Porous Lining Research Articles

Analytical buckling scheme of a functionally graded porous liner reinforced by nanocomposites encased in an egg-shaped pipe

This study uses the FGP-GPLs (functionally graded porous metal reinforced by graphene platelets) to rehabilitate the egg-shaped liner-pipe system. The water penetrates the cracked pipe and surrounds the thin-walled liner, resulting in hydrostatic pressure that may contribute dominantly to the buckling of the thin-walled liner. The critical buckling pressure is derived analytically by combining the thin-walled shell theory, a refined displacement function, and the energy scheme. It is found the egg-shaped FGLs liner sustains higher buckling pressure than the circular FGP-GPLs one. Furthermore, a finite element model is developed to verify the theoretical solutions. The results indicate the numerical equilibrium paths agree well with the analytical ones. In addition, the present analytical predictions are compared successfully with other close-formed solutions. Finally, parametric analyses indicate that the addition of GPLs may significantly improve the stability of the egg-shaped liner, while the increase of pores decreases the stability of the liner. The thickness of the GPLs has a slight effect on the stability of the liner when the volume of GPLs is constant. Thus, thick GPLs may be recommended in engineering practices to reduce the manufacturing cost.

The Effect of Wall'S Porous Liner on MHD Couette Flow of Carreau Fluid in an Inclined Channel under the Convective Conditions

The Effect of Wall'S Porous Liner on MHD Couette Flow of Carreau Fluid in an Inclined Channel under the Convective Conditions

New porous absorber simulation techniques in the context of finite element modelling

Porous liners are widely used as vibration and acoustics isolation materials due to their high absorbing qualities in a wide frequency range. In a car body porous plates are laid on top of a metal structure to prevent vibroacoustic wave propagation inside the passenger cabin. Unfortunately, currently used FEM (finite element method) simulation models for poroelasticity Biot's equations are still unable to efficiently describe such coupled structure-liner-fluid systems due to the lack of modelling precision. The current paper focuses on the importance of the phenomena taking place on the structure-liner interface during dynamic excitations in the frequency range of 10-1000 Hz. Measurements of transfer functions for numerous foam samples with varying boundary conditions have been conducted in a vacuum chamber to estimate the effect of interface conditions. New simulation approaches are presented to account for the observed phenomena. Moreover, the issues of measurement uncertainties regarding foam material parameters (or Biot parameters) and poor measurement reproducibility have been addressed and corresponding parameter optimization schemes have been implemented. As a result, a significant improvement in the agreement between simulation and measurement results has been achieved. All simulations have been conducted in a custom FEM code based on the open-source Deal II library.

Structural optimization of an encased bi-material FGP-GNF pipeline-liner system with novel polyhedral configurations

This article proposes a novel thin-walled polyhedral functionally graded porous (FGP) liner consolidated by graphene nanofillers (GNF) to rehabilitate the cracked pipeline. A buckle propagation may occur since the liner is subjected to hydrostatic pressure and temperature variational field simultaneously. A cosine function is developed to describe the deformed shape of the liner. Both pores and the GNF are distributed symmetrically on the cross-section of the liner, which also has a polyhedral profile to improve its bending stiffness. The nonlinear equilibrium equations are accurately obtained by introducing the thin-walled shell theory and the principle of minimum potential energy. The critical buckling pressure is obtained by solving the nonlinear equilibrium equations. Analytical solutions are compared successfully with other closed-form results to accomplish the verification when the FGP-GNF polyhedral liner reduces to an isotropic circular one. Furthermore, one improvement factor is proposed to analyze the effect of different polyhedral shapes on the buckling pressure of the encased polyhedral FGP-GNF liner. Finally, parameters are evaluated to further understand the buckling behavior of the FGP-GNF polyhedral liner, including the number of polygons, porosity coefficient, mass fraction, geometric shape of the GNF, radius-to-thickness ratio, temperature field, etc.

Natural ventilation system with thin microperforated panel (MPP) component for wideband sound insulation

Natural ventilation system plays a pivotal role in building sustainability. However, the design is challenging due to the conflict between opening area requirements and sound insulation capability. Here, we design and experimentally demonstrated such a system with attenuation and bandwidth enhancement. For this, we use MPP components in L-shaped cavity that can be tuned at the targeted frequency range individually, while its overall thickness is reduced due to the benefit of the L-shape that forms a coiled backing air cavity. Moreover, adopting the MPP components allow the system to be easily tuned at various frequency regimes under fixed thickness, particularly at a low frequency that might be difficult for the porous liner cases. It is found that sound insulation bandwidth of 1000 Hz and more can be produced by such a system where the transmission loss of 20 dB and above are pronounced. Most of the features in the theoretical calculation are also found in the experimental results for the same structures. The results are promising for green building applications where sound insulation and air circulation need to be present simultaneously from the natural ventilation system.

Porous liner coated inlet duct: a novel approach to attenuate automotive turbocharger inlet flow-induced sound propagation

Automotive turbochargers generate high-frequency noise, especially at their inlet air duct, which has become a long-standing problem for both passengers and pedestrians and hence is required to be mitigated by provisions such as the use of absorptive materials and novel inlet duct designs. This paper proposes utilizing a thin porous material coating liner on the inlet duct of the turbocharger compressor in order to absorb the incident excitation and hence, broadband reduction of the flow-induced sound wave propagation. To this end, first, a sound-absorbing inlet duct model is designed based on efficient structural parameters. Then, three different types of absorptive materials are used as coating liners to analyze the impact of varying material properties on the acoustic absorption performance of the system. Meanwhile, a sensitivity analysis is carried out to evaluate the influence of coating layer thickness on the system’s flow-induced sound insulation performance. The research involves applying a finite element approach to conducting acoustic pressure and poroacoustics studies over the desired frequency range of human hearing (1–20 kHz). In this regard, sound transmission loss (TL) and sound pressure level (SPL) are investigated for the models with and without liners. The results indicate that sound-absorbing materials can be employed to significantly diminish flow-induced sound levels in the turbocharger inlet duct. According to the results, absorptive liners would considerably increase the maximum TL and lessen the sharp drop in TL that appeared in the model without liners at around 4321 Hz. In addition, the average TL has increased due to the replacement of valleys with peaks. The sensitivity analyses demonstrated that denser absorptive materials and larger liner thicknesses are associated with higher TL levels and better sound attenuation response. By adding 15 mm of rock wool liner to the designed inlet duct, the average TL and root mean square of TL were increased up to and respectively. The proposed design procedure of this study unlocks a fundamental approach that can be practically applied to many promising fields, such as aerospace and automotive engineering.

An investigation on the modelling of a finite porous liner for the sound propagation in a rectangular duct

Acoustic liners take an essential role in the noise attenuation in ducts. In this work, the multimodal method based on the finite-difference method is extended to predict the acoustic field in a rectangular duct lined with a finite porous material and validated by the experiment. A modified immersed interface method is developed for the air–porous interface problem in the extended multimodal method without flow. When the flow exists, the treatments of the air–porous interface problem and the continuity of pressure between the wall and liner are also given. Three ways of describing the porous liner using the surface impedance at normal incidence named normal impedance, the surface impedance at grazing incidence named shear impedance and a cavity filled with the equivalent fluid of porous material are introduced. The comparison among the three ways reveals that the extended method of treating liners using a cavity filled with the equivalent fluid is more accurate for the acoustic evaluation of porous liners. The analysis finds that the shear impedance can reasonably present the influence of porous material during the comparisons of transmission loss curves of the liners with different lengths and depths at different Mach numbers. In most cases, the prediction by the shear impedance is closer to that simulated by the cavity filled with porous material than the normal impedance. Normal impedance is hardly utilized to describe the porous material and is only reliable when the cavity is very short and deep.

Experimental Investigation of Aerostatic Journal Bearings Made of Carbon Fiber-Reinforced Carbon Composites

Abstract This study describes experimental results using carbon fiber-reinforced carbon (C/C) material for porous journal bearings under static conditions. Exerted radial forces of up to 90 N, a supply pressure of up to 6 bar, and a maximum rotational speed of 8000 rpm were tested. The occurrence of pneumatic hammering was not observed under these operating points. Triangulation sensors were mounted vertically and horizontally as well as in front of and behind the tested bearing. These sensors measure the eccentricity and misalignment. The orbit analysis demonstrated an improvement in concentricity with an increment in the supply pressure. The layered structure of the C/C material used for the porous liner is presented. A rotational speed below 8000 rpm negligibly influenced the load-carrying capacity and the flowrate. The vertical misalignment of the shaft was determined in relation to the force-applied test bearing. In addition, two vertically positioned sensors on the support-bearing housing were used to discern the misalignment in the absolute system. On the other hand, reducing the speed to 1000 rpm increased the concentricity error. The shaft showed no significant signs of use after the experiments. The measurements confirm the suitability of the material for porous bearings.

Analysis of a transpiration cooled LOX/CH[formula omitted] rocket thrust chamber

Transpiration cooling has been theoretically identified as a more efficient thermal protection system, compared to regenerative and film cooling techniques. The availability of porous light-weight high-temperature materials, such as ceramic matrix composites (CMCs), is making transpiration cooling an attractive solution for use in future re-usable rocket thrust chambers for cheaper access to space. In this study, a numerical framework, utilizing the industry standard computational fluid dynamics (CFD) code ANSYS CFX, for the simulation of transpiration cooled rocket thrust chambers is presented. The framework is shown to be suitable for predicting the performance, both in-terms of thermal protection and thrust produced, of thrust chambers that utilise transpiration cooling systems. A liquid oxygen (LOX) and methane (CH4) oxidiser and fuel combination is used, although the method is not limited to these substances. Foreign gas transpiration is modelled by a multi-component model. Different porous liner geometries and reservoir conditions are studied to demonstrate their effect on the performance of the thrust chamber. The numerical framework was developed to design a sub-scale transpiration cooled rocket thrust chamber ground test.

Hydraulically optimal porous liner around a porous lens: Strack’s problem revisited

ABSTRACT A porous barrier bounded by two confocal ellipses is filled with material of a hydraulic conductivity different from the ambient one in order to control the flow rate inside. Optimization problems are solved by describing the flow through a medium consisting of zones of different properties. For three-component composites, viz. three zones demarcated by two confocal ellipses, an explicit rigorous solution of refraction problems for potential fields of Darcian 2-D saturated flows is used. An aquifer, an elliptical ‘core’ and an elliptical annulus, which serves as a liner of the core, have contrasting hydraulic conductivities (control variables). The magnitude of the velocity in the core, total flow rate, travel time along streamlines, hydraulic gradient in the core are objectives in optimization. A single maximum of the magnitude of velocity in the ‘core’ is found at a certain conductivity of the annulus, similarly to the Strack circular annulus refracting a unidirectional flow. This maximum can be higher or lower than the velocity at infinity, i.e. the liner can amplify or lessen the incident flow. Applications to in situ ore leaching, permeable reactive barriers, porous waste repositories, aquifer permeameters and formation damage due to suffusion in the vicinity of pumping wells are discussed. Abbreviations: ISL: in situ leaching; RAF: reduction–amplification factor.

Efficiency of charges of different structures in deformation and destruction of metal obstructions

The paper presents the experimental data and a comparison between the volume of the crater in the metal under cylindrical and cone charges, devices of cumulative effect of various designs from several explosives: explosive plasma generator, a shaped charge with a solid liners, shaped charge with a porous liners, shaped charge with a new liner materials and in tubular charge of explosive.It is shown that the criterion of the maximum volume of the crater formed increases the efficiency from the explosive plasma generator to the external charge of explosive, shaped charge with a solid and porous liners, tubular charge of explosive. The highest efficiency has shaped charge with a new liner materials that generates additional energy in the target at penetration of the shaped charge jet.The ways of improving the charges of various designs and advanced materials for them are determined by the criterion of the maximum volume of the crater in the target.

Numerical assessment of the vibration control effects of porous liners on an over-the-wing propeller configuration

An over-the-wing position of propellers comes with noise shielding and significantly reduced sound emission to the ground. A drawback of this configuration may be the additional impact due to the passing propeller blades on the airfoil’s surface inducing structure-borne sound in the wing. This structural sound propagates within the wing and the fuselage and can radiate further into the cabin as airborne sound. In order not to trade the advantage of reduced noise transmission to the ground with higher sound pressure levels within the cabin, a remedy is proposed, which consists in placing a poroelastic liner on the wing’s surface below the rotor where the blade tips move closely to the airfoil’s skin. In this work, a numerical approach to assess the effects of porous liners for an over-the-wing propeller configuration is presented. A simplified generic channelwing structure is exposed to pressure fluctuations on its surface which are caused by an over-the-wing propeller. Porous liners are applied to the wing’s surface where the blade tips pass in close proximity. Structural vibrations are determined using the finite element method in frequency domain. Surface data is obtained from CFD computations. The porous material is represented by Biot’s theory.

Potential of Metal Fibre Felts as Passive Absorbers in Absorption Silencers

The growing noise exposure of residents, due to a rising number of flights, causes significant impacts on physical health. Therefore it is necessary to reduce the noise emission of aircrafts. During take-off, the noise generated by the jet engines is dominating. One way to lower the noise emission of jet engines is to build an absorption silencer by using porous liners. Because of the high thermic and corrosive attacks as well as high fatigue loads, conventional absorbers cannot be used. A promising material is sintered metal fibre felts. This study investigates the suitability of metal fibre felts for the use as absorption material in silencers. The influences of pore morphology, absorption coefficient, determined with perpendicular sound incidence, as well as geometric parameters of the silencer to the damping are identified. To characterise the material, the parameters fibre diameter, porosity and thickness are determined using three-dimensional computer tomography images. The damping potential of absorption silencers is measured using an impedance tube, which was modified for transmission measurements. The essential parameter to describe the acoustic characteristics of porous materials is the flow resistivity. It depends on the size, shape and number of open pores in the material. Finally a connection between pore morphology, flow resistivity of the metal fibre felts and damping potential of the absorption silencer is given.

Mechanical effect of shaped charges with porous liners

This paper presents experimental data on the penetration of shaped charges with porous liners into metal targets located at distances smaller than or comparable to the diameter of the charge and some experimental data on the velocity of the jets from the investigated charges with liners of metal powders.

The Use of Perforated Damping Liners in Aero Gas Turbine Combustion Systems

This paper considers the use of perforated porous liners for the absorption of acoustic energy within aero style gas turbine combustion systems. The overall combustion system pressure drop means that the porous liner (or “damping skin”) is typically combined with a metering skin. This enables most of the mean pressure drop, across the flame tube, to occur across the metering skin with the porous liner being exposed to a much smaller pressure drop. In this way porous liners can potentially be designed to provide significant levels of acoustic damping, but other requirements (e.g., cooling, available space envelope, etc) must also be considered as part of this design process. A passive damper assembly was incorporated within an experimental isothermal facility that simulated an aero-engine style flame tube geometry. The damper was therefore exposed to the complex flow field present within an engine environment (e.g., swirling efflux from a fuel injector, coolant film passing across the damper surface, etc.). In addition, plane acoustic waves were generated using loudspeakers so that the flow field was subjected to unsteady pressure fluctuations. This enabled the performance of the damper, in terms of its ability to absorb acoustic energy, to be evaluated. To complement the experimental investigation a simplified one-dimensional (1D) analytical model was also developed and validated against the experimental results. In this way not only was the performance of the acoustic damper evaluated, but also the fundamental processes responsible for this measured performance could be identified. Furthermore, the validated analytical model also enabled a wide range of damping geometry to be assessed for a range of operating conditions. In this way damper geometry can be optimized (e.g., for a given space envelope) while the onset of nonlinear absorption (and hence the potential to ingest hot gas) can also be identified.

The Porosity of Liner Effect on the Shaped Charge Jet Penetration

Shocking temperature rise of the shaped charge with porous liner before collapse was calculated based on the Herrman equation of state. Shaped charges with 36mm charge diameter were used to fire at the 603 armor steel target, the penetration-standoff curves(P-S) of the shaped charge liner with 88.6% and 90.3%T.D were measured and compared. It is shown that proper porosity is helpful to lengthen the jet break up time and penetration depth，which is of significance for the application of porous liner.

Penetration of Porous Jets

Jets that emanate from high density porous liners are most widely used for penetration into Earth materials. These shaped-charges differ from those that contain solid copper liners in three major aspects: the porosity, the usually higher initial density, and the very short standoff in which they typically operate. Because penetration depth is commonly very difficult to increase by means of high density solid liners, it is important to understand the benefit of using porous liners in utilization of high density materials. The models published so far to describe the performance of jets formed by porous liners are based on the modification of the virtual origin model to suit this special case, which limits the accuracy of their predictions. Here we present a more general analysis that does not depend on the virtual origin assumption. Our study employs the SCAN semi-analytical code into which a new model for porous jet behavior is incorporated. It is used to explain the benefit of using this type of liner for oil-well penetration, hence penetration into low density targets, as opposed to penetration into hard steel.

Acoustic viscous damper for centrifugal gas compressor

An acoustic viscous damper for a compressor including a porous liner located within the discharge duct, the porous liner having a plurality of holes for passage of a purge working fluid therethrough into the discharge duct.

Rayleigh–Ritz approach for predicting the acoustic performance of lined rectangular plenum chambers

The purpose of this study was to predict the acoustic performance of a fully lined rectangular plenum chamber having inlet and outlet ports at arbitrary locations. Because no exact analytic solution exists for this reactive-resistive silencer configuration, numerical methods are only available for a three-dimensional analysis. The lined plenum chamber was modeled as a piston-driven rectangular tube without mean flow and the acoustic pressure in the lined chamber was obtained by superposing the acoustic pressures due to each harmonically fluctuating piston. Air pore and skeleton material of the porous liner was reduced to an equivalent medium; thus, its acoustic characteristic was given by bulk-reacting liner properties. A single weak variational statement, which satisfies the conditions of the oscillating piston and all necessary boundary conditions, was developed. The Rayleigh-Ritz method was employed as the numerical scheme for the derived variational statement. Using a transfer matrix and measured material properties, all possible types of lined plenum chambers were tested. Computed results were compared with the predicted transmission loss by the locally reacting liner model and experimental results. Transmission loss predicted by the Rayleigh–Ritz method using the bulk-reacting liner model agreed well with the measured one.

Surface roughness effect on finite journal bearings with flexible porous liners

The effects of surface roughness on the static characteristics of finite porous journal bearings under hydrodynamic lubrication conditions are investigated in this paper. The well-established Christensen stochastic theory of hydrodynamic lubrication of rough surfaces is used to incorporate the effects of surface roughness into the Reynolds equation. The analysis takes into account the flexibility of the porous liner by using a thin liner model. The effects of velocity slip at the surface of the porous medium are considered in the analysis by using the Beavers-Joseph criterion. The mathematical model is then solved numerically by finite-difference methods for mean hydrodynamic pressure, which in turn gives the hydrodynamic load. The effects of the surface roughness parameter, surface pattern, eccentricity ratio, length-to-diameter ratio, permeability parameter, and flexibility parameter on the hydrodynamic load-carrying capacity, attitude angle, and friction factor are discussed.