• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.7
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• pp.85-91
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• 2005

Supersonic jet fighter aircraft must have been guaranteed appropriate for controllability and stability in HAoA(High Angle of Attack) region. Limit value of aircraft enter the deep stall at HAoA is related to problem of aircraft configuration design. But, In order to guarantee the aircraft safety in HAoA, control law is designed using digital Fly-By-Wire flight control system in modern versions of supersonic jet fighter aircraft. Also, In order to recovery if aircraft enter the deep stall or spin, anti-spin control law and MPO(Manual Pitch Override) mode is designed. AoA limiter and MPO is designed in longitudinal axis and HAoA departure prevention logic, roll command limiter, rudder fader and anti-spin logic is designed in lateral-directional axis. In this paper, we introduce the T-50 HAoA flight control law and propose that aircraft stability and adequate of these control law from HAoA flight test.

• Structural Engineering and Mechanics
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• v.11 no.1
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• pp.35-48
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• 2001

The objective of this study is to investigate the stability behavior of steel cable-stayed bridges by comparing the buckling loads obtained by means of finite element methods with eigen-solver. In recent days, cable-stayed bridges dramatically attract engineers' attention due to their structural characteristics and aesthetics. They require a number of design parameters and present a high degree of static indetermination, especially for long span bridges. Cable-stayed bridges exhibit several nonlinear behaviors concurrently under normal design loads due to the individual nonlinearity of substructures such as the pylons, stay cables, and bridge deck, and their interactions. The geometric nonlinearities arise mainly from large displacements of cables. Strong axial and lateral forces acting on the bridge deck and pylons cause structural nonlinear behaviors. The interaction is among the substructures. In this paper, a typical three-span steel cable-stayed bridge with a variety of design parameters has been investigated. The numerical results indicate that the design parameters such as the ratio of $L_1/L$ and $I_p/I_b$ are important for the structural behavior, where $L_1$ is the main span length, L is the total span length of the bridge, $I_p$ is the moment of inertia of the pylon, and $I_b$ is the moment of inertia of the bridge deck. When the ratio $I_p/I_b$ increases, the critical load decreases due to the lack of interaction among substructures. Cable arrangements and the height of pylon are another important factors for this type of bridge in buckling analysis. According to numerical results, the bridges supported by a pylon with harp-type cable arrangement have higher critical loads than the bridges supported by a pylon with fan-type cable arrangement. On contrary, the shape of the pylon does not significantly affect the critical load of this type of bridge. All numerical results have been non-dimensionalized and presented in both tabular and graphical forms.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.361-364
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• 2005

Some bogie frames manufactured in 1999, 2000 year have the fatal problem. Three or four years later, the cracked end beam among them have discovered in 2002, 2003 year. The crack situation of the end beam have a bad effect on brake system. In that case, the cars would be in danger of derailment. To improve the end beam, a research of covering the whole field of welded type bogie frame was started. Main line real tests were performed at Young-Dong line. The stress of main positions for bogie frame was measured. Also up-down direction and left-right direction vibration acceleration of the bogie frame were measured. At this time the tests were performed for the three types bogie. The test result concludes that the crack cause of the end beam is not brake load but vibration at running mainly. It is estimated that the life of the improved car which end beam reinforced is safe within the car permitted life(25 years). The improvement methods of the end beam are presented by construction modification, parts modification. The integrity evaluation is inspected by analysis the real line test results, the improvement methods of the end beam.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.1
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• pp.81-90
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• 1985

For the prediction of the real vibration and stability behaviour of rotor-beaing systems, various additional effects were considered, which are simplified or neglected by conventional modeling of real rotors. These are specially coupled spring and damping coefficients of journal bearings, spring and damping coefficients of external supporting elements for bearings, static load exerting on gears or pulleys by power transmissions, excitation through the gear tolerance or failure, and positive or negative spring and damping characteristics of magnetic or sealing friction force. Considering these effects, a computer program for the calculation of free and forced vibration of rotating shafts supported by two or more bearings is developed, based on the transfer matrixed method. The reliability of the calculated resutls were ascertianed by comparing with the measured data on high speed rotors supported by two journal bearings.

• Geomechanics and Engineering
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• v.32 no.5
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• pp.523-540
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• 2023

The failure of slope can cause remarkable damage to either human life or infrastructures. Stabilizing piles are widely utilized to reinforce slope as a slip-resistance structure. The workability of pile-stabilized slopes is affected by various parameters. In this study, the performance of earth slope reinforced with piles and the behavior of piles under static load, by shear reduction strength method using the finite difference software (FLAC^3D) has been investigated. Parametric studies were conducted to investigate the role of pile length (L), different pile distances from each other (S/D), pile head conditions (free and fixed head condition), the effect of sand density (loose, medium, and high-density soil) on the pile behavior, and the performance of pile-stabilized slopes. The performance of the stabilized slopes was analyzed by evaluating the factor of safety, lateral displacement and bending moment of piles, and critical slip mechanism. The results depict that as L increased and S/D reduced, the performance of slopes stabilized with pile gets better by raising the soil density. The greater the amount of bending moment at the shallow depths of the pile in the fixed pile head indicates the effect of the inertial force due to the structure on the pile performance.

• Geomechanics and Engineering
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• v.36 no.3
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• pp.277-293
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• 2024

Shored Mechanically Stabilized Earth (SMSE) walls are types of soil retaining structures that increase soil stability under static and dynamic loads. The damage caused by an earthquake can be determined by evaluating the probabilistic seismic response of SMSE walls. This study aimed to assess the seismic performance of SMSE walls and provide fragility curves for evaluating failure levels. The generated fragility curves can help to improve the seismic performance of these walls through assessing and controlling variables like backfill surface settlement, lateral deformation of facing, and permanent relocation of the wall. A parametric study was performed based on a non-linear elastoplastic constitutive model known as the hardening soil model with small-strain stiffness, HSsmall. The analyses were conducted using PLAXIS 2D, a Finite Element Method (FEM) program, under plane-strain conditions to study the effect of the number of geogrid layers and the axial stiffness of geogrids on the performance of SMSE walls. In this study, three areas of damage (minor, moderate, and severe) were observed and, in all cases, the wall has not completely entered the stage of destruction. For the base model (Model A), at the highest ground acceleration coefficient (1 g), in the moderate damage state, the fragility probability was 76%. These values were 62%, and 54%, respectively, by increasing the number of geogrids (Model B) and increasing the geogrid stiffness (Model C). Meanwhile, the fragility values were 99%, 98%, and 97%, respectively in the case of minor damage. Notably, the probability of complete destruction was zero percent in all models.

• Journal of Biosystems Engineering
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• v.41 no.4
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• pp.288-293
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• 2016

Purpose: The purpose of this study was to investigate the key factors in designing a three-wheeled two-row soybean reaper (riding type) that is suitable for soybean production, and ensure worker safety by proposing optimal work conditions for the prototype of the designed machine in relation to the slope of the road. Methods: A three-wheeled two-row soybean reaper (riding type) was designed and its prototype was fabricated based on the local soybean-production approach. This approach was considered to be closely related to the prototype-designing of the cutter and the wheel driving system of the reaper. Load distribution on the wheels of the prototype, its minimum turning radius, static lateral overturning angle, tilt angle during driving, and The working and rear overturning (back flip) angle were measured. Based on the gathered information, investigations were conducted regarding optimal work conditions for the prototype. The investigations took into account driving stability and worker safety. Results: The minimum ground clearance of the prototype was 0.5 m. The blade height of the prototype was adjusted such that the cutter was operated in line with the height of the ridges. The load distribution on the prototype's wheels was found to be 1 (front wheel: F): 1.35 (rear-left wheel: RL): 1.43 (rear-right wheel: RR). With the ratio of load distribution between the RL and RR wheels being 1: 1.05, the left-to-right lateral loads were found to be well-balanced. The minimum turning radius of the prototype was 2.0 m. Such a small turning radius was considered to be beneficial for cutting work on small-scale fields. The sliding of the prototype started at $25^{\circ}$, and its lateral overturning started at $39.3^{\circ}$. Further, the critical slope angle for the worker to drive the prototype in the direction of the contour line on an incline was found to be $12.8^{\circ}$, and the safe angle of slope for the cutting was measured to be less than $6^{\circ}$. The critical angle of slope that allowed for work was found to be $10^{\circ}$, at which point the prototype would overturn backward when given impact forces of 1,060 N on its front wheel. Conclusions: It was determined that farmers using the prototype would be able to work safely in most soybean production areas, provided that they complied with safe working conditions during driving and cutting.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2002.05a
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• pp.193-197
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• 2002

The tribological properties and van der Waals attractive forces and the thermal stability of films are very important characteristics of highly hydrophobic fluorocarbon (FC) films for the long-term reliability of nano system. The effect of thermal annealing on films and van der Waals attractive forces and friction coefficient of films have been investigate d in this study. It was coated Al wafer which was treated O2 and Ar that ocatfluorocyclobutane ($C_4_{8}$) and Ar were supplied to the CVD chamber in the ratio of 2:3 for deposition of FC Films. Static contact angle and dynamic contact angle were used to characterize FC films. Thickness of films was measured by variable angle spectroscopy ellipsometer (VASE). Nanotribological data was got by atomic force microscopy (AFM) to measure roughness, lateral force microscopy (LFM) to measure friction force, and force vs. distance (FD) curve to evaluate adhesion force. FC films were cured in N2 and vacuum. The film showed the slight changes in its properties after 3 hr annealing. FTIR ATR studies showed the decrease of C-F peak intensity in the spectra as the annealing time increased. A significant decrease of film thickness has been observed. The friction force of Al surface was at least thirty times higher than ones with FC films. The adhesive force of bare Al was greater than 100 nN. After deposit FC films adhesive force was decreased to 40 nN. The adhesive force of films was decreased down to 10 nN after 24 hr annealing. During 24 hr annealing in $N_2$and vacuum at $100^{\circ}C$ film properties were not changed so much.

• Journal of Biosystems Engineering
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• v.43 no.4
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• pp.311-319
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• 2018

Purpose: The aim of this study is to develop a small combine for harvesting miscellaneous cereal crops. Methods: A prototype small combine was designed and constructed. Its specifications and basic performance were investigated. Results: The prototype small combine for harvesting miscellaneous cereal crops was designed and constructed to reflect similar specifications as those of the conventional combine. The prototype small combine comprises a diesel engine with the rated power/speed of 22.0 kW/2,600 rpm, three-stage primary and two-stage speed range transmission shifts, and a double acting threshing part. The maximum travel speeds of the prototype combine are approximately 0.72 m/s, 2.50 m/s, 0.30 m/s at the low, high speed range shifts in the forward direction, and while traversing in the reverse direction, respectively. The minimum radius of turning was approximately 1.50 m. In a static lateral overturning test, the prototype combine overturned neither to the right nor to left on a $30^{\circ}$ slope. The results of an oilseed rape harvesting test included the maximum operating speed of 0.32 m/s, the grain loss ratio of approximately 9.0%, and the effective field capacity of approximately 10.3 a/h. Additionally, among the outputs in grain outlet, the whole grains, damage grains, and materials other than grain (MOG) ratios accounted for 97.4%, 0.0%, and 2.6%, respectively. Conclusions: The prototype small combine for harvesting miscellaneous cereal crops indicates good driving ability and stability. The results of the oilseed rape harvesting test reveal that the harvesting performance must be enhanced such that the separating and cleaning parts are more suitable for each type of crop, thus reducing grain loss and foreign substances among the outputs in grain outlet. An improved small prototype combine could be used effectively to mechanize the harvesting of miscellaneous cereal crops in small family farms or semi-mountainous areas.

• Earthquakes and Structures
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• v.25 no.5
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• pp.359-367
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• 2023

High-rise structures are considered as symbols of economic power and leadership. Developing countries like India are also emerging as centers for new high-rise buildings (HRB). As the land is expensive and scarce everywhere, construction of tall buildings becomes the best solution to resolve the problem. But, as building's height increases, its stiffness reduces making it more susceptible to vibrations due to wind and earthquake forces. Several systems are available to control vibrations or deflections; however, outrigger systems are considered to be the most effective systems in improving lateral stiffness and overall stability of HRB. In this paper, a 42-storey RCC HRB is analyzed to determine the optimum position of outriggers of different materials. The linear static analysis of the building is performed with and without the provision of virtual outriggers of reinforced cement concrete (RCC) and pre-stressed concrete (PSC) at different storey levels by response spectrum method using finite element based Extended3D Analysis of building System (ETABS) software for determining responses viz. storey displacement, base shear and storey drift for individual models. The maximum allowable limit and percentage variations in earthquake responses are verified using the guidelines of Indian seismic codes. Results indicate that the outriggers contribute in significantly reducing the storey displacement and storey drift up to 28% and 20% respectively. Also, it is observed that the PSC outriggers are found to be more efficient over RCC outriggers. The optimum location of both types of outriggers is found to be at the mid height of building.