External Corners Research Articles

Impact of Density Gradients on the Stress Level Within a Green Ceramic Compact During Drying

: Internal water content and mechanical stress distributions during convective drying were simulated for a homogeneous and a heterogeneous (with density gradients) annular compact of a green ceramic agglomerate. A diffusive model for water transfer and an elastic model for structural mechanics were applied. Based on experimental measurements, the material apparent density was numerically implemented as a function of spatial coordinates and the key material properties (moisture diffusivity and the Young's modulus) were implemented as functions of material density. The heterogeneous compact (with density peaks at the top edges) exhibited three times larger circumferential tensile stress at the top external radius corner than that exhibited by the homogeneous one.

Experimental investigation of turbulence-driven secondary motion over a streamwise external corner

Turbulence-driven secondary motion (known as secondary flow of Prandtl's second kind) is the result of the anisotropy of Reynolds stresses. It is associated with internal or external turbulent flow in the vicinity of streamwise corners. In the last six decades the flow along the streamwise internal corner has attracted the attention of many researchers, but it is only recently at the University of Melbourne that an experimental investigation on a flow over an external corner has been undertaken. Although the turbulence-driven secondary motions are generally much smaller than those resulting from skewing of the mean spanwise vorticity (known as secondary flow of Prandtl's first kind), they have a pronounced effect on peripheral wall shear stress distributions and heat transfer rates in the corner region. In the present study the details of turbulence-driven secondary motion over the external corner are explored experimentally and a counter-rotating helical streamwise vortex pair symmetrically placed around the corner bisector is found. As expected, all mean velocity and Reynolds stress profiles on both surfaces at the same spanwise distance from the corner agree quite well, having nominal deviation. The secondary flow is observed to be directed away from the corner bisector and then flow back towards the wall. It is also revealed that far from the corner, the flow develops as a nominal two-dimensional flat-plate boundary-layer flow.

A Measurement of Illusional Amount of the Height about Internal Corner and External Corner Figures in Interior Space

A Measurement of Illusional Amount of the Height about Internal Corner and External Corner Figures in Interior Space

Flow along streamwise corners revisited

In this paper we investigate the three-dimensional laminar incompressible steady flow along a corner formed by joining two similar quarter-infinite unswept wedges along a side-edge. We show that a four-region construction of the potential flow arises naturally for this flow problem, the formulation being generally valid for a corner of an arbitrary angle (π−2α), including the limiting cases of semi- and quarter-infinite flat-plate configurations. This construction leads to five distinct three-dimensional boundary-layer regions, whereby both the spanwise length and velocity scales of the blending intermediate layers are O(δ), with Re−1/2 [Lt ] δ [Lt ] 1, Re being a reference Reynolds number supposed to be large. This reveals crucial differences between concave and convex corner flows. For the latter flow regime, the corner-layer motion is shown to be mainly controlled by the secondary flow which effectively reduces to that past sharp wedges with solutions being unique and existing only for favourable streamwise pressure gradients. In this regime, the corner-layer thickness is shown to be O(Re−0.5+α/π/δ2α/π), −½π [les ] α [les ] 0, which is much smaller than O(Re−1/2) for concave corner flows.Crucially, our numerical results show conclusively that, for α ≠ 0, closed streamwise symmetrically disposed vortices are generated inside the intermediate layers, confirming thus the prediction made by Moore (1956) for a rectangular corner, which has so far remained unconfirmed in the literature.For almost planar corners, three-dimensional corner boundary-layer features are shown, as in (Smith 1975), to arise when α ∼ O(1/ln Re). On the other hand, we show that the flow past a quarter-infinite flat plate would be attained when both values of the streamwise pressure gradient and external corner angle (π+2α) become O(1/ln Re) or smaller.Numerical results for all these flow regimes are presented and discussed.

Experimental investigation of turbulent boundary layer developing along a streamwise external corner (chine)

Turbulent viscous fluid flow is always accompanied by a secondary flow if the flow is not exactly two-dimensional or exactly axisymmetric. The classic example is duct flow, where counter-rotating pairs of vortices appear in each corner, distorting the isoaxialvelocity contours. The present investigation of the turbulent boundary-layer development along a streamwise external corner (chine) also shows distortion of the isoaxialvelocity contours which predicts the presence of a pair of counter-rotating vortices. These vortices or secondary flow are induced by inequality of Reynolds stresses around the corner. The direct effect of this corner flow is to increase the drag force. A series of experimental investigations at the University of Melbourne provided, in qualitative terms, the general behaviour expected from this class of flow as revealed by Elder [J. Fluid Mech. 9 (1960) 133] and Xu and Pollard [Phys. Fluids 13 (2001) 3321]. This flow is also expected to exhibit symmetry about the corner bisector. Our measurements indicate quasi-symmetry about the bisector all along the corner.

建物最上層におけるL字形接合部の耐力機構モデル

In this paper some load-resistant models of Lrshaped beam-column joints on the top story of a building frame are proposed based on experimental research results. It is presented in the models that, for the external corner joints, not only shear mechanisms but flexural mechanisms also affect the joint strength. The flexural strength of the joint is determined by the anchorage strength of beam longitudinal reinforcement when the frame is subjected to closing moment. Subjected to opening moment it is influenced by transverse reinforcement in the joint and the projected development length of the beam or column longitudinal reinforcement. The calculated load capacities of the joints were compared with the experimental results, and good agreement was obtained.

Verification jig for implant-supported prostheses: A comparison of standard impressions with verification jigs made of different materials

Statement of Problem. Implant verification jigs are routinely used during the fabrication of implant-supported prostheses. The dimensional accuracy of these jigs is unknown. Purpose. The purposes of this study were to (1) compare the dimensional accuracy of verification jigs with that of conventional impression procedures and (2) measure the dimensional accuracy of 3 resin materials used to fabricate verification jigs. Material and Methods. Thirty verification jigs and 20 impressions were made of 3 externally hexed Steri-Oss implants in a master stone base according to the following groups (n = 10 per group): (Group 1) Jig: GC pattern resin; (Group 2) Jig: Duralay resin; (Group 3) Jig: Triad gel resin; (Group 4) Impression: closed-tray impression copings; and (Group 5) Impression: open-tray impression copings. A stone base was fabricated for each experimental jig and impression. Master stone base and experimental stone bases were measured with the following methods: X and Y coordinates of each implant center were obtained with a traveling microscope by averaging the X and Y coordinates of the implant external hex corners. The origins of the coordinates during measurement of each base were arbitrary. Distances between implant center points were calculated by use of the Pythagorean theorem. Vertical measurements (Z-plane) were obtained with a digital caliper at the 2 terminal-implant locations. Interimplant distances and vertical measurements were subtracted from those of the master base, and the resultant distortion values were analyzed with analysis of variance and Tukey Studentized range tests. Statistical significance was set at P<.05. Results. Verification jigs were not significantly more accurate than standard impression procedures. Open-tray impressions showed a significantly greater vertical distortion (Z-R location: 262 ± 158 μm; P=.0001; Z-L location 333 ± 189; P=.0001) compared with the other groups. Triad gel jigs showed a significantly greater distortion in one interimplant distance (C-L) than closed-tray impressions (P=.04), whereas Duralay jigs exhibited significant greater distortion than closed-tray and open-tray impressions in the interimplant distance R-C (P=.006). Although not significantly different from other groups, the closed-tray group showed the lowest mean distortion values in all measurements. Conclusion. Within the limitations of this study, the accuracy provided by verification jigs was not significantly superior to standard impression procedures. The results suggest that jig fabrication does not improve the dimensional accuracy of stone casts. Open-tray impressions showed a significantly greater inaccuracy in the vertical plane. (J Prosthet Dent 2002;88:329-36.)

Simulation of rotational arc sensing in gas metal arc welding

A mathematical model for the behaviour and interaction of power source, electrode extension, welding arc, and welding joint geometry is applied to simulation of seam tracking signals from high speed rotating electrodes in gas metal arc welding of carbon steel. Sensor signals from a tilted electrode approaching internal and external fillet corners are analysed, as well as the frequency dependence of signal amplitude from a perpendicular electrode. The simulations are compared with experimental results from other references showing good agreement. The current signals are stronger than predicted from static arc characteristics, suggesting important dynamic effects in the behaviour of the electrode extension.

Weakly singular stress-BEM for 2D elastostatics

A weakly singular stress-BEM is presented in which the linear state regularizing field is extended over the entire surface. The algorithm employs standard conforming C0 elements with Lagrangian interpolations and exclusively uses Gaussian integration without any transformation of the integrands other than the usual mapping into the intrinsic space. The linear state stress-BIE on which the algorithm is based has no free term so that the BEM treatment of external corners requires no special consideration other than to admit traction discontinuities. The self-regularizing nature of the Somigliana stress identity is demonstrated to produce a very simple and effective method for computing stresses which gives excellent numerical results for all points in the body including boundary points and interior points which may be arbitrarily close to a boundary. A key observation is the relation between BIE density functions and successful interpolation orders. Numerical results for two dimensions show that the use of quartic interpolations is required for algorithms employing regularization over an entire surface to show comparable accuracy to algorithms using local regularization and quadratic interpolations. Additionally, the numerical results show that there is no general correlation between discontinuities in elemental displacement gradients and solution accuracy either in terms of unknown boundary data or interior solutions near element junctions. Copyright © 1999 John Wiley & Sons, Ltd.

Development of the micromilling process for high-aspect-ratio microstructures

At the macroscale, the milling process is very versatile and capable of creating three-dimensional features and structures. Adaptation of this process at the microscale could lead to the rapid and direct fabrication of micromolds and masks to aid in the development of microcomponents. This task has been undertaken, and results of the process indicate it can become an increasingly useful method. The micromilling process is characterized by milling tools that are currently in the range from 22-100 /spl mu/m in diameter and made by the focused-ion beam machining process. The tools are used in a specially designed, high-precision milling machine. Results are comparable to other processes currently used to fabricate mold and mask features. The micromilling process can create trench-like features with nearly vertical sidewalls and good smoothness. External corners are sharp and stepped features can be machined simply by programming those shapes. The process is direct, and therefore dimensional errors do not accumulate as can occur with serial fabrication processes.

しわの非接触３‐Ｄ測定システムの開発とその応用

The skin surface is characterized by small ridges, prominences and furrows that change with aging and degree of sun expose. Quantifying such geometric characteristics as the ridges and furrows on the skin surface can provide cosmetic researchers with a means of assessing changes in wrinkles and understanding the wrinkling process.Many attempts have been tried to analyze the features of wrinkles in order to evaluate the efficacy of anti-wrinkles preparations. However, measurement systems proposed up to now have been unable to provide 3-D information about wrinkle shapes. The authors have developed a new non-contact 3-D measurement system to profile wrinkles based on a fringe scanning method using a sinusoidal grating pattern instead of interference fringes generated by laser. The grating projection system makes it possible to capture the three-dimensional nature of the objective. Another feature of the new device is that fringe scanning is introduced to the grating projection system. The system provides a greater density of measurement points and eliminates the influence of skin surface anomalies such as spots, freckles, moles, etc. Using this system, the depth of wrinkles can be obtained within 1.0 second with a depth accuracy of less than ±14μm over an area of 12.5mm×15mm.3-D measurements of wrinkles were taken on the external corners of the eyes of 599 Japanese women ranging in age from 20 to 67. A mathematical model is proposed which aims to assist in understanding the effects of aging and the efficacy of cosmetic products.

A knowledge-based approach to design for manufacturability

In the light of growing global competition, organizations are increasingly under pressure to produce products of high quality and reliability at reasonable cost. The integration of design and manufacturing activities into one common engineering effort has been recognized as a key strategy for survival and growth. Design for Manufacturability (DFM) aims at integrating product design and process design to achieve cost and quality objectives. The implementation of the DFM approach requires the collaboration of both the design and manufacturing functions within an organization. However, due to the divergent orientations of these functions, implementation of the DFM approach has been found to be neither straightforward nor easy. Of the several methodologies available, process-driven design is recognized as one of the more effective DFM approaches. The primary objective of this research is to address the major criteria for manufacturability in the DFM approach using expert systems methodology. An expert system has been developed in two modules--one for process selection and manufacturing cost estimation and the other for evaluation of design features for manufacturability on a CAD system. The expertise for primary process selection is developed for casting and forging processes. The specialized processes considered are die casting, investment casting, sand casting, precision forging, conventional die forging, and open die forging. The processes considered for secondary process selection are end milling and drilling. The cost estimation expertise is developed for the die casting process, milling and drilling operations, and manual assembly operations. A design for a hanger used in the furniture industry is used to demonstrate the process selection and cost estimation capability of the expert system. Three different solid models created in CATIA are used to demonstrate evaluation of design features for manufacturability with respect to milling and drilling operations on a CNC milling machine. The set of manufacturability criteria considered are: (1) perpendicularity of holes to drill entry and exit surfaces, (2) conformance of hole diameters to available standard tool sizes, (3) compatibility of hole depths with respect to hole diameters, (4) adjacency of holes lying on the same surface, (5) rounded inside corners instead of sharp corners in square holes, and (6) chamfered corners instead of rounded external corners. The results obtained from the application of the expert system suggest that the use of a knowledge-based approach to generate accurate cost estimates and analyze design features for manufacturability during the design phase is certainly feasible. Such systems would enhance the quality of design decisions in organizations, resulting in improved competitiveness in the market.

Prediction of inviscid supersonic/hypersonic aircraft flowfields

A spatial marching method called streamline coordinate Riemann axial marching (SCRAM) has been developed to solve the Euler equations for supersonic and hypersonic flow numerically. The equations are formulated in terms of Riemann-type variables using a local streamline coordinate system. Expressed in this way, the equations model wave propagation in a very physical manner with no high Mach number restrictions. High efficiency is achieved on a vector processor. The procedure has been coupled with a versatile grid generation method that automatically sections complex cross-sectional grids into simpler domains on the basis of singular geometry points, such as sharp internal or external corners. SCRAM predictions have been validated by comparison with test data for several realistic aircraft configurations, including cases with nonzero sideslip. The comparisons include force and moment data and surface pressure data. A fully iterative procedure has been developed to start the SCRAM code on arbitrary blunt-nosed configurations and also to handle embedded subsonic regions. An efficient procedure for predicting the effect of control surface deflections has been incorporated and validated against test data. Real gas results for a cone are compared with the analytic solution.

Simulation of Three-Dimensional Shear Flow Around a Nozzle-Afterbody at High Speeds

Turbulent shear flows at supersonic and hypersonic speeds around a nozzle-afterbody are simulated. The three-dimensional, Reynolds-averaged Navier-Stokes equations are solved by a finite-volume and implicit method. The convective and the pressure terms are differenced by an upwind-biased algorithm. The effect of turbulence is incorporated by a modified Baldwin-Lomax eddy viscosity model. The success of the standard Baldwin-Lomax model for this flow type is shown by comparing it to a laminar case. These modifications made to the model are also shown to improve flow prediction when compared to the standard Baldwin-Lomax model. These modifications to the model reflect the effects of high compressibility, multiple walls, vortices near walls, and turbulent memory effects in the shear layer. This numerically simulated complex flowfield includes a supersonic duct flow, a hypersonic flow over an external double corner, a flow through a non-axisymmetric, internal-external nozzle, and a three-dimensional shear layer. The specific application is for the flow around the nozzle-afterbody of a generic hypersonic vehicle powered by a scramjet engine. The computed pressure distributions compared favorably with the experimentally obtained surface and off-surface flow surveys.

Investigation of surface crack opening displacement and its application in pressure vessels and piping

An expression for the surface crack opening displacement (SCOD) in a plate under both tension and bending is presented, on the basis of earlier results obtained from studying stress intensity factors of a flat elliptical crack buried in an infinite body. This expression has been successfully developed in pressure vessels and piping applications, and was experimentally verified in the problem of full-circumferential surface cracks at external nozzle corners in spherical vessels. This practical application showed that the developed expression could be used successfully to evaluate surface crack growth depth in pressure vessels and piping and to monitor their growth rates.

Cold bridging at corners: Surface temperature and condensation risk

This paper describes theoretical modelling and experimental measurements of the wall temperatures in the corners of buildings. A dimensionless cold bridge temperature (DCBT) is proposed as a parameter to characterise cold bridges. A simple resistance model is suggested as an improved method for calculating cold bridge temperatures in corners. This model shows reasonable agreement with both finite-element modelling and measured data. Theoretical studies suggest that an increased internal surface resistance at the comer results in a substantial increase in cold bridging. During transient conditions the DCBT can vary by 50%. The impact of external corners on the risk of mould growth is discussed. Mean internal relative humidities lower than the normally accepted value of 70% are suggested for rooms with significant cold bridges.

Natural convection in open-ended cavities with a porous obstructing medium

The buoyancy-driven convection in an open-ended cavity with an obstructing medium such as a porous material is analyzed in this work. The numerical results of the flow and temperature fields for the range of Darcy-Rayleigh number, Ra ⩽ 350 are given. The importance of the external corners in vorticity generation and flow instability augmentation is discussed. The presence of ‘humps’ as well as the periodic behavior in the variation of the Nusselt number with time are studied. The effects of important variables such as the aspect ratio, the temperature difference, and the Darcy-Rayleigh number on the flow field and the cavity Nusselt number are investigated. Comparisons are also made with previously reported studies of natural convection in a cavity filled with a porous medium.

Laser Hardening of Ring Grooves in Medium Speed Dieselengine Pistons

Internal combustion engine durability is enhanced if the side faces of the ring grooves in the pistons have a wear resistant surface. The present work concerns the development of a technique to achieve local hardening of medium speed steel crowned and cast iron pistons, based on the use of a 5 kW industrial laser. Specific aspects of the development which are discussed include: beam coupling and choice of absorbing coatings, choice of beam power density/interaction time, metallurgy, treatment of the edges of external corners, back tempering, and induced distortion and surface changes. The work has resulted in the treatment of prototype pistons for evaluation in engine trials.

Conical flow near external axial corners as a bifurcation problem

Etude, sur la base de la theorie de l'ecoulement potentiel conique, de l'ecoulement supersonique autour d'une configuration formee de deux ailes delta attachees l'une a l'autre par un bord commun et formant un coin externe

Investigation of the Conical Flowfield Around External Axial Corners.

An experimental investigation has been made of the supersonic flowfield around symmetric and asymmetric external axial corners formed by the juncture of two wedges. The measurements were performed at a Mach number of 2.95 in a 15-cmxl5-cm blow-down wind tunnel at a Reynolds number of 4 x 10/cm. A five-hole conical-head probe that measures pitot pressure and flow angularity was used to explore the flowfield; also, surface oil-flow pictures were taken. The main purpose of the experiments was to provide an answer to questions about the nature of the conical stagnation points. In the symmetric case three conical stagnation points were detected: a saddle point at the corner, flanked by a node on each wedge surface. In the asymmetric configuration, the flow was found to spill over the corner toward the lower pressure side, forming a separated region. Depending on the degree of asymmetry, the separated region contained one or more vortices. It is suggested that a nodal conical stagnation point occurs on the lower pressure surface beyond the separated region.