• Journal of Communications and Networks
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• v.13 no.5
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• pp.472-480
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• 2011

In this paper, we investigate two new candidate transmission schemes, non-orthogonal frequency reuse (NOFR) and beam-hopping (BH). They operate in different domains (frequency and time/space, respectively), and we want to know which domain shows overall best performance. We propose a novel formulation of the signal-to-interference plus noise ratio (SINR) which allows us to prove the frequency/time duality of these schemes. Further, we propose two novel capacity optimization approaches assuming per-beam SINR constraints in order to use the satellite resources (e.g., power and bandwidth) more efficiently. Moreover, we develop a general methodology to include technological constraints due to realistic implementations, and obtain the main factors that prevent the two technologies dual of each other in practice, and formulate the technological gap between them. The Shannon capacity (upper bound) and current state-of-the-art coding and modulations are analyzed in order to quantify the gap and to evaluate the performance of the two candidate schemes. Simulation results show significant improvements in terms of power gain, spectral efficiency and traffic matching ratio when comparing with conventional systems, which are designed based on uniform bandwidth and power allocation. The results also show that BH system turns out to show a less complex design and performs better than NOFR system specially for non-real time services.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.10a
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• pp.185-190
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• 1995

In recent years, many researcher have been interested in the stability of a thin beam. Among them, Pai and Nayfeh[1] had investigated the nonplanar motion of the cantilever beam under lateral base excitation and chaotic motion, but this study is associated with internal resonance, i.e. one to one resonance. Also Cusumano[2] had made an experiment on a thin beam, called Elastica, under bending loads. In this experiment, he had shown that there exists out-of-plane motion, involving the bending and the torsional mode. Pak et al.[3] verified the validity of Cusumano's experimental works theoretically and defined the existence of Non-Local Mode(NLM), which is came out due to the instability of torsional mode and the corresponding aspect of motions by using the Normal Modes. Lee[4] studied on a thin beam under bending loads and investigated the routes to chaos by using forcing amplitude as a control parameter. In this paper, we are interested in the motion of a thin beam under torsional loads. Here the form of force based on the natural forcing function is used. Consequently, it is found that small torsional loads result in instability and in case that the forcing amplitude is increasing gradually, the motion appears in the form of dynamic double potential well, finally leads to complex motion. This phenomenon is investigated through the poincare map and time response. We also check that Harmonic Balance Method(H.B.M.) is a suitable tool to calculate the bifurcated modes.

• Structural Engineering and Mechanics
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• v.59 no.2
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• pp.343-371
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• 2016

In this paper thermo-mechanical vibration analysis of a porous functionally graded (FG) Timoshenko beam in thermal environment with various boundary conditions are performed by employing a semi analytical differential transform method (DTM) and presenting a Navier type solution method for the first time. The temperature-dependent material properties of FG beam are supposed to vary through thickness direction of the constituents according to the power-law distribution which is modified to approximate the material properties with the porosity phases. Also the porous material properties vary through the thickness of the beam with even and uneven distribution. Two types of thermal loadings, namely, uniform and linear temperature rises through thickness direction are considered. Derivation of equations is based on the Timoshenko beam theory in order to consider the effect of both shear deformation and rotary inertia. Hamilton's principle is applied to obtain the governing differential equation of motion and boundary conditions. The detailed mathematical derivations are presented and numerical investigations are performed while the emphasis is placed on investigating the effect of several parameters such as porosity distributions, porosity volume fraction, thermal effect, boundary conditions and power-low exponent on the natural frequencies of the FG beams in detail. It is explicitly shown that the vibration behavior of porous FG beams is significantly influenced by these effects. Numerical results are presented to serve benchmarks for future analyses of FG beams with porosity phases.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.143-150
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• 2002

This paper presents the application of continuous wavelet transform for determination of dynamic parameters of continuous beam subjected to moving load. Morlet wavelet is used as mother wavelet in wavelet transform. Dynamic parameters are estimated from the magnitudes and arguments of the wavelet coefficients obtained by wavelet transforming the response time histories of joints on the beam. This study shows that the estimated parameters such as natural frequencies, dmping ratios and mode shapes are to be well-compared with those of the finite element analysis.

• Korean Journal of Geomatics
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• v.1 no.1
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• pp.69-74
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• 2001

In conventional photogrammetry, three-dimensional coordinates are obtained from two consecutive images of a stationary object photographed from two exposure stations, separated by a certain distance. However, it is impossible to photograph moving objects from two stations with one camera at the same time. Various methods to overcome this obstacle were devised e. g. taking the left and right scenes simultaneously with one camera using a beam splitter attached to the front, thus creating a stereo scene in one image. A beam splitter consists of two outer mirrors and two inner mirrors. This paper deals with research where the optical principles of the beam splitter were evaluated based on light path phenomena between the outer mirrors and the inner mirrors. A mathematical model of the geometric configuration was derived for the beam splitter. This allows us to design and control a beam splitter to obtain maximum scale and maximum base-height ratio by stepwise application of the mathematical model. The results show that the beam splitter is a very useful tool for stereophotography with one camera. The optimum geometric configurations ensuring maximum scale and base-height ratio are closely related to inner and outer reflector sizes, their inclination angles and the offsets between the outer mirrors.

• Journal of the Korean Institute of Landscape Architecture
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• v.30 no.4
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• pp.92-104
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• 2002

This study investigates, analyzes, and summarizes Dansplantation techniques and methods through practical methodology centering on fieldwork in order to present effective planting methods for large trees that have important significance. The conclusions are as follows : 1. The transplantation process of a large tree generally consists of the stages of digging up a tree, manufacturing a carrier frame, loading the tee on a vehicle, transporting, transplanting the tree, installing a strut and maintaining and managing the new transplant. In addition, planting a tree on a mounted place includes the primary procedures of trimming out the root, and preparing for transplanting the tree on a mounted place, as well as the secondary work of trimming out the root, transplanting a tree on a mounted place, maintenance and management. 2. In order to decide on a transplantation method for a large-sized tree, a structure calculation has to be performed first. That is, one must calculate the weight of the tree and the allowable stress of the strut (H-beam, etc.) fhst and then decide on the upper method through computer modeling based upon this structural calculation. 3. As a result of the analysis of a transplanted tree using the life soil method, it was confirmed that large quantities of feeder roots had developed around the root within a short time after the transplantation. The life soil method has proven to be very effective for transplantation of large-sized trees. 4. As for the production method of an H-beam strut frame, it was found that the manufacturing process and disassembly process were simple and proper; therefore, the H-beam frame is an appropriate structure to be used in the transplantation of large trees. 5. The concavo-convex method, which consists of filling the life soil in the concavo-convex area around the root, was found to be a method that promotes the growth of feeder roots within a short period of time and saves the supply of water at the same time.

• Steel and Composite Structures
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• v.44 no.1
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• pp.17-31
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• 2022

This investigation studies the characteristics of wave dispersion in sigmoid functionally graded (SFG) curved beams lying on an elastic substrate for the first time. Homogenization process was performed with the help of sigmoid function and two power laws. Moreover, various materials such as Zirconia, Alumina, Monel and Nickel steel were explored as curved beams materials. In addition, curved beams were rested on an elastic substrate which was modelled based on Winkler-Pasternak foundation. The SFG curved beams' governing equations were derived according to Euler-Bernoulli curved beam theory which is known as classic beam theory and Hamilton's principle. The resulted governing equations were solved via an analytical method. In order to validate the utilized method, the obtained outcomes were compared with other researches. Finally, the influences of various parameters, including wave number, opening angle, gradient index, Winkler coefficient and Pasternak coefficient were evaluated and indicated in the form of diagrams.

• Geomechanics and Engineering
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• v.32 no.2
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• pp.125-135
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• 2023

Nonlinear vibration analysis of composite beam reinforced by carbon nanotubes resting on the nonlinear viscoelastic foundation is investigated in this study. The material properties of the composite beam is considered as a polymeric matrix by reinforced carbon nanotubes according to different distributions. With using Hamilton's principle, the governing nonlinear partial differential equations are derived based on the Euler-Bernoulli beam theory. In the nonlinear kinematic assumption, the Von Kármán nonlinearity is used. The Galerkin's decomposition technique is utilized to discretize the governing nonlinear partial differential equation to nonlinear ordinary differential equation and then is solved by using of multiple time scale method. The nonlinear natural frequency and the nonlinear free response of the system is obtained. In addition, the effects of different patterns of reinforcement, linear and nonlinear damping coefficients of the viscoelastic foundation on the nonlinear vibration responses and phase trajectory of the carbon nanotube reinforced composite beam are investigated.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.47 no.5
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• pp.68-73
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• 2015

Electron beam irradiation is also an eco-friendly treatment compared to other physical and chemical treatments. In this study, we attempted to evaluate the possibilities of energy savings by applying electron beam irradiation to the refining process. After softwood unbleached kraft pulp (UKP) was irradiated with electron beams at 50 and 100 kGy, it was beaten in a laboratory beater, and then its freeness and fiber properties were analyzed. The physical properties of their fiber handsheet were also and measured. As the irradiation dose of the electron beam and the beating time increased, lower freeness and fiber lengths of the UKP were observed. Handsheets made from UKP that was irradiated by electron beam and beaten showed a reciprocal relationship with the irradiation dose of the electron beam, in particular, the strength of the handsheets decreased dramatically at 100 kGy of irradiation. Therefore, it was confirmed that electron beam irradiation is effective in reducing the beating time or beating energy. But the irradiation dose must be controlled under 50 kGy to minimize the loss of paper strength.

• Steel and Composite Structures
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• v.45 no.2
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• pp.293-303
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• 2022

In order to improve the seismic resilience of coupled wall structure, coupling beam with fuse has been developed to reduce the post-earthquake damage. However, the fuses often have a build-up I-shaped section and are relatively heavy to be replaced. Moreover, the fuse and the beam segments are usually connected by bolts and it is time-consuming to replace the damaged fuse. For reducing the repair time and cost, a novel quickly replaceable coupling beam with buckling-restrained energy dissipaters is developed. The fuse of the proposed coupling beam consists of two chord members and bar-typed energy dissipaters placed at the corners of the fuse. In this way, the weight of the energy dissipater can be greatly reduced. The energy dissipaters and the chords are connected with hinge and it is convenient to take down the damaged energy dissipater. The influence of ratio of the length of coupling beam to the length of fuse on the seismic performance of the structure is also studied. The seismic performance of the coupled wall system with the proposed coupling beam is compared with the system with reinforced concrete coupling beams. Results indicated that the weight and post-earthquake repair cost of the proposed fuse can be reduced compared with the typical I-shaped fuse. With the increase of the ratio of the beam length to the fuse length, the interstory drift of the structure is reduced while the residual fuse chord rotation is increased.