Shape Sensing Innovations Dramatically Improve Structural Design Tools

sensors
Shape Sensing Innovations Dramatically Improve Structural Design Tools (DRC-TOPS-24)
Useful for transportation, infrastructure, and aerospace
Overview
Advances in fiber optic shape sensing developed at NASA's Armstrong Flight Research Center are enabling the development of next-generation flexible aircraft wings that maximize structural efficiency and reduce weight, improving fuel efficiency. These same advances will help engineers design stronger bridges, buildings, ocean vessels, and more. Fast algorithms use distributed fiber optic wavelength data to determine shape deformation of large curved and flexible structures. Dramatically improving upon earlier two- and three-dimensional (2D and 3D) shape-sensing tools by tracking multiple orientation angles—displacement, twist, and rotation—at the same time, Armstrong's technology converts distributed surface strain data into deformed shapes that can be displayed and analyzed in real time. Developed to help NASA researchers characterize complex test articles and design new aerospace structures, the innovations also will be useful for multiple applications in the transportation, infrastructure, and medical industries.

The Technology
Armstrong's technologies provide a convenient way to calculate distributed deformed orientation angles—that is, roll, pitch, and yaw—as well as determine the deformed shape of an object in 3D space. Developed to facilitate monitoring and control of flexible aircraft designs when used in conjunction with Armstrong's multi-patented FOSS technology, these new tools improve shape-sensing accuracy for highly deformable structures such as bridges, wind turbines, robotic instruments, and much more. These tools also can be integrated into commercial fiber optic sensing systems. How It Works Researchers developed a technology that uses curved displacement transfer functions to determine 3D shape and calculate the operational load of a structure. It works by dividing the structure into multiple small domains, whose junctures match sensing stations, so that data is collected in a piecewise, nonlinear fashion. The innovation calculates structural stiffness (bending and torsion) and operational loads (bending moments, shear loads, and torques) in near real time. The method tracks rotations and orientation by employing quaternion mathematical operations, a faster process than rotation matrices used in previous shape-sensing algorithms. The result is an algorithm that can track multiple angles—displacement, twist, and rotation—at the same time to enable curvilinear shaping sensing. Armstrong researchers have validated the method on the large-scale passive aeroelastic tailored (PAT) wing. Why It Is Better These new technologies advance the ability of fiber optic sensing systems to determine the shape and operational loads of nonlinear flexible surfaces. They can improve the structural integrity of a range of large structures—from buildings and bridges to ocean vessels and aircraft. These innovations reliably provide highly accurate critical information in real time, enabling corrective action to avert disasters. For more information about the full portfolio of FOSS technologies, see DRC-TOPS-37 or visit https://technology-afrc.ndc.nasa.gov/featurestory/fiber-optic-sensing
Benefits
  • Improved safety: Monitors structural deformations of large structures
  • Increased accuracy: Improves 3D shape-sensing accuracy for highly flexible structures by recording distributed twist
  • Real time: Enables quaternion-based mathematical operations, which are computationally faster than more commonly used rotation matrices
  • Compatible: Works with a range of fiber optic sensing systems, including NASA's award-winning Fiber Optic Sensing System (FOSS) portfolio

Applications
  • Transportation and Infrastructure Structural health monitoring of buildings, bridges, oil platforms, ocean vessels, wind turbines, and other large structuresLoad balancing on cargo shipsDesigning truck and automobile frames and suspension for dynamic control and handling
  • AerospaceReal-time structural health monitoring Controlling flexible aircraft wings and morphing structuresRefueling unmanned aerial vehicles (UAVs) in flightDesigning aircraft structures
  • MedicalPerforming robotic surgeryEvaluating anthropomorphic test figures
Technology Details

sensors
DRC-TOPS-24
DRC-016-040 DRC-017-024
Presentation of wing load test results, January 2019 https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20190000062.pdf

Paper presented at AIAA SciTech Forum 2019 https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20190000082.pdf
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This technology can be applied to most optical frequency domain reflectometry (OFDR) fiber optic strain sensing systems. It is particularly well suited to Armstrong's FOSS technology, which uses efficient algorithms to determine from strain data in real time a variety of critical parameters, including twist and other structural shape deformations, temperature, pressure, liquid level, and operational loads. How It Works This technology enables smart-sensing techniques that adjust parameters as needed in real time so that only the necessary amount of data is acquired—no more, no less. Traditional signal processing in fiber optic strain sensing systems is based on fast Fourier transform (FFT), which has two key limitations. First, FFT requires having analysis sections that are equal in length along the whole fiber. Second, if high resolution is required along one portion of the fiber, FFT processes the whole fiber at that resolution. Armstrong's adaptive spatial resolution innovation makes it possible to efficiently break up the length of the fiber into analysis sections that vary in length. It also allows the user to measure data from only a portion of the fiber. If high resolution is required along one section of fiber, only that portion is processed at high resolution, and the rest of the fiber can be processed at the lower resolution. Why It Is Better To quantify this innovation's advantages, this new adaptive method requires only a small fraction of the calculations needed to provide additional resolution compared to FFT (i.e., thousands versus millions of additional calculations). This innovation provides faster signal processing and precision measurement only where it is needed, saving time and resources. The technology also lends itself well to long-term bandwidth-limited monitoring systems that experience few variations but could be vulnerable as anomalies occur. More importantly, Armstrong's adaptive algorithm enhances safety, because it automatically adjusts the resolution of sensing based on real-time data. For example, when strain on a wing increases during flight, the software automatically increases the resolution on the strained part of the fiber. Similarly, as bridges and wind turbine blades undergo stress during big storms, this algorithm could automatically adjust the spatial resolution to collect more data and quickly identify potentially catastrophic failures. This innovation greatly improves the flexibility of fiber optic strain sensing systems, which provide valuable time and cost savings to a range of applications. For more information about the full portfolio of FOSS technologies, see DRC-TOPS-37 or visit https://technology-afrc.ndc.nasa.gov/featurestory/fiber-optic-sensing
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