• Journal of the Korean Society of Visualization
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• v.7 no.1
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• pp.14-20
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• 2009

In comparison with previous researches fur swirling flow, the spiral flow self-generated in the spiral flow nozzle has some different characteristics. It is not needed a compulsive tangential momentum to get its velocity component and has long potential core, relatively low swirl ratio, and high focusing ability. In this study, the self-generated mechanism of the spiral flow was clarified and the effect on the width of annular slit on spiral flow characteristics was investigated experimentally and numerically. As a result, the existence of tangential velocity component regardless of a compulsive angular momentum is clarified and the results obtained by experiment have a satisfactory agreement with those by numerical method, quantitatively and qualitatively.

• 한국가시화정보학회:학술대회논문집
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• 2007.11a
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• pp.143-148
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• 2007

In comparison with previous researches for swirling flow, the spiral flow self-generated in the spiral flow nozzle has some different characteristics. It is not needed a compulsive tangential momentum to get its velocity component and has long potential core, relatively low swirl ratio, and high focusing ability. In this study, the self-generated mechanism of the spiral flow was clarified and the effect on the width of annular slit on spiral flow characteristics was investigated experimentally and numerically. As a result, the existence of tangential velocity component regardless of a compulsive angular momentum is clarified and the results obtained by experiment have a satisfactory agreement with those by numerical method, quantitatively and qualitatively.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.888-893
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• 2008

In This paper proposes the control algorithm for quadruped robots on irregularly sloped uneven surface. Body balance is important in stable running locomotion. Since the body balance is determined by the forces applied at the feet during touchdown phase, the ground reaction force is controlled for stable running. To control the forces at each foot, the desired force is generated. The generated desired force is compared with actual contact force, then, the difference between them modifies the foot trajectory. The desired force is generated by combination of the rate change of the angular and linear momentum at flight. Then the rate change of momentum determines each force distribution. The distribution of the force is carried out by fuzzy logic. The computer simulation is carried out with the commercial software RecurDyn$^{(R)}$. Dynamic model simulation program show that the stable running on the irregularly sloped uneven surface are accomplished by the proposed method.

• Coupled systems mechanics
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• v.4 no.1
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• pp.1-18
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• 2015

The state-based peridynamics is considered a nonlocal method in which the equations of motion utilize integral form as opposed to the partial differential equations in the classical continuum mechanics. As a result, the enforcement of boundary conditions in solid mechanics analyses cannot follow the standard way as in a classical continuum theory. In this paper, a new approach for the boundary condition enforcement in the state-based peridynamic formulation is presented. The new method is first formulated based on a convex kernel approximation to restore the Kronecker-delta property on the boundary in 1-D case. The convex kernel approximation is further localized near the boundary to meet the condition that recovers the correct boundary particle forces. The new formulation is extended to the two-dimensional problem and is shown to reserve the conservation of linear momentum and angular momentum. Three numerical benchmarks are provided to demonstrate the effectiveness and accuracy of the proposed approach.

• Interaction and multiscale mechanics
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• v.7 no.1
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• pp.525-542
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• 2014

The state-based peridynamics is considered a nonlocal method in which the equations of motion utilize integral form as opposed to the partial differential equations in the classical continuum mechanics. As a result, the enforcement of boundary conditions in solid mechanics analyses cannot follow the standard way as in a classical continuum theory. In this paper, a new approach for the boundary condition enforcement in the state-based peridynamic formulation is presented. The new method is first formulated based on a convex kernel approximation to restore the Kronecker-delta property on the boundary in 1-D case. The convex kernel approximation is further localized near the boundary to meet the condition that recovers the correct boundary particle forces. The new formulation is extended to the two-dimensional problem and is shown to reserve the conservation of linear momentum and angular momentum. Three numerical benchmarks are provided to demonstrate the effectiveness and accuracy of the proposed approach.

• Wind and Structures
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• v.32 no.2
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• pp.81-87
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• 2021

The aim of the current study is to compare the performance of large 2 MW and 3 MW wind turbines operating on existing onshore wind farms using Blade Element Momentum (BEM) theory and Angular Momentum (AM) theory and illustrate the performance characteristic curves of the turbines as a function of wind speed (U∞). To achieve this, the measurement data obtained from two different Wind Energy Power Plants (WEPPs) located in the Hatay region of Turkey was used. Two different horizontal-axis wind turbines with capacities of 2 MW and 3 MW were selected for evaluation and comparison. The hub-height wind speed (UD), turbine power output (P), atmospheric air temperature (Tatm) and turbine rotational speed (Ω) data were used in the evaluation of the turbine performance characteristics. Curves of turbine power output (P), axial flow induction factor (a), turbine rotational speed (Ω), turbine power coefficient (CP), blade tip speed ratio (λ), thrust force coefficient (CT) and thrust force (T) as a function of U∞ were obtained for the 2 MW and 3 MW wind turbines and these characteristic curves were compared. Results revealed that, for the same wind speed conditions, the higher-capacity wind turbine (3 MW) was operating at higher turbine power coefficient rates, while rotating at lower rotational speed ratios than the lower-capacity wind turbine (2 MW).

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.5
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• pp.65-73
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• 2004

CMG(Control Momentum Gyro) is a control device being used for spacecraft attitude control constructing relatively large amount of torque compared to conventional body-fixed reaction wheels. The CMG produces gyroscopic control torque by continuously varying the angular momentum vector direction with respect to the spacecraft body. The VSCMG(Variable Speed Control Momentum Gyro) has favorable advantages with variable speed to lead to better control authority as well as singularity avoidance capability. Attitude dynamics with a VSCMG mounted on a two-axis gimbal system are derived in this study. The dynamic equation may be considered as an extension of the single-axis counterpart. Also, a feedback control law design is addressed in conjunction with the dynamic equations of motion.

• The Journal of Advanced Prosthodontics
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• v.2 no.4
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• pp.148-153
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• 2010

PURPOSE. The aim of this study was to investigate a comparison of implant bone bed preparation with Er,Cr:YSGG laser and conventional drills on the relationship between implant stability quotient (ISQ) values and implant insertion variables. MATERIALS AND METHODS. Forty implants were inserted into two different types of pig rib bone. One group was prepared with conventional drills and a total of 20 implants were inserted into type I and type II bone. The other group was prepared with a Er,Cr:YSGG laser and a total of 20 implants were inserted into type I and type II bone. ISQ, maximum insertion torque, angular momentum, and insertion torque energy values were measured. RESULTS. The mean values for variables were significantly higher in type I bone than in type II bone (P < .01). In type I bone, the ISQ values in the drill group were significantly higher than in the laser group (P < .05). In type II bone, the ISQ values in the laser group were significantly higher than in the drill group (P < .01). In both type I and type II bone, the maximum insertion torque, total energy, and total angular momentum values between the drill and laser groups did not differ significantly (P ${\geq}$ .05). The ISQ values were correlated with maximum insertion torque (P < .01, r = .731), total energy (P < .01, r = .696), and angular momentum (P < .01, r = .696). CONCLUSION. Within the limitations of this study, the effects of bone bed preparation with Er,Cr:YSGG laser on the relationship between implant stability quotient (ISQ) values and implant insertion variables were comparable to those of drilling.

• Current Optics and Photonics
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• v.3 no.4
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• pp.275-284
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• 2019

Chirality is ubiquitous in physics and biology from microscopic to macroscopic phenomena, such as fermionic interactions and DNA duplication. In photonics, chirality has traditionally represented differentiated optical responses for right and left circular polarizations. This definition of optical chirality in the polarization domain includes handedness-dependent phase velocities or optical absorption inside chiral media, which enable polarimetry for measuring the material concentration and circular dichroism spectroscopy for sensing biological or chemical enantiomers. Recently, the emerging field of non-Hermitian photonics, which explores exotic phenomena in gain or loss media, has provided a new viewpoint on chirality in photonics that is not restricted to the traditional polarization domain but is extended to other physical quantities such as the orbital angular momentum, propagation direction, and system parameter space. Here, we introduce recent milestones in chiral light-matter interactions in non-Hermitian photonics and show an enhanced degree of design freedom in photonic devices for spin and orbital angular momenta, directionality, and asymmetric modal conversion.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.5
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• pp.389-397
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• 2021

The control characteristics after the failure of the control moment gyros, the actuators for satellite attitude control, were analyzed. In particular, the situation where one out of four failed was considered. For the most commonly used pyramids and box-90 structures, the singularities and singular surfaces after failure were analyzed and compared. Dynamic equations for the process of reducing the wheel speed after the failure were derived. The process of stabilizing the angular velocity of a satellite while absorbing the momentum of the faulty module by the three normal modules was analyzed. For singular shapes, the remaining CMGs may be locked or excessively shake. The authors proposed that it can be prevented by rearranging the gimbal angles.