Influence Of Geometrical Constraints Research Articles

Influence of geometric constraints on aircraft design

The paper considers the requirements to helicopter operating conditions, forming geometrical constraints at the design stages and their influence on the geometrical appearance of the helicopter as a whole, structural design and layout of individual components and assemblies of helicopters. The methodology of forming the system of geometrical constraints is based on the generalised requirements to ensure the operational and technical characteristics of the helicopter: ensuring the basing and production of take-off and landing operations on marine vessels, ensuring transportability, ease of access to the cockpit, ease of access to the units during maintenance, reducing the labour intensity of individual helicopter maintenance operations.

Droplet breakup in a parallel microchannel with asymmetrical geometric constraints

Here we demonstrate the influence of downstream geometric constraints on droplet breakup and subsequent distribution dynamics in a microdevice containing constricted and parallel microchannels. The microfluidic configuration consists of a sequential connection of T-junction, branching-junction, and two parallel arms with different converging-straight-diverging (CSD) sections at the downstream. Geometric asymmetry was incorporated by only varying the CSD section in terms of converging-diverging angle, throat-width, and throat-length. We observed two distinct breakup regimes, namely obstructed and tunnel for all three microdevices. We found the degree of breakup asymmetry resulting from downstream feedback to increase with increasing continuous phase Reynolds number and dispersed phase capillary number. Our results show that the droplet split asymmetry and the influence of geometric constraints are more discerning for tunnel regime than the obstructed breakup. It highlights the significance of downstream feedback in a constricted and parallel microchannel network.

Stretching a Polymer Chain in a Confined Space

The quantitative characterization of micromechanical properties of polymer biomaterials and the development of advanced biological micro-/nano- technology and devices need to quantitatively analyze the statistical thermodynamic properties and behaviors of polymer chains such as biological macromolecules in complex microenvironment. In the process of achieving this goal, the cross research of continuum mechanics and statistical thermodynamics plays a very important role. Aiming at the mechanics problems in this field, starting from the force stretching of DNA molecules, and by introducing several theoretical models describing the statistical thermodynamic properties of polymer chains, it is pointed out that the wormlike chain model has more significant advantages in describing the relationship between force and configuration change of semi-flexible polymer chains than other ideal random chain models, so that the qualitative and quantitative understanding of the statistical thermodynamic properties and behavior of polymers in complex microenvironment has become largely dependent on the relevant research progresses based on the wormlike chain model. Based on this fact, by reviewing the research on the influence of geometric constraints on the random conformation distribution of polymer chains, the research on the statistical thermodynamic model of polymer chains under the simultaneous action of tension and constraints, and the simulation research on the statistical physical properties of polymer chains based on high-performance computers, the latest progress and challenging problems in the research of statistical thermodynamic properties and behavior of worm chains under different constraints and stress microenvironments are summarized. Finally, through summary and analysis, it is pointed out that the study of statistical thermodynamics of worm chain in complex microenvironment is an important basis for understanding life phenomena from the molecular and cell scale, developing advanced micro- and nano- technology and constructing the constitutive relationship of soft matter. At present, it has become a very challenging frontier topic in the interdisciplinary of mechanics.

About Compression Fracture

The paper discusses fracture processes occurring under compressive loads. The processes are considered from two points of view: (i) compression fracture mechanisms and their effect on the strength and fracture resistance of the material, and (ii) the effect of geometric constraints on the stress-strain state and fracture conditions of bodies (natural objects) with cracks and crack-like defects. These are particularly the effects associated with crack surface contact, friction, and loading history. Fracture structures are described which form in the conditions of high-rate compression under extreme loads typical of tectonic processes and deep hydrocarbon production. The structures include crack-like compaction regions in highly porous brittle materials (rocks) formed under compression, which present a new form of quasi-brittle mode I fracture (a compression crack). A method is proposed for estimating the effective strength of compressed bodies with one dimension (thickness) being much smaller than the other two and that have through-thickness variable properties and/or composition. As an example, the ice cover strength with respect to longitudinal compression is considered taking into account a partial loss of the ice bearing capacity. The influence of geometric constraints on the fracture mechanisms in fractured thin bodies is discussed. It is shown that the compression fracture of bodies with elongated through holes (or crack-like defects), whose length is much larger than the body thickness, occurs by a mechanism induced by the overlapping of crack surfaces.

Numerical Simulation of Micro-Galvanic Corrosion in Al Alloys: Effect of Geometric Factors

A finite element model for simulating the propagation of intermetallic particle driven micro-galvanic corrosion in an Al-matrix model system is presented. The model revealed dynamic changes related to localized corrosion, including the moving dissolution boundary, the deposition of reaction products (Al(OH)3), and their blocking effect. Modelling was focused on the effects of key geometric parameters, including the radius of cathodic particle (range 0.5 to 4 μm) and the width of an assumed anodic ring surrounding the particle (range 0.1 to 2 μm). Simulations revealed the dynamic flow of molecular and ionic species, along with influence of geometrical constraints. For ring widths below 0.5 μm, deposition of Al(OH)3 inside the dissolving volume was inhibited due to limited transport of OH− and O2 into a constrained volume − resulting in local acidification. An increase in cathodic particle radius at given ring width resulted in a greater dissolution by providing a larger cathodic area for O2 reduction, quantifying the effect of cathode/anode ratio. The model was also developed to include two cathodic particles to explore any interaction. The present study reveals a physicochemical model that contributes toward a framework for multi-process localized corrosion systems, which can be further adapted to commercial alloy systems.

Beautification and efficiency improvement of 3D modelling with the help of geometric constraints

We emphasise on the influence of geometric constraints in 3D reconstruction. In fact, we have used a new approach of 3D reconstruction which is based on bundle adjustment optimisation and constraints. Our purpose is to achieve 3D reconstruction in a simple, fast and efficient way without any prior information about cameras and 3D space. Constraints use brings us many advantages; it helps us to reduce estimated parameters number and stabilises good results quality. We try as much as possible through a comparative analysis to prove the importance of constraints use, in terms of results reliability, process speed and convergence rate. We use uncalibrated views, so we don't have any pertinent initial values used in Levenberg-Marquardt. On the hand, and thanks to the estimation of cameras' positions with constraints during Levenberg-Marquardt optimisation, we solve with the convergence problem satisfactorily. Several data will be used with the aim to demonstrate the efficiency of our present approach under different uses and kinds of constraints.

Beautification and efficiency improvement of 3D modelling with the help of geometric constraints

We emphasise on the influence of geometric constraints in 3D reconstruction. In fact, we have used a new approach of 3D reconstruction which is based on bundle adjustment optimisation and constraints. Our purpose is to achieve 3D reconstruction in a simple, fast and efficient way without any prior information about cameras and 3D space. Constraints use brings us many advantages; it helps us to reduce estimated parameters number and stabilises good results quality. We try as much as possible through a comparative analysis to prove the importance of constraints use, in terms of results reliability, process speed and convergence rate. We use uncalibrated views, so we don't have any pertinent initial values used in Levenberg-Marquardt. On the hand, and thanks to the estimation of cameras' positions with constraints during Levenberg-Marquardt optimisation, we solve with the convergence problem satisfactorily. Several data will be used with the aim to demonstrate the efficiency of our present approach under different uses and kinds of constraints.

Frustrated packing of spheres in a flat container under symmetry-breaking bias.

We study statistical properties of packings of monodisperse spheres in a flat box. After "gravitational" filling and appropriate agitation, a nearly regular (in plane) but frustrated (normal to the plane) triangular lattice forms, where beads at individual sites touch either the front or back wall. It has striking analogies to order in antiferromagnetic Ising spin models. When tilting the container, Earth's gravitational field mimics external forces similar to magnetic fields in the spin systems. While packings in vertical containers adopt a frustrated state with statistical correlations between neighboring sites, the configurations continuously approach the predictions of a random Ising model when the cell tilt is increased. Our experiments offer insights into both the influence of geometrical constraints on random granular packing and a descriptive example of frustrated ordering.

Uniform Field Solenoid Optimization Study

A numerical study was performed on homogeneous field synthesis problem. The influence of geometrical constraints on the important characteristics of uniform field solenoids was studied. These characteristics are: complexity of the shape of current distribution, peak field strength in windings, and relative cost of the solenoid. For superconducting magnets, minimization of the peak field is considered to be one of the primary goals of optimization. An algorithm based on linear programming was proposed to calculate the optimal coil arrangements with minimal peak field. These results were compared to ones obtained by another method, a regularization technique for the field error least squares problem.

Patterns in diversity of anurans along an elevational gradient in the Western Ghats, South India

AbstractAim To examine patterns in anuran species richness along an elevation gradient and identify factors that govern anuran species richness on a tropical elevational gradient.Location Sampling for anurans was carried out in Kalakad Mundanthurai Tiger Reserve (KMTR) in the southern Western Ghats, India.Methods Night‐time sampling for anuran species richness was carried out from 20 November 2004 to 20 April 2005, during the north‐east monsoon and dry seasons, using transects (50 × 2 m) and visual encounter surveys along the streams. The entire gradient was classified into thirteen 100‐m elevation zones. Sampling at the alpha (single drainage basin) level was carried out in the Chinnapul River drainage basin (40–1260 m a.s.l.) and at the gamma (landscape) level in four drainage basins. Additionally, published records were used to arrive at an empirical species richness (S) for the entire landscape. Mid‐Domain Null software was used to test for the possible influence of geometric constraints on anuran species at both the alpha and gamma levels. The influence of area under each elevation zone on empirical S was tested. The pattern in anuran species richness along the elevational gradient was investigated using: (1) species boundaries in each elevation zone and their habitat correlates, (2) abiotic factors as predictor variables, (3) mean snout vent lengths of anurans, and (4) correlation between the matrices of distance in the elevation zones based on microhabitat parameters and species composition. Cluster analysis on species presence–absence in the elevation zones was used to categorize the entire gradient into high, middle and low elevations. In these three elevation categories, pattern in composition of species was examined for endemism in Western Ghats–Sri Lanka biodiversity hotspot, uniqueness to an elevation zone, adaptations of adults and modes of breeding.Results Species richness at the alpha level increased linearly with elevation, while at the gamma level there were three peaks. Maximum species richness was observed at the highest elevation (1200 m) at both the alpha and the gamma levels. The observed patterns differed significantly from mid‐domain null predictions. The multi‐modal pattern in species richness was a consequence of overlapping species range boundaries. Soil temperature was the best single measure in explaining the majority of variation in species richness at the alpha level (r2 = 0.846, P < 0.01). However, soil moisture was the best predictor when both the alpha and the gamma sites were pooled (r2 = 0.774, P < 0.01). Anuran body size decreased with an increase in elevation. The highest proportions of endemic and unique species were found at high elevations (> 700 m). The proportion of arboreal anurans increased from low to high elevation. Anurans exhibiting direct development were predominantly found at high elevations.Main conclusions Geometric constraints did not influence anuran species richness along the elevational gradient. Overlapping range boundaries influenced species richness at the gamma level. Abiotic factors such as soil temperature and moisture influenced anuran species richness in the mountain range. The ‘Massenerhebung effect’ could be responsible for range restriction and endemism of anurans, differences in guilds and mode of reproduction. These findings highlight the importance of cloud forests for endemic anurans.

The influence of modeling assumptions on the modal analysis of vocal fold structures

Finite-element modal analysis studies of several vocal fold structural models were performed in vacuo under a variety of assumptions. The sensitivity of the vocal folds to changes in geometry and tissue properties was investigated. The Ritz method and the finite-element code adina were used to perform linear modal analysis of two-dimensional and three-dimensional models of the human vocal folds. The results allow for comparison and evaluation of various modeling approaches. In particular, the influence of geometrical constraints was shown to introduce errors of varying magnitude depending on the degree of anisotropy of the vocal fold tissue. [Research supported by the National Institute for Deafness and Other Communication Disorders.]

Photochemistry of .alpha.'-substituted .beta.,.gamma.-cyclopropyl cyclic ketones. Influence of geometric constraints and substituent effects on competitive Norrish type I photoreactions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPhotochemistry of .alpha.'-substituted .beta.,.gamma.-cyclopropyl cyclic ketones. Influence of geometric constraints and substituent effects on competitive Norrish type I photoreactionsRoger K. Murray Jr. and Thomas M. FordCite this: J. Am. Chem. Soc. 1980, 102, 9, 3194–3198Publication Date (Print):April 1, 1980Publication History Published online1 May 2002Published inissue 1 April 1980https://doi.org/10.1021/ja00529a050RIGHTS & PERMISSIONSArticle Views118Altmetric-Citations5LEARN 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 (641 KB) Get e-Alerts Get e-Alerts

Error matrices in gas-electron diffraction: II. Influence of weight matrix

The properties of three different forms of error matrices in electron diffraction are investigated, assuming the presence of stationary, Gaussian, Markovian noise in the primary data. The error matrices studied are M x p based on the optimum weight matrix P the bona fide error matrix M x w based on the nonoptimum weight matrix W , and the false error matrix M x o commonly calculated by diffractionists using the formula for the optimum error matrix while incorporating a nonoptimum weighting. Simple formulae relating the elements of the various matrices are derived in the case where W is the best diagonal weight matrix and where geometric constraints are not imposed on parameters. The influence of geometric constraints is tested. Calculations indicate that diagonal weight matrices in ordinary circumstances give results imperceptibly inferior to the results obtained with the best nondiagonal weight matrices. Elements of M x w closely approach those of M x p whereas elements of the false error matrix, taken alone, may be very misleading.