Up and Running with Autodesk Inventor Professional Simulation in …aucache.autodesk.com/au2012/sessionsFiles/2038/2976/handout_2038... · Up and Running with Autodesk Inventor Professional

Up and Running with Autodesk Inventor Professional

Simulation in 90 Minutes! Wasim Younis - Author of Up and Running Inventor Professional Simulation books

MA2038 - 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 (http://vrblog.info) - 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 Consultant @ Symetri (http://www.symetri.co.uk) – one of the largest Platinum Autodesk manufacturing value added reseller in Northern Europe.

[email protected]

Up and Running with Autodesk Inventor Professional Simulation in 90 Minutes

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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.


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Dynamic Simulation Workflow

The process of creating a Dynamic Simulation study involves four core steps.

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.

Step 1

Step 2

GROUP together all components and assemblies with no

relative motion between them

CREATE JOINTS between components that have relative

motion between them

CREATE ENVIRONMENTAL CONDITIONS

to simulate reality

ANALYZE RESULTS

Step 3

Step 4


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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.

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.


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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

Step 2

IDEALIZATION – Simplify Geometry, including setting up the

analysis

BOUNDARY CONDITIONS – Apply constraints loads

including defining contacts and mesh setting

including exporting loads from simulation

RUN SIMULATION AND ANALYZE– Analysis and

interpretation of results, via various tools to determine FOS

including convergence of results

OPTIMIZATION –If needed modify geometry to meet design

goals including reducing weight etc

including changing original material

Step 3

Step 4

http://en.wikipedia.org/wiki/Engineering

http://en.wikipedia.org/wiki/Stress_%28physics%29

http://en.wikipedia.org/wiki/Force


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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.


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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.


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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 = 𝟎.𝟏𝟐𝟐𝟓𝟕 𝒙 𝑽𝟐

Where:

F is force in Newtons (N)

A is the cross section of the LED display panel in Meters (approx 2m2)

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 = 𝟎.𝟏𝟐𝟐𝟓𝟕 𝒙 𝟐𝟓𝟐 = 76.6 (25mph) 𝑷 = 𝟎.𝟏𝟐𝟐𝟓𝟕 𝒙 𝟓𝟎𝟐 = 306.4 (50mph)

𝑭𝒐𝒓𝒄𝒆 𝑭 = 𝟐 𝒙 𝟕𝟔.𝟔 𝒙 𝟐 = 𝟑𝟎𝟔𝐍 𝑭𝒐𝒓𝒄𝒆 𝑭 = 𝟐 𝒙 𝟑𝟎𝟔.𝟒 𝒙 𝟐 = 𝟏𝟐𝟐𝟓.𝟕𝐍


9

Frame Analysis Frame Analysis is normally associated with analyzing large structures mainly comprising of uniform cross-

section 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

Step 2

IDEALIZATION – Create main structures using Content

Centre and/or Frame Generator

BOUNDARY CONDITIONS – Apply constraints loads

including setting up rigid links.

including exporting loads from simulation

RUN SIMULATION AND ANALYZE Analysis and

interpretation of results, via various tools.

OPTIMIZATION – If needed customize materials and beam

properties to create an optimum design

Step 3

Step 4


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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)

𝑴max = Total length x Load = 100 x 100 = 10,000Nmm

𝒚 = 5mm

𝑰 =𝜋

64( ∅outside

4 - ∅inside

4 ) =

𝜋

64( 10

4 - 9

4 ) = 168.8mm

4

𝝈𝒎𝒂𝒙 =𝑀𝑦

𝐼(10000 𝑥 5)/168.8 = 296 N/mm

2


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Stress Analysis Results - using 4 noded tetrahedron elements - 316 N/mm2 or (316 MPa)

% difference = 6.75. 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 - 287 N/mm2

% difference = 3%. This is almost 50% better

than using tetrahedron elements.

Frame Analysis Results - using beam elements - 296 N/mm2

% difference = 0%. This is because frame

analysis does not have the stress singularity

issues as in stress analysis.


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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.


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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.

http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field 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.

http://www.linkedin.com/groups?home=&gid=2061026&trk=anet_ug_hm

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.

http://vrblog.info

Documents

Up and Running with Autodesk Inventor Professional Simulation in …aucache.autodesk.com/au2012/sessionsFiles/2038/2976/handout_2038... · Up and Running with Autodesk Inventor Professional