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The telecommunications industry manufactures
sophisticated electronics equipment that is subjected to harsh environmental
conditions. Large sheetmetal cabinets which resemble household refrigerators may
contain equipment that handle tasks such as transmitting and receiving cellular
phone signals. The electronics equipment in these cabinets must function with
practically perfect reliability while subjected to loads due to wind, rain,
floods, solar heating, internal heat generation, transportation and
installation, and earthquakes. This industry is able to enjoy a tremendous
return on investment in finite element analysis because of the combination of
short product development cycles, ever increasing performance requirements, time
and expenses for creating and testing prototypes, and severe mechanical loads
associated with electronics cabinets.
Many manufacturers of telecommunications
equipment cabinets design and test their products according to a set of
standards from the Bell Communications Research (Bellcore) code. One of the most
challenging parts of the Bellcore code for mechanical design engineers is a set
of response spectra that represent seismic loads due to earthquakes. ANSYS in
combination with Pro/ENGINEER is a powerful tool set for performing seismic
analysis according to the Bellcore code.
Pro/ENGINEER is a de facto standard for design
and solid modeling in the telecommunications industry. Pro/MESH, a module of
Pro/ENGINEER, is used to create an ANSYS finite element model that is fully
associative to the Pro/ENGINEER model and all deliverables. Pro/MESH is uniquely
capable of creating ANSYS finite element meshes of telecommunications cabinets
because of its ability to convert an assembly of 3D solid parts of an
electronics cabinet to a shell finite element mesh. ANSYS performs the response
spectrum finite element analysis.
| A response spectrum is a curve
that represents the maximum accelerations, velocities, or displacements for
single degree of freedom systems subject to a dynamic event such as an
earthquake. If the natural frequency of a single degree of freedom system is
known, then the response spectrum curve can be used determine that maximum
acceleration exhibited by that single degree of freedom system during an
earthquake. There are 4 Bellcore response spectrum curves that correspond to
4 different geographical zones in the United States. A telecommunications
product such as a cable TV or cellular phone cabinet is tested using the
response spectrum that corresponds to the geographical location in which the
cabinet will be installed. Since the Zone 4 response spectrum is the most
severe spectrum, the Zone 4 response spectrum is most often used to test and
certify the equipment. |
Figure 1. Bellcore
Seismic
Pro/ENGINEER Buttons |
ANSYS performs response spectrum analysis in a
sequence of steps. ANSYS first calculates the natural frequencies of the finite
element model. Next, ANSYS scales each mode according to the mode's natural
frequency and its corresponding acceleration on the response spectrum curve.
Finally, ANSYS combines the modes to create a total system response.
Figure 2. Response
Spectrum Curve
Plotted in Pro/ENGINEER |
The
ANSYS-Pro/ENGINEER Interface (APEI) from ANSYS and a product called the
Bellcore Response Spectrum Library from DRD Technology enable casual FEA
users to perform this type of analysis using ANSYS while working entirely in
Pro/ENGINEER. The ANSYS-Pro/ENGINEER Interface enables a Pro/ENGINEER user
to perform simple types of ANSYS analysis such as linear static and normal
modes solutions entirely from within the Pro/ENGINEER graphical user
interface (GUI). The APEI also allows ANSYS results to be reviewed and
Pro/ENGINEER parts and assemblies to be optimized from the Pro/ENGINEER GUI. |
The APEI is frequently bundled with a subset of
the ANSYS solver in a product called ANSYS/ProFEA. The APEI, however, can be
bundled with any ANSYS solver so that all types of ANSYS analysis can be
performed from the Pro/ENGINEER GUI. The APEI does not automatically support all
of the analysis capabilities in the complete ANSYS product, but it provides
tools for customizing the Pro/ENGINEER GUI so that any capability in the
complete ANSYS product can be accessed. The Bellcore Response Spectrum Library
is an example of how the APEI can be customized.
The Bellcore
Response Spectrum Library provides a set of buttons in the Pro/ENGINEER GUI
so that the any of the 4 Bellcore Zone response spectrum curves can be
selected for analysis. Figure 1 shows the set of 4 response spectra buttons
that the Bellcore Response Spectrum Library provides. After selecting a
specific response spectrum, the response spectrum curve can be viewed
graphically as shown in Figure 2. The appropriate analysis options are
automatically set so that the response spectrum analysis is performed when
the analysis button that initiates a problem solution is selected. There is
also a custom button that automatically combines the vibration modes for
postprocessing. Figure 3 shows the GUI button for combining the modes and
the stresses for a cabinet that result from combining the modes. Since the
ANSYS finite element model is fully associative with the Pro/ENGINEER model
and all of its deliverables, Pro/ENGINEER models of telecommunications
cabinets can be efficiently optimized according to their Bellcore response
spectrum behavior. |
Figure 3. Stress
Contours from
Seismic Analysis |
DRD provides implementation services for
companies that want to do Bellcore seismic analysis using the Bellcore Response
Spectrum Library, including a custom version of the ANSYS dynamics course.
You can obtain additional information on the Bellcore Response Spectrum Library
from DRD Technology Corporation.
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