• Geomechanics and Engineering
• /
• v.11 no.1
• /
• pp.117-139
• /
• 2016

Previous studies for soil movements induced by tunneling have primarily focused on the free soil displacements. However, the stiffness of existing structures is expected to alter tunneling-induced ground movements, the sheltering influences for underground structures should be included. Furthermore, minimal attention has been given to the settings for the shield machine's operation parameters during the process of tunnels crossing above and below existing tunnels. Based on the Shanghai railway project, the soil movements induced by an earth pressure balance (EPB) shield considering the sheltering effects of existing tunnels are presented by the simplified theoretical method, the three-dimensional finite element (3D FE) simulation method, and the in-situ monitoring method. The deformation prediction of existing tunnels during complex traversing process is also presented. In addition, the deformation controlling safety measurements are carried out simultaneously to obtain the settings for the shield propulsion parameters, including earth pressure for cutting open, synchronized grouting, propulsion speed, and cutter head torque. It appears that the sheltering effects of underground structures have a great influence on ground movements caused by tunneling. The error obtained by the previous simplified methods based on the free soil displacements cannot be dismissed when encountering many existing structures.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.49 no.6
• /
• pp.421-430
• /
• 2000

This paper describes an optimal design method which is applied a weighted least square (WLS) method for Magnetic Resonance Imaging (MRI) system. An optimal design approach is presented for a homogeneity superconducting magnet with the superconducting active shield especially for a magnetic resonance imaging system. The WLS is used to obtain the optimal configurations using the least amount and minimum volume of conductor, exhibiting the smallest level of field inhomogeneity and resulting in the least level of stray field. The proposed model is used to design a multiple-shield configuration for a 1.5 T MRI magnet. The field homogeneity is required less than 5 gauss stray field contour within 4m axially and 3m radially from origin. The designed magnet with the actively magnetic shielding coil out of main coils is analyzed by FEM and theoretical analysis method, investigated the field homogeneity.

• Proceedings of the IEEK Conference
• /
• 2009.05a
• /
• pp.350-353
• /
• 2009

The shielding enclosure is very essential device to test the electromagnetic wave power generated by various RF equipments. Some standards for the shielding enclosures were established to test them in right method. Generally, There are IEEE-STD-299 and MIL-STD-285 and NSA-65-6 of the method for measuring the effectiveness of shielding enclosures, the IEEE-STD-299 combined MIL-STD-285 and NSA-65-6 about the method for measuring shielding effectiveness(SE) about 1969 years, but, the measurement point of 299 proposal is many points(including shielding wall, seam, coner beat, shielding door, etc) and demand long time of measurement. To improve SE test method for shielding enclosures was studied and suggested to develop a proper test procedure. First, we measure reference level as frequency range and H/V polarization, secondly, measure leakage point, and finally, measure shield effect and calculate SE. Our method has a merit of the less measurement point than IEEE-STD-299, and shorten time than 299, and define representation SE of shielding enclosure effectively.

• Fire Science and Engineering
• /
• v.34 no.4
• /
• pp.36-44
• /
• 2020

It is necessary to predict the activation time of fire detectors accurately to improve the reliability for evaluating the required safe egress time (RSET) in performance-based fire safety design. In this study, problems of the plunge test, which is widely applied in assessing fire detectors, were examined through experiments and numerical simulations. In addition, a new shield-cup test method was proposed to address these problems. A fire detector evaluator (FDE) developed in a previous study was applied to ensure measurement accuracy and reproducibility. During the plunge tests, a significant measurement error was observed in the activation time of the smoke detector because of the rapid flow change when the detector was input. However, during the shield-cup tests, slight changes occurred in the flow inside the FDE when the detector as exposed to smoke. In conclusion, the proposed shield-cup test method is expected to be useful for evaluating the response characteristics of fire detectors more accurately in simulated fire environments.

• Progress in Superconductivity and Cryogenics
• /
• v.2 no.2
• /
• pp.26-31
• /
• 2000

This paper deals with finite element analysis of 2GVA superconducting generator which has slitted electrothermal shield in d-axis (SES). Three phase fault is considered torque of the S.C.G. Using the result, generator parameters are calculated by F.E.M. The results are compared with superconducting generator having conventional electrothermal shield (CES). The result shows that quick response excitation could be applied to superconducting generator with slitted electrothermal shield.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2002.10a
• /
• pp.319-326
• /
• 2002

During the construction period of submarine shield tunnel, which is built firstly in very soft marine clay layer 40m deep in Korea, wide range problems were encountered such as safe launching against high earth pressure at shield entrance, technique of shield face pressure control when passing through complex multi-layered soils This paper introduces successful construction practice through development of state-of-the-art construction method and field monitoring.

• Proceedings of the KIEE Conference
• /
• 2008.04c
• /
• pp.247-248
• /
• 2008

This paper describes the influence of shield(Arc shield) on the electric fields in a vacuum interrupter(VI). The equipotential line and electric field in a VI are analysed by a finite element method at various shield length. in result, The electric potentials of Arc shield edge was increased because the length too short or long approach the source. it confirmed that equipotential line was influenced that shape and length by end shield. finally this pater proposed to optimal length and shape by arc shield.

• Proceedings of the KIEE Conference
• /
• 1998.11c
• /
• pp.913-915
• /
• 1998

This paper describes the application of two and three dimensional electric field analysis for vacuum interrupter with spiral contacts. The electric potentials of floating arc shield and electric fields in a vacuum interrupter are analysed at various gap distances from 1mm to 12mm. The electric potentials of floating shield is increased with the gap distance, which is because the relative position of shield is closer to the fixed contact so that the capacitance distribution inside interrupter is varied. The calculated results show that the maximum value of electric field in a vacuum interrupter with floating shield is nearly same to that without shield at short gap distance below 5mm, however at longer gaps more intensive electric field is achieved in interrupter with shield comparing with the model without shield, which is due to the influence of charged floating shield.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.06a
• /
• pp.478-479
• /
• 2008

this paper describes the electric field distribution interpretation along a shield form inner vacuum interrupter(VI). The equipotential line and electric field and field vector in a VI are analysed by a finite element method at various shield form. in result, The equipotential line and electric field distribution was affected to VI shield form. The reason is as it gets distortion of equipotential line done. shield of cup type is how to electric field distribution, finally, this paper recognized whether or not affected, and proposed gap with the most suitable shield length and an external insulation.

• Structural Engineering and Mechanics
• /
• v.84 no.5
• /
• pp.699-706
• /
• 2022

Settlement control techniques are critical for the safety of shield tunnel constructions, especially for facing complex situations. In this study, the shield tunnel structure from Huaita east road station to Heping Road station in Xuzhou metro No.3 line (China) is taken as engineering background, which has various complex problems of the upper-soft and lower-hard composite stratum conditions, twin curve shield tunnels, and underpass the foundation of the piled raft. The deformation characteristics of shield tunnelling passing through buildings are explored. Subsequently, comprehensive research methods of numerical simulation and field measurement are adopted to analyzing the effectiveness of settlement control by using the top grouting technique. The results show that the settlement of the buildings has obvious spatial characteristics, and the hysteresis effect can be obviously observed in soil deformation caused by shield construction. Meanwhile, the two shield constructions can cause repeated disturbances, reducing the soil deformation's hysteresis effect. Moreover, the shield tunnel's differential settlement is too large when a single line passes through, and the shield construction of the outer curve can cause more significant disturbance in the tunnel than the inside curve. Notably, the proposed process control parameters and secondary topgrouting method can effectively control the deformation of the shield tunnel, especially for the long-term deformation.