NEESit MacBook Accelerometer and Video Sensor Platform (iseismograph) for Education and Research

Transcription

1 NEESit MacBook Accelerometer and Video Sensor Platform (iseismograph) for Education and Research Lelli Van Den Einde, Wei Deng, Patrick Wilson, Ahmed Elgamal, and Paul Hubbard University of California, San Diego, Abstract - Current Macintosh laptop computers are equipped with a 3-axis accelerometer that detects sudden shock and impact and enables the hard drive to freeze and save its contents. In addition, the newer Intel-based MacBook and MacBookPro laptops have built-in isight video cameras for use in video conferencing communications. The Network for Earthquake Engineering Simulation (NEES) Cyberinfrastructure Center (NEESit) has exploited these capabilities and has developed an educational and research platform for measurement and recording of vibrations and dynamic response. The system employs the NEESit Real-time data Viewer (RDV) that enables the real-time streaming of acceleration data synchronized with video, and automatically saves data into a database repository (NEEScentral). Through NEEScentral, earthquake engineering students and research collaborators worldwide can access the recorded data online and engage in joint projects, potentially at a worldwide scale. The following paper provides an overview of the information technology framework for the NEESit MacBook Accelerometer and Video Sensor Platform (iseismograph) and its capabilities, and provides an example of its potential for collaboration through a classroom application for undergraduate education in earthquake engineering. Index Terms Data streaming, earthquake engineering, MacBook, real-time. INTRODUCTION Earthquake engineering education initiatives are continuously being developed to provide learning opportunities for students and educators at all levels, as well as continuing education for practitioners. With information technology increasingly being incorporated into the field of earthquake engineering, the development of education and research tools to stimulate interest in engineering and science at the earliest levels and promote the development of future leaders in earthquake engineering mitigation at the undergraduate and graduate levels has been facilitated. The Network for Earthquake Engineering Simulation (NEES) Cyberinfrastructure Center (NEESit) has developed an innovative platform for earthquake engineering education and research making use of commercial off-the-shelf technology and open source software tools. The NEESit MacBook Accelerometer and Video Sensor Platform (iseismograph) makes use of newer Intel-based MacBook and MacBook Pro laptops that are equipped with a 3-axis accelerometer to detect motion and a built-in isight video camera for use in video conferencing communications. It provides a system that enables students and researchers to measure and record vibrations and dynamic response in a laboratory or real-life setting, and archives the data in the NEES central data repository (NEEScentral [1]). The system employs open source software (the NEESit Real-time data Viewer (RDV) [2] and Data Turbine [3] and [4]), which provide an interface and the middleware for viewing realtime, streaming acceleration data synchronized with video. The data is automatically stored into a project in the NEEScentral database, which provides an environment that promotes worldwide collaboration. Highlights of the NEESit MacBook Sensor Platform include: Real-time acceleration data acquisition and video capture Real-time data and video archiving and replay of historical data Synchronization between sensor data and video images Automatic upload of synchronized data into the NEEScentral Data Repository for worldwide access Collaboration platform for sharing data sets. The following paper describes elements of the NEESit MacBook application. Details about the underlying information technology (IT) framework are initially presented followed by an overview of a pilot classroom project applied to an undergraduate earthquake engineering course that utilized the technology. All software and documentation is available for use and can be accessed from the NEESit iseismograph software page [5]. INFORMATION TECHNOLOGY FRAMEWORK I. The MacBook Hardware Most of the recent Macintosh laptop computers today are equipped with a 3-axis accelerometer (Sudden Motion T4A-18

2 Sensor or SMS [6]). The original MacBook Pro uses the Kionix KXM three-axis accelerometer chip, with a dynamic range of +/- 2g and a bandwidth up to 1.5 KHz. The built-in accelerometer helps to freeze the hard drive and save its contents when a sudden motion is detected. The newer Intel-based MacBook and MacBookPro also have built-in isight cameras. Combined with open source software packaged by NEESit (iseismograph), these MacBooks can serve as a flexible, cost-effective and portable education-and-outreach tool. All of these features come in a small package (12.78" x 8.92" x 1.08") based on Apple s specification for a MacBook 13". With proper calibration, they can also be used for real-time gravity or acceleration measurements. II. Using the iseismograph Software to Configure your MacBook System The iseismograph software can be downloaded from NEESit's iseismograph software page [5] and installed on a local MacBook laptop. Once downloaded (Safari by default saves a tar file in the Desktop directory), a Terminal window can be opened (Finder->Go->Utilities->Terminal), and the commands shown in Figure 1 can be executed to extract the files contained in the tar file to the local home directory. Following these commands, three icons will be created on the local desktop, allowing the user to easily launch the required programs to record and upload data. channels show up in the application, as illustrated in the left pane in Figure 3. FIGURE 2 ICONS CREATED ON DESKTOP. FIGURE 3 INITIAL RDV INTERFACE WITH DATA AND VIDEO CHANNELS. FIGURE 1 TERMINAL WINDOW TO EXTRACT FILES. As shown in Figure 2, the first icon is used to clean up any historical data that was previously captured by the iseismograph program, the second icon is used to launch iseismograph to capture the real-time accelerometer data and video, and the third icon is used to upload the recorded data to the NEEScentral data repository (described in further detail in Section IV). After double-clicking on the run_experiment.sh icon, the user should wait for seconds until the green light of the isight camera comes on, and both data and video III. Displaying Synchronized Data Using the Real-time Data Viewer (RDV) and Data Turbine The window shown in Figure 3 is the main user interface for the Real-time Data Viewer (RDV) [2], which was launched by the run_experiment.sh script. RDV provides a graphical display for the user to view and analyze live or archived time-synchronized data from a Data Turbine server ([3] and [4]), which is running in the background to collect and synchronize the data. In iseismograph, the Data Turbine server is setup to archive several hours of data. The data can be streamed in real-time or replayed over the full timeline of recorded data. The run_experiment.sh script also launches two data acquisition programs (sms-rbnb and ISightToRbnb) in the background to stream the accelerometer data and T4A-19

3 video files from the isight camera into the Data Turbine server. As highlighted as numbered boxes in Figure 4, the RDV user interface is composed of five main panels: 1) Control panel; 2) Channels panel; 3) Properties panel; 4) Data Viewing panel; and 5) Event Marker panel. All available channels from the Data Turbine server are listed inside the Channels panel (box 2 in Figure 4), and are organized by source names (for example, Apple Accelerometer, isight). To show the channels available for viewing from a particular source, the user must double-click on the source name. Once the channels are expanded, a new data panel is opened in the Data Viewing panel (box 4 in Figure 4). When channels are selected and data panels are opened, a user can click on the Real-time button on the Control panel (box 1 in Figure 4) to start viewing the real-time streaming of data and video. FIGURE 4 RDV DISPLAYING SYNCHRONIZED DATA AND VIDEO IN REAL-TIME. The Data Viewing panel (box 4 in Figure 4) plots the time-series data for the acceleration in the z-direction directly adjacent to the video panel for the isight camera. During an experiment, these panels can be used to observe the real-time sensor readings and synchronized video. At any time during or after an experiment, clicking on any location on the timeline inside the Control panel (box 1 in Figure 4) will allow the user to replay archived data synchronized with video. When reviewing archived data, the user can click on the Play button inside the Control panel to replay the data at the original data rate. The playback rate can also be adjusted so data is presented slower or faster than real-time to aid in analysis. At the bottom of the RDV window an Event Marker panel (box 5 in Figure 4) allows the user to make notes about important events during an experiment. Once an event marker is added from this panel, it is displayed on the global timeline in the Control panel, which makes it possible to quickly point out "interesting" data points for later review. Additionally, an automated data upload script was created that looks for specific start and stop markers to automatically identify the time range for uploading data to the NEEScentral data repository (automated script is described in more detail in Section V). More information about the RDV user interface can be found in the RDV User Guide [7]. A video demonstrating the iseismograph application can be found on YouTube [8]. IV. Sharing Data via the NEEScentral Data Repository NEEScentral [1] is the data repository for the NEES initiative and provides a collaborative portal environment that allows students and researchers from disparate locations to share data and resources through an easy to use web interface. NEEScentral provides a centralized location for researchers to securely organize, store, and share data and metadata in a non-proprietary format. After obtaining a NEEScentral user account [9], users are able to create private workspaces and invite other registered NEEScentral users to participate. Data residing in NEEScentral can be searched and exported, and customizable reports can be generated. Refer to the NEEScentral User Guide for more detailed information about the features and how to use the data repository [10]. NEEScentral is organized in a conceptual hierarchy as shown in Figure 5. The hierarchy provides a single, highlevel, standardized model for storing data that is universal to all disciplines in the earthquake engineering community. The organizational hierarchy is based on four directory levels: project, experiment or simulation, trial or run, and data. At the coarsest level of the hierarchy is the project directory, which provides a general container for secure data sharing within a collaborative team. The second level provides extensive mechanisms for inputting metadata about the setup of an experiment or simulation, including information about input motions, coordinate spaces, sensor location plans, and scale factors. Experiments and simulations contain one or more trials or runs that define further changes to configuration parameters. At the lowest level of the hierarchy are directories for archiving the data associated with each experiment. NEEScentral also provides the capability to create unstructured projects where users can create their own directory structure rather than using the NEES hierarchy as described in Figure 5. FIGURE 5 NEESCENTRAL PROJECT HIERARCHY STRUCTURE. T4A-20

4 The NEESit iseismograph has been integrated directly with NEEScentral allowing the synchronized data and video captured with the system to be uploaded automatically to the NEEScentral data repository. The tool used for automatic upload is described in more detail in the following section. V. Automatic Transmission of Data Wirelessly into NEEScentral Once the data is successfully captured in the Data Turbine server s archive, the upload_data.sh script can be executed to transmit data via MacBook s wireless network interface into the NEEScentral data repository. To use this script, the MacBook needs to be verified to have Internet access via its wireless network interface. The best way to verify this is to use a browser to access and check if the webpage can be shown. After launching the upload_data.sh script, it will ask a number of questions that describe where the data is to be uploaded in the NEEScentral data repository (such as NEEScentral login information, the project and experiment where the data will reside, etc) (refer to Figure 6). Once this information is inputted, the data is automatically transmitted into the NEEScentral data repository. FIGURE 6 INTERACTIVE DATA UPLOAD SCRIPT. document providing general recommendations for instructors wishing to effectively use the iseismograph system in a classroom exercise similar to this earthquake engineering pilot program can be found in [11]. I. Project Objective Developing an understanding of fundamental principles of structural dynamics is critical at the most basic level in earthquake engineering. The objective of this classroom exercise was to create an experimental configuration that students with limited or no exposure to these fundamental principles could use to measure dynamic properties of an actual physical structure. The UCSD pilot project demonstrated measurement of the first natural frequency and damping ratio of an adjustable length cantilever beam in free vibration. By imposing a displacement on the beam and measuring the acceleration response after the beam is released, these dynamic properties were determined. Length of the cantilever beam was varied to demonstrate the effects of changing the length in the free vibration response. II. Experiment Setup A simple structure was constructed for this experiment, which consisted of a 9' long timber beam of known elastic modulus that was attached to the top of a heavy concrete block by an adjustable clamp (Figure 7). A rigid fixity was assumed at the clamp. To minimize the impact of the MacBook mass on the free vibration response, it was secured to the beam near the clamped end. The length of the cantilever beam was considered to be the length from the clamp to the end of the beam. Students were able to easily change the beam length by loosening the clamp and pulling or pushing the beam. A pilot earthquake engineering classroom project, which was conducted utilizing the NEESit iseismograph platform, is described in the following section and includes high level instructions for how to use the technology to understand the dynamic response of a cantilever beam. To support this educational example, a special project was created in NEEScentral and each student in the class was given login access to the shared workspace. In addition to promoting the basic understanding of earthquake engineering concepts, the NEEScentral collaborative environment also provides the opportunity to increase the technological capabilities of the students. PILOT EARTHQUAKE ENGINEERING CLASSROOM PROJECT Assessment of the functionality and potential for educational application of the iseismograph system was made through a pilot classroom project conducted at the University of California, San Diego (UCSD). Approximately 90 students participated in this exercise as a project for an undergraduate earthquake engineering course. Benefits to the students included visual and quantitative demonstration of basic dynamic principles and early exposure to methods of data acquisition and processing of experimental data. A III. Class Logistics FIGURE 7 FREE VIBRATION TESTING APPARATUS. Several simple steps were required in preparation for conducting the class experiment utilizing the NEESit software and services. Initially, the instructor and each student were required to register for a free account at T4A-21

5 NEEScentral [9]. A class project was created at NEEScentral and an Experiment was created under the project. Each student was added as a member of the project and experiment, and was given privileges to view, create and edit the project. This allowed them the proper permissions to upload and download data to and from the site. For the pilot project, students were divided into teams of six students. For each team, a trial was created under the project experiment in NEEScentral. This allowed each team to send their data to their respective trial. With the project, experiment and trials created in NEEScentral, and the appropriate privileges given to the students, each team was able to conduct the experiment and automatically archive their data in NEEScentral by following the instructions found in the experimental procedure handout [12]. The use of NEEScentral as a collaboration environment to share data and course documents can be applied to many kinds of educational applications regardless of the use of the iseismograph platform. IV. Representative classroom data sets Each team of students was required to submit a report describing the classroom project which included a comparison of theoretical predictions and experimental results for the pilot cantilever beam experiment. Theoretical analysis included predicting the natural frequency of vibration, (ω) of the cantilever beam based on (1), where E is the modulus of elasticity (assumed as 1350 ksi for the wood used in this experimented), I is the mass moment of inertia as calculated by (2), and b, h, L, and m are the beam width, beam thickness, beam length, and mass of the beam per unit length (assumed as 0.2 lb/in), respectively. For simplicity, the mass of the MacBook was ignored (recall that the MacBook should be secured near the clamped end of the beam to minimize its impact on the natural frequency of the beam). Students analyzed the data by reviewing the acceleration response graph from the experiment. An example is shown in Figure 8 for the case where the cantilever beam length was 77.7". During the experiment, students recorded the beam width (b = 15.4") and thickness (h = "). Using these measured dimensions as well as given properties and equations, the theoretically predicted natural frequency could be determined. For the described example case, the theoretical natural frequency was calculated as 14.2 rad/sec or 2.3 Hz. The students were able to evaluate the experimental natural frequency by counting the peaks in the acceleration response graph (Figure 8) over a given period of time. For this case, the observed natural frequency was 2.4 (1) (2) Hz. Students also used the logarithmic decrement method to approximate the observed damping in the beam [13]. Following the analysis of their own data, each team was able to download data from other teams, approximate the natural frequency from the experimental acceleration response graph and back-calculate the length of the beam that was used during other experiments. FIGURE 8 EXPERIMENTAL ACCELERATION RESPONSE OF CANTILEVER BEAM. SUMMARY: POTENTIAL FOR EDUCATION AND RESEARCH The pilot earthquake engineering classroom project described herein provides an example use case for the NEESit MacBook Accelerometer and Video Sensor Platform (iseismograph) for educational purposes that allows simple earthquake engineering concepts to be introduced in a novel manner. The unique collaborative framework shows great potential for other education and research efforts. Because the MacBook laptop hardware provides an inexpensive sensor and data acquisition system, it can be placed in the field (such as mounted on a bridge) and used for real-time health monitoring applications. The framework provides the essential elements to allow for automated on-line continuous monitoring of structural systems. Data streamed in real-time from the accelerometer and the isight video camera enables researchers and students to remotely observe the performance and vibration response of the structural systems. Because of the regular automated archival of the data into the NEEScentral Data Repository, researchers can access archived data for further analyses. Furthermore, if left in a data acquiring mode, the NEESit iseismograph system can serve as a live seismograph that measures acceleration and captures video during a real earthquake event. Other similar software development efforts have leveraged the MacBook technology [15], or have used similar SMS sensor technology for IBM Thinkpad laptops with a Linux operating system [16]. T4A-22

6 ACKNOWLEDGMENT The authors would like to acknowledge Jason Hanley, Moji Soltani and Terry Weymouth for their software development contributions to this platform, and the National Science Foundation for funding this effort through the Network for Earthquake Engineering Simulation (NEES) effort (Award CMS ). Furthermore, the authors would like to acknowledge CREARE [3] and the Open Source Data Turbine Initiative [4] for their contributions to developing the middleware that supports this iseismograph platform. One of the data acquisition programs (sms-rbnb) used in this platform was built on the SMS Java Library [17]. REFERENCES [1] NEEScentral Data Repository: [2] NEESit RDV Software Page: [3] CREARE Commercial Data Turbine Software: [4] Open Source Data Turbine Initiative: [5] NEESit iseismograph software page: [6] MacBook Sudden Motion Sensor [7] RDV User Guide: [8] YouTube Video of iseismograph: [9] NEEScentral User Account Page: [10] NEEScentral User Guide: [11] Deng, W., and Wilson, P., Using iseismograph and the NEEScentral Data Repository for Earthquake Engineering Experiments, NEESit, TN , Cantilever-Beam-Experiment-Instructions.pdf. [12] Wilson, P., and Deng, W., Cantilever Beam Experiment using the NEEScentral Data Sharing Archive, NEESit, TN , Beam-Experiment.pdf. [13] Chopra, A. K., (2001). Dynamics of Structures, Second Edition, Prentice Hall, Upper Saddle River, New Jersey: p. 52. [14] [15] Apple Software application (SeisMac): [16] SMS on Thinkpad/Linux [17] SMS Java Library: AUTHOR INFORMATION Lelli Van Den Einde Assistant Director, NEES Cyberinfrastructure Center, San Diego Supercomputer Center, University of California, San Diego, Wei Deng, Production Infrastructure Support Manager, NEES Cyberinfrastructure Center, San Diego Supercomputer Center, University of California, San Diego, Patrick Wilson, Graduate Student, Department of Structural Engineering, University of California, San Diego, Ahmed Elgamal, Professor, Department of Structural Engineering, University of California, San Diego, Paul Hubbard, Software Developer and co-pi, CLEOS, San Diego Supercomputer Center, University of California, San Diego, T4A-23