You can use flow blockages to model 3D obstructions in a fluid volume using a simplified geometry representation of the original part.
A Flow Blockage simulation object provides a resistance to flow either completely diverting the flow or to let the flow pass through with a slight drop in pressure.
Catalytic converter geometry
You can create three types of Flow Blockage:
Nguyễn Thế Quang Dũng NX-PLM 2011 年 11 月 5
日 Solid — Models a 3D obstruction with solid material properties that blocks the 3D flow and is usually defined to exchange heat with the fluid by convection at its polygon faces. You can also model surface friction.
Catalytic converter fluid flow with half side solid blockage
Porous – Isotropic — Models an obstruction with fluid material properties, which equally impedes the flow with the same resistance values in every direction but does not entirely block the flow.
Catalytic converter fluid flow with half side isotropic blockage
Porous – Orthotropic — Models an obstruction with fluid material properties, which impedes the flow in three orthogonal directions with a different resistance value in each direction but does not entirely block the flow.
Catalytic converter fluid flow with half side orthotropic blockage
10. Solving the model
Solution options
You can set simulation options in the Solution dialog box. The most commonly used settings are located on the Solution Details and the Ambient Conditions tabs. You should always review the settings on the other tabs when they apply to the model you are solving.
Nguyễn Thế Quang Dũng NX-PLM 2011 年 11 月 5
日For steady state solutions setting expected values for the solution on the Initial Conditions tab may save analysis time.
For a transient analysis, you must specify a Start Time and an End Time in the Transient Setup tab, and review the other settings. You can set global initial boundary conditions in the Initial Conditions tab.
For a large model, deselecting the options for unneeded results types on the Results Options tab can improve processing time and reduce the size of the results file.
Turbulence Models
The flow solver uses the Reynolds-Averaged Navier Stokes (RANS) methods to solve for turbulence.
You set the Turbulence Model for your flow analysis on the Solution Details page of the Solution dialog box.
In the flow solver, you have the following options to model turbulence:
Fixed Viscosity
Defines uniform turbulence levels throughout the model, therefore it can be inaccurate and should only be used for an initial study.
Mixing Length
Ideal for validated applications or quick initial analyses during early design stages.
κ-ε
It is widely used in the industry, and is more accurate than the Fixed Viscosity or Mixing Length models, however it must be used with wall functions.
Not ideal for large pressure gradients, flow separation, or free shear flow.
κ-ω
Allows integration through the viscous sublayer. No wall functions are required.
Better predicts large pressure gradients.
Shear Stress Transport (SST)
Is a combination of the κ-ω and the κ-ε models. It behaves as the κ-ω formulation in the inner parts of the boundary layer, and as a κ-ε model in the free stream.
It is a better model for adverse pressure gradients and separating flow.
This model is computationally expensive.
Refreshing results
After you run a solution you can request additional results sets not included in the Results Option tab of the Solution dialog box.
In the Results Options tab expand the Control group, click on Refresh Results, and follow the instructions given by the interface.
Nguyễn Thế Quang Dũng NX-PLM 2011 年 11 月 5
日 Performing a restartYou usually restart an analysis in the following situations:
A steady state analysis has reached its iteration limit but has not converged yet.
A transient analysis has been run and you wish to continue the analysis over a new end time.
You have stopped a steady state or transient analysis and wish to continue the run.
You want re run your model with different properties but want to reuse information already calculated. For example you want to change an object's emissivity but reuse previously calculated view factors.
To perform a simulation restart use the options available in the Restart tab of the Solution dialog box.
Solver Parameters
Use Solver Parameters to control time step, convergence, speed calculation time, or to adjust the solver for unusual modeling situations. For example you must set an appropriate time step for natural convection problems.
After every solution, you should verify the convergence of the model. Review the message files for global heat balance and mass balance for flow problems. Investigate warnings and check the view factor sums for radiation problems.
Solving
When you select Solve , the solver generates an input file, then automatically begins processing.
An Information window displays model check results.
The Analysis Job Monitor dialog box lists the solve status for single or multiple runs.
The Solution Monitor displays all errors, warnings, and information messages from the module currently executing.
o Click Inspect to scroll and check current solution status. These messages are also available after the solution is completed.
o Click Stop to halt the current solution and discard the results. Restarting is not possible.
o Click Pause to stop solution and recover results for post processing. In complex models pause the solution to inspect the results after a few iterations, verify its
integrity, and continue the run. Continue the solve using the Restart tab at the Solution dialog box.
11. Mapping overview
NX Flow allows results transfer from a source model to another solver.
Flow forces mapping
Flow mapping associates the face of the fluid element source model to the closest nodes on the target model.
Nguyễn Thế Quang Dũng NX-PLM 2011 年 11 月 5
日 Static pressure and shear stress results are mapped to vector forces generated by the fluid on the surface of the target model.
General considerations
The FEM global coordinate system from target model must be the same as in the source model.
Both models should be geometrically congruent but do not need to have the same mesh.
Mapped flow forces are written in a result file (*.bun).
Pressure results mapped in to an structural analysis displaying deformation results
12. Suggested activity
In this activity, you perform a flow analysis of fluid passing through a valve.
Launch the Flow analysis of a valve activity.
Electronic Systems Cooling and coupled thermal flow
1. Introduction
NX Electronic Systems Cooling is an NX Advanced Simulation application that you can use to model the cooling and thermal management for electronic systems.
Create your simulation using these types of tools:
Boundary conditions, modeling, and simulation objects — To specify loads, constraints, and other objects that characterize a specific portion of the model. Although assigned to
geometric features of the model (points, edges, faces, or solid bodies), boundary conditions are ultimately applied to the elements by the solver.
Solution definition tools — To set controls and specify solver parameters that govern the entire model. They are always applied to the solution as a whole, not to specific elements or geometry.
Modifying the model
To change geometry, access the idealized part using the Part Navigator and the Modeling application.
A part update applies the change to the idealized part and marks the mesh for update.
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日Mesh changes in the Finite Element model (FEM) are automatically propagated to the Simulation.
You can override the mesh collector properties, defined in the FEM file, by using Edit Attributes Overrides, or an Override Set simulation object in in the Simulation file.
You can access and modify any simulation entity using the Simulation Navigator. Selecting an object highlights the corresponding elements or graphics symbols in the graphics window. You can also copy or clone any boundary condition or solution.
Modeling conduction
The thermal solver uses a finite volume formulation for modeling heat conduction between elements that share nodes, provided that:
Thermal conductivity and specific heat properties are defined for the elements. Specific heat is required only for transient analyses.
2D elements have thickness physical property defined.
1D elements have a beam section defined.
0D elements have a mass and diameter defined.
Modeling convection
You can model convection implicitly using boundary conditions provided that you define a Convection to Environment constraint on:
Faces of 3D solids
2D elements
1D elements with cross area defined
0D elements with diameter defined
You can use different types according to the phenomena modeled.
Convection to Environment
Use this option when you know either the Convection Coefficient or Parameter and Exponent and the fluid temperature.
Free Convection to Environment
Use this option when you want to use a specific free convection correlation (example: hot air rising).
Forced Convection to Environment
Use this option when you want to use a specific forced convection correlation (example: fans).
Both in transient and steady state solves, the solver calculates a single convection coefficient value for the entire convecting surface based on the characteristic information you specify.
Convection can also be explicitly model using a coupled NX Thermal and Flow solution by simulating the fluid volume and the embedded volumes and surfaces in a model.
Nguyễn Thế Quang Dũng NX-PLM 2011 年 11 月 5
日 Modeling radiationThe software simulates radiation based on view factors between radiating elements. The solver calculates black body view factors between all radiation elements. To calculate radiative
conductances, it combines these factors with thermo-optical properties, which you define for every radiating element.
For surfaces that do not obey the gray body approximation, ray-traced view factors can be calculated instead of black body view factors.
You can calculate radiation between surfaces defined by:
Faces of 3D solid elements.
The top and/or bottom of 2D shell elements based on the orientation of the element normals that you specify.
The implied surface of 1D beam elements based on the section properties you define.
The implied surface of 0D concentrated mass elements based on the diameters you specify.
If you want an element or group of elements to participate in radiation exchange, you must apply Thermo-Optical Properties and define a Radiation simulation object to calculate view factors between these elements.
Modeling fluid flow
The flow solver is an implicit code that uses a conservative finite volume formulation to solve the Reynolds Averaged Navier-Stokes (RANS) equations describing fluid flow.
All elements you include in a flow solution must be 3D elements for which you assign the following fluid material properties.
Mass density
Dynamic Viscosity
Thermal conductivity and specific heat
Coefficient of thermal expansion
Gas constant
For coupled solutions, the solver automatically simulates convection for fluid elements that touch solid walls, or where you define Flow Surface simulation objects. Convection properties can be tailored where appropriate.
2. Workflow and file structure
Step Task Application and file type
1. Create or import the model.
Modeling part file (.prt)
2. Simplify the model using NX Modeling and Advanced Simulation commands.
Modeling and Advanced Simulation
idealized part file (_i.prt)
Nguyễn Thế Quang Dũng NX-PLM 2011 年 11 月 5
日Step Task Application and file type
3. Define materials, physical properties, and thermo-optical properties.
Advanced Simulation FEM file (.fem)
4.
Mesh the model and define mesh collectors to organize meshes and assign physical properties.
Associate all FEMs to their corresponding parts when using an assembly FEM.
Advanced Simulation FEM file (.fem) Assembly FEM file (.afm)
5.
Define solution options and solver parameters.
Define loads, constraints, and other special boundary conditions.
Solve and review solution messages.
Advanced Simulation Simulation file (.sim)
6.
Review and display results using post-processing tools.
Refresh results to obtain additional results sets.
Advanced Simulation Simulation file (.sim)
3. Creating a fluid volume
While the solid mesh for a design part occupies the part itself, the fluid mesh occupies the void between the bodies.
Because the void itself is not a body, you must create a solid body to occupy the void, You create the solid body in the Modeling application then mesh this body with 3D fluid elements with the NX meshing tools or using Fluid Domain simulation object in the FEM or Simulation files respectively.
Nguyễn Thế Quang Dũng NX-PLM 2011 年 11 月 5
日 Electronics fan and heatsinkExtracted fluid volume of the electronics fan and heatsink
You can model the geometry of the fluid inside an assembly or a part with a complex internal cavity.
You can also model multiple fluids in a single model, provided no mixing takes place.
You can create a fluid volume using one of these methods:
Define a sketch representing the 2D shape of a regular fluid volume and then Extrude and/or Revolve the sketch. Use this technique if you know the shape and dimensions of the fluid volume.
Use Boolean operations to create the fluid volumes. You create a solid representing the enclosed space and select the Unite, Subtract, or Intersect to modify the shape of the volume based on the intersecting solid component geometry. Use this technique if you want to create this fluid volume for single use in an analysis and if you are not interested in maintaining links for geometry updates.
Create the enclosed fluid volume as a separate part file and component in your assembly file structure using the WAVE Geometry Linker command. This command copies an instance of the geometry of the inner volume and the components from the assembly part file. You then modify the contour to represent the fluid volume by using the Delete Face command (on the Synchronous Modeling toolbar). Use this technique if you want to maintain a link to the geometry of assembly components to allow for geometry updates.
4. Defining element and model properties
Physical properties
Physical properties define characteristics of your part that are not being explicitly modeled. Use the properties in the Physical Properties Manager dialog box to describe the physical qualities and characteristics of an element, such as thickness, layer stack definition, and others.
You can define physical properties to specify:
A spherical Concentrated Mass with a diameter and mass that you specify for 0D elements.
For example, you can model the effect of rivets in a riveted plate under thermal loads by creating 0D elements at the appropriate locations and then assigning a concentrated mass to them. You can also use 0D elements to model the mass of liquid inside a soda can without modeling the liquid volume as a 3D mesh.
A linear uniformly varying Non-Structural Mass in Mass per Length units, for 1D Beam elements. Use this to add additional capacitance to 1D elements.
A Thickness value, or a Non-Structural Mass value in mass per area units, for Thin Shell collectors of 2D Shell elements. Use the Non-Structural Mass to add weight without
Nguyễn Thế Quang Dũng NX-PLM 2011 年 11 月 5
日explicitly modeling geometry and meshing elements for it. For example, material inserts and surface coatings.
A Layer Definition for a Multi-Layer Shell Uniform collector type definition for 2D shell elements, in which you specify the Total Thickness and the Number of Layers.
Use this property to model multiple layers with detailed through-plane conduction and conduction.
A layer Stack Definition for a Multi-Layer Shell Non-Uniform collector type definition for 2D shell elements, in which you define a layer stack with multiple Layer modeling objects.
Each layer can have defined different materials, thickness, and thermo-optical properties.
Use this property to model conductive or radiative heat transfer through the physical layers of a sandwich material construction. For example, you can use Multi-Layer Shell Non-Uniform to model accurate heat transfer through composite materials.
When you define a physical property in the active FEM file, you assign it to a mesh collector. The meshes and their elements are assigned to the mesh collector inherit those physical properties.
Modeling objects
Use modeling objects to define particular properties for specific entities or for the whole model. You can create or modify modeling objects from the Modeling Objects Manager or from the solution, simulation objects, loads, and constraint dialog boxes.
Some NX Electronic Systems Cooling modeling objects include:
External Conditions
Fan Speed Controller
Non-Newtonian Fluid
Planer Head Loss
Scalar
5. Defining boundary conditions
Define appropriate thermal loads and constraints to simulate your model.
Boundary condition Description Thermal Loads
Lets you define known heat sources in your model. You can define thermal loads over geometry or elements as:
A Heat Load
An area-based Heat Flux
A volumetric Heat Generation
Temperature
Lets you specify a known temperature for the geometry or elements that you select, regardless of heat flow. This temperature can be constant, time varying, or spatially distributed.
Convection to Implicitly models natural and forced convection based on a heat transfer
Nguyễn Thế Quang Dũng NX-PLM 2011 年 11 月 5
日 Boundary condition DescriptionEnvironment
coefficient or standard correlation.
You specify the known heat Convection Coefficient value or the Correlation and the Characteristic Information.
Simple Radiation to Environment
Models area-dependent radiation of surfaces with known emissivities and view factors to a radiative environment temperature.
You can specify a value for Emissivity and View Factor from zero to one.
Flow Boundary Condition
Models flow boundary conditions, like inlet, outlet, opening, internal, and recirculation fans.
For more information on all simulation objects see the Advanced Simulation online help.
Boundary Conditions → Solver Specific Simulation Objects→ Solver Specific Simulation Objects
→ NX Thermal and Flow, NX Electronic Systems Cooling, and NX Space Systems Thermal .
6. Defining thermal couplings
Use the Thermal Couplings family of simulation objects to model:
Heat transfer between the surfaces of solid objects or components that are physically or thermally in contact.
Create generalized conductances defined by a coefficient.
The use of thermal couplings can ease meshing tasks and reduce model size and complexity during the solution.
Heat paths can be modeled within the model defining:
Conduction using a Thermal Coupling simulation object.
Radiation using a Thermal Coupling — Radiation simulation object
Conduction and radiation for a perfect contact using a Surface-to-Surface Contact simulation object.
Convection using a Thermal Coupling — Convection simulation object.
One way or user-specified conduction using a Thermal Coupling — Advanced simulation object.
A complete description on how to manually calculate thermal coupling values is available in the online help.
Conducting heat paths
You usually create a Thermal Coupling between parallel surfaces. If you create thermal couplings between non-parallel surfaces and edges, you introduce inaccuracies. The farther the two surfaces are from parallel, the greater the inaccuracy.
Nguyễn Thế Quang Dũng NX-PLM 2011 年 11 月 5
日 You define thermal couplings between: The faces of 3D meshed bodies
Faces meshed with 2D elements
Polygon edges or curves meshed with 1D elements
Points meshed with 0D elements.
Most geometry/mesh combinations are supported. The software uses the area of the primary region and the direction of the surfaces normals to calculate the magnitude of the heat path, as shown in the table.
Select Heat Transfer Calculation Area
Face of polygon body meshed with 3D elements
Polygon face surface area Polygon face meshed with 2D elements Polygon face surface area
Polygon face surface area Polygon face meshed with 2D elements Polygon face surface area