The ACEL,OMEGA, and DOMEGA commands specify acceleration, angular velocity, and angular accel-
eration, respectively, in global Cartesian directions. The CMACEL command is similar to the ACEL
command, except that the translational acceleration applies to a component and not the whole structure.
NoteThe ACEL command applies an acceleration field (not gravity) to a body. Therefore, to apply
gravity to act in the negative Y direction, you should specify a positive Y acceleration.Use the CGOMGA and DCGOMG commands to specify angular velocity and angular acceleration of a
spinning body which is itself revolving about another reference coordinate system. The CGLOC command
specifies the location of the reference system with respect to the global Cartesian origin. You can use
these commands, for example, to include Coriolis effects in a static analysis.
You can also use the CMOMEGA and CMDOMEGA commands to specify the rotational velocity and
acceleration effects for element components you define. You either specify an axis and the scalar vector
quantity, or define the three components of the rotational value and the point in space you are consid-
ering. You can use these commands for Element components only.
Inertia loads are effective only if your model has some mass, which is usually supplied by a density
specification. (You can also supply mass to the model by using mass elements, such as MASS21, but
density is more commonly used and is more convenient.) As with all other data, the program requires
you to use consistent units for mass. If you are accustomed to the U. S. Customary system of units, you
might sometimes wish to use weight density (lb/in^3 ) instead of mass density (lb-sec^2 /in/in^3 ), for conveni-
ence.
Use weight density in place of mass density only under these conditions:
- The model only be used in a static analysis.
- No angular velocity or angular acceleration is applied.
- Gravitational acceleration is unity (g = 1.0).
A handy way to specify density so that you can use it readily in either a "convenient," weight-density
form or "consistent," mass-density form is to define a parameter for gravitational acceleration, g:
Table 2.9: Ways of Specifying Density
Convenient Form Consistent Form Description
g = 1.0 g = 386.0 Parameter definition
MP,DENS,1,0.283/g MP,DENS,1,0.283/g Density of steel
ACEL,,g ACEL,,g Gravity load2.5.10. Applying Ocean Loads
Ocean loading includes the effects of waves, current, drag, and buoyancy. Loading is input globally via
the ocean family of commands (OCxxxxxx).
Three ocean-loading input groups exist:
- Basic (required for any ocean loading)
Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential informationApplying Loads