Welcome to Dr. Layer
1.0. This User's Guide is designed to provide a brief overview of what
Dr. Layer can do, and to present the basic mechanisms for using the program.
Virtually all the functionality of the program is also presented in the
accompanying exercises, and since the exercises present the program features
in the context of the underlying concepts and principles, they provide
the recommended way to be introduced to the program. The material here
is useful for quick reference and review, and presumes a reasonable knowledge
of wave propagation modeling and analysis.
Dr. Layer's operation is controlled via menu commands
(with associated keyboard accelerators), manipulation
tools, scale buttons, the load
tool bar, and time control buttons. The
program displays the results of its calculations visually in the form
of animated displacements, and also in the form of dynamically generated
time history plots. There are also mechanisms for getting numerical values.
The simplest way to see the program in action is to simply start it up
and press and hold down the 'g' key (for "go") on the keyboard.
This causes time to run forward, and one can observe the corresponding
wave propagation for the default program configuration.
Time can be controlled using either the keyboard or the time control
- To run time forward: Press and hold the 'g' key or click and
hold the time forward button:.
- To reset time to zero: Type the '0' key or click on the time
- The current analysis time is displayed in the feedback pane
at the bottom of the screen.
- The analysis time step size can be controlled via the Time Step menu
(there are combinations of material properties and time steps that intentionally
lead to unstable results, so beware).
- The display time step can be controlled via the Animation Speed menu.
Internally, this command controls how many analysis time steps are computed
between screen updates.
Dr. Layer's tool palette is illustrated below (Windows version: the Mac
version is similar but grouped a bit differently):
- The Arrow Tool is used to select and manipulate objects.
- The Panner and Camera Orbit Tools are used to change
the viewing point and camera orientation via clicking and dragging.
- The Plot Box Tool is used to create
one of the various types of plot boxes:
- Displacement time history plots are created by clicking
on the relevant layer. The top node in the layer is used as the
- Fast Fourier Transform (FFT) plots of a displacement
history can be created by clicking on the time history plot.
- Stress-strain plots can be created by control-clicking
(i.e., holding down the control key while clicking) on the desired
Dr. Layer has a suite of scaling buttons for adjusting various aspects
of the display. The Windows version scaling toolbar is shown below (again,
the Mac version has the same tools, but uses a different grouping):
These controls are self-explanatory in regards to their functions. Note
the following, however:
scaling buttons will continue to scale as long as they are held down.
It is not necessary to click multiple times to get this effect.
The Zoom In/Out functionality
is also available via the keyboard: type and hold 'a' to zoom in,
and 'A' (i.e., shift-A) to zoom out.
Plot boxes are used by Dr. Layer to display various characteristics of
a given layer motion. There are three types of plot boxes available:
- Displacement time history plots show the displacement of the
top point of the layer to which they are attached as a function of time.
- Fast Fourier Transform (FFT) plots display the
frequency content of the displacement time history to which they are
- Stress-strain plots show the stress-strain response of the
top material element within the layer to which it is attached.
The figure below shows an example of each of these plot boxes:
- To create a plot box, use the Plot Box
Tool to click (or control-click in the case of a stress-strain plot)
on the desired layer or plot.
- To relocate a plot box, click and drag it by either its gray
header bar or its bottom/side outline border.
- To remove a plot box, click in the close box on the right side
of the header bar, or click anywhere on the plot box to select it, and
then type the Delete key.
- To see a numerical value for a displacement time history, click
on the plot at the desired location, and the corresponding time/displacement
values will be displayed in the feedback pane at the bottom of the screen:
general, plots will automatically scroll as necessary as time is running.
Once you have manually scrolled a plot, though, the automatic scrolling
will cease until time is reset to zero.
- Plot boxes can be added or removed at any time, but they only accumulate
data beginning from the time they are installed, with the exception
of FFT plots, which always plot the according to the data accumulated
in the target time history. FFT plots can use up to the first 1024 points
in a time history.
Plotting FFT's will slow down the animation speed significantly,
especially as the length of the time histories increase.
Dr. Layer has a number of application-specific menu commands. The relevant
portion of the menu bar is shown below:
- Wave Speed settings are layer-specific: to assign a particular
layer a new wave speed, select it using the Arrow Tool, and then choose
the desired wave speed from the Wave Speed menu. Multiple layers can
be selected by shift-clicking, and all layers can be selected quickly
via the Select All Layers command in the Edit menu (Ctrl-A/Cmd-A keyboard
- Damping settings are global: i.e., they are applied uniformly
to all layers.
- Time Step settings control the size of the time step used for
the numerical integration.
|As mentioned above, there are unstable combinations
of material properties and time steps built into the program intentionally.
If you observe the layers disappearing from view, stop time running,
reset, and choose a smaller time step.
- Animation Speed settings control the frequency at which screen
updates are drawn. At the slowest setting, Dr. Layer redraws the scene
after every time step. At the faster settings, the redrawing occurs
- The Options menu contains a variety of commands and settings.
The menu itself is shown below:
- The Units and Number Formatting commands bring up
dialogs for choosing units and significant figure display.
- The Released Base option is only available for Pulse and
Ramp Loads. After the pulse or ramp load has been applied, the base
node will be given a stress-free boundary condition, and so both the
top an bottom of the layer assemblage will reflect waves in the same
- The Radiation Damping option is only available in combination
with the Released Base option. The base node is given a special damping
value that models a semi-infinite layer: i.e., the boundary reflection
- The Material Model command brings up the dialog box shown
below, which can be used to set material behavior parameters. Note
that the elastic stiffness and density values are set implictly via
the Wave Speed menu commands.
- The Plot Ground Motion command causes a plot box to be attached
to the base node of the layer stack. Such a plot box already exists
by default, but in the event it gets deleted, this command will cause
a new one to be installed.
- The Wire Frame Layers command results in the layer display
showing a mesh rather than solid colors. This can be useful to see
certain aspects of a motion more clearly. A zoomed-in view of a wire
mesh depiction is shown below:
- The Grid popup menu allows one to adjust aspects of the
Load Tool Bar
The ground motion can be set and controlled via the Load Tool Bar,
the Windows version of which is shown below:
- The Load Popup allows you to choose any of the four built-in
ground motions indicated below. The Sinusoidal, Pulse, and Ramp loadings
are all displacement controlled, while the Earthquake load is acceleration