A simpler method to evaluate electromagnetic shielding performance at X-band has been required to develop new types of windows for civil and defense aircraft. In this study, we propose a new simple measurement method using a tiny piece of specimen for evaluating the characteristics of PMMA (Polymethyl methacrylate) plate coated ITO (Indium Tin Oxide) layer with different surface electric resistivity. The surface electric resistivity of each specimen is about 10[Ω/sq.], 30[Ω/sq.], 40[Ω/sq.], respectively. The experimental results were compared with a conventional method and proposed method. The maximum electromagnetic shielding value for 10[Ω/sq.] of the specimen reached 30[dB]. These results obtained by proposed method are consistent with the conventional measurement method and analysis results. Therefore, it was confirmed that the our proposed method is effective as an evaluation method of an electromagnetic wave shielding material using a thin film.
The flow reattachment process at low angles of attack near the trailing edge was investigated by focusing on flow disturbances induced by a dielectric barrier discharge plasma actuator (PA) attached at 65% chord of NACA0012 airfoil. The PA was operated at the burst frequency of 10 ≦ fb ≦ 300Hz and the Reynolds number of 5 × 104. We calculated the amplitude of induced flow disturbances near the trailing edge using visualization images. In the cases of burst frequency of 90Hz ≦ fb ≦ 150Hz and the angle of attack of 1.5º, the amplitude increased exponentially until x/c = 0.95 and saturated in the rearward of this position. The saturation point of the disturbance was considered to the position where the flow reattached to the airfoil surface. The lift coefficient with PA did not show the peak value near the frequency where the maximum value of the spatial growth rate is obtained from the linear stability theory. The increase in the lift coefficient became almost constant over a wide frequency range. This is because the spatial growth rate was almost constant within this frequency range, so that the reattachment position was almost constant.
A flying car which is also called electrical Vertical Take-Off and Landing (eVTOL) or Urban Air Mobility is envisioned to be a new air mobility. The purpose of this study is to verify the safety of passengers, a vehicle body and a take-off and landing area (vertiport), and to calculate a design strength requirement of a vertiport by simulating the impulsive load on emergent landing. The impulsive load simulation based on equation of motion of a flying car with or without a parachute is conducted to evaluate the dynamic effects of the impulsive load to a vertiport, a vehicle body and fuselage, and passengers. The spring-damper mechanism is introduced to evaluate force and acceleration of a fuselage. As a result, a conventional heliport and an emergency take-off and landing area in Tokyo have enough strength against the impulsive load of a landing flying car. Moreover, the crushable of a fuselage, and a seat, and an air bag need to absorb most of the impulsive load to protect passengers. A destroy probability against a vertiport by the impulsive load of repeated landing is calculated based on operational frequency with Poisson process.
Ignition property of reduced-toxicity hypergolic bipropellant was investigated under the condition that various parameters such as concentration, mixture ratio, propellant temperature were changed. 3-Methylaminopropylamine doped with sodium borohydride was used as a fuel, and propellant grade hydrogen peroxide was used as an oxidizer. As a result, it was found that this bipropellant has two ignition mode. Under the condition that concentrations of hydrogen peroxide and sodium borohydride are higher than certain values, ignition delay times are less than 4msec and do not depend on mixture ratio. On the other hand, ignition delay times become larger as mixture ratio increases under the condition of lower concentration. Even in the former ignition mode, it was observed that the growth of flame almost stopped for a while just after ignition under the high mixture ratio conditions. It was also found that temperature of hydrogen peroxide has some effect on ignition delay time, whereas that of fuel has little effect. Considering from these experimental results, ignition model formed by three phases was proposed. In this model, the cooling effect by unreacted hydrogen peroxide in condensed phase is considered to have potent effect on ignition delay time and post ignition behavior. This feature is caused by high optimum mixture ratio and exothermic self-decomposition property of hydrogen peroxide.
In this study, a special THINC scheme, so called β-variable THINC scheme, is proposed and embedded into the BVD (boundary variation diminishing) formulation to construct a high-fidelity scheme for compressible flows. The slope parameter β of THINC function is determined adaptively based on the solution structure so that the THINC function can be selected for a wider spectrum of solution profiles to prevent numerical oscillations in the BVD algorithm. Hence, a hybrid scheme combining the 4th-order unlimited polynomial and the β-variable THINC scheme based on the BVD principle has been devised to accurately capture both smooth and discontinuous solutions. The benchmark tests revealed that the numerical scheme presented in this paper is competitive to the other existing schemes such as MUSCL and WENO schemes.
Unwanted signal such as spoofing, jamming, and multipath is one of the major error factors in GNSS positioning. The purpose of this research is to mitigate the unwanted signal especially multipath error using an array antenna with six elements. We verified the effectiveness of the DCMP (Directionally Constrained Minimization of Power) algorithm to mitigate the unwanted signal. DCMP algorithm is one of the signal synthesis methods using the array antenna and can direct the ``Null'' to the unwanted signal direction by setting some constraint conditions. Testing in multipath-rich environment showed that the positioning accuracy was improved by constraining the ``Null'' toward the building which reflected GNSS signal.