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The fully tailless configuration has lower observability, less structural weight and less drag, and it is considered one of the preferred designs for the next generation of efficient supersonic combat aircraft. In the conceptual design of such novel aircraft, a parametric geometry model is essential for multidisciplinary design analysis and optimization (MDAO). This paper presents a parametric three-dimensional (3D) geometry modeling methodology and tool for MDAO in the conceptual design of a notional supersonic tailless combat aircraft (STCA). The geometries of the STCA components (wing, fuselage and propulsion) are defined specifically by a set of parameters. In particular, the inlet and nozzle geometries are defined with the required details. Based on the geometric relationships among the STCA components, an approach involving master-dependent parameters is proposed. The geometry model generated by the approach has features such as the fuselage being blended smoothly with the wing and the propulsion being well integrated with the fuselage. Moreover, the geometry model can be generated by simply specifying the values of the master parameters, and the number of parameters required to generate the geometry model is reduced substantially. Based on the methodology, a parametric geometry modeling tool for the STCA conceptual design is developed using a Visual Basic (VB) script in the CATIA V5 platform. The applicability of the tool is validated with several case studies.

The vertical-takeoff–horizontal-landing (VTHL) two-stage-to-orbit (TSTO) system is a kind of novel launch vehicle in which a reusable first stage can take off vertically like a rocket and land horizontally like an airplane. The advantage of the VTHL TSTO vehicle is that the launch costs can be reduced significantly due to its reusable first stage. This paper presents an application of multidisciplinary analysis optimization on preliminary sizing in conceptual design of the VTHL TSTO vehicle. The VTHL TSTO concept is evaluated by multidisciplinary analysis, including geometry, propulsion, aerodynamics, mass, trajectory, and static stability. The preliminary sizing of the VTHL TSTO vehicle is formulated as a multidisciplinary optimization problem. The focus of this paper is to investigate the impacts of the first-stage reusability and propellant selection on the staging altitude and velocity, size, and mass of the VTHL TSTO vehicles. The observations from the results show that the velocity and altitude of the optimal staging point are determined mainly by the reusability of the first stage, which in turn affects the size and mass of the upper stage and the first stage. The first stage powered by hydrocarbon fuel has a lower dry mass compared with that powered by liquid hydrogen.

One essential problem in aircraft conceptual design is initial sizing in which the aircraft primary parameters such as weight, size, and thrust are estimated for given design requirements. The airbreathing hypersonic aircraft is a type of novel aircraft and has significant differences from conventional aircraft in terms of its flight speed and propulsion system. Traditional initial sizing methods are not suitable for this type of novel aircraft. This paper presents an improved initial sizing method for the conceptual design of airbreathing hypersonic aircraft. An illustrative airbreathing hypersonic aircraft is used to describe the detailed procedure of the method. The weight and size of the aircraft are estimated through the simultaneous solution of the weight equation and the volume equation. Constraint analysis is applied to determine the solution space of the thrust-to-weight ratio and the wing loading. A thrust trade is conducted to find the minimum takeoff gross weight of the aircraft. The impacts of technology parameters on the weight, size, and thrust are investigated by sensitivity analyses. The presented method is based on rational derivation. It can be expected that the initial sizing results from the method are reasonable and satisfactory for conceptual design of the airbreathing hypersonic aircraft.

A special feature of airbreathing hypersonic aircraft is the complex coupling between aerodynamic and propulsive performances. This study presents a rapid analysis methodology for the integration of these two critical aspects in the conceptual design of airbreathing hypersonic aircraft. Parametric modeling is used to generate a three-dimensional geometric model of an aircraft. The integrated aerodynamic and propulsive analysis is performed using a loosely coupled method. The aerodynamic analysis uses Euler equations to solve the inviscid aerodynamic forces, while the viscous forces are estimated using semi-empirical engineering methods. The propulsion system is modeled using hybrid one- and three-dimensional approaches. The inlet aerodynamic performance is simulated using three-dimensional simulation based on the Euler equations. The ramjet performance is estimated using a quasi-one-dimensional mathematical model. Nozzle simulation is performed using a one-dimensional plume method. The entire computational process is integrated and can be run automatically. The usefulness of the method is demonstrated through aerodynamic and propulsive performance evaluations in the conceptual design of a notional airbreathing hypersonic aircraft.

Due to the high density of grain boundaries (GBs), nanocrystalline metals possess superior properties, including enhanced strength, work hardening, and fatigue resistance, in comparison to their conventional counterparts. The expectation of GB migration is critical for grain coarsening and GB annihilation in these materials, significantly affecting the polycrystalline network and mechanical behavior. Here, we perform molecular dynamics (MD) simulations on gold (Au) nanocrystals containing multiple parallelly arranged GBs, with a focus on the investigation of annihilation mechanisms of low-angle grain boundaries (LAGBs). It is observed that the shear-coupled motion of LAGBs, consisting of dislocations, gives rise to their preliminary migration with the reduced separation distance between GBs. With subsequent GB motion, the LAGBs encountered with neighboring GBs, and can be annihilated by various mechanisms, including dislocations interpenetration, dislocations interaction, or dislocations absorption, depending on the specific configuration of the neighboring GB. These findings enhance our understanding of GB interactions and shed light on the controlled fabrication of high-performance nanocrystalline metals.

To investigate more efficient aircraft configurations which have less environmental impact, this paper develops a multidisciplinary analysis framework integrated with the airframe and propulsion analysis modules. The characteristics for propulsion, aerodynamics, weight, performance, cost, emissions, and noise can be rapidly predicted by the framework. The impact of propulsion installation with large diameter engines on aircraft weight and drag are considered in the framework. A wide-body aircraft was taken as an example for the optimization to investigate the tradeoffs between the cost metric and the environmental performance metrics. Several cases for single objective and multiobjective optimizations were performed. In the single objective optimizations, the direct operating cost, the cumulative noise, the oxides of nitrogen emissions during landing-takeoff cycle, and the mission oxides of nitrogen emissions were considered as an objective and minimized, respectively. The different objectives resulted in designs with different airframe parameters and engine cycle parameters. In the multiobjective optimizations, the direct operating costs and environmental performances were considered as the objectives simultaneously. The optimization results were the Pareto fronts for the minimum direct operating costs and environmental performances, which illustrate the quantitative relationships between the economic metric and the environmental performances.

According to simulation lightning experiments and eddy current analysis results, a three-dimensional finite element model of composite laminated plates with shield is established. By applying electric-thermal boundary and the coupling relationship between them, the lightning strike damage results under the protection of shield are realistically simulated with the commercial finite element analysis software, ABAQUS. Considering the coupling effect of heat, electricity, and force during lightning strike, the load distribution field of copper mesh and carbon fiber panel with lightning current inducted is analyzed. Comparing the thermal stress distribution of the specimen surface under various current loads, it is shown that the stress of carbon fiber panel is significantly lower than the one of the copper screen when the specimen structure suffers heavy current, since the copper network plays a role of endergonic protection. Simulation data are consistent with the test results, thus the method can be used for other similar research.

A new reliability-based design optimization (RBDO) method based on support vector machines (SVM) and the Most Probable Point (MPP) is proposed in this work. SVM is used to create a surrogate model of the limit-state function at the MPP with the gradient information in the reliability analysis. This guarantees that the surrogate model not only passes through the MPP but also is tangent to the limit-state function at the MPP. Then, importance sampling (IS) is used to calculate the probability of failure based on the surrogate model. This treatment significantly improves the accuracy of reliability analysis. For RBDO, the Sequential Optimization and Reliability Assessment (SORA) is employed as well, which decouples deterministic optimization from the reliability analysis. The improved SVM-based reliability analysis is used to amend the error from linear approximation for limit-state function in SORA. A mathematical example and a simplified aircraft wing design demonstrate that the improved SVM-based reliability analysis is more accurate than FORM and needs less training points than the Monte Carlo simulation and that the proposed optimization strategy is efficient.

Parts of emission from the aircraft engine are doing harm to the environment. The greenhouse gas emission (CO2 equivalent) per passenger per thousand kilometers is used to measure the emissions in this work. And a new estimation method of emissions for aircraft conceptual design was proposed, based on the ICAO aircraft engine emissions databank and the response surface fitting methods. Because the amounts of greenhouse effects of various pollutant gases rely on altitudes, the estimation accuracy of emission was improved by refining the flight dynamics models in various stages of mission profile. The impacts of the wing configuration on greenhouse effect were discussed, after verifying the accuracy of this proposed method. The results indicate that the greenhouse gas emissions could be reduced by appropriately increasing wing sweep and aspect ratio.

Elderly patients are susceptible to dose-dependent perioperative hypotension caused by propofol. This study investigates whether general anesthesia induction with ciprofol reduces subsequent propofol maintenance requirements and improves hemodynamic stability compared to propofol induction in elderly patients undergoing total knee arthroplasty (TKA). In this prospective, double-blind, randomized controlled trial, 52 elderly participants (≥ 65 years, ASA I-III) undergoing TKA were randomly allocated to receive propofol (2 mg/kg) or ciprofol (0.4 mg/kg) for anesthesia induction. All participants received standardized anesthesia protocol for maintenance. The primary outcome was the average propofol infusion rate. Secondary outcomes included intraoperative norepinephrine utilization, mean arterial pressure (MAP) fluctuations, time to extubation, and postoperative modified Aldrete scores. Data were analyzed using -tests, Wilcoxon rank-sum, or Chi-square/Fisher's exact tests as appropriate. The mean age was 70.62 ± 3.86 years in the ciprofol group and 69.08 ± 3.52 years in the propofol group with balanced sex distribution. During anesthesia maintenance, the ciprofol group required a significantly lower propofol infusion rate than the propofol group (2.70 ± 0.75 mg/kg/h vs. 4.18 ± 1.66 mg/kg/h; mean difference, -1.48 mg/kg/h; [95% confidence interval, -2.19 to -0.77], = 0.009). Additionally, the ciprofol group presented with a lower norepinephrine utilization rate (46.2% vs. 84.6%, = 0.004) and a reduced median norepinephrine infusion rate (0 [interquartile range (IQR), 0-0.05] μg/kg/min vs. 0.05 [IQR, 0.01-0.08] μg/kg/min, = 0.030). Norepinephrine initiation was significantly delayed in the ciprofol group ( = 0.047). No significant differences were observed in MAP variability or postoperative modified Aldrete scores. In relatively healthy elderly patients undergoing total knee arthroplasty, anesthesia induction with ciprofol is associated with reduced propofol maintenance requirements and decreased intraoperative norepinephrine utilization. Ciprofol may represent a promising alternative for anesthesia induction in this population, although further multicenter validation is warranted.