The Experts below are selected from a list of 23220 Experts worldwide ranked by ideXlab platform
Dimitriadis Grigorios - One of the best experts on this subject based on the ideXlab platform.
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The impact of Circularity defects on bridge stay cable dry galloping stability
'Elsevier BV', 2018Co-Authors: Benidir Adel, Flamand Olivier, Dimitriadis GrigoriosAbstract:peer reviewedaudience: researcher, professionalThe present work studies the influence of Circularity defects, on the aerodynamic behaviour of stay cables of cable-stayed bridges. It focuses on wind tunnel tests on High-Density Polyethylene cable covers with and without helical fillets, in a range of Reynolds numbers from the sub-critical to the critical regime. The paper considers the impact of Circularity defects on the aerodynamic stability of cable sheaths by testing various amplitudes of imposed ovalization. The defects are artificially applied on real sheaths whose original cross-sections are close to circular. The experiment consists in measuring surface pressures to investigate how the amplitude of ovalization influences the flow around the sheaths, especially in the critical Reynolds number regime when transition in the boundary layer occurs. The analysis is based on bifurcation diagrams and Proper Orthogonal Decomposition. The investigation demonstrates that important Circularity defects can significantly increase the bi-stable nature of the flow around a sheath at the critical regime. Nevertheless, the introduction of a helical fillet de-correlates the flow around the sheath, causing jumps in lift that have different sign along its length
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The impact of Circularity defects on bridge stay cable dry galloping stability
2018Co-Authors: Benidir Adel, Flamand Olivier, Dimitriadis GrigoriosAbstract:The present work studies the influence of Circularity defects, on the aerodynamic behaviour of stay cables of cable-stayed bridges. It focuses on wind tunnel tests on High-Density Polyethylene cable covers with and without helical fillets, in a range of Reynolds numbers from the sub-critical to the critical regime. The paper considers the impact of Circularity defects on the aerodynamic stability of cable sheaths by testing various amplitudes of imposed ovalization. The defects are artificially applied on real sheaths whose original cross-sections are close to circular. The experiment consists in measuring surface pressures to investigate how the amplitude of ovalization influences the flow around the sheaths, especially in the critical Reynolds number regime when transition in the boundary layer occurs. The analysis is based on bifurcation diagrams and Proper Orthogonal Decomposition. The investigation demonstrates that important Circularity defects can significantly increase the bi-stable nature of the flow around a sheath at the critical regime. Nevertheless, the introduction of a helical fillet de-correlates the flow around the sheath, causing jumps in lift that have different sign along its length.Peer reviewe
Norbert Willenbacher - One of the best experts on this subject based on the ideXlab platform.
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coke slurries with improved higher heating value and good processability via particle shape design
Chemical Engineering & Technology, 2017Co-Authors: L Jampolski, T Jakobs, T Kolb, Norbert WillenbacherAbstract:Coke-water slurries can be used as biogenic intermediates in conversion of residual biomass into high value fuels such as liquefied petroleum gas or synthetic natural gas. The effect of particle size and shape on the flow behavior of slurries including coke particles obtained from fast pyrolysis was investigated. Particles were shaped in a planetary ball mill and equivalent sphere diameter and Circularity were used to characterize size and shape. An increased Circularity resulted in a strong decrease in slurry viscosity. Accordingly, a higher mass fraction of particles can be mixed into the slurry, thus, increasing the higher heating value while still preserving good processing properties.
Ignacio Velezpareja - One of the best experts on this subject based on the ideXlab platform.
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analytical solution to the Circularity problem in the discounted cash flow valuation framework
2010Co-Authors: Felipe Mejiapelaez, Ignacio VelezparejaAbstract:In this paper we propose an analytical solution to the Circularity problem between value and cost of capital. Our solution is derived starting from a central principle of finance that relates value today to value, cash flow, and the discount rate for next period. We derive a general formulation for the equity value, E, for the cost of unlevered equity, firm value and the weighted average cost of capital, WACC, without Circularity. We furthermore compare the results obtained using these formulas with the results using the Adjusted Present Value approach (no Circularity) and the iterative solution of Circularity based upon the iteration feature of a spreadsheet. We conclude that all methods produce the same answer.
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analytical solution to the Circularity problem in the discounted cash flow valuation framework
2010Co-Authors: Felipe Mejia, Ignacio VelezparejaAbstract:Since the Modigliani and Miller 1958 seminal paper, there has been a problem posed by the fact that the discount rate to value cash flows depends on the value of thesecash flows. This gives raise to the Circularity problem.In this paper we propose an analytical solution to this Circularity problem. Our solution is derived starting from a central principle of finance which states that value today is equal to value of next period plus cash flow of next period, discounted with the discount rate of next period. We derive a general formulation for the equity value, E, at a given period and propose a general formula that depends on the value of equity and cash flow to equity for next period, the values of debt and tax savings, TS, at actual period, the discount rate for the TS in the next period, , the cost of debt, Kd, and the unlevered cost of equity, Ku. We then present this formula for two special cases: one for equal to Kd and another for equal to Ku. From the expression for E we derive the formulation with no Circularity for total value that depends on free cash flow, FCF, and TS. We also derive the weighted average cost of capital, WACC, without Circularity. However, we acknowledge that this formulation is less intuitive than the traditional textbook WACC formulation. We furthermore compare the results obtained using these formulas with the resultsusing the Adjusted Present Value approach (no Circularity) and the iterative solution of Circularity based upon the iteration feature of a spreadsheet. Our conclusion is that, as expected, all methods produce the same answer and the analyst should use the simplest method available, which means using the Adjusted PresentValue, APV, with the appropriate discount rate for the TS. When this discount rate is equal to Ku, the cost of unlevered equity, the APV method results in the capital cash flow, CCF, approach.
Mehrdad Ghoreishi - One of the best experts on this subject based on the ideXlab platform.
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statistical analysis of repeatability in laser percussion drilling
The International Journal of Advanced Manufacturing Technology, 2006Co-Authors: Mehrdad GhoreishiAbstract:This study investigates the effect of six parameters in the repeatability of drilled holes in laser percussion drilling process by means of statistical techniques. Peak power, pulse width, pulse frequency, number of pulses, gas pressure and focal plane position were considered as independent process parameters. Experiments were designed with the aim of reducing the number of required experiments. The response surface method was used to develop the models for required responses. The significant factors in the process were selected based on the analysis of the variance (ANOVA). The experiments were conducted in mild steel sheet with a thickness of 2 mm. Each experiment was repeated 35 times in order to investigate the repeatability of the process. The equivalent entrance diameter, percentage of standard deviation of entrance diameter (%STD Eq Dia), Circularity (ratio of minimum to maximum Feret’s diameter) and its standard deviation (STD Circularity) were selected as process characteristics. The %STD Eq Dia and STD Circularity, respectively, show the repeatability of equivalent diameter and Circularity in the process.
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comparative statistical analysis of hole taper and Circularity in laser percussion drilling
International Journal of Machine Tools & Manufacture, 2002Co-Authors: Mehrdad Ghoreishi, Lin LiAbstract:Abstract The present study investigates the relationships and parameter interactions between six controllable variables on the hole taper and Circularity in laser percussion drilling. Experiments have been conducted on stainless steel workpieces and a comparison was made between stainless steel and mild steel (IMechE Part B: J. Eng. Manufact. (in press)). Laser peak power, laser pulse width, pulse frequency, number of pulses, assist gas pressure and focal plane position were selected as independent process variables. The central composite design (CCD) was employed to plan the experiments in order to achieve required information with reduced number of experiments. The process performance was evaluated in terms of equivalent entrance diameter, hole taper and hole entrance Circularity. The ratio of minimum to maximum Feret’s diameter was considered as Circularity characteristic of the hole. The models of these three process characteristics were developed by linear multiple regression technique. The initial models were computed according to the least squares procedure and were finalised by stepwise regression method. The significant coefficients were obtained by performing analysis of variance (ANOVA) at 1, 5 and 7% levels of significance. The final models were checked by complete residual analysis and finally were experimentally verified. It was found that the pulse frequency had a significant effect on the hole entrance diameter and hole Circularity in drilling stainless steel unlike the drilling of mild steel where the pulse frequency had no significant effect on the hole characteristics.
Lin Li - One of the best experts on this subject based on the ideXlab platform.
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comparative statistical analysis of hole taper and Circularity in laser percussion drilling
International Journal of Machine Tools & Manufacture, 2002Co-Authors: Mehrdad Ghoreishi, Lin LiAbstract:Abstract The present study investigates the relationships and parameter interactions between six controllable variables on the hole taper and Circularity in laser percussion drilling. Experiments have been conducted on stainless steel workpieces and a comparison was made between stainless steel and mild steel (IMechE Part B: J. Eng. Manufact. (in press)). Laser peak power, laser pulse width, pulse frequency, number of pulses, assist gas pressure and focal plane position were selected as independent process variables. The central composite design (CCD) was employed to plan the experiments in order to achieve required information with reduced number of experiments. The process performance was evaluated in terms of equivalent entrance diameter, hole taper and hole entrance Circularity. The ratio of minimum to maximum Feret’s diameter was considered as Circularity characteristic of the hole. The models of these three process characteristics were developed by linear multiple regression technique. The initial models were computed according to the least squares procedure and were finalised by stepwise regression method. The significant coefficients were obtained by performing analysis of variance (ANOVA) at 1, 5 and 7% levels of significance. The final models were checked by complete residual analysis and finally were experimentally verified. It was found that the pulse frequency had a significant effect on the hole entrance diameter and hole Circularity in drilling stainless steel unlike the drilling of mild steel where the pulse frequency had no significant effect on the hole characteristics.