An In-depth Look At Dynamic Simulation And Stress

Transcript

An In-Depth Look at Dynamic Simulation and Stress Analysis Tools Ravi Akella – Autodesk, Inc. Maxime Debono – Autodesk, Inc. In this session, we'll first explain Dynamic Simulation and Stress Analysis and some reminders about the physics behind these tools. We’ll follow this with a discussion on how utilizing the simulation tools for Digital Protoyping can help manufacturers get to market faster. We’ll explain how to adopt and use the digital prototyping philosophy, and study workflows that solve classic engineering problems. We’ll finish the class with a Q&A session. About the Speaker: Ravi joined Autodesk in January 2006, and is a Product Manager for Inventor at the Manufacturing Solutions Division (MSD). Formerly, Ravi was a Solutions Engineer with MSD sales team and a member of the Simulation Experts Group. Ravi has experience presenting the capabilities of Autodesk Inventor to the CAD industry press, at Autodesk University 2006 and at Autodesk’s annual training event for reseller engineers. Prior to joining Autodesk, Ravi worked at LMS International, makers of engineering analysis software built to work with CATIA V5. While at LMS, he gained considerable experience in kinematics and dynamics, FEA, and solid mechanics. Ravi earned a Master of Science degree in Structural Mechanics from The University of Iowa in Iowa City in 2002. [email protected] An In-Depth Look at Dynamic Simulation and Stress Analysis Tools What is Simulation? The Merriam Webster dictionary defines simulation as “the imitative representation of the functioning of one system or process by means of the functioning of another or examination of a problem often not subject to direct experimentation by means of a simulating device”. In the case of Autodesk Inventor Professional for Simulation, the intent is to imitatively represent the functioning of a mechanical device being designed using the 3D CAD tools in Autodesk Inventor by adding aspects of the physical world like gravity and friction to the model and applying the numerical methods of Multibody Dynamics. Why do simulation? We live in a physical world whose laws are described in Newtonian physics. However, in the past 3D CAD models existed in an environment where a feather could move a brick and mechanisms could be driven without concern to the forces and torques required to drive them in the real world. In the spirit of functional design, Autodesk Inventor Professional for Simulation allows us to simulate reality. The key to understanding simulation is the realization that the best investigative models are simplified representations of the real thing where the simplifications hinge on valid assumptions. Where did this technology come from? The Dynamic Simulation functionality in Autodesk Inventor Professional for Simulation is a result of Autodesk acquiring Solid Dynamics based in Roanne, France an established simulation software developer and services provider in August 2005. The company was founded in 1992 by Fabien Chojnowski and Laurent Chojnowski. The one focus of this team has been to create the best in class kinematics and dynamics physics simulation software tools for engineers and designers. How does it all work? Dynamic Simulation can help us answer the ultimate question that we’ve all been dying to answer; how much time will it take for the DeLorean to get to 88 mph so that the lightning bolt can charge the flux capacitor? An In-Depth Look at Dynamic Simulation and Stress Analysis Tools The key equation being Newton’s 2nd law of motion… F = M.a = M.dv/dt (sum of external forces = mass x acceleration) where M: mass F: external force A: acceleration V: velocity X: position T: time The acceleration is then: a = dv/dt = F/M The velocity is found by integrating the acceleration: v = dx/dt = F/M.t The position is found by integrating the velocities: x = ½.F/M.t2 So at every timestep the Dynamic Simulation solver in Autodesk Inventor Professional is doing the following calculations.. An In-Depth Look at Dynamic Simulation and Stress Analysis Tools What is the relation between Dynamic Simulation and FEA? Finite Element Analysis, as you might already be aware, is a method employed to determine the strength of components when subjected to a given set of boundary conditions and applied forces. The following is a simplified way to understand the relationship between the Dynamic Simulation and FEA. For FEA the structure, which in our case is a part, is segmented into elements and the singular mass is divided into a mass matrix. In Autodesk Inventor Professional for Simulation the part FEA analysis available assumes linear elastic deformations so it’s based on Hooke’s Law. For systems that obey Hooke's law, the extension produced is proportional to the load. So, the static equilibrium of each of the elements, for the whole structure is calculated as: K*X=F where K: stiffness matrix X: displacement of nodes F: external forces In most FEA analyses, the force F is an educated guess, which makes the accuracy of the resulting deformations only as good as the initial guess of the force. An In-Depth Look at Dynamic Simulation and Stress Analysis Tools Dynamic Simulation removes the dependence on educated guesses for applied forces in part FEA analysis by introducing Newton’s second law of motion into the mix. Dynamic Simulation segments the time taken for a mechanical event to happen into individual time steps. Time Time Step The dynamic equilibrium of the mechanism at each time step is then calculated as: M*A=F where M : mass matrix A : articular accelerations F : external forces Hence, Dynamic Simulation now arms us with an accurate value of the force acting on the part for part FEA analysis. An In-Depth Look at Dynamic Simulation and Stress Analysis Tools What are the hands-on exercises all about? The lab exercises will allow you to experience creating and solving real world design problems using Autodesk Inventor Professional for Simulation. Exercise #1 Challenge: Given the desired motion of the follower, create the required cam. Dynamic Simulation topics covered • Manual and automatic joint creation • Applying an imposed motion on a joint’s degree of freedom • Spline interpolation in the input grapher • Tracing the motion of point during the simulation • Export trace to sketch An In-Depth Look at Dynamic Simulation and Stress Analysis Tools Exercise #2 Challenge: Given the desired behavior of the bike suspension, create a spring that is appropriately sized. Dynamic Simulation topics covered • Changing the quantity along the x-axis in the input grapher • Use the Unknown Force feature • Determine the distance between two points at every time step of the simulation • Changing the quantity along the x-axis in the input grapher An In-Depth Look at Dynamic Simulation and Stress Analysis Tools Exercise #3 Challenge: Given that the desired effort applied by the gripper needs to be 1000 N, determine the amount of force needed to be applied by the actuator/jack. Dynamic Simulation topics covered • Redundant constraints: what, why and how • Applying an external force to the mechanism • Sizing the actuator An In-Depth Look at Dynamic Simulation and Stress Analysis Tools Exercise #4 Challenge: Ensure that the parts in the window lever mechanism are of adequate strength Dynamic Simulation topics covered: • Tips & Tricks related to the new automatic constraint translation • Creating Rolling/Sliding joints • Tips & Tricks related to exporting motion loads to Stress Analysis • Perform FEA on desired part and check for strength and robustness In Conclusion… This hands-on lab is intended to introduce some real-world examples where Dynamic Simulation can be used to create and validate designs in an Inventor Digital Prototype and to explain some of the theory behind Dynamic Simulation. Our goal will be met if after the session you leave with a sense of understanding and confidence that allows you to tackle your own design challenges using Dynamic Simulation in Autodesk Inventor Professional.