Thick Perforated Plates Research Articles

The effect of freestream turbulence on convection enhancement by a flexible strip

Turbulence generators such as a 25.4 mm tall, 12.7 mm wide (W) and 0.1 mm thick rectangular flexible strip can provide a robust means of enhancing convective heat transfer. This wind-tunnel study aimed at uncovering the effect of freestream turbulence on heat convection enhancement of a flat surface by a flexible strip. The freestream turbulence was furnished by a 6 mm thick orificed perforated plate (OPP) with 57% perforation consisting of 38.1 mm diameter (D) holes. The OPP was installed at 10D, 13D and 16D upstream of the strip, to achieve 11%, 9% and 7% turbulence. The investigation was conducted at a Reynolds number based on the strip width of 6000. The convective heat transfer augmentation was analyzed in terms of Nusselt number with respect to the reference no-strip case (Nu/Nu0). The flow turbulence was characterized with the help of a 3D hotwire probe. The freestream turbulence is found to diminish the flexible-strip induced Nu/Nu0 significantly. This is principally because Nu0 increases considerably with increasing freestream turbulence. It is of practical significance that the flexible strip always increases Nu, and this improvement is largest with respect to an otherwise ‘laminar’ freestream.

Investigation of passive control of the wake past a thick plate by stability and sensitivity analysis of experimental data

In this paper we propose a strategy, entirely relying on available experimental data, to estimate the effect of a small control rod on the frequency of vortex shedding in the wake past a thick perforated plate. The considered values of the flow Reynolds number range between $Re\simeq 6.6\times 10^{3}$ and $Re=5.3\times 10^{4}$. By means of particle image velocimetry, an experimental database consisting of instantaneous flow fields is collected for different values of suction through the body surface. The strategy proposed here is based on classical stability and sensitivity analysis applied to mean flow fields and on the formulation of an original ad hoc model for the mean flow. The mean flow model is obtained by calibrating the closure of the Reynolds averaged Navier–Stokes equations on the basis of the available experimental data through an optimisation algorithm. As a result, it is shown that the predicted control map agrees reasonably well with the equivalent one measured experimentally. Moreover, it is shown that even when turbulence effects are neglected, the stability analysis applied to the mean flow fields provides a reasonable estimation of the vortex shedding frequency, confirming what is known in the literature and extending it up to $Re=5.3\times 10^{4}$. It is also shown that, when turbulence is taken into account in the stability analysis using the same closure that is calibrated for the corresponding mean flow model, the prediction of the vortex shedding frequency is systematically improved.

Transmission loss analysis of thick perforated plates for valve contained pipelines

Valve contained pipelines have witnessed a great growth and there exists a lot of noise caused by valves. Thick perforated plates are especially used is valve contained pipelines for the noise control, but there are limited literatures about its noise control performances under different structural parameter of thick perforated plates, which limits its popularization and application. In this paper, transmission loss (TL) predictions of various thick perforated plates are carried out to analyze the noise control performances. Finite element method (FEM) is implemented to simulate the acoustic response, and TL is achieved by the sound pressure of four points on both sides of the thick perforated plates. Adopted numerical method shows good agreements with the existing research works and the results indicate that reducing the margin of the plates can enhance TL of some frequencies. Similar to chamber mufflers, the maximum TL depends on the area ratio and the frequency range with the best noise control performance is related to the plate thickness. Meanwhile, the low velocity flow does not affect the TL curve so much and in the situation of supersonic flow, and the TL curve turns into a periodic shape, which may weaken the effects of noise control. Besides, based on the analytical solution of TL for the chamber muffler, a linear correction formula of maximum TL is proposed for the thick perforated plate. This work can give several advices for similar perforated plates design works and someone who are dealing with decreasing the noise effects from the valves in pipelines.

Wind Force Coefficients for Designing Porous Canopy Roofs

Wind force coefficients for designing porous canopy roofs have been investigated based on a series of wind tunnel experiments. Gable, troughed and mono-sloped roofs were tested. The roof models were made of 0.5 mm thick perforated duralumin plates, the porosity of which was changed from 0 to about 0.4. Overall aerodynamic forces and moments acting on the roof model were measured in a turbulent boundary layer with a six-component force balance for various wind directions. The results indicate that the wind loads on canopy roofs generally decrease with an increase in porosity of the roof. Assuming that the roof is rigid and supported by the four corner columns with no walls, the axial forces induced in the columns are regarded as the most important load effect for discussing the design wind loads. Two loading patterns causing the maximum tension and compression in the columns are considered. Based on a combination of the lift and moment coefficients, the design wind force coefficients on the windward and leeward halves of the roof are presented for the two loading patterns as a function of the roof pitch and porosity. The effect of porosity is taken into account as a reduction factor of the wind loads.

Homogenized Elastic-Viscoplastic Behavior of Thick Perforated Plates with Pore Pressure

The homogenized elastic-viscoplastic behavior of thick perforated plates with pore pressure is investigated for macro-material modeling. To this end, the homogenized behavior is analyzed using a FE homogenization method of periodic solids. It is assumed that the base metal of perforated plates exhibits the elastic-viscoplastic behavior based on Hooke’s law and Norton’s power-law. The resulting homogenized behavior is simulated using an elastic-viscoplastic macro-material model developed for pore-pressurized anisotropic open-porous bodies. It is shown that the macro-material model suitably represents the macro-anisotropy and macro-volumetric compressibility that are revealed by the FE homogenization analysis in the presence and absence of pore pressure.

Homogenized Elastic-Viscoplastic Behavior of Anisotropic Open-Porous Bodies

This lecture presents constitutive modeling of the homogenized elastic-viscoplastic behavior of pore-pressurized anisotropic open-porous bodies. The base solids are assumed to be metallic materials at small strains and rotations. First, by describing micro-macro relations relevant to periodic unit cells of anisotropic open-porous bodies with pore pressure, constitutive features are discussed for the viscoplastic macrostrain rate in steady states. Second, on the basis of the constitutive features found, the viscoplastic macrostrain rate is represented as an anisotropic function of Terzaghi’s effective stress. Third, the resulting viscoplastic equation is used to simulate the homogenized elastic-viscoplastic behavior of an ultrafine plate-fin structure and a thick perforated plate subjected to macroscopic loading in the absence and presence of pore pressure. The corresponding FE homogenization analysis is performed for comparison to validate the developed viscoplastic equation.

Homogenised elasto-viscoplastic material modelling of thick perforated plates at high temperature

In this study, homogenised elasto-viscoplastic behaviour of thick perforated plates at high temperature was investigated for macro-material modelling. Homogenised stress–strain relations of a periodic unit cell of thick perforated plates subjected to simple and complex loading were analysed using a homogenisation method for periodic solids. The base metals of perforated plates were assumed to exhibit elasto-viscoplasticity based on Hooke’s law and Norton’s power-law, and the material parameters of modified 9Cr–1Mo steel at 550°C were employed. The resulting homogenised stress–strain relations were simulated using a recently developed elasto-viscoplastic macro-material model based on a general form of the quadratic equivalent stress. It has been shown that this macro-model successfully represents the macro-anisotropy and macro-volumetric compressibility that were revealed by the homogenisation analysis in uniaxial, biaxial and triaxial stress states.

Homogenised elasto-viscoplastic material modelling of thick perforated plates at high temperature

Homogenised elasto-viscoplastic material modelling of thick perforated plates at high temperature

Glulam-concrete composites: experimental investigation into the connection system

Received: October 5, 2010; Revised: December 19, 2010Timber-concrete composite structures work appropriately when a suitable connection system is included because the degree of interaction between the materials stiffs the structural system. Thereby, it is extremely important to improve the knowledge about their connection system. The purpose of this paper is to show the results obtained by experimental investigation into push-out shear tests of glulam-concrete specimens. The specimens were designed to simulate the behaviour of composite T beams and the connection system was constituted by steel hooks – got by the division of steel bars used in reinforced concrete members – and by perforated steel plates, both glued with epoxy adhesive. They were tested under shear forces with constant loading rate. Six specimens of each group were made, considering two different diameters for the hooks (8 and 10 mm) and 4.75 mm thick perforated steel plates. The stiffness reached by steel hooks confirms their suitability for the use in composite timber-concrete systems.

Linear and non-linear behaviour of steel plates with circular and rectangular holes under shear loading

In this work, linear buckling and the non-linear behaviour of steel plates with one perforation subjected to shear loading was studied. The influence of the dimension, position with respect to the two main axes, shape (circular or rectangular) and orientation of a hole with respect to the panel slenderness and aspect ratio were all investigated. In both circular and rectangular holes, the strong influence of hole dimensions on the shear buckling coefficient was observed, and the values of the shear buckling coefficient fell with the plate aspect ratio. Small differences in buckling coefficients were noted in rectangular plates with various hole diameters, and buckling coefficients were practically not influenced by the orientation of the rectangular hole. In both rectangular and circular holes, the coefficient remained constant, regardless of hole position for a given distance from the edge. Linear buckling and non-linear behaviour were compared by observing different shear failure modes for slender and thick perforated plates. Elastic and plastic regions were found, on the basis of critical slenderness, for some common geometries.

Non-linear analysis of perforated steel plates subjected to localised symmetrical load

Although the literature contains a number of studies which have been developed to describe the non-linear behaviour of ordinary plates, few works are available on perforated plates, and studies on non-linear behaviour of perforated plates under localised symmetrical load are not studied in depth. The aim of this paper is to provide some insights into the elasto-plastic behaviour of plate girder web panels with circular holes under localised symmetrical load. Numerical analyses of square and rectangular perforated plates with centred and eccentric holes were developed. Results provide new insights into post-critical mechanisms in perforated plates subjected to localised loads when the length of the symmetrical compressive load, hole diameter and steel yield limit vary. An increase in the critical slenderness of the plate (a value at which transition from elastic to plastic collapse occurs) and a corresponding reduction in the elastic critical load occur when the dimensions of the hole increase. A further increase in the critical slenderness occurs when the length of the localised load is reduced. High-performance steel may be subject to buckling with a lower possibility of post-critical mechanisms: a reduction in critical slenderness occurs when the steel grade increases. Lastly, numerical analyses of slender and thick perforated plates were developed and their results compared.

Enhanced transmission through two-period arrays of subwavelength holes

A two-period array of subwavelength holes in a perfect electrically conducting plate permits enhanced transmission of incident plane waves with wavenumbers near those of leaky waves supported by the array. A simple periodic impedance sheet model explains this phenomenon and provides an approximate expression for the transmission peak location. Transmission through thin perforated plates is studied using a full-wave solver to verify model-theoretic observations. Transmission coefficient peak splitting and narrowing phenomena, associated with thick perforated plates, are explored.

FREE VIBRATION OF SYMMETRICALLY LAMINATED THICK-PERFORATED PLATES

This paper investigates the free vibration of symmetrically laminated, thick, doubly connected plates of arbitray plate perimeter for the outer boundary and a hole defined by a super-elliptical equation which is able to describe a rectangle, ellipse or quasi-rectangle. The laminated perforated plates can be subject to free, simply supported, or clamped edge conditions. Convergence and comparisons with established work have been studied to ensure accuracy of results. Efforts are made to interpret the frequency results to provide physical insight to the problem.

Stresses of Thick Perforated Plates With Reinforcement of Tubes and Their Effective Elastic Constants

Based on the concept of equivalent solid plate, this paper deals with thick perforated plates with triangular or square patterns of holes reinforced by tubes. The results obtained show that the tubes connected (by welding or expanding) to the perforated plates lead to a noticeable stiffening effect which is neglected or considerably underestimated by current design codes. The stresses of tubesheets calculated based on the effective elastic constants given by this method are in better agreement with the experimental results than those based on the effective elastic constants given by current codes.

Reliability Problems of Heat Transfer Equipment

In its simplest form, a heat exchanger consists of a bundle of tubes arranged between two thick perforated tube plates and enclosed by an outer shell. Covers over the tube plates allow one fluid to pass inside the tubes while a second hotter or cooler fluid is introduced via openings in the shell. Since they contain no moving parts it might be expected that heat exchangers would be highly reliable pieces of equipment. However, everyday experience with small domestic and automotive heaters and coolers suggests this is not always the case. In the case of mass-produced items such as these, replacement of a defective component is usually relatively straightforward and inexpensive. However, for the much larger heat exchangers used in the process chemical and power industries, a single failure may result in significant financial losses.

Elastoplastic analysis of thick perforated plates with application to prestressing anchor heads

The elastoplastic finite element stress analysis of a prestressing anchor head is described. The anchor head constitutes part of an unbonded tendon system for a prestressed concrete nuclear reactor vessel. The anchor head, which is a thick plate with a central region perforated by a large number of holes, is analyzed using an equivalent homogeneous material with numerically determined effective elastic constants and yield stress. Maximum inelastic tensile strains are calculated as a function of anchor head load level, and related to observed failure modes.

Effective Elastic Constants for Thick Perforated Plates With Square and Triangular Penetration Patterns

An exact formulation is presented of the relationship between the effective elastic constants for thick perforated plates (generalized plane strain) and thin perforated plates (plane stress). Extensive numerical results covering a wide range of ligament efficiencies and Poisson’s ratios are given for plates with square and triangular penetration patterns.