Measuring and Analyzing the Effects of Waves in an Experimental Basin Using PXI Express

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"With the PXI standard, we can acquire and measure distributed data by integrating up to 18 dedicated modules per chassis. This modular concept facilitates software development because the capturing, processing, and analyzing modules are independently designed, but we can perform the execution as a whole, either in sequences or in parallel."

- Álvaro Álvarez Vázquez, Instituto de Hidráulica de Cantabria

The Challenge:
Creating an instrumentation and measurement system to enhance education and research in the laboratories at the Environmental Hydraulics Institute of Cantabria.

The Solution:
Using PXI Express and GPIB products to create a system that integrates different interfaces to acquire, process, and analyze signals; perform automatic calibration; and visualize and analyze results.

Author(s):
Álvaro Álvarez Vázquez - Instituto de Hidráulica de Cantabria
Pedro Lomónaco - Instituto Hidráulico de Cantabria
Christian Klinghammer - Instituto Hidráulico de Cantabria
Andrés Mendoza - Instituto Hidráulico de Cantabria

The Cantabria Coastal and Ocean Basin (CCOB) is a group of three experimental systems integrated for marine engineering research. It consists of an experimental management system, a physical modeling system, and a numerical modeling system.

System Setup

The physical modeling system performs tests to measure hydrodynamic processes and wave-structure interactions that include the effects of sediment transport, tsunamis, wave-current interaction, and wind. It consists of a tank with multidirectional waves, currents, and wind that can operate in a range of depths (from shallow to deep waters), as well as a wave and current flume able to generate solitary waves representing a tsunami wave.

The numerical modeling system includes several bidimensional and tridimensional models that virtually represent the flume and the basin. It is a numerical mirror of the physical modeling facilities.

The experimental managing system integrates the numerical and physical modeling systems so we can optimize the design, construction, and measurement process during the tests in the physical model; calibrate and validate the numerical mirrors against the test results; and generate additional numerical cases that support alternative designs that extend the applicability of empirical formulations.

Figure 1 shows the CCOB’s wave basin, which is the most relevant experimental facility in the system. It can carry out marine and coastal engineering tests in any depth range, from deep waters to coastal areas. It can generate multidirectional waves, omnidirectional currents and winds, and has a 6 m diameter pit to test marine platforms in deep waters, as well to experiment with measuring instruments and submarine-maneuver training.

Data Capture

We can use the CCOB physical modeling system to directly compare any phenomena or parameter characterized with a numerical model. As an initial result for any trial or test performed, we must perform measurements based on the models and phenomena simulated. Thus, we need a series of sensors—from free surface movement sensors, dynamic pressure, load cells, anemometers, strain gages, ultrasonic distance measurement devices, laser systems, video images or photographs—within an integrated system that can combine the captured data and synchronize the different events as they occur for later analysis and extraction of results.

To accomplish this, we created a system based on PXI Express with GPIB connectivity devices, Ethernet, RS232, RS485, IEEE 1394, multifunction DAQ devices, and NI BNC-2090A connector blocks mounted on racks.

We developed the system on a rack structure for easy expansion, connectivity, and transportation. The rack structure includes a keyboard, video, mouse console for simple operation and local configuration of the entire system (see Figure 2).

With the system we created, we can

  • Capture various signals (such as analog, digital, voltage, current, images, and streaming) in a combined and synchronized manner at sampling speeds that exceed several kHz, which meets the Nyquist Theorem with ease in all available sensors.
  • Control the start and fire the signals to measure using internal or external triggers, depending on the test’s requirements.
  • Obtain continuous data acquisition during long periods of time because the system is connected, via a Gigabit Ethernet fiber-optic network, to a high-capacity data storage server. For local test, the 500 GB controller’s hard disk gives us high recording autonomy.
  • Visualize the measurements taken in real time, program certain system alerts, and graphically represent and record results using NI LabVIEW software or specific tools developed with the PXI system’s programming libraries.
  • Calibrate and adjust all sensors manually, with the user controlling each status or level used as reference values, or automatically, letting the system control the calibration tool and the equipment to calibrate.
  • Visualize real-time processing and postprocessing for the combination of different magnitudes within the same measurement parameter (for example, weighting the acceleration of an object and the deformation of a load cell to obtain the force caused by the object) and perform data postprocessing using tools such as NI DIAdem software or MathWorks, Inc. MATLAB® software.

Conclusion

We equipped Cantabria Environmental Hydraulic Institute with a measurement system based on the PXI Express architecture to acquire and measure data in CCOB laboratory’s experiments and tests.

With the PXI standard, we can acquire and measure distributed data by integrating up to 18 dedicated modules per chassis. This modular concept facilitates software development because the capturing, processing, and analyzing modules are independently designed, but we can perform the execution as a whole, either in sequences or in parallel.

We created instrumentation systems that can successfully facilitate an experimental management system that combines the physical test results with the numerical results, a basic work tool needed in the projects carried out by the Environmental Hydraulic Institute of Cantabria.

MATLAB® is a registered trademark of MathWorks, Inc.

Author Information:
Álvaro Álvarez Vázquez
Instituto de Hidráulica de Cantabria
Spain

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