Using NI LabVIEW to Operate a Large-Scale Public Earthquake Simulator

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"Our estimated cost savings regarding software development using LabVIEW is approximately 50 percent. "

- Michael Schulze, Anco Engineers

The Challenge:
Creating an easy-to-use software and hardware solution for controlling large public earthquake simulators.

The Solution:
Using NI LabVIEW software and data acquisition hardware to create a program capable of controlling the motion of the simulator and processing simulated earthquake signatures to produce a realistic experience for users.

Paul Ibanez - Anco Engineers
Michael Schulze - Anco Engineers

Earthquake simulators are used in science parks and museums around the world to educate the public on the effects of seismic events. At Anco Engineers, Inc., we provide systems and services for vibration testing of materials, equipment, and structures, and we are experienced seismic shake table designers for customers worldwide. We set out to develop multimedia drive software for educational shake tables for science parks that would be easy to use and technically realistic. 

We faced two challenges on this project. First, we needed  an easy-to-use, cost-effective hardware and software solution that had multimedia capabilities. The program also required an intuitive user interface that accommodated a variety of different languages. The application had to provide a simple tool for generating theoretical earthquakes with specific spectral energy signatures required to satisfy a variety of conditions such as accommodating spectral responses set forth by building codes in earthquake zones. Both programs have been developed so that museum operators can control these relatively complex systems with ease and very little training.

Previous Limitations

Driving a multiaxis, large stroke shake table is a well-understood science. Integrating hardware with fast computer processors and data acquisition boards has become significantly easier in recent years. However, earlier versions of our driver software were limited to transferring only relatively unprocessed earthquake data to the actuators in a laboratory environment, without more sophisticated signal preprocessing features and multimedia capabilities. Older versions lacked a unified program that gave clients the ability to generate a theoretical quake that simulated specific spectral energy scenarios. Previously, simulated scenarios could not include the effects of building height (resonance), soil composition, and individual quake wave types.

Multimedia Integration and Signal Processing

We chose LabVIEW as the development and deployment tool because of its seamless integration with NI hardware, its parallel programming architecture capabilities, and the multitude of native math and signal analysis functions. We wrote a program to efficiently process a variety of large earthquake signature files containing acceleration time histories. These signature files contained real and simulated earthquake data. Using the 16-bit, two-channel NI PCI-6221 M Series analog voltage output board and a variety of its digital line outputs, the program controls two heavy-duty large stroke displacement actuators, monitors all interlocks and safety features, and simultaneously runs a series of custom-streamed audio and video files through a dual-video graphics array (VGA) output. These videos are then projected onto large viewing screens during the earthquake rides. To enhance the “earthquake” experience, the chosen PCI-6221 board facilitates further control through its many digital output lines that activate flashing lights, smoke machines, and sound effects at selected time intervals and time lengths.

To minimize personnel training needs, a simple graphic user interface (GUI) was the driving force to develop an unintimidating and easy-to-use program. The library of more than 50 real and simulated earthquake scenarios can be used simply by dragging and dropping files within the designated submenus, providing the option of building a series of earthquakes in a matter of minutes. These earthquakes can be linked in batches and executed in sequences that may last a few seconds or several minutes.

Each earthquake has certain characteristic signatures, and its energy distribution is identified by the strength (magnitude on Richter scale), wave frequency, and wave amplitude. During a quake, waveforms propagate differently depending on soil type, and they interact in different ways with buildings, depending on the type of structure. For civil engineers, it is important to model these interactions and generate required response spectra (RRS) for buildings to predict the structure’s behavior during an earthquake.

At Anco Engineers, Inc., we generated a program using native spectral and frequency analysis tools in LabVIEW to compute transient random waveforms based on specific RRS curves. This automated and iterative process generates data in a matter of seconds that satisfies the required energy and frequency distribution of the entered RRS and produces conformance according to the IEEE 344 multiaxis stationary/independence tests.

Overcoming Frequency-Dependent Amplitudes

As with most dynamic large stroke actuators that move large masses, constant amplitudes over a certain frequency range can be a limiting factor. Therefore, specific corrections to the drive signal are made to compensate for a drop in amplitude at higher frequencies. We made provisions for such cases, and our driver software can generate – if needed – these corrections on the fly using system-specific transfer functions. Again, we used the signal processing and filtering function of LabVIEW to significantly simplify our programming efforts so that we could focus on building the public shake table while reducing program development costs.  

Cost Savings Using LabVIEW and NI Hardware

Our estimated cost savings regarding software development using LabVIEW is approximately 50 percent. The flexibility of LabVIEW with respect to its filtering options, spectral functions, seamless integration with NI hardware, and accommodation of complex data sets with mathematical functions made this effort particularly successful. In addition, our theoretical earthquake generation program significantly decreased our data generation time. Generating a specific RRS-qualifying earthquake previously took approximately 20 minutes, but is now complete in a matter of five to 10 seconds. LabVIEW made it possible to produce intuitive, easy-to-use GUIs that require very little training and troubleshooting skill.

Computer and Operating System

We used a standard dual-core PC with 1 GB of RAM with a dual VGA output running Windows XP SP2 OS and with a LabVIEW 8.2 and 8.5 run-time engine. The program suite was developed in the LabVIEW Professional Development System for Windows. We also used the PCI-6221 board connected to an NI BNC-2110 connector block.

Current System Installation

Public educational shake tables are currently being installed at museums and science parks in France, India, and the United States. Some museums are placing the shake table in an earthquake type “disaster zone” with fake crumbled concrete, smoke, and other visual effects that emphasize the importance of earthquake research and building code reinforcement. The average size of the shake table is approximately 4 m (approximately 13 ft) in height and can accommodate six to nine people on multiple platforms.

Author Information:
Michael Schulze
Anco Engineers
1965-A 33rd. St.
Boulder, CO 80301
Tel: 303-443-7580

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