Wire-mesh Model Research Articles

On the mitigation of landing gear noise using a solid fairing and a dense wire mesh

A solid fairing and a wire-mesh fairing consisting of very fine wires and pores are numerically and experimentally investigated for the mitigation of landing gear noise. A slightly modified LAGOON landing gear and two configurations, one equipped with a solid fairing and the other with a wire-mesh fairing, are numerically simulated using the Improved Delayed Detached-Eddy Simulation (IDDES) in combination with the Ffowcs Williams and Hawkings (FW-H) analogy. Instead of resolving the detailed flow features through the wire mesh, a recently proposed numerical model is used to represent the effect of the wire-mesh fairing. The simulated flow fields and the far-field noise spectra are validated against the experiments conducted in an anechoic wind tunnel. The superiority of the recently proposed wire-mesh model over a classical wire-mesh model in modelling both the aerodynamic and aeroacoustic effects of the wire mesh is demonstrated. Results also show that the dense wire-mesh fairing functions very similarly to the solid fairing and that significant noise can be reduced through the installation of a solid fairing or a wire-mesh fairing upstream of the landing gears. For the baseline landing gear, the torque link and the brakes are identified noise sources. With the aerodynamic penalty of a 50% increase in drag, both fairings mitigate the pressure fluctuation on the torque link and brakes, resulting in the reduction of surface noise sources. The noise directivity shows that a solid fairing or a dense wire-mesh fairing contributes to a noise reduction of 4-6 dB in all radial directions. The findings in this study pave the way for the low-noise design of aircraft landing gears.

Numerical Wire Mesh Model for the Simulation of Noise-Reduction Devices

This study deals with the development of a numerical wire mesh screen model for the unsteady simulation of aeroacoustic configurations. Such devices are indeed of growing interest for practical applications because they potentially lead to significant noise-reduction effects. Numerical simulations including wire mesh screens are therefore of major interest to optimize their possible location and properties, as well as to get a better understanding of the involved physical phenomena. On the basis of several finely resolved unsteady simulations (direct numerical simulation and large-eddy simulation) of the flow through an isolated wire mesh sample, a numerical wire mesh screen model is proposed and calibrated. An application of the method to the tandem cylinder test case is then performed for different screen locations and porosities. The introduction of wire mesh screens in the flow is observed to lead in some cases to a significant reduction of the radiated noise, by up to 8 dB.

A Multi-Stage Model for the Electromagnetic Shielding Effectiveness Prediction of an Infinite Conductor Plane With Periodic Apertures

This paper focuses on the shielding effectiveness (SE) prediction of the periodic aperture array on an infinite conductor plane against a plane electromagnetic wave with its wavelength much larger than the size of a unit cell of the array. Especially, the existing analytical expressions of SE are combined to cover the entire range of the aperture rate, which is defined as the ratio of the side length of the aperture to that of the unit cell. The combination is carried out by bridging the small aperture model and the wire mesh model. Then, a multi-stage model based on the piecewise function of the aperture rate is presented to calculate the SE for any aperture rate. The model is also extended to consider different wave polarization and incident angles. The results of the model are in good agreement with those from the full-wave simulation. The applicability of the model to a different thickness and aperture shape is discussed. In addition, the upper-limit frequency at which the model is no longer applicable is also analyzed.

A study on development effect of horizontal well with SRV in unconventional tight oil reservoir

Unconventional tight oil and gas are the main body of the increase of reserve and production in Ordos Basin. Based on the tight oil reservoir in Ordos Basin, a 7 point pattern well group numerical mechanism model with a multi-stage and multi-cluster horizontal production well in the middle and 6 vertical injection wells on the edge is established. PR3 equation of state model is used in the numerical model. The stimulated reservoir volume of horizontal well is realized by local grid refinement, and the wire-mesh model is used to simulation hydraulic fracture network. Application of the model, the development effect factors of tight oil reservoir are analyzed, which contain development methods (depletion development, water flooding development and CO2 flooding development), reservoir permeability, SRV size, fracture density, fracture conductivity and cluster spacing. The results of this paper can offer suggestions to fractured horizontal well design and tight oil reservoir development.

Numerical Simulation of Shale Gas Production

Shale gas reservoirs require a large fracture network to maximize well performance. Microseismic fracture mapping has shown that large fracture networks can be generated in many shale reservoirs. The application of microseismic fracture mapping measurements requires estimation of the structure of the complex hydraulic fracture or the volume of the reservoir that has been stimulated by the fracture treatment. There are three primary approaches used to incorporate microseismic measurements into reservoir simulation models: discrete modeling of the complex fracture network, wire-mesh model, and dual porosity model. This paper discuss the different simulation model, the results provided insights into effective stimulation designs and flow mechanism for shale gas reservoirs.

Computer planning for distraction osteogenesis.

Distraction osteogenesis of the mandible has found an application in the treatment of patients with a variety of different mandibular deformities. Compared with the relatively simple unidirectional distraction of long bones as described by Ilizarov, the three-dimensional distraction of the mandible is extremely complex. Whereas experience with orthognathic surgery clearly demonstrates that careful presurgical planning is necessary to achieve predictable outcomes, there are few reported methods for the planning of mandibular distraction. The authors have developed a method for planning distraction osteogenesis of the mandible that involves the use of three-dimensional modeling and animation to simulate distraction osteogenesis in virtual reality. The first step in the authors' treatment planning process is to obtain a three-dimensional computerized scan of the facial skeleton. From this scan, a three-dimensional wire-mesh model is built using animation software. With the same software, a virtual distractor is built and installed on the wire-mesh model. The osteotomies and the distraction process are then simulated. Finally, a recipe for sequencing the linear and angular changes of the distractor is calculated. The authors have used this planning process in seven patients (age range, 4 to 10 years): four with unilateral mandibular deformities and three with bilateral. The planning process has yielded predictable and reproducible results.

Modelling catalytic combustion of carbon monoxide and hydrocarbons over catalytically active wire meshes

A new way of preparing catalytically active wire meshes through a thermal-spray technique is described. A metal substrate (e.g. Kanthal AF) was plasma-sprayed with a composite ceramic/polymer-powder. The polymer content of the sprayed layer was burnt off whereupon a well-defined macro-porosity was created. By treating the so obtained material with an alumina-sol the specific surface area could be increased by a factor of 50 or more. The ceramic layer was finally activated with precious metals through an impregnation step. A numerical model was developed to compare the performance of wire-mesh-, monolith- and pellets catalysts. The model describes the resistance to internal and external mass- and heat transfer and the effects of axial dispersion. The wire-mesh model was verified through experiments. Different evaluation parameters were derived to compare the catalyst performance relative to the catalyst volume, the geometric weight, the catalyst weight, the pressure drop and the temperature response. Wire-mesh catalysts offer the following advantages: high mass and heat transfer numbers, moderate pressure drop, insignificant effects of pore diffusion and axial dispersion, thermal and mechanical strength, geometric flexibility, excellent thermal response, simplicity in the catalyst recovery. The cost of a wire-mesh catalyst is expected to be competitive to other alternatives.

Coding for the storage and communication of visualisations of 3D medical data

The transmission of the large store of information contained in 3D medical data sets through limited capacity channels, is a critical procedure in many telemedicine applications. In this paper, techniques are presented for the compression of visualisations of 3D image data for efficient storage and transmission. Methods are first presented for the transmission of the 3D surface of the objects using contour following methods. Alternatively, the visualisation at the receiver may be based on a series of depth maps corresponding to some motion of the object, specified by the medical observer. Depth maps may be transmitted by using depth map motion compensated prediction. Alternatively, a wire-mesh model of the depth map may be formed and transmitted by encoding the motion of its nodes. All these methods are used for the transmission of the 3D image with visualisation carried out at the receiver. Methods are also developed for efficient transmission of the images visualised at the encoder site. These methods allow remote interactive manipulation (rotation, translation, zoom) of the 3D objects, and may be implemented even if the receiver is a relatively simple and inexpensive workstation or a simple monitor. In all above cases, the coding of binocular views of the 3D scene is examined and recommendations are made for the implementation of coders of stereo views of 3D medical data.

Corroboration of a moment-method calculation of the maximum mutual coupling between two HF antennas mounted on a helicopter

A moment-method calculation is described of the maximum mutual coupling (or minimum isolation) between two loop antennas mounted on the tail-cone of a helicopter at the low-frequency end of the aircraft HF band. The wire-mesh mathematical model of the aircraft is constructed with a high sampling density in an attempt to produce estimates of the required nearfield dependent parameters with sufficient precision to calculate the maximum mutual coupling with acceptable accuracy. The calculation is a fairly demanding test of the procedure adopted for the construction of the mathematical model, because it depends upon the accuracy with which both near-field and far-field parameters are determined. This mathematical model does not incorporate any empirically derived information, and the calculation was of necessity performed in advance of an aircraft being available for experimental purposes. The difficulty of assessing the credibility of calculated results under such circumstances is considered. NEC was used as the solution code for the wire-mesh model. An independent corroboration of the calculation was made possible by the siting and configuration of the proposed antennas. This allowed a simple equivalent circuit model of the arrangement to be constructed, values of the circuit elements to be estimated, and hence an independent approximate determination of the maximum coupling to be made. The degree of consistency between the results obtained by these two methods is considered to enhance the confidence which can be placed in the results obtained using momentmethod mathematical models of this type when applied to near-field aircraft HF antenna problems.

An interactive computer graphic system for 3-D stereoscopic reconstruction from serial sections: Analysis of metastatic growth

An interactive computer graphic system has been developed for 3-D reconstruction of stained serial sections. The system has been used for 3-D reconstruction of portions of mouse lung containing melanoma nodules. A stereoscopic color picture of a wire mesh model of the reconstructed object is produced. The volume, surface area, and sphericity index of structures such as tumor nodules can be computed.

Radar cross section of a rectangular conducting plate by wire mesh modeling

Radar cross section of a conducting rectangular plate is investigated numerically and experimentally by a wire mesh model as a function of plate size and incidence angle. Numerical examples also include the edge-on incidence where physical optics and the geometrical theory of diffraction fail.

On the field distribution of an aperture

A study of the field distribution in a square aperture on a plane conducting screen illuminated by a plane electromagnetic wave at normal incidence is presented. In solving the problem, the square aperture is first formulated into a complementary square plate scattering problem. The distribution of current on the plate is then found by solving the corresponding wire mesh model with the aid of a computer program for linear wire antennas. A simple averaging process is then introduced in a straightforward manner to convert the currents flowing along the wires into continuously distributed equivalent surface currents on the square plate. The surface current density is, in turn, equal to the value of magnetic field intensity by the boundary condition for a perfect conductor. Finally, a direct application of the electromagnetic form of Babinet's principle gives the electric field distribution of the aperture. The far zone field in terms of a radar cross section of a square plate compares well with an experiment. A discussion is also included comparing the electric field distribution of a square aperture and circular apertures.

Fluid flow through a solid-liquid dendritic interface

Fluid flow through a dendritic solid-liquid interfacial zone, during solidification, has been observed in a series of Sn-Pb alloys. It was found that liquid penetrates only a short distance into the zone, relative to the total thickness of the zone. The amount of solid present at the point of maximum penetration varies from 12 to 22 pct, and depends on the alloy concentration. Flow due to volume shrinkage, thermal convection, or solute convection well inside the zone, was not detected. Fluid flow through a wire mesh model of a thin section of the solid-liquid dendritic zone was examined. The results are not in agreement with that predicted for flow through a porous barrier, which had been found applicable to interdendritic fluid flow.