Blast simulation using advanced Finite Element Methods

We earlier discussed the differences between Implicit and Explicit analysis and Newton Raphson method for implicit analysis. In this blog post we will discuss advanced simulation methods for performing a blast loading simulation on a simple steel plate. There are numerous application areas for performing a blast simulation, some examples are (a) designing military/infantry vehicles capable of resisting mine blast explosions, (b) design of blast resistant concrete structures or (c) design of bridges. It is not feasible to test the designs directly by conducting a physical/field blast test unless the design is fool proof, it would result into tremendous costs if primitive designs are tested on field. A finite element simulation is thus a cost effective option for designing blast resistant structures.

Lets consider an example of vehicle subjected to a mine blast for the purpose of understanding. In this simulation, a TNT explosive charge would be placed on ground beneath the vehicle. For the purpose of simplicity we would consider a simple plate and a small charge of 1 kg TNT. There are two most common methods to simulate the blast loading effect:

1. Use of a simplified CONWEP function
2. Use of Arbitrary Lagrangian Eulerian (ALE) method

Article in progress. Meanwhile please refer my thesis on blast simulation: http://bit.ly/thesis_amogh

Arbitrary Lagrangian Eulerian (ALE) method in LS Dyna

The finite element method which we generally use is termed as a lagrangian formulation. Although the normal methods tends to be feasible for usage in short duration impact applications such as crash analysis, applications concerned with very short transient loadings, such as blast analysis require better simulation algorithms. The use of plain Lagrangian Formulation in large deformation problems leads to severe distortion of mesh rendering it incapable of yielding accurate results.

Newton-Raphson method for Implicit Analysis

Few months back I blogged about difference between explicit dynamic and implicit analysis. Concisely summarizing, an implicit analysis is the one which is independent of time and explicit is the one which is of a short duration and time dependent. In this post, I would be going into details regarding an Implicit Finite Element Analysis. Newton-Raphson (NR) method is the commonly used method for most of the implicit FE solvers. In simple numerical terms, the N-R method is used for finding successively better approximations. Figure 1 shows the general iterative process for an implicit analysis. Click here to read more about N-R method. 

MADYMO - Occupant Safety Simulation Software

MaDyMo stands for Mathematical Dynamic Models and is an Occupant Safety Simulation software.  It is created by TNO Automotive Safety Solutions (TASS). Madymo is equipped with a multibody (MB) dynamics, finite element (FE) as well as a computational fluid dynamics (CFD) solver. The primary application of Madymo is to study the safety of occupants and injury risks in a vehicle crash scenario.

True, Engineering and Effective Stress Strain

True Stress - Strain Curve:
The engineering stress-strain curve is based entirely on the original dimensions of the specimen hence does not give a true indication of the deformation characteristics of a metal because. The dimensions change continuously during the test..

Cyber infrastructure in engineering design

 

Multiobjective Optimization and Trade Offs Using Pareto Optimality

LS Prepost 3.2 released for mac

LS-PrePost an advanced pre/post-processor delivered free with LS-DYNA has now a Mac version. LS Prepost supports all the keywords for LS Dyna. Other pre processors that can be used for creating an input deck for LS Dyna include Hypermesh, Oasys, Ansys etc. LS-PrePost runs on Windows, Linux, and Unix utilizing OpenGL graphics to achieve fast rendering and XY plotting. The latest build can be downloaded from LSTC's FTP Site. The tutorials and online documentation for LS Prepost can be found here.

Consistent Unit System in LS Dyna

Explicit Dynamics software LS Dyna has no default unit system. The user needs to provide all the values in a consistent system according to which the solver gives results. If the user inputs mass in Tonnes and length in meters, the solver will assume the length to be in 'mm'

Implicit and Explicit Finite Element Analysis

Implicit and Explicit are two types of approaches that can be used to solve the finite element problem. The implicit approach is useful in problems in which time dependency of the solution is not an important factor [e.g. static, structural etc.] whereas Explicit Dynamics approach is most helpful in solving high deformation time dependent problems such as Crash, Blast, Impact etc.

Volumetric Locking in Hyperelastic Finite Elements

Volumetric Locking is exhibited by incompressible materials such as rubber having poisson's ratio near or equal to 0.5 resulting in an overly stiff response. The overly stiff response is depicted in figure below.

Non Linear Hyperelastic Finite Element Analysis

This post would share Need To Knows & discuss some tips and tricks related to Non Linear HyperElastic FE Analysis.

NeedToKnow#1: The poisson's ratio of Rubber although being 0.5 is considered as 0.4955 in a Finite Element Analysis. The reason being that the Bulk modulus becomes infinity at Poissons ratio of 0.5. Also the volumetric strain equals near zero.

NeedToKnow#2: Nearly or Fully Incompressible Material (with Poisson's ratio nearly 0.5) exhibit Volumetric Locking in Fully Integrated Elements

Engineering Design & Analysis

This Blog is intended to share the knowledge in the Engineering Design and Finite Element Analysis domain.