Figure 1. Bellcore Seismic
Pro/ENGINEER Buttons
Bellcore Response Spectrum Analysis using
ANSYS and Pro/ENGINEER
Andy Bax and Chris Andersen
DRD Technology Corporation
Tulsa, OK
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 |
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 |
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 |
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.
