OrcaFlex Manual - Orcina

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System Modelling: Data and Results, Lines Section Turn 312 w The amount by which the track azimuth increases over this section. A positive value denotes a turn to the left, when viewed from above, and a negative value denotes a turn to the right. A value of zero can be entered to specify a straight track section. Section Radius The radius of curvature of the circular arc. The radius equals (180L)/(πT), where L is the section length and T is the absolute value of section turn, in degrees. For straight sections (i.e. if Section Turn = 0) the radius is reported as Infinity. Notes: This is a reported value, not an editable data item, and is hence always shown in grey. Section X and Y With a profiled or sloping seabed the actual track on the seabed will have a slightly different radius of curvature – see Laying out the Line. The global X and Y coordinates of the end of this track section. You can either edit these X and Y coordinates explicitly, on the line data form, or else by dragging the end point on a 3D view. If you edit X or Y then OrcaFlex fits a circular arc (starting at the previous section's end point) through the new end point and the Section Length and Section Turn are automatically updated to match this new arc. Section Z The global Z coordinate of the section end point on the seabed. This is a reported value, not an editable data item, and is hence always shown in grey. Section Arc Length The total arc length to the end of the section. This is a reported value, not an editable data item, and is hence always shown in grey. Section Azimuth The azimuth direction at the end of the section. This is a reported value, not an editable data item, and is hence always shown in grey. Track Pen This controls how the track is drawn. You can switch between the options of drawing the track in the chosen pen and not drawing it at all. Laying out the Line The track data defines a sequence of straight lines and circular arcs in the horizontal plane, which are then projected vertically onto the seabed to define the track itself. The program then lays the line out along the track, allowing for any As Laid Tension specified by the user on the line data form. Because the line is modelled as a series of straight segments, when the line is laid out along a curved track it will repeatedly 'cut corners' and so the length of line laid along a given curved track section will be slightly shorter than the length of that section. The size of this discrepancy reduces as more segments are used. If End A is above the seabed then the height above the seabed varies linearly between End A and the first track section point, reaching the seabed at the end of the first track section. If the end of the last track section is reached before all the line has been laid out, then the rest of the line is laid out in a straight line in the direction of the end of the track. Sloping and profiled seabeds The track on the seabed is obtained by projecting the specified circular arcs or straight sections vertically down onto the seabed. With a horizontal seabed this vertical projection has no effect on the shape of the track. But with a sloping seabed the vertical projection does not preserve distances and this causes some effects that users should note: � The section lengths and arc lengths that appear in the prescribed starting shape data table are lengths in the horizontal plane, i.e. before projection down onto the seabed. With a sloping seabed the true section and arc lengths on the seabed will differ, the difference depending on the slope of the seabed. The actual arc lengths can be obtained by running the static analysis and looking at the Full Results table for the line.
w 313 System Modelling: Data and Results, Lines � The section radius reported in the prescribed starting shape data table is that of the circular arc in the horizontal plane, i.e. before projection down onto the seabed. When the circular arc is projected down onto a sloping seabed the resulting track section is slightly elliptical rather than circular, so again the actual radius of curvature will differ. The actual radii of curvature can be obtained by running the static analysis and looking at the Full Results table for the line. User Specified Starting Shape Starting Shape The User Specified Starting Shape statics method places each node at the position specified in this table. If torsion is modelled then node orientations can also be specified. Drag and Wake Drag Formulation A number of authors have proposed formulae to model how the drag force on a line varies with the incidence angle. OrcaFlex offers the choice of the Standard, Pode or Eames formulations. All of these use drag coefficients that are specified on the Line Types data form. For details of the formulations see the Line Theory section. Line Wake Interference To include wake interference modelling you must first define one or more wake interference models. See the Wake Models button on the Line data form. You must then specify which line sections to include in wake modelling, by either being included as a wake generator (an 'upstream' section) or as a section that reacts to wake (a 'downstream' section), or both (a downstream section that reacts to wake generated further upstream, but also generates its own wake that further downstream sections might react to). For details see the Line Wake Interference Data on the Drag & Wake page of the Line Data Form. Notes: Wake modelling does not include the wake effect of one part of a line on another part of the same line – it only includes wake effects on other lines. To model the wake effect of one part of a catenary on another part beyond the sag bend, you need to model the catenary as two lines, joined with a dummy 6D buoy at the sag bend. How Wake Effects Are Modelled Also, wake modelling is only included in the static analysis if the Statics Method is set to Whole System Statics. It is not included if the Separate Buoy and Line Statics method is specified. This is because wake effects require that the static positions of the lines involved are calculated together, not separately. The wake models are steady state models of wake effects. Also OrcaFlex does not model the effect that wake takes time to convect downstream. OrcaFlex therefore only attempts to model the steady wake effects. Wake is generated when there is fluid velocity relative to the upstream cylinder, so both fluid motion and upstream cylinder motion can contribute to the wake. Therefore the velocity OrcaFlex uses as the input to the wake model is the steady relative velocity Vs given by Vs = [undisturbed current velocity vector at upstream cylinder centre] - [any steady starting velocity specified for the model] The wake effects therefore do not include any effects of wave motion, or of any changes in upstream cylinder velocity during a simulation. Note: OrcaFlex does not model combined wake effects. If a given 'downstream' node is in the modelled wake of more than one 'upstream' node, then OrcaFlex chooses to apply the wake effects of the upstream node that gives the strongest wake effect at that downstream position when the wake effects from other upstream nodes (which give weaker wake effects at that point) are ignored. So if you are modelling riser arrays, for example, then the wake effects at any given point are modelled as if they came from the upstream wake-generating node that gives largest wake effect in isolation, i.e. as if the other upstream nodes were absent.
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w Orcina Ltd. Daltongate Ulverston
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Contents 4 w 3.4 Libraries 40 3.4.1
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Contents 6 w 5.6 Dynamic Analysis 1
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Contents 8 w 6.5.23 Wave Scatter Co
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Contents 10 w 8.12 Results 444 8.13
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Introduction, Installing OrcaFlex
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Introduction, References and Links
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Introduction, References and Links
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w 2 TUTORIAL 2.1 GETTING STARTED 21
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w 23 Tutorial, Dynamic Analysis sha
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w 3 USER INTERFACE 3.1 INTRODUCTION
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w Simulation Paused 27 User Interfa
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w Keys on Main Window New model Ope
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w Rotate viewpoint left (decrement
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w General: StaticsMethod: Whole Sys
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w A text data file saved by OrcaFle
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w 37 User Interface, Model Browser
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w Cut/Copy Cut or Copy the selected
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w 3.4.1 Using Libraries 41 User Int
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w 43 User Interface, Libraries Once
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w 3.5.1 File Menu New Deletes all o
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w New Vessel New Line New 6D Buoy N
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w 3.5.5 View Menu Change Graphics M
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w Preferences 51 User Interface, Me
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w 53 User Interface, 3D Views 3D Vi
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w 55 User Interface, 3D Views � D
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w 57 User Interface, 3D Views a lin
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w 59 User Interface, 3D Views � F
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w Replay Period 61 User Interface,
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w Frame interval in real time 63 Us
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w Numeric 65 User Interface, Data F
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w � For lines you must specify th
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w 69 User Interface, Results this i
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w 71 User Interface, Results Let th
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w 73 User Interface, Results remain
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w Results 75 User Interface, Result
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w Replays 77 User Interface, Graphs
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w Axes 79 User Interface, Spreadshe
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w Command Line Parameters 81 User I
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w Wire Frame Graphics Codec 83 User
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Automation, Batch Processing Multi-
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Automation, Batch Processing 88 w N
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Automation, Batch Processing Assign
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Automation, Batch Processing Line T
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Automation, Text Data Files Data in
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Automation, Text Data Files SHEAR7L
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Automation, Text Data Files 4.3.2 A
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Automation, Post-processing 108 w F
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Automation, Post-processing 110 w N
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Automation, Post-processing Referen
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Automation, Post-processing Command
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Automation, Post-processing Figure:
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w 5 THEORY 5.1 COORDINATE SYSTEMS 1
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w 125 Theory, Object Connections Di
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w 127 Theory, Static Analysis Final
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w 129 Theory, Static Analysis metho
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w 131 Theory, Dynamic Analysis for
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w Static Starting Position Simulati
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w 135 Theory, Friction Theory The n
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w where μ = magnitude of the vecto
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w 139 Theory, Extreme Value Statist
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w where σ = GPD scale parameter ξ
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w 143 Theory, Environment Theory Th
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w where Pu(z) = Nc(z/D)su(z)D Pu-su
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w 147 Theory, Environment Theory
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w Repenetration Offset After Uplift
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w 151 Theory, Environment Theory sp
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w Extrapolation Stretching 153 Theo
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w 155 Theory, Environment Theory st
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w 157 Theory, Vessel Theory individ
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w 159 Theory, Vessel Theory RAOs ca
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w 161 Theory, Vessel Theory Notes:
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w 163 Theory, Vessel Theory ω is t
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w surge/sway/heave M M.L roll/pitch
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w 167 Theory, Vessel Theory that co
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w 169 Theory, Vessel Theory separat
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w 171 Theory, Vessel Theory At this
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w Segment 1 Segment 2 Segment 3 Act
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w 175 Theory, Line Theory � If to
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w where component of M2 in the Sx2
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w The hysteresis model is described
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w � (90,90,90) sets Ex along -GX,
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w = v1 + p' + ω×p Therefore its a
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w y End A Stress ID z Stress OD O S
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w 5.12.16 Hydrodynamic and Aerodyna
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w 189 Theory, Line Theory Another w
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w Drag Chain Seabed Interaction 191
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w 193 Theory, Line Theory OrcaFlex
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w 195 Theory, 6D Buoy Theory clashi
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w 197 Theory, 6D Buoy Theory For Lu
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w 199 Theory, 6D Buoy Theory (due t
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w 201 Theory, 6D Buoy Theory Note:
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w α is the angle between the relat
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w 5.13.6 Contact Forces Contact For
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w Dynamic Analysis 207 Theory, Winc
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w 209 Theory, Shape Theory Finally,
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Modal Analysis, Theory 432 w For si
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Fatigue Analysis, Commands 436 w Fo
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Fatigue Analysis, Load Cases Data f
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