ORG. POLÍTICA NRO
1.7. Miembros de las juntas receptoras del voto
You can define a mesh:
On geometry created in the Modeling application or imported from other CAD modeling packages.
Using primitives in the FEM file to create structured 2D or 3D meshes based on a simple geometric form type. You must specify the size, location, and orientation based on an associated coordinate system, and mesh density of the elements.
You can define primitives by:
Points — Allow you to specify three-dimensional coordinates to define key points to provide the shape information of the primitive.
Parameters — Allow you to define the primitive in relation to the X, Y, and Z-axes of a coordinate system using angular and linear values.
You can position the primitive with respect to the global coordinate system by translating or rotating the primitive's origin. You can define a primitive mesh and define a mesh collector to assign material, physical, and thermo-optical properties to it. Alternatively, you can define a mesh collector first and then assign the primitive mesh you create to it.
When you create a primitive with 2D elements, the top side of each 2D element faces a specific direction by default, depending on the type of primitive.
With three-dimensional primitives, such as the Box Primitive or Sphere Primitive, the top sides of the associated 2D elements face outward, away from the primitive.
With two-dimensional primitives, such as the Rectangle Primitive or Disc Primitive that you create by specifying parameters, the top sides of the associated 2D elements face the +Z direction.
With two-dimensional primitives, such as the Rectangle Primitive or Disc Primitive, that you create by selecting points, the top sides of the associated 2D elements are determined by the right hand rule, using the sequence P1, P2, P3 to define a rotation.
Note
3D elements have no top or bottom side, so the rules do not apply to primitives created with these elements (example: Solid Brick Primitive, Solid Cylinder Primitive).
4. Defining element and model properties
Nguyễn Thế Quang Dũng NX-PLM 2011 年 11 月 5
日 Physical propertiesPhysical 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
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 Multi-Layer Insulation (MLI) material used to cover spacecraft.
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 Space Systems Thermal modeling objects include:
Ablation-Charing
Active Heater Controller
Duct Head Loss
Joint
Joint — Orbital Tracker
Layer
Nguyễn Thế Quang Dũng NX-PLM 2011 年 11 月 5
日 Monte Carlo Settings
Orbit
Thermo-Optical Properties / Thermo-Optical Properties — Advanced
Thermostat
Thermo-optical properties
Use the Thermo-Optical Properties or Thermo-Optical Properties — Advanced modeling objects to define Emissivity, which is required for all radiation modeling.
Absorptivity is required to model radiative heat transfer in the solar band. To model specular and transmissive effects, you can also define a Thermo-Optical Properties — Advanced modeling object with values for:
Specular Reflectivity
Transmissivity
Index of Refraction
You can model radiation in different bands defining corresponding thermo-optical properties in a Thermo-Optical Properties — Advanced modeling object, and choosing one of the following two types:
Select Gray to define constant or temperature varying values for infrared Emissivity and a value for Absorptivity when want to define properties in the solar spectrum.
Select Non-Gray — Wavelength Dependent to define wavelength dependent values of non-gray Emissivity, Specular Reflectivity and Transmissivity.
Emissivity and absorptivity values can be constant or defined in function of a Bidirectional
Reflectance Distribution Function (BRDF). Specular Reflectivity and Transmissivity can be defined in terms of direction of incidence and angle of incidence.
Note
When you define Thermo-Optical Properties or Thermo-Optical Properties — Advanced for a 2D mesh, you should always first check the element normals to identify the top and bottom sides of the mesh.
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
Nguyễn Thế Quang Dũng NX-PLM 2011 年 11 月 5
日 Boundary condition Descriptionvarying, or spatially distributed.
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.
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.
You define thermal couplings between:
The faces of 3D meshed bodies
Faces meshed with 2D elements
Polygon edges or curves meshed with 1D elements
Nguyễn Thế Quang Dũng NX-PLM 2011 年 11 月 5
日 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 Curve or polygon edge meshed with 1D
elements
Length of polygon edge x perimeter of the associated beam cross section
Mesh point meshed with 0D element Surface of a sphere of the 0D element's diameter Radiating heat paths
The Thermal Coupling — Radiation simulation object models simple radiation between close parallel surfaces, or between objects at great distances. It does this by creating radiative heat paths (radiative conductances) between elements with view factors greater than 0.
The Thermal Coupling — Radiation simulation object calculates radiative heat transfer q:
q=σ x GBVF x ε1 x A1 (T12
+ T22
) (T1 +T2) You define either of the following:
Element emissivities
Gray Body View Factor
Effective Emissivity (Emissivity * Gray Body View Factor) Where
σ is the Stefan-Boltzmann constant.
GBVF is the specified gray body view factor.
ε1 is the emissivity of the primary elements.
A1 is the area of overlap of the primary element with the secondary element.
T1 is the absolute temperature of the primary elements.
T2 is the absolute temperature of the secondary elements.
7. About radiation enclosures and view factors
View Factors
A view factor represents the fraction of radiative energy that is emitted from one entity and arrives to a second entity. The thermal solver uses view factors to compute radiative heat transfer.
Two parallel surfaces in close proximity have a view factor that tends to unity. Two surfaces that are nearly co-planar have a view factor that tends to zero.
Nguyễn Thế Quang Dũng NX-PLM 2011 年 11 月 5
日 View factor calculationEnclosures
An enclosure divides the space into compartments on which view factors for a radiation requests are calculated. View factor calculation is expensive in terms of machine resources, therefore defining radiation enclosures saves solution time.
For radiation requests with transmissivity thermo-optical properties defined, the solver will automatically track rays that go through elements.
You can indicate that an enclosure radiates to ambient. In this case the solver will create radiative conductances from a point at a very large distance outside the model to elements of the enclosure visible to the point.
Nguyễn Thế Quang Dũng NX-PLM 2011 年 11 月 5
日Radiation heat is exchanged from:
Heatsource to mesh B.
Radiation heat is exchanged only from the heatsource to mesh B because thermo-optical properties are not defined on the bottom side of the 2D elements.
To model radiation to environment the elements of mesh A must have bottom thermo-optical properties.
Radiation simulation object
Use a Radiation simulation object to create view factor calculation requests for enclosures comprised of selected geometry or elements.
To simulate radiation exchange you must define:
Entities with Thermo-Optical Properties with a specified value for emissivity and/or absorptivity.
A Radiation simulation object. You can create one of these types of radiation requests:
o All Radiation to let the thermal solver detect enclosures.
o Enclosure Radiation where you define the relevant enclosures by selecting entities with the top and/or bottom thermo-optical properties defined.
The solver can use one of these techniques as the black body view factor calculation method:
Hemicube Rendering — This technique uses your computer's graphics card to calculate view factors quickly and accurately. You can only use this option if your computer's graphics card supports the Open Graphics Library (OGL) standard.
Nguyễn Thế Quang Dũng NX-PLM 2011 年 11 月 5
日 Deterministic — This is an analytical approach that uses a ray casting algorithm, which calculates the black body view factors based on the mathematical definition of view factor or form factor.
Monte Carlo — This technique determines view factors as part of the radiative exchange calculation. It uses a ray casting algorithm with statistical sampling to evaluate the radiative exchange in an enclosure. This technique is useful when:
o You want to model the effect of partial illumination of elements.
o You define bi-directional reflectance distribution functions (BRDFs) and scattering coefficients in the Thermo-Optical Properties – Advanced modeling object that you have assigned to a mesh collector to model diffuse reflection and transmission.
Specular reflection is the perfect reflection of radiation from a surface, in which a ray from a single incoming direction is reflected into a single outgoing direction. The law of reflection describes such behavior. Specular reflections are not included in radiation interchange unless you specifically request them. To include specular reflections you must:
Define values for Specular Reflectivity and Transmissivity in the Thermo-Optical Properties – Advanced modeling object that you define and assign to your specular surface.
Clear the Ignore specular and transparent effects for radiation request calculations check box in the Radiation Parameters page of the Solver Parameters dialog box.