Current Issue : October - December Volume : 2018 Issue Number : 4 Articles : 5 Articles
Understanding the effect of flexibility on the aerodynamic characteristics of the wing is one of the most important considerations\nfor successfully designing a flapping wing micro aero vehicle (FMAV). This paper aims at providing a systematic synthesis on the\nflexibility effects on the hovering performance of the bionic wing based on the numerical analysis approach. We construct a novel\nthree-dimensional bionic wing, which has lumped flexibility at the root, and develop an iterative coupling program to simulate the\ninteraction between the flexible wing and fluid. The effects of flexibility on the hovering performance of the three-dimensional\nflapping wing are investigated, and the results indicate that the best performance of the wing is achieved when the wing flaps at\nresonance and has the density close to the natural insect wing. The feasibility of using lumped flexibility wings driven by a\nsimple harmonic flapping for designing efficient FMAV is also concluded in this study....
A solid rocket motor is one of the critical components of solid missiles, and its life and reliability mostly depend on the mechanical\nbehavior of a composite solid propellant (CSP). Effective mechanical properties are critical material constants to analyze the\nstructural integrity of propellant grain. They are estimated by a numerical method that combines the Voronoi cell finite element\nmethod (VCFEM) and the homogenization method in the present paper. The correctness of this combined method has been\nvalidated by comparing with a standard finite element method and conventional theoretical models. The effective modulus and\nthe effective Poisson�s ratio of a CSP varying with volume fraction and component material properties are estimated. The result\nindicates that the variations of the volume fraction of inclusions and the properties of the matrix have obvious influences on the\neffective mechanical properties of a CSP. The microscopic numerical analysis method proposed in this paper can also be used to\nprovide references for the design and the analysis of other large volume fraction composite materials....
This work focuses on the wake encounter problem occurring when a light, or very light,\naircraft flies through or nearby a wind turbine wake. The dependency of the aircraft normal load factor\non the distance from the turbine rotor in various flight and environmental conditions is quantified.\nFor this research, a framework of software applications has been developed for generating and\ncontrolling a population of flight simulation scenarios in presence of assigned wind and turbulence\nfields. The JSBSim flight dynamics model makes use of several autopilot systems for simulating\na realistic pilot behavior during navigation. The wind distribution, calculated with OpenFOAM,\nis a separate input for the dynamic model and is considered frozen during each flight simulation.\nThe aircraft normal load factor during wake encounters is monitored at different distances from the\nrotor, aircraft speeds, rates of descent and crossing angles. Based on these figures, some preliminary\nguidelines and recommendations on safe encounter distances are provided for general aviation\naircraft, with considerations on pilot comfort and flight safety. These are needed, for instance,\nwhen an accident risk assessment study is required for flight in proximity of aeolic parks. A link to\nthe GitHub code repository is provided....
The article establishes a seven-degree-of-freedom projectile trajectory model for a new type of spinning projectile. Based on this\nmodel, a numerical analysis is performed on the ballistic characteristics of the projectile, and the trajectory of the dual-spinning\nprojectile is filtered with the unscented Kalman filter algorithm, so that the measurement information of projectile onboard\nequipment is more accurate and more reliable measurement data are provided for the guidance system. The numerical\nsimulation indicates that the dual-spinning projectile is mainly different from the traditional spinning projectile in that a degree\nof freedom is added in the direction of the axis of the projectile, the forebody of the projectile spins at a low speed or even holds\nstill to improve the control precision of the projectile control system, while the afterbody spins at a high speed maintaining the\ngyroscopic stability of the projectile. The trajectory filtering performed according to the unscented Kalman filter algorithm can\nimprove the accuracy of measurement data and eliminate the measurement error effectively, so as to obtain more accurate and\nreliable measurement data....
Design and simulation of an unmanned aerial vehicle (UAV) highly depends on the thrust produced by a motor-propeller\ncombination. The aim of this paper is to model a generalized mathematical relationship between the motor RPM and the\ncorresponding thrust generated for the preliminary design process of low Reynold�s number applications. A method is\ndeveloped to determine a generalized mathematical model which relates inflow velocity to coefficient of thrust using\nexperimental data from 291 motor-propeller data points, comprising of input RPM and corresponding output thrust. Using this\nrelationship, the Force Constant is calculated, which defines each Thrust-RPM mathematical model. In the first part, expression\nof the inflow ratio obtained from Blade Element and Momentum Theory (BEMT) is approximated to a simplified form. In the\nlater part, the proposed mathematical model is validated against two new sets of pairs of motor-propeller combinations. A\nspecial note in the Appendix talks about the application of this mathematical model. The computed results are found to be in\ngood agreement with the experimental data....
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