions or modelling, element selections, defining the boundary conditions (describing the loads, displacements and support properties, etc.) and initial values like velocities, adjusting the contact algorithms, total time and timestep size definition. For more elaboration, mass scaling factor and/or hourglass controls can be adjusted. Considering the information given, the geometry should be meshed as smooth shapes as possible. During the mesh generation element, sizes are so prominent, will affect the simulation time, according to the number of the elements. If the mesh is coarse, there will be a weak approximation and short period of

through the process again and again, until the convergence criteria will be satisfied.

the solution steps is given below:

74 Autonomous Vehicle

simulation performance in a better way.

**6.1. Crash simulations of the vehicles**

processing is post-processing.

can be said that FEM code has done its job properly.

care of precisely.

Regarding the details of the post-processing, we will start to observe and evaluate the simulation outputs, step by step. While we are investigating the steps of the impact scenario, kinetic energy change, absorbed energy amount, deformations and displacements, strain and stress distribution, and some other major issues should be appraised attentively and the results should be validated with the real crash tests. Besides, the effects of the different components, deformation characteristics, and the changes of the parameters must be observed and the behavioral outcomes of the incident should be crosschecked with the real situation. The literature is replete with numerous of interesting researches about the crash-worthiness of the vehicles and the occupant safety including the Anthropomorphic Test Dummy (ATD) test and simulations [23–27]. Especially LSDYNA conferences are popular with the presentations of the explicit dynamics simulations and also most of the papers can be reachable from the internet site of "DynaLook" [28]. For a better representation of an explicit dynamics simulation, **Figure 7** demonstrates the full vehicle crash scenario [29].
