• Wind and Structures
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• v.8 no.6
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• pp.443-454
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• 2005

Wind loading is very important, even dominant in some cases, to large-span single-layer reticulated shells. At present, usually equivalent static methods based on quasi-steady assumption, as the same as the wind-resistant design of low-rise buildings, are used in the structural design. However, it is not easy to estimate a suitable equivalent static wind load so that the effects of fluctuating component of wind on the structural behaviors, especially on structural stability, can be well considered. In this paper, the effects of fluctuating component of wind load on the stability of a single-layer reticulated spherical shell model are investigated based on wind pressure distribution measured simultaneously in the wind tunnel. Several methods used to estimate the equivalent static wind load distribution for equivalent static wind-resistant design are reviewed. A new simple method from the stability point of view is presented to estimate the most unfavorable wind load distribution considering the effects of fluctuating component on the stability of shells. Finally, with comparisive analyses using different methods, the efficiency of the presented method for wind-resistant analysis of single-layer reticulated shells is established.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.3
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• pp.129-135
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• 2000

Air-dynamic bearings are increasingly used in supporting small high-speed rotating bodies. This study investigates the effects of design parameters on the axial stiffness of spiral-grooved air bearings of various curvatures. Design parameters are fundamental clearance, groove depth, and bearing number. The pressure distribution at the clearance between the stator and rotor of the bearing is obtained by solving the Reynolds equation, and the supporting load and the axial linear stiffness are calculated from the pressure distribution. It is found that a larger curvature increases the axial linear stiffness more and that there exist an optimal groove depth for the linear stiffness of the air bearing. It is also found that the linear stiffness has a linear relationship with the bearing number.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.149-156
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• 2002

Field measurements were carried out in this study to investigate the behavior of cut and cover tunnel such as the distribution and the magnitude of the earth pressure during back fill process of the ground material. Three kinds of measuring instruments, such as the earth pressure load cell, the concrete strain gauge and the reinforcing bar meter of embedded type in concrete structure were installed and measured. Earth pressure load cells, installed after construction of the tunnel lining, measure the outside forces acting on the tunnel lining with radial directions. Three load cells were installed at the crown, the right and the left shoulder of the tunnel, respectively. Three sets of reinforcing bar meter were installed in the double reinforcements of the tunnel lining and their locations were the same with the position of the earth pressure load cells. Concrete strain gauge was installed only one site of the upper compressive part at the tunnel crown. Based on the measuring results in the field, the deformation and the earth pressure acting on the tunnel lining were investigated with the back fill process of the ground material. Considerations on the validity of the measuring results were paid. For the analysis of measurements, after dividing back fill process into three steps, various factors which affect on the behavior of tunnel lining were investigated at each step.

• Journal of Mechanical Science and Technology
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• v.15 no.1
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• pp.66-80
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• 2001

In brake systems, a proportioning valve(P. V), which reduces the brake line pressure on each wheel cylinder for the anti-locking of rear wheels, is closely related to the safety of vehicles. However, it is impossible for current P. V. s to completely control brake line pressure because, mechanically, it is an open loop control system. In this paper we describe an electronic brake force distribution system using a direct adaptive fuzzy controller in order to completely control brake line pressure using a closed loop control system. The objective of the electronic brake force distribution system is to change the cut-in-pressure and the valve slop of the P. V in order to obtain better performance of the brake system than with mechanical systems.

• Geomechanics and Engineering
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• v.37 no.4
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• pp.383-393
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• 2024

Monopile foundations of offshore wind turbines embedded in soft clay are subjected to the long-term cyclic lateral loads induced by winds, currents, and waves, the vibration of monopile leads to the accumulation of pore pressure and cyclic strains in the soil in its vicinity, which poses a threat to the safety operation of monopile. The researchers mainly focused on the hysteretic stress-strain relationship of soft clay and kinds of stiffness degradation models have been adopted, which may consume considerable computing resources and is not applicable for the long-term bearing performance analysis of monopile. In this study, a modified cyclic stiffness degradation model considering the effect of plastic strain and pore pressure change has been proposed and validated by comparing with the triaxial test results. Subsequently, the effects of cyclic load ratio, pile aspect ratio, number of load cycles, and length to embedded depth ratio on the accumulated rotation angle and pore pressure are presented. The results indicate the number of load cycles can significantly affect the accumulated rotation angle of monopile, whereas the accumulated pore pressure distribution along the pile merely changes with pile diameter, embedded length, and the number of load cycles, the stiffness of monopile can be significantly weakened by decreasing the embedded depth ratio L/H of monopile. The stiffness degradation of soil is more significant in the passive earth pressure zone, in which soil liquefaction is likely to occur. Furthermore, the suitability of the "accumulated rotation angle" and "accumulated pore pressure" design criteria for determining the required cyclic load ratio are discussed.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.6
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• pp.77-87
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• 2012

Recently, Load and Resistance Factor Design (LRFD) based on reliability analysis has become a global trend for economical and rational design. In order to implement the LRFD, quantification of uncertainty for load and resistance should be done. The reliability of result relies on input variable, and therefore, it is important to obtain exact uncertainty properties of load and resistance. Since soil stress is the main reason causing the settlement or deformation of ground and load on the underground structure, it is essential to clarify the uncertainty of soil stress distribution for accurately predict the uncertainty of load in LRFD. In this study, laboratory model test on silty sand bed under probabilistic load is performed to observe propagation of upper load uncertainty. The results show that the coefficient of variation (COV) of soil stress are varied depending on location due to non-linear relationship between upper load increment and soil pressure increment. In addition, when the load uncertainty is transmitted through ground, COV is decreased by damping effect.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.6
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• pp.31-38
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• 2005

Aerodynamic influence coefficient linearly relates pressure with downwash in panel method for load analysis in which the viscosity of a flow is ignored and the compressibility cannot be taken into account in transonic region. Since the planform of an aerodynamic surface determines the coefficient, the panel method has a limit to the analysis of low Reynolds number flow. The accuracy of the pressure distribution can be improved by a direct correction to the pressure or a correction to the downwash, which is considered the change of camber or thickness, using the aerodynamic coefficients from wind tunnel test as constraints. A premultiplying correction method as well as a postmultiplying correction method is applied to a micro air vehicle to provide more accurate aerodynamic pressure for trim and load analyses. Theoretical aerodynamic pressure is obtained from the panel method. Correction factor matrix and correct pressure coefficient are computed for the conditions with two constraints in addition to single constraint. The postmultiplying correction method gives a better improvement in pressure distribution on micro air vehicle due to the flow characteristics on it.

• Tribology and Lubricants
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• v.10 no.2
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• pp.30-38
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• 1994

The thermohydrodynamic(THD) performance of a large tilting pad journal bearing is investigated both theoretically and experimentally. The theory takes into account the three dimensional variation of lubricant viscosity and eddy viscosity, and the inlet pressure. Owing to the inlet pressure effect, the film pressure and load capacity are increased but the mixing temperature and bearing surface temperature are decreased. The continuous distribution of the film pressure and film thickness and the bearing surface temperature are measured along with the shaft speed and the bearing load, and they are compared with the theoretical results. The results obtained by the experiment are in good agreement with those by the theory including the inlet pressure effect. It is suggested that the three dimensional turbulent THD analysis including the inlet pressure effect is very useful to predict the performance of the large tilting pad journal bearing more accurately.

• Tribology and Lubricants
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• v.14 no.1
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• pp.7-13
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• 1998

The static characteristics of a five-pad tilting pad journal bearing of load on pad (LOP) type have been investigated experimentally under the different values of bearing load and shaft speed. The diameter and length of the bearing are 300.91 mrn and 149.8 mm, reslx;ctively. Circumferential distribution of the film pressure, film thickness, journal surface temperature and beating surface temperature are measured. A noticeable inlet pressure rise is observed at the entrance of each pad, especially the bottom pad. The inlet pressure is increased by the increase of shaft speed as well as bearing load. In the five-pad tilting pad joumal bearing of LOP type, almost all of beating load is being carried only by the bottom pad. The maximum bearing surface temperature is observed at near the minimum film thickness. It is observed that the metal temperature of the mid-plane is higher than that of the edge at the inlet region, while the metal temperature of the edge is higher than that of the mid-plane at the outlet region.

• Tribology and Lubricants
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• v.8 no.1
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• pp.30-37
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• 1992

The displacement and pressure field of liquid crystals are analyzed numerically and compared with classical Reynolds theory. A plane slider bearing is employed as a simple example considering elasticity, permeability and splay effect which are the inherent characteristics of layered liquid crystals. Due to the geometric constraint of thin wedge and the strong anchoring behavior of the liquid crystals dislocations are inevitable. A finite element method is used to solve five coupled nonlinear equations. The load characteristics based on the pressure distribution along the gap shows that the liquid crystals can carry large load compared to the conventional lubricants.