3 d model generation for deformation analysis using laser scanning data of a cooling tower
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3 d model generation for deformation analysis using laser scanning data of a cooling tower

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3 d model generation for deformation analysis using laser scanning data of a cooling tower 3 d model generation for deformation analysis using laser scanning data of a cooling tower Presentation Transcript

  • 3D MODEL GENERATION FOR DEFORMATION ANALYSIS USING LASER SCANNING DATA OF A COOLING TOWER
    C. Ioannidis(a), A. Valani(a), A. Georgopoulos(a), E. Tsiligiris(b)
    (a)Department of Rural and Surveying Engineering, National Technical University of Athens
    Email: cioannid@survey.ntua.gr
    (b)Public Power Corporation S.A.
    Greece
  • Introduction
    The Hellenic Public Power Corporation S.A. required the 3D survey of the external and internal surfaces and the production of a 3D solid model of an old cooling tower in order to record its current state, decide for repairs if necessary and investigate the possibility of upgrading it. NTUA was assigned with the task and the details of the survey and the results are presented.
  • Equipment
    HDS2500 (FOV 40ox40o)
    HDS3000 (FOV 360o horizontal and 270o vertical angle)
    spot size = 6mm
    position accuracy = ±6mm (in 50m range)
    Reflectorless total station
    View slide
  • The tower in numbers
    56 m
    80 diagonals
    97 m
    40
    pedestals
    83 m
    View slide
  • The tower in numbers
    Sn: Geodetic station
    Ln: Scanner set up
    26 stations of the geodetic network that was established (3 stations inside the tower)
    2,900 geodetically acquired check points
    22,000,000 points acquired by the laser scanners
    27 scanner set ups
    6 days of fieldwork
  • Registration
    27 scans to register
    20 scans for the interior of the tower
    10 for the lower part
    10 for the upper part
    7 scans for the exterior of the tower
    16 targets were measured and used for registering the 10* scans of lower part of the interior
    20 targets were measured and used for registering the scans of the exterior
    * 10 scans that cover the upper part of the interior were acquired with no targets
  • Registration with no targets
    Object shape
    The top of the tower is a horizontal ring
    Solution approximation
    A plane is fitted on a selection of points that belong on the top horizontal ring and through the coefficients of the equation of the plane the ω and φ rotations that must be applied so that the plane be horizontal are calculated
    Solution refinement
    The upper- and lower- part point clouds are compared via difference vectors that are calculated on a grid defined on the overlapping area and the relative ω and φ rotations and relative translation are thus eliminated
  • Registration
    Cyclone was used for the registration
    All of the scans registered in a common reference system
    For all overlapping scans cloud constraints were created
    There were no common targets nor overlapping scans between the interior and exterior
    Interior: 53 constraints (30 cloud constrains)
    Mean Absolute Error= 5 mm
    Exterior: 39 constraints (7 cloud constraints)
    Mean Absolute Error= 4 mm
  • 3D Modeling for Finite Element Analysis
    Finite Element Analysis (FEA): a computer-based numerical technique for calculating the strength and behavior of engineering structures
    3D Models for FEA:
    Ordinary CAD models are usually unsuitable
    A mesh of a NURBS surface is normally required
    Required formats: IGES, ACIS, STEP and STL
    3D Model characteristics:
    Simplified models
    “Geared” for FEA
  • Data preparation for 3D modeling
    Noise removal
    Creation of different point clouds for the parts of the tower
    Creation of 3D faces for parts that were impossible to scan (e.g. pedestals, inside part of the shell extending from the lintel up until the doorstep)
  • 3D Modeling of the Cooling-Tower
    Data: Laser scanner point clouds and 3D faces
    S/W: Raindrop Geomagic Studio 7
    SHAPE MODE
    PHASE MODE
    Boundary
    definition
    Exporting
    to IGES
    Corrections of
    polygonal mesh
    NURBS creation
    and corrections
    Assembly of
    Tower parts
    Grid
    definition
    Polygonal mesh
    creation
    Patch definition
    and corrections
  • Shape Mode
    Polygonal mesh
    creation
    Assembly of
    Tower parts
    Corrections of
    polygonal mesh
    Boundary
    definition
  • Shape Mode
    Polygonal mesh
    creation
    Assembly of
    Tower parts
    Corrections of
    polygonal mesh
    Boundary
    definition
  • Important corrections
    • Deletion of crossing triangles
    • Deletion of floating triangles
    • Hole filling
    • Spike removal
    • Relaxing
    Shape Mode
    Polygonal mesh
    creation
    Assembly of
    Tower parts
    Corrections of
    polygonal mesh
    Boundary
    definition
  • Shape Mode
    Polygonal mesh
    creation
    Assembly of
    Tower parts
    Corrections of
    polygonal mesh
    Boundary
    definition
  • Phase Mode
    Patch definition
    and corrections
    Grid
    definition
    NURBS creation
    and corrections
    Exporting
    to IGES
  • Phase Mode
    Patch definition
    and corrections
    Grid
    definition
    NURBS creation
    and corrections
    Exporting
    to IGES
  • Phase Mode
    Patch definition
    and corrections
    Grid
    definition
    NURBS creation
    and corrections
    Exporting
    to IGES
  • Phase Mode
    Patch definition
    and corrections
    Grid
    definition
    NURBS creation
    and corrections
    Exporting
    to IGES
  • Accuracy evaluation
    GEODETIC DATA
    1250 geodetically acquired points on the external surface of the tower
    Only 146 points deviate more than ± 3 cm from the polygonal surface model (μ =-1 cm, σ =±1.5 cm)
  • Accuracy evaluation
    MATHEMATICAL SURFACE
    A one-sheeted hyperboloid was fitted on the data and using the equation 18.000 simulation points were calculated
    There are areas where deviations of ±20 cm are observed but the greatest part fits the mathematical model quite well (μ =-2.4 cm, σ =±4cm)
  • Conclusions
    The use of a commercial laser scanner (±6mm at 50m) and the processing of the acquired data with Cyclone (registrations) and Geomagic (3D model generation) leads to results of adequate accuracy and satisfying quality for applications such as this
  • Thank you for your attention