This paper investigates the design of an unmanned helicopter simulation system with Matlab, and completes the development of modeling, the navigation system, device input system, control system and virtual reality system, eventually accomplishing a simulation system which can freely alternate between manned mode and unmanned mode. Based on flight tests, it is shown that the simulation and test results agree well, indicating that the simulation system accurately describes the characteristics of helicopter dynamics and the control system.
To improve the total efficiency of centrifugal compressors, it is necessary to reduce disk friction loss, which is expressed as the power loss. In this study, to reduce the disk friction loss due to the effect of axial clearance and surface roughness is analyzed and methods to reduce disk friction loss are proposed. The rotating reference frame technique using a commercial CFD tool (FLUENT) is used for steady-state analysis of the centrifugal compressor. Numerical results of the CFD analysis are compared with theoretical results using established experimental empirical equations. The disk friction loss of the impeller is decreased in line with increments in axial clearance until the axial clearance between the impeller disk and the casing is smaller than the boundary layer thickness. In addition, the disk friction loss of the impeller is increased in line with the increments in surface roughness in a similar pattern as that of existing experimental empirical formulas. The disk friction loss of the impeller is more affected by the surface roughness than the change of the axial clearance. To minimize disk friction loss on the centrifugal compressor impeller, the axial clearance and the theoretical boundary layer thickness should be designed to be the same. The design of the impeller requires careful consideration in order to optimize axial clearance and minimize surface roughness.
The analytical method based on the lifting-surface theory for calculating power and efficiency of the multi-wing cascade configurations of an elastically supported flapping wing power generator is presented. The theoretical results of the power and efficiency for the single, two-wing and three-wing configurations are presented, and the effects of distance between the wings, the oscillation mode (in-phase and anti-phase mode) and aspect ratio on the power and efficiency are clarified. For the single and two-wing configurations, the theoretical results are compared with the experimental data obtained for a hydroelectric power generator, and reasonable agreement of the theory and experiment is obtained. For the effect of aspect ratio, it is shown that the increments of power and efficiency for the middle wing of the three-wing configuration in anti-phase mode of oscillation that are expected by increasing the aspect ratio from three to ten are approximately 61% and 43% at the wing distance of 1.5 chords, respectively.
As the first Korean multi-mission geostationary satellite, Chollian was launched on June 27, 2010. Chollian is being successfully controlled using a satellite ground control system (SGCS) developed by ETRI. A mission planning subsystem (MPS) in SGCS gathers mission requests from users, performs complex mission scheduling, and generates a conflict-free mission schedule. In this paper, we provide an overview of the current mission scheduling algorithms of the Chollian satellite, select three representative constraint checking schemes among these algorithms, and implement new graphics processing unit (GPU)-based constraint checking schemes for the three representative schemes. We compare the performance of the GPU-based and CPU-based constraint checking schemes based on the size of the problem set and the time complexity of the problem. Finally, we suggest a strategy to determine whether or not to adopt GPU for a satellite mission scheduling algorithm.
A time delay control methodology is adopted to cope with degraded control performance due to control surface damage of unmanned aerial vehicles, especially in the case of the automatic landing phase. It is a crucial challenge to maintain consistent control performance even under fault environments such as stuck and/or incipient actuator faults. Flight control systems designed using conventional feedback control methods in such cases may result in unsatisfactory performance, and even worse, may not guarantee the closed-loop stability, which is fatal for aircraft in the state of auto-landing. To overcome the shortfalls of the conventional approach, the time delay control scheme is adopted. This scheme is known to be robust against disturbance, model uncertainties and so on. Motivated by the fact that the abrupt and/or incipient actuator faults focused on in this paper could be considered as model uncertainties, we consider the application of the time delay controller to designing a fault tolerant control system. To show the effectiveness of the time delay control method, a nonlinear 6-DOF simulation is performed under model uncertainties and wind disturbances, and control performance is compared with that of conventional controllers in the case of multiple and single actuator faults.
A new analytical method to calculate the electric current density between two probes in carbon-fiber-reinforced plastic (CFRP) is presented. Unidirectional CFRP has strongly orthotropic electric conductance. Even when electric current is applied to a CFRP plate using two probes on a single surface, the electric current density is not uniform along the cross-section. The electric current is concentrated near the surface where an electric current is applied. Although it is important to know the electric current density in the CFRP plate for the analysis of lightning effects, the density is difficult to calculate using a three-dimensional finite element model. In the present study, the orthotropic coordinate is transformed into a uniform coordinate. Laplace’s equation is solved using the potential theory for a perfect fluid. Equations solved employing an infinite-body approximation are verified with a finite element model. As a result, the new analysis method is demonstrated to be efficient for unidirectional CFRP. The limitations of the method are also discussed.
Viscous flow simulations of the HART II rotor were conducted using a flow solver based on unstructured meshes. To capture the blade-vortex interaction (BVI) phenomena accurately, a series of solution-adaptive mesh refinements was carried out. The blade deformation was considered using the HART II rotor measurement. Calculations were made for isolated-rotor and rotor-fuselage configurations, to investigate the fuselage effect on the blade loading and the rotor wake structure. The inclusion of fuselage significantly improves the trim control prediction, which results from the more accurate prediction of rotor inflow at the front and rear portions of the rotor disk. This improved trim control also leads to an improvement in the blade loading prediction for the rotor-fuselage configuration. From the solution-adaptive mesh refinement study, it was found that high-frequency blade loading caused by BVI can be obtained more accurately as the mesh is further refined, whereas the low-frequency loading is mostly independent to the mesh resolution. The predicted vortex core positions at the retreating side of the rotor were well matched with measurements, whereas a relatively large difference between the prediction and the measurement was observed at the advancing side.
The momentum balance model is applied to a long duct for prediction of the position of the pseudo-shock and its effectiveness is discussed. The model was previously applied to a short duct, where the downstream edge of the shock is at the edge of the duct. In a long duct, the upstream and downstream edges are separated from the duct edges, and the pseudo-shock is in the middle of the duct. The results calculated using the model are compared with experimental results. They showed reasonable agreement. The model will be effective to predict the position of the pseudo-shock even in a long duct.