This paper investigates the acceleration performance of a disk-shaped magnetohydrodynamics (MHD) accelerator. Quasi-1-dimensional (Q1D) numerical simulation employing the MacCormack scheme was developed. For the longer channel length of 0.9 m, thermal loss was estimated at over 60% and effective acceleration could not be achieved owing to large heat loss and large friction loss. For shorter channel lengths, thermal loss can be reduced below 20% owing to the smaller heat and the friction losses. However, with too short a channel length, accelerator performance was decreased by the MHD compression due to excessive Faraday current density. The effect of ratio of cross sectional area on performance was also studied. For a larger area ratio, the gas can be accelerated smoothly throughout the MHD channel. However, for the excessive expansion case of a sevenfold channel, gas velocity near the exit decreased due to transition to a “generator mode”. For the best acceleration performance, the design channel length should be as short as possible preventing compression at the channel inlet. The area ratio should be large enough to prevent the compression but not too large, to prevent transition to a “generator mode”.
The boundary layer transition is predicted using the law of mass conservation. The increasing ratio of the boundary layer thickness to the laminar boundary layer thickness at the transition is introduced. Formulas and equations for laminar and turbulent boundary layers are used to predict the transition Reynolds number. The effect of the momentum deficit at the leading edge is also incorporated in this approach under compressible flow conditions. The calculated transition Reynolds number shows reasonable agreement with the experimental results. Under the compressible flow conditions, the calculation simulates the bucket of the transition Reynolds number with a Mach number, the change in the transition Reynolds number due to wall cooling, and the increase in the transition Reynolds number with increase in the bluntness Reynolds number.
An observer-based disturbance estimation method has been developed. A polynomial approximation of the disturbance is introduced, and the disturbance observer is constructed. The observer gain is optimized so that the estimation error is minimized. In this method, the estimated disturbance is adjusted by feedback of the estimated output error at several arbitrary time points. The design parameters related to the multipoint feedback determine the properties of the disturbance model. The proposed method is applied to aircraft dynamics and verified by numerical simulations and flight testing data. The simulation results show that the proposed method estimates disturbance input precisely.
The developability of thin circular cylindrical shells of infinite length leads to the postbuckling modes described by Yoshimura for shells under axial compression. Yamaki et al. calculated and measured experimentally the postbuckling modes of a cylindrical shell of finite length under axial compression. However, they did not calculate the buckling mode of the cylinder. To clarify the entire process of mode changes during buckling and postbuckling, an axial buckling mode is calculated and drawn for the cylinder whose corresponding postbuckling modes have been investigated by Yamaki et al. The axial postbuckling modes of finite length cylinders are shown to be deployable on flat surfaces due to the developability of cylindrical shells.
The distribution of lateral deviation is modeled in oceanic airspace where Strategic Lateral Offset Procedure (SLOP) is used. SLOP allows a pilot to select to fly not only on a defined route but also on a path 1 or 2 nautical miles (NM) on the right of the predefined route, which makes the distribution asymmetrical. Therefore, a new probability density function accounting for the SLOP effect is proposed. The model parameters are estimated based on the maximum likelihood algorithm. Fast convergence is achieved by using Newton’s method and a variable neighborhood search algorithm. The model fitness is investigated based on the Bayesian information criterion (BIC), frequency distribution, and distribution of the core parameter. Finally, an accurate lateral deviation model is obtained, which helps to identify the ratio of aircraft using the SLOP.
For flight safety, space is often restricted while the vehicle climbs to the target. A general two-dimensional (2-D) vehicle model is unsuitable for ascent when space is restricted because it considers only longitudinal degrees of freedom. Requiring into ascent in three-dimensional (3-D) scenarios as well as into relationships between the 2-D and 3-D trajectories. This paper reports 2-D and 3-D ascent phase minimum time-to-climb and minimum fuel-to-climb problems in different restricted spaces. The Gauss Pseudospectral Method (GPM) is used to transform the trajectory optimization problem into a Nonlinear Program (NLP) problem that can be solved by SNOPT based on a correct initial guess. The results in different restricted spaces illustrate the effect on 2-D and 3-D flight trajectories. Numerical evidence of optimality to trajectories is verified by estimating co-state information and the Hamiltonian.
In many modern gas turbine engine ground-based power plants, used for power generation, several auxiliary systems are integrated with the main gas generator to improve the generated output power or reduce fuel consumption. Two of the most effective practices are regeneration and intercooling. The first recovers part of the enthalpy in exhaust gas to pre-heat air before introducing it into the combustion chamber. The second cools the air during compression to reduce the work, and consequently obtain more power at the output shaft. These techniques are not used in gas turbine engines for propulsion mainly due to the extra weight and size caused by the heat exchangers and more complex flow patterns that result. However, if we could overcome these difficulties by means of compact heat exchangers the same benefits obtained for the ground-based plants could be obtained for aero engines. In particular the turboprop engine seems to be the best suited to this purpose due to its smaller mass flow rate and gas path. A thermodynamic cycle analysis shows the advantages of introduction of regeneration and intercooling in a turboprop engine in terms of increased power and reduced fuel consumption.
A free-piston double-diaphragm shock tube with 70×70 mm cross-section at test section is newly developed to investigate thermochemical nonequilibrium phenomena behind a shock wave. This paper presents the performance of the shock tube and the measurement system newly developed. Experimental investigations to clarify its characteristics are conducted for various operational parameters, such as rupture pressure of the first diaphragm and initial pressures in the low-pressure tube, the high-pressure tube, and the compression tube. Based on the characteristics experiment, a performance map of the shock tube is obtained by changing the operation parameters. The result shows that the shock tube can generate the post-shock condition corresponding to super-orbital reentry flight conditions. The newly developed measurement system enables us to obtain a spatial distribution of spectra behind a shock wave with high spatial and time resolution. A description of the measurement system and typical examples of the measured spectra are presented.
A novel star identification algorithm for GEO objects orientation is presented greatly. The quadrangle patterns are successfully generated by Delaunay triangulation applied to the sphere point set, which reduces the memory and identification time cost compared to the conventional triangle match algorithm. The guide database consisting of three correlative data tables is constructed to arrange the data efficiently. Furthermore, an index array is introduced to search the database rapidly. At validation, 60 images recorded by the GEO surveillance camera are used to implement the algorithm, which gives an identification rate ranging from 99.38% to 95.52% at various positional noise amplitudes. The achievable performance is demonstrated by comparison with two published algorithms.
In future space developments, welding in space may be required for repairs to the International Space Station and for constructing lunar bases and space structures. This paper describes the results of applying the space diode laser (DL) welding process, which the authors proposed in 2002. To use the DL welding process in space, it is necessary to prevent metal deposition on optical devices. We investigated a technique for preventing metal deposition in which the nozzle is installed at optical devices and a shielding gas is ejected from the nozzle outlet. Metal deposition can be reduced by blowing inert gas from the nozzle. The shielding gas argon completely prevents metal deposition on optical devices when the argon pressure in the nozzle is over 19.9 Pa and argon is ejected from the nozzle outlet.