Redundancy (engineering)

Summary

In engineering, redundancy is the intentional duplication of critical components or functions of a system with the goal of increasing reliability of the system, usually in the form of a backup or fail-safe, or to improve actual system performance, such as in the case of GNSS receivers, or multi-threaded computer processing. In many safety-critical systems, such as fly-by-wire and hydraulic systems in aircraft, some parts of the control system may be triplicated, which is formally termed triple modular redundancy (TMR). An error in one component may then be out-voted by the other two. In a triply redundant system, the system has three sub components, all three of which must fail before the system fails. Since each one rarely fails, and the sub components are expected to fail independently, the probability of all three failing is calculated to be extraordinarily small; it is often outweighed by other risk factors, such as human error. Redundancy may also be known by the terms "major

Official source

https://en.wikipedia.org/wiki/Redundancy_(engineering)

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In airborne laser scanning a high-frequency trajectory solution is typically determined from inertial sensors and employed to directly geo-reference the acquired laser points. When low-cost MEMS inertial sensors are used, such as in lightweight unmanned aerial vehicles, non-negligible errors in the estimated trajectory project to the final point-cloud, resulting in unsatisfactory accuracy on the ground. There are different multi-sensor fusion approaches to correct the point-cloud errors caused by an imperfect trajectory determination. Mismatches between different optical observations and/or in the overlapping regions of the point-cloud can allow the correction of the final point-cloud, either directly, by means of rigid transformations, or indirectly, via improving the scanner trajectory estimation. In this work we propose to fuse lidar and cameras in a single adjustment based on dynamic networks, considering 2D tie-points from the imagery and 3D tie-points from overlapping point-cloud sections. On a challenging corridor mapping scenario, we show that considering either 2D or 3D tie-points, along with inertial and GNSS observations, results in a remarkably accurate point-cloud, even when low-cost inertial sensors are employed and in presence of challenging surface textures, such as high vegetation. Furthermore, since the distribution of the 2D and 3D tie-points is complementary, considering them together further increases the robustness of the adjustment due to higher redundancy. By employing the proposed approach within this controlled example, we were able to improve the final point-cloud accuracy by more than three times with respect to conventional geo-referencing methodology and to reduce the magnitude of the errors.

2022

BugSifter: A Generalized Accelerator for Flexible Instruction-Grain Monitoring

Babak Falsafi, Sotiria Fytraki, Boris Robert Grot, Yusuf Onur Koçberber, Jennifer Bedke Sartor, Evangelos Vlachos

Software robustness is an ever-challenging problem in the face of today's evolving software and hardware that has undergone recent shifts. Instruction-grain monitoring is a powerful approach for improved software robustness that affords comprehensive runtime coverage for a wide spectrum of bugs and security exploits. Unfortunately, existing instruction-grain monitoring frameworks, such as dynamic binary instrumentation, are either prohibitively expensive (slowing down applications by an order of magnitude or more) or offer limited coverage. This work introduces BugSifter, a new design that drastically decreases monitoring overhead without sacrificing flexibility or bug coverage. The main overhead of instruction-grain monitoring lies in execution of software event handlers to monitor nearly every application instruction to check for bugs. BugSifter identifies common monitoring activities that result in redundant monitoring actions, and filters them using general, light-weight hardware, eliminating the majority of costly software event handlers. Our proposed design filters 80-98% of events while monitoring for a variety of commonly-occurring bugs, delegating the rest to flexible software handlers. BugSifter significantly reduces the overhead of instruction-grain monitoring to an average of 40% over unmonitored application time. BugSifter makes instruction-grain monitoring practical, enabling efficient and timely detection of a wide range of bugs, thus making software more robust.

2012

Resistance and ductility of FRP composite hybrid joints

Thomas Keller, Lulu Liu, Xin Wang

An experimental investigation of the load-bearing behavior and ductility of FRP hybrid double-lap joints composed of both adhesively-bonded and bolted connection parts was conducted. Amongst other things, the effects of the adherends’ fiber architecture (uni- or multidirectional), adhesive type (stiff or flexible), and displacement rate were examined. The resistances of the hybrid joints with flexible adhesive corresponded to the full summation of the resistances of the bonded and bolted connection parts. The ultimate failure loads of these joints were furthermore significantly improved by increasing the displacement rate, while the deformation capacity did not decrease. The hybrid joints with multidirectional adherends and flexible adhesive exhibited high joint efficiencies and excellent ductility and thus may increase the overall safety of redundant engineering structures composed of brittle FRP members. These joints may also fulfill fail-safe conditions as required in European standards.

2020