Mech-HT 120 Lect-03 Mech Approach

8/13/2019 Mech-HT 120 Lect-03 Mech Approach

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Chapter 3

The MechanicalApplication Approach

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ANSYS MechanicalHeat Transfer


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Mechanical Application Approach

Training Manual Chapter ContentsMechanical Application Approach:A. Workbench ReviewB. Engineering DataC. Preprocessing in MechanicalD. Thermal Boundary ConditionsE. Functional Boundary ConditionsF. Solution Setu


G. Workshop


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Training Manual A. Workbench Review Recall that there are two ways of starting the Mechanical application:

Launched from the Start menu


or from a supported CAD system


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Training Manual . . . Workbench Review The Workbench project schematic is a graphical representation of the

workflow defining a system or group of systems From the toolbox the selection can be dragged and dropped onto the

schematic or simply double clicked



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Training Manual . . . Workbench Review By dropping applications and/or systems into various locations in the

schematic, an overall analysis project is defined Connectors indicate the level of data exchange between systems

In the example below a structural system is dragged and droppedonto a thermal system at the Model cell (A4)

Before completing the operation notice there are a number ofoptional drop targets that will provide various types of linkage



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Training Manual . . . Workbench Review By dropping the structural system at the Solution level we obtain a

structural system that is coupled to the thermal solution


Notice, the CandidateDrop Target

Indicates Data WillBe Shared From

Fields A2 to A4, andTransferred from A6


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Training Manual . . . Workbench Review The Units menu in Workbench:

Allows access to predefined unit systems Allows the creation of custom unit systems Controls unit display for Engineering Data,

Parameters and Charts Activate the Units System dialog to control


Units can be Displayed in theActive Project System or asThey were Defined in TheirSource (e.g. CAD System)


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Training Manual B. Engineering Data The Engineering Data application provides overall control for material

properties Engineering data can be opened stand alone (as a precursor to starting

a project for example)

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To Edit the Engineering

Data in an ExistingProject RMB > Edit orDouble Click

To Open the Engineering DataStandalone, Add from the

Component Systems in the Toolbox(Drag/Drop or Double Click), Then

RMB > Edit or Double Click


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Training Manual . . . Engineering Data The Engineering Data application is displayed below. Individual

controls and components are described next

Properties for MaterialOutline Filter


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Toolbox

PropertyChart

Selected Below

Properties ofMaterial Selected

Above

Outline of Filtered Materials


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Training Manual . . . Engineering Data The window interaction provides cascading data presentation To view or modify materials one generally follows a work flow shown here:

data source > material > individual property

Display Property inTabular and Graphical

Format



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Choose Data Source(Library)

Choose Material

Choose Property


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Training Manual . . . Engineering Data

The Engineering Data field represents thelist of materials which have been importedfor use in the current project.

Check box allowslibrary to be unlocked

for editing.

Outline Filter



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st o ava a e mater alibraries is displayed. These maybe ANSYS supplied or userdefined.

Favorites are materials which will beavailable in every project without the needto import from a library.

Browse for existinglibraries or choose

new library location.


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Training Manual . . . Engineering Data To add a material from a library:

Highlight the data source (library) in theoutline filter from which you wish toimport the material

Locate the material in the outline and clickthe + next to it to add it to the projectsEngineering Data



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If you now highlight the projectsEngineering Data you will see the newmaterial is included


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Training Manual C. Preprocessing in Mechanical In a Mechanical model individual

parts are assigned different materialproperties in the Details for each part

In assembly models contact regions



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are use to re ate eat trans er romone body to another


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Training Manual . . . Preprocessing in Mechanical If parts are in contact heat transfer can occur between them. If parts are out of contact no heat transfer takes place (see pinball

explanation below).

Summary:

Initially Touching Inside Pinball Region Outside Pinball RegionBonded Yes Yes NoNo Separation Yes Yes NoRough Yes No No

Contact TypeHeat Transfer Between Parts in Contact Region?



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For Bonded and No Separation contact the pinball region determineswhen contact occurs and is automatically defined and set to a relativelysmall value to accommodate small gaps in the model.

Remember , thermal contact involves no status changes. The initialstatus of the contact controls heat transfer throughout the solution.

Frictionless Yes No No

Frictional Yes No No


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Training Manual . . . Preprocessing in Mechanical If the contact is bonded or no separation,

then heat transfer will occur (solid greenlines) when the surfaces are within the

pinball radius



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Pinball Radius

In this Figure on the Right, theGap Between the Two Parts isBigger Than the Pinball Region,So No Heat Transfer Will OccurBetween the Parts


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Training Manual . . . Preprocessing in Mechanical The amount of heat flow across a contact interface is defined by the

contact heat flux q :

where T contact is the temperature of the contact surface and T target is thetemperature of the corresponding target surface

contact target T T TCC q =



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By default, TCC is set to a relatively high value based on the largestmaterial conductivity defined in the model KXX and the diagonal of theoverall geometry bounding box ASMDIAG

This essentially provides perfect conductance between parts

ASMDIAGKXX TCC / 000,10=


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Training Manual . . . Preprocessing in Mechanical Depending on license, users may define a thermal contact

conductance value (TCC) for Pure Penalty or Augmented Lagrange Formulations

TCC is input for each contact region in the Details view If thermal contact resistance is known, invert this value and divide by thecontacting area to obtain TCC value



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Thermal Contact Conductance CanBe Input Which is the Same asIncluding Thermal ContactResistance at a Contact Interface


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Training Manual . . . Preprocessing in Mechanical Spot welds provide discreet heat transfer points:

Spot welds are defined in the CAD software (currently onlyDesignModeler and Unigraphics)

T2



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T1


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Training Manual . . . Preprocessing in Mechanical Mesh controls are accessed by highlighting the mesh branch and

inserting the desired controls.



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Note extensive discussion of mesh controls in Mechanical is in theIntroductory course. Thermal applications requiring specificmeshing considerations will be addressed later as needed.


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Training Manual D. Thermal Boundary Conditions As with other disciplines, thermal loads are applied by first

highlighting the environment branch (here, Steady State Thermal)and scoping the loads to regions of the model



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Select a Model Region thenRMB to Apply a Load


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Training Manual . . . Thermal Boundary Conditions Temperature:

Imposes a temperature on vertices, edges, surfaces or bodies. Temperature is the degree of freedom which is solved for in Mechanical.

Heat Flow: A heat flow rate can be applied to a vertex, edge, or surface. The load isdistributed for multiple selections.

Heat flow has units of energy/time.



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Heat flux can be applied to surfaces (edges in 2D). Heat flux has units of energy/time/area.

A positive value for heat load will add energy to the system.


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Training Manual . . . Thermal Boundary Conditions Perfectly insulated (heat flow = 0):

Available to remove surfaces from previously applied boundaryconditions

Internal Heat Generation: An internal heat generation rate can be applied to bodies only Heat generation has units of energy/time/volume

Coupling:



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cope o ver ces, e ges or aces Coupling temperatures constrains the calculated temperatures (results)

to be the same for the entire scope of the coupling


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Training Manual . . . Thermal Boundary Conditions Convection:

Applied to surfaces (or edges in 2D analyses) Convection q is defined by a film coefficient h , the surface area A, and the

difference in the surface temperature T surface & ambient temperatureT ambient

ambient surface T T hAq =


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h and T ambient are user input values The film coefficient h can be constant or temperature dependent


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Training Manual . . . Thermal Boundary Conditions Temperature-Dependent

Convection: Select Tabular (Temperature) for

the coefficient type Enter coefficient vs temperature

tablular data In the details, specify how

temperature is to be handled for



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h(T)


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Training Manual . . . Thermal Boundary Conditions Several common convection correlations can be imported from a

sample library. New correlations can be stored in libraries. See Functional Boundary Conditions in the next section regarding

creating, exporting and importing correlations.



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Training Manual . . . Thermal Boundary Conditions Radiation:

Applied to surfaces (edges in 2D analyses)

Where: = Stefan-Boltzman constant = Emmisivity A = Area of radiatin surface

44ambient surface R T T FAQ =



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F = Form factor (1)

Provides for radiation to ambient only, not between surfaces (form factorassumed to be 1)

Stefan Boltzman constant is set automatically based on the activeworking unit system


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Training Manual E. Non Constant Boundary Conditions Magnitudes for heat loads can be defined as a constant, a table or a

function in Mechanical Tabular and functional definitions can be exported and imported for

reuse

Directional quantities can be defined in terms of local coordinate systems



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Table/function loads may be defined in terms of time, temperature orspatial location (depending on the load type)

Note: time is used for steady state multi-step and transient analyses


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Training Manual . . . Non Constant Boundary Conditions A tabular load is entered by changing the magnitude field to tabular

Depending

on the Load,Several TableOptions maybe Available



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Values are entered directly in the table (time and heat flow in thebelow case)

The graph displays automatically


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Training Manual . . . Non Constant Boundary Conditions Functional loads are specified similar to tables by entering a function

in the magnitude field

Functions are defined in terms of primary variables:



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, , ,

Convection, heat flux, heat flow, heat generation and radiation (time)

Functions are entered using standard algebraic entry: Examples (primary variables shown in red ):

10 * time

12+.25 * x

Note: primary variables are case sensitive


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Training Manual . . . Non Constant Boundary Conditions Supported Functions:

sin(x), cos(x), tan(x): trigonometric functions asin(x), acos(x), atan(x): arc functions

pow(x,y): power of x to y sqrt(x): square root of x log(x): natural logarithm of x log10(x): common logarithm of x

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o e: e un s use n unc ona npu arecontrolled by the working units and indicated inthe details for the boundary condition


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Training Manual . . . Non Constant Boundary Conditions The resolution of the interpolation used by

function loads can be controlled bymodifying the Number of Segments usedfor the function (default = 200) in the GraphControls details

When spatially varying functions are defined

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(min/max)


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Training Manual . . . Non Constant Boundary Conditions Spatially varying temperature example:

A spatially varying temperature load is applied tothe face shown using the function (100 + z)

The z coordinates of the face range from 0 to 25mm

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The temperature load is set up using the functionand controls shown here

Note the Table isPopulated with the

Function Values


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Training Manual . . . Non Constant Boundary Conditions The temperature result shows the

variation along the face where theload is applied

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Following the solve, the variation inthe applied temperature can beviewed as a contour on the scopedregion


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Training Manual . . . Non Constant Boundary Conditions A function that is to be reused in

future analyses can be saved byexporting



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The Function LoadCan Now Be

Imported andUsed Again


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Training Manual F. Solution Setup In Mechanical the Analysis Settings are

used to set the solution options for theanalysis

Step Controls allow multi-step analyses to be

setup for steady state or transient thermalanalyses Solver Type allows Direct or Iterative solver

selection (default = Program Controlled) Nonlinear Controls, discussed in cha ter 5



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Output Controls: allows selection of content

and frequency of result storage Analysis Data Management: controls the

content, location and units for the files createdand stored

Visibility: controls the content of the graph

when viewing loads


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Training Manual G. Results and Postprocessing Various results are available for postprocessing:

Temperature Heat Flux

Reaction Heat Flow Rate User defined results



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In Mechanical, results are usually requested before solving, but theycan be requested afterwards, too

A new solution is not required for retrieving output of a solved model


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Training Manual . . . Results and Postprocessing User defined results can be viewed

and accessed from the Worksheetview of the Solution branch

User defined results can be addedfrom the Worksheet using the RMBoption



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Training Manual . . . Results and Postprocessing Temperature:

Temperature is a scalar quantity and has nodirection associated with it



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Workshop 3

Thermal Contacts



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ANSYS MechanicalHeat Transfer

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Mech-HT 120 Lect-03 Mech Approach

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