| 1. |
- Ataei, Mohammad A., et al.
(författare)
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Fuzzy analytical hierarchy process approach for ranking the sawability of carbonate rock
- 2012
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Ingår i: International Journal of Rock Mechanics And Mining Sciences. - : Elsevier BV. - 1365-1609 .- 1873-4545. ; 50, s. 83-93
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Tidskriftsartikel (refereegranskat)abstract
- A new classification system is presented to evaluate and ranking the sawability of carbonate rock. The sawability of carbonate rock is classified into five categories: excellent, good, fair, poor and very poor. The sawability is assumed to depend on the uniaxial compressive strength, Young's modulus, Mohs hardness, and a new abrasivity index. The FAHP approach is used to determine the weights of the above-mentioned parameters by decision makers. Moreover, in this paper, a new classification system was developed to modify Schimazek's F-abrasiveness factor. In this new abrasivity classification, each parameter has a different importance coefficient. The new abrasivity index of carbonate rocks can be obtained from this new abrasivity classification system. The calculated sawability index of developed classification is applied for Iranian carbonate rocks to evaluation the energy consumption in rock sawing process. A variety of two groups of carbonate rocks (seven types) were saw using a fully instrumented laboratory sawing rig at different feed rates, peripheral speeds, and depth of cut. Then, a new statistical model was obtained using multiple regression method based on operating parameters and rock sawability index
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| 2. |
- Baudoin, Eric, et al.
(författare)
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Effect of partial premixing on stabilization and local extinction of turbulent methane/air flames
- 2013
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Ingår i: Flow, Turbulence and Combustion. - : Springer Science and Business Media LLC. - 1573-1987 .- 1386-6184. ; 90:2, s. 269-284
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedThe stabilization characteristics and local extinction structures of partially premixed methane/air flames were studied using simultaneous OH-PLIF/PIV techniques, and large eddy simulations employing a two-scalar flamelet model. Partial premixing was made in a mixing chamber comprised of two concentric tubes, where the degree of partial premixing of fuel and air was controlled by varying the mixing length of the chamber. At the exit of the mixing chamber a cone was mounted to stabilize the flames at high turbulence intensities. The stability regime of flames was determined for different degree of partial premixing and Reynolds numbers. It was found that in general partially premixed flames at low Reynolds numbers become more stable when the level of partial premixing of air to the fuel stream decreases. At high Reynolds numbers, for the presently studied burner configuration there is an optimal partial premixing level of air to the fuel stream at which the flame is most stable. OH-PLIF images revealed that for the stable flames not very close to the blowout regime, significant local extinction holes appear already. By increasing premixing air to fuel stream successively, local extinction holes grow in size leading to eventual flame blowout. Local flame extinction was found to frequently attain to locations where locally high velocity flows impinging to the flame. The local flame extinction poses a future challenge for model simulations and the present flames provide a possible test case for such study.
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| 3. |
- Baudoin, Eric, et al.
(författare)
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Effect of partial premixing on stabilization and local extinction of turbulent methane/air flames
- 2011
-
Ingår i: Proceedings of the 17th Mediterranean Combustion symposium, MCS 7. - 9788888104126
-
Konferensbidrag (refereegranskat)abstract
- The stabilization characteristics and local extinction structures of partially premixed methane/air flames were studied using simultaneous OH-PLIF/PIV techniques, and large eddy simulations employing a two-scalar flamelet model. Partial premixing was made in a mixing chamber comprised of two concentric tubes, where the degree of partial premixing of fuel and air was controlled by varying the mixing length of the chamber. At the exit of the mixing chamber a cone was mounted to stabilize the flames at high turbulence intensities. The stability regime of flames was determined for different degree of partial premixing and Reynolds numbers. It was found that in general partially premixed flames at low Reynolds numbers become more stable when the level of partial premixing of air to the fuel stream decreases. At high Reynolds numbers, for the presently studied burner configuration there is an optimal partial premixing level of air to the fuel stream at which the flame is most stable. OH-PLIF images revealed that for the stable flames not very close to the blowout regime,significant local extinction holes appear already. By increasing premixing air to fuel stream successively, local extinction holes grow in size leading to eventual flame blowout. Local flame extinction was found to frequently attain to locations where locally high velocity flows impinging to the flame. The local flame extinction poses a future challenge for model simulations and the present flames provide a possible test case for such study.
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| 4. |
- Fahlkrans, Johan, 1980-, et al.
(författare)
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Influence of tempering on contact fatigue
- 2011
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Ingår i: International Journal of Microstructure and Materials Properties. - 1741-8410 .- 1741-8429. ; 6:6, s. 465-478
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Tidskriftsartikel (refereegranskat)abstract
- Most components are tempered after heat treatment operations such as case hardening or induction hardening. The common opinion is that the martensitic structure after heat treatment is too brittle and tempering is necessary to increase toughness.Tempering is an additional operation which leads to increased costs by energy, handling, and investments. Eliminating tempering from the heat treatment process leads to increased productivity, energy savings, and lowered environmental impact.Two carburised steels, Ovako 253A (?EN 22NiCrMo12-5F mod. A) and EN 20NiCrMo2 (SAE 8620, SS2506), were tested for contact fatigue resistance in a roller to roller rig. The tested samples were characterised with respect to amount of fatigue damage, residual stress, amount of retained austenite and hardness. The objective was to determine if tempering is always necessary after a heat treatment operation.The contact fatigue tests show that tempering results in lower contact fatigue resistance. Further, fatigue cracks were found to have initiated in different ways between tempered and untempered steel.
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| 5. |
- Feas, Xesus, et al.
(författare)
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Molecularly imprinted polyallylamine hydrogels: another reassessment
- 2010
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Ingår i: Polymer International. - : Wiley. - 0959-8103. ; 59:1, s. 11-15
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Tidskriftsartikel (refereegranskat)abstract
- Researchers in the scientific community actively discuss the fact that polymer hydrogels synthesized by crosslinking polly(allylamine hydrochloride) (PAH) with epichlorohydrin (EPI) in the presence of D-glucose-6-phosphate monobarium salt do not show or show imprinting on the molecular level. In the work reported here, a polymer hydrogel was synthesized in the presence of flumequine (FQ) by crosslinking PAH with EPI in an aqueous system. The extent of FQ binding was assessed using liquid chromatography coupled with laser-induced fluorescence detection. A hydrogel-imprinting system was found to display FQ selectivity in binding assays (75.1 and 41.9%) compared with hydrogel formed in the absence of a template (41.6 and 20.4%). High-magnification scanning electron microscopy (SEM) images show that both of the hydrogels are highly ordered, exhibiting a 'honeycomb' pattern distribution. For the effect of the template molecule in the polymer structure (i.e. the imprinting effect in hydrogel morphology), appreciable differences were observed for images obtained. The non-imprinted polymer had a uniform, smoothly shaped surface. By contrast, the hydrogel molecular imprinting polymer surface was more globular. This difference was likely caused by the structure of the target molecule. Binding experiment results correlate with surface morphology, as analysed using SEM, and indicate that imprinted hydrogels have recognizable cavities with an affinity for used FQ from the imprint. (C) 2009 Society of Chemical Industry
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| 6. |
- Hosseini-Hashemi, Sh., et al.
(författare)
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Accurate free vibration analysis of thick laminated circular plates with attached rigid core
- 2012
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 331:25, s. 5581-5596
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the free vibration behavior of laminated transversely isotropic circular plates with axisymmetric rigid core attached at the center. The governing equations of motion are obtained based on Mindlin's first-order shear deformation plate theory. Two possible categories of vibration modes related to up-down translation of the core and wobbly rotation of the core about a diameter are studied. Accurate natural frequencies hitherto not reported in the literature are presented for a wide range of thickness-to-radius ratio, inner-to-outer radius ratio, mass and moment of inertia ratios of the core and various boundary conditions at the outer edge of the plate. Numerical results are compared with those of a three-dimensional finite element method (3-D FEM) to demonstrate the high accuracy and reliability of the current analysis.
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| 7. |
- Hosseini-Hashemi, Sh., et al.
(författare)
-
Free vibration analysis of functionally graded elliptical plates
- 2012
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Ingår i: International journal of Maritime Technology. - 2345-6000. ; 8:15, s. 43-60
-
Tidskriftsartikel (refereegranskat)abstract
- This paper deals with a free vibration analysis of functionally graded elliptical plates with different classical boundary conditions on the basis of polynomial-Ritz method and classical plate theory. The proposed admissible function is capable to obtain accurate natural frequencies of various classical boundary conditions namely, clamped, free and simply supported edges. The mechanical properties of the FG plate are assumed to vary continuously through the thickness of the plate and obey a power law distribution of the volume fraction of the constituents. The convergency of applied polynomial-Ritz method is investigated. In order to verify the accuracy of the present solution, a comprehensive comparison study is performed with the available results in the literature for homogeneous elliptical plate and FG circular plate. Also, the numerical results of the present solution for FG elliptical plate are compared with those of the finite element method (FEM). Finally, the effects of the plate geometry and inhomogeneity on the natural frequencies are investigated and some vibrational mode shapes related to symmetric-symmetric, symmetric-antisymmetric, antisymmetric- symmetric and antisymmetric- antisymmetric states are presented.
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| 8. |
- Hosseini, Seyed, 1981, et al.
(författare)
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A Methodology for Temperature Correction When Using Two-Color Pyrometers : Compensation for Surface Topography and Material
- 2014
-
Ingår i: Experimental mechanics. - : Springer Science and Business Media LLC. - 0014-4851 .- 1741-2765. ; 54:3, s. 369-377
-
Tidskriftsartikel (refereegranskat)abstract
- In this investigation, the applicability of the two-color pyrometer technique for temperature measurements in dry hard turning of AISI 52100 steel was studied, where both machined surfaces as well as cutting tools were considered. The impacts of differing hard turned surface topography on the two-color pyrometer readings was studied by conducting temperature measurements on reference samples created using cutting tools with different degrees of tool flank wear. In order to conduct measurements in a controlled environment, a specially designed furnace was developed in which the samples were heated step-wise up to 1,000 °C in a protective atmosphere. At each testing temperature, the temperatures measured by the two-color pyrometer were compared with temperatures recorded by thermocouples. For all materials and surfaces as studied here, the two-color pyrometer generally recorded significantly lower temperatures than the thermocouples; for the hard turned surfaces, depending on the surface topography, the temperatures were as much as 20 % lower and for the CBN cutting tools, 13 % lower. To be able to use the two-color pyrometer technique for temperature measurements in hard turning of AISI 52100 steel, a linear approximation function was determined resulting in three unique equations, one for each of the studied materials and surfaces. By using the developed approximation function, the measured cutting temperatures can be adjusted to compensate for differing materials or surface topographies for comparable machining conditions. Even though the proposed equations are unique for the hard turning conditions as studied here, the proposed methodology can be applied to determine the temperature compensation required for other surface topographies, as well as other materials. © 2013 Society for Experimental Mechanics.
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| 9. |
- Hosseini, Seyed, 1981, et al.
(författare)
-
Characterization of the Surface Integrity induced by Hard Turning of Bainitic and Martensitic AISI 52100 Steel
- 2012
-
Ingår i: Procedia CIRP. - : Elsevier BV. - 2212-8271. ; 1:1, s. 494 - 499
-
Konferensbidrag (refereegranskat)abstract
- Depending on the process parameters and the tool condition, hard turned surfaces can consist of a “white” and a “dark” etching layer having other mechanical properties compared to the bulk material. X-ray diffraction measurements revealed that tensileresidual stresses accompanied with higher volume fraction of retained austenite are present in the thermally induced white layer. While compressive residual stresses and decreased retained austenite content was found in the plastically created white layer. The surface temperature was estimated to be ~1200 C during white layer formation by hard turning.
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| 10. |
- Hosseini, Seyed, 1981
(författare)
-
Characterization of White Layers induced by Hard Turning of AISI 52100 Steel
- 2013
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hard turning is a machining process applied to metallic materials with hardness above 45 HRC. The process offers high production flexibility and sustainable manufacturing since it allows performing both rough and finishing machining of complex geometries in one single setup. With respect to surface integrity, hard turning can generate beneficial compressive residual stresses and good surface quality with small dimensional variation. However, deterioration of the cutting tool generates tensile residual stresses and also alters the surface microstructure, i.e. leads to formation of white layers. Since the mechanisms for white layer formation are not yet fully understood, there is limited understanding of whether there exists different types of white layers possessing different mechanical properties. Therefore, additional processing steps are often added to remove the white layers and to generate compressive residual stresses. By hard turning at different cutting speeds, 30 m/min to 260 m/min, and different tool conditions, it was possible to generate surface integrities with and without white layers on AISI 52100 steel. After hard turning with fresh cutting tools, only discontinuous and thin white layers were detected, while in case of turning with cutting tools with excessive flank wear, white layers up to 3 μm in thickness were observed. White layers formed at 30 m/min are characterized by reduced retained austenite content, deformed M3C carbides and compressive or low tensile residual stresses. In contrast, when white layers created at higher cutting speeds e.g. 260 m/min, significantly increased retained austenite contents, un-affected M3C carbides and high tensile residual stresses were measured. Temperature measurements with a novel two-color pyrometer at the cutting edge revealed large differences in cutting temperature for the studied cutting conditions, i.e. cutting temperatures higher than 900°C were measured at a cutting speed of 260 m/min, while during machining at 30 m/min, temperatures of about 550°C were measured. Microstructural characterization by use of transmission electron microscopy showed that the white layers consist of nanocrystalline and sub-microsrystalline grains ranging from 10 to 200 nm in diameter. The results show that there are different types of white layers, which are predominantly thermally or mechanically induced. Hence, depending on the formation mechanisms, different mechanical properties can be obtained.
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| 11. |
- Hosseini, Seyed, 1981, et al.
(författare)
-
Cutting temperatures during hard turning : Measurements and effects on white layer formation in AISI 52100
- 2014
-
Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 214:6, s. 1293-1300
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Tidskriftsartikel (refereegranskat)abstract
- This paper concerns the temperature evolution during white layer formation induced by hard turning of martensitic and bainitic hardened AISI 52100 steel, as well as the effects of cutting temperatures and surface cooling rates on the microstructure and properties of the induced white layers. The cutting temperatures were measured using a high speed two-colour pyrometer, equipped with an optical fibre allowing for temperature measurements at the cutting edge. Depending on the machining conditions, white layers were shown to have formed both above and well below the parent austenitic transformation temperature, Ac1, of about 750 C. Thus at least two different mechanisms, phase transformation above the Ac1 (thermally) and severe plastic deformation below the Ac1 (mechanically), have been active during white layer formation. In the case of the predominantly thermally induced white layers, the cutting temperatures were above 900 C, while for the predominantly mechanically induced white layers the cutting temperatures were approximately 550 C. The surface cooling rates during hard turning were shown to be as high as 104-105 C/s for cutting speeds between 30 and 260 m/min independent of whether the studied microstructure was martensitic or bainitic. Adding the results from the cutting temperature measurements to previous results on the retained austenite contents and residual stresses of the white layers, it can be summarised that thermally induced white layers contain significantly higher amounts of retained austenite compared to the unaffected material and display high tensile residual stresses. On the contrary, in the case of white layers formed mainly due to severe plastic deformation, no retained austenite could be measured and the surface and subsurface residual stresses were compressive. © 2014 Elsevier B.V.
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| 12. |
- Hosseini, Seyed, 1981, et al.
(författare)
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Determination of Stresses and Retained Austenite in Carbon Steels by X-rays - A Round Robin Study
- 2011
-
Ingår i: Experimental Mechanics. - : Springer Science and Business Media LLC. - 1741-2765 .- 0014-4851. ; 51:1, s. 59-69
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Tidskriftsartikel (refereegranskat)abstract
- Residual stresses and retained austenite are twoimportant process-related parameters which need to becontrolled and monitored carefully during production andheat treatment of products. X-ray diffraction techniques arenormally used in this context, and the purpose of thepresent study was to investigate the reproducibility andaccuracy of these methods for medium and high carbonsteels. The work was carried out as a round robin studyincluding nine different laboratories in Sweden and Finland.Stress measurements were carried out on three specimens etched to three different depths, 0 μm, 230 μm and 515 μm. Retained austenite measurements were carried out on three specimens containing approximately 11, 17 and 30 vol.-% of this phase. The stress measurements showed good reproducibility with standard deviations of typically 4% on flat and smooth surfaces and not more than about 8% on etched surfaces. Estimations revealed that specimen misalignment and improper X-ray spot location were the main sources behind the variation in the stress recordings. The determination of retained austenite showed a standard deviation of typically 15% between the different contributors. However, by using identical evaluation methodsfor all raw data, the data spread could be narrowed by afactor of 3 to 4 despite the fact that different experimental settings were used in the individual laboratories.
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| 13. |
- Hosseini, Seyed, 1981, et al.
(författare)
-
Dissolution of iron-chromium carbides during white layer formation induced by hard turning of AISI 52100 steel
- 2014
-
Ingår i: Procedia CIRP. - : Elsevier BV. - 2212-8271. ; 14, s. 107-112
-
Konferensbidrag (refereegranskat)abstract
- The (Fe, Cr)3C carbide morphology in the surface region of hard turned bainitic AISI 52100 steel was investigated using both experimental techniques and simulations, where microstructural analysis was correlated with analytical studies of the carbide dissolution kinetics using DICTRA1. The experimental results showed that for both predominantly thermally and mechanically induced white layers no significant carbide dissolution took place down to a depth of 20 μm below the machined surfaces. This was confirmed by the analytical results from DICTRA, which showed that no significant carbide dissolution should take place during hard turning given the short contact times. Within the hard turned surfaces up to ∼12% of the carbides were elongated, indicating plastic deformation of the carbides during machining.
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| 14. |
- Hosseini, Seyed M., et al.
(författare)
-
Effect of freestream turbulence on roughness-induced crossflow instability
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The effect of freestream turbulence on generation of crossflow disturbances over swept wings is investigated through direct numerical simulations. The set up follows the experiments performed by Downs et al. in their TAMU experi- ment. In this experiment the authors use ASU(67)-0315 wing geometry which promotes growth of crossflow disturbances. Distributed roughness elements are locally placed near the leading edge with a span-wise wavenumber, to ex- cite the corresponding crossflow vortices. The response of boundary layer to external disturbances such as roughness heights, span-wise wavenumbers, Rey- nolds numbers and freestream turbulence characteristics are studied. It must be noted that the experiments were conducted at a very low level of freestream turbulence intensity (T u). In this study, we fully reproduce the freestream isotropic homogenous turbulence through a DNS code using detailed freestream spectrum data provided by the experiment. The generated freestream fields are then applied as the inflow boundary condition for direct numerical simulation of the wing. The geometrical set up is the same as the experiment along with application of distributed roughness elements near the leading edge to precipi- tate stationary crossflow disturbances. The effects of the generated freestream turbulence are then studied on the initial amplitudes and growth of the bound- ary layer perturbations. It appears that the freestream turbulence damps out the dominant stationary crossflow vortices.
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| 15. |
- Hosseini, Seyed Mohammad, et al.
(författare)
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Effect of Scaling of Blade Row Sectors on the Prediction of Aerodynamic Forcing in a Highly-Loaded Transonic Turbine Stage
- 2012
-
Ingår i: Proceedings of the ASME Turbo Expo 2011, Vol 6, Parts A And B. - New York : American Society of Mechanical Engineers. - 9780791854662 ; , s. 1297-1307
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Konferensbidrag (refereegranskat)abstract
- The viability of a scaling technique in prediction of forced response of the stator and rotor blades in a turbine stage has been examined. Accordingly the so called parameter, generalized force, is defined which describes the excitation of a modeshape due to the unsteady flow forces at a certain frequency. The capability of this method to accurately predict the generalized forces serves as the viability criterion. The scaling technique modifies the geometry to obtain an integer stator, rotor blade count ratio in an annulus section while maintaining steady aerodynamic similarity. A non-scaled configuration is set up to serve as the reference case. Further configurations with different scaling ratios are also generated for accuracy comparison. Unsteady forces are calculated through 3D Navier-Stokes simulations by VolSol, which is based on an explicit, time-marching. A general purpose finite element model of blades is also provided to enable modal analysis with the harmonic forces. The generalized forces of stator and rotor blades revealed high sensitivity towards modification of stator blades while acceptable accuracy was obtained by moderate modifications of the rotor blades for first harmonic forces. Moreover the influence of variable blade's structural characteristics proved to be remarkable.
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| 16. |
- Hosseini, Seyed Mohammad, 1985-
(författare)
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Stability and transition of three-dimensional boundary layers
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A focus has been put on the stability characteristics of different flow types existing on air vehicles. Flow passing over wings and different junctions on an aircraft face numerous local features, ranging from different pressure gradients, to interacting boundary layers. Primarily, stability characteristics of flow over a wing subject to negative pressure gradient is studied. The current numerical study conforms to an experimental study conducted by Saric and coworkers, in their Arizona State University wind tunnel experiments. Within that framework, a passive control mechanism has been tested to delay transition of flow from laminar to turbulence. The same control approach has been studied here, in addition to underling mechanisms playing major roles in flow transition, such as nonlinear effects and secondary instabilities.Another common three-dimensional flow feature arises as a result of streamlines passing through a junction, the so called corner-flow. For instance, this flow can be formed in the junction between the wing and fuselage on a plane. A series of direct numerical simulations using linear Navier-Stokes equations have been performed to determine the optimal initial perturbation. Optimal refers to a perturbation which can gain the maximum energy from the flow over a period of time. Power iterations between direct and adjoint Navier- Stokes equations determine the optimal initial perturbation. In other words this method seeks to determine the worst case scenario in terms of perturbation growth. Determining the optimal initial condition can help improve the design of such surfaces in addition to possible control mechanisms.
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| 17. |
- Hosseini, Seyed M., et al.
(författare)
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Stabilization of a swept-wing boundary layer by distributed roughness elements
- 2013
-
Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press (CUP). - 0022-1120 .- 1469-7645. ; 718, s. R1-
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Tidskriftsartikel (refereegranskat)abstract
- The stabilization of a swept-wing boundary layer by distributed surface roughness elements is studied by performing direct numerical simulations. The configuration resembles experiments studied by Saric and coworkers at Arizona State University, who employed this control method in order to delay transition. An array of cylindrical roughness elements are placed near the leading edge to excite subcritical cross-flow modes. Subcritical refers to the modes that are not critical with respect to transition. Their amplification to nonlinear amplitudes modifies the base flow such that the most unstable cross-flow mode and secondary instabilities are damped, resulting in downstream shift of the transition location. The experiments by Saric and coworkers were performed at low levels of free stream turbulence, and the boundary layer was therefore dominated by stationary cross-flow disturbances. Here, we consider a more complex disturbance field, which comprises both steady and unsteady instabilities of similar amplitudes. It is demonstrated that the control is robust with respect to complex disturbance fields as transition is shifted from 45 to 65% chord.
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| 18. |
- Hosseini, Seyed Mohammad, et al.
(författare)
-
Study of Flame Dynamics and Flashback Mechanism in a Gas Turbine Combustor Using Simultaneous OH-PLIF and PIV
- 2010
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Ingår i: AIAA 2010-6668. - Reston, Virigina : American Institute of Aeronautics and Astronautics.
-
Konferensbidrag (refereegranskat)abstract
- The present study aims to investigate the effects of burner geometry on flame characteristics, stabilization, and the occurrence of flashback using the Triple Annular Research Swirler (TARS). A premixing tube is placed at the exit of the burner. Simultaneous Planar Laser Induced Fluorescence (PLIF) of OH radicals indicating the reacting zone and Particle Image Velocimetry (PIV) for flow field mapping, were applied to study the flow- and flame-dynamics during transition from flame stabilized in the combustion chamber to flame flashback in the mixing tube. Particular attention was placed on the flame behavior/dynamics near the lean blow out (LBO). The flow field featured a central recirculation zone (CRZ), and an annular swirling jet with internal and external shears layers. The movement of the flame front relative to the upstream stagnation point of the vortex breakdown at different conditions was studied. Simultaneous planar measurements using laser diagnostics, namely, Planar Laser Induced Fluorescence (PLIF) of OH radicals and Particle Image Velocimetry (PIV), have been carried out. With mixing tube and at lean cases, vortex breakdown and the flame holding occurred close to the tube exit. As the equivalence ratio was increased, the flame entered intermittently into the premixing tube. Increasing further the equivalence ratio, the flame was stabilized inside the premixing tube. Different statistical evaluations were performed on the data to obtain better understanding of the flame stabilization mechanism. They included PDF of the axial velocity, mean velocity field and mean intensity of the OH radical, two-dimensional correlation between PIV and LIF data, POD analysis of the velocity vectors, distribution of OH radical intensity and binary images of density distribution of the seeding particles.
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| 19. |
- Hosseini, Seyed, 1981, et al.
(författare)
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Microstructure characterization of white layer formed by hard turning and wire electric discharge machining in high carbon steel (AISI 52100)
- 2012
-
Ingår i: Advanced Materials Research. - 1662-8985 .- 1022-6680. ; 409, s. 684-689
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Konferensbidrag (refereegranskat)abstract
- White layers, formed during hard turning and wire electric discharge machining, werecharacterized by means of X-ray diffraction, scanning electron microscopy and transmissionelectron microscopy. Different cutting speeds and flank wear were utilized in order to obtaindifferent thermally and/or plastically deformed white layer. Since the white layer after wire electricdischarge machining is mainly thermally induced, it was used as a reference structure. In theinvestigation, both bainitic and martensitic structures were studied. With a constant flank wear of0.175 mm the thickness of the white layer increased from 1.5 μm to 3 μm as the cutting speed wasincreased. In both processes the white layer were characterized by nano-sized grains and surfacetensile residual stresses. M3C carbides were observed in the hard turned white layer, indicating thatthe time and temperature needed for completely dissolving the carbides were not reached duringcutting. For both materials the white layers formed by wire electric discharge machining consistedof ~ 30 vol. % of retained austenite. Observation regarding the volume fraction of the retainedaustenite in the white layer formed by hard turning for martensitic material showed an increase inthe volume fraction of retained austenite from ~ 2 - 3 vol. % to ~ 6 vol. %, while this observationwas not seen in the white layer formed in the bainitic material.
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| 20. |
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| 21. |
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| 22. |
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| 23. |
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| 24. |
- Iudiciani, Piero, et al.
(författare)
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Proper Orthogonal Decomposition for experimental investigation of swirling flame instabilities
- 2010
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Ingår i: Paper AIAA 2010-584. - Reston, Virigina : American Institute of Aeronautics and Astronautics.
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Konferensbidrag (refereegranskat)abstract
- An experimental investigation of both confined and unconfined flames on a Triple Annular Research Swirler (TARS) is presented. The paper focuses on post-processing techniques aiming at extracting information on the dynamics that are lost through classical statistics approach. POD together with a derived a-posteriori phase averaging procedure successfully reconstructed the dynamics of flames under thermo-acoustic instabilities in the confined case. For unconfined flames, an analysis of the azimuthal modes is performed.
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| 25. |
- Lundin, Per, 1971, et al.
(författare)
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A study of the surface integrity after machining by means of non-destructive testing methods
- 2013
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Ingår i: Proceedings of the International Conference on Advanced Manufacturing Engineering and Technologies Vol. 2. - Stockholm. - 9789175018935 ; , s. 283-292
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Konferensbidrag (refereegranskat)abstract
- During metal machining, depending on the cutting conditions, surface and subsurface microstructure alteration are occasionally observed. These alternations are normally referred as “white” and “dark” layers. Due to their different mechanical properties in comparison to the unaffected material, they will have an impact on the finished part. Controlling the quality of the machined parts regarding the surface microstructure alteration by means of non-destructive testing (NDT) methods would be beneficial from production point of view. In this study, the surface integrity of AISI 52100 steel machined at different cutting conditions resulting in white and dark layers with different characteristics were studied. Surface topography, microstructure and residual stresses were examined by using light scattering, optical microscopy and x-ray diffraction (XRD) techniques. Whilst surface characterization was emphasized, one NDT method – magnetic Barkhausen noise (BN) technique – is not well defined for this purpose. The correlation between all the applied techniques was therefore investigated and a preliminary model was developed for the influence of surface roughness, stress conditions and white and dark layer thicknesses on BN signal.
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| 26. |
- Schmidt, Oliver T., et al.
(författare)
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Optimal initial perturbations in streamwise corner-flow
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Localised optimal initial perturbations are studied to gain an understanding of the global stability properties of streamwise corner-flow. A self-similar and a modified base-flow are considered. The latter mimics a characteristic deviation from the self-similar solution, commonly observed in experiment. Poweriterations in terms of subsequent direct and adjoint linearised Navier-Stokes solution sweeps are employed to converge optimal solutions for two optimisation times. The optimal response manifests as a wave packet that initially gains energy through the Orr mechanism and continues growing exponentially thereafter. The study at hand represents the first global stability analysis of streamwise corner-flow and confirms key observations made in theoretical and/or experimental work on the subject. Namely, the presence of an inviscid instability mechanism in the near-corner region and a destabilising effect of the characteristic mean-flow deformation found in experiment.
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| 27. |
|
|
| 28. |
|
|
