Sediment accumulation on the bed of open sewers and drains reduces hydraulic efficiency and can cause localized flooding.Slotted invert traps installed underneath the bed of open sewers and drains can eliminate sedime...Sediment accumulation on the bed of open sewers and drains reduces hydraulic efficiency and can cause localized flooding.Slotted invert traps installed underneath the bed of open sewers and drains can eliminate sediment build-up by catching sediment load.Previous three-dimensional(3D)computational studies have examined the particle trapping performance of invert traps of different shapes and depths under varied sediment and flow conditions,considering particles as spheres.For two-dimensional and 3D numerical modeling,researchers assumed the lid geometry to be a thin line and a plane,respectively.In this 3D numerical study,the particle trapping efficiency of a slotted irregular hexagonal invert trap fitted at the flume bottom was examined by incorporating the particle shape factor of non-spherical sewage solid particles and the thicknesses of upstream and downstream lids over the trap in the discrete phase model of the ANSYS Fluent 2020 R1 software.The volume of fluid(VOF)and the realizable k-turbulence models were used to predict the velocity field.The two-dimensional particle image velocimetry(PIV)was used to measure the velocity field inside the invert trap.The results showed that the thicknesses of upstream and downstream lids affected the velocity field and turbulent kinetic energy at all flow depths.The joint impact of the particle shape factor and lid thickness on the trap efficiency was significant.When both the lid thickness and particle shape factor were considered in the numerical modeling,trap efficiencies were underestimated,with relative errors of-8.66%to-0.65%in comparison to the experimental values of Mohsin and Kaushal(2017).They were also lower than the values predicted by Mohsin and Kaushal(2017),which showed an overall overestimation with errors of-2.3%to 17.4%.展开更多
Objective To assess the outcome of inverted V-shaped valgus osteotomy as a treatment for congenital coxa vara in children. Methods Between Feb. 1990 and Jan. 2000,27 patients (35 hips) with congenital coxa vara underw...Objective To assess the outcome of inverted V-shaped valgus osteotomy as a treatment for congenital coxa vara in children. Methods Between Feb. 1990 and Jan. 2000,27 patients (35 hips) with congenital coxa vara underwent inverted V-shpaed valgus osteotomy. There were 16 males and 11 females. The average age was 7. 8 years (range:3 to 14 years). They all presented with limp or concomitant pain in the older children. The clinical result was evaluated according to Shi’s criteria. The X-ray films of preoperative, postoperative and the most recent follow-up periods were analyzed. Results Twenty-two patients (28 hips) were followed-up for a mean of 5. 4 years (14 months to 9 years). According to Shi’ s criteria, the excellent and good results accounted for 82. 1 % of cases. The preoperative NS angle, HE angle and ATD value were 94.5° ±9.1° ,67.2° ± 1.8° and - 3.8 mm ± 6. 9 mm respectively whereas those of the immediate postoperative were 148.0° ± 6.5°, 28.6° ± 4.3° and 27.5 mm ± 3. 1 mm; and展开更多
The increasing use of power electronic devices can deteriorate the power quality by introducing voltage and current harmonics.In islanded microgrids,the presence of nonlinear loads can distort the point of common coup...The increasing use of power electronic devices can deteriorate the power quality by introducing voltage and current harmonics.In islanded microgrids,the presence of nonlinear loads can distort the point of common coupling(PCC)voltage,while the dead-time effect can also bring additional circulating current harmonics among parallel inverters.To simultaneously attenuate the PCC voltage harmonics and suppress the dead-time induced circulating current harmonics,this paper proposes a coordinated control strategy for harmonic mitigation of parallel inverters.The proposed control strategy allows inverter impedances to be properly reshaped at selective harmonic frequencies.As a consequence,the PCC voltage harmonics are filtered by the inverter operating in the harmonic compensation mode(HCM),whereas the dead-time induced circulating current harmonics are suppressed by the inverter operating in the harmonic rejection mode(HRM).Experimental results from an islanded microgrid prototype with two parallel inverters are provided to validate the effectiveness of the proposed control strategy.展开更多
文摘Sediment accumulation on the bed of open sewers and drains reduces hydraulic efficiency and can cause localized flooding.Slotted invert traps installed underneath the bed of open sewers and drains can eliminate sediment build-up by catching sediment load.Previous three-dimensional(3D)computational studies have examined the particle trapping performance of invert traps of different shapes and depths under varied sediment and flow conditions,considering particles as spheres.For two-dimensional and 3D numerical modeling,researchers assumed the lid geometry to be a thin line and a plane,respectively.In this 3D numerical study,the particle trapping efficiency of a slotted irregular hexagonal invert trap fitted at the flume bottom was examined by incorporating the particle shape factor of non-spherical sewage solid particles and the thicknesses of upstream and downstream lids over the trap in the discrete phase model of the ANSYS Fluent 2020 R1 software.The volume of fluid(VOF)and the realizable k-turbulence models were used to predict the velocity field.The two-dimensional particle image velocimetry(PIV)was used to measure the velocity field inside the invert trap.The results showed that the thicknesses of upstream and downstream lids affected the velocity field and turbulent kinetic energy at all flow depths.The joint impact of the particle shape factor and lid thickness on the trap efficiency was significant.When both the lid thickness and particle shape factor were considered in the numerical modeling,trap efficiencies were underestimated,with relative errors of-8.66%to-0.65%in comparison to the experimental values of Mohsin and Kaushal(2017).They were also lower than the values predicted by Mohsin and Kaushal(2017),which showed an overall overestimation with errors of-2.3%to 17.4%.
文摘Objective To assess the outcome of inverted V-shaped valgus osteotomy as a treatment for congenital coxa vara in children. Methods Between Feb. 1990 and Jan. 2000,27 patients (35 hips) with congenital coxa vara underwent inverted V-shpaed valgus osteotomy. There were 16 males and 11 females. The average age was 7. 8 years (range:3 to 14 years). They all presented with limp or concomitant pain in the older children. The clinical result was evaluated according to Shi’s criteria. The X-ray films of preoperative, postoperative and the most recent follow-up periods were analyzed. Results Twenty-two patients (28 hips) were followed-up for a mean of 5. 4 years (14 months to 9 years). According to Shi’ s criteria, the excellent and good results accounted for 82. 1 % of cases. The preoperative NS angle, HE angle and ATD value were 94.5° ±9.1° ,67.2° ± 1.8° and - 3.8 mm ± 6. 9 mm respectively whereas those of the immediate postoperative were 148.0° ± 6.5°, 28.6° ± 4.3° and 27.5 mm ± 3. 1 mm; and
基金This research was supported by the National Research Foundation,Prime Minister’s Office,Singapore under the Energy Programme and administrated by the Energy Market Authority(EP Award No.NRF2015EWT-EIRP002-007)。
文摘The increasing use of power electronic devices can deteriorate the power quality by introducing voltage and current harmonics.In islanded microgrids,the presence of nonlinear loads can distort the point of common coupling(PCC)voltage,while the dead-time effect can also bring additional circulating current harmonics among parallel inverters.To simultaneously attenuate the PCC voltage harmonics and suppress the dead-time induced circulating current harmonics,this paper proposes a coordinated control strategy for harmonic mitigation of parallel inverters.The proposed control strategy allows inverter impedances to be properly reshaped at selective harmonic frequencies.As a consequence,the PCC voltage harmonics are filtered by the inverter operating in the harmonic compensation mode(HCM),whereas the dead-time induced circulating current harmonics are suppressed by the inverter operating in the harmonic rejection mode(HRM).Experimental results from an islanded microgrid prototype with two parallel inverters are provided to validate the effectiveness of the proposed control strategy.
