The boundary value problem for low aspect ratio, pointed wings at sonic speed Recent developments in theory

The measurement of quality in auditorium acoustics by subjective scaling methods—A review of developments in theory and practice

Crystal growth velocity was measured in a mercurous chloride system in a two-zone transparent furnace as a function of the Rayleigh number by varying a/L, where a is the radius of the growth tube and L is the transport length. Growth velocity data showed different trends at low and high aspect ratio, a result that does not support the velocity-aspect ratio trend predicted by theories. The system cannot be scaled on the basis of measurements done at a low aspect ratio. Some change in fluid flow behavior occurs in the growth tube as the aspect ratio increases.

Voluminous research exists on the effect of combination of low Reynolds number flow over low aspect ratio flat plate wings for usage in micro-aerial vehicles and UAVs, as they also fly under similar conditions and combination of low aspect ratio and low Reynolds number. It has been well established by many researchers (Torres and Mueller in AIAA 42(5):865–873, 2004; Okamoto and Azuma in AIAA 49(6):1135–1150, 2011; Mizoguchi and Itoh in AIAA 51(7):7–52, 2013; Shields and Mohseni in AIAA 50(1):85–99, 2012; Mizoguchi and Kajikawa in Trans Jpn Soc Aero Sp Sci 59(2):56–63, 2016; Pelletier and Mueller in J Aircr 37(5):825–832, 2000; Liu and Hsiao in J Mech 28(01):77–89, 2012; Taira and Colonius in J Fluid Mech 623:187–207, 2009) that low aspect ratio wings in low Reynolds number flow gives a higher lift coefficient and stall angle is also increased which is quite different from the high aspect ratio wing. Also, it is a well-established fact in the existing literature that linear theories cannot be applied as in case of high aspect ratio wings because of non-linear increase in lift coefficient. The reason for such increase in lift and stall angle has been attributed to wingtip vortices that become prominent in low aspect ratio wings called the vortical lift which keeps on increasing up to a certain high angle of attack till it interacts with the separation bubble. In the past, very limited work has been done to study the vortices and their contribution in enhancement of aerodynamic characteristics. In the present work, flat plate model with corrugations at an aspect ratio (AR) of 1.0 are studied and compared with flat plate wing of AR 1.0; also flow visualization in water tunnel has been carried out at Reynolds number of 102 to ascertain the flow physics involved.

Experiments regarding vortex-induced vibration (VIV) on floating circular cylinders with low aspect ratio, L/D = 0.5, and different free-end conditions were carried out in a recirculation water channel. The floating circular cylinders were elastically supported by a set of linear springs to provide low structural damping on the system. Four different free-end corner shape conditions were tested, namely r/R = 0.0, 0.25, 0.5 and 1.0; where r/R is the relation between chamfer rounding radius, r, and the radius of cylinder, R. These different free-end conditions were selected to promote changes in the structures shedding around the free end of the cylinder. The aims were to understand the free-end effects on the VIV of floating circular cylinders with very low aspect ratio. The range of Reynolds number covered 2,800 < Re < 55,400. All the results presented here complement the work presented previously for a floating circular cylinder with L/D = 2.0 by Gambarine et al. (2016) [6] - Experimental study of the influence of the free end effects on vortex-induced vibration of floating cylinder with low aspect of ratio, OMAE2016-54623. The present results showed that the amplitudes in both directions were the highest for the semi-sphere case, r/R = 1.0. The amplitudes were almost the same for the other radius values, 0.0 < r/R ≤ 0.5; in which the maximum amplitudes decreased with increasing the corner radius. A critical value, L/Dcrit = 0.5, in which only the free-end structures affect the VIV behavior of the cylinder piercing the free-surface could be stated. The conclusion was that the cylinder free-end affects the VIV behavior for cylinders with very low-aspect ratio.

Low aspect ratio control surfaces may be used on supersonic airplanes and guided missiles. Their deflections will generally create gaps which are approximately in the flight direction (e.g., all-movable tails and variable-incidence wings). The aerodynamic effects of such gaps have nearly always been neglected in theoretical investigations. These gap effects are properly neglected for high aspect ratio control surfaces but, since these effects increase with decreasing aspect ratio, they may be important for low aspect ratio control surfaces. The purpose of this paper is to obtain some understanding of the effects of streamwise gaps in low aspect ratio lifting surfaces at supersonic speeds by investigating a simplified configuration whose gap effects are expected to be typical. The configuration consists of a flat lifting half-delta wing which is adjacent and normal to a vertical wall such that the wing side edge is parallel to the wall and forms a streamwise gap. The usual assumptions of linearized supersonic wing theory are made and the following wing characteristics are studied as functions of gap size, Mach Number, and leading edge sweep: spanwise lift distribution, lift, center of pressure, drag due to lift, and vorticity at the trailing edge. In addition, in connection with wing-tail interference, the strengths and initial positions of the rolled-up trailing vortices are investigated. An illustrative example of the gap effects on wingtail interference is also presented. Viscous effects in the gap, which are important for very small gaps, are discussed qualitatively. E{k', v) — incomplete elliptic integral of second kind =

A dual-role theory of the aspect ratio of the nanofillers for the thermal conductivity of graphene-polymer nanocomposites

3R29. Theory of Porous Media: Highlights in Historical Development and Current State. - R de Boer (Inst fur Mechanik, Univ Essen, Fachbereich 10 Bauwesen, Essen, D-45117, Germany). Springer-Verlag, Berlin. 2000. 618 pp. ISBN 3-540-65982-X. $95.00. Reviewed by N Katsube (Dept of Mech Eng, Ohio State Univ, 206 W 18th Ave, Columbus, OH 43210).This book consists of historical and recent development of porous material theory, can be used as a reference book in this area. In the early and classical era, general development of continuum mechanics such as Cauchy's formulation of the stress concept, the development of linear elasticity theory, and the foundation of thermodynamics are summarized. At the end of each chapter, biographical notes of the important contributors are outlined. There the readers could learn about the lives of these prominent researchers, including their characters, and the nature of scholarly debates. The readers can also learn about how the lives of these researchers were influenced by the historical events, and how failure in one event had led to success in another. In the modern era, the emphasis is placed on the porous materials. The historical review includes the controversy between Fillunger and von Terzaghi and the subsequent development of the theory by Biot and others. Further development of elasticity and plasticity theories and a more modern framework of continuum mechanics and mixture theory are also discussed. The current state of porous material theory reflects the author's work as well as the related work developed mostly in Europe. It is based on the assumption that the deformation gradient of the constituent can be separated into the part due to the real material and the part due to the change of the pores in size and shape through a multiplicative decomposition process. In developing constitutive theories, the principle of material objectivity as well as entropy inequality is employed. An extensive development of a porous material theory is presented based on these theoretical frameworks.Theory of Porous Media: Highlights in Historical Development and Current State is a great book to have if you would like to know about the historical development of porous material theory since many of the letters and articles written by the researchers in early days are not available in English. In addition, if you would like to follow the recent development of porous material theory, which is consistent with the above stated assumptions, this book will provide an extensive review. However, the reader should be aware that this is not the only approach available in the area of porous materials. There are a number of different approaches available for the development of constitutive behavior of porous materials. These other approaches are more phenomenologically based and often motivated by experimental observations. The developed models are verified by experimental data and used to solve important practical problems.

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ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTComments upon Recent Developments in Theory of FiltrationB. F. Ruth, R. E. Montonna, and G. H. MontillonCite this: Ind. Eng. Chem. 1931, 23, 7, 850–851Publication Date (Print):July 1, 1931Publication History Published online1 May 2002Published inissue 1 July 1931https://doi.org/10.1021/ie50259a036RIGHTS & PERMISSIONSArticle Views57Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (326 KB) Get e-Alerts

Theories of generation of acoustic and magnetohydrodynamic waves are briefly reviewed with a special emphasis on their applicability to stellar convection zones. Recent developments in these theories and possible directions for future studies are discussed. A new approach allowing to extend the Lighthill-Proudman theory of sound generation to a non-isothermal medium is also presented.

The objective of this paper is to characterize the droplet deformation during transport and to show how the droplet morphology changes at different gap heights in digital microfluidics systems. The aspect ratio defined as the ratio between the gap height to the electrode side length will be varied within the range of high to extremely low. In this way, we will demonstrate that the droplet morphology significantly changes during transport when the aspect ratio is changed. Analogous to the channel dimensions, the gap height and the electrode side length are the two most important geometrical variables affecting droplet motion in digital microfluidic systems. In this study, the droplet deformation was found to be minimal at higher aspect ratios. Contrarily, the droplet will exhibit severe necking and elongation at very low aspect ratios. The deformation and necking patterns were found to be similar to the necking pattern that happens during splitting. However, the droplet exhibits this necking when it is only driven by one activated electrode during the transport process. On the other hand, the droplet is pulled by driving forces from two opposite directions in the conventional splitting process. Extended simulations are performed to investigate the effect of changing the aspect ratio and the actuation voltage used. The simulations were performed by FLOW-3D software which uses the volume of fluid (VOF) technique. The results confirm the effect of changing the gap height on the droplet behavior during motion. The extreme deformation and necking happens only at very low aspect ratios. In this case, the transport process starts by moving a small portion of the droplet toward the activated electrode. When this small portion advances toward the activated electrode the rest of the droplet is not greatly affected or pulled toward the same direction. It can be noticed that the remaining portion of the droplet is not moving at the initial stages of motion and the droplet start to be squeezed gradually through a neck instead of moving in a bulk form. Further observations demonstrated droplet elongation and delayed response of the back portion of the droplet compared to the motion of the leading edge. Analyzing the motion by analytical models can be inaccurate as they assume that the droplet retains its circular shape. Therefore, CFD simulations can demonstrate the droplet behavior better than the analytical models where the droplet exhibits severe deformation and deviation from the circular shape.

Summary The pressure sensitivity of rock elastic properties and seismic velocities is dependent upon pore space, grain size, grain sorting and cementation. An increasing effective pressure gradually reduces the throats between pore. It forces closure of compliant pores with low aspect ratio and reduces porosity. It also changes contact configuration that brings more cement in load bearing network. Present study models stress dependent velocity changes through this mechanical rearrangement of pore and contact system. Although a granular rock is likely to have pore with a spectrum of aspect ratio, we put forward the concept of an ‘effective aspect ratio’ that simulates the rock elastic behavior. Such ratio can be inverted through effective medium solution. It is observed that the effective aspect ratio increases with increasing pressure due to gradual closure of compliant pores having low aspect ratio. This inturn reflects into stress sensitivity of velocities. Using dry core measurements of shear and compression velocities on variety of sandstone under multi-pressure conditions, the validity of proposal is demonstrated. The present work also suggests a stress dependent matrix shear modulus. It accounts for the changing inter-granular frictional force and grain slippage/rotation tendencies, and varying cement contacts in matrix network. It is concluded that matrix shear modulus is significantly affected under low to moderate stress conditions, while changes are small in well cemented granular rocks. The varying aspect ratio and matrix shear modulus can be represented by uniform power laws and govern the changing velocities. It provides a rock intrinsic view to explain the stress dependent elastic behavior and is found applicable to sandstone with different cementation and porosity.

The role of occupant behavior in low carbon oriented residential community planning: A case study in Qingdao

On vortex shedding from low aspect ratio dual step cylinders

A method was devised for estimating aspect ratio, wing ratio, wing area, wing loading, and wing length from study skins of bats. These measures were taken of 136 species representing 15 families. Wing area and loading are positively, and wing length negatively, correlated with size. Aspect and tip ratios are independent of size and of each other. Distinctive combinations of some of these variables characterize groups of bats that presumably have similar flight modes. Speed is positively correlated with aspect ratio and tip index, but regresses significantly only on the former. Long tips coupled with low aspect ratio may characterize hoverers. Long wings and short tips may characterize bats that are capable of remaining airborne at slow speeds. Most bats with low aspect ratios are forest dwellers, whereas species with high aspect ratios are migrants and foragers in open areas.