Slit Walls Research Articles

ГИДРОДИНАМИКА И СТРУКТУРА ПОТОКА В ЩЕЛЕВОЙ ФИЛЬТРУЮЩЕЙ ПЕРЕГОРОДКЕ

The purpose is to study the influence of the structural characteristics of the slit filter partition on the hydrodynamics and structure of the gas flow in the channels of the partition, which is necessary to develop a method for calculating the hydraulic resistance and creating the most energy-efficient conditions of the slit filter. To study the flow structure in the slit channels, a mathematical description of the flow in the channel model for the corridor and staggered slit partitions is developed, which allows to determine the local flow rate at any point of the channel of the filtering partition, to construct velocity profiles in any cross-section of the channel depending on the type of the slit partition. The modeling of velocity profiles in the channels of the corridor and staggered structure of slit partitions for different wire diameters and the number of its layers, depending on the filtration rate, is performed. It was found that for slit filter walls with a wire diameter from 0.5 to 1.4 mm, the number of layers from 2 to 7 at a filtration rate within 0.05-0.2 m/s during the flow occurs in laminar mode, and the flow around the wire turns during the transition mode. It is established that the stabilization of the velocity distribution over the cross section of the channel in the slit partition occurs after the fourth layer of turns. The mathematical dependence for the calculation of the hydraulic resistance of the slit filter partition taking into account its structural characteristics and the hydrodynamic regime of the gas flow is proposed.

Shake table tests on RC frame infilled by slitted masonry panels

Unreinforced masonry infill walls are widely used as non-structural partitions in RC frames. The effects of infills on the structural responses are often ignored in the design process since they are generally considered as expendable elements. However, recent studies have shown that not only shear damage can be inflicted to the columns braced by the infill walls, but also that the structural stability can be jeopardised by the fall-off of the infills. This paper presents the development of new detailing methods for the infill walls, which features slit panels, isolation gaps between the infills and columns, and anchorage of the infills. The proposed detailing methods were tested and verified experimentally using shake-table tests on five 1/3-scale infilled RC frame specimens with different combinations of the features stated above. The design and construction of the shake-table test specimens have taken into account the similitude requirements. The test results indicate that the proposed detailing method effectively reduced the undesirable interaction between column and infill walls. And the use of proper anchorage could prevent the fall off of infills from the bounding frame. Furthermore, the specimens with slit infill walls displayed better seismic performances, which could be attributed to the rocking behaviour of the sub-panels with increased aspect ratios.

Concentrated aqueous sodium chloride solution in clays at thermodynamic conditions of hydraulic fracturing: Insight from molecular dynamics simulations.

To address a high salinity of flow-back water during hydraulic fracturing, we use molecular dynamics (MD) simulations and study the thermodynamics, structure, and diffusion of concentrated aqueous salt solution in clay nanopores. The concentrated solution results from the dissolution of a cubic NaCl nanocrystal, immersed in an aqueous NaCl solution of varying salt concentration and confined in clay pores of a width comparable to the crystal size. The size of the nanocrystal equals to about 18 Å which is above a critical nucleus size. We consider a typical shale gas reservoir condition of 365 K and 275 bar, and we represent the clay pores as pyrophyllite and Na-montmorillonite (Na-MMT) slits. We employ the Extended Simple Point Charge (SPC/E) model for water, Joung-Cheatham model for ions, and CLAYFF for the slit walls. We impose the pressure in the normal direction and the resulting slit width varies from about 20 to 25 Å when the salt concentration in the surrounding solution increased from zero to an oversaturated value. By varying the salt concentration, we observe two scenarios. First, the crystal dissolves and its dissolution time increases with increasing salt concentration. We describe the dissolution process in terms of the number of ions in the crystal, and the crystal size and shape. Second, when the salt concentration reaches a system solubility limit, the crystal grows and attains a new equilibrium size; the crystal comes into equilibrium with the surrounding saturated solution. After crystal dissolution, we carry out canonical MD simulations for the concentrated solution. We evaluate the hydration energy, density profiles, orientation distributions, hydrogen-bond network, radial distribution functions, and in-plane diffusion of water and ions to provide insight into the microscopic behaviour of the concentrated aqueous sodium chloride solution in interlayer galleries of the slightly hydrophobic pyrophyllite and hydrophilic Na-MMT pores.

Seismic Behavior of Self-Centering Modular Panel with Slit Steel Plate Shear Walls: Experimental Testing

AbstractThe self-centering modular panel with a slit steel plate shear wall (SCMP-SW) is a new seismic load-resisting structural component that combines recentering capabilities and energy dissipat...

Higher-order lubrication analytic solutions of viscoelastic flows in slowly varying slits

A regular perturbation method in which the small parameter is taken as the characteristic frequency of variation of a two-dimensional slit wall height is applied to the creeping flow of a viscoelastic fluid. The Upper-Convected Maxwell model has been chosen as the constitutive equation. The equations of motion are expressed in terms of the stream function as the only unknown. The stream function is expressed then as a regular perturbation expansion up to the fourth order in the small parameter. When these expansions are written for slits with slowly varying walls of any shape, curvature and higher-order derivatives appear in the expansion solution. From the stream function solution, we distinguish two different types of viscoelastic higher-order effects: one is symmetric and the other is a loss of fore-and-aft flow symmetry due to the convected derivatives appearing in the constitutive equation. The expansion is formally validated with a ratio between two consecutive higher-order terms. It shows that the accuracy of the perturbation will depend on four factors: the small parameter ϵ, the Weissenberg number We0, the local depth h and the shape of the slit. In some instances, Padé approximants can restore a diverging perturbation expansion and extend the range of viscoelastic levels for which the expansion is usable. Results for diverging and for converging flows in a wedge, as well as flows in corrugated slits, are checked against Finite Elements Method calculations. At the same level of viscoelasticity, the stress profiles are completely different in a diverging flow from a converging flow. In particular, the shear stress component of the stress tensor becomes non-monotonic in divergent flows.

Experimental and numerical study on the hysteretic behavior of composite partially restrained steel frame-reinforced concrete infill walls with vertical slits

The work presented in this study aimed to investigate the hysteretic behavior of composite partially restrained (PR) steel frame-reinforced concrete infill walls (PSRCW) with vertical slits, which consisted of a PR steel frame, a slit-reinforced concrete (RC) infill wall, and shear connectors. An experimental program at one-third scale of a one-bay by three-story PSRCW with vertical slits was tested under horizontal cyclic loading. The seismic behavior was examined in terms of the lateral load-carrying capacity, ductility, deformability, lateral stiffness, and energy dissipation. The results showed that this kind of structure exhibited superior ductility and deformability, as well as excellent energy-dissipation capacity. The slit RC infill walls exhibited flexure-dominated behavior and significantly increased the lateral load-carrying capacity. In contrast, the slit RC infill walls decreased the rotation demand on the PR connections from earthquake, which avoided the fracture failure of the beam-to-column connection. Additionally, the test results were verified, and relative parametric analyses of PSRCW with vertical slits were conducted by using a simplified macro fiber model to illustrate the factors that influence the structural hysteretic behavior.

Experimental and analytical study of steel slit shear wall

A steel slit shear wall has vertical slits and when it is under lateral loads, the section between these slits has double-curvature deformation, and by forming a flexural plastic hinge at the end of the slit, it dissipates the energy on the structure. In this article, Experimental, numerical and analytical analyses are performed to study the effect of slit shape and edge stiffener on the behavior of steel slit shear wall. Seismic behavior of three models with different slit shapes and two models with different edge stiffener shapes are studied and compared. Hysteresis curves, energy dissipation, out of plane buckling, initial stiffness and strength are discussed and studied. The proposed slit shape reduces the initial stiffness, increases the strength and energy dissipation. Also, edge stiffener shape increases the initial stiffness significantly.

Slit wall aspect ratio effect on the stability and heat transfer characteristics of Taylor-Couette flow

Abstract Taylor-Couette flow in the annulus was investigated by numerical simulation. The stability of Taylor-Couette flow and its heat transfer process of four different models were studied. By comparing the result in four different models, it is found that the Nusselt number of the model with slit aspect ratio of 0.75 is larger than the result of other models, with the further increasing of aspect ratio, the heat transfer performance of the fluid in the annular gap is not enhanced significantly. The Nusselt number of the model with aspect ratio of 0.75 increases as the Reynolds number increases. Additionally, the temperature gradient has the inhibition effect on the transition from laminar Couette flow to Taylor vortex flow, and as the temperature gradient increasing, this effect becomes more obvious. Finally, the fitting empirical formulas of the model with aspect ratio of 0.75 were obtained at different conditions.

Axial slit wall effect on the flow instability and heat transfer in rotating concentric cylinders

The slit wall effect on the flow instability and heat transfer characteristics in Taylor-Couette flow was numerically studied by changing the rotating Reynolds number and applying the negative temperature gradient. The concentric cylinders with slit wall are seen in many rotating machineries. Six different models with the slit number 0, 6, 9, 12, 15 and 18 were investigated in this study. The results show the axial slit wall enhances the Taylor vortex flow and suppresses the azimuthal variation of wavy Taylor vortex flow. When negative temperature gradient exists, the results show that the heat transfer augmentation appears from laminar Taylor vortex to turbulent Taylor flow regime. The heat transfer enhancement become stronger as increasing the Reynolds number and slit number. The larger slit number model also accelerates the flow transition regardless of the negative temperature gradient or isothermal condition.

Electrochemical machining of a narrow slit by cathodic compound feeding

Narrow slits are widely used in aerospace, instrument and meter, and heat-transfer equipment. Electrochemical machining (ECM) has the advantage of being free of tool wear, heat-affected zone, and machining deformation, and is suitable for high-precision machining of narrow slits. However, conventional cathodic continuous linear feeding causes serious stray removal at the narrow slit side wall and results in poor forming precision. This paper presents a new compound feeding method with vibration superimposed on a continuous linear feeding method and investigates the electrochemical machining of a narrow slit using this method. Its influence on narrow slit formation based on the numerical analysis of an electric field is studied as well. The results indicate that compound feeding is superior to linear feeding in terms of less stray removal and a smaller slit width. Comparative experiments of the compound and linear feeding with voltage pulses are also conducted based on a self-developed ECM system, with vibration frequencies from 0 to 50 Hz and vibration amplitudes from 0 to 2 mm. The results demonstrate that not only the average slit width and side-wall slope are smaller, but also the localization of the narrow slit electrochemical machining can be significantly enhanced by compound feeding.

Cyclic Behavior of Multirow Slit Shear Walls Made from Low-Yield-Point Steel

AbstractThe steel slit shear wall has attracted much attention as a lateral force-resisting system. However, issues such as fractures formed at the slit ends and pinched hysteresis reduce energy dissipation. To address these issues, the authors have developed a steel slit shear wall made from low yield point steel that has a low yield stress and large ductility and strain hardening. Steel slit shear walls made from low-yield-point steel dissipated energy at small lateral drifts, shear deformation was evenly distributed among all rows, fracture was eliminated, and fat hysteresis without the requirement for out-of-plane constraints was feasible. By adjusting dimensions of the link (segment divided by slits) and the number of rows of links while maintaining the required shear strength and stiffness, a small width-to-thickness ratio for the links was achievable to ensure the in-plane behavior of links and thus good energy dissipation. The combined hardening model developed using commercially available softwar...

Effects of solvent and wall roughness on the dynamics and structure of a single polymer in a slit

The structure and dynamics of polymers in confinements (such as porous media, channels and slits) depend not only on the characteristic length scales of the confinements but also on solvent types and interactions between polymers and confinement constituents. In this study, we show by performing both molecular dynamics (MD) and Langevin dynamics (LD) simulations that the lateral diffusion of a single flexible polymer in a good solvent in a slit should be determined by a complicated interplay among the slit height (H), solvent types and slit wall roughness. The slit wall roughness is tuned by employing either corrugated walls or smooth walls. We find from simulations that only when solvent molecules are implemented explicitly in MD simulations, the wall roughness makes a qualitative difference in the lateral diffusion coefficient (D∥) of the polymer: as H is decreased, D∥ increases for smooth walls while D∥ decreases for corrugated walls. Such a qualitative difference in D∥ should be a solvent-mediated effect, which is not observed for implicit solvent models in LD simulations. The single polymer in the slit with the explicit solvent model follows Zimm dynamics while the polymer follows Rouse dynamics with the implicit solvent models. In the meantime, the wall roughness hardly affects the structure of the polymer in the slit. The density distribution functions of monomers (ρm(z)) and solvent molecules (ρs(z)) do not depend on whether the walls are corrugated or smooth. The radius of gyration (Rg) is also insensitive to the wall roughness. On the other hand, the solvent model gives rise to a qualitative difference in ρm(z) and Rg, especially when the height (H) of the slit is small. For sufficiently small values of H, ρm(z) depends on the size of solvent molecules used in the explicit solvent model. However, regardless of the solvent model and wall roughness, the scaling exponent (ν) of Rg and the degree of polymerization (N) (i.e., Rg∼Nν) changes gradually from 0.6 to 0.75 as H decreases.

Numerical simulation of slit wall effect on the Taylor vortex flow with radial temperature gradient

Abstract Numerical simulation was applied to investigate the Taylor vortex flow inside the concentric cylinders with a constant radial temperature gradient. The reliability of numerical simulation method was verified by the experimental results of PIV. The radial velocity and temperature distribution in plain and 12-slit model at different axial locations were compared, and the heat flux distributions along the inner cylinder wall at different work conditions were obtained. In the plain model, the average surface heat flux of inner cylinder increased with the inner cylinder rotation speed. In slit model, the slit wall significantly changed the distribution of flow field and temperature in the annulus gap, and the radial flow was strengthen obviously , whichpromote d the heat transfer process at the same working condition. Keywords : Taylor vortex flow, Slit wall, temperature gradient, heat transfer, numerical simulation 1. Introduction In 1923, Taylor[1] discovered the secondary flow existed in the annulus gap between two relatively rotating concentric cylinders, which is called Taylor-Couette flow. Since then, a lot of scholars carried out in-depth research on it. Yang[2] studied the transition process of Taylor-Couette flow by flow visualization method, the aluminum particles were added to investigate the stability of flow field, they found as the rotation speed increased, the aluminum particles have the axial motion before the transition to Taylor vortex flow. Kedia et al.[3] studied the effects of heat transfer on Taylor-Couette flow, and found the heat transfer decreased with Grashof number in axisymmetric Taylor vortex flow regime, and increased with Grashof number after the flow becomes non-axisymmetric. Lee and Minkowycz [4] studied heat transfer characteristics by using the naphthalene sublimation technique in the annular gap between two short concentric cylinders which had either two walls or one plain plain and one axially slit wall, and yielded qualitative information regarding heat transfer but did not address the flow phenomena inside the annular gap. Liu[5] studied the axial wall slits effect on the Taylor vortex flow in the gap between two concentric cylinders by Particle Image Velocimetry, and found the existence of slit wall accelerated the transition process.

Spatial and spectral selective characteristics of the plasmonic sensing using metallic nanoslit arrays

A novel spatial and spectral selective plasmonic sensing based on the metal nanoslit arrays has been proposed and investigated theoretically, which shows a high performance in the multiplexing biomolecular detections. By properly tuning the geometric parameters of metal nanoslit arrays, the enhanced optical fields at different regions can be obtained selectively due to the excitation of SPP, cavity mode (CM), and their coupling effects. Simulation results show that the resonances of the metal nanoslit arrays at different spatial locations and different wavelengths can be achieved simultaneously. A relative bigger red-shift of 57nm can be realized when a layer of biomolecular film is adsorbing at the slit walls, and the corresponding total intensity difference will be enhanced near 10 times compared to that at the top surface. In addition, when a BSA protein monolayer is adsorbing at slit walls with different slit widths, the corresponding wavelength shifts can reach to more than 80nm by modulating the widths of the slit. The simulated results demonstrate that our designed metal nanoslit arrays can serve as a portable, low-cost biosensing with a high spatial and spectral selective performance.

Controlling Orientational and Translational Order of Iron Oxide Nanocubes by Assembly in Nanofluidic Containers.

We demonstrate that spatial confinement can be used to control the orientational and translational order of cubic nanoparticles. For this purpose we have combined X-ray scattering and scanning electron microscopy to study the ordering of iron oxide nanocubes that have self-assembled from toluene-based dispersions in nanofluidic channels. An analysis of scattering vector components with directions parallel and perpendicular to the slit walls shows that the confining walls induce a preferential parallel alignment of the nanocube (100) faces. Moreover, slit wall separations that are commensurate with an integer multiple of the edge length of the oleic acid-capped nanocubes result in a more pronounced translational order of the self-assembled arrays compared to incommensurate confinement. These results show that the confined assembly of anisotropic nanocrystals is a promising route to nanoscale devices with tunable anisotropic properties.

Asymptotics of pressure tensor in fluid-filled finite slits

Asymptotic formulas have been derived for pressure tensor in a liquid- or gas-filled circular slit between the faces of two identical cylinders. The problem has being solved based on the asymptotic principle of interbody dispersion interactions in liquid media, while the calculations have been performed in terms of the Irving–Kirkwood pressure tensor. The final result has the form of normal pressure as a function of slit radius and width and the location inside the slit, with the location being specified by a radial coordinate and the distances from the slit walls. The contribution of edge effects at equal width and radius of a slit has been estimated to be as high as 70%.

Seismic damage evaluation of reinforced concrete buildings with slit walls

Purpose – The purpose of this paper is to investigate a reinforced concrete multi-storey building with dissipative structural walls. These walls can improve the behaviour of a tall multi-storey building. The authors’ main objective is to evaluate the damage of a building with dissipative walls in comparison with that of a building with solid walls. Design/methodology/approach – In this paper, a comparative nonlinear dynamic analysis between a building with slit walls and then the same building with solid walls is performed by means of SAP2000 software and using a layer model. The solution to increase the seismic performance of a building with structural walls is to create slit zones with short connections in to the walls. The short connections are introduced as a link element with multi-linear pivot hysteretic plasticity behaviour. The hysteretic rules and parameters of these short connections were proposed by the authors and used in this analysis. In this study, the authors propose to evaluate the damage of a building with reinforced concrete slit walls with short connections using seismic analysis. Findings – Using the computational model created by the authors for the slit wall, a seismic analysis of a multi-storey building with slit walls was done. From the results obtained, the advantages of the proposed model are observed. Originality/value – Using a simple computational model, created by the authors, that consume low processing resources and reduces processing time, a nonlinear dynamic analysis on high-rise buildings was done. Unlike other studies on slit walls with short connections, which are focused mostly on the nonlinear dynamic behaviour of the short connections, in this paper the authors take into consideration the whole structural system, wall, connections and frames.

Boundary-Layer Effects on Acoustic Transmission Through Narrow Slit Cavities.

We explore the slit-width dependence of the resonant transmission of sound in air through both a slit array formed of aluminum slats and a single open-ended slit cavity in an aluminum plate. Our experimental results accord well with Lord Rayleigh's theory concerning how thin viscous and thermal boundary layers at a slit's walls affect the acoustic wave across the whole slit cavity. By measuring accurately the frequencies of the Fabry-Perot-like cavity resonances, we find a significant 5% reduction in the effective speed of sound through the slits when an individual viscous boundary layer occupies only 5% of the total slit width. Importantly, this effect is true for any airborne slit cavity, with the reduction being achieved despite the slit width being on a far larger scale than an individual boundary layer's thickness. This work demonstrates that the recent prevalent loss-free treatment of narrow slit cavities within acoustic metamaterials is unrealistic.

Cyclic behavior of prefabricated reinforced concrete frame with infill slit shear walls

A composite structural system consisting of prefabricated reinforced concrete frame with infill slit shear walls (PRCFW), with good ductility, is a new type of earthquake resistant structure. Pseudo-static tests were performed to evaluate the seismic behavior of the PRCFW system. Two one-bay, two-story PRCFW specimens were both built at onehalf scale. Additional computational research is also conducted to enhance the nonlinear analytical capabilities for this system. Combined with the concrete damaged plastic (CDP) model provided by finite element program ABAQUS and the constitutive model of concrete proposed by Chinese code, the damage process of the PRCFW structure under cyclic load is simulated. The simulated results show a good agreement with the test data, the dynamic behavior of the PRCFW system can be simulated sufficiently accurate and efficient to provide useful design information. The experimental and numerical study show that this system has the potential to offer good ductility and energy absorption capacity to dissipate input energy, and stiffness adequate for controlling drift for buildings located in earthquake-prone regions.

Seismic damage evaluation of reinforced concrete slit walls

Purpose – The purpose of this paper is to investigate a dissipative reinforced concrete structural wall that can improve the behavior of a tall multi-storey building. The main objective is to evaluate the damage of a dissipative wall in comparison with that of a solid wall. Design/methodology/approach – In this paper, a comparative nonlinear dynamic analysis between a dissipative wall and a solid wall is performed by means of SAP2000 software and using a layer model. The solution to increase the seismic performance of a reinforced concrete structural wall is to create a slit zone with short connections. The short connections are introduced as a link element with multi-linear pivot hysteretic plasticity behavior. The behavior of these short connections is modeled using the finite element software ANSYS 12. In this study, the authors propose to evaluate the damage of reinforced concrete slit walls with short connections using seismic analysis. Findings – Using the computational model created in the second section of the paper, a seismic analysis of a dissipative wall from a multi-storey building was done in the third section. From the results obtained, the advantages of the proposed model are observed. Originality/value – A simple computational model was created that consume low processing resources and reduces processing time for a dynamic pushover analysis. Unlike other studies on slit walls with short connections, which are focussed mostly on the nonlinear dynamic behavior of the short connections, in this paper the authors take into consideration the whole structural system, wall and connections.