• Journal of Mechanical Science and Technology
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• 제20권8호
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• pp.1139-1148
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• 2006

This paper addresses the analytical modeling and dynamic response of the advanced composite rotating blade modeled as thin-walled beams and incorporating viscoelastic material. The blade model incorporates non-classical features such as anisotropy, transverse shear, rotary inertia and includes the centrifugal and coriolis force fields. The dual technology including structural tailoring and passive damping technology is implemented in order to enhance the vibrational characteristics of the blade. Whereas structural tailoring methodology uses the directionality properties of advanced composite materials, the passive material technology exploits the damping capabilities of viscoelastic material (VEM) embedded into the host structure. The VEM layer damping treatment is modeled by using the Golla-Hughes-McTavish (GHM) method, which is employed to account for the frequency-dependent characteristics of the VEM. The case of VEM spread over the entire span of the structure is considered. The displayed numerical results provide a comprehensive picture of the synergistic implications of both techniques, namely, the tailoring and damping technology on the dynamic response of a rotating thin-walled b ε am exposed to external time-dependent excitations.

• Journal of Power Electronics
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• 제16권5호
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• pp.1763-1772
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• 2016

To reduce system complexity and implementation costs, fully-controlled H-bridge (FHB) modules and diode H-bridge PFC (DHB) modules are cascaded to form a hybrid cascaded H-bridge rectifier (HCHR). In this paper, the advantages of such a HCHR over other cascaded rectifiers are analyzed depending on the numbers of FHB modules and DHB modules. Therefore, to assign proper numbers to these two kinds of modules for the HCHR, a configuration determination method is investigated under balanced and imbalanced loads. Three principles are also presented to guide the configuration determination for the HCHR. In addition, the constraints for selecting the step-up ratio and filter inductance are derived based on a phasor diagram analysis. The proposed configuration determination method is validated by simulations under three different conditions in the PSIM environment. Finally, experiments are carried out on a scaled-down prototype where the configuration can be easily adjusted. The feasibility of the proposed theory is then verified by experimental results.

• Journal of Magnetics
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• 제18권4호
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• pp.443-453
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• 2013

Maglev wind turbine generator (MWTG) technology has been widely studied due to its low loss, low maintenance cost, and high reliability. However, the dynamics of the magnetic bearing system differ fromthe those of the traditional mechanical bearing system. A horizontal axial MWTG supported with a permanent magnetic bearing is designed in this research and the radial forces and the natural frequencies of the rotor system are studied. The results show that the generatorhas a cyclical magnetic forceand an unreasonable bearing stiffness may mean that the rotor system needs to work in the resonance region; the bearing stiffness is the key factor to avoid this problem. This is the main rule of the bearing stiffness design in the MWTG, and this rule can also be used in other maglev permanent magnet motors.

• 대한산업공학회지
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• 제27권2호
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• pp.118-134
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• 2001

The research in the field of quality engineering has mainly focused on the manufactured products. The philosophy and concept of the existing quality engineering should be equally applicable in the coming e-Business era. However, there would be numerous new quality-related issues in the e-Business environment, due to the fundamental change in the business processes, which did not exist in the past. This paper first proposes a framework for quality engineering research suited for the e-Business environment, and then identifies major quality-related issues that should be resolved in the near future. It also evaluates the potential usefulness and limitations of the existing quality engineering tools in resolving such issues.

• 한국기계가공학회지
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• 제17권5호
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• pp.149-154
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• 2018

To improve the efficiency and lifetime of filters, we analyze the element distribution at the entrance and exit by using the flow inside a filter, confirming that the internal structure affects the filter efficiency. The flow in the pipe is predicted through computer simulations, and the filtration efficiency of each element is compared through experiments. The efficiency and lifetime of the filter are indirectly improved through the element distribution at the filter outlet according to the internal structure. Because pressure loss from the structure inevitably occurs, the efficiency and lifetime of filters against pressure loss must be considered.

• 한국가시화정보학회지
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• 제18권3호
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• pp.84-89
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• 2020

Cancer cells secrete angiogenic factors, and nearby vasculatures make new blood vessels essential for cancer development and metastasis in response to these soluble factors. Many efforts have been made to elucidate cancer-endothelial cell interactions in vitro. However, not much is known due to the lack of a suitable co-culture platform. Here, we introduce a 3D printing-based microfluidic system that mimics the in vivo-like cancer-endothelial cell interactions. The tumoroids and endothelial cells are co-cultured, physically separated by porous fibrin gel, allowing communication between two cell types through soluble factors. Using this microfluidic system, we were able to visualize new vessel formation induced by tumoroids of different origins, including liver, breast, and ovary. We confirmed that the ovarian tumoroids most induced angiogenesis while the other two cancer types suppressed it. Utilization of the proposed co-culture platform will help the researchers unveil the underlying mechanisms of the dynamic interplay between tumor and angiogenesis.

• Geomechanics and Engineering
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• 제29권6호
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• pp.627-643
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• 2022

Water-rock interactions have a significant influence on the mechanical behavior of rocks. In this study, uniaxial compression and tension tests on different water-treated sandstone samples were conducted. Acoustic emission (AE) monitoring and micro-pore structure detection were carried out. Water-rock interactions and their effects on rock mechanical behavior were discussed. The results indicate that water content significantly weakens rock mechanical strength. The sensitivity of the mechanical parameters to water treatment, from high to low, are Poisson ratio (𝜇), uniaxial tensile strength (UTS), uniaxial compressive strength (UCS), elastic modulus (E), and peak strain (𝜀). After water treatment, AE activities and the shear crack percentage are reduced, the angles between macro fractures and loading direction are minimized, the dynamic phenomenon during loading is weakened, and the failure mode changes from a mixed tensile-shear type to a tensile one. Due to the softening, lubrication, and water wedge effects in water-rock interactions, water content increases pore size, promotes crack development, and weakens micro-pore structures. Further damage of rocks in fractured and caved zones due to the water-rock interactions leads to an extra load on the adjoining coal and rock masses, which will increase the risk of dynamic disasters.

• 센서학회지
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• 제32권6호
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• pp.335-339
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• 2023

Skin-compatible electronics have evolved to achieve both conformality and stretchability for stable contact with deformable biological skin. While existing research has largely concentrated on alternative materials, the potential of Parylene-based thin-film electrodes for stretchable on-skin applications remains relatively untapped. This study proposes an engineering strategy to achieve stretchability using the Parylene thin-film electrode. Unlike the conventional Parylene thin-film electrode, we introduce morphological adaptability via controlled microscale slits in the Parylene electrode structure. The slits-containing device enables unprecedented stretchability while maintaining critical electrical insulation properties during mechanical deformation. Finally, the demonstration on human skin shows the mechanical adaptability of these Parylene-based bioelectrodes while their electrical characteristics remain stable during various stretching conditions. Owing to the ultra-thinness of the Parylene coating, the wearable bioelectrode not only achieves stretchability but also conforms to the skin. Our findings broaden the practical use of Parylene thin-film bioelectrodes.

• 마이크로전자및패키징학회지
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• 제23권2호
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• pp.19-28
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• 2016

This paper presents an overview of selected advanced measurement technologies for the mechanical properties of polymers used for flexible and stretchable electronic packaging. Over the years, a variety of flexible and stretchable electronics have been developed due to their potential applications for next generation IT industry. To achieve more flexible and wearable devices for practical applications, the usage of polymeric components has been increased significantly. Therefore, accurate measurement of mechanical properties of the polymers is necessary in order to design mechanically reliable devices. However, the measurement has been challenging due to the soft nature and thin applications of polymers. Here, we describe novel measurement technologies of mechanical properties of polymers for flexible and stretchable electronics.

• Journal of Mechanical Science and Technology
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• 제17권4호
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• pp.484-491
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• 2003

For most of linear time-varying (LTV) systems, it is difficult to design time-varying controllers in analytic way. Accordingly, by approximating LTV systems as uncertain linear time-invariant, control design approaches such as robust control have been applied to the resulting uncertain LTI systems. In particular, a robust control method such as quantitative feedback theory (QFT) has an advantage of guaranteeing the frozen-time stability and the performance specification against plant parameter uncertainties. However, if these methods are applied to the approximated linear. time-invariant (LTI) plants with large uncertainty, the resulting control law becomes complicated and also may not become ineffective with faster dynamic behavior. In this paper, as a method to enhance the fast dynamic performance of LTV systems with bounded time-varying parameters, the approximated uncertainty of time-varying parameters are reduced by the proposed QFT parameter-scheduling control design based on radial basis function (RBF) networks.