9. ON-SCREEN OPTIONS

Note that the keys used to operate Michlet are case sensitive, i.e. pressing a will give a different result to pressing A.

Also note that Michlet doesn't often ask for confirmation when you press a key to request an action. This can be a bit bewildering for a start, but it is often better than being asked to confirm everything you want to do.

Lines Drawings

This screen shows lines drawings of the vessel as well as geometric and other details.

To see what options are available, press ?. (You must press the Esc key to return to the Lines Drawing screen before using the listed options).

The panel at the right of the screen shows the following quantities:

Note that LCB is given as (metres) from the centre of the hull. Negative LCB means that the LCB is aft of centre.

Other hull plots

If there is more than one hull, press the number corresponding to the hull you want to display.

Other menus

Other menus are available from the Lines Drawing screen. Remember to use upper case letters to invoke these menus:

The options available from these menus will be described in detail later in this section.

Section and waterplane areas

If there is more than one hull in the vessel or ensemble, press the number corresponding to the hull to see the area curve for that particular hull. You can return to the Lines Drawing screen by pressing the Esc key.

Views

There are several views of the vessel available from the Lines Drawing screen. To change the current hull, press the appropriate hull number. E.g. to see details for the second hull, press 2.

Non-dimensional plots are used for the horizontal views because too much detail is lost for thin hulls.

When the vertical sections of more than one hull are displayed, each plot is shown true-scale for that hull only. Thus a small outrigger can look much deeper than a hull with a larger draft.

Editing parameters

Some of the parameters describing the hulls can be changed from the Lines Drawing screen. Pressing the following (lower case) letters will bring up a prompt for you to key in a value and then to press the Enter key. To abort the input, press the Esc key.

If you key in a value that is out of range for a particular parameter, the original value of that parameter will be retained. No warning that this has occured is given in the current version. Always check that the value you have entered has been accepted.

You cannot change the longitudinal or the lateral separation distance for hull 1: its centre is always located at the co-ordinate origin. (Refer to Figure 3.1).

Editing offsets

Please note that offsets cannot be edited if the trim or sinkage have been set to non-zero values.

When the lines drawing of a hull is displayed, one section is highlighted; it is in white while all other sections are in another colour. Also, a small light-red cross is located at one of the waterlines along the highlighted section. To move the highlighted section, use the x and X keys to move backwards or forwards, respectively, through the hull sections. Note that the bowmost section will never be highlighted as it cannot have other than all zero offsets. The sternmost section can be highlighted as that section can have non-zero offsets. (The only signal to Michlet that a hull has a transom stern is the existence of non-zero stern offsets.) To move the red cross from one waterline to the next, use the z and Z keys.

There are two ways to change the value of an offset at the location of the red cross. The first is to press y or Y which decreases or increases (respectively) the highlighted offset by a (non-dimensional) increment. This increment can be changed by pressing I and entering the desired increment. The second method is to input the (non-dimensional) offset directly. To do this press i and then enter the value.

(I've never tried to input an entire hull this way myself. I use these options to fiddle around with bulbs or to do some quick fairing of lines.)

Editing mathematical offset series

Some hull formulae can be specified on-screen. To begin specification of the new (mathematical) hull series, press n. You will prompted to input the appropriate parameters.

On-screen choices include:

Details for these hull series are given in another section of the manual.

Copying offsets

If there is more than one hull loaded, you can copy offsets from other hulls to the currently displayed hull. Press C and then the number corresponding to the hull you wish to copy from. Other parameters such as displacement, length, draft, trim etc., will not be copied.

For example, suppose that there are three hulls loaded and that the current hull is Hull 2. To copy offsets from Hull 3, press C, and then press 3. Hull 2 will now have the same (non-dimensional) offsets as Hull 3.

This feature of Michlet can be very useful for 'evolving' good hull shapes. For example, suppose you have five hulls loaded. You can make small changes to one of the hulls, assess and compare the drag of all hulls, and then replace the worst hull in the collection with the best hull. You could then make further small changes to one of the hulls. Continuing this process should result in a hull 'better' than we started with.

The optimisation module, GODZILLA, is an attempt at automating this evolutionary design process, and is described later in this manual.

Resistance Graphs

There are two main categories of resistance graphs in Michlet, namely hull drag plots, and ship drag plots. Hull drag plots are for each hull considered as if it were the only hull in the ensemble, i.e. wave interference effects between hulls are not relevant. Ship drag plots include wave interference effects between the hulls that comprise the entire ensemble. Of course, for monohulls there is no such interference.

Hull resistance graphs

If there is more than one hull, you can see results for other hulls by pressing the appropriate number when a plot is displayed.

Ship resistance graphs

When any resistance plot is displayed, you can save the plot as a .pcx file. Press S, then enter a filename. The .pcx extension will be appended by Michlet. You cannot save hull resistance data (e.g. by using lowercase s) as can be done in some other Michlet plots. Resistance is saved on exit from the program.

Wave Analysis Plots

Pressing W in the Lines Drawing screen brings up the Wave Analysis module. From here you can edit parameters that control the location at which wave elevations are calculated and also the speed for which the plots will be calculated. The initial values of these parameters are input via the in.mlt file.

To change the speed at which the wave pattern will be calculated, press u and then enter a value. The value entered must lie between the minimum speed and maximum speed specified in the in.mlt file.

Figure 9.1: Polar, longitudinal and transverse wave cuts

In the figure above, the co-ordinate origin is at the centre of Hull 1 (refer back to Figure 3.1).

Available plots are:

To edit the parameters defining the extent of the various cuts and contour domains, press the lower case letter corresponding to the relevant cut or domain. This will bring up a small menu. To then change a particular parameter, press the letter corresponding to that parameter and enter the desired value.

Wave elevations can take quite a long time to compute. For finite depth, considerably more. These times can be reduced by using fewer grid points, but then the plot might not look as clear as for a finer grid. Using a smaller value of Ntheta will reduce calculation time, but accuracy could be seriously impaired. For supercritical depth-based Froude numbers, Ntheta must be very large otherwise the wave pattern will be seen to 'drop out' for large distances from the ship.

The dimensions for the wave elevation patches in the examples have been chosen in order to give a true aspect ratio (or acceptably close).

When either of the two wave elevation patches are displayed, press c to 'clip' the wave pattern above and below a maximum height. For example, if the maximum wave amplitude is 1.0 metre, and a 'clip' value of 0.5 is entered, all amplitudes above 0.5 metres will be in white, all elevations below -0.5 will be black. Note that the wave elevations are not re-calculated, but merely re-displayed with new colours. Some very dramatic patterns can be made by using a very small value (e.g. 0.001).

When any wave elevation plot is displayed, you can save the plot as a .pcx file. Press S, then enter a filename. The .pcx extension will be appended by Michlet. To save wave elevation data press s. Note that in the Demo and Basic versions of Michlet, you will not be able to save wave elevation plots or data.

Ship Motion Graphs

The only plots available are for the experimental sinkage and trim: i.e. the values appearing in the in.mlt file. If these are not specified, plots will not be available.

Pressure Signature Plots

Pressing P in the Lines Drawing screen brings up the Pressure Signature module. From here you can edit parameters that control the location at which bottom pressures are calculated and also the speed for which the plots will be calculated. The initial values of these parameters are input via the in.mlt file.

The method to change the parameters controlling the plot is identical to that used to change rectangular wave elevation plots described earlier in this section.

When the pressure patch is displayed, press c to 'clip' the contour plot above and below a maximum value. For example, if the maximum pressure is 1.0 Pascal, and a 'clip' value of 0.5 is entered, all pressures above 0.5 Pascal will be in red, all elevations below -0.5 will be blue.

When the pressure plot is displayed, you can save the plot as a .pcx file. Press S, then enter a filename. The .pcx extension will be appended by Michlet. To save pressure data press s. Note that in the Demo, Basic and Pro versions of Michlet, you will not be able to save pressure plots or data.


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