Up and Running with Autodesk Inventor Professional Simulation in 90 Minutes!

Transcription

1 Up and Running with Autodesk Inventor Professional Simulation in 90 Minutes! Wasim Younis - Author of Up and Running Inventor Professional Simulation books MA This class will present a workflow for effectively using the simulation tools in Autodesk Inventor Professional software. After this class, you will be able to confidently apply this technology to your own workplace. The class highlights top Inventor simulation tips, ways to solve real-life design problems with Inventor Professional simulation tools, and additional guidance to make you an expert in only 90 minutes. Learning Objectives At the end of this class, you will be able to: Describe best practices for using Inventor Simulation tools List tips for using Inventor Simulation tools Solve real-life design problems Optimize your designs About the Speaker Wasim Younis (UK) is an Inventor Simulation consultant and trainer with more than 15 years of experience in the manufacturing field. He has been involved with Inventor Simulation software when it was first introduced, and is well-known throughout the Inventor Simulation community. Wasim contributes articles, whitepapers, tips and tricks and tutorials to various forums. He regularly authors simulation Tips and Tricks articles on his own Virtual Reality blog ( - a blog dedicated to the Autodesk Inventor Simulation Community. He also runs a dedicated forum for simulation users on LinkedIn Up and Running with Autodesk Inventor Simulation Wasim has a bachelor s degree in Mechanical Engineering from the University of Bradford and a master s degree in CAE from Staffordshire University. Currently he is a Senior Simulation Symetri ( one of the largest Platinum Autodesk manufacturing value added reseller in Northern Europe. younis_wasim@hotmail.com

2 Introduction I welcome you all to my lecture at Autodesk University 2012 and I hope you will find it stimulating. In my years of training and working with Inventor users. I have seen many who were struggling to make the most of Inventor's tremendous and powerful Simulation technology, and to integrate it in the design process. In my opinion, one significant reason for this struggle is the lack of confidence in applying Inventor Simulation to the user's own product and development environment. As a result of this lack of confidence designer/engineers continue to produce products which are overdesigned. It is my aim in this lecture to arm you with key knowledge to help you apply this technology to your own design, hopefully with some confidence. Inventor Simulation can perform three types of analyses, as illustrated below. 1. Dynamic Simulation - allows you to simulate mechanisms and determine forces, reactions etc 2. Stress Analysis - allows you analyze designs for strength and help to reduce weight 3. Frame Analysis - allows you analyze large scale structures 4. Optimization - allows to optimize designs - This is cloud based. Dynamic Simulation Allows the designer to convert assembly constraints automatically to mechanical joints, provides the capability to apply external forces including gravity, and allows the effects of contact friction, damping and inertia to be taken into account. As a result of this, Dynamic Simulation provides reaction forces, velocities, acceleration and much more. With this information the designer can re-use reaction forces automatically to perform finite element analysis, hence reducing risks and assumptions. Ultimately all this information helps the designers to build an optimum product, as illustrated. 2

3 Dynamic Simulation Workflow The process of creating a Dynamic Simulation study involves four core steps. Step 1 GROUP together all components and assemblies with no relative motion between them Step 2 CREATE JOINTS between components that have relative motion between them Step 3 CREATE ENVIRONMENTAL CONDITIONS to simulate reality Step 4 ANALYZE RESULTS The most time consuming process with the Dynamic Simulation Workflow is step 2 creating joints and this can be greatly affected by Step 1 grouping components. Furthermore Step 2: The process of creating joints can be broken down into 2 stages as discussed below Stage 1 Create standard joints. Stage 2 Create nonstandard joints. Stage 1 - there are three options to create standard joints, and, again each has its own advantages and disadvantages. Option 1 Use Automatically Convert Constraints to Standard Joints. Advantage This is by far the quickest way to create joints. 1. With 2012 version you now have the option to retain joints created once you switch of Automatically Convert Constraints to Standard Joints tool, and then carry on creating joints using either option 2 or 3. Disadvantages Can be tedious to go through all joints converted for a large assembly. Cannot repair redundancies within the Simulation environment. Cannot create Standard joints with the Simulation environment, with the exception of Spatial joint. 3

4 Option 2 Manually convert assembly constraints. Advantages Can manipulate the type of joint created from constraints. Can create standard joints within the Simulation environment. Can repair redundancies for all standard joints not created from constraints. Disadvantage This method is slower than option 1. Option 3 Create standard joints from scratch Advantages Complete control over how standard joints are created. Can repair redundancies for all standard joints created. Disadvantages This method is the slowest. Does not make use of the assembly constraints. Stage 2 Comprises of creating nonstandard joints that do not make use of assembly constraints and includes the following type of Joints : Rolling Sliding 2D Contact Force Note: Rolling joints for spur gears,designed using Design Accelerator, can be created automatically. In this presentation I will demonstrate Option 2 which makes use of existing assembly constraints. The example will go through the complete workflow from step 1 through to step 4 including tips and guidance. The example to be used will be a British Waterways canal bridge which traditionally can be operated by pulling a chain attached to the bridge arm to raise the deck, which can weigh many tons. As part of an ongoing programme of safety improvements, these bridges are being modified to allow them to be operated from either side of the canal and to provide restraint to a large moving mass. The visual impact of any modifications must be minimised due to the heritage value of the canals, which is closely regulated. The solution required is to lift and lower the bridge in a controlled manner whilst allowing operation from either side of the canal. The method chosen for opening/closing the bridge is a hydraulic cylinder (jack), which is to be placed underneath the bridge deck. Dynamic Simulation will help us to determine the size of the jack required to fully open the bridge. The focus of this presentation will be on the joint creation process. 4

5 Stress Analysis Stress analysis is an engineering discipline that determines the stress in materials and structures subjected to static or dynamic forces or loads. The aim of the analysis is usually to determine whether the element or collection of elements, usually referred to as a structure or component, can safely withstand the specified forces and loads. This is achieved when the determined stress from the applied force(s) is less than the yield strength the material is known to be able to withstand. This stress relationship is commonly referred to as factor of safety (FOS) and is used in many analyses as an indicator of success or failure in analysis. Factor of Safety = Yield Stress Calculated Stress = Ultimate Stress Calculated Stress Stress Analysis Workflow The process of creating a Stress Analysis study involves four core steps Step 1 IDEALIZATION Simplify Geometry, including setting up the analysis Step 2 BOUNDARY CONDITIONS Apply constraints loads including defining contacts and mesh setting including exporting loads from simulation Step 3 RUN SIMULATION AND ANALYZE Analysis and interpretation of results, via various tools to determine FOS including convergence of results Step 4 OPTIMIZATION If needed modify geometry to meet design goals including reducing weight etc including changing original material 5

6 In Stress Analysis, in my opinion, the most important step is idealization. This greatly has an impact on the speed and accuracy of the results. The second most important aspect of stress analysis is the interpretation of result, including how to overcome stress singularities, briefly mentioned below and further discussed within lecture. Stress Singularities Stress Singularities are a major concern when analyzing results as they considerably distort results. They are also a main cause for non-convergence of results. So, the first question is -what is stress singularity? This can be best explained by the following example. This bracket has a localized high stress around the force applied on a point. This stress can be considerably higher than the operational stress and applying a more dense mesh around this simply leads to a much higher stress. This phenomenon is known as stress singularity where the stress becomes infinite, as illustrated by the following formula: Stress (infinite) = Force Area of point (almost = 0) Therefore, to avoid stress singularities when applying loads, it is recommended not to apply loads at points and small edges. Stress Singularities can also occur by applying constraints on points and small edges even faces with sharp corners as illustrated below. In the above example, stress singularities resulted from using automatic convergence, whereas the image on next page of the same model is showing very little change in stress in the area of interest by using the default mesh and no automatic convergence. Therefore, interpret results with care. 6

7 Finally, another cause of stress singularity is over-simplification of components. Let s look at the following example. In this example, the fillets have been removed to simplify the analysis; however, when using automatic convergence, the maximum stress value does not converge as all the stress is concentrated around the edge, as shown. In this scenario it would advisable to unsuppress the fillets (or, in cases when fillets are not modeled, use fillets to distribute loads). So, in brief to avoid stress singularities within models is to: 1. Avoid applying loads on points and small edges. 2. Avoid restraining faces with sharp corners, including points and small edges. 3. Apply fillets and chamfers to evenly distribute loads. 7

8 In this section of the presentation I will use the following traffic sign post example, as illustrated below. The purpose of the analysis is to determine whether the structure is strong enough to withstand the wind speeds exerted on the structure and LED panel. The wind speeds will be calculated using the following formula (googled on world wide web) Force F = A x P x Cd and P = x V 2 Where: F is force in Newtons (N) A is the cross section of the LED display panel in Meters (approx 2m 2 ) P is the pressure in Pascals (N/m) V is the wind speed in (Mph) Cd is the drag coefficient ( 2 to be used for rectangular flat areas) For a wind speed of 25 and 50 mph we get the total force's to be; P = x 25 2 = 76.6 (25mph) P = x 50 2 = (50mph) Force F = 2 x x 2 = 306N Force F = 2 x x 2 = N 8

9 Frame Analysis Frame Analysis is normally associated with analyzing large structures mainly comprising of uniform crosssection channels/frames. Typical examples include bridges, structural platforms, towers etc. Some examples are illustrated below. Frame Analysis, within Autodesk Inventor Simulation, allows the user to define criteria for static and modal analysis, including pre-stressing. In addition, Frame Analysis uses beam elements instead of the 3D tetrahedron and thin elements, that are used within the Stress Analysis environment. This significantly helps to speed up analysis times within frame analysis. Frame Analysis Workflow The process of creating an analysis (both stress and modal) involves four core steps: Step 1 IDEALIZATION Create main structures using Content Centre and/or Frame Generator Step 2 BOUNDARY CONDITIONS Apply constraints loads including setting up rigid links. including exporting loads from simulation Step 3 RUN SIMULATION AND ANALYZE Analysis and interpretation of results, via various tools. Step 4 OPTIMIZATION If needed customize materials and beam properties to create an optimum design 9

10 The following tube example demonstrates the benefits of using frame analysis over stress analysis when analyzing structures ( with length to thickness ratio typically 100 to 1) with uniform cross sectional properties. Initially we will determine theoretical results for the tube. We will fix the tube at one end and apply a load of 100N at the other end Tube data to be used is as follows; Length = 100mm Diameter = 10mm Thickness = 0.5mm Material = Mild Steel Using the classical Bending Stress Equation: M I = σ y = E R we can determine maximum stress (at fixed end) M max = Total length x Load = 100 x 100 = 10,000Nmm y = 5mm I = π ( 4 4 outside - inside ) = π ( ) = 168.8mm σmax = My I (10000 x 5)/168.8 = 296 N/mm 2 10

11 Stress Analysis Results - using 4 noded tetrahedron elements N/mm 2 or (316 MPa) % difference = Although this value is acceptable (within 10%) the difference is primarily due to stress singularities as refining the mesh around the high stress area will result in higher stresses. This is discussed later in the chapter Stress Analysis Results - using 4 noded shell elements N/mm 2 % difference = 3%. This is almost 50% better than using tetrahedron elements. Frame Analysis Results - using beam elements N/mm 2 % difference = 0%. This is because frame analysis does not have the stress singularity issues as in stress analysis. 11

12 In this final section of the presentation I will use the following example of a skid, commonly used within the offshore industry worldwide. In this example the main requirements is to satisfy DNV standards using Frame Analysis including 4 point and 2 point lift. This is typical testing's for offshore containers/baskets (commonly referred to as skids). In the presentation I will illustrate how to simulate skids with slings to get a more realistic behavior of skids and more importantly yielding in more accurate results. 12

13 Further Reading The material in this handout and lecture is based on my Up and Running with Autodesk Inventor Professional Series. The book's cover all three simulations in a lot more depth with guidance and tips throughout the books. The following books are available from Amazon worldwide. keywords=wasim+younis+autodesk Additional Resources On LinkedIn there is a dedicated support forum for Inventor Simulation Users around the world. Here you can post any question on Inventor Simulation and get help from fellow peers from around the world, including myself. The Support forum is named Up and Running with Autodesk Inventor Simulation. To join the forum you first have to sign up to LinkedIn, which is free. In addition the support forum there is also a dedicated simulation blog called Virtual Reality again hosted by me. This blog is also one of places where you can download the dataset to go with the books, mentioned earlier in the further reading section. 13