• Journal of Biosystems Engineering
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• v.16 no.2
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• pp.124-132
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• 1991

This study was carried out to obtain the information needed in the development of forward speed control system and the improvement of combine performance. The effects of variety, grain moisture content and forward speed on the combine load characteristics were investigated through experiments. The results of this study are summarized as follows. 1. A data acquisition system was developed to measure the engine speed and the torques and speeds of the threshing cylinder, dean-grain auger and tailings-return auger. The system consisted of transducers, signal conditioner, interface board and microcomputer. The system accuracy is better than ${\pm}2.3%$ full scale. 2. Linear regression equations were obtained for the torque, speed and power requirement of threshing cylinder for different paddy varieties, grain moisture contents and feed rates. 3. The maximum value of relative frequency for threshing cylinder torque decreased as the increase in feed rate and moisture content. The range of torque fluctuation was 1.2~3.7 and 1.2~1.9 times the average and maximum torque, respectively. The maximum value of power spectrum density (PSD) appeared to be about 11 Hz regardless of paddy variety, grain moisture content and feed rate. 4. The speed of tailings return thrower decreased rapidly at below 900rpm, and it fell to near zero about 3 seconds after that time. When the travelling of combine harvester was stopped immediately after sensing the overload, it took about 7 seconds for a full recovery of the no-load speed of tailings return thrower.

• Structural Engineering and Mechanics
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• v.26 no.6
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• pp.725-739
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• 2007

In recent years there are many plate bending elements that emerged for solving both thin and thick plates. The main features of these elements are that they are based on mix formulation interpolation with discrete collocation constraints. These elements passed the patch test for mix formulation and performed well for linear analysis of thin and thick plates. In this paper a member of this family of elements, namely, the Discrete Reissner-Mindlin (DRM) is further extended and developed to analyze both thin and thick plates with geometric nonlinearity. The Von K$\acute{a}$rm$\acute{a}$n's large displacement plate theory based on Lagrangian coordinate system is used. The Hu-Washizu variational principle is employed to formulate the stiffness matrix of the geometrically Nonlinear Discrete Reissner-Mindlin (NDRM). An iterative-incremental procedure is implemented to solve the nonlinear equations. The element is then tested for plates with simply supported and clamped edges under uniformly distributed transverse loads. The results obtained using the geometrically NDRM element is then compared with the results of available analytical solutions. It has been observed that the NDRM results agreed well with the analytical solutions results. Therefore, it is concluded that the NDRM element is both reliable and efficient in analyzing thin and thick plates with geometric non-linearity.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.6
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• pp.507-515
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• 2017

Flexible multibody simulations are widely used in the industry to design mechanical systems. In flexible multibody dynamics, deformation coordinates are described either relatively in the body reference frame that is floating in the space or in the inertial reference frame. Moreover, these deformation coordinates are generated based on the discretization of the body according to the finite element approach. Therefore, the formulation of the flexible multibody system always deals with a huge number of degrees of freedom and the numerical solution methods require a substantial amount of computational time. Parallel computational methods are a solution for efficient computation. However, most of the parallel computational methods are focused on the efficient solution of large-sized linear equations. For multibody analysis, we need to develop an efficient formulation that could be suitable for parallel computation. In this paper, we developed a subsystem synthesis method for a flexible multibody system and proposed efficient parallel computational schemes based on the OpenMP API in order to achieve efficient computation. Simulations of a rotating blade system, which consists of three identical blades, were carried out with two different parallel computational schemes. Actual CPU times were measured to investigate the efficiency of the proposed parallel schemes.

• Journal of Navigation and Port Research
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• v.29 no.10 s.106
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• pp.839-845
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• 2005

A rudder roll control system is developed and analyzed to control the yawing and rolling motion of ship in irregular waves. The 4-DOF maneuvering equations of motion are derived to carry out the simulation of the motion of a ship and the wave forces are considered as the external forces of a ship in the simulation. The wave forces in the time domain analysis are generated from the frequency transfer function calculated by 3-D source distribution method. The rudder roll control system is developed by linear combination of PD rudder controllers of yawing and rolling motion. Rudder rate speed and Schilling rudder are considered to increase the roll reduction efficiency.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.1 s.178
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• pp.113-120
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• 2006

This paper proposed the control algorithm fur aspheric surface grinding and was verified by the experiment. The functions of the algorithm were simultaneous control of the position and interpolation of the aspheric curve. The non-linear formula of the tool position was derived from the aspheric equations and the shape of the tool. The function was partitioned by an certain interval and the control parameters were calculated at each control section. The movement in a session was interpolated with acceleration and velocity. The position error was feed-backed by rotary encorder. The concept of feedback algorithm was correcting position error by increasing or decreasing the speed. In the experiment, two-axis machine was controlled to track the aspheric surface by the proposed algorithm. The effect of the control and process parameters was monitored. The result showed that the maximum tracking error was under sub-micro level for the concave and convex surfaces.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.3
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• pp.322-329
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• 2001

A study of the shock wave turbulent boundary layer interaction is presented. The focus of the study is the interactions of the shock waves with the turbulent boundary layer on the falt plate. Three examples are investigated. The computations are performed, using mixed explicit-implicit generalized Galerkin finite element method. The linear equations at each time step are solved by a preconditioned GMRES algorithm. Numerical results indicate that the implicit scheme converges to the asymptotic steady state much faster than the explicit counterpart. The computed surface pressures and skin friction coefficients display good agreement with experimental data. The flowfield manifests a complex shock wave system and a pair of counter-rotating vortices.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2005.10a
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• pp.55-61
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• 2005

A rudder roll control system is developed and analyzed to control yawing and rolling motion of ship in irregular waves. The 4-DOF maneuvering equations of motion are derived to carry out the simulation of the motion of a ship and the wave forces are considered as the external forces of a ship in the simulation. The wave forces in the time domain analysis are generated from the frequency transfer function calculated by 3-D source distribution method. The rudder roll control system is developed by linear combination of PD rudder controllers of yawing and rolling motion Rudder rate speed and Schilling rudder are considered to increase roll reduction efficiency.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.387-391
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• 2009

The experimental study on the ducted fan for the propulsion system of a small UAV has been performed. In this paper, to investigate the three-dimensional unsteady flow field characteristics of the ducted fan, it was measured by using a $45^{\circ}$ inclined hot-wire from hub to tip at inlet, behind the rotor and outlet of the ducted fan. The hot-wire signal data was acquired at fixed yaw angle. The data was averaged by using the PLEAT (Phase Locked Ensemble Averaging Technique), and then three of non-linear equations were solved simultaneously by using the Newton-Rhapson numerical method. Flow characteristics such as tip vortex, secondary flow and tip leakage flow were confirmed through axial, radial and tangential contour plot.

• Coupled systems mechanics
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• v.8 no.2
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• pp.129-146
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• 2019

The main goal of this work is to develop a numerical simulator to study an isothermal single-phase two-component flow in a naturally fractured oil reservoir, taking into account advection and diffusion effects. We use the Peng-Robinson equation of state with a volume translation to evaluate the properties of the components, and the discretization of the governing partial differential equations is carried out using the Finite Difference Method, along with implicit and first-order upwind schemes. This process leads to a coupled non-linear algebraic system for the unknowns pressure and molar fractions. After a linearization and the use of an operator splitting, the Conjugate Gradient and Bi-conjugated Gradient Stabilized methods are then used to solve two algebraic subsystems, one for the pressure and another for the molar fraction. We studied the effects of fractures in both the flow field and mass transport, as well as in computing time, and the results show that the fractures affect, as expected, the flow creating a thin preferential path for the mass transport.

• Journal of Ocean Engineering and Technology
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• v.19 no.2 s.63
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• pp.67-73
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• 2005

This paper describes depth, heading and speed control of an underwater vehicle that has four stern thrusters of which forces are coupled in the diving and, steering motion, as well as the speed of the vehicle. The optimal linear quadratic controller is designed based on a linearized- state space model, developed by combining the dynamic equations of speed, steering and diving motion. The designed controller gives provides an optimal thrust distribution, minimizing the given performance index to control speed, depth and heading simultaneously. To validate the performance of the controller, a simulation and tank-test are carried out with DUSAUV (Dual Use Semi-Autonomous Underwater Vehicle), developed by KORDI as a test-bed for testing new underwater technologies. Optimal gains of the controller are tuned, using a computer simulation environment with a nonlinear 6-DOF numerical DUSAUV model, developed by PMM (Planner Motion Mechanism) test. To verify the performance of the presented controller in experiment, a tank-test with DUSAUV is carried out in the ocean engineering basin in KORDI. The experimental results are also compared with the simulation results to investigate the accordance of the numerical and the real mode.