# Results: Producing results

You can access results by either clicking on the select results button on the toolbar or by using the select results menu item; the select results form then appears. There is a keep open switch on the form's popup menu, which allows you to choose whether the form automatically closes when you select a result, or alternatively stays open (and on top) until you explicitly close it. If the values of a graph are required in text form then click the values button – this give the values in a spreadsheet window.

The select results form allows you to select the results you want by specifying:

### Result type

This option allows you to select which of the various types of results output you require. Results are available as text tables (static state, instantaneous value, summary results, statistics, linked statistics, extreme value statistics, line clashing reports or air gap reports) or as graphs (time histories, cycle histograms, range graphs, XY graphs, spectral density graphs or spectral response graphs). The types of results available depend on the current model state and the solution method.

### Object

The object for which you want results.

### Period

For some result types you must specify the period of the simulation to be included. This can be:

• One of the numbered stages of the simulation.
• The whole simulation.
• A specified period, defined by a start and end time. These time values can be set to '~' which is interpreted as simulation start time and simulation finish time respectively.
• The latest wave (only available for regular wave simulations) which is defined to be the wave period immediately preceding the latest simulation time.
• The static state period.
• The instantaneous value period gives results at the instantaneous calculation state, or the active replay time. When a replay is active, the results are reported for the active replay time. Otherwise the results are for the latest simulated time, or the static state.

### Include restart parent models

For restart analyses, if this option is checked, results from the selected restart parent models are collated.

This option is only available for certain results types: time histories, cycle histograms, range graphs and XY graphs.

### Variable

The desired variable(s).

Definitions of the results can be obtained by selecting them in the variable list box and then pressing F1.

### Frequency domain extreme statistics storm duration

The storm duration for which the most probable maximum is reported after conducting a frequency domain simulation.

## Logging for time domain results

The results tables are taken directly from the current state of the model. All the other results are derived from the simulation log file which OrcaFlex creates automatically when a simulation is run. As the simulation progresses, OrcaFlex samples the variables for each object at regular intervals and stores the sampled values in the log file. All time histories, statistics and range graphs are derived from the simulation log file.

You can control the time resolution of the results by setting the target sample interval data item on the general data form. This must be done before the simulation is started. Decreasing the sample interval will improve the time resolution of the results (and increase the number of samples taken). However, because more samples are taken this will also increase the size of the simulation file that is created.

## Spike logging

A special algorithm is used for logging time domain results that tend to vary rapidly to ensure that any spikes that may occur between samples are recorded. We refer to this algorithm as spike logging. The following variables are spike logged:

• Line results: Effective tension, torque, clash force, clash energy, solid contact force, end force results and vortex force results. In addition other results which are derived from these quantities are effectively spike logged by association. Such variables include wall tension, normalised tension, direct tensile strain, ZZ strain, worst ZZ strain, direct tensile stress, von Mises stress, max von Mises stress and ZZ stress.
• Link results and winch results: Tension and velocity.
• Solid results: Contact force magnitude.
• General results: Implicit solver iteration count and implicit solver time step.

OrcaFlex monitors spike logged variables at every time step and notes the maximum and minimum values that they took since the last log sample. Then, when it is time to take the next log sample, OrcaFlex does not necessarily log the instantaneous value at the time the sample is taken. Instead it logs in such a way that it records both the minimum and maximum value that the variable took during the previous log interval.

How does OrcaFlex record both the maximum and minimum when it's only logging one new sample value? The answer is that as well as (potentially) modifying the new sample OrcaFlex also modifies (if necessary) the previous log sample, which has already been written, but which can be updated.

For example, let the previous sample (already logged) be $X_1$ at sample time $T_1$ and the new instantaneous value be $X_2$ at new sample time $T_2$, and suppose for simplicity that $X_1 \lt X_2$. Also suppose that, in between times $T_1$ and $T_2$, the variable $X$ took a minimum of $X_{\mathrm{min}}$ and a maximum of $X_{\mathrm{max}}$. Then, if $X_{\mathrm{min}} \lt X_1$ and $X_{\mathrm{max}} \gt X_2$, OrcaFlex changes the previous sample from $X_1$ to $X_{\mathrm{min}}$ and the new sample from $X_2$ to $X_{\mathrm{max}}$.

What if the previously logged sample $X_1$ was already recording a maximum spike from the previous log interval? In that case OrcaFlex cannot change the previous sample to $X_{\mathrm{min}}$, since that would lose the recording of that previous spike. To cover this situation, OrcaFlex keeps track of which samples are recording a maximum and which are recording a minimum. If $X_1$ was already recording a maximum (from the previous log interval) then we cannot now use it to record a minimum, so OrcaFlex instead leaves the previous sample recording $X_{\mathrm{max}}$ and uses the new sample to record $X_{\mathrm{min}}$.

The algorithm is rather complex, but the net effect is:

• No spikes are missed, i.e. all minima and maxima are recorded.
• A spike might be reported up to one log sample interval away from when it actually occurred.
• The maximum from one log interval might be combined with the maximum from the next log interval and recorded as a single maximum (the larger) at the intervening sample point.