129,650 research outputs found
Contact Pressure Measurement System in Cross Wedge Rolling
No full textIn the cross wedge rolling process (CWR), plastic deformation is geared by a driving torque transmitted by friction on die surface. Friction plays a role which has to be further identified in this metal forming process. The local contact pressure between a cylindrical billet and flat dies seems to be a relevant parameter to characterize the severe contact conditions during the rolling. This paper deals with an experimental measurement technology, which has been designed and implemented on a semi-industrial CWR test bench with plate configuration. This measurement system using pin and piezoelectric sensor is presented, with an analysis of the system operation and design detail. Characterization of systematic error and calibration tests are then explained. Additional tests performed on hot steel preforms allow to check the ability of the contact pressure measurement system to resist under severe operating conditions. Realistic results for varying temperatures are then discussed
Spectral Properties of Wedge Problems
No full textThis paper presents our recent results on the study of the scattering and diffraction of an incident plane wave by wedge structures. A review about the impenetrable wedge problem at skew incidence and about the penetrable wedge at normal incidence is discussed. In particular we focus the attention on the spectral properties of the solution in the angular domain. These studies seem to provide a new tool to enhance the fast computation of the solution in terms of fields via a quasi-heuristic approac
A Green's function for diffraction by a rational wedge
No full textIn this paper we derive an expression for the point source Green's function for the
reduced wave equation, valid in an angular sector whose angle is equal to a rational
multiple of 77. This Green's function can be used to find new expressions for the field
produced by the diffraction of a spherical wave by a wedge whose angle can be
expressed as a rational multiple of n. The expressions obtained will be in the form of
source terms and real integrals representing the diffracted field. The general result
obtained is used to derive a new representation for the solution of the problem of diffraction by a mixed hard-soft half plane
The measurement of near wall flows using pneumatic wedge probes.
No full textThe three hole, wedge-type pneumatic pressure probe represents a robust
traverse probe design which is widely used for total and static pressure and yaw angle
measurements in turbomachinery. However, unsteady flows are incorrectly averaged due
to pneumatic meaning errors in the pressure pipes. Wedge probes also fail to measure the
correct static pressure when operating in close proximity to a wall through which the
probe is inserted. Thirdly, the aerodynamic calibration obtained for a wedge-type probe
in a closed wind tunnel differs appreciably from that obtained in an open jet. If not
corrected, these errors will corrupt any calculation of turbomachinery blade row
performance.
In this investigation, the second and third effects described above have been
addressed. A factorial experiment was completed in which the influence of seven
variables on the wall proximity effect was quantified. Flow visualisation studies were
performed to understand the responsible flow mechanisms. Two regions of re-circulating
flow were identified in the probe wake, the structure of which depended on the probe
immersion. Similar re-circulatory flows were resolved from three-dimensional
computational fluid dynamics (CFD) calculations of the flow over a wedge probe. A link
between the probe wake re-circulations and flow over the wedge faces was established.
Based on this understanding of the flow structures, a model was developed from which
the wall proximity effect could be predicted for a given set of conditions.
Wedge probe calibrations were completed in a closed wind tunnel and in two
open jets. Discrepancies in the static pressure coefficient and yaw angle sensitivity results
were found. These were partially explained in terms of modifications to the probe wake
structure which occurred when the probes were calibrated in the open jet facilities.
Procedures for correcting the wall proximity effect and for avoiding the facility
dependence of wedge probe calibrations were developed from this understanding of the
flow mechanisms involved.
Based on the findings of this investigation, a novel wedge probe was designed to
minimise the wall proximity effect. This probe demonstrated a reduction in the wall
proximity effect, from 20% dynamic head with current designs, to 3% dynamic head at
flows typical of high speed turbomachinery
Skew Incidence on Concave Wedge With Anisotropic Surface Impedance
No full textThe diffraction of a plane wave at skew incidence by an arbitrary-angled concave wedge with anisotropic impedance faces is studied. Concave wedges are of interest in wireless propagation models, in particular on modeling buildings and reflectors. The solution is obtained via the generalized Wiener-Hopf technique for arbitrary impedance wedges using a numerical-analytical approach. The numerical results show the spectral properties of the fields, GTD/UTD diffraction coefficients, and total field
Cylindrical-wave diffraction by a rational wedge
No full textIn this paper, new expressions for the field produced by the diffraction of a cylindrical wave by a wedge, whose angle can be expressed as a rational multiple of π are given. The solutions are expressed in terms of source terms and real integrals that represent the diffracted field. The general result obtained includes as special cases, Macdonald's solution for diffraction by a half plane, a solution for Carslaw's problem of diffraction by a wedge of open angle 2π\3, and a new representation for the solution of the problem of diffraction by a mixed soft-hard half plane
The Wiener-Hopf solution of the isotropic penetrable wedge problem: diffraction and total field
No full textThe diffraction of an incident plane wave by an isotropic penetrable wedge is studied using generalized Wiener-Hopf equations, and the solution is obtained using analytical and numerical-analytical approaches that reduce the Wiener-Hopf factorization to Fredholm integral equations of second kind. Mathematical aspects are described in a unified and consistent theory for angular region problems. The formulation is presented in the general case of skew incidence and several numerical tests at normal incidence are reported to validate the new technique. The solutions consider engineering applications in terms of GTD/UTD diffraction coefficients and total field
On state-space elastostatics within a plane stress sectorial domain: the wedge and the curved beam
No full textThe plane stress sectorial domain is analysed according to a state-space formulation of the linear theory of elasticity. When loading is applied to the straight radial edges (flanks), with the circular arcs free of traction, one has the curved beam; when loading is applied to the circular arcs, with the flanks free of traction, one has the elastic wedge. A complete treatment of just one problem (the elastic wedge, say) requires two state-space formulations; the first describes radial evolution for the transmission of the stress resultants (force and moment), while the second describes circumferential evolution for determination of the rates of decay of self-equilibrated loading on the circular arcs, as anticipated by Saint-Venant’s principle. These two formulations can be employed subsequently for the curved beam, where now radial evolution is employed for the Saint-Venant decay problem, and circumferential evolution for the transmission modes. Power-law radial dependence is employed for the wedge, and is quite adequate except for treatment of the so-called wedge paradox; for this, and the curved beam, the formulations are modified so that ln r takes the place of the radial coordinate r. The analysis is characterised by a preponderance of repeating eigenvalues for the transmission modes, and the state-space formulation allows a systematic approach for determination of the eigen- and principal vectors. The so-called wedge paradox is related to accidental eigenvalue degeneracy for a particular angle, and its resolution involves a principal vector describing the bending moment coupled to a decay eigenvector. Restrictions on repeating eigenvalues and possible Jordan canonical forms are developed. Finally, symplectic orthogonality relationships are derived from the reciprocal theorem
Generalized Wiener-Hopf Equations for Wedge problems involving arbitrary linear media
No full textThis paper provides new functional equations in angular regions that turn useful to study wedge problems in presence of arbitrary linear media. The enforcement of the boundary conditions on these equations reduces the wedge problems to Generalized Wiener-Hopf (GWHE) equations that can be approached with standard solution techniques. This procedure is briefly illustrated in this pape
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