1,721,459 research outputs found
Guided wave propagation and interaction with ice layers in marine structures
No full textReliable and autonomous monitoring systems have been increasingly considered to enhance metal and composite-based maritime structures. The main goal is to continuously assess the overall condition of the structure using several nodes of sensors to ensure safety and cost-effective maintenance during the lifetime. To achieve the detection of small emerging flaws, ultrasound wave propagation in thin sheets is successfully adopted to interrogate both metallic and composite structures. However, ships are operating in water environment and even in polar regions, making the correct extraction of damage parameters from ultrasound signals quite challenging. An interesting and practically important aspect deals with icing problems, where thin layers of ice emerge in direct contact with the ship’s hull. This may lead to misinterpretations of measured signals, inducing false alarms and potentially missing damage detection. Guided wave propagation should be investigated in this contribution accounting for these aspects to prevent misleading interpretation. A finite element model has been considered including ice models to address the effect of an emerging ice layer on wave propagation using both pitch-catch and pulse-echo approaches. Numerical results show that reflections generated at the discontinuity raise with the thickness and length of ice layer. The ice accretion affects the transmitted energy, whose result is even more visible in the direct propagation analysis. The outcomes definitely prove the ability of guided waves to detect ice and the modeling is well suited for preliminary design of further experiments
Preliminary results of FMCW radar measurements at 60GHz for ice build up detection on the surface of a composite panel
No full textRenewable energy sources have gained much attention due to the urge to get clean energy. Among the main options being studied, wind energy is a strong contender because of its reliability thanks to the maturity of the technology and relative cost competitiveness. In order to harvest wind energy more efficiently and to improve safety considerations, the wind turbines blades must be monitored regularly to ensure that they are in good condition. This is even truer in cold climate areas where, because of sub-zero temperatures and humid environment for larger periods of the year, icing represents a significant threat to the performance and durability of wind turbines. Therefore, a structural health monitoring (SHM) system is of primary importance. Recently, there has been a significant interest in employing high frequency radar imagery for Non-Destructive Testing (NDT) and Non-Destructive Evaluation (NDE). The main motivations for using this technology are: it allows penetration of most non-metal and non-polarized materials, it provides the ability for in-depth information, and the millimeter waves pose no health risk to the operator. The main goal of this research is to check the ability of a frequency-modulated continuous-wave (FMCW) radar in performing real-time ice detection onto a glass fibre plate when it works in the frequency band from 57-64 GHz. The technology effectiveness to achieve the aforesaid task is proved in a climatic chamber under controlled humidity and thermal conditions
Oyster tongers, Chesapeake Bay, Md.
No full textArtist's depiction of Oyster tongers, Chesapeake Bay, Maryland, 1971-1981. Postmark date: March 21, 1981; Message included
Footbridge and harbor, St. Michaels, Maryland
No full textArtist's depiction of footbridge and harbor, St. Michaels, Maryland, circa 1971-1983. Message reads: "Dear J and J, Hope to see you in May. Will be here every weekend and Mondays in May except Mem. Day Weekend when we go to Paupac and all of June until 22nd when we go north for summer. Let us know when you plan to come north. Weather is finally getting nice here. Best to you both, Herb and Edie." Postmark date: April 14, 1983; Message included
Robert Morris Inn, 1710, Oxford, Maryland
No full textArtists' depiction of Robert Morris Inn, Oxford, Maryland, circa 1907-1914. Drawn and published by J.B. Moll, Jr
Investigation on guided waves propagation across ice layers
No full textIcing conditions are threatening for a variety of engineering applications. When accreting on the aircraft surface, ice may lead to catastrophic accidents while its deposition on turbine blades can overload the components reducing power and inducing damage. The first way to protect engineering constructions from icing issues deals with early detection of ice. Ultrasound has been demonstrated to be effective for detecting changes of the structure which it is propagating through. Guided waves interact with emerging flaw and discontinuity, including ice accreting on the surface. This paper introduces an experimental campaign carried out on composite structures subject to icing. The building up of planar ice onto surface structure is analysed. Furthermore, a parametric investigation is carried out by finite element modelling to look into the interaction between wave and ice while varying its dimension. Experimental findings demonstrate the ability of guided waves to detect ice layers accreting onto surface. In addition, the ice is likely to be identified from the scattering of guided waves resulting in different transmission and reflection characteristics. Instead, numerical outcomes show how the interaction of guided waves depends upon the thickness and length of the ice
Surface ice detection on composite plates with ultrasonic guided waves
No full textThe paper presents an integrated active system for ice detection on composite plates with ultrasonic guided waves. The aim is to efficiently detect ice formation and growing on complex structures to ensure safety in transportation vehicles. Ice may lead to serious hazards and its early detection is crucial to avoid catastrophic events. In addition, structural health monitoring based on wave propagation benefits from its early detection preventing misleading interpretation of ultrasound signals. Guided wave propagation, likely adopted for damage monitoring in complex structures, can be likewise adopted to reveal the presence of the ice and characterize its dimension. Experimental tests have been carried out in this work to investigate the effect of an emerging ice layer on wave propagation using the pitch-catch approach. Different measurements have been carried out on a glass fiber composite panel integrated with light piezoelectric actuators. The icing condition is simulated using a climate chamber where water is used to trigger the ice formation. The ultrasonic data have been recorded with a dedicated acquisition system. Results show that reflections generated at the ice location are quite visible in the propagating waves indicating waves as ice sensitive. In addition waterfall diagram and RMS analysis show that ice significantly changes the signals. The outcomes and their post-processing analysis definitely prove the ability of guided waves to detect ice
A New Generation of Piezoceramic Frequency Steerable Acoustic Transducers for the Rapid Inspection of Large Areas of Metallic Plate Structures
No full textThis study introduces a new type of directional transducer designed for Ultrasonic Guided Waves (GWs)-based Structural Health Monitoring (SHM) applications. GWs inspection typically involves controlling several piezoelectric transducers placed on the component being inspected. However, the deployment of such systems is impeded by weight penalties, complex circuitry, and maintenance concerns arising from extensive wiring. To address these challenges and simplify hardware while reducing costs, shaped transducers with inherent directional capabilities such as Frequency Steerable Acoustic Transducers (FSATs) can be utilized. FSATs make use of spatial filtering that varies with frequency, establishing a direct correspondence between signal propagation direction and the spectral characteristics of transmitted or received signals. The new generation of FSATs eliminates the 180° ambiguity issue present in previous FSATs, enabling 360° surface scanning for defect detection through excitation frequency variation with minimal software/hardware requirements in a quick manner. Finite Element (FE) simulations along with experimental validations using Scanning Laser Doppler Vibrometer (SLDV) were carried out to validate the transducer performance, showing a robust frequency-dependent unidirectionality of the proposed device
- …
