Tamer Elnady

Bio: Tamer Elnady is an academic researcher from Ain Shams University. The author has contributed to research in topics: Noise & Muffler. The author has an hindex of 14, co-authored 51 publications receiving 713 citations. Previous affiliations of Tamer Elnady include Royal Institute of Technology.

Discovery of a big void in Khufu’s Pyramid by observation of cosmic-ray muons

Abstract: The Great Pyramid or Khufu’s Pyramid was built on the Giza Plateau (Egypt) during the IVth dynasty by the pharaoh Khufu (Cheops), who reigned from 2509 to 2483 BC$^1$ . Despite being one of the oldest and largest monuments on Earth, there is no consensus about how it was built. To better understand its internal structure, we imaged the pyramid using muons, which are by-products of cosmic rays that are only partially absorbed by stone. The resulting cosmic-ray muon radiography allows us to visualize the known and potentially unknown voids in the pyramid in a non-invasive way. Here we report the discovery of a large void (with a cross section similar to the Grand Gallery and a length of 30m minimum) above the Grand Gallery, which constitutes the first major inner structure found in the Great Pyramid since the 19$^{th}$ century. This void, named ScanPyramids Big Void, was first observed with nuclear emulsion films installed in the Queen’s chamber (Nagoya University), then confirmed with scintillator hodoscopes set up in the same chamber (KEK) and re-confirmed with gas detectors12 outside of the pyramid (CEA)This large void has therefore been detected with a high confidence by three different muon detection technologies and three independent analyses. These results constitute a breakthrough for the understanding of Khufu’s Pyramid and its internal structure. While there is currently no information about the role of this void, these findings show how modern particle physics can shed new light on the world’s archaeological heritage

Validation of an Inverse Semi-Analytical Technique to Educe Liner Impedance

Abstract: In this paper, the acoustic impedance of a liner is educed by a novel semi-analytical inverse technique. The liner sample is placed flush with the solid walls in a rectangular duct with grazing flo ...

On Semi-Empirical Liner Impedance Modeling with Grazing Flow

Abstract: Noise is created at the front of turbofan engines where a large-diameter fan spins at high speed to continuously compress a large volume of air. The engine is wrapped in a nacelle that has acoustic treatment to damp and absorb noise generated by the fan. This acoustic treatment is commonly of the locally reacting type. The impedance of these liners is what determines their efficiency to absorb sound waves. A lot has been published on modeling the impedance of liners, but there are still some unanswered questions. There are different criteria for defining the end correction that is added due to the finite length of the orifices and the effect of the interaction between neighboring orifices. There are several models available for the effect of grazing flow. The aim of the current paper is to contribute to answering some questions through impedance measurements on a large number of liners with grazing flow. Empirical expressions for the liner impedance were deduced. The perforate model is also of interest to the car silencers applications. A new impedance measurement technique is also proposed in this paper, which is based on liner educing methods.

An inverse analytical method for extracting liner impedance from pressure measurements

Abstract: The in-situ method has been used for a long time as an easy, quick and direct method for measuring the acoustic impedance of locally reacting liners with and without flow. Several drawbacks and problems have been reported with the use of this method, which motivated the development of indirect methods to deduce the impedance from the measurement of the pressure field. A new inverse analytical technique is presented in this paper. The liner sample is placed inside a rectangular duct. The amplitude of the plane wave incident towards the lined section is measured using the two-microphone technique. The reflection coefficient at the exit plane is also measured using the same technique. These measured values are fed to an analytical model for sound propagation through the lined section, which is constructed using mode-matching. A minimization scheme is used to find the liner impedance value in the complex plane to match the calculated sound field to the measured one at the microphone positions already used for the two microphone measurements. The results show that the proposed technique can educe or measure the impedance to an acceptable accuracy.

Harnessing Multiple Folding Mechanisms in Soft Periodic Structures for Tunable Control of Elastic Waves

Abstract: Mechanical instabilities in periodic porous elastic structures may lead to the formation of homogeneous patterns, opening avenues for a wide range of applications that are related to the geometry of the system. This study focuses on an elastomeric porous structure comprising a triangular array of circular holes, and shows that by controlling the loading direction, multiple pattern transformations can be induced by buckling. Interestingly, these different pattern transformations can be exploited to design materials with highly tunable properties. In particular, these results indicate that they can be effectively used to tune the propagation of elastic waves in phononic crystals, enhancing the tunability of the dynamic response of the system. Using a combination of finite element simulations and experiments, a proof-of-concept of the novel material is demonstrated. Since the proposed mechanism is induced by elastic instability, it is reversible, repeatable, and scale-independent, opening avenues for the design of highly tunable materials and devices over a wide range of length scales.

Exploiting Microstructural Instabilities in Solids and Structures: From Metamaterials to Structural Transitions

Abstract: Instabilities in solids and structures are ubiquitous across all length and time scales, and engineering design principles have commonly aimed at preventing instability. However, over the past two decades, engineering mechanics has undergone a paradigm shift, away from avoiding instability and toward taking advantage thereof. At the core of all instabilities—both at the microstructural scale in materials and at the macroscopic, structural level—lies a nonconvex potential energy landscape which is responsible, e.g., for phase transitions and domain switching, localization, pattern formation, or structural buckling and snapping. Deliberately driving a system close to, into, and beyond the unstable regime has been exploited to create new materials systems with superior, interesting, or extreme physical properties. Here, we review the state-of-the-art in utilizing mechanical instabilities in solids and structures at the microstructural level in order to control macroscopic (meta)material performance. After a brief theoretical review, we discuss examples of utilizing material instabilities (from phase transitions and ferroelectric switching to extreme composites) as well as examples of exploiting structural instabilities in acoustic and mechanical metamaterials.

A New Type of Muffler Based on Microperforated Tubes

Abstract: Microperforated plate (MPP) absorbers are perforated plates with holes typically in the submillimeter range and perforation ratios around 1%. The values are typical for applications in air at stand ...

Failure of the Ingard–Myers boundary condition for a lined duct: An experimental investigation

Abstract: This paper deals with experimental investigation of the lined wall boundary condition in flow duct applications such as aircraft engine systems or automobile mufflers. A first experiment, based on a microphone array located in the liner test section, is carried out in order to extract the axial wavenumbers with the help of an “high-accurate” singular value decomposition Prony-like algorithm. The experimental axial wavenumbers are then used to provide the lined wall impedance for both downstream and upstream acoustic propagation by means of a straightforward impedance education method involving the classical Ingard–Myers boundary condition. The results show that the Ingard–Myers boundary condition fails to predict with accuracy the acoustic behavior in a lined duct with flow. An effective lined wall impedance, valid whatever the direction of acoustic propagation, can be suitably found from experimental axial wavenumbers and a modified version of the Ingard–Myers condition with the form inspired from a previous theoretical study [Auregan et al., J. Acoust. Soc. Am. 109, 59–64 (2001)]. In a second experiment, the scattering matrix of the liner test section is measured and is then compared to the predicted scattering matrix using the multimodal approach and the lined wall impedances previously deduced. A large discrepancy is observed between the measured and the predicted scattering coefficients that confirms the poor accuracy provided from the Ingard–Myers boundary condition widely used in lined duct applications.