OrcaFlex Manual - Orcina

User Interface, Results
Empirical Cumulative Distribution
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This smoothing technique is only applied if there is more than 200s of data in the time history.
From any time history graph you can use the pop-up menu to obtain the empirical cumulative distribution graph for
that time history. This graph shows what proportion of the samples in the time history are less than or equal to a
given value.
These graphs are sometimes referred to as Exceedence Plots since they can sometimes be used to estimate the
probability that the variable will exceed a given value.
Warning: The samples in a time history are not independent. They have what is called 'serial correlation',
which often affects the accuracy of statistical results based on them.
Rainflow half-cycle Empirical Cumulative Distribution
From any time history graph you can use the pop-up menu to obtain the rainflow half-cycle empirical cumulative
distribution graph for that time history. The curve on this graph is produced in the following way:
1. The time history is analysed using the rainflow cycle-counting algorithm. For details of this algorithm see the
paper by Rychlik.
2. The rainflow algorithm produces a list of half-cycles associated with the time history. The empirical cumulative
distribution of these half-cycles is then plotted.
3.9.9 Range Graphs
Range graphs are only available for a selection of variables and they are only available for Lines. They show the
values the variable took, during a specified part of the simulation, as a function of arc length along the Line. In
particular:
� Range graphs show the minimum, mean and maximum values that the variable took during the specified part of
the simulation with the exception that the Line Clearance range graphs only show the minimum value.
� Effective tension range graphs have extra curves showing the segment Euler load and the Allowable Tension
value (as specified on the Line Types data form).
� Bend Moment range graphs have an extra curve showing the maximum permitted bend moment
(EI / Minimum Bend Radius specified on the Line Types data form).
� Curvature range graphs have an extra curve showing the maximum permitted curvature (the reciprocal of the
Minimum Bend Radius specified on the Line Types data form).
� Stress range graphs show the Allowable Stress (as specified on the Line Types data form).
� A Standard Deviation curve can also be added to a range graph – to do this edit the graph's properties (by
double clicking on the graph) and set the Standard Deviation curve's visible property (by default the curves are
not visible). Two curves are then drawn, at Mean ± xσ, where x is a user chosen value and σ is the standard
deviation. The standard deviation is calculated from all the samples that lie in the simulation period chosen for
the graph.
Warning: Be careful not to assume that 95% of the data lie in the interval Mean ± 2σ. This common guideline
is based on the assumption that the data are sampled from a Normal (i.e. Gaussian) distribution.
To obtain a Range Graph:
� Select Range Graph on the Results form.
� Select the object required.
� Select the arc lengths required. This can be the entire line, a selected arc length range, or a selected line section.
� Select the variable required (see Selecting Variables).
� Select the period required.
� CLICK the Graph button.
Range graphs are displayed in Graph Windows and they are "live" – i.e. they are regularly updated during the
simulation. You can therefore set up one or more graph windows at the start of a simulation and watch the graphs
develop as the simulation progresses. If you reset the simulation then the curves will be removed but the graphs will