1. 5 th floor 90-14 Hanho Bldg. SamSung-Dong KangNam-Gu Tel: 02-539-5212, Fax: 02-539-5213 http://www.ablemax.co.kr Introduction to RADCAD Radiation Analyzer

2. 2 http://www.ablemax.co.kr Capabilities Monte Carlo Ray Tracing (MCRT) Oct Cell Acceleration True curved geometric surfaces Transparent and Specular properties Angular dependent properties Sun/Planet/Star Tracking Surfaces Display model in Orbit

3. 3 http://www.ablemax.co.kr Analysis Groups Allows the user to break a model into multiple radiation analysis “jobs” based on prior knowledge of no radiation between the groups (i.e. Internal enclosures are a good example)

4. 4 http://www.ablemax.co.kr Analysis Group Why is this an advantage?  One file vs. three makes reduces chances of bookkeeping mistakes  3 separate jobs will run faster and use less disk space than one large job

5. 5 http://www.ablemax.co.kr Surface Properties Different Optical Properties for each side of a surface A surface can be present in more than one analysis group. For example, the top side may be in External, while the bottom side may be in Internal

6. 6 http://www.ablemax.co.kr Active Side Verification Thermal  Model  Display Active Sides command  Green – Side seen is active and opposite side is inactive  Blue – Side seen is inactive and opposite side is active  Gold – Both sides active  Dark Blue – Neither Side Active  Red – Not in the analysis group Active Display Preferences  Shaded mode  Arrows  Can also show MLI surfaces and surfaces with area contact conductance

7. 7 http://www.ablemax.co.kr Orbits Several Types Supported  Basic Circular Orbit given altitude and beta angle  Keplerian Full Orbital Parameter input  Geo Latitude, Longitude, Altitude Weather balloons, objects on the planet  Vector List Input time, sun/planet vectors, distance from planet Used for trajectory type analysis  Free Molecular Heating Thermal  Orbit  Manage Orbits Thermal  Orbit  Edit Current Orbits Thermal  Orbit  View From  *  Sun, Star, Subsolar, Planet North, Vernal Equinox, Ascending Node, Orbit Normal

8. 8 http://www.ablemax.co.kr Displaying the model in Orbit Thermal  Orbit  View Vehicle  *  Set Orbit Position/Prefs Allows the user to scale the model  Next Position and Previous Position allow the user to move the model around the orbit Hint :: You can right click to repeat the last command Also, the toolbars work well for this

9. 9 http://www.ablemax.co.kr Model Viewing Thermal  Model Checks  View Model from Sun/Planet  Displays only the model (not the orbit)  Good for checking trackers  Good for orienting trackers when post processing SINDA data

10. 10 http://www.ablemax.co.kr Trackers Allow surfaces of your model to track the planet, sun, or a star Thermal  Articulators  Create Tracker  Can be active always, in shade, in sun, between user input orbit positions  Surfaces are attached to a tracker  Trackers can be nested  A surface can be attached to more than 1 tracker Allow user specified range of motion Color coded

11. 11 http://www.ablemax.co.kr What is a grey body radk? Use to determine the radioactive energy transferred between two nodes. Q rad ij =  Radk ij (T i 4 -T j 4 )   is the Stephan Boltzmann constant

12. 12 http://www.ablemax.co.kr Ways to calculate radks Calculate View Factors Monte Carlo (RadCAD, TSS) Nusselt Sphere (TRASYS) Contour Integral (TMG) Hemi Cube (TMG) Radiosity Solution Progressive (RadCAD) Gebhart (TRASYS, TMG, TSS) Oppenheim (TMG) Radks Calculate Radks Monte Carlo (RadCAD, TSS, Nevada)

13. 13 http://www.ablemax.co.kr Radiosity vs. Direct Radk Calcs Radiosity  Advantages Fast Can save disk space for heatrate calculations  Disadvantages Energy assumed to be equally distributed about a surface (must build model with this in mind) Cannot handle specular and transmissive properties

14. 14 http://www.ablemax.co.kr Calculating Radks Setup the run  Current Default Analysis Group Thermal  Radiation Analysis Groups  Current Default Orbit (if created) Thermal  Orbit Set Current  Thermal  Radiation  Set Radiation Analysis Control – Number of rays, energy cut off, oct cells Output – Filenames, starting ids, cutoff factors Nodes – Specify specific nodes to be calculated Positions – Set positions to be calculated Ray Plot – Plot the calculated rays on the model

15. 15 http://www.ablemax.co.kr RadCAD Calculations Thermal  Radiation  Calc*  View Factors  RADKS from View Factors Progressive Radiosity Solution View Factors must be calculated first  RADKS Ray Trace  Heating Rates Direct/VF Progressive Radiosity Solution View Factors must be calculated first  Heating Rates Ray Trace User will be prompted to verify the analysis group and orbit, if necessary If a database already exist, a test will be performed to determine if a restart is possible. If it is possible, you will be prompted to replace the database or append results.

16. 16 http://www.ablemax.co.kr RadCAD Calculations Case Set Manager  Allows setting up all the different analysis group and orbit combinations Stores the input/output data for each “job” Number of rays, oct cell levels, output filenames, etc… Can solve all jobs with the click of a single button Default is to REUSE the radiation calculations if nothing has changed in the model.

17. 17 http://www.ablemax.co.kr MCRT Methods View Factor  A view factor, F ij, represents the fraction of energy that leaves surface i and is incident on surface j. Interchange Factor  The interchange factor, B ij, represents the fraction of energy that leaves surface i and is absorbed at surface j, by all possible paths.

18. 18 http://www.ablemax.co.kr View Factor Calculations

19. 19 http://www.ablemax.co.kr View Factor Calculations (cont.) View Factors sum to 1 Reciprocity is not enforced  F ij A i != F ji A j  Always approached as more rays are shot How is each ray shot?  Random starting location on a surface  Random angle from the surface  Intersection test to other surfaces in the model Starting Location  Must have equal distribution per unit area  For a rectangle with origin 0,0 X start = len * random Y start = h * random Where random is a number between 0 and 1 y x len h

20. 20 http://www.ablemax.co.kr Starting Location (cont.)  For a disc centered at 0,0 In Polar coordinates R 2 = r * r * random a = 2 * pi * random Starting Angle View Factor Calculations (cont.) y x a R r p Top View p = 2 * pi * random cos 2 t = random t

21. 21 http://www.ablemax.co.kr Intersection Test  Performed with every surface in the model Classical solution, Oct Cells change this  If there is a hit, determine the distance to the surface Why you can’t have surfaces in the same plane  Smallest distance is determined to be the first surface hit View Factor Calculations (cont.)

22. 22 http://www.ablemax.co.kr Oct Cells breaks the model down into regions so that smaller number of intersection tests may be performed Oct Cell acceleration does not change the results, only arrives at them faster 2D Oct Cell Example  Create a bounding box around the model  Subdivide the cells (Example 3)  Determine which surfaces are in which cells Oct Cells

23. 23 http://www.ablemax.co.kr Consider a ray from surface 1  Perform self hit test  Intersection test to #2  Ray Propagated through empty cells  Intersection test with #3  Intersection test with 3+4  Hit on 4 is found Oct Cells (cont.)

24. 24 http://www.ablemax.co.kr Calculating the cells takes CPU time  Made up for in shooting the rays faster Increasing the subdivisions  Takes longer to calculate the cells, usually a factor of 4 Amazing how fast this is  Requires more memory Default subdivisions is 7  Usually <= 9  10 may run you out of memory Optimal number of subdivisions and surfaces per cell are model dependent Oct Cells (cont.)

25. 25 http://www.ablemax.co.kr Oct Cells (cont.) Look at varying the subdivisions for the tetra model SubdivisionsCPU Time*fasterCell Time None43.211.21 135.281.21 219.522.21 310.274.21 48.615.02.03 58.295.21.13 68.175.28.47

26. 26 http://www.ablemax.co.kr Optimize Cells command  Shoots 100 rays per node  Resets the random seed so same rays are shot each time  Varies the subdivisions from 5 to 8  Varies the surfaces per cell from 8 to 12  Projects results out to 5000 rays to determine optimal subdivisions and surfaces per cell Oct Cells (cont.)

27. 27 http://www.ablemax.co.kr Start same as view factor Set the energy Eray = emissivity Determine the first hit surface Get the properties of the surface  Emissivity and transmissivity  Can be dependent on incident angle Determine how to reflect the ray  Dependent on transmissivity and specularity Adjust Energy of the ray  Eabsorbed = Eray * emissivity of surface hit  Eray = Eray - Eabsorbed Re-emit the ray from the hit surface Interchange Factor Calculations

28. 28 http://www.ablemax.co.kr How does a ray stop?  Completely absorbed by hitting a surface with emissivity = 1  Ray goes to space No Surfaces hit  When the ray energy percentage is less than the energy cutoff factor, the ray is either completely absorbed or completely reflected, based on a random number and the emissivity of the surface hit. Interchange Factor Calculations Energy cutoff =.1 Incoming ray, Eray =.05% random <=.4 ray is completely absorbed random >.4 ray is completely reflected

29. 29 http://www.ablemax.co.kr The interchange factor from the emitting node to every other node can be calculated by:  B ij = Energy Absorbed by J/Energy Emitted by I Interchange Factor Calculations

30. 30 http://www.ablemax.co.kr Surfaces that overlap in the same 3d space will cause incorrect results using MCRT Thermal  Model Checks  Check Overlapping Surfaces… Overlapping Surfaces

31. 31 http://www.ablemax.co.kr Radk = e i B ij A i Interchange factors are calculated twice, once from node i to j and once from node j to i  Radks are combined with a weighting scheme to the more accurately calculated RADK Radk with B ij or B ji > B ij cutoff are output to SINDA At the bottom of the radk output file will be the summary information for the output radks  The “List if %kept is off by more than” parameter can be used to minimize the output so that only values in error are printed. RADKS

32. 32 http://www.ablemax.co.kr Random starting location on a surface Shoot ray towards the source  As opposed to shooting a bunch of rays from the source Determine if a ray can see the source  Direct Incident calculation Absorb energy at the starting location Propagate the ray same calculating radks Absorbed Energy is comprised of two components  Direct Absorbed is the amount of energy absorbed from the direct incident calculation for the node  Reflect absorbed is the amount of energy absorbed from the reflection off of other surfaces To improve accuracy, more rays must be shot from the surface that gets the incident heat from the source Heating Rate Calculations Earth 1 2

33. 33 http://www.ablemax.co.kr Calculates interchange factors from view factors  Heating rates from direct incident and view factors Advantages  Faster to calculate view factor than radk  Heating rate reflection matrices are not recalculated every source/position Less Disk Space Loss this advantage if geometry is moving Disadvantages  Assumes energy is equally distributed about a surface People have lived with this assumption for years with TRASYS  No specular reflections  No transmissive surfaces Progressive Radiosity

34. 34 http://www.ablemax.co.kr Uniform distributed energy assumption Progressive Radiosity (cont.) Consider Incident Energy Radiosity distributes the energy to be reflected over surface 1, thus over predicting the energy going to 2 MCRT reemits the energy from the hit point, thus correctly predicting the energy at 2 1 2 1 2 1 2

35. 35 http://www.ablemax.co.kr A good test to determine if a model is good for radiosity networks is to calculate the radks using radiosity and also using MCRT and to compare them. Large differences in the radks will require model refinement before progressive radiosity is begun. Progressive Radiosity (cont.)

36. 36 http://www.ablemax.co.kr Before any discussion on error estimation is considered, you must be aware that energy is always conserved in MCRT.  B ij sums are always around 1. This is comparable to the RKSUM used to verify TRASYS models  If a radk is a little high in one location, it will be a little lower in another to compensate. Best way to get comfortable on how many rays to check out the temperature differences as you shoot more rays. MCRT is a statistical process Each radk has an error associated with it. 1.645 is a 90% confidence interval Error Estimation

37. 37 http://www.ablemax.co.kr Error Estimation (cont.) 1K2K5K10K20K50K100K1M.001164.5116.373.552.36.823.316.45.2.002116.282.252.36.826.16.411.63.7.00573.451.932.823.216.410.47.32.3.0151.836.623.216.411.67.35.21.6.0236.425.816.311.58.15.23.61.2.0522.716.010.17.24.93.52.2.7.115.611.07.04.93.52.21.6.5.210.47.44.73.32.31.51.0.3.55.23.72.31.71.2.7.5.2 Number of rays Bij

38. 38 http://www.ablemax.co.kr Error with TRASYS Not intended to be a put down TRASYS section. This is so people can realize that previous methods also had error, and the cumulative results were acceptable. These examples all came from existing TRASYS models while comparing results to MCRT. Direct View Factor Calculation Error d d L L/dClosedTRASYS%Error 10..2819.380535.0 6.7.2765.349826.5 6.6.2763.27311.2 1..1998.20000.1

39. 39 http://www.ablemax.co.kr Error with TRASYS Shading Calculation dMCRTTRASYS%Error 1.5.01871.01689-9.8 1.9.02315.01284-44.5 2.1.02399.03447+43.7 2.5.02317.02719+17.3 3 2 1 All surface 1x1

40. 40 http://www.ablemax.co.kr Error with TRASYS Radiosity Solution – Propagated Errors 1 23 Infinitely long VF1-2 = VF2-3 = VF32 =.5 e =.3 B11 =.259 B21 =.370 B31 =.370 RK Sum =.999 Change View Factors to be off by 2% or.49 B11 =.2397.7% error B21 =.3495.7% error RK Sum =.937

41. 41 http://www.ablemax.co.kr For initial runs and debugging of models, only shoot about 2000 rays. For final runs, 5-20K rays should be considered.  Remember that rays are cumulative, shoot 2K the first time, and add more to them. Check the temperatures, if they change significantly, repeat the process. You will develop a keen sense of how many rays is best for your type of models over time. Consider using error criteria for the input  For example, use 20K rays, 5 percent error control  Setting the program to 100K rays, 1 percent error control is generally overkill. How many rays to shoot

42. 42 http://www.ablemax.co.kr Radks for Parallel Plates Objects Overview of how Thermal Desktop works Overview of Radiation Calculation functionality Compute the radks between two parallel plates and to space Plate: Length x width = 10 x 5 inches 12 inches Surface 1 Surface 2

43. 43 http://www.ablemax.co.kr 1. or Thermal >Optical Properties>Edit Property Data Solar Absorptivity = 0.23 Infrared Emissivity = 0.8 White Paint Radks for Parallel Plates

44. 44 http://www.ablemax.co.kr 2. or Thermal  Preferences Length m  in Radks for Parallel Plates

45. 45 http://www.ablemax.co.kr 3. or Thermal > Surfaces /Solids>Rectangle (create a 10x5 square in the x-y plane at Z=0 for the bottom surface Origin point : 0, 0 Point for +X axis and X-size : 10, 0 Point to set XY plane and Y-size : 0, 5 Top Side Active Radks for Parallel Plates

46. 46 http://www.ablemax.co.kr 4. or Thermal>Preferences Unselect 5. or Modify>Copy Select objects: Click on any part of the rectangle Press Specify base point or displacement, or [Multiple]: 0, 0, 12 Press Radks for Parallel Plates

47. 47 http://www.ablemax.co.kr 6. or Thermal  Edit Radks for Parallel Plates Select objects: Click on the newly created surface (top plate) Press change node ID

48. 48 http://www.ablemax.co.kr 6. or Thermal>Model Checks>Active Display Preferences Radks for Parallel Plates Set the display preferences for active side Verification. Colors indicating active sides are always available with the shade command. If only colors are being displayed, the shade command will automatically be executed.

49. 49 http://www.ablemax.co.kr 7. or Thermal>Model Checks>Display Active Sides Radks for Parallel Plates Verify that correct active sides have been input

50. 50 http://www.ablemax.co.kr 8. Select Thermal>Radiation Calculations>Set Radiation Analysis Data… 100000 Oct-tree acceleration is not necessary for this small problem. The default for List if % kept is off by more than: is set to 10%.  only the surfaces with errors are printed. Radks for Parallel Plates

51. 51 http://www.ablemax.co.kr 9. Select Thermal>Radiation Calculations>Calc Radks Ray Trace Calculates radks for the Analysis Group Base using the Monte Carlo ray-tracing method Output file “SINDA.K” will be generated in the working directory. 10. Select Thermal>Radiation Calculations>Calc Radks Ray Trace (again) Radks for Parallel Plates

52. 52 http://www.ablemax.co.kr 11. SINDA.K File for Parallel Plates Radks for Parallel Plates

53. 53 http://www.ablemax.co.kr 12. Select Thermal>Radiation Calculations>Set Radiation Analysis Data… Plot the calculated rays on the model Radks for Parallel Plates

54. 54 http://www.ablemax.co.kr 13. Command: ltscale Enter new linetype scale factor : 0.5 (Ltscale: determines # of dots, smaller values mean more dots) 14. Select Thermal>Radiation Calculations>Calc Radk Ray Trace Radks for Parallel Plates

55. 55 http://www.ablemax.co.kr 15. or Thermal>Radiation Calculations>Clear Ray Plot Radks for Parallel Plates

56. 56 http://www.ablemax.co.kr Objects Calculating orbital heating rates – Monte Carlo ray tracing Viewing a model in orbit Post processing heating rates Adjusting the color bar while in paper space Using the Case Set Manager to set up multiple heating rate jobs Radks for Parallel Plates

57. 57 http://www.ablemax.co.kr Initial View Orbital Heating Rates What will be learned: Calculating orbital heating rates Viewing a model in orbit Post processing heating rates Adjusting the color bar while in paper space Using the Case Set Manager to set up multiple heating rate jobs In this example, orbital heating rates using Monte Carlo ray tracing will be computed.

58. 58 http://www.ablemax.co.kr 1. Select Thermal>Orbit>Manage Orbits 1 2 Beta angle: angle between the vector to the sun and the orbital plane Orbital Heating Rates

59. 59 http://www.ablemax.co.kr 1. Select Thermal>Orbit>Manage Orbits (continued) 1 2 Orbital Heating Rates

60. 60 http://www.ablemax.co.kr 2. or Thermal>Orbit>Display Preferences 2 Orbital Heating Rates

61. 61 http://www.ablemax.co.kr 3. or Thermal>Orbit>Orbit Display off To verify the orientation of the model by viewing it as it appears from sun – be sure to do this step first Orbital Heating Rates

62. 62 http://www.ablemax.co.kr 4. or Thermal>Model Checks>View Model From Sun/Planet>Set Orbit Position/Location View From the Sun Orbital Heating Rates

63. 63 http://www.ablemax.co.kr 5. Select Thermal>Radiation Calculations>Calc Heating Rates Ray Trace Compute orbital heating rates for solar albedo, and planet shine using full Monte Carlo. Orbital Heating Rates

64. 64 http://www.ablemax.co.kr 6. Select Thermal>Post Processing>Manage Datasets Orbital Heating Rates

65. 65 http://www.ablemax.co.kr 7. or Thermal>Post Processing>Color Bar Preferences Orbital Heating Rates

66. 66 http://www.ablemax.co.kr 8. Select View>3D View>Back Total absorbed flux using the sum of all heating rate sources (solar albedo, and planet shine) 9. Select View>3D View>Right Orbital Heating Rates

67. 67 http://www.ablemax.co.kr 10. or Thermal>Model Checks>View Model From Sun/Planet>Set Orbit Position/Location Orbital Heating Rates

68. 68 http://www.ablemax.co.kr 11. Select View>3D View>SE Isometric 12. or Thermal>Post Processing>Edit Current Dataset Orbital Heating Rates

69. 69 http://www.ablemax.co.kr 13. Select Thermal>Radiation Calculations>Set Radiation Analysis Data… 14. Select Thermal>Radiation Calculations>Calc Heating Rates Ray Trace Orbital Heating Rates

70. 70 http://www.ablemax.co.kr 15. or Thermal>Post Processing>Edit Current Dataset Bring up the dataset editing dialog box and select OK to reload the data 16. Select Thermal>Orbit>Manage Orbits Orbital Heating Rates

71. 71 http://www.ablemax.co.kr 17. or Thermal>Case Set Manager Add beta30 Add beta90 Orbital Heating Rates

72. 72 http://www.ablemax.co.kr 17. or Thermal>Case Set Manager (continued) Double click beta30 Orbital Heating Rates

73. 73 http://www.ablemax.co.kr 17. or Thermal>Case Set Manager (continued) Deselect Run Case Orbital Heating Rates