Interface hints

Selecting a substrate material

A substrate in SlownessBuddy is defined by its material file, following the TMX standard. Material files should be placed in a unique directory; by default such material files are provided in the ConstMat directory of your SlownessBuddy root directory.

A list of preset cuts can be chosen from to help avoid cut definition errors. The list of preset cuts is defined in the text file cuts.txt of your SlownessBuddy root directory. You can edit this file and add new preset cuts, but be sure to conform to the format of the file that comes with the original distribution!

Choosing an angular range

You have to enter *sensible* values for the min and max angles (as the program is far from being error proof...). It is important to set the number of samples properly if you want that angular samples be spaced nicely: for instance, to obtain values for all angles from 0° to 90° with a 1° step, select 91 samples.

The choice of the number of samples has another implication. The beam-steering and GAMMA are obtained from a finite difference estimation of the first and second derivatives of the slowness as a function of the phase angle. The elementary difference is equal to the step between two consecutive angular samples (this is designed to minimize computations). You might find that using more samples for a given angular range increases the accuracy, or else results in noise if the step is too small! This is a logical side effect.

In FEM/BEM computations, you might be surprised (at least some have been) that two more samples are computed. This is because one more sample on the left of the min angle and one more sample on the right of the max angle are required to estimate the beam-steering and GAMMA for the first and last point.

Setting the output directory

At start-up you are asked to select an output directory. This is where SlownessBuddy stores computation results. The function used to select this directory is a somewhat pirated version of the "modal file dialog" of Windows as available in Compaq Fortran 6.1. Actually it works properly with NT4 but not with Windows 98... (it has not been tested with Win95, Win2000 or XP). Alternatively, set this directory manually in the SBPrefs.dat file (this is located in the directory from which SlownessBuddy is run and stores the configuration of the program).

Setting the initial slowness

Please be advised that the value chosen for the initial slowness is decisive for the algorithms to work properly. Unfortunately, there is no way to know beforehand which value to use and you will have to guess. It is usually safe to select "Slow shear SSBW" for a SAW, "Fast shear SSBW" for a (slow) PSAW, and "Longitudinal SSBW" for a fast PSAW. HOWEVER, whenever the slowness is expected to be very different from a given bulk wave velocity (for instance in a thick grating or under an aluminum layer) try several values before concluding that no wave exists! You will certainly have to be smart here.