Showing papers in "Journal of The Korean Society for Aeronautical & Space Sciences in 1997"

A Study on Stress Analysis of Tire Tread Block

Abstract: The deformation behavior of a tire tread rubber in contact with the roadway is complicated under the traction and breaking conditions. Because it is closely connected with running conditions and wear of tire, its proper analysis is difficult in theoretical and experimental method though many studies have been proceeded. In this paper, distributions of contact pressure and the shearing stress of a tread rubber block of truck tire subjected to compressive load P and lateral load Q are obtained. This analysis calculation predicts markedly different contact pressure distribution from those given previously by this analysis for a wide range of shape factor variation. Futher, we gave two kind of analysis by the energy method and the finite element method (ABAQUS code) on the contact pressure and the shearing stress of a tread block under P and Q. These analytical results are compared with each other and the previous ones and then show that the highest contact pressure remains moderate]y finite but not to be considerably large as predicted by the previous FEM analysis.

The Effect of Fe Compounds for Burning Catalyst on HTPB/AP Propellant

Abstract: A study on three catalysts for burning rate enhancement has been carried out by considering burning rate, mechanical properties, and processibility in the HTPB/AP solid propellant. The selected catalysts were Butacene grafted by silicone-ferrocene in HTPB, acylaziridinyl ferrocene (AAF), and superfine iron oxide(SFIO) which was 3nm in diameter. In the case that AAF or SFIO were added in propellant, the pot life of HTPB propellant was drastically decreased, but Butacene propellant showed high end-of-mix viscosity and low viscosity build-up curve. It was found that the mechanical properties of HTPB propellant have been worse by addition of Butacene or AAF except SFIO. The order of efficiency of burning catalyst was proved to be AAF>SFIO>Butacene as based on catalyst content and AAF>Butacene>SFIO as based on Fe content in propellant due to the different reaction rate of each flame in HTPB/AP propellant combustion.

Selection of Initial Frozen Orbit Eccentricity and Evolution of the Orbit Due to Perturbations

Abstract: An initial frozen orbit eccentricity was calculated using analytical expressions of terms only. Then the time variations of orbital mean eccentricity and argument of perigee were investigated when the order of the Earth's gravity model was increased from terms. For the Earth gravity model upto , an initial frozen eccentricity with the smallest variation was found. The realistic frozen orbit parameter evolution was obtained when various orbital perturbations such as gravitational forces of the Sun and the Moon, solar radiation forces, and air drags were applied.

An Alternative Computing Algorithm of the Penalized Weighted Residual Method for the Structural Dynamics

Abstract: In this paper, an alternative computing algorithm of the penalized weighted residual method is suggested which adopts step-by-step solving procedure like conventional time integration methods and is applied to the vibration analysis of the Timoshenko beam and the composite Mindlin plate. By the proposed computing procedure, it is possible to use the penalized weighted residual method with the saving of computer's memory compared to the direct solving procedure of the full space-time domain. According to the purpose of users, the direct solving procedure of full space-time domain or the step-by-step sequential solving procedure can be chosen in application of the penalized weighted residual method. Especially, the step-by-step sequential solving procedure can be effectively used in a conventional computing environment with small memory like desktop computer. To obtain a stable solution, a study is carried out and as a result, it can be known that the reduced integration in time domain gives an unconditionally stable solution even in the stiff systems frequently encountered in structural dynamics.

A Study on the Structural Behavior for the Design of the Small Aircraft Composite Propeller Blade by Considering Bird Strike Impact

Abstract: The development of aircraft composite propeller is necessarily required because recently changing metal propeller to composite propeller is a global tendency due to the improvement of composite manufacture technique and good characteristics of composite materials. The composite propeller blade must be safely designed about static and dynamic loads. The structural stability of composite propeller blades in this study was analyzed by the Finite Element Method. When the static load was acted on the composite propeller, linear and nonlinear analysis was performed with the three different types of blade structure. In order to analyze the problem of the dynamic impact load acted on the blade of shell-spar-foam structure by bird strike, Newmark method was used for linear direct transient analysis. And the Campbell diagram was drawn as the result of eigenvalue problem analysis about the composite propeller. The Natural frequencies of the shell-spar-foam blade were compared with the forced frequencies by engine rotational speed and it was found that the resonance phenomenon did not occurr in the blade. The results of the above structural analysis will be used as technical data fer the design optimization of composite propeller blade.

Flow Characteristics of the Transitional Boundary Layer on the NACA0012 Airfoil

Abstract: The transitional boundary layer on the NACA0012 airfoil is investigated at low Reynolds numbers. The streamwise mean and fluctuating velocity profiles and wall shear stress distribution are measured. Turbulent characteristics of the flow are different from the flat plate transitional flow. Double-peak distributions of the streamwise RMS fluctuating velocity in the near wall region during transition are observed, and the third peak is detected at the outer region of boundary layer at the initial stages of transition. Maximum values of RMS fluctuating velocity occur at . Velocity fluctuations during transition is not intermittent and the amplitude i9 much larger than that of downstream turbulent region. The frequency characteristics are similar to those of flat plate flow in high adverse pressure gradient, however more sensitive to the adverse pressure gradient.

Active Vibration Control of Composite Grid Structure by Piezoceramic Sensors and Actuators

Abstract: This paper is concerned with the active vibration control of grid structures by means of piezoceramic actuators and sensors. The vibration control technique for the grid structure used in this paper is based on the positive position feedback control, which has been successfully used for the vibration control of beam structures. The decentralized and centralized positive position feedback control methodologies are developed using the symmetric and anti-symmetric properties of bending and torsional modes of the grid structure. Electronic circuits for the realization of control schemes are explained in detail. The control techniques prove its effectiveness by experiments.

Measurement of Mean Particle Sizes and Fuel Concentrations of the Sprays from a Centrifugal Two-Nozzle Injector by Light Integrating Diaphragm (LID) Method

Abstract: Spray characteristics of a centrifugal two-nozzle injector were experimentally studied using the light integrating diaphragm method (LID) based on small angle laser light scattering. The theories on the small angle scattering were reviewed, which could be used to measure the size of liquid fuel droplets and the fuel concentrations. LID technique was successfully applied in one burner compartment in a test facility of gas turbine combustor. The measurement of Sauter mean diameter with LID method has an accuracy of about 5% for liquid fuel droplets. Kerosene or water sprays from the dual swirl fuel nozzle were tested under various conditions in terms of the fuel supply pressure and air-assisting. It was found that the droplet size decreases as the injection pressure increases and more when the injection is assisted by air. The experimental results imply that the low pressure air-assisted injection can simulate the realistic high pressure injection.

On the Attitude Control of a Satellite with Incomplete Set of Reaction Wheels

Abstract: Attitude control of a satellite is the process of orienting the satellite in a specified, predetermined direction. It consists of attitude stabilization and attitude maneuver control. In this study, when a part of actuators of the satellite becomes out of order, an alternative control algorithm has been suggested using the remaining actuators as a backup means. When two of four reaction wheels of the satellite fail, the alternative control algorithm for attitude control depends on the positions of the failed reaction wheels. When the failed wheels are placed opposite to each other, it is possible to control the attitude of the satellite using the only remaining two reaction wheels. However, when they are placed adjacent to each other, the attitude control would still be possible using the proper combination of the remaining wheels and dissimilar actuators. It has been found by a series of simulation that the currently suggested control algorithm would be successful in controlling the attitude of the satellite with defective reaction wheels.

Static Structural Test and Analysis of Basic Trainer

Abstract: There are several specifications which specify the requirement for strength and the procedures for the airframe strength substantiation. Structural tests and stress analysis should be peformed to prove the static safety of airframe. For the substantiation of a basic trainer, stress analysis for the whole airframe elements and full scale static test were performed by the procedure specified in MIL-SPECs and FAR 23. In this paper, the results of analysis and test were compared. Through agreement of both results, the static safety of the airframe is confirmed in the envelope of the flight and ground operation of design criteria.

Numerical Computation of Flows about an Aircraft with Flow-through Inlet

Abstract: An Euler solver which can use arbitrary multi-block grid systems has been developed. This solver uses MUSCL approach for the higher order of spatial discretization error. Furthermore, it has the exit boundary condition given in terms of mass flow rate so that it can simulate the flows through engine inlet. The flow-through exit boundary condition, unlike Murman's method, does not have to regenerate inlet duct grid for the different mass flow rates. The solver has been tested on a generic missile and its results have been compared with the experimental and computational results. Mixed internal and external flows around a jet trainer with a pitot type inlet have been computed.

Computations of Hypersonic Flowfield around a Blunt Body with Roe's FDS and AUSM+ Schemes

Abstract: The hypersonic flowfield around a blunt body was numerically analyzed with 2D Navier-Stokes equations. Roe's FDS and AUSM+ schemes were used for spatial discretization and MUSCL was used fer higher order spatial accuracy. AE-ADI scheme was used for time integration. Roe's FDS needed an entropy fix to avoid the carbuncle phenomena near stagnation line. The entropy fix, however, decreased the solution accuracy in the boundary layer, so the value of entropy fix should be decreased in the boundary layer for the accurate solutions. The accuracy of the wall heat transfer solution was especially influenced by the amount of entropy fix. AUSM+ is one of the hybrid flux splitting schemes which were designed to combine the accuracy of FDS and the robustness of FVS. Numerical analysis with AUSM+ did not show the carbuncle phenomena. Furthermore, AUSM+ could give the accurate solutions in the boundary layer without boundary layer corrections.

Comparison of the Rotor Wake Modeling in Hovering Motion

Abstract: The time marching free wake model of the helicopter rotor in hovering motion is compared with the prescribed wake model. The flows are assummed to three-dimensional unsteady potential flow. In prescribed wake method, an empirical formula from experimental results is used to calculate the wake geometry until the computed thrust coefficient is well agreed with the given thrust value. However, in free wake method the wake shed from the trailing edge of the rotor blade makes the global wake geometry without any particular restriction. For the case of the single blade rotor in hover, the thrust and lift distribution along the span are obtained and the radial and axial wake geometries that is, the inner vortex sheet and the tip vortex line are calculated. The numerical results are in good agreement with the results obtained from the prescribed wake geometry. The computed free wake geometry is also at least qualitatively in good agreement with the experimental wake geometry which is represented by three wake region; revolutions of well defined tip vortex lines, recirculated and expanded zones of far wakes.

An Experimental Study on the Intake Boundary Layer Diverters for Transonic Aircraft

Abstract: It was tried in this paper to find out how the boundary layer diverters which prevent the boundary layer flow developed through the fuselage and strake from flowing into the air intake influence on the performance of the intake. The pressure recovery and distortion were measured at the engine face at various aircrat attitudes and airflow rates of the intake. The model was 1/7 scale of single engine aircraft with turbofan engine at the aft fuselage and bifurcated duct having intake at both side of the fuselage. It was found that intake performance is closely related with boundary layer diverter height and suitable height could be selected based on the intake performance at given maneuver and air flow rate conditions.

Study on the three-axes attitude controller design of Satellite using reaction wheel

Abstract: Attitude controller of small satellite was designed in this paper. Four reaction wheels give a control torque to the satellite. At first, the design of wheel speed controller was performed by using linear model and then it was considered that each nonlinear effect to this system by inserting nonlinearity. The design purpose of wheel speed controller is that the outputs(wheel angular velocity or wheel angular momentum) show the fast response to the desired momentum. The PI controller was used in order to get the fast response speed without overshoot. Three-axis attitude control was performed by using precede reaction wheel model after completing wheel speed controller. Reaction wheels have a 'pyramid' configuration which all four wheels are skewed and one wheel is a redundancy. Same as the wheel speed controller, PI controller was used and designed to coincident with the given bandwidth of the satellite. If the inputs that compensate the attitude error due to the external disturbances or perform the mission of the satellite are given to the attitude controller, it can be acquired that attitude error, wheel angular momentum, angular velocity of the satellite, and etc.

Development of a Cylindrical Type Piezoelectric Vibrating Gyroscope

Abstract: Vibratory gyroscopes have important advantages in comparison with the traditional designed mechanical gyroscopes based on large conservation of angular momentum. There are reasons that they are low power devices and have long operating time with almost instant start-up time and they can be packed into a small working volume far small size of itself. Additional]y, they are low cost, high reliability, and the capability of working in severe environment. In this paper, the feasibility of such a vibratory gyroscope is introduced. The vibration analysis is conducted by ANSYS code. The vibratory piezoelectric gyroscope with control circuit far drive and output pick-off is manufactured and evaluated.

An Experimental Study on Characteristics of Chemiluminescence Emission of Doubled Jet Burner Flame

Abstract: In industrial combustor, high loading combustion is pursued to accomplish a small-sized eqipment. Turbulent premixed flame is advantageous to high loading combustion. And in this case, turbulent burning velocity is an important factor that determines combustion loading. Since the turbulent burning velocity of distributed reaction flame is higher than that of wrinkled laminar name, distributed reaction flame is watched industrially. We measured overall averaged radical luminescence intensity with image processing system and then made a comparing study of combustion characteristics. And we measured local radical luminescence intensity with local measuring system, and researched chemiluminescence emission characteristics. As a result, the radical luminescence intensity distribution through the image processing system is useful to elucidate the characteristics of general burner flame. The distribution of CH radical luminescence intensity shows similar trend with that of local equivalence ratio. When the turbulent intensity is increased with central direction flux, doubled jet burner flame coresponds to the distributed reation flame judging from the distribution of fluctuating temperature, radical luminescence intensity and local equivalence ratio. And in the strong turbulence field of doubled jet burner, the radical luminescence randomly exists due to small size eddies.

Dynamic Behavior of Aircraft Landing Gear with Typical Dual-Chamber Shock-Absorbers

Abstract: In this paper dynamic analysis of aircraft landing gear during landing impact and taxiing with typical dual-chamber shock absorbers are conducted. A simplified model for the dynamic analysis is developed by assuming a three-masses system, i.e. sprung, unspurng and rotating masses. Kinematic equations are given, in which stroke, stroke velocity, tire deflection, the slip velocity between the tire surface and the ground are considered. Force relations are discussed dealt with internal shock shrut force, hydraulic force, bearing friction, tire vertical reaction and tire drag force fer single dual-chamber shock absorber. The analytical results for the three typical types of shock-absorber are obtained under design impact and taxiing conditions. Some main characteristics describing dynamic behavior of dual-chamber shock-absorbers, such as, overlaod, unsprung displacement, absorbed energy and tire deflection are presented. It demonstrates that there are respectively advantages and disadvantages for different types of dual-chamber shock absorbers, which is helpful far aircraft landing gear design.

Numerical Simulation of Flow Structure and Heat Transfer in 3-D Turbulent Flows with Imbedded Longitudinal Vortex

Abstract: Heat transfer characteristics and flow structure in turbulent flows through a flat plate 3-D turbulent BL containing built-in vortex generators have been analyzed by means of technique of Crank-Nicolson finite difference method. Under the slender flow approximation, the steady three-dimensional Navier-Stokes and energy equations are solved by C-N method. Longitudinal vortex in turbulent BLs belongs to the class of slender turbulent flow, in which velocity gradients in transverse direction are much larger than streamwise direction and the governing equations can be parabolized along this direction. The method is used space marching technique to economize on the computing time and the storage. This paper used the eddy diffusivity model and standard model to predict heat transfer and flow field in the turbulent flow with imbedded longitudinal vortex. The results show boundary layer distortion due to vortices, such as strong spanwise flow divergence and boundary layer thinning. The heat transfer and skin friction show the relatively good results in comparison with experimental data. The vortex core moves slightly away from the wall and grows slowly; consequently the longitudinal vortices strongly perturb the velocity field of turbulent BLs and enhance the exchange of fluid between the well and the core region which causes high heat transfer augmentation over a very long distance downstream.

Dynamic Response of Landing Gear Taxiing on Uneven Runways

Abstract: An analytical landing gear model of simulating actual aircraft taxiing behavior by the power spectral density method is formulated. The dynamic model deals with not only shock-absorber non-linear damping and air-spring stiffness, but also tire non-linear damping and stiffness. The validity of this model is demonstrated with a comparison of frequency-domain and time-domain analytical results of dynamic response for two aircrafts, Boeing 707 and Boeing 737-94. The equivalent linearization technique in probabilistic method is introduced to treat landing gear non-linear parameters such as shock-absorber air-spring force, hydraulic damping and Coulomb friction, and tire stiffness. It is concluded that the air-spring stiffness and damping of shock-absorber have a great effect on root-mean-square of sprung-mass overload. The decrease of air-spring stiffness and increase of shock-absorber damping cause on obvious reduction in vibration level. An approach for determining the lower limit of air-spring stiffness and the upper limit of shock-absorber damping is presented, which is useful to assess and improve dynamic properties of aircraft as well as landing gears. For instance, it may give 43% and 60% reduction in root-mean-square sprung-mass overload(i.e., aircraft gravity overload) respectively for Boeing 707 and Boeing 737-94 aircraft by selecting the presented air-spring stiffness and shock-absorber damping.

A Study on Real Time Linear Simulation and Control for Aircraft Gas Turbine Engine

Abstract: The performance of aero gab turbine engine should be optimized because it is directly related to overall aircraft performance. In this study, by using the dynamic simulation program DYNGEN with modifying the block data component maps into new maps of an aero gas turbine engine, a nonlinear dynamic simulation was performed to predict the overall engine performance at two cases of flight conditions such as M=0, sea lever=0, and M=0.6, altitude=1.5km. Also by using an interpolation scheme for sampling data about several operating points, a real time linear simulation was derived for nonlinear gas turbine engine and was compared with other cases such as the 3% rpm step model, the 5% rpm step model, and the 6% rpm step model within operating range. Finally control schemes such as the PI (Proportional-Integral) and the optimal LQR(Linear Quadratic Regulator) compensator were applied to improve an engine dynamic performance with step fuel flow rate. Comparing the results, it was proven that the LQR controller can suppress the overshoot of turbine inlet temperature more effectively than the PI controller.

Comparison between Quaternion Error Model and Equivalent Tilt Error Model

Abstract: In this paper, we compare the linear quaternion error model(LQEM) and the linear equivalent tilt error model(LETEM) both of which are widely used fur the analysis of the strapdown inertial navigation systems(SDINS) based on the quaternions. Since the major difference between them occurs due to the approximations of the attitude error, this paper focuses on the modeling accuracy with respect to the attitude error. For the comparison, we derived a nonlinear error model which includes all the higher order terms of the attitude error. Using the derived nonlinear error model, the difference between LQEM and LETEM was analytically revealed. As a substitute for LQEM and LETEM, a linear error model which improves modeling accuracy with respect to the attitude error was also derived. Finally, a simple simulation far verification was performed.

Terminal Guidance Algorithms of Missiles Maneuvering in the Vertical Plane

Abstract: This paper presents real-time onboard terminal guidance algorithms of anti-tank and anti-ship missiles with constrained flight path angle at impact. Presupposing that targets are stationary or slowly moving compared with the missile, missile motion is described by a point mass second order kinematic equations in the vertical plane. The linear dynamic model is followed by application of linear quadratic optimization techniques considering soft and hard terminal boundary conditions. Two performance indices are considered; One consists of terminal miss distance and control efforts along the whole range, the other terminal miss distance and a linear combinations of overall control efforts and flight heights. Generally, the former gives rise to Pop-up/Dive height profile, the latter so-called Vertical Bunt height profile showing in the final stage of missile's trajectory a sharp rise followed by sharp fell to the target. Exploiting acceleration command profile obtained from a closed form solution, minimum range to begin the terminal guidance mode has been calculated. To substantiate our conclusion, results of the 6-D.O.F. simulation have been illustrated.