University of Texas VSP Structural Analysis Module Update - Demonstration

Transcription

1 University of Texas VSP Structural Analysis Module Update - Demonstration VSP Workshop, San Luis Obispo, CA Hersh Amin Armand J. Chaput Department of Aerospace Engineering and Engineering Mechanics, University of Texas at Austin 7 August Armand J. Chaput

2 Overview of VSP SAM Process VSP Model Grumman A6E Intruder Wing Today s Lineup VSP SAM Version 1 Overview Tutorial: Shrenk s Approximation (Air Loads) Load Factor: 9.75 g Version 2 Overview Tutorial: Shrenk s Approximation (Air Loads) Load Factor: 9.75 g Wing fuel External stores (external fuel tanks) Note: corresponding files can be found at:

3 Overview of VSP SAM Process Vehicle Sketch Pad Parametric Internal Geometry Parametric External Geometry External and Internal Mesh Generation UT Input Executable (Java) Wing Trim Thickness and Material Properties Boundary Conditions and Load Cases CalculiX Input File UT Convergence Executable (Java) Solution Files Thickness Calculation Mass Calculation Stress Convergence CalculiX FEM Input FEM Solution FEM Post Process and Graphics Output Files

4 Overview of VSP SAM Process Vehicle Sketch Pad Vehicle Sketch Pad Parametric Internal Geometry Parametric External Geometry External and Internal Mesh Generation VSP process through mesh generation

5 Overview of VSP SAM Process UT Input Executable Deletes non-primary load carrying structure - Typically leading and trailing edge devices Deletes non-load carrying skin panels - To represent typical fabric or film skin sections UT Input Executable (Java) Wing Trim Thickness and Material Properties Boundary Conditions and Load Cases CalculiX Input File

6 Overview of VSP SAM Process UT Input Executable Spars, Ribs and Skins can be defined as different materials UT Input Executable (Java) Wing Trim Thickness and Material Properties Boundary Conditions and Load Cases CalculiX Input File Required Thickness defined by input Design Nominal Stress (DNS) objective and Minimum Gauge

7 Overview of VSP SAM Process UT Input Executable 2D linear load at defined constant chord fraction - Input based on root and tip running load 2D elliptical and Schrenk approximations - Input based on flight design gross weight and n z Discrete point loads (Fxx, Fyy, Fzz, Mxx, Myy, Mzz) - GUI inputs at defined % span and % chord locations Discrete mass loads (n z ) (v2+ feature) - GUI inputs at defined spar # and % span or rib # and % chord locations with multiple attachment points on ribs and/or spars Multiple Load Cases (v2+ feature) - GUI inputs for multiple 2D linear, elliptical or Schrenk approximations with varying angle of attacks and varying load distributions on spars Fuel Loads (v2+ feature) - GUI inputs for adding fuel tanks between ribs and spars - Applies pressure loads and inertial loads on the skin UT Input Executable (Java) Wing Trim Thickness and Material Properties Boundary Conditions and Load Cases CalculiX Input File Boundary conditions define which rib is fixed from translation in the x, y and z axis

8 Overview of VSP SAM Process CalculiX Solutions UT Input Executable (Java) Wing Trim Thickness and Material Properties Boundary Conditions and Load Cases CalculiX Input File Users can see status messages while VSP SAM is running. Messages can have information on VSP SAM s current stress convergence iteration, Load cases and/or Wing trim operation. CalculiX FEM Input FEM Solution FEM Post Process and Graphics Output Files

9 Overview of VSP SAM Process CalculiX Solutions Left click in white area brings up menu Menu provides range of stress & displacement viewing options Option shown is von Mises stress Solution viewing area CalculiX FEM Input FEM Solution FEM Post Process and Graphics Output Files Mouse commands rotate and zoom solution

10 Overview of VSP SAM Process UT Convergence Executable Simple Von Mises stress-based structural Summary of theory and method used to back out required Nodal thicknesses thickness resizing algorithm developed An enabling capability for FEM based Background structural mass property estimation Part of the objective of the project is to be able to determine the optimized thickness of each part of the wing for a given working stress. This backing out the thicknesses aims to do that. The procedure used by Node our team and thickness the theory behind it resizing is described. is based on Theory user defined design nominal stress ( DN ) We or begin minimum with an arbitrary 3D gage, element as shown whichever below: larger UT Convergence Executable (Java) Solution Files Thickness Calculation Mass Calculation Stress Convergence Thickness t i = ( / DN ) t i VSP The blue SAM plane represents iterates a plane lying stress in one of the 3 to principal mass axes, showing convergence that the element can be arbitrarily oriented. We can then describe the stress acting on this plane as follows: We know seek to find the required thickness for a given working stress as defined by the user:

11 Overview of VSP SAM Process Mass Calibration Method Build VSP Model Use actual Area, Taper Ratio, Dihedral, Thickness, and Span Model the actual Spar locations. Model the actual Rib locations. Generate Mesh Choose mesh size depending on wing size. Typically 100 elements spanwise (Half-Span/100). Generate meshes. If mesh size > 5 Mb, increase mesh size. Mass Convergence Minimum Gauges & DNS Constant Minimum Gauge Initial Design Nominal Stress (DNS) = Initial guess Vary DNS for ribs, spars and skins until final wing structure weight matches expected value.

12 Overview of VSP SAM VSP Model Information

13 VSP Model A6E Intruder Intermediate & Outer sections Only No Center Section

14 VSP Model Why A6E Intruder? Available in Metal and Composite Good Mass Properties Internal Fuel and External Stores Larger Operating Flight Envelope Good for the purpose of Software Calibration

15 VSP Model A6E Planform BL 38.9 All locations and linear dimensions in inches Tip Chord (BL 305): = 5.18 BL 66 BL 78 Sweep: BL 144 Root Chord (BL 66): ~ = c 0.05 c 28 BL 305 BL NOTE: Currently VSP SAM does not support Multi-Section Wing which limits this analysis to intermediate and outer sections only which will be combined into single wing section

16 VSP Model A6E Airfoil NACA-6 Series Airfoil t/c (BL 66): ~ t/c (BL 305): ~ NOTE: Only Root and Tip t/c ratios will be used since adding additional t/c ratios need multi-section wing which is not currently supported by VSP SAM

17 BL 305 BL 318 BL BL 78 BL 66 BL 38.9 BL 0 VSP Model A6E Spars FS 0 All locations and linear dimensions in inches 29.5 Drawing warped L/R 0.05 c FS c 28 FS c 0.83 c 0.70 c?

18 VSP Model A6E Ribs Rib 0 9 Ribs including Root and Tip Rib Spar 1 NOTE: To further simply the model, all ribs are placed parallel to free stream. Spar 0 Rib 8

19 VSP Model Information Build A6E VSP Model

20 VSP Model Adding a new wing 1 3 2

21 VSP Model Modifying the new wing (A6E Planform) Delete all sections except section ID: 0 4 Set Tip Chord, Root Chord, & Sweep 6 Set Span, & Projected Span

22 VSP Model Modifying the new wing (A6E Airfoil) Airfoil ID: Type: (Dropdown menu) NACA 6-series NACA 6-series 3 t/c ratio: ( Thick slider)

23 VSP Model Modified A6E wing geometry 1 2

24 VSP Model FEM Geometry 1 2

25 VSP Model A6E FEM Geometry (Spars) 3 Spar ID: Position: ( Position: Slider) Sweep Angle: ( Rel checkbox) Checked Checked Relative Sweep Angle: ( Sweep Slider)

26 VSP Model A6E FEM Geometry (Ribs) Rib ID: Position ( Position Slider)

27 VSP Model Finished A6E FEM Geometry 1 2 Location of Ribs and Spars

28 VSP Model Generate A6E Mesh Bigger element size yields bigger mesh and faster run time

29 VSP SAM Required Files 1 Geom File: <Wing_Name>_calculix_geom.dat Thick File: <Wing_Name>_calculix_thick.dat Copy the Geom File and the Thick File in a separate directory to run SAM NOTE: SAM working directory (next slide) must not have any spaces in its path.

30 VSP SAM Import VSP Mesh Set directory for VSP Mesh Files. You can choose either calculix_geom or calculix_thick file. 1 2 NOTE: having spaces in the directory path will result in crash. 1 3 Open Set the directory of the CalculiX folder (use default with typical installation) 2 Save 3 Open GUI inputs from previous session or Save GUI inputs for future sessions 3

31 VSP SAM Sign Conventions Z Origin is always at wing Apex and parallel to the VSP coordinate system. NOTE: All Axis are parallel or perpendicular to the Datum regardless of wing sweep, dihedral or angle of attack Y Y axis goes into the page α X X axis goes chordwise Y axis goes spanwise Datum Z axis goes normal to the Datum Applies to all the load factors including n x, n y, and n z

32 Build A6E VSP Model VSP SAM Version 1

33 VSP SAM Version 1 Features: Skin Trim Feature Load Spar Approximations Boundary Condition Separate FEM Models Special Case: Zero Node Thickness Stress Convergence and Node Sizing Mass Calculation

34 VSP SAM Skin Trim Feature Remove non-load carrying skin panels which can be fabric sections of the skin, landing gear hatches, etc. Skin trim must be defined by Inboard/Outboard rib and Forward/Aft spar

35 VSP SAM Load Spar Approximations Planform Shape, Elliptical and Schrenk s Approximations: Schrenk s Load distribution is equivalent to average of elliptical load distribution and the actual planform shape distribution of the wing.

36 VSP SAM Boundary Condition Rib 0 is fixed from translation in the x,y and z axis as shown in the CalculiX results file. As a result, this particular wing structure is a cantilever beam with Rib 0 as the stationary plane. Any Rib can be defined as a fixed rib such as a Body Rib as shown in the figure below. Rib 0 Body Rib

37 VSP SAM Separate FEM Models Version 0 contains Single FEM model results from original VSP s output files When node thickness is resized to meet user defined DNS objective, different node thickness requirements at intersections distort elements which results in CalculiX error Version 1 Splits FEM into separate Skin, Rib, and Spar FEM models using Rigid Body Elements to make connections at rib-skin, spar-skin, and rib-spar intersections Thicker elements at ribskin, spar-skin, and rib-spar intersections

38 VSP SAM Special Case: Zero Node Thickness Set of vertical nodes from a spar, with the horizontal lines representing the thickness of each node and the Red Arrow represents the force applied to this set Thickness of some nodes approaches at nearly zero after convergence Solution: Apply average thickness of the adjacent nodes to the affected node z y Before After NOTE: Set of nodes from a spar is only used as an example, The same method applies to any affected node within the FEM model

39 Summary of theory and method used to back out required Nodal thicknesses VSP SAM Stress Convergence and Node Sizing Background Part of the objective of the project is to be able to determine the optimized thickness of each part of the wing for a given working stress. This backing out the thicknesses aims to do that. The procedure used by our team and the theory behind it is described. Theory We begin with an arbitrary 3D element as shown below: 1 and Thickness 1 corresponds to each node Thickness t i = ( / DNS ) t i The blue plane represents a plane lying in one of the 3 principal axes, showing that the element can be arbitrarily oriented. We can then describe the stress acting on this plane as follows: We know seek to find the required thickness for a given working stress as defined by the user: Solving equation (1) for the force, and plugging into equation (2) it can be shown that we get: By using the max principal stress in any given element for we can ensure that the element is sized for the worst case scenario. This is the theory behind the procedure used.

40 VSP SAM Mass Calculation

41 VSP SAM Version 1 A6E Tutorial for v1

42 VSP SAM (version 1) A6E Wing Geometry Initial Thickness definitions 3 3 Set boundary conditions (Fixed Rib) which indicates which Rib is fixed from translation in x, y, and z direction and Convergence Tolerance which ends the iterative process when the mass difference between previous iteration and current iteration converges to the user defined tolerance

43 VSP SAM (version 1) A6E Wing Trim Before Trim After Trim Wing Box of the A6E Intruder Wing

44 VSP SAM (version 1) A6E Wing Trim (cont d) Leading Edge Trim Trailing Edge Trim Device Trim definition to reveal the Wing Box of the A6E Intruder Wing

45 VSP SAM (version 1) A6E Material Properties 1 2 Set Material Properties such as Young s Modulus, Poisson s Ratio, Yield Stress and Ultimate Stress 3 Assign materials defined (2) to each component and set the Design Nominal Stress (DNS) as well as Density and Minimum Gauge (minimum thickness) for each component NOTE: Throughout VSP SAM, ft and lbm will be the nominal units. 3 For this case, properties of 2024 T3 Aluminum Alloy is used which is a nominal material for metal wings, and Minimum gauge of typical military aircraft wing is used. MIL-HDBK-5, Table (d)

46 Load fraction lbf/ft VSP SAM (version 1) A6E Aircraft Weight Wing External Loads (distributed) Running Load p Fuel inertia relief NOTE: Only 73 % of the Flight DGW will be used since this analysis only involves the intermediate and outer sections of the A6E Wing y/b Wing External Load Fraction External load Inertia relief Flight Design Gross Weight (DGW): lbm y/b Load Fraction at BL66 (root): 0.73 of Flight DGW lbm

47 VSP SAM (version 1) A6E Load Case NOTE: All of the Aircraft Load will be placed on Spar 0 Only due to VSP SAM version 1 limitation 4

48 VSP SAM Running SAM 1 Press Run button to initialize SAM 2 Press Stop button to quit SAM 1 2

49 A6E Tutorial for v1 A6E v1 Results

50 VSP SAM Viewing CalculiX Results 1 NOTE: These files can be found in the same directory where VSP Mesh files are located In version 2, Wing1_N represents CalculiX results for Case ID 1 set in Load Case tab at iteration N. Highest N represents the final iteration. NOTE: In version 1, Wing1 from WingN is used where N represents the iteration number. Wing_initial represents the initial iteration and Wing_final represents the final iteration.

51 VSP SAM Viewing CalculiX Results (cont d) 1 2 Translate Model: Use Right Mouse Button 3 Rotate Model: Use Left Mouse Button Zoom in/out Model: Hold scroll wheel while dragging the mouse

52 VSP SAM Mass Results File NOTE: These files can be found in the same directory where VSP Mesh files are located mass.csv consists of mass values of each component as well as volume and surface area at each iteration. NOTE: VSP SAM only outputs the mass values in mass.csv file. It does not plot any values as of right now.

53 VSP SAM (version 1) A6E Mass Results Skin Rib Spar Total Mass (lbm):

54 VSP SAM (version 1) A6E Stress Results (Iteration 0) DNS Skin: ksi Spars: ksi Ribs: ksi

55 VSP SAM (version 1) A6E Stress Results (Iteration 7) DNS Skin: ksi Spars: ksi Ribs: ksi

56 A6E v1 Results VSP SAM Version 2

57 VSP SAM Version 2 Features: Multiple Load Spars & Angle of Attack Multiple Load Cases Wing Fuel Loads Discrete Mass Loads

58 VSP SAM Multiple Load Spars & Angle of Attack Based on Angle of Attack (α), loads are split in x and z directions. Each spar can be assigned a load fraction of the Total Load in order to get the resultant force applied on the wing. Red Arrow represents the resultant force applied on the wing α > 0 z α = 0 x

59 VSP SAM Multiple Load Cases More than one Load case can be assigned with varying Angles of Attack and varying Load Spar Distributions. Constructs new FEM model from using Max Stress on each node and Max Thickness of each node out of all the user-defined load cases. The new FEM model is used to calculate final mass estimate. All 4 points of the flight envelope can be analyzed Positive High Alpha 2 Positive Low Alpha 3 Negative Low Alpha Negative High Alpha

60 VSP SAM Wing Fuel Loads Fuel Tanks are defined by forward/aft spar and inboard/outboard rib

61 VSP SAM Discrete Mass Loads Adds inertial loads on the spars and/or ribs with multiple attachment points. User defines spanwise/chordwise fraction along with spar/rib numbers and load fraction of the Total Load for a given attachment point. Adds load along the neutral axis of the rib or spar (figure 2). Distributes loads based on the distance from user-defined spar/rib location (figure 1). Node 1 Node 2 D 1 D 2 figure 2 Location figure 1 Loads are applied in the n z direction

62 VSP SAM Version 2 A6E Tutorial for v2

63 VSP SAM (version 2) A6E Initial Inputs 1 1 Same inputs as version 1: Wing Trim (Devices Tab) Wing Geometry

64 VSP SAM (version 2) A6E Material Properties 1 2 Same inputs as version 1 3 Different DNS for each component. Same Minimum Gauge and Density as version 1

65 VSP SAM (version 2) A6E Load Case Load Parameters: Spar #: % of Load: Fixed End Moment:

66 VSP SAM (version 2) A6E Wing Fuel Tanks 78. Starboard Wing Integral Fuel Tank Fuel Tanks 91. Outer Panel Integral Fuel Tank 84. Outer Wing Missile Pylon 201. Inboard Wing Pylon

67 VSP SAM (version 2) A6E External Stores Rib 0 Rib 1 Rib 4 Rib 8 Rear View z y Pylon Tank w/adapter External Stores: Inboard: Outboard: Pylon (lbm): Inboard Fuel Tank Outboard Fuel Tank Tank w/adapter (lbm): Fuel (lbm): Total Mass (lbm): Spar 0 Top View Attachment Points x y Spar 1

68 VSP SAM (version 2) Adding A6E External Stores Mass ID: Mass(lbm): Load Factor (n z ): Rib #: 1 4 Chordwise Fraction: Note: All masses are attached at ribs

69 VSP SAM (version 2) Adding A6E Wing Fuel Tank ID: Inboard Rib 4 Outboard Rib FWD Spar Aft Spar

70 A6E Tutorial for v2 A6E v2 Results

71 VSP SAM (version 2) A6E Mass Results Skin Rib Spar Total Mass (lbm):

72 VSP SAM (version 2) A6E Stress Results (Iteration 0) DNS Skin: ksi Spars: ksi Ribs: ksi

73 VSP SAM (version 2) A6E Stress Results (Iteration 6) DNS Skin: ksi Spars: ksi Ribs: ksi

74 Questions?