The rapid development of emerging concepts and technologies, e.g., modularity, standardization, and fractionation, has resulted in the miniaturization of satellites and simplification of mission design, as well as a move towards more responsive and economical systems. However, the current customized and labor-intensive design philosophy is not naturally appropriate for enabling the application of these concepts and technologies. Therefore, a value-centric architecture for spacecraft design and certification is proposed in this paper to address this need. Firstly, the characteristics of different types of spacecraft are compared and summarized. In parallel, a survey on the current design and certification frameworks of large and complex systems is carried out. Taking in the experience of the frameworks, a generic design and certification architecture is developed from a value-centric perspective. Apart from keeping the critical advantages from the traditional methodologies, the new approach is capable of solving the problems inherent themselves. The results of a preliminary case study clearly show that the approach proposed can effectively capture, analyze, and optimize the value of different system designs, appealing to the growth of the space market.
Numerical simulation of plasma flow and the self-heating characteristics of a LaB6 hollow cathode were performed using a hybrid-PIC model. For a discharge current of 30 A and mass flow rate of 3 mg/s, the influences of an emitter temperature profile and model parameter included in an anomalous resistivity model on the plasma flow and energy flux were investigated. In the simulation, the discharge voltage was fixed at a predetermined value and the maximum emitter temperature was periodically adjusted to keep the discharge current constant. The results show that the present model predicts the keeper floating voltage within an accuracy of 20%. It is found that the main reason for the emitter temperature to rise is due to ion bombardment and accompanying recombination energy, and that the maximum emitter temperature can be kept lower as the emitter temperature profile becomes uniform. It is also shown that thermal input into the emitter is decreased when anomalous resistivity increases.
Friction stir-welded (FSW) joints are evaluated under two welding conditions to investigate their properties for application to aircraft structures. It is found that the welding condition affects the hardness profile, static strength, and fracture location. The tool mark near the burr, the kissing bond, the burr, and the edge of the specimen within the base material are found to be the origins of fatigue fractures in FSW joints, and the welding condition affects these origins and fatigue life. The kissing bond is not the origin of a fracture when low stress is applied. The fatigue life of a FSW joint is longer than that of a riveted joint. An evaluation of fatigue crack growth for each case via observation of the fracture surface indicates that the crack growth rate when the kissing bond is the origin of the fracture is close to that of the base material. The crack growth rate when the tool mark near the burr is the origin of the fracture is different from that of the base material: Overestimating the stress intensity factor range based on assuming the crack geometry contributes to the difference.
Today, multirotor helicopters (MRHs) play an important role in a broad range of applications such as transportation, observation and construction, and the safety of MRH flight is a matter of great concern. This study contributes to clarifying an aerodynamic aspect that enables the prediction of MRH behavior in unsteady conditions through flight tests. In working towards a comprehensive mathematical model that determines unsteady aerodynamics, a quadcopter is equipped with a data acquisition system to gather flight data including acceleration, angular rates, flow angles, airspeed and rotational speed. Based on the data collected, the combined blade element momentum theory is utilized to calculate steady and unsteady aerodynamic parameters. It is found that the experimental aerodynamic coefficients agree well with the theoretical results for steady forward flight. However, the conventional theory was insufficient to model the aerodynamic parameters under unsteady conditions. A new model to predict aerodynamic parameters under unsteady flight is proposed and validated on the basis of the flight data.
The fundamental nature of viscous incompressible flow is investigated by integrating the first and second laws of thermodynamics. The free energy of fluid, the fundamental thermodynamic function for system equilibrium, is shown to be a synthetic combination of the entropy production rate, flow steadiness and Lagrange function (kinetic energy – potential energy). When the flow is stationary and there is no energy exchange at the boundary, the principle of minimum entropy production rate in the thermodynamics of irreversible processes is extended to the space integration of the flow field. The results for minimizing the dynamic drag of fluid flow are discussed.
This paper presents a method to optimize the dimensions of z-stiffened panels under a compressive load. Buckling coefficient curves for local buckling and stiffener lateral buckling are developed. The effects of transverse shear, coupling of buckling modes, and stiffeners on one side of the skin are considered in the column buckling stress estimation. An optimization tool is developed using MS-Excel. Examples of the design charts are presented and a design guideline is derived.