• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.41 no.1
• /
• pp.31-39
• /
• 2013

A Quad Tilt Wing UAV is a new concept hybrid UAV having the advantages of both fixed-wing and rotary-wing aircraft. This paper presents longitudinal flight dynamic characteristics of a Quad Tilt Wing UAV. The designed Quad Tilt Wing UAV is a configuration of a tandem wing type aircraft with an actuating motor and propeller mounted at each wing. Momentum theory is used to calculate the thrust, and nonlinear modeling is performed considering lift and drag generated by slip stream effect of propellers. Also, Force and moment variation at each tilting angle is considered. Static trim on longitudinal axis is analyzed via numerical simulation. Componentwise force contribution was analyzed at each trim mode. Dynamic characteristics were evaluated through eigenvalue analysis for a linear model at each flight mode. It is verified that longitudinal dynamic characteristics are changing from unstable to stable state by continuous transition of dominant poles.

• Structural Engineering and Mechanics
• /
• v.78 no.2
• /
• pp.163-174
• /
• 2021

Track-bridge interaction has become an essential part in the design of bridges and rails in terms of modern railways. As a unique ballastless slab track, the longitudinal continuous slab track (LCST) or referred to as the China railway track system Type-II (CRTS II) slab track, demonstrates a complex force mechanism. Therefore, a comprehensive track-bridge interaction study between multi-span simply supported beam bridges and the LCST is presented in this work. In specific, we have developed an integrated finite element model to investigate the overall interaction effects of the LCST-bridge system subjected to the actions of temperature changes, traffic loads, and braking forces. In that place, the deformation patterns of the track and bridge, and the distributions of longitudinal forces and the interfacial shear stress are studied. Our results show that the additional rail stress has been reduced under various loads and the rail's deformation has become much smoother after the transition of the two continuous structural layers of the LCST. However, the influence of the temperature difference of bridges is significant and cannot be ignored as this action can bend the bridge like the traffic load. The uniform temperature change causes the tensile stress of the concrete track structure and further induce cracks in them. Additionally, the influences of the friction coefficient of the sliding layer and the interfacial bond characteristics on the LCST's performance are discussed. The systematic study presented in this work may have some potential impacts on the understanding of the overall mechanical behavior of the LCST-bridge system.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.13 no.6
• /
• pp.998-1005
• /
• 2010

Rifling force has a torsion impulse effect on the gun tube and thus generates undesirable vibration of the gun tube about its bore axis, putting additional stress on the projectile. High rifling force at the muzzle of the gun tube may adversely influence the trajectory of the projectile. And, the service life of rifled gun barrels is known to depend on the rifling force. Rifling force along the path of the projectile in the longitudinal direction of the gun tube can be described with projectile mass, projectile velocity, gas pressure curve and rifling angle. Under the same conditions, the character of the rifling of the gun barrel decisively influences the rifling force curve. To reduce the above mentioned harmful effect, locally distinct maximum of rifling force has to be avoided and maximum rifling force needs to be minimized. The best way to minimize the maximum rifling force is to design a rifling angle function so that the rifling force curve has a near trapezoidal shape. In this paper a new approach to make the optimal rifling force curve is described. The rifling angle determining the rifling force is developed by combined Fourier series and polynomial function to satisfy both the convergence and boundary condition matching problems.

• Journal of the Korea Concrete Institute
• /
• v.25 no.1
• /
• pp.19-28
• /
• 2013

The longitudinal axial strain in the plastic hinge region of reinforced concrete (RC) columns influences on the structural behavior of RC structures subjected to reversed cyclic loading. This strain decreases the effective compressive strength of concrete and increases the lateral displacements between stories by causing the elongation of member length. This paper investigated the effects of the axial force on the elongation of a RC member by using a sectional analysis of RC members. The analytical and experimental results indicated that the axial force decreased the axial strain in the plastic hinge region of RC columns. In this study, a model was proposed to predict the axial strain of RC columns. The proposed model considering the effects of axial force ratio consisted of three path types ; Path 1-loading region, Path 2-unloading region, and Path 3-reversing cyclic loading region. The axal strains predicted by the proposed model were compared with the test results of RC columns with various axial force ratios, and agreed reasonably with the observed longitudinal strains.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2001.11a
• /
• pp.941-946
• /
• 2001

The objectives of this study are to investigate effective stiffness of Rectangular reinforced concrete bridge columns. It is reasonable to use yielding effective stiffness of columns in seismic bridge design, especially in case that plastic hinges form at the bridge columns. In this study, the material nonlinear analysis was conducted for 3, 240 column sections of which variables were the concrete compressive stress, the steel yielding stress, the longitudinal steel location parameter, the longitudinal steel ratio, the axial load level, and the diameter of section. Based on the analytical results, an effective stiffness including two variables(longitudinal steel ratio and axial load ratio) was proposed by regression analyses, and it is compared with test results and the proposed equation for yielding effective stiffness of circular bridge columns.

• The Transactions of the Korean Institute of Electrical Engineers D
• /
• v.50 no.3
• /
• pp.130-135
• /
• 2001

In this paper, an observer-based adaptive controller is proposed to control the longitudinal motion of vehicles. The standard gradient method will be used to estimate the vehicle parameters, mass, time constant, etc. The nonlinear model between the driving force and the vehicle acceleration will be chosen to design the state observer for the vehicle velocity and acceleration. It will be shown that the proposed observer is exponentially stable, and that the adaptive controller proposed on this paper is stable. It will be proved that the errors of the relative distance, velocity and acceleration converge to zero asymptotically fast, and that the overall system is also asymptotically stable. The simulation results are presented to investigate the effectiveness of the proposed method.

• Computers and Concrete
• /
• v.10 no.6
• /
• pp.663-681
• /
• 2012

This paper presents a parametric study of the plastic hinge length of circular reinforced concrete columns using a three-dimensional finite element analysis method, and using the Taguchi robust design method to reduce computational cost. Parameters examined include the longitudinal reinforcing ratio, the shear span-to-depth ratio, the axial force ratio and the concrete compressive strength. The study considers longitudinal reinforcement with yield strengths of 414 MPa and 685 MPa, and proposes simplified formulas for the plastic hinge length of circular reinforced concrete columns, showing that increases in plastic hinge length correlate to increases in the axial load, longitudinal reinforcing and shear span-to-depth ratios. As concrete strength increases, the plastic hinge length decreases for the 414 MPa case but increases for the 685 MPa case.

• Journal of the Korean Society for Railway
• /
• v.5 no.1
• /
• pp.1-9
• /
• 2002

Where the track is continuously welded over the bridge, the longitudinal forces will be distributed interactively between the track and the sub-structure by the rail-bridge interaction mechanism. The ratio between the longitudinal forces transmitted in each elements depends on the magnitude of the ballast resistance and the stiffness of the sub-structures. In this paper, the main factors affect on the longitudinal rail force are discussed and the parametric study for the behavior of CWR(Continuous Welded Rail) track was executed. It is concluded that the horizontal ballast resistance and the stiffness of the bridge sub-structure are the significant parameters affecting the stability of the continuous welded rail track.

• The Transactions of the Korean Institute of Electrical Engineers
• /
• v.40 no.5
• /
• pp.496-500
• /
• 1991

The effects of annealing with and without magnetic field on magnetic properties of amorphous Fe-B-Si cores have been investigated as a function of toroidal stress. By decreasing the toroidal stress, the magnetic properties of the amorphous ribbon have beenimproved. Near 180 domain walls exist in the thermally annealed toroidal cores, but the domain walls exist in the thermally annealed toroidal cores, but the domain walls are not parallel to the longitudinal direction of the ribbon. In the specimen annealed with a magnetic field strength of 10 Oe in the longitudinal ribbon length axis, the domains are nearly parallel to the longitudinal direction due to the field induced uniaxial anisotropy resulting in further increase in the remanent magnetization and decrease in the coercive force and loss.

• Multiscale and Multiphysics Mechanics
• /
• v.1 no.3
• /
• pp.261-270
• /
• 2016

The longitudinal velocity (forward speed) having significant importance in proper running of railway wheelset on track, depends greatly upon the adhesion ratio and creep analysis by implementation of suitable dynamic system on contamination. The wet track condition causes slip and slide of vehicle on railway tracking, whereas high speed may also increase slip and skidding to severe wear and deterioration of mechanical parts. The basic aim of this research is to design appropriate model aimed estimator that can be used to control railway vehicle forward velocity to avoid slip. For the filtration of disturbance procured during running of vehicle, the kalman filter is applied to estimate the actual signal on preferered samples of creep co-efficient for observing the applied attitude of noise. Thus error level is detected on higher and lower co-efficient of creep to analyze adhesion to avoid slip and sliding. The skidding is usually occurred due to higher forward speed owing to procured disturbance. This paper guides to minimize the noise and error based upon creep coefficient.