• Journal of Institute of Control, Robotics and Systems
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• v.14 no.9
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• pp.916-924
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• 2008

In this paper dynamic modeling parameters were estimated using a frequency domain estimation method. A systematic flight test method was employed using preprogrammed multistep excitation of the swashplate control input. In addition when one axis is excited, the autopilot is engaged in the other axis, thereby obtaining high-quality flight data. A dynamic model was derived for a small scale unmanned helicopter (CNUHELI-020, developed by Chungnam National University) equipped with a Bell-Hiller stabilizer bar. Six degree of freedom equations of motion were derived using the total forces and moments acting on the small scale helicopter. The dynamics of the main rotor is simplified by the first order tip-path plane, and the aerodynamic effects of fuselage, tail rotor, engine, and horizontal/vertical stabilizer were considered. Trim analysis and linearized model were used as a basic model for the parameter estimation. Doublet and multistep inputs are used to excite dynamic motions of the helicopter. The system and input matrices were estimated in the frequency domain using the equation error method in order to match the data of flight test with those of the dynamic modeling. The dynamic modeling and the flight test show similar time responses, which validates the consequence of analytic modeling and the procedures of parameter estimation.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.10
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• pp.1257-1262
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• 2014

The variances of atomization characteristics with the misalignment of injectors defined as the fraction of skewness for various angles of impingement and pressure conditions were studied using the doublet impinging injectors with a like-on-like arrangement. Water was used as simulant and the spray characteristics along with the changes in the skewness were analyzed using the methods of spray image photography. Experiment was carried for the impinging nozzles of orifice diameter of 1.2 mm within Reynolds numbers ranging from $9{\times}10^3-4.5{\times}10^4$ and the fraction of skewness considered for the experiment ranges from 0.0 to 0.9 at ambient temperature condition. Flat sheet with a distinct rim produced perpendicular to the plane of impinging jets goes ondisappear and sheet appears comparatively shorterwith the increase in fraction of skewness resulting the atomization of fluid droplet very close to impingement point with decrease in breakup length and increase in spray angle up to certain extent. The maximum allowable skewness was found as the result. The skewness up to the certain extent can be considered as the parameter to control the atomization characteristics of simulant inside the combustion chamberproviding the high economic performance of fuel and time.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.7
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• pp.29-35
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• 2002

Aeroelastic characteristics of a deployable missile control fin have been investigated. A deployable missile control fin is modeled by a 2-dimensional typical section. Supersonic Doublet-Point method is used for the computation of supersonic unsteady aerodynamic forces and Karpel's Minimum-State approximation is used for the aerodynamic approximation. Root-locus method and time-integration method are used for the linear and nonlinear flutter analyses. For the nonlinear flutter analysis the deployable hinge is represented by a asymmetric bilinear spring and is linearized by using the describing function method. From the flutter analyses, the effects of nonlinear parameters on the aeroelastic characteristics are investigated.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.23 no.4
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• pp.22-29
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• 2015

Quadrotor is widely used in variable application nowadays. Due to its inherent unstable characteristics, control system to augment the stability is essential for quadrotor operation. To design control system and verify its performance through simulation, accurate dynamic model is required. Quadrotor dynamic model is simply compared with conventional rotorcraft such as helicopter. However, the accurate dynamic model of quadrotor is not easy to develop because of the highly correlated aerodynamic effect of each rotor. In this paper, quadrotor dynamic model is identified from the flight data using frequency domain approach. Flight test of quadrotor is performed in closed loop configuration with stability augmentation system included. Frequency sweep input is applied in each of lateral, longitudinal, yaw and heave axis separately. The bare dynamic model is identified from the flight data of quadrotor responses and thrust measurement through Pulse Width Modulation(PWM) data. The frequency responses of identified model match well with those of flight data, and time responses of identified model for doublet input in each axis are also shown to agree with flight data.

• The Korean Journal of Physiology and Pharmacology
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• v.15 no.6
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• pp.371-382
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• 2011

We performed experiments using Aplysia neurons to identify the mechanism underlying the changes in the firing patterns in response to temperature changes. When the temperature was gradually increased from $11^{\circ}C$ to $31^{\circ}C$ the firing patterns changed sequentially from the silent state to beating, doublets, beating-chaos, bursting-chaos, square-wave bursting, and bursting-oscillation patterns. When the temperature was decreased over the same temperature range, these sequential changes in the firing patterns reappeared in reverse order. To simulate this entire range of spiking patterns we modified nonlinear differential equations that Chay and Lee made using temperature-dependent scaling factors. To refine the equations, we also analyzed the spike pattern changes in the presence of potassium channel blockers. Based on the solutions of these equations and potassium channel blocker experiments, we found that, as temperature increases, the maximum value of the potassium channel relaxation time constant, ${\tau}_n(t)$ increases, but the maximum value of the probabilities of openings for activation of the potassium channels, n(t) decreases. Accordingly, the voltage-dependent potassium current is likely to play a leading role in the temperature-dependent changes in the firing patterns in Aplysia neurons.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.3
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• pp.31-39
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• 1999

In this paper, numerical experiment is attempted to analyze and compare the combustion efficiency of the burning sprays due to OFO, FOF triplet / FOOF split doublet injectors. Preconditioned Wavier-Stokes equation system with low Reynolds number $\kappa$-$\varepsilon$ model for turbulence closure, is LU-SGS time-integrated. Spray processes are modeled by DSF analysis with experimentally determined injection characteristics. n-heptane/air global reaction model approximates the combustion for simplicity, and the influence of turbulence on the chemical reaction is included using eddy dissipation model. The results showed the FOF triplet injector of highest combustion efficiency, whereas the OFO type of poet performance. It was also observed that the droplet mean diameter and the average gas temperature due to the mixing efficiency, are the representative parameters for the performance design of combustion.

• Advances in aircraft and spacecraft science
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• v.4 no.4
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• pp.353-369
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• 2017

Flutter is a dangerous phenomenon encountered in flexible structures subjected to aerodynamic forces. This includes aircraft, buildings and bridges. Flutter occurs as a result of interactions between aerodynamic, stiffness, and inertia forces on a structure. In an aircraft, as the speed of the flow increases, there may be a point at which the structural damping is insufficient to damp out the motion which is increasing due to aerodynamic energy being added to the structure. This vibration can cause structural failure, and therefore considering flutter characteristics is an essential part of designing an aircraft. Scientists and engineers studied flutter and developed theories and mathematical tools to analyze the phenomenon. Strip theory aerodynamics, beam structural models, unsteady lifting surface methods (e.g., Doublet-Lattice) and finite element models expanded analysis capabilities. Periodic Structures have been in the focus of research for their useful characteristics and ability to attenuate vibration in frequency bands called "stop-bands". A periodic structure consists of cells which differ in material or geometry. As vibration waves travel along the structure and face the cell boundaries, some waves pass and some are reflected back, which may cause destructive interference with the succeeding waves. This may reduce the vibration level of the structure, and hence improve its dynamic performance. In this paper, for the first time, we analyze the flutter characteristics of a wing with a periodic change in its sandwich construction. The new technique preserves the external geometry of the wing structure and depends on changing the material of the sandwich core. The periodic analysis and the vibration response characteristics of the model are investigated using a finite element model for the wing. Previous studies investigating the dynamic bending response of a periodic sandwich beam in the absence of flow have shown promising results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.54-59
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• 2005

Nonlinear aeroelastic analyses of a missile control fin are performed considering backlash and dynamic stiffness of actuator. Doublet-Hybrid method is used for the calculation of subsonic unsteady aerodynamic forces, and aerodynamic forces are approximated by the minimum-state approximation. For nonlinear flutter analysis backlash is represented by a free-play and is linearized by using the describing function method. Also, dynamic stiffness is function of frequency and is calculated by solving equation of motion for actuator. The linear and nonlinear flutter analyses show that the aeroelastic characteristics are significantly dependent on the backlash and dynamic stiffness. From the nonlinear flutter analysis, various types of limit cycle oscillations are observed in a range of air speeds below the linear divergent flutter boundary. The nonlinear flutter characteristics and the nonlinear aeroelastic responses are also investigated in the time domain.

• BMB Reports
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• v.37 no.2
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• pp.153-158
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• 2004

The acid-labile subunit (ALS) is known to interact with the IGF binding protein (IGFBP) in the presence of insulin-like growth factors (IGFs). Studies, however, indicate that ALS forms a doublet with IGFBP3, independent of IGFs. To characterize the structural domain required for the IGF-free ALS-IGFBP3 interaction, seven recombinant human IGFBP3 mutants were generated: three deletion mutants and four site-specific mutants that had altering N-terminal regions of IGFBP3. ALS and IGFBP3 mRNAs were co-injected into Xenopus oocytes, and their products were cross-linked and immunoprecipitated using antisera against ALS or IGFBP3. Among the deletion mutants, the mutant of D40 (deleted in 11-40th amino acids) exerted no effect in the interaction with ALS, while D60 (${\Delta}11$-60) demonstrated a moderate reduction. D88 (${\Delta}11$-88), however, showed a significant decrease. In the case of site-specific mutants, the mutation that alterated the IGF binding site (codons 56 or 80) exerted a significant reduction in the interaction, whereas codons 72 or 87 showed no significant change in the interaction with ALS. The stability of the ALS-IGFBP3 interaction was analyzed according to a time-dependent mode. Consistent with the binding study, mutants on the IGF binding sites (56 or 80) consistently show a weakness in the ALS-IGFBP3 interaction when compared to the mutants that covered the non-IGF binding sites (72 or 87). This study suggests that the N-terminal of IGFBP3, especially the IGF binding site, plays an important role in interacting with ALS as well as in stabilizing the dual complex, independent of IGFs.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.17 no.2
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• pp.93-98
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• 2024

This paper presents the method to extract the ultrawide-band (UWB) signal and proposes the simple impulse radar system for sensing real-based target within close-range area. The proposed impulse radar system consists of impulse generator, ultrawide-band antennas, function generator, and digital oscilloscope. It is verified by experiment that a differentiated Gaussian pulse is generated with 200ps of pulse width and corresponding spectrum from 0.3 to 4.7 GHz once a sinusoidal wave with 10MHz is excited. The Gaussian doublet is received by identical antennas and it is shown that the UWB pule width of 328ps and its spectrum is from 0.9 to 4.4 GHz. It is confirmed that the UWB pulse is extracted when the real-based targets such as circular target with 4cm radius and corner reflector are placed at the close-range area.