• Title/Summary/Keyword: Mechanical Shim

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Research on Mechanical Shim Application with Compensated Prompt γ Current of Vanadium Detectors

  • Xu, Zhi
    • Nuclear Engineering and Technology
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    • v.49 no.1
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    • pp.141-147
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    • 2017

  • Mechanical shim is an advanced technology for reactor power and axial offset control with control rod assemblies. To address the adverse accuracy impact on the ex-core power range neutron flux measurements-based axial offset control resulting from the variable positions of control rod assemblies, the lead-lag-compensated in-core self-powered vanadium detector signals are utilized. The prompt ${\gamma}$ current of self-powered detector is ignored normally due to its weakness compared with the delayed ${\beta}$ current, although it promptly reflects the flux change of the core. Based on the features of the prompt ${\gamma}$ current, a method for configuration of the lead-lag dynamic compensator is proposed. The simulations indicate that the method can improve dynamic response significantly with negligible adverse effects on the steady response. The robustness of the design implies that the method is of great value for engineering applications.

  • https://doi.org/10.1016/j.net.2016.08.015 인용 PDF KSCI

Performance Predictions of Gas Foil Journal Bearing with Shim Foils (심포일을 갖는 가스 포일 저널 베어링의 성능 예측)

  • Hwang, Sung Ho;Moon, Chang Gook;Lee, Jong Sung;Kim, Tae Ho
    • Tribology and Lubricants
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    • v.34 no.3
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    • pp.107-114
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    • 2018

  • This paper presents a computational model of a gas foil journal bearing with shim foils between the top foil and bumps, and predicts its static and dynamic performance. The analysis takes the previously developed simple elastic foundation model for the top foil-bump structure and advances it by adding foil models for the "shim foil" and "outer top foil." The outer top foil is installed between the (inner) top foil and bumps, and the shim foil is installed between the inner top foil and outer top foil. Both the inner and outer top foils have an arc length of $360^{\circ}$, but the arc length of the shim foil is shorter, which causes a ramp near its leading edge in the bearing clearance profile. The Reynolds equation for isothermal and isoviscous ideal gas solves the hydrodynamic pressure that develops within the bearing clearance with preloads due to the ramp. The centerline pressure and film thickness predictions show that the shim foil mitigates the peak pressure occurring at the loading direction, and broadens the positive pressure as well as minimum film thickness zones except for the shortest shim foil arc length of $180^{\circ}$. In general, the shim foil decreases the journal eccentricity, and increases the power loss, direct stiffness, and damping coefficients. As the shim foil arc length increases, the journal eccentricity decreases while the attitude angle, minimum film thickness, and direct stiffness/damping coefficients in the horizontal direction increase.

  • https://doi.org/10.9725/kts.2018.34.3.107 인용 PDF KSCI