Curved Side Walls Research Articles

The structure of cross-ventilation flow in an isolated cylindrical building: Numerical study

Cross-ventilation serves as an efficient means to expel pollutants and heat from buildings, requiring no energy consumption due to variations in wind pressure. The structure of the cross-ventilation flow significantly influences ventilation effectiveness. However, limited attention has been given to understanding the impact of a building's cross-section on the structure of cross-ventilation flow. This study aims to fill this gap by numerically investigating the cross-ventilation flow structure in an isolated cylindrical building. The numerical simulation results are validated against reported experimental data, indicating a negligible simulation error of 0.8 % in the volume ventilation rate. This attests to the accuracy of the numerical method in predicting cross-ventilation flow in isolated buildings. As airflow traverses the cylindrical building along the curved side walls, pressure loss diminishes, facilitating increased air inflow. This results in a more horizontal entry of the incoming jet compared to that in a square building. Analysis of Root-Mean-Square streamwise-velocity and turbulence kinetic energy reveals greater airflow fluctuation outdoors for the square building and increased turbulence indoors for the cylindrical building. Notably, the volume ventilation rate of the cylindrical building demonstrates an 8.3 % improvement. Furthermore, the air exchange rate in the cylindrical building surpasses that of the square building by 1.38 times.

Hierarchical Self‐Assembly of Curved Aromatics: From Donor–Acceptor Porphyrins to Triply Periodic Minimal Surfaces

AbstractA saddle‐shaped π‐extended zinc porphyrin containing a peripheral pyridyl ligand undergoes quantitative self‐assembly into a cyclic trimer. The trimer has a prismatic structure with negatively curved side walls, which promote the formation of supramolecular organic frameworks stabilized by dispersion interactions. The first framework type, UWr‐1, has the npo topology, with a hexagonal structure analogous to the Schwartz H triply periodic minimal surface. Co‐crystallization of the trimer with either C60 and C70 produces the isomorphous cubic UWr‐2 and UWr‐3 phases, characterized by the ctn network topology and a structural relationship to the Fischer‐Koch minimal surface S. All three phases contain complex labyrinths of solvent‐filled channels, corresponding to very large probe‐accessible volumes (68 % to 76 %). The UWr‐2 network could be partly desolvated while retaining its long range dimensional order, indicating remarkable strength of the dispersion interactions in the crystal. A theoretical analysis of noncovalent interactions shows the role of geometrical matching between the negatively curved porphyrin units and positively curved fullerenes.

Hierarchical Self-Assembly of Curved Aromatics: From Donor-Acceptor Porphyrins to Triply Periodic Minimal Surfaces.

A saddle-shaped π-extended zinc porphyrin containing a peripheral pyridyl ligand undergoes quantitative self-assembly into a cyclic trimer. The trimer has a prismatic structure with negatively curved side walls, which promote the formation of supramolecular organic frameworks stabilized by dispersion interactions. The first framework type, UWr-1, has the npo topology, with a hexagonal structure analogous to the Schwartz H triply periodic minimal surface. Co-crystallization of the trimer with either C60 and C70 produces the isomorphous cubic UWr-2 and UWr-3 phases, characterized by the ctn network topology and a structural relationship to the Fischer-Koch minimal surface S. All three phases contain complex labyrinths of solvent-filled channels, corresponding to very large probe-accessible volumes (68 % to 76 %). The UWr-2 network could be partly desolvated while retaining its long range dimensional order, indicating remarkable strength of the dispersion interactions in the crystal. A theoretical analysis of noncovalent interactions shows the role of geometrical matching between the negatively curved porphyrin units and positively curved fullerenes.

The effect of side walls on particles mixing in rotating drums

In this paper, we study the effects of the presence and shape of side walls and of the overall length of rotating cylindrical drums on the mixing of particles with differing sizes by application of the discrete element method (DEM). By varying the semi-axis of the spheroidally shaped side walls and the length of the overall drum, we observe the formation of circulation patterns near the side walls. Although there is a vast amount of literature studying mixing regimes in rotating drums, little is known about the effect of the side walls of the drum on particle mixing. The results of our study demonstrate that introducing curved side walls induces a strong circulation pattern near these side walls, but has, paradoxically, a negative impact on mixing and actually promotes segregation. The cause for this segregation is the difference in velocity of differently sized particles near the curved side walls. Large particles accumulate at the curved side walls, whereas small particles move away from the curved side walls. When the length of the drum is increased, the overall effect of the side walls is decreased, although it does remain observable, even in very large drums.

Simulating of heat transfer enhancement via a water-based nanofluid in enclosures with curved side walls

This paper deals with heat transfer and fluid flow of natural convection in enclosures (square enclosure and enclosures with concave/convex walls) filled with water based Cu, and subjected to a constant imposed wall temperature. The governing equations of momentum and energy are formulated using the dimensionless form of transport equations in bipolar coordinates for a laminar two-dimensional incompressible and Newtonian flow which is expressed in terms of stream-function, vorticity and temperature. The resulting equations are numerically solved using the finite volume method (FVM) implemented in an in house-built computer code. The key parameters governing the problem are the Rayleigh number up to 105, the Prandtl number of 6.2 and nanoparticles' volume fraction from 0 to 0.2. The relevant results are presented in terms of isotherms and streamlines. It is found that the heat transfer increases with nanoparticles' volume fraction for the entire range of Rayleigh number considered. Besides this, heat transfer in the square enclosure remains better than for the other enclosures with curved walls.

Investigation on Thermal Efficiency via Entropy Generation Analysis Within Cavities with Curved Walls Subjected to Differential/Rayleigh-Benard Heating

The computational study of natural convection within enclosures with curved (concave/convex) walls (curved side walls or top and bottom walls) is carried out via entropy generation analysis. Two heating strategies are considered such as: (a) differential and (b) Rayleigh-Benard heating. The numerical simulation has been carried out for air at Prandtl numbers, Pr = 0.7 for various Rayleigh numbers (103 ≤ Ra ≤ 105) with different wall curvatures. A comparative study of the heating strategies is carried out in detail for a number of test cases with different wall curvatures. Finally, the optimal situation is recommended based on the less entropy production and and high heat transfer rate.

Impact of the shape of the needle tip on the efficacy of flushing implantable port chambers.

To follow international guidelines and protect healthcare workers from needle stick injuries, manufacturers now provide safety non-coring needles. Numerical simulations show the potential efficacy of infusion and flushing flow in straight and curved side wall port chambers from a beveled non-coring needle (BNCN) or a bevel-free cannula (BFC). In straight and curved side wall port chambers, the stream of flow with a BNCN is determined by the direction of the bevel, whereas the outlet stream from a BFC leads to a cylindrical symmetric flow. This, along with the position of the BFC impacts the wall shear rate of the port chamber, and the hydraulic resistance within the chamber. This last factor has never been the subject of extensive hydrodynamic study. Caregiver safety and patient comfort are paramount but physics show that the shape of the needle tip affects the hydrodynamics of the injected flow. The presence of a bevel at the needle tip is a key factor for ensuring efficient flushing of the port. The absence of a bevel may increase hydraulic resistance and deposits in the port chamber. Implantable port flushing protocols must take this notion into account if the patency of port chambers is to be maintained. The clinical impact of this study has yet to be determined.

On the finite element based evaluation of Nusselt numbers for curved walls

Two heating strategies are considered such as (a) differential heating with the curved side walls and (b) Rayleigh–Bénard heating with the curved horizontal walls for the study of natural convection. The simulations are carried out involving various Rayleigh numbers (103 ≤ Ra ≤ 105) and Prandtl number, Pr=7 for various elements with different cases based on the wall concavities and convexities. The Gaussian quadrature based Galerkin finite element method has been used to obtain the smooth solutions of velocity and temperature components within the curved computational domain. The local Nusselt numbers along the curved walls are derived in a generic form for various concave and convex walls and the local Nusselt numbers are evaluated based on the finite element method using the element basis functions. The error in the heat balance for the differential heating case is larger than the Rayleigh–Bénard heating strategy for all the concave and convex enclosures. At a specific heating strategy with a given element number, the error is larger for the convex enclosure with the high wall curvature. In addition, the minimum error in the heat balance is obtained for the finest grid with 32×32 bi-quadratic elements involving both the heating strategies with the concave and convex walls. The convergence in the local and average Nusselt numbers via the finite element method is obtained even at the coarser grid with 16×16 bi-quadratic elements corresponding to 33×33 grid points for most of the cases. The comparative study indicates that, the finite volume method [1] and finite difference method [2] require 121×121 grid points to obtain the converged solution whereas, the finite element method offers the converged solution for the grid corresponding to 33×33 grid points for natural convection in curved/wavy domains.

Mixed-scale channel networks including Kingfisher-beak-shaped 3D microfunnels for efficient single particle entrapment.

Reproducible research results for nanofluidics and their applications require viable fabrication technologies to produce nanochannels integrated with microchannels that can guide fluid flow and analytes into/out of the nanochannels. We present the simple fabrication of mixed-scale polydimethylsiloxane (PDMS) channel networks consisting of nanochannels and microchannels via a single molding process using a monolithic mixed-scale carbon mold. The monolithic carbon mold is fabricated by pyrolyzing a polymer mold patterned by photolithography. During pyrolysis, the polymer mold shrinks by ∼90%, which enables nanosized carbon molds to be produced without a complex nanofabrication process. Because of the good adhesion between the polymer mold and the Si substrate, non-uniform volume reduction occurs during pyrolysis resulting in the formation of curved carbon mold side walls. These curved side walls and the relatively low surface energy of the mold provide efficient demolding of the PDMS channel networks. In addition, the trigonal prismatic shape of the polymer is converted into to a Kingfisher-beak-shaped carbon structure due to the non-uniform volume reduction. The transformation of this mold architecture produces a PDMS Kingfisher-beak-shaped 3D microfunnel that connects the microchannel and the nanochannel smoothly. The smooth reduction in the cross-sectional area of the 3D microfunnels enables efficient single microparticle trapping at the nanochannel entrance; this is beneficial for studies of cell transfection.

Fe-Simulation of Hot Continuous Rolling of 40Cr Alloy Steel Round Bar and Roll Pass Design

40Cr alloy steel is widely used in the mechanical manufacturing industry and the quality of its rolled round bar has a great consequence on the quality and useful time of the final mechanical parts. By analyzing the characteristics of thermal plasticity of 40Cr steel, the Hensel-Spittel flow stress model of 40Cr steel was established in this study. For the possible continuous rolling schedule of Φ80mm 40Cr steel from 200mm×200mm billet, the advanced technology of viscoplastic FEM by LARSTRAN/SHAPE was used to create 3-D thermo-mechanical coupled simulation models for 8-pass hot continuous rolling processes. From the rolling process simulation the stress, strain, temperature distribution and rolling force variation were obtained. The simulation results included the comparison of plastic deformation of round pass with curved side wall and round pass with straight-side wall as well as the cause of rolling defect (e.g. crack). Based on the numerical analysis the reliable roll pass sequence wa constructed, which was verified by actual tests.

Bejan's heatlines and numerical visualization of convective heat flow in differentially heated enclosures with concave/convex side walls

Numerical simulation for natural convection flow in fluid filled enclosures with curved side walls is carried out for various fluids with several Prandtl numbers (Pr = 0.015, 0.7 and 1000) in the range of Rayleigh numbers (Ra = 103–106) for various cases based on convexity/concavity of the curved side walls using the Galerkin finite element method. Results show that patterns of streamlines and heatlines are largely influenced by wall curvature in concave cases. At low Ra, the enclosure with highest wall concavity offers largest heat transfer rate. On the other hand, at high Ra, heatline cells are segregated and thus heat transfer rate was observed to be least for highest concavity case. In convex cases, no significant variations in heat and flow distributions are observed with increase in convexity of side walls. At high Ra and Pr, heat transfer rate is observed to be enhanced greatly with increase in wall convexity. Results indicate that enhanced thermal mixing is observed in convex cases compared to concave cases. Comparative study of average Nusselt number of a standard square enclosure with concave and convex cases is also carried out. In conduction dominant regime (low Ra), concave cases exhibit higher heat transfer rates compared to square enclosure. At high Ra, low Pr, concave cases with P1P1′=0.4 is advantageous based on flow separation and enhanced local heat transfer rates.

Bifurcations and eddy genesis of Stokes flow within a sectorial cavity

This work analyzes the Stokes flow generated in a sectorial driven cavity formed by a pair of curved stationary side walls capped by straight translating lids.The flow is governed by two physical control parameters: the cavity aspect ratio, A=r2r1 (where r1 and r2 are the radii of the inner and outer curved side walls, respectively) and the ratio (S=U1U2) of the upper to the lower lid speed. A boundary value problem is formulated, which is solved analytically for the streamfunction, ψ, expressed as an infinite series of Papkovich–Faddle eigenfunctions. The streamfunction solution is then expanded about any stagnation point to reveal changes in the local flow structure as A and S are varied. At critical values of A and S, stagnation point bifurcations arise and the local flow topology is transformed.For S∈[−1,0) and A∈[1.6,6.5), the various flow transformations are tracked as A is decreased and hence the means is identified by which new eddies appear and become fully developed. The key results are shown in an (S,A) control space diagram which exhibits an intricate structure due to the intersection and confluence of eight bifurcation curves representing flow bifurcations at degenerate critical points. There are eight points where two critical curves intersect and the flow bifurcations are described.It is shown that, for S≠0, the number of eddies increases from 1 to 3 via several key flow transformations, which become more complicated as |S| is reduced. For S=0, as A is decreased slowly, the number of eddies also increases, in this case, from 1 to 2 via the development of corner eddies.

Devices For Displaying Modal Patterns

The present invention provides an acoustic display device for displaying modal patterns in response to sound from a sound source. The display device (10) has a substantially circular housing (12), which housing (12) includes a continuous curved side wall (13a), a substantially flat base wall (13b), and open end (13c). The open end (13c) is closed by diaphragm (14), thereby forming closed chamber (15). Excitation of the diaphragm can be effected by introducing vocal sounds to the underside of the diaphragm via one of a plurality of sound connecting means (22) that include a flexible tubular section (30), which terminates in a mouthpiece (32). A user can place the mouthpiece over their mouth and nose and make vocal sounds, which are delivered to the interior of the chamber (15). The mouthpiece (32) can be substituted with a sound collector (60) having a 'horn' shape and an annular flange for engagement with a loudspeaker. The other ends (24) of the sound connecting means (22), within the closed chamber (15), each contain a non-return valve so that pressure within the chamber is maintained. The device can also include weight locating means (21a, 21b, 21c) or magnetic tensioning means (80, 84) for tuning the diaphragm. Removable covers having different markings can assist in analysing the patterns produced. Two or more integral curved spirit levels (38) in conjunction with adjustable feet (40) enable accurate levelling of the diaphragm.

Simulation of liquid sloshing in curved‐wall containers with arbitrary Lagrangian–Eulerian method

AbstractThere are many challenges in the numerical simulation of liquid sloshing in horizontal cylinders and spherical containers using the finite element method of arbitrary Lagrangian–Eulerian (ALE) formulation: tracking the motion of the free surface with the contact points, defining the mesh velocity on the curved wall boundary and updating the computational mesh. In order to keep the contact points slipping along the curved side wall, the shape vector in each time advancement is defined to modify the kinematical boundary conditions on the free surface. A special function is introduced to automatically smooth the nodal velocities on the curved wall boundary based on the liquid nodal velocities. The elliptic partial differential equation with Dirichlet boundary conditions can directly rezone the inner nodal velocities in more than a single freedom. The incremental fractional step method is introduced to solve the finite element liquid equations. The numerical results that stemmed from the algorithm show good agreement with experimental phenomena, which demonstrates that the ALE method provides an efficient computing scheme in moving curved wall boundaries. This method can be extended to 3D cases by improving the technique to compute the shape vector. Copyright © 2007 John Wiley & Sons, Ltd.

B118 両側に曲面壁を有する2次元噴流の流れの特性

Flow characteristics of a two-dimensional jet with curved side walls have been studied experimentally. Four kinds of cylindrical walls were provided as the side walls, and they were combined and attached to a nozzle. Velocity was measured by a hot-wire probe. Mean velocity profiles, the decay of jet maximum velocity, and the growth of the jet half-width were clarified. The maximum velocity decays as the radius of the smaller cylindrical wall becomes large. When the radius of the smaller cylindrical wall exceeds a certain radius, the jet half-width increases suddenly.

Case Study: Acoustic Design of a Restored Theatre in Thessaloniki

This paper discusses the acoustics of a restored theatre in Thessaloniki, Greece. The paper presents the acoustic design principles, discusses the employment of these principles and concludes with an assessment of the success of the design. The acoustic design changes included improvement of direct sound, provision of ceiling and walls reflections, positioning of diffusers, optimising reverberation time and minimising background noise levels. Steeper seating rakes were constructed in the stalls, boxes and balconies. Curved ceiling reflectors were positioned in a new wire frame false ceiling. Lateral wall reflectors were introduced, as were curved side walls near the stage to act as diffusers. Diffusers were positioned in the rear walls and in balcony fronts. Reverberation times were predicted, measured and compared with earlier data, based on the change of volume, the number and design of seats and the volume per seat ratio. Finally, noise level measurements were obtained in most of the spaces in the theatre. Assessment of the success of the design is based on measurement results and on the subjective acceptance by theatre goers.

Bass drum acoustic muffling apparatus

First Page

A note on the effects of polymer additives on the formation of Goertler vortices in an unsteady flow

The addition of a polymer to a fluid has been observed to delay the transition to turbulence. The question then arises: Can the polymer delay the appearance of a hydrodynamic instability, such as the one that leads to Goertler vortices? The experimental technique was the same as that used in Maxworthy [Turbulence Measurements in Liquids (Univ. of Missouri—Rolla, Rolla, MO, 1971), pp. 32–38], where a cylindrical container of fluid in solid body rotation was suddenly brought to rest. The diffusing boundary layer on the curved side wall became unstable to a Goertler vortex pattern after a time that could be related to the initial rotation rate and the critical Goertler number (Gc). For small concentrations of polymer, the increase in Gc was linear in concentration for both Separan AP30 and polyethylene oxide. This number seemed to asymptote to a value of 9.5 for the Separan AP30 above a concentration of 0.10% by weight and to a value of 7.5 for the polyethylene oxide above a concentration of 0.07%. The wavelength of the instabilities increased due to the presence of the polymer; for a 0.1% concentration, the increase was 50% to 90%, depending on the initial rotation speed.

Tire-soil interaction model for turning (steered) tires

A review of the experimental information on the development of lateral forces on tires traveling at an angle to their center plane is presented and the usefulness of the consideration of the lateral forces for the development of an analytical model is evaluated. Major components of the lateral force have been identified as the forces required to balance the tractive force and the drawbar pull vectorially. The lateral forces are generated by the shear stresses developing in the contact area and the horizontal component of the normal stresses acting on the in-ground portion of the curved side walls of the tire. The tire-soil interaction model for steady state straight travel has been expanded to include the necessary algorithms for the calculation of these lateral forces. The pattern of tractive force-slip and longitudinal-lateral force relationships is in general agreement with experiments.

Loudspeaker with cone driven horn

First Page