Journal of Aerospace Engineering

The problem of determining an optimal feasible trajectory, for a fixed wing flying vehicle moving in a dynamical three-dimensional space, is addressed in this paper, and an analytical solution is proposed. With explicitly considering the boundary conditions and kinematic constraints as well as by satisfying the collision avoidance criterions, trajectories are described in terms of three parameterized polynomials, and the family of feasible trajectories are found. Then, the desired near shortest trajectory is chosen from the feasible trajectories by optimizing a performance index with respect to $L_2$ norm. This trajectory and its associated steering controls are achieved analytically. Computer simulations validate that this approach is computationally efficient and real-time implementable.

Thermal buckling analysis of laminated smart composite plates subjected to uniform temperature distribution has been presented. Shape memory alloy (SMA) fibers whose material properties depend on temperature have been used as a smart material. A three-dimensional layerwise plate model has been employed in developing the system equations using variational approach. Finite-element method has been adopted for discretization of the laminate. Lagrangian interpolation functions have been used to approximate the displacement components along the thickness as well as in the in-plane direction. The actual variation of prebuckling stresses has been accounted for in the derivation of the geometric stiffness matrix of the laminates. An incremental load technique has been used in the analysis to take into account the nonlinearity in the material properties of the SMA arising due to their temperature dependence. The effects of thickness ratio, orthotropic ratio, fiber orientation, aspect ratio, stacking sequence and various boundary conditions on the critical buckling temperature have been examined in details. The results have been validated with those available in the literature.

This paper addresses a computational procedure to assess the lethality of kinetic energy projectile warheads against tactical ballistic missile payloads with an innovative and rational damage metric. The individual lethality of different projectile geometries impacting at hypervelocity at different configurations is estimated via a numerical damage index computed from hydrocode simulations. The highest count of possible impacts to the payload is achieved by optimizing the warhead’s configuration and time of detonation, a priori knowledge of the target’s location and speed. The total damage to the payload characterizes the warhead’s lethality for the particular engagement conditions. An example shows the application of the process and potential advantages.

The formulation of the dynamic equations of motion proposed by Udwadia-Kalaba is discussed from the point of view of numerical efficiency. Since this formulation requires the computation of a pseudoinverse matrix, it has investigated the influence of the method of pseudoinverse computation on the dynamic simulation of an overconstrained linkage. Finally, it has been proposed that a new dynamic equation which explicitly computes accelerations also in the case of mathematical models with rank deficient Jacobian and mass matrices.

The electromechanical impedance technique employs surface-bonded lead zirconate titanate piezoelectric ceramic patches as impedance transducers for structural health monitoring and nondestructive evaluation. The patches are bonded to the monitored structures using finitely thick adhesive bond layer, which introduces shear lag effect, thus invariably influencing the electromechanical admittance signatures. This paper presents a new simplified impedance model to incorporate shear lag effect into electromechanical admittance formulations, both one-dimensional and two-dimensional. This provides a closed-form analytical solution of the inverse problem, i.e. to derive the true structural impedance from the measured conductance and susceptance signatures, thus an improvement over the existing models. The influence of various parameters (associated with the bond layer) on admittance signatures is investigated using the proposed model and the results compared with existing models. The results show that the new model, which is far simpler than the existing models, models the shear lag phenomenon reasonably well besides providing direct solution of a complex inverse problem.

Experimental investigation is essential to improve the understanding of aerospace flows. During the last years, effort has been put on the development of optical diagnostics capable of imaging or yielding data from the flow in a nonintrusive way. The application of some of these techniques to supersonic and hypersonic flows can be highly challenging due to the high velocity, strong gradients, and restricted optical access generally encountered. Widely used qualitative and semiquantitative optical flow diagnostics are shadowgraph, schlieren, and interferometry. Laser-based techniques such as laser Doppler anemometry and particle image velocimetry are well established for investigation of supersonic flows, but as yet their use in hypersonic flows has been limited. Other relevant measurement techniques include particle tracking velocimetry, Doppler global velocimetry, laser-two-focus anemometry, background oriented schlieren and laser induced fluorescence methods. This paper reviews the development of these and further optical measurement techniques and their application to supersonic and hypersonic aerospace flows in recent years.

Three concepts for the shelters on the moon are presented here. It is envisaged that the first robots will land on the moon and start preparing sites for advanced bases and also for future human presence. These robots will encounter severe radiation and micrometeor hits when they are exposed to the lunar atmosphere. During the period of intense solar radiation these robots have to be temporarily sheltered, since shielding on the robots may not be adequate to protect the instruments. The construction of these shelters has to be performed with very little equipment support. This paper presents concepts and their feasibility analysis for the fabrication of shelters under such stringent constraints.

A strategy for confinement of flexural vibrations in flexible structures by proper selection of their geometrical and physical parameters is proposed. We first show that the problem of vibration confinement can be formulated as an inverse eigenvalue problem (IEP) where the mode shapes and/or natural frequencies are assumed and the geometrical and physical properties are unknown functions of the space variables. It is required that the assumed modes form a complete and independent set of spatial functions that satisfy the boundary conditions and guarantee confinement within the desired spatial subdomain(s) of the structure. Using simple spatial functions, such as polynomials and exponentials, we determined approximate solutions of the geometrical and physical parameters by applying the orthogonality of the mode shapes with respect to the stiffness and mass density. The order of the selected polynomials or exponentials depends on the number of modes retained in the discretized model. Numerical simulations are presented on a beam and then on a plate to examine convergence of the solution to the IEP. We show that convergence is attained with few assumed mode shapes. The approximated parameters are finally substituted into the forward eigenvalue problem to confirm confinement at the desired locations.

The stress generated by the horizontal compression of a vertical column of granular material is investigated. The column is open at the top so that the material is free to flow upward in the slot as it is compressed. This simple geometry has interesting mechanics because both elastic and frictional regimes coexist, and it is also relevant to problems involving the insulating material in cryogenic storage tanks. Two methods are used to investigate this problem: traditional continuum modeling and discrete element simulation. The continuum model assumes that the column consists of a frictional region near the top of the column and a linearly elastic region near the bottom. Analytic solutions are obtained for each region and predictions for the location of the transition are made based on intersections of the two solutions. A discrete element simulation of the same geometry is performed to compare with the results from the continuum model. Various conditions of wall friction and particle stiffness are simulated. Based on the outcome of this comparison, we verify that in a compressing slot there are essentially two distinct regions: a frictional flow region near the top of the column that results in an exponential increase in stress with depth. This eventually saturates leading to a linear-elastic plane strain region. The location of the transition between these two regions depends on the material properties and the state of the compression.

Our goal is the oscillation susceptibility analysis in the framework of a nonlinear mathematical model in the so-called ADMIRE or Aero Data Model in a Research Environment. First, we analyze the oscillation susceptibility along the path of the longitudinal flight equilibriums when the flight control system (FCS) is decoupled. After that, a similar analysis is undertaken in the case when the FCS is coupled. For decoupled FCS, it is shown that on the path of the longitudinal flight equilibriums there exists a saddle-node where stability is lost and fold bifurcation occurs. Maneuvers are simulated showing the effect of an instantaneous change of the elevator angle, and the evolution of the unstable equilibriums (due to the maneuvers) to the corresponding exponentially stable equilibriums. It is shown numerically that at the saddle-node oscillations occur when the elevator angle is less than the critical value and the start is from the saddle-node. More precisely, it is shown that if the plane state parameters coincide with the saddle-node coordinates and the elevator angle is changed instantaneously from the critical value to a value which is less than this value, then two of the state parameters $\left(\alpha ,q\right)$ begin to oscillate with the same period and the third parameter $\left(\theta \right)$ increases, tending to infinity. Thus, the orbit of the system evolves spiraling. It is shown also, that if the elevator angle is reset, the plane returns to a stable equilibrium. Therefore, a soft or no catastrophic stability loss takes place. When the FCS is coupled, the plane for every value of the amplification factor has a unique equilibrium which is exponentially stable and attracts all the equilibriums which exist in decoupled case. In this case, there are no bifurcation points on the equilibrium path. The dependence of the equilibrium and of the relaxation period on the amplification factor value is found numerically. Finally, it is concluded that when the FCS is decoupled, then along the path of the longitudinal equilibriums oscillations can occur, but when the FCS is coupled and the pilot can modify (instantaneously) only the amplifier factor value, then the vehicle, defined by the considered numerical data, is not anymore susceptible to oscillation.

We present a closed form analytical solution of the Possio integral equation of aeroelasticity for the sonic case $M=1$ , both time-domain and Laplace domain, including a numerical example for the flutter speed, where the flutter mode differs from that for $M=0$ . A noteworthy feature is that the Kutta condition is not satisfied and is not needed for uniqueness of solution.

Despite significant work over many years, using either one of the micromechanics based or phenomenological approaches, there are still prospects of much improvement to be made in constitutive modeling of shape memory alloys (SMAs). This is especially true if we sufficiently target the general scope in the modeling, i.e., including such important attributes as (1) multiaxiality; (2) possible asymmetry in tension and compression; (3) accounting for pseudoelasticity and pseudoplasticity; (4) rate dependence; and (5) effects of shape memory training under cyclic loading. The desire for comprehensive modeling of SMA materials provides the primary motivation for the inelastic model described here. Its theoretical formulation employs two main ingredients: (1) multiplicity of hardening mechanisms and (2) the partition of the energy storage/dissipation that is so vital in capturing the extremes of pseudoelasticity and pseudoplasticity in SMAs. For the purpose of validation and assessment part of the model capabilities, we report the results of a large number of simulations that were inspired by recent experimental test results under both monotonic and cyclic as well as uniaxial and multiaxial stress conditions.

This paper presents a new, simple, and exact solution to the formation keeping of satellites when the relative distance between the satellites is so large that the linearized relative equations of motion no longer hold. We employ a recently proposed approach, the Udwadia-Kalaba approach, which makes it possible to explicitly obtain the desired control function without making any approximations related to the nonlinearities in the underlying dynamics. We use an inertial frame of reference to describe the motion of a satellite and since no approximations are made, the results obtained apply to situations even when the distance between the satellites is arbitrarily large. The paper deals with a projected circular formation, but the methodology in this paper can be applied to any desired configuration or orbital requirements. Numerical simulations confirm the brevity and the accuracy of the analytical solution to the dynamical control problem developed herein.

The equations described free longitudinal and lateral vibrations of the rectilinear elastic beams with the rectangular cross section are derived based on the theory of linear elasticity and the method of integrodifferential relations. The original system of partial differential equations is reduced to the system of ordinary differential equations with constant coefficients. The influence of geometrical and elastic properties of the beam on eigenvalues and eigenfunctions are investigated. The existence of the different displacement and internal stress types of the longitudinal motions are shown. The presence of two frequency zones corresponded to different kinds of the characteristic solutions for the lateral vibrations is detected.

The effects of the collision of a near-earth object (NEO) with the Earth could be catastrophic on a local, regional, or global scale depending on the size of the NEO. Therefore, there is considerable interest in determining ways to mitigate the threat posed by these objects. This paper presents a method using the attachment of a tether and ballast mass to alter the trajectory of a NEO on an Earth-intersecting orbit so that it avoids hitting the Earth. Furthermore, a parametric study of such a system is conducted over a wide range of parameters that describe the orbit and the system itself. For each set of parameters, a resulting “miss distance” due to the attachment of the tether and ballast mass is calculated. The results demonstrate that such a system could be used to protect the Earth from Earth-intersecting NEOs.

This work isolates cases of nondetection, false alarm, and insensitivity for a general class of problems dealing with the detection and characterization of existence, location, and extent of singularities embedded in signals or in their derivatives when employing kurtosis- and pseudofractal-based methods for the detection and characterization process. The nondetection, false alarm, and insensitivity for these methods are illustrated on an example problem of damage identification and calibration in beams where the singularity to be identified lies in the derivative of the measured signal. The findings are general, not constrained to linear systems, and are potentially applicable to a wide range of fields including engineering system identification, fault detection, health monitoring of mechanical and civil structures, sensor failure, aerospace engineering, and biomedical engineering.