• Journal of Magnetics
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• v.20 no.3
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• pp.273-283
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• 2015

In this study, we propose an analytical model for studying magnetic fields in radial-flux permanent-magnet eddy-current couplings by considering the effects of slots and iron-core protrusions on the eddy currents. We focus on the analytical prediction of the air-gap field by considering the influence of eddy currents induced in conducting bars. In the proposed model, the permanent magnet region is treated as the source of a time-varying magnetic field and the moving-conductor eddy current problem is solved based on the resolution of time-harmonic Helmholtz equations. The spatial harmonics in the air gap and in slots, as well as the time harmonics are all considered in the analytical calculation. Based on the proposed field model, the electromagnetic torque is computed by using the Maxwell stress tensor method. Nonlinear finite element analysis is performed to validate the analytical model. The proposed model can be used for permanent-magnet eddy-current couplings with any slot-pole combination.

• Nuclear Engineering and Technology
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• v.53 no.2
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• pp.446-454
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• 2021

Critical heat flux (CHF) has traditionally been evaluated using look-up tables or empirical correlations for nuclear power plants. However, under complex moving condition, it is necessary to reconsider the CHF characteristics since the conventional CHF prediction methods would no longer be applicable. In this paper, the additional forces caused by motions have been added to the annular film dryout (AFD) mechanistic model to investigate the effect of moving condition on CHF. Moreover, a theoretical model of the natural circulation loop with additional forces is established to reflect the natural circulation characteristics of the loop system. By coupling the system loop with the AFD mechanistic model, a CHF prediction program called NACOM for natural circulation loop under moving condition is developed. The effects of three operating conditions, namely stationary, inclination and rolling, on the CHF of the loop are then analyzed. It can be clearly seen that the moving condition has an adverse effect on the CHF in the natural circulation system. For the calculation parameters in this paper, the CHF can be reduced by 25% compared with the static value, which indicates that it is important to consider the effects of moving condition to retain adequate safety margin in subsequent thermal-hydraulic designs.

• Geomechanics and Engineering
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• v.38 no.3
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• pp.215-229
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• 2024

Because of the various patterns of deep-water inrush and complicated mechanisms, accurately predicting mine water inflows is always a difficult problem for coal mine geologists. In study presented in this paper, the water inrush channels were divided into four basic water diversion structures: aquifer, rock fracture zone, fracture zone and goaf. The fluid flow characteristics in each water-conducting structure were investigated by laboratory tests, and multistructure and multisystem coupling flow analysis models of different water-conducting structures were established to describe the entire water inrush process. Based on the research of the water inrush flow paths, the analysis model of different water inrush space structures was established and applied to the prediction of mine water inrush inflow. The results prove that the conduction sequence of different water-conducting structures and the changing rule of permeability caused by stress changes before and after the peak have important influences on the characteristics of mine water-gushing. Influenced by the differences in geological structure and combined with rock mass RQD and fault conductivity characteristics and other mine exploration data, the prediction of mine water inflow can be realized accurately. Taking the water transmitting path in the multistructure as the research object of water inrush, breaking through the limitation of traditional stratigraphic structure division, the prediction of water inflow and the estimation of potentially flooded area was realized, and water bursting intensity was predicted. It is of great significance in making reasonable emergency plans.

• Geomechanics and Engineering
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• v.14 no.6
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• pp.589-600
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• 2018

For foundations in permafrost regions, the displacement characteristics are uncertain because of the randomness of temperature characteristics and mechanical parameters, which make the structural system have an unexpected deviation and unpredictability. It will affect the safety of design and construction. In this paper, we consider the randomness of temperature characteristics and mechanical parameters. A stochastic analysis model for the uncertain displacement characteristic of foundations is presented, and the stochastic coupling program is compiled by Matrix Laboratory (MATLAB) software. The stochastic displacement fields of an embankment in a permafrost region are obtained and analyzed by Neumann stochastic finite element method (NSFEM). The results provide a new way to predict the deformation characteristics of foundations in permafrost regions, and it shows that the stochastic temperature has a different influence on the stochastic lateral displacement and vertical displacement. Construction disturbance and climate warming lead to three different stages for the mean settlement of characteristic points. For the stochastic settlement characteristic, the standard deviation increases with time, which imply that the results of conventional deterministic analysis may be far from the true value. These results can improve our understanding of the stochastic deformation fields of embankments and provide a theoretical basis for engineering reliability analysis and design in permafrost regions.

• Bulletin of the Korean Chemical Society
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• v.32 no.6
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• pp.1980-1984
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• 2011

A temperature- and coverage-dependant quasi-reversible change in two-photon photoemission (2PPE) of chemisorbed 1-phenyl-1-propyne (PP) on Cu(111) is reported. For PP on Cu(111) at 300 K probed at a photon energy of 4.13 eV, two broad peaks of comparable intensity show final state energies of 7.25 and 7.75 eV above the Fermi level. The former peak could be assigned to the first image potential state (IS, n = 1) and/or unoccupied molecular orbital (UMO), located at 3.1 eV above the Fermi level. The latter is plausibly attributed to a mix of unoccupied higher-order IS (and/or UMO) and occupied surface state (SS) of Cu(111). With decreasing the temperature, the former 2PPE peak shows a shift in position by about 0.2 eV, and the latter exhibits a dramatic increase in intensity. In the system, intermolecular interactions (and/or order-disorder transition) of PP and substrate lattice temperature may play a significant role in change in photoexcitation lifetime (or excitation cross-section), and the unoccupied molecular orbital (UMO)-metal (IS) charge transfer coupling. Our unique 2PPE results provide a deeper insight for understanding photoexcitation charge transfer with temperature in an organic molecule/metal system.

• Geomechanics and Engineering
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• v.38 no.2
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• pp.125-137
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• 2024

In paste backfill mining, cemented coal gangue-fly ash backfill (CGFB) can effectively utilize coal-based solid waste, such as gangue, to control surface subsidence. However, given the pressurized water accumulation environment in goafs, CGFB is subject to coupling effects from water pressure and chloride ions. Therefore, studying the influence of pressurized water on the chlorine salt erosion of CGFB to ensure green mining safety is important. In this study, CGFB samples were soaked in a chloride salt solution at different pressures (0, 0.5, 1.5, and 3.0 MPa) to investigate the chloride ion transport characteristics, hydration products, micromorphology, pore characteristics, and mechanical properties of CGFB. Water pressure was found to promote chloride ion transfer to the CGFB interior and the material hydration reaction; enhance the internal CGFB pore structure, penetration depth, and chloride ion content; and fill the pores between the material to reduce its porosity. Furthermore, the CGFB peak uniaxial compression strain gradually decreased with increasing soaking pressure, whereas the uniaxial compressive strength first increased and then decreased. The resulting effects on the stability of the CGFB solid-phase hydration products can change the overall CGFB mechanical properties. These findings are significant for further improving the adaptability of CGFB for coal mine engineering.

• Wind and Structures
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• v.27 no.1
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• pp.11-27
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• 2018

The straight-cone steel cooling tower is a novel type of structure, which has a distinct aerodynamic distribution on the internal surface of the tower cylinder compared with conventional hyperbolic concrete cooling towers. Especially in the extreme weather conditions of strong wind and heavy rain, heavy rain also has a direct impact on aerodynamic force on the internal surface and changes the turbulence effect of pulsating wind, but existing studies mainly focus on the impact effect brought by wind-driven rain to structure surface. In addition, for the indirect air cooled cooling tower, different additional ventilation rate of shutters produces a considerable interference to air movement inside the tower and also to the action mechanism of loads. To solve the problem, a straight-cone steel cooling towerstanding 189 m high and currently being constructed is taken as the research object in this study. The algorithm for two-way coupling between wind and rain is adopted. Simulation of wind field and raindrops is performed with continuous phase and discrete phase models, respectively, under the general principles of computational fluid dynamics (CFD). Firstly, the rule of influence of 9 combinations of wind sped and rainfall intensity on flow field mechanism, the volume of wind-driven rain, additional action force of raindrops and equivalent internal pressure coefficient of the tower cylinder is analyzed. On this basis, the internal pressures of the cooling tower under the most unfavorable working condition are compared between four ventilation rates of shutters (0%, 15%, 30% and 100%). The results show that the 3D effect of equivalent internal pressure coefficient is the most significant when considering two-way coupling between wind and rain. Additional load imposed by raindrops on the internal surface of the tower accounts for an extremely small proportion of total wind load, the maximum being only 0.245%. This occurs under the combination of 20 m/s wind velocity and 200 mm/h rainfall intensity. Ventilation rate of shutters not only changes the air movement inside the tower, but also affects the accumulated amount and distribution of raindrops on the internal surface.

• Korean Journal of Remote Sensing
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• v.34 no.6_2
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• pp.1229-1238
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• 2018

We examined if a state of sea-ice in Bering Sea acts as a prelude of variation in that of Chukchi Sea by using satellites-based Arctic sea-ice concentration time series. Datasets consist of monthly values of sea-ice concentration during 36 years (1982-2017). Time series analysis armed with Transfer entropy is performed to describe how sea-ice data in Chukchi Sea is affected by that in Bering Sea, and to explain the relationship. The transfer entropy is a measure which identifies a nonlinear coupling between two random variables or signals and estimates causality using modification of time delay. We verified this measure checked a nonlinear coupling for simulated signals. With sea-ice concentration datasets, we found that sea-ice in Bering Sea is influenced by that in Chukchi Sea 3, 5, 6 months ago through the transfer entropy measure suitable for nonlinear system. Particularly, when a sea-ice concentration of Bering Sea has a local minimum, sea ice concentration around Chukchi Sea tends to decline 5 months later with about 70% chance. This finding is considered to be a process that inflow of Pacific water through Bering strait reduces sea-ice in Chukchi Sea after lowering the concentration of sea-ice in Bering Sea. This approach based on information theory will continue to investigate a timing and time scale of interesting patterns, and thus, a coupling inherent in sea-ice concentration of two remote areas will be verified by studying ocean-atmosphere patterns or events in the period.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.255-255
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• 2009

에폭시수지에 유기화된 층상실리케이트 나노입자를 충진하여 에폭시-나노콤포지트 제조하였다. 에폭시-나노콤포지트는 열적, 기계적 특성이 매우 우수한 콤포지트로서 실란처리에 따른 동적 기계적 특성 (Dynamic Mechanical Analysis)과 가교밀도와의 관계를 조사였다. 나노입자의 충진함량은 3wt%로 충진하였고, Silane Coupling Agent는 에폭시실란으로서 3-Glycidoxypropyltrimethoxysilane이 사용되었다. 실란처리함량은 0.5, 1, 1.5 wt%로서 적용하여 제조된 샘플이다. DMA Storage modulus특성으로 glass state($40^{\circ}C$)에서는 원형에폭시의 경우 2054, 실란처리되지 않은 나노콤포지트 3967, 실란처리된 나노콤포지트는 4867MPa을 나타내었다. rubbery state($140^{\circ}C$)에서는 원형에폭시의 경우 1458, 실란처리되지 않은 경우 2506, 실란처리된 나노콤포지트는 2638MPa을 나타내었다. 또한 실란처리함량에따른 가교밀도변화는 0.5wt%에서는 0.803, 1 wt%에서는 0.671, 1.5wt%에서는 $0.762[mol/cm^3]$이로서 에폭시원형과 실란미처리된 나노콤포지트 그리고 실란처리된 나노콤포지트순으로 glass state와 rubbery state에서의 특성이 크게 향상된 결과를 얻었다. 이는 실란이 고분자와 무기물사이의 결합력을 강화시켜 열적기계적 특성향상을 가져 오는 것으로 볼 수 있다. 가교밀도의 실란처리함량의 변화에 있어서 과량의 함량 첨가는 에폭시와 나노층상실리게이트 표면처리된 잔유량이 오히려 특성의 저하를 가져오는 것으로 볼 수 있다.

• Coupled systems mechanics
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• v.7 no.3
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• pp.297-319
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• 2018

In this paper, the vibro-acoustic behaviors of vibrational cylindrical shells are investigated by using structural intensity approach. The reducing interior noise method for vibrating cylindrical shells is proposed by altering and redistributing the structural intensity through changing the damping property of the structure. The concept of proposed novel method is based on the properties of structural intensity distribution on cylindrical shells under different load and damping conditions, which can reflects power flow in the structures. In the study, the modal formulas of structural intensity are developed for the steady state vibration of cylindrical shell structures. The detailed formulas of structural intensity are derived by substituting modal quantities, in which the effect of main parameters such as weight coefficients and distribution functions on structure intensity are analyzed and discussed. Numerical simulations are first carried out based on the structural intensity analytical solutions of modal formulas. Through simulating the coupling vibration and acoustical radiation problems of cylindrical shell, the relationship between vibro-acoustic and structural intensity distribution is derived. We find that for cylindrical shell, by properly arranging damping conditions, the structural intensity can be efficiently changed and further the noise property can be improved. The proposed methodology has important implications and potential applications in the vibration and noise control of fuselage structure.