Journal of Aerospace Engineering

This paper describes a spacecraft trajectory planning algorithm based on the calculus of variations which can solve 6-degree-of-freedom spacecraft docking and proximity operations problems. The design of a cost functional which trades off fuel use, obstacle clearance distance, and arrival time is discussed. The nonlinear orbital dynamic equations are treated as dynamic constraints. The Euler-Lagrange equations for this functional are derived, as is the Pontryagin criteria for the optimal control input given realistic saturating on-off thrusters. The indirect collocation method is chosen to solve the attendant boundary-value problem for its lack of sensitivity to initial conditions; continuation is used to further improve the algorithm’s robustness. The manipulation of the Euler-Lagrange equations and the transversality condition into a form suitable for use with existing collocation codes is discussed. Results are shown for an end-to-end docking maneuver with a tumbling satellite.

This paper simulates the three-dimensional axisymmetric triaxial compression of JSC-1A lunar regolith simulant under lunar and terrestrial gravity environments under a wide range of confining pressures and relative densities. To accomplish this, the discrete element method (DEM), using Particle Flow Code In Three-Dimensional (PFC3D) software, was employed. The paper focuses on the peak and the critical state (CS) friction angles, which were predicted in the ranges of 35.4°–82.7° and 31.2°–79.8°, respectively, depending on the specimen density and confining pressure. A significant increase in peak and CS friction angles was predicted at near-zero confining pressure. The DEM results validated an empirical model that relates the peak friction angle with the CS friction angle, relative density, and mean effective stress at the CS. Comparison of DEM results with lunar in situ measurements of friction angle, from Apollo missions and other extraterrestrial laboratory experiments under a microgravity environment, shows a favorable agreement.

Fire risk in high-rise buildings is of special concern to the fire community, since it is crucial but still technically extremely challenging to significantly improve the current fire fighting capabilities when a calamity happens above the “seven story limit.” In fact, at the moment, there is a lack of effective means for fire fighting in this rare but potentially deadly and costly accidents. To address this problem, in this work we provide a preliminary exploration of a new concept for fire suppression: the use of rotorcraft vehicles for aerial fire fighting in high-rise buildings. If available, such system could effectively support fire fighting efforts conducted with conventional means; moreover, it could provide for one of the very few alternatives to classic systems in certain critical cases such as postearthquake fires. At first, we analyze the operative context with the help of a few reference realistic scenarios which allow for the estimation of some key physical parameters. Next, we evaluate two alternative fire extinguishing technologies, and we identify in the water impulse cannon the solution which seems to be the most effective and compatible with the use on-board a rotorcraft for the scopes considered in this work. The analysis leads us to the identification of a target vehicle as a possible candidate platform for the development of a fire fighting helicopter. Finally, we propose a preliminary design of the fire fighting kit, and we evaluate the handling qualities of the vehicle during operations with reference to the ADS-33 normative.

Shock-wave interaction with an elastic structure is investigated using a coupled numerical analysis approach, which considers solid-fluid interaction within an arbitrary Lagrangian-Eulerian framework. The analysis is performed considering a compressive shock wave, where the shock front is followed by constant pressure. An analysis procedure, which considers the change in the fluid domain due to the deformation of the solid and changes in the overpressure due to the movement of the elastic structure, is developed. Approximate numerical procedures for solving the Riemann problem associated with the shock are implemented within the Godunov finite volume scheme for the fluid domain. The influences of parameters such as structural stiffness and mass of the system on the displacement, velocity, and energy of the elastic structure following the shock-wave incidence are investigated. Immediately after the contact of the shock wave with the solid surface the pressure at the face of the elastic solid rises to a value which is equal to that obtained off of a fixed rigid wall. Subsequently, the motion of the piston produces changes in the applied pressure. The overpressure applied to the elastic system does not have a fixed profile but it depends on its elastic stiffness and structure mass. It is shown that there is a continuous exchange of energy between the air and the moving elastic structure, which produces a damped motion of the solid. The effect of damping is considerable for the cases of low elastic stiffness and low structural mass, where the resulting motion of the solid is nonoscillatory. The conventional analysis procedure, which ignores the energy exchange between the air and the moving solid, predicts an undamped oscillatory response of the structure for all cases considered. It is shown that neglecting the interaction between the air and solid can produce significant error in the total energy of the structure and the dynamic load factor when the resulting motion is nonoscillatory.

Nonlinear filtering theory, based upon the Fokker-Planck equation and Bayes’ rule, has been around since the 1970s. This method does not require linearized dynamics and/or measurement models, and also the assumption of the Gaussian process is not necessary. However, it is extremely difficult to obtain an analytical solution of the Fokker-Planck equation with only a few exceptions, and normally the solution is obtained through numerical approaches. In this paper, this type of nonlinear filtering method is reinvestigated and applied to a relative orbit estimation problem. The time evolution of the state conditional probability density function between measurements is obtained by solving the associated Fokker-Planck equation numerically using the numerical scheme called the alternating direction implicit method. To further mitigate the computational load, an enhanced moving domain technique is employed and the probability distribution function is partitioned.

The clear-air turbulence is difficult to detect and predict and yet affects the flight safety the most. A transport aircraft in encountering a severe turbulence frequently develops a sudden plunging motion with the abrupt change in altitude. The aerodynamic forces and moments involved are dynamic and nonlinear and are not well known. The main objective in the present paper is to present the dynamic and nonlinear aerodynamics estimated with the flight data recorder data of a transport aircraft through a fuzzy-logic algorithm. The algorithm is utilized to establish a thrust model and aerodynamic models for all aerodynamic coefficients including the effects of turbulence. The static and dynamic stability derivatives for the subject transport aircraft are demonstrated to be highly nonlinear and unsteady in response to a severe clear-air turbulence in transonic flight.

The feasibility of using the transfer matrix method (TMM) to analyze open-variable thickness circular cylindrical shells exposed to a high-temperature field is explored theoretically. In the approach to the problem, the thermal degradation (TG) of thermoelastic characteristics of the material is considered. Natural frequencies and mode shapes for the cylindrical shells are investigated in detail by combining the vibration theory with the TMM. The governing equations of vibration for this system are expressed by the matrix differential equations, and the coefficient matrices are derived. After the relationship between the transfer matrix and the coefficient matrix is established, the fourth-order Runge-Kutta method is used numerically to solve the matrix equation. Once the transfer matrix of single component has been obtained, the product of each component matrix can compose the matrix of the entire structure. The frequency equations and mode shape are formulated in terms of the elements of the structural matrices. Finite-element numerical simulation has validated the present formulas of natural frequencies. Numerical illustrations, supplying pertinent information on the implications of the TG, are presented for various curvatures, aspect ratios, boundary conditions, and thickness ratios, and the pertinent conclusions are outlined.