PURPOSE: To evaluate corneal higher-order aberrations induced by overnight or thokeratology for myopia. DESIGN: Prospective, noncomparative, consecutive, inte rventional case series. METHODS: A prospective study was c...PURPOSE: To evaluate corneal higher-order aberrations induced by overnight or thokeratology for myopia. DESIGN: Prospective, noncomparative, consecutive, inte rventional case series. METHODS: A prospective study was conducted in 64 eyes of 39 patients with overnight orthokeratology for myopia, who were followed up for at least 3 months and attained uncorrected visual acuity of 20/20 or better. Co rneal height data were obtained with computerized videokeratography (TMS-2N, To mey), and wavefront aberration was derived using Zernike polynomials. Higher-or der aberrations of the cornea were calculated for 3-and 6-mm pupils. RESULTS: Orthokeratology significantly reduced manifest refraction from -2.60 ±1.13 (me an ±SD) diopters to-0.17 ±0.31 diopters (P< .0001, paired ttest). Root-mean -square (RMS) of third-order (coma-like) aberrations significantly increased by orthokeratology for both 3-mm (P< .0001, paired t test) and 6 mm (P < .0001) pupils. Fourth-order RMS (spherical-like) aberrations increased significantly by the treatment for both 3 mm (P< .0001) and 6-mm (P < .0001) pupils. Vertica l coma significantly changed from positive to negative for both 3-mm (P=.0323) and 6 mm (P< .0001) pupils. Horizontal coma significantly increased to the posit ive direction for both 3-mm (P< .0001) and 6 mm (P< .0001) pupils . Increases i n the third-and fourth-order RMS showed significant positive correlations with the amount of myopic correction for 3 mm (Pearson correlation coefficient, r= .452, P=.0001 for third-order RMS, r=.381, P=.0017 for fourth-order RMS) and 6 mm (r=.499, P< .0001, r=.455, P=.0001) pupils .CONCLUSIONS: Corneal higher-o rder aberrations significantly increased, even in clinically successful orthoker atology cases. The increases in the higher-order aberrations correlated with th e magnitude of myopic correction.展开更多
To clarify the influences of the tip clearance flows on the unsteady cavitating flow, the three-dimensional unsteady cavitating flows through both the two-dimensional cascades and the three-dimensional inducer with an...To clarify the influences of the tip clearance flows on the unsteady cavitating flow, the three-dimensional unsteady cavitating flows through both the two-dimensional cascades and the three-dimensional inducer with and without tip clearance are performed numerically. The governing equations for the compressible fluid flow with the DES turbulence model are employed with the assumption of the isentropic process of liquid phase. The evolution of cavities is represented as the source/sink of vapor phase. The basic equations in the curve linear coordinate are solved by the finite difference method. As the results of the three-dimensional cavitating flows through the two-dimensional cascades, the tip clearance flows from the pressure side to the suction side of the blade produces the tip vortex cavitation, which affects the sheet cavitation on the leading edge of the next blade and enhances the blockage effect near the casing than the flows without tip clearance. On the other hand, in the case of the three-dimensional inducer, the large backflow cavitation is observed around the inlet of the inducer, where the cavities are developed on the casing by the tip clearance flows. The large pressure gradient between the non-cavitating pressure side and the cavitating suction side enhances the tip clearance flows. The calculation considering the tip clearance reproduces the developed cavitation region similar to that of experimental visualizations. Additionally, the backflow cavitation rotates with the speed slower than the rotation speed of the inducer. Then, the rotation of backflow cavitation causes the periodic fluctuation of the outlet pressure greater than that of the inlet pressure.展开更多
In the present research, a bubble dynamics based model for cavitating flow simulations is extended to higher void fraction region for wider range of applications. The present bubble model is based on the so-called Ray...In the present research, a bubble dynamics based model for cavitating flow simulations is extended to higher void fraction region for wider range of applications. The present bubble model is based on the so-called Rayleigh-Plesset equation that calculates a temporal bubble radius with the surrounding liquid pressure and is considered to be valid in an area below a certain void fraction. The solution algorithm is modified so that the Rayleigh-Plesset equation is no more solved once the bubble radius （or void fraction） reaches at a certain value till the liquid pressure recovers above the vapor pressure in order to overcome this problem. This procedure is expected to stabilize the numerical calculation. The results of simple two-dimensional flow field are presented compared with the existing bubble model.展开更多
文摘PURPOSE: To evaluate corneal higher-order aberrations induced by overnight or thokeratology for myopia. DESIGN: Prospective, noncomparative, consecutive, inte rventional case series. METHODS: A prospective study was conducted in 64 eyes of 39 patients with overnight orthokeratology for myopia, who were followed up for at least 3 months and attained uncorrected visual acuity of 20/20 or better. Co rneal height data were obtained with computerized videokeratography (TMS-2N, To mey), and wavefront aberration was derived using Zernike polynomials. Higher-or der aberrations of the cornea were calculated for 3-and 6-mm pupils. RESULTS: Orthokeratology significantly reduced manifest refraction from -2.60 ±1.13 (me an ±SD) diopters to-0.17 ±0.31 diopters (P< .0001, paired ttest). Root-mean -square (RMS) of third-order (coma-like) aberrations significantly increased by orthokeratology for both 3-mm (P< .0001, paired t test) and 6 mm (P < .0001) pupils. Fourth-order RMS (spherical-like) aberrations increased significantly by the treatment for both 3 mm (P< .0001) and 6-mm (P < .0001) pupils. Vertica l coma significantly changed from positive to negative for both 3-mm (P=.0323) and 6 mm (P< .0001) pupils. Horizontal coma significantly increased to the posit ive direction for both 3-mm (P< .0001) and 6 mm (P< .0001) pupils . Increases i n the third-and fourth-order RMS showed significant positive correlations with the amount of myopic correction for 3 mm (Pearson correlation coefficient, r= .452, P=.0001 for third-order RMS, r=.381, P=.0017 for fourth-order RMS) and 6 mm (r=.499, P< .0001, r=.455, P=.0001) pupils .CONCLUSIONS: Corneal higher-o rder aberrations significantly increased, even in clinically successful orthoker atology cases. The increases in the higher-order aberrations correlated with th e magnitude of myopic correction.
文摘To clarify the influences of the tip clearance flows on the unsteady cavitating flow, the three-dimensional unsteady cavitating flows through both the two-dimensional cascades and the three-dimensional inducer with and without tip clearance are performed numerically. The governing equations for the compressible fluid flow with the DES turbulence model are employed with the assumption of the isentropic process of liquid phase. The evolution of cavities is represented as the source/sink of vapor phase. The basic equations in the curve linear coordinate are solved by the finite difference method. As the results of the three-dimensional cavitating flows through the two-dimensional cascades, the tip clearance flows from the pressure side to the suction side of the blade produces the tip vortex cavitation, which affects the sheet cavitation on the leading edge of the next blade and enhances the blockage effect near the casing than the flows without tip clearance. On the other hand, in the case of the three-dimensional inducer, the large backflow cavitation is observed around the inlet of the inducer, where the cavities are developed on the casing by the tip clearance flows. The large pressure gradient between the non-cavitating pressure side and the cavitating suction side enhances the tip clearance flows. The calculation considering the tip clearance reproduces the developed cavitation region similar to that of experimental visualizations. Additionally, the backflow cavitation rotates with the speed slower than the rotation speed of the inducer. Then, the rotation of backflow cavitation causes the periodic fluctuation of the outlet pressure greater than that of the inlet pressure.
文摘In the present research, a bubble dynamics based model for cavitating flow simulations is extended to higher void fraction region for wider range of applications. The present bubble model is based on the so-called Rayleigh-Plesset equation that calculates a temporal bubble radius with the surrounding liquid pressure and is considered to be valid in an area below a certain void fraction. The solution algorithm is modified so that the Rayleigh-Plesset equation is no more solved once the bubble radius （or void fraction） reaches at a certain value till the liquid pressure recovers above the vapor pressure in order to overcome this problem. This procedure is expected to stabilize the numerical calculation. The results of simple two-dimensional flow field are presented compared with the existing bubble model.
