We study avalanches in a model for a planar crack propagating in a disordered medium. Due to long-range interactions, avalanches are formed by a set of spatially disconnected local clusters, the sizes of which are distributed according to a power law with an exponent tau{a}=1.5. We derive a scaling relation tau{a}=2tau-1 between the local cluster exponent tau{a} and the global avalanche exponen...

In earlier work we developed inductive coupling for surface-mounted Lamb wave transducers operating at relatively low frequencies, such as 300 kHz. We now report on similar inductively-coupled transducers at higher (multiple MHz) frequencies. Our investigation was motivated by a particular application, to examine a box girder top flange, using transducers mounted along the flange edge. We emplo...

We investigate experimentally a Casimir-like effect in a three-dimensional pile of rice, which has a power-law avalanche size distribution. We observe the change in distance between two Plexiglas sheets placed on the pile parallel to each other and parallel to the mean avalanche flow direction, while rice grains are continuously and uniformly falling on top of the pile. The resulting avalanches...

This study performed a quantitative validation on a recently developed pressure sensitive transducer system, the F-Scan sensor system. The results indicate that the sensor is adequate for determination of pressure distribution under contact conditions with soft materials. The linear response of the sensor was up to 1.7 MPa with good homogeneity throughout sensor cells. However, the sensor is se...

In this paper, the detection and the localization of a local perturbation are assessed by analysing the frequency changes only (fundamental mode and overtones). After describing the method used herein applied to the bending beam and based on the perturbation theory, experimental application to a 1D plexiglas beam is shown using frequency and modal analysis technique. The damage is considered as...

The well known zero in the group velocity of the first-order symmetric (S1) plate wave mode has been exploited in air-coupled ultrasonic imaging to obtain significantly higher sensitivity than can be achieved in conventional air-coupled scanning. At the zero group velocity point at the frequency minimum of the S1 mode, a broad range of wavenumbers couple into the first-order symmetric mode at n...

Flow diagnosis using non-invasive techniques such laser Doppler anemometer (LDA) is an important tool to improve the design of artificial heart valves. In the present study, an experimental protocol to obtain flow velocity field and colour coded maps of turbulent eddies dimensions using LDA measurements in a 25 mm bovine pericardium bio prosthesis valve is reported. A transparent Plexiglas cham...

Experiments have been carried out in a 0.1 m internal diameter, 1.88 m height vertical Plexiglas column with an antenna type modified air sparger in the gas-liquid distributor section. This arrangement provides uniform mixing of the fluids, ensures the gas entering the fluidizing section as fine bubbles and reduces the pressure drop encountered through a conventional distributor used for the pu...

The experimental apparatus was composed of a water circulation system, an air supply system, a test section and a measurement system~ Air and water were used as working fluids. . The test section was a vertical rectangular channel of 10mmxlOOmmx700mm made of Plexiglas as shown in Fig.l. The measuremen.t system consisted of the UVP and a personal computer to record and treat data. Water was fed ...

This paper presents results of a comprehensive, large scale experimental study devoted to establishing the relation between the quality of initial gas (mal)distribution, as created by common liquid collecting devices used in redistribution sections of packed columns, and the hydraulics of a structured packing bed. Both dry and wet bed experiments were conducted with air/water system under ambie...