A Defects Localization Algorithm Based on the Lamb Wave of Plate Structure

2020 ◽  
Vol 4 (2) ◽  
Author(s):  
Fei Deng ◽  
Honglei Chen
Keyword(s):  
Fuzzy Control ◽  
Control Parameter ◽  
Lamb Waves ◽  
Numerical Models ◽  
Search Problem ◽  
Localization Algorithm ◽  
The Time Domain ◽  
The Individual ◽  
Imaging Algorithms ◽  
Defect Imaging

Abstract Defect imaging algorithms play an important role in Lamb waves based researches of nondestructive testing (NDT) and structural health monitoring (SHM). In classical algorithms, the location or distribution of defects is visualized through mapping the amplitude or phase information of signals gotten by multiple inspection pairs from the time domain to every discrete spatial grid of plates. It is time-consuming in the detection of plates with large size and many transducers. Transforming the defect imaging problem into a scattering source search problem, an intelligent defect localization algorithm was proposed for NDT and SHM with the Lamb waves and sparse array. In the algorithm, the elliptic trajectory-dependent individuals of every inspection pair were extracted first, then the defect position was identified by analyzing the distribution of individuals these located at the intersection of multiply elliptic trajectories. Considering the fuzzy and diversity characteristics in the detection of defects, a fuzzy control parameter and an adaptive individual updating strategy based on the k-means algorithm were introduced to ensure the robustness of the algorithm. The effectiveness of the proposed algorithm was verified by numerical models and experiments. The influences of the fuzzy control parameter and the individual updating strategy on the performance of the algorithm were analyzed furthermore.

scholarly journals Comparison of Two Numerical Algorithms for Computing the Effects of Mistuning of Fan Flutter

2016 ◽  
Author(s):  
L. Salles ◽  
M. Vahdati
Keyword(s):  
Numerical Models ◽  
Three Dimensional ◽  
Numerical Algorithms ◽  
Mode Shapes ◽  
Minimal Amount ◽  
Aeroelastic System ◽  
Cpu Time ◽  
Influence Coefficients ◽  
Non Linear ◽  
The Time Domain

The aim of this paper is to study the effects of mistuning on fan flutter and to compare the prediction of two numerical models of different fidelity. The high fidelity model used here is a three-dimensional, whole assembly, time-accurate, viscous, finite-volume compressible flow solver. The Code used for this purpose is AU3D, written in Imperial College and validated for flutter computations over many years. To the best knowledge of authors, this is the first time such computations have been attempted. This is due to the fact that, such non-linear aeroelastic computations with mistuning require large amount of CPU time and cannot be performed routinely and consequently, faster (low fidelity) models are required for this task. Therefore, the second model used here is the aeroelastic fundamental mistuning model (FMM) and it based on an eigenvalue analysis of the linearized modal aeroelastic system with the aerodynamic matrix calculated from the aerodynamic influence coefficients. The influence coefficients required for this algorithm are obtained from the time domain non-linear Code by shaking one blade in the datum (tuned) frequency and mode. Once the influence coefficients have been obtained, the computations of aero damping require minimal amount of CPU time and many different mistuning patterns can be studied. The objectives of this work are to: 1. Compare the results between the two models and establish the capabilities/limitations of aeroelastic FMM, 2. Check if the introduction of mistuning would bring the experimental and computed flutter boundaries closer, 3. Establish a relationship between mistuning and damping. A rig wide-chord fan blade, typical of modern civil designs, was used as the benchmark geometry for this study. All the flutter analyses carried out in this paper are with frequency mistuning, but the possible consequences of mistuned mode shapes are briefly discussed at the end of this paper. Only the first family of modes (1F, first flap) is considered in this work. For the frequency mistuning analysis, the 1F frequency is varied around the annulus but the 1F mode shapes remain the same for all the blades. For the mode shape mistuning computations, an FE analysis of the whole assembly different mass blades is performed. The results of this work clearly show the importance of mistuning on flutter. It also demonstrates that when using rig test data for aeroelastic validation of CFD codes, the amount mistuning present must be known. Finally, it should be noted that the aim of this paper is the study of mistuning and not steady/unsteady validation of a CFD code and therefore minimal aerodynamic data are presented.

scholarly journals Autonomous feature type selection based on environment using expectation maximization in self-localization

2018 ◽  
Vol 15 (6) ◽  
pp. 172988141881470
Author(s):  
Nezih Ergin Özkucur ◽  
H Levent Akın
Keyword(s):  
Expectation Maximization ◽  
Autonomous Robots ◽  
Expectation Maximization Algorithm ◽  
Sensory Information ◽  
Ground Truth ◽  
Local Environment ◽  
Localization Algorithm ◽  
Data Set ◽  
Public Data ◽  
The Individual

Self-localization in autonomous robots is one of the fundamental issues in the development of intelligent robots, and processing of raw sensory information into useful features is an integral part of this problem. In a typical scenario, there are several choices for the feature extraction algorithm, and each has its weaknesses and strengths depending on the characteristics of the environment. In this work, we introduce a localization algorithm that is capable of capturing the quality of a feature type based on the local environment and makes soft selection of feature types throughout different regions. A batch expectation–maximization algorithm is developed for both discrete and Monte Carlo localization models, exploiting the probabilistic pose estimations of the robot without requiring ground truth poses and also considering different observation types as blackbox algorithms. We tested our method in simulations, data collected from an indoor environment with a custom robot platform and a public data set. The results are compared with the individual feature types as well as naive fusion strategy.

scholarly journals Stochastic modeling of transient surface scalar and momentum fluxes in turbulent boundary layers

2021 ◽  
Author(s):  
Marten Klein ◽  
David O. Lignell ◽  
Heiko Schmidt
Keyword(s):  
Boundary Layers ◽  
Control Parameter ◽  
Layer Structure ◽  
Numerical Models ◽  
Turbulent Boundary Layers ◽  
Transport Processes ◽  
Surface Fluxes ◽  
One Dimensional ◽  
Weather And Climate ◽  
Normal Transport

<p>Turbulence is ubiquitous in atmospheric boundary layers and manifests itself by transient transport processes on a range of scales. This range easily reaches down to less than a meter, which is smaller than the typical height of the first grid cell layer adjacent to the surface in numerical models for weather and climate prediction. In these models, the bulk-surface coupling plays an important role for the evolution of the atmosphere but it is not feasible to fully resolve it in applications. Hence, the overall quality of numerical weather and climate predictions crucially depends on the modeling of subfilter-scale transport processes near the surface. A standing challenge in this regard is the robust but efficient representation of transient and non-Fickian transport such as counter-gradient fluxes that arise from stratification and rotation effects.</p><p>We address the issues mentioned above by utilizing a stochastic one-dimensional turbulence (ODT) model. For turbulent boundary layers, ODT aims to resolve the wall-normal transport processes on all relevant scales but only along a single one-dimensional domain (column) that is aligned with the vertical. Molecular diffusion and unbalanced Coriolis forces are directly resolved, whereas effects of turbulent advection and stratification are modeled by stochastically sampled sequence of mapping (eddy) events. Each of these events instantaneously modifies the flow profiles by a permutation of fluid parcels across a selected size interval. The model is of lower order but obeys fundamental conservation principles and Richardson's 1/4 law by construction.</p><p>In this study, ODT is applied as stand-alone tool in order to investigate nondimensional control parameter dependencies of the scalar and momentum transport in turbulent channel, neutral, and stably-stratified Ekman flows up to (friction) Reynolds number <em>Re</em> = <em>O</em>(10<sup>4</sup>). We demonstrate that ODT is able to capture the state-space statistics of transient surface fluxes as well as the boundary-layer structure and nondimensional control parameter dependencies of low-order flow statistics.<br>Very good to reasonable agreement with available reference data is obtained for various observables using fixed model set-ups. We conclude that ODT is an economical turbulence model that is able to not only capture but also predict the wall-normal transport and surface fluxes in multiphysics turbulent boundary layers.</p>

scholarly journals COMBINING DATA-DRIVEN AND NUMERICAL MODELLING APPROACHES TO STORM EROSION PREDICTION

2020 ◽  
pp. 38
Author(s):  
Joshua Simmons ◽  
Kristen Splinter
Keyword(s):  
Numerical Models ◽  
Individual Performance ◽  
Study Data ◽  
Data Driven ◽  
Erosion Prediction ◽  
Trade Offs ◽  
Combining Data ◽  
Erosion Models ◽  
Using Data ◽  
The Individual

Physics-based numerical models play an important role in the estimation of storm erosion, particularly at beaches for which there is little historical data. However, the increasing availability of pre-and post-storm data for multiple events and at a number of beaches around the world has opened the possibility of using data-driven approaches for erosion prediction. Both physics-based and purely data-driven approaches have inherent strengths and weaknesses in their ability to predict storm-induced erosion. It is vital that coastal managers and modelers are aware of these trade-offs as well as methods to maximise the value from each modelling approach in an increasingly data-rich environment. In this study, data from approximately 40 years of coastal monitoring at Narrabeen-Collaroy Beach (SE Australia)has been used to evaluate the individual performance of the numerical erosion models SBEACH and XBeach, and a data-driven modelling technique. The models are then combined using a simple weighting technique to provide a hybrid estimate of erosion.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/v53dZiO8Y60

Integrating Electromagnetic Acoustic Transducers in a Modular Robotic Gripper for Inspecting Tubular Components

2021 ◽  
Vol 79 (7) ◽  
pp. 715-727
Author(s):  
Hamidreza Nemati ◽  
Fernando Alvidrez ◽  
Ankit Das ◽  
Nihar Masurkar ◽  
Manoj Rudraboina ◽  
...  
Keyword(s):  
Power Plants ◽  
Lamb Waves ◽  
Signal To Noise Ratio ◽  
Ultrasonic Inspection ◽  
Electromagnetic Acoustic Transducers ◽  
Acoustic Transducers ◽  
Main Challenge ◽  
Critical Components ◽  
Spiral Coils ◽  
The Time Domain

Tubular structures are critical components in infrastructure such as power plants. Throughout their life, they are subjected to extreme conditions or suffer from defects such as corrosion and cracks. Although regular inspection of these components is necessary, such inspection is limited by safety-related risks and limited access for human inspection. Robots can provide a solution for automatic inspection. The main challenge, however, lies in integrating sensors for nondestructive evaluation with robotic platforms. As part of developing a versatile lizard-inspired tube inspector robot, in this study the authors propose to integrate electromagnetic acoustic transducers into a modular robotic gripper for use in automated ultrasonic inspection. In particular, spiral coils with cylindrical magnets are integrated into a novel friction-based gripper to excite Lamb waves in thin cylindrical structures. To evaluate the performance of the integrated sensors, the gripper was attached to a robotic arm manipulator and tested on pipes of different outer diameters. Two sets of tests were carried out on both defect-free pipes and pipes with simulated defects, including surface partial cracking and corrosion. The inspection results indicated that transmitted and received signals could be acquired with an acceptable signal-to-noise ratio in the time domain. Moreover, the simulated defects could be successfully detected using the integrated robotic sensing system.

Fog forecasting for Schiphol airport at sub-kilometre scale.  

2021 ◽  
Author(s):  
Gert-Jan Steeneveld ◽  
Roosmarijn Knol
Keyword(s):  
Spatial Resolution ◽  
Numerical Models ◽  
Wrf Model ◽  
Horizontal Resolution ◽  
Physical Processes ◽  
Radiation Fog ◽  
Fog Forecasting ◽  
Elevation Data ◽  
The Individual ◽  
The Impact

<p>Fog is a critical weather phenomenon for safety and operations in aviation. Unfortunately, the forecasting of radiation fog remains challenging due to the numerous physical processes that play a role and their complex interactions, in addition to the vertical and horizontal resolution of the numerical models. In this study we evaluate the performance of the Weather Research and Forecasting (WRF) model for a radiation fog event at Schiphol Amsterdam Airport (The Netherlands) and further develop the model towards a 100 m grid spacing. Hence we introduce high resolution land use and land elevation data. In addition we study the role of gravitational droplet settling, advection of TKE, top-down diffusion caused by strong radiative cooling at the fog top. Finally the impact of heat released by the terminal areas on the fog formation is studied. The model outcomes are evaluated against 1-min weather observations near multiple runways at the airport.</p><p>Overall we find the WRF model shows an reasonable timing of the fog onset and is well able to reproduce the visibility and meteorological conditions as observed during the case study. The model appears to be relatively insensitive to the activation of the individual physical processes. An increased spatial resolution to 100 m generally results in a better timing of the fog onset differences up to three hours, though not for all runways. The effect of the refined landuse dominates over the effect of refined elevation data. The modelled fog dissipation systematically occurs 3-4 h hours too early, regardless of physical processes or spatial resolution. Finally, the introduction of heat from terminal buildings delays the fog onset with a maximum of two hours, an overestimated visibility of 100-200 m and a decrease of the LWC with 0.10-0.15 g/kg compared to the reference.</p>

scholarly journals Flow Ripple Reduction of Axial-Piston Pump by Structure Optimizing of Outlet Triangular Damping Groove

Processes ◽  
2020 ◽  
Vol 8 (12) ◽  
pp. 1664
Author(s):  
Haocen Hong ◽  
Chunxiao Zhao ◽  
Bin Zhang ◽  
Dapeng Bai ◽  
Huayong Yang
Keyword(s):  
Numerical Models ◽  
Structural Parameters ◽  
Piston Pump ◽  
Axial Piston Pump ◽  
Discharge Flow ◽  
Flow Ripple ◽  
Ripple Reduction ◽  
Simulation Results ◽  
The Time Domain ◽  
Axial Piston

The triangular damping groove on the valve plate can effectively reduce the discharge flow ripple of an axial piston pump, which structural parameters will directly affect the pump’s dynamic characteristics. Herein, a multi-parameter data-based structure optimizing method of the triangular damping groove is investigated using numerical models and simulation results. The mathematical models of a nine-piston pump are proposed and developed by MATLAB/Simulink, and the simulation results are verified by experimental results. Then, the effects of width angle and depth angle on discharge flow are analyzed. Based on the analysis of groove parameters, an optimizing index, which considering the time domain characteristics of discharge flow, is proposed. As results show, comparing with the initial specific groove structure, the amplitude of flow ripple is reduced from 14.6% to 9.8% with the optimized structure. The results demonstrate that the outlet flow ripple can be significantly reduced by the optimized structure, and the proposed multi-parameter optimizing method can play a guiding significance in the design of low-ripple axial piston pumps.

scholarly journals The Influence of Additive Manufacturing Processes on the Performance of a Periodic Acoustic Metamaterial

2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
John Kennedy ◽  
Lara Flanagan ◽  
Luke Dowling ◽  
G. J. Bennett ◽  
Henry Rice ◽  
...  
Keyword(s):  
Experimental Validation ◽  
Individual Cell ◽  
Numerical Models ◽  
Manufacturing Processes ◽  
Microscopic Scale ◽  
Acoustic Metamaterial ◽  
3D Print ◽  
Internal Cavities ◽  
The Individual ◽  
Benchmark Structures

Advancements in 3D print technology now allow the printing of structured acoustic absorbent materials at the appropriate microscopic scale and sample sizes. The repeatability of the fundamental cell unit of these metamaterials provides a pathway for the development of viable macro models to simulate built-up structures based on detailed models of the individual cell units; however, verification of such models on actual manufactured structures presents a challenge. In this paper, a design concept for an acoustic benchmark metamaterial consisting of an interlinked network of resonant chambers is considered. The form chosen is periodic with cubes incorporating spherical internal cavities connected through cylindrical openings on each face of the cube. This design is amenable to both numerical modelling and manufacture through additive techniques whilst yielding interesting acoustic behaviour. The paper reports on the design, manufacture, modelling, and experimental validation of these benchmark structures. The behaviour of the acoustic metamaterial manufactured through three different polymer-based printing technologies is investigated with reference to the numerical models and a metal powder-based print technology. At the scale of this microstructure, it can be seen that deviations in surface roughness and dimensional fidelity have a comparable impact on the experimentally measured values of the absorption coefficient.

Influence sampling of trailing variables of dynamical systems

2017 ◽  
Vol 3 (1) ◽  
Author(s):  
Paul Krause
Keyword(s):  
Data Assimilation ◽  
Numerical Models ◽  
Discrete Control ◽  
Dynamical Instability ◽  
Lorenz Equations ◽  
Control Scheme ◽  
Insertion Method ◽  
Order Of Magnitude ◽  
Large Systems ◽  
The Individual

AbstractFor dealing with dynamical instability in predictions, numerical models should be provided with accurate initial values on the attractor of the dynamical system they generate. A discrete control scheme is presented to this end for trailing variables of an evolutive system of ordinary differential equations. The Influence Sampling (IS) scheme adapts sample values of the trailing variables to input values of the determining variables in the attractor. The optimal IS scheme has affordable cost for large systems. In discrete data assimilation runs conducted with the Lorenz 1963 equations and a nonautonomous perturbation of the Lorenz equations whose dynamics shows on-off intermittency the optimal IS was compared to the straightforward insertion method and the Ensemble Kalman Filter (EnKF). With these unstable systems the optimal IS increases by one order of magnitude the maximum spacing between insertion times that the insertion method can handle and performs comparably to the EnKF when the EnKF converges. While the EnKF converges for sample sizes greater than or equal to 10, the optimal IS scheme does so fromsample size 1. This occurs because the optimal IS scheme stabilizes the individual paths of the Lorenz 1963 equations within data assimilation processes.

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