Numerical investigations into Nonlinear Vibro-ultrasonics and Surface Vibration Comparison method for detection of defects in a composite laminate

2021 ◽  
pp. 1-40
Author(s):  
Ashish Kumar Singh ◽  
Vincent B.C. Tan ◽  
Tong Earn Tay ◽  
Heow Lee
Keyword(s):  
Composite Structures ◽  
Composite Laminate ◽  
Numerical Study ◽  
Comparison Method ◽  
Proof Of Concept ◽  
New Approach ◽  
Surface Vibration ◽  
Ultrasonic Methods ◽  
Experimental Works ◽  
Contact Acoustic Nonlinearity

Abstract This paper begins with a numerical study based on earlier experiments of nonlinear vibro-ultrasonic behaviour of a composite laminate with a delamination defect upon sinusoidal linear sweep signal excitation . A methodology to model laminates with cross-ply layup is presented which can be extended to any layup if desired. In comparison to experiments where it is challenging to visualize the fine details of vibrations, simulations make it easier to visualize and helps in optimizing the defect probing methods. The paper goes on to discuss with the help of numerical results that a separation gap between the delamination surfaces occurs to be a common cause for the failure of nonlinear vibro-ultrasonic methods to detect delamination defects. This constraint can often be overcome with application of higher excitation amplitudes as has been demonstrated in several experimental works. However in this study, a new approach named Surface vibration comparison method (SVCM) to probe delamination defects in the absence of contact acoustic nonlinearity is proposed as a proof-of-concept. The technique is then evaluated for detection of weak kissing bond defects in composite beam specimens. Both the experimental and simulation results show potential of the method as damage detection technique in thin composite structures.

scholarly journals Enhancement of Region of Interest CT Reconstructions through Multimodal Data

2018 ◽  
Vol 4 (1) ◽  
pp. 331-335
Author(s):  
David Schote ◽  
Tim Pfeiffer ◽  
Georg Rose
Keyword(s):  
Substantial Reduction ◽  
Region Of Interest ◽  
Proof Of Concept ◽  
Multimodal Data ◽  
New Approach ◽  
Full Field ◽  
Lack Of Information ◽  
Ct Data ◽  
Flight Measurements

AbstractComputed tomography (CT) scans are frequently used intraoperatively, for example to control the positioning of implants during intervention. Often, to provide the required information, a full field of view is unnecessary. I nstead, the region-of-interest (ROI) imaging can be performed, allowing for substantial reduction in the applied X-ray dose. However, ROI imaging leads to data inconsistencies, caused by the truncation of the projections. This lack of information severely impairs the quality of the reconstructed images. This study presents a proof-of-concept for a new approach that combines the incomplete CT data with ultrasound data and time of flight measurements in order to restore some of the lacking information. The routine is evaluated in a simulation study using the original Shepp-Logan phantom in ROI cases with different degrees of truncation. Image quality is assessed by means of normalized root mean square error. The proposed method significantly reduces truncation artifacts in the reconstructions and achieves considerable radiation exposure reductions.

Experimental Investigations Into Nonlinear Vibro-Acoustics for Detection of Delaminations in a Composite Laminate

2018 ◽  
Vol 2 (1) ◽  
Author(s):  
Ashish Kumar Singh ◽  
Vincent B. C. Tan ◽  
Tong Earn Tay ◽  
Heow Pueh Lee
Keyword(s):  
Frequency Dependence ◽  
Composite Laminate ◽  
Excitation Frequency ◽  
Excitation Amplitude ◽  
Experimental Investigations ◽  
Frequency Sweep ◽  
Ultrasonic Methods ◽  
Acoustic Methods ◽  
Different Depths ◽  
Excitation Frequencies

In recent years, nonlinear vibro-acoustic methods have shown potential to identify defects which are difficult to detect using linear ultrasonic methods. However, these methods come with their own challenges such as frequency dependence, requirement for a high excitation amplitude, and difficulties in distinguishing nonlinearity from defect with nonlinearity from other sources to name a few. This paper aims to study the dependence of nonlinear vibro-acoustic methods for detection of delaminations inside a composite laminate, on the excitation methods and excitation frequencies. It is shown that nonlinear vibro-acoustic methods are highly frequency dependent and commonly used excitation signals which utilize particular values of excitation frequencies might not always lead to a clear distinction between intact and delaminated regions of the specimen. To overcome the frequency dependence, signals based on frequency sweep are used. Interpretation of output response to sweep signals to identify damage is demonstrated using an earlier available approach, and a simpler approach is proposed. It is demonstrated that the damage detection with sweep signal excitations is relatively less dependent on excitation frequency than the conventional excitation methods. The proposed interpretation technique is then applied to specimens with delamination of varying sizes and with delaminations at different depths inside the laminate to demonstrate its effectiveness.

scholarly journals Detection of Material Degradation of a Composite Cylinder Using Mode Shapes and Convolutional Neural Networks

Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6686
Author(s):  
Bartosz Miller ◽  
Leonard Ziemiański
Keyword(s):  
Neural Networks ◽  
Convolutional Neural Networks ◽  
Composite Structures ◽  
Vibration Mode ◽  
Numerical Study ◽  
Mode Shapes ◽  
Zone Size ◽  
Composite Cylinder ◽  
Material Degradation ◽  
Damaged Zone

This paper presents a numerical study of the feasibility of using vibration mode shapes to identify material degradation in composite structures. The considered structure is a multilayer composite cylinder, while the material degradation zone is, for simplicity, considered a square section of the lateral surface of the cylinder. The material degradation zone size and location along the cylinder axis are identified using a deep learning approach (convolutional neural networks, CNNs, are applied) on the basis of previously identified vibration mode shapes. The different numbers and combinations of identified mode shapes used to assess the damaged zone size and location were analyzed in detail. The final selection of mode shapes considered in the identification procedure yielded high accuracy in the identification of the degradation zone.

scholarly journals Tuning Alginate Microparticle Size via Atomization of Non-Newtonian Fluids

Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7601
Author(s):  
Beatriz Arauzo ◽  
Álvaro González-Garcinuño ◽  
Antonio Tabernero ◽  
María Pilar Lobera ◽  
Jesús Santamaría ◽  
...  
Keyword(s):  
Particle Size ◽  
Numerical Study ◽  
Pressure Ratio ◽  
Barium Chloride ◽  
Newtonian Fluids ◽  
Dimensionless Numbers ◽  
Experimental Conditions ◽  
New Approach ◽  
Hydrogel Beads ◽  
Key Factor

A new approach based on the atomization of non-Newtonian fluids has been proposed to produce microparticles for a potential inhalation route. In particular, different solutions of alginate were atomized on baths of different crosslinkers, piperazine and barium chloride, obtaining microparticles around 5 and 40 microns, respectively. These results were explained as a consequence of the different viscoelastic properties, since oscillatory analysis indicated that the formed hydrogel beads with barium chloride had a higher storage modulus (1000 Pa) than the piperazine ones (20 Pa). Pressure ratio (polymer solution-air) was identified as a key factor, and it should be from 0.85 to 1.00 to ensure a successful atomization, obtaining the smallest particle size at intermediate pressures. Finally, a numerical study based on dimensionless numbers was performed to predict particle size depending on the conditions. These results highlight that it is possible to control the microparticles size by modifying either the viscoelasticity of the hydrogel or the experimental conditions of atomization. Some experimental conditions (using piperazine) reduce the particle size up to 5 microns and therefore allow their use by aerosol inhalation.

scholarly journals Numerical Simulation on Micro-damage Detection In CFRP Composites Based on Nonlinear Ultrasonic Guided Waves

2021 ◽  
Keyword(s):  
Damage Detection ◽  
Composite Structures ◽  
Guided Waves ◽  
Second Harmonic ◽  
Wave Mode ◽  
Guided Wave ◽  
Reinforced Plastics ◽  
Matrix Cracks ◽  
Nonlinear Ultrasonic ◽  
Contact Acoustic Nonlinearity

Abstract. Micro-damages such as pores, closed delamination/debonding and fiber/matrix cracks in carbon fiber reinforced plastics (CFRP) are vital factors towards the performance of composite structures, which could collapse if defects are not detected in advance. Nonlinear ultrasonic technologies, especially ones involving guided waves, have drawn increasing attention for their better sensitivity to early damages than linear acoustic ones. The combination of nonlinear acoustics and guided waves technique can promisingly provide considerable accuracy and efficiency for damage assessment and materials characterization. Herein, numerical simulations in terms of finite element method are conducted to investigate the feasibility of micro-damage detection in multi-layered CFRP plates using the second harmonic generation (SHG) of asymmetric Lamb guided wave mode. Contact acoustic nonlinearity (CAN) is introduced into the constitutive model of micro-damages in composites, which leads to the distinct SHG compared with material nonlinearity. The results suggest that the generated second order harmonics due to CAN could be received and adopted for early damage evaluation without matching the phase of the primary waves.

Can hydrological model identifiability be improved? Stress-testing the concept of stochastic calibration

2021 ◽  
Author(s):  
Vasileios Kourakos ◽  
Andreas Efstratiadis ◽  
Ioannis Tsoukalas
Keyword(s):  
Dependence Structure ◽  
Hydrological Models ◽  
Proof Of Concept ◽  
Rainfall Runoff ◽  
Predictive Capacity ◽  
New Approach ◽  
Stochastic Inputs ◽  
Promising Strategy ◽  
Synthetic Time Series ◽  
Temporal Windows

<p>Hydrological calibrations with historical data are often deemed insufficient for deducing safe estimations about a model structure that imitates, as closely as possible, the anticipated catchment behaviour. Ιn order to address this issue, we investigate a promising strategy, using as drivers synthetic time series, which preserve the probabilistic properties and dependence structure of the observed data. The key idea is calibrating a model on the basis of synthetic rainfall-runoff data, and validating against the full observed data sample. To this aim, we employed a proof of concept on few representative catchments, by testing several lumped conceptual hydrological models with alternative parameterizations and across two time-scales, monthly and daily. Next, we attempted to reinforce the validity of the recommended methodology by employing monthly stochastic calibrations in 100 MOPEX catchments. As before, a number of different hydrological models were used, for the purpose of proving that calibration with stochastic inputs is independent of the chosen model. The results highlight that in most cases the new approach leads to stronger parameter identifiability and stable predictive capacity across different temporal windows, since the model is trained over much extended hydroclimatic conditions.</p>

Numerical Study of Density-Currents Using the Non-Staggered Grid Fractional-Step-Method

2000 ◽  
Author(s):  
J. Rafael Pacheco ◽  
Arturo Pacheco-Vega ◽  
Sigfrido Pacheco-Vega
Keyword(s):  
Numerical Study ◽  
Density Variation ◽  
Staggered Grid ◽  
Mapping Technique ◽  
Fractional Step ◽  
Density Currents ◽  
Step Method ◽  
Fractional Step Method ◽  
New Approach ◽  
Flow Equations

Abstract A new approach for the solution of time-dependent calculations of buoyancy driven currents is presented. This method employs the idea that density variation can be pursued by using markers distributed in the flow field. The analysis based on the finite difference technique with the non-staggered grid fractional step method is used to solve the flow equations written in terms of primitive variables. The physical domain is transformed to a rectangle by means of a numerical mapping technique. The problems analyzed include two-fluid flow in a tank with sloping bottom and colliding density currents. The numerical experiments performed show that this approach is efficient and robust.

scholarly journals Experimental and numerical study of the domestic hot water production with PV panels and a heat pump

2019 ◽  
Vol 111 ◽  
pp. 01066
Author(s):  
F. J. Aguilar ◽  
D. Crespí ◽  
P. V. Quiles
Keyword(s):  
Heat Pump ◽  
Computer Model ◽  
Numerical Study ◽  
Hot Water ◽  
Water Production ◽  
Storage Tanks ◽  
European Standard ◽  
Photovoltaic Panels ◽  
Domestic Hot Water ◽  
Experimental Works

This article presents an experimental and modelling work which uses a compact domestic hot water heat pump (DHW-HP) that is simultaneously powered from photovoltaic panels (PV) and from the grid. Results from more than 240 days of experimental works have been used in order to develop and to validate the computer model of the system. The program, implemented in MATLAB, is computationally ‘light’ enough to allow mid-term simulations yet also detailed enough to accurately and coherently portray stratification within thermal storage tanks. Finally, as an example of the model capabilities, it has been used to simulate a domestic hot water tapping cycle from the European Standard EN 16147.

scholarly journals New approach to simplifying and optimising acute malnutrition treatment in children aged 6–59 months: the OptiMA single-arm proof-of-concept trial in Burkina Faso

2019 ◽  
Vol 123 (7) ◽  
pp. 756-767 ◽  
Author(s):  
Maguy Daures ◽  
Kevin Phelan ◽  
Mariama Issoufou ◽  
Séni Kouanda ◽  
Ousmane Sawadogo ◽  
...  
Keyword(s):  
Burkina Faso ◽  
Real Life ◽  
Acute Malnutrition ◽  
Proof Of Concept ◽  
New Approach ◽  
Multivariate Survival ◽  
Arm Circumference ◽  
Mid Upper Arm Circumference ◽  
Programme Outcomes ◽  
Therapeutic Food

AbstractThe Optimising treatment for acute MAlnutrition (OptiMA) strategy trains mothers to use mid upper arm circumference (MUAC) bracelets for screening and targets treatment to children with MUAC < 125 mm or oedema with one therapeutic food at a gradually reduced dose. This study seeks to determine whether OptiMA conforms to SPHERE standards (recovery rate > 75 %). A single-arm proof-of-concept trial was conducted in 2017 in Yako district, Burkina Faso including children aged 6–59 months in outpatient health centres with MUAC < 125 mm or oedema. Outcomes were stratified by MUAC category at admission. Multivariate survival analysis was carried out to identify variables predictive of recovery. Among 4958 children included, 824 (16·6 %) were admitted with MUAC < 115 mm or oedema, 1070 (21·6 %) with MUAC 115–119 mm and 3064 (61·8 %) with MUAC 120–124 mm. The new dosage was correctly implemented at all visits for 75·9 % of children. Global recovery was 86·3 (95 % CI 85·4, 87·2) % and 70·5 (95 % CI 67·5, 73·5) % for children admitted with MUAC < 115 mm or oedema. Average therapeutic food consumption was 60·8 sachets per child treated. Recovery was positively associated with mothers trained to use MUAC prior to child’s admission (adjusted hazard ratio 1·09; 95 % CI 1·01, 1·19). OptiMA was successfully implemented at the scale of an entire district under ‘real-life’ conditions. Programme outcomes exceeded SPHERE standards, but further study is needed to determine if increasing therapeutic food dosages for the most severely malnourished will improve recovery.

scholarly journals Numerical Study of T-Shaped Micromixers with Vortex-Inducing Obstacles in the Inlet Channels

Micromachines ◽  
2020 ◽  
Vol 11 (12) ◽  
pp. 1122
Author(s):  
Chih-Yang Wu ◽  
Bing-Hao Lai
Keyword(s):  
Fluid Dynamics ◽  
Reynolds Number ◽  
Particle Tracking ◽  
Concentration Distribution ◽  
Numerical Study ◽  
Fluid Mixing ◽  
Sudden Increase ◽  
New Approach ◽  
Mixing Performance ◽  
Flow Modification

To enhance fluid mixing, a new approach for inlet flow modification by adding vortex-inducing obstacles (VIOs) in the inlet channels of a T-shaped micromixer is proposed and investigated in this work. We use a commercial computational fluid dynamics code to calculate the pressure and the velocity vectors and, to reduce the numerical diffusion in high-Peclet-number flows, we employ the particle-tracking simulation with an approximation diffusion model to calculate the concentration distribution in the micromixers. The effects of geometric parameters, including the distance between the obstacles and the angle of attack of the obstacles, on the mixing performance of micromixers are studied. From the results, we can observe the following trends: (i) the stretched contact surface between different fluids caused by antisymmetric VIOs happens for the cases with the Reynolds number (Re) greater than or equal to 27 and the enhancement of mixing increases with the increase of Reynolds number gradually, and (ii) the onset of the engulfment flow happens at Re≈125 in the T-shaped mixer with symmetric VIOs or at Re≈140 in the standard planar T-shaped mixer and results in a sudden increase of the degree of mixing. The results indicate that the early initiation of transversal convection by either symmetric or antisymmetric VIOs can enhance fluid mixing at a relatively lower Re.

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