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In supersonic flight, airfoils generate strong sonic boom and wave drag accompanied by shock waves and expansion waves. The Busemann biplane is representative of an airfoil that has the possibility of realizing low drag. With the aim of realizing a new concept of supersonic transport, aerodynamic design and analysis are discussed based on computational fluid dynamics. Traditional biplane airfoils were extended to three-dimensional wings with a design Mach number of 1.7. Euler simulations of three-dimensional biplane wings of several configurations were conducted. Because of the existence of wing tips, three-dimensional biplane wings do not perform as well as two-dimensional biplane airfoils. This is because the areas affected by Mach cones originated from the wing tips, which precludes the occurrence of an appropriate pressure wave interaction. Thus, the wing tip area has a large drag coefficient. To overcome these problems, a tapered wing is herein considered. After parametric studies, a wing planform was determined, the taper ratio and aspect ratio of which were 0.25 and 5.12, respectively. Aerodynamic design of wing section shapes of the three-dimensional tapered biplane wing was conducted using an inverse-problem method. The designed biplane wing shows a better lift-to-drag ratio performance than the two-dimensional flat-plate airfoil in the range where the lift coefficient is more than 0.17. Tapered wings were also found to have several span sections that achieve better performances than two-dimensional biplane airfoils. DOI: 10.2514/1.40313

Objective: To examine the association between hospital surgical volume of caesarean hysterectomy and surgical morbidity in women with placenta accreta spectrum (PAS). Design: Population‐based retrospective cohort study. Setting: National Inpatient Sample, January 2016 to December 2018. Population: Six thousand and ten women with PAS who underwent caesarean hysterectomy in 738 centres. Methods: (1) Comprehensive modelling for relative hospital surgical volume cut‐point selection, (2) multinomial regression analysis for characterising hospital surgical volume, and (3) binary logistic regression analysis to examine the volume–outcome relationship. Main outcome measures: Surgical morbidity (haemorrhage, coagulopathy, shock, urinary tract injury, and death). Results: The majority of centres had five surgeries over the 3‐year period (468 centres, 63.4%) and were grouped as the low‐volume group. Surgical morbidity decreased after a relative hospital surgical volume of 25 cases (24 centres, 3.3%) was reached, grouped as the high‐volume group. The remaining centres were grouped as the mid‐volume group (246 centres, 33.3%). In multivariable analysis, women in the high‐volume group were more likely to be Black, have lower median household income, medical comorbidity, previous caesarean delivery, placenta praevia or placenta percreta, and to have undergone surgeries at large urban teaching hospitals compared with those in the low‐volume group (all, P < 0.05). After controlling for patient demographics, hospital characteristics and pregnancy factors, performance of caesarean hysterectomy at high‐volume centres was associated with a 22% decreased risk of surgical complications compared with surgery at the low‐volume centres (adjusted odds ratio 0.78, 95% CI 0.64–0.94). Conclusion: Caesarean hysterectomy for PAS is a rare surgical procedure. Higher hospital surgical volume may be associated with improved surgical outcome in PAS. Higher hospital caesarean hysterectomy volume may be associated with improved surgical outcome in PAS. Higher hospital caesarean hysterectomy volume may be associated with improved surgical outcome in PAS. [ABSTRACT FROM AUTHOR]