• Structural Engineering and Mechanics
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• v.48 no.3
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• pp.415-434
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• 2013

This work is concerned with transverse vibrations of axially traveling nanobeams including strain gradient and thermal effects. The strain gradient elasticity theory and the temperature field are taken into consideration. A new higher-order differential equation of motion is derived from the variational principle and the corresponding higher-order non-classical boundary conditions including simple, clamped, cantilevered supports and their higher-order "offspring" are established. Effects of strain gradient nanoscale parameter, temperature change, shape parameter and axial traction on the natural frequencies are presented and discussed through some numerical examples. It is concluded that the factors mentioned above significantly influence the dynamic behaviors of an axially traveling nanobeam. In particular, the strain gradient effect tends to induce higher vibration frequencies as compared to an axially traveling macro beams based on the classical vibration theory without strain gradient effect.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.6
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• pp.216-222
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• 2001

The paper presents the dynamic stability of a flexible shoe in drum brake systems subjected to a frictional force. The frictional force between the drum and the shoe is assumed as a distributed frictional force, while the shute is modeled as an elastic beam supported by two translational springs at both ends and elastic foundations. Governing equations of motion are derived by energy expressions, and their numerical results are obtained by employing the finite element method. The critical distributed frictional force and the instability regions are demonstrated by changing the stiffness of two translational springs and elastic foundation parameters. It is also shown that the beam loses its stability by flutter and divergence depending on the stiffness of elastic supports and elastic foundation parameters. Time responses of beams corresponding to their instability types are also demonstrated.

• Nuclear Engineering and Technology
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• v.55 no.10
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• pp.3866-3873
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• 2023

In 4th^-generation storage rings, whether to operate the beam as round or flat is a critical question. A round beam has equal horizontal and vertical emittances, and is an efficient solution to reduce strong intra-beam scattering effects and lengthen the Touschek lifetimes, but a flat beam produces a brighter photon beam than a round beam. To provide both beams concurrently rather than bifurcating the beam time, this paper presents the exploitation of beam dynamics and the cutting-edge fast pulser that supports concurrent operation of round beam and flat beam.

• Journal of Internet Computing and Services
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• v.23 no.3
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• pp.13-20
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• 2022

IEEE 802.11ay Wi-Fi is the next generation wireless technology and operates in mmWave band. It supports the MU-MIMO (Multiple User Multiple Input Multiple Output) transmission in which an AP (Access Point) can transmit multiple data streams simultaneously to multiple STAs (Stations). To this end, the AP should perform MU-MIMO beamforming training with the STAs. For efficient MU-MIMO beamforming training, it is important for the AP to estimate signal strength measured at each STA at which multiple beams are used simultaneously. Therefore, in the paper, we propose a deep learning-based link quality estimation scheme. Our proposed scheme estimates the signal strength with high accuracy by utilizing a deep learning model pre-trained for a certain indoor or outdoor propagation scenario. Specifically, to estimate the signal strength of the multiple concurrent beams, our scheme uses the signal strengths of the respective single beams, which can be obtained without additional signaling overhead, as the input of the deep learning model. For performance evaluation, we utilized a Q-D (Quasi-Deterministic) Channel Realization open source software and extensive channel measurement campaigns were conducted with NIST (National Institute of Standards and Technology) to implement the millimeter wave (mmWave) channel. Our simulation results demonstrate that our proposed scheme outperforms comparison schemes in terms of the accuracy of the signal strength estimation.

• Journal of the Korea Concrete Institute
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• v.16 no.4 s.82
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• pp.451-458
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• 2004

This study describes the basic concept and the applicability of Hybrid Reinforcement System using conventional steel reinforcing bars and Fiber Reinforced Polymer bars. The concrete bridge decks are assumed to be supported by beams and reinforced with two layers of reinforcing bars. In concrete bridge deck using HRS, the top tensile force for negative moment zone on beam supports is assumed to be resisted by FRP reinforcing bars, and the bottom tensile force for positive moment zone in the middle of hem supports is assumed to be resisted by conventional steel reinforcing bars, respectively. The FRP reinforcing bars are non-corrosive. Thus, the steel reinforcement is as far away as possible from the top surface of the deck and protected from intrusion of corrosive agent. HRS concrete bridge deck has sufficient ductility at ultimate state as the following reasons; 1) FRP bars have lower elastic modulus and higher ultimate strain than steel re-bars have, 2) FRP bars have lower ultimate strain if provided higher reinforcement ratio, 3) ultimate strain of FRP bars can be reduced if FRP bars are unbonded. Test results showed that FRP and HRS concrete slabs are not failed by FRP bar rupture, but failed by concrete compression in the range of ordinary reinforcement ratio. Therefore, in continuous concrete bridge deck using HRS, steel reinforcing bars for positive moment yield and form plastic hinge first and compressive concrete fail in the bottom of supports or in the top of the middle of supports last. Thus, bridge deck consumes significant inelastic strain energy before its failure.

• Journal of Sensor Science and Technology
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• v.9 no.4
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• pp.297-306
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• 2000

To improve the performance of MEMS devices, fabricating single-crystalline silicon HARS (high aspect ratio structure) with thicknesses of up to several tens of micrometers has been an active research topic in recent years. However, achieving electrical isolation, which is required for actuating a structure or sensing an electrical signal, has been one of the main problems in single-crystalline silicon HARS fabrication technologies. In this paper, new isolation technologies using high aspect ratio oxide beams and sidewalls are developed to achieve electrical isolation between electrodes of single-crystalline silicon HARS. The developed isolation technologies use insulating oxide structural supports from either the structural sides or from the bottom. In this case because the trench oxide supports have a depth of several tens of ${\mu}m$, the effects of residual stress must be considered. In this paper, insulating supports are fabricated using PECVD TEOS films, the residual stress of the insulating supports is measured, and the effect of the residual stress on the structure is analyzed. It is shown using microresonators, that the developed isolation technologies can be effectively used for HARS using single-crystalline silicon.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.1
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• pp.49-60
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• 2014

For simple and accurate analysis for behaviors of multi-span suspension bridges which are expected to be frequently constructed as strait-crossing bridges, the deflection theory as the peculiar theory of a suspension bridge can be applied. This paper performs a structural analysis for four-span suspension bridges using the deflection theory. Simply-supported beams with tension are used for girders and the deflections of the beams due to the vertical loads and moments at supports are calculated. The calculation is performed iteratively until the deflections satisfy the compatibility equations of cables. The results of the deflection theory analysis considering tower rigidity are compared with those of the finite element analysis for verification. Importance of the tower rigidity for four-span suspension bridges is confirmed using various compatibility equations of the cable due to variation of the constraint conditions between main cable and top of towers. In addition, the simple parametric analysis for variation of the center tower rigidity is performed.

• Journal of KSNVE
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• v.8 no.6
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• pp.1166-1171
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• 1998

The influences of the coupler consisting of stiffness and mass between neighboring two spans on mode localization are studied theoretically, and the results are confirmed by numerical examples. The mass of the coupler makes a structure sensitive to mode localization especially in higher modes while the stiffness does in all modes. A new type of delocalization phenomenon is observed for the first time in some modes for which mode localization does not occur or is very weak although structural disturbances are severe. A spring-mass system consisting of two substructures and a coupler connecting them is considered in the part of analytical study. As example structures for numerical analysis. simply supported continuous two-span beams with a coupler having a rotational stiffness and a mass moment of inertia on the mid support are considered.

• Journal of the Korea Concrete Institute
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• v.25 no.5
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• pp.555-564
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• 2013

An effective method was proposed in this study which can improve the strengthening effect of continuous girder bridges by external tendons. The improvement of the proposed strengthening method in comparison with conventional methods was analyzed by applying equivalent load concept. In order to verify the strengthening effect, the enhancement of load-carrying capacity achieved by external prestressing was investigated through the test of continuous beams that were or were not strengthened by the external prestressing. The continuous beams were fabricated by making the deck slab continuous according to general construction practice of an actual concrete girder bridge. The test results showed that the deflections and strains of the strengthened beam were significantly reduced when comparing with those of the non-strengthened beam for the same level of external loads, and the stiffness of the member increased by strengthening. In particular, it was verified that the proposed method can effectively reduce the tensile stresses of the deck caused by negative moment at the intermediate supports of a continuous bridge.

• Structural Engineering and Mechanics
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• v.26 no.6
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• pp.673-685
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• 2007

Reinforced concrete beams can be strengthened in a structural retrofit process by attaching steel plates to their sides by bolting. Whilst bolting produces a confident degree of shear connection under conditions of either static or seismic overload, the plates are susceptible to local buckling. The aim of this paper is to investigate the local buckling of unilaterally-restrained plates with point supports in a generic fashion, but with particular emphasis on the provision of the restraints by bolts, and on the geometric configuration of these bolts on the buckling loads. A numerical procedure, which is based on the Rayleigh-Ritz method in conjunction with the technique of Lagrange multipliers, is developed to study the unilateral local buckling of rectangular plates bolted to the concrete with various arrangements of the pattern of bolting. A sufficient number of separable polynomials are used to define the flexural buckling displacements, while the restraint condition is modelled as a tensionless foundation using a penalty function approach to this form of mathematical contact problem. The additional constraint provided by the bolts is also modelled using Lagrange multipliers, providing an efficacious method of numerical analysis. Local buckling coefficients are determined for a range of bolting configurations, and these are compared with those developed elsewhere with simplifying assumptions. The interaction of the actions in bolted plates during buckling is also considered.