The aerodynamic heating to a super-orbital reentry capsule with ablation heat protection was studied numerically by using thermochemical nonequilibrium full-viscous-shock layer (VSL) equations. A species model composed of 11 air species and 6 carbonic species was used. In the case of the super-orbital reentry, radiative heat flux to the wall cannot be neglected. The intensity of emission spectrum is strongly dependent on rotational, vibrational, electron and electronic temperatures, so that a thermal nonequilibrium analysis is needed to predict these temperatures more accurately. Therefore, a 3-temperature model composed of translational-rotational, vibrational and electron-electronic temperatures was adopted. Stagnation heat fluxes to the wall with and without ablation were calculated at various wall temperatures. Results for the reentry flight conditions at an altitude of 64 km showed that the stagnation heat fluxes with and without ablation are almost equal below a wall temperature of 3,200 K, whereas at wall temperatures over 3,200 K, the stagnation heat flux is reduced owing to significant sublimation of ablation material.
An innovative method of semi-active vibration suppression based on an energy-recycling approach using piezoelectric transducers is described. Piezoelectric transducers attached to or embedded in structures can convert the mechanical energy of the structure into electrical energy or, conversely, electrical energy into mechanical energy. Conventional methods have focused on how to effectively dissipate the transferred electrical energy. With our new energy-recycling method, the electrical energy is stored in the transducer functioning as a capacitor and is reused to suppress vibration of the structure, instead of simply being dissipated. This paper presents an advanced energy-recycling method to suppress multiple-mode vibration of beam structures with multiple transducers. Several control strategies based on active control theories are derived from formulae on the dynamics of a beam structure with piezoelectric transducers and electricity. We demonstrate the ability to suppress not only transient vibrations but also vibrations excited by sinusoidal and random forces.
This paper describes the deployment characteristics of a modular mesh antenna. The antenna consists of seven modules and is 10 m in diameter. Each module consists of a mesh surface and a deployable truss structure. Three motors cooperate to control the antenna deployment. The synchronization errors caused by asynchronous deployment motion depend on two factors: length of released control cable, and control cable failure. A deployment test is conducted on a 7-module assembly suspended from the ceiling in the cup-down configuration. We measured the displacement of the slide hinge along the center axis, the tensions in the control cables, and the strains in the rib structure members during deployment. We evaluated the effect of synchronization errors on the tension in the control cable and the strain in the rib structure members. We conclude that synchronization errors do not disturb the deployment motion and do not cause any structural failures when all modules are controlled by cables.
With regard to the development of a liquid-fuel rocket engine, knowledge of unsteady characteristics of turbopumps is essential in attempts to increase rocket reliability. Numerical simulation is very advantageous in determining the unsteady characteristics of turbopumps, and knowledge thus obtained can contribute to decreasing the cost and the number of experiments. In the present study, the effect of compressibility of cryogenic propellants, such as liquid hydrogen (LH2) and liquid oxygen (LOX), and the effect of nonlinearity of flow on the dynamic response of a high-pressure turbopump were considered. The results of calculation were compared with a nonlinear incompressible mathematical model. The effects of dynamic characteristics of a cavitating inducer, such as cavitation compliance and mass flow gain factor, as well as the effect of pipe elasticity and that of an accumulator for the POGO suppressor, were also analyzed.
Ignition delays of a cool flame (τ1) and a hot flame (τt) were measured experimentally for single n-decane, n-dodecane, n-tetradecane and n-hexadecane droplets, which have similar volatilities to common commercial hydrocarbon fuels, in hot air. Droplet diameter was 0.7 mm. Ambient pressure was 0.3 and 1.0 MPa. Ambient temperature was 550 K to 1000 K. Results show the similarity of the examined fuels in terms of reactivity of the low- and high-temperature reactions. Values of τ1 and τt were longer for fuels with lower volatility. Values of τ2 (=τt−τ1) were similar for examined fuels. Both the ignition limits of cool and hot flames were similar between fuels, but were slightly lower for less-volatile fuels.
The accuracies of unstructured grid methods for flutter analysis were investigated. Time accurate flow simulations with moving boundary were carried out on three types of unstructured grids. The results are compared with a recent report obtained by a structured, parallel flow solver. Semi-structured triangular grids and isotropic fine grids show similar results and agree well with the data. Poor grid resolution can result in wrong responses of the wing motion near the flutter boundary even when the same grid distribution is used on the wing. Typical wing responses for the lower- and higher-frequency modes are elaborated.
The dynamics of human pilots were studied quantitatively in relation to the change in the dynamic stability characteristics of an aircraft. Data was collected for three pilots who performed a control of bank-angle on a flight simulator simulating aircraft dynamics incorporating a large variety of Dutch roll characteristics. The dynamics of the pilots were expressed by a transfer function, which included dead time, gain, lead time constant, and lag time constant. To determine these parameters, the dynamic characteristics of a pilot were identified by the acquired data using an output error model. The pilot dead time was thought to be 0.3 sec, because the error between the actual data for aileron deflection angle in bank-control and the output of the transfer function for a pilot is smallest in these cases. We discovered that the preferred flying qualities of an aircraft for a pilot correspond to a gain, Kp, for the pilot greater than the set value depending on the flight conditions, a lead time constant, TL, for the pilot of less than 0.8 s, and a lag time constant, Tl, for the pilot of less than 0.3 sec.
This paper describes a collision avoidance problem for aircraft. In a conventional avoidance problem, it is assumed that the target information is certain. However, information may not be always certain, and handling of uncertain information has not been discussed. Therefore, a new control law is proposed to deal with uncertain information and to obtain correct information. The uncertainty depending on position, which is defined in the inertial or relative coordinate system, is dealt with in this paper. To cover each coordinate system, the proposed control law is applied to the ‘corner’ and ‘in-fog’ problems. Several elements are defined to express uncertainty of target information. Simulation results show that severe avoidance caused by conventional law is improved to obtain satisfactory performance by dealing with uncertain information.
Transient lift on a flat-plate airfoil in an incompressible uniform flow for a step increase in angle of attack is solved by applying Fourier transformation to a previously reported extended lift on an oscillating flat-plate airfoil with wake vortices assumed to move downstream at an arbitrary and constant velocity. The transient lift, which depends both on the position of the airfoil rotation axis and on the convection velocity of the wake vortices, includes a new term that is not reported in the classical theories. This term yields initial impulsive variations in lift. The relationship between the present solution and Wagner’s classical function is also clarified.