• Safety and Health at Work
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• v.4 no.3
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• pp.149-155
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• 2013

Background: Stochastic resonance whole-body vibration training (SR-WBV) was tested to reduce work-related musculoskeletal complaints. Methods: Participants were 54 white-collar employees of a Swiss organization. The controlled crossover design comprised two groups each given 4 weeks of exercise and no training during a second 4-week period. Outcome was daily musculoskeletal well-being, musculoskeletal pain, and surefootedness. In addition, participants performed a behavioral test on body balance prior to when SR-WBV started and after 4 weeks of SR-WBV. Results: Across the 4-week training period, musculoskeletal well-being and surefootedness were significantly increased (p < 0.05), whereas musculoskeletal pain was significantly reduced only in those who reported low back pain during the last 4 weeks prior to the study (p < 0.05). Body balance was significantly increased by SR-WBV (p < 0.05). Conclusion: SR-WBV seems to be an efficient option in primary prevention of musculoskeletal complaints and falls at work.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.41 no.4
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• pp.213-219
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• 2018

Mechanical components are to be produced with accurate dimensions in order to function properly in assemblies of a machine. Once designs of mechanical components are created, designers examine the designs by adopting many known experimental methods. A primary test method includes stress and strain evaluation of structural parts. In addition, fatigue test and vibration analysis are an important test method for mechanical components. Real experiments at a laboratory are established when products are manufactured. Since design changes should be done before producing the designs in factories, rapid modifications for new designs are required in production industries. FEM simulation is a proper choice for a design evaluation with speed at a detail stage in design process. This research focuses modeling and mechanical simulation of a mechanical component in order to ensure structural safety. In this paper, a universal joint, being used in driving axels of vehicles, is studied as a target component. A design model is created and tested in some ways by using commercial software of FEM. The designed component is being twisted to transmit heavy power and thus, torsional stress should be under strengths of the component's material. The next is fatigue analysis to convince fatigue cycles to be within the endurance limit of the material. Another test is a vibration analysis for rotational components. This research draws final conclusions from these test analyses and recommends whether the designed model is under safety condition in terms of mechanical structure.

• Journal of Aerospace System Engineering
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• v.16 no.5
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• pp.78-85
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• 2022

Multicopter-type unmanned aerial vehicles (UAV) are increasingly for cargo transportation to mountainous and island regions, image information acquisition in disaster areas, and emergency rescue transport. In order to successfully perform these tasks, the aircraft structure must be able to safely support the loads induced by flight conditions while ensuring the vibration and aeroelastic stability of the prop-rotor. This study introduced a structural analysis model of a 40kg payload multicopter with an engine-generator hybrid power system. The deformation and stress distribution are investigated depending on the load conditions. In addition, the vibration characteristics and aeroelastic stability of the prop-rotor were also presented to flight speed and aircraft pitch angle. The maximum thrust generated by the prop-rotor and the landing load applied to the multicopter under normal and emergency landing conditions were reviewed., It confirmed that the structure could support without failure. In addition, it confirmed that the damping characteristics of each primary locate in the constant region according to the aircraft's flight speed and the prop-rotors rotating speed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.10
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• pp.1108-1118
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• 2009

A Very High Temperature Gas Cooled Reactor (VHTR) has been selected as a high energy heat source of the order of $950^{\circ}C$ for nuclear hydrogen generation, which can produce hydrogen from water or natural gas. A primary hot gas duct (HGD) as a coaxial double-tube type cross vessel is a key component connecting a reactor pressure vessel and an intermediate heat exchanger in the VHTR. In this study, a structural sizing methodology for the primary HGD of the VHTR is suggested in order to modulate a flow-induced vibration (FIV). And as an example, a structural sizing of the horizontal HGD with a coaxial double-tube structure was carried out using the suggested method. These activities include a decision of the geometric dimensions, a selection of the material, and an evaluation of the strength of the coaxial double-tube type cross vessel components. Also in order to compare the FIV characteristics of the proposed design cases, a fluid-structure interaction (FSI) analysis was carried out using the ADINA code.

• Computational Structural Engineering
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• v.10 no.3
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• pp.225-231
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• 1997

The dynamic characteristics of Control Element Drive Mechanism(CEDM) for Korea Standard Nuclear Power Plant are studied with the CEDM modeled as a secondary mass in a simplified two degree of freedom system, while the reactor vessel as a primary mass. The optimal .mu.-f curve is developed to reduce the response amplitudes of both primary and secondary masses. In order to improve a design it is proposed that the natural frequency ratio, f, should be converged to 0.93, the mass ratio, .mu., should not be reduced, and the result should be converged to the optimal .mu.-f curve. Optimal design for CEDM components has been carried out and the response amplitude ratios of reactor are reduced 10.5 - 19.7% while those of CEDM are reduced 6.3 - 3.4%.

• Journal of Power System Engineering
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• v.14 no.3
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• pp.33-38
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• 2010

Technology of vehicle industry has been developing and it is required a better vehicle performance than before. Therefore, the consumers are asking not only an economic efficiency, functionality, polished design, ride comfort and silence but also a driving stability. The ride comfort, silence and driving stability are influenced by the size of vehicle and various facilities. But the principal factor is a room noise and vibration sensed by a driver and passenger. Thus, the NVH of vehicle has been raised and used as a principal factor for evaluation of vehicle performance. The primary objective of this study is an optimized design of powertrain mounting system. To optimized design was applied MSC.Nastran optimization modules. Results of dynamic analysis for powertrain mounting system was investigated. By theses results, design variables was applied 12 dynamic spring constant. And the weighting factor according to translational displacement and rotational displacement applied 3 cases. The objective function was applied to minimize displacement of powertrain. And the design variable constraint was imposed dynamic spring constant ratio. The constraint of design variable for objective function was imposed bounce displacement for powertrain.

• Smart Structures and Systems
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• v.30 no.4
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• pp.339-351
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• 2022

Evaluating the current condition of existing structures is of primary importance for economic and safety reasons. This can be addressed by Structural System Identification (SSI). A reliable static SSI depends on well-designed sensor configuration and loading cases, as well as efficient parameter estimation algorithms. Static SSI by the Measurement Error-Minimizing Observability Method (MEMOM) is a model-based deterministic static SSI method that could estimate structural parameters from static responses. In the current state of the art, this method is only applicable when structures are subjected to one loading case. This might lead to lack of information in some local regions of the structure (such as the null curvatures zones). To address this issue, the SSI by MEMOM using multiple loading cases is proposed in this work. Observability equations obtained from different loading cases are concatenated simultaneously and an optimization procedure is introduced to obtain the estimations by minimizing the discrepancy between the predicted response and the measured one. In addition, a Genetic-Algorithm (GA)-based Optimal Sensor Placement (OSP) method is proposed to tackle the OSP problem under multiple static loading cases for the very first time. In this approach, the Fisher Information Matrix (FIM)'s determinant is used as the metric of the goodness of sensor configurations. The numerical examples of a 3-span continuous bridge and a 13-story frame, are analyzed to validate the applicability of the extended SSI by MEMOM and the GA-based OSP method.

• Korean Journal of Optics and Photonics
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• v.22 no.6
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• pp.262-268
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• 2011

MIRIS(Multi-purpose Infra-Red Imaging System) is the main payload of the STSAT-3(Korea Science and Technology Satellite. 3), which is being developed by KASI(Korea Astronomy & Space Institute). EOC(Earth Observation Camera), which is one of two infrared cameras in MIRIS, is the camera for observing infrared rays from the Earth in the range of $3{\sim}5{\mu}m$. The optical system of the EOC is a Cassegrain prescription with aspheric primary and secondary mirrors, and its aperture is 100mm. A ring type flexure supports the EOC primary mirror with pre-loading in order to withstand expected load due to the shock and vibration from the launcher. Here we attempt to use the same mechanism by which a retainer supports the lens. Through opto-mechanical analysis it was confirmed that the EOC primary mirror is effectively supported.

• Smart Structures and Systems
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• v.1 no.1
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• pp.83-101
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• 2005

This paper summarizes the application of a rational methodology for the structural assessment of older reinforced concrete Tunisian bridges. This methodology is based on ambient vibration measurement of the bridge, identification of the structure's modal signature and finite element model updating. The selected case study is the Boujnah bridge of the Tunis-Msaken Highway. This bridge is made of a continuous four-span simply supported reinforced concrete slab without girders resting on elastomeric bearings at each support. Ambient vibration tests were conducted on the bridge using a data acquisition system with nine force-balance accelerometers placed at selected locations of the bridge. The Enhanced Frequency Domain Decomposition technique was applied to extract the dynamic characteristics of the bridge. The finite element model was updated in order to obtain a reasonable correlation between experimental and numerical modal properties. For the model updating part of the study, the parameters selected for the updating process include the concrete modulus of elasticity, the elastic bearing stiffness and the foundation spring stiffnesses. The primary objective of the paper is to demonstrate the use of the Enhanced Frequency Domain Decomposition technique combined with model updating to provide data that could be used to assess the structural condition of the selected bridge. The application of the proposed methodology led to a relatively faithful linear elastic model of the bridge in its present condition.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.619-624
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• 2002

A prestressed/precast concrete system was used to build the new Asian Olympic Stadium Project in Pusan, Korea. The stadium(mainly intended for cycle racing) is designed for the 2002 Asian Olympic Games and has a seating capacity of 20,000 spectators plus a few private suites. More than 1300 prestressed/precast components were used and they include single columns, primary beams, cantilever beams, double riser stands, and double tees. Especially, a total of 24 cantilever beams is used on the fourth story for the stands and double tees. These 8m long beams are post-tensioned to prevent cracking, to increase their durability and to serve serviceability by vibration. A cantilever section with cast-in-place topping is 800mm wide and 1500mm deep. Cantilever beams are connected to the column with the corbel by cast-in place concrete. Bonded post-tensioning tendons were assembled at the job site. Dead-end anchorages were installed in the end of cantilever beams and live-end anchorage is the opposite of them. This article presents the geometric layouts, design features and so on.