• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.4
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• pp.111-116
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• 2018

This research examines the drop impact of an external cooling unit package of an air conditioner system. The packaging is composed of a shock-absorbing material, which protects the package contents by absorbing the impact energy and other parts for fixture. Accurate quantification of the impact acceleration experienced by the package contents is necessary to design an effective packaging with minimal volume and sufficient shock absorbing capacity. Explicit time integration was used for the drop impact analyses. A finite element model of the package was constructed, material testing and material model selection were carried out, and sensors for data acquisition were modeled to obtain accurate simulation results. The results were compared with real physical test data. Due to imprecise modeling of the damping, the acceleration and strain values predicted by the simulation were larger than those from physical test. However, the trend of the history data and the peak deceleration value in the direction of impact showed good agreements. Thus, the analysis model and scheme are suitable for the design of an air conditioner cooling unit package.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.54-63
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• 2022

This paper is a study on the friction damper, which is one of the seismic reinforcement devices for structures. This study developed a damper by replacing the internal friction material with ultra high molecular weight polyethylene (UHMWPE), a type of composite material. In addition, this study applied a multi-friction method in which the internal structure where frictional force is generated is laminated in several layers. To verify the performance of the developed multi-friction damper, this study performed a characteristic analysis test for the basic physical properties, wear characteristics, and disc springs of the material. As a result of the wear test, the mass reduction rate of UHMWPE was 0.003%, which showed the best performance among the friction materials based on composite materials. Regarding the disc spring, this study secured the design basic data from the finite element analysis and experimental test results. Moreover, to confirm the quality stability of the developed multi-friction damper, this study performed an seismic load test on the damping device and the friction force change according to the torque value. The quality performance test result showed a linear frictional force change according to the torque value adjustment. As a result of the seismic load test, the allowable error of the friction damper was less than 15%, which is the standard required by the design standards, so it satisfies the requirements for seismic reinforcement devices.

• Journal of the Korean Geosynthetics Society
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• v.21 no.2
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• pp.57-65
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• 2022

This study simulated the shock wave propagation through the tamping material between explosives and hole wall at blasting works and verified the effect of tamping materials. The Arbitrary Lagrangian-Eulerian(ALE) method was selected to model the mixture of solid (Lagrangian) and fluid (Eulerian). The time series analysis was carried out during blasting process time. Explosives and tamping materials (air or water) were modeled with finite element mesh and the hole wall was assumed as a rigid body that can determine the propagation velocity and shock force hitting the hole wall from starting point (explosives). The numerical simulation results show that the propagation velocity and shock force in case of water were larger than those in case of air. In addition, the real site at blasting work was modeled and simulated. The rock was treated as elasto-plastic material. The results demonstrate that the instantaneous shock force was larger and the demolished block size was smaller in water than in air. On the contrary, the impact in the back side of explosives hole was smaller in water, because considerable amount of shock energy was used to demolish the rock, but the propagation of compression through solid becomes smaller due to the damping effect by rock demolition. Therefore, It can be proven that the water as the tamping media was more profitable than air.

• Computers and Concrete
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• v.14 no.6
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• pp.745-765
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• 2014

In this paper, it is aimed to determine the finite element model updating effects on the structural behavior of long span concrete highway bridges. Birecik Highway Bridge located on the 81stkm of Sanliurfa-Gaziantep state highway over Firat River in Turkey is selected as a case study. The bridge consist of fourteen spans, each of span has a nearly 26m. The total bridge length is 380m and width of bridge is 10m. Firstly, the analytical dynamic characteristics such as natural frequencies and mode shapes are attained from finite element analyses using SAP2000 program. After, experimental dynamic characteristics are specified from field investigations using Operational Modal Analysis method. Enhanced Frequency Domain Decomposition method in the frequency domain is used to extract the dynamic characteristics such as natural frequencies, mode shapes and damping ratios. Analytically and experimentally identified dynamic characteristics are compared with each other and finite element model of the bridge is updated to reduce the differences by changing of some uncertain parameters such as section properties, damages, boundary conditions and material properties. At the end of the study, structural performance of the highway bridge is determined under dead load, live load, and dynamic loads before and after model updating to specify the updating effect. Displacements, internal forces and stresses are used as comparison parameters. From the study, it is seen that the ambient vibration measurements are enough to identify the most significant modes of long span highway bridges. Maximum differences between the natural frequencies are reduced averagely from %46.7 to %2.39 by model updating. A good harmony is found between mode shapes after finite element model updating. It is demonstrated that finite element model updating has an important effect on the structural performance of the arch type long span highway bridge. Maximum displacements, shear forces, bending moments and compressive stresses are reduced %28.6, %21.0, %19.22, and %33.3-20.0, respectively.

• Journal of the Korean Geotechnical Society
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• v.34 no.10
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• pp.5-16
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• 2018

The ever-increasing amount of waste vinyl is causing big environmental problems. In particular, those from farming industry are sometimes left on site or even illegally reclaimed due to the lack of environmental concerns and capacity for collection, which worsens the situation. It is, therefore, believed that the recycling of waste vinyl is the most ideal solution in the viewpoint of environmental preservation. In this context, the potential of vinyl strip as a ground reinforcing material is investigated to expand the application of waste vinyl recycling. In this study, a series of uniaxial compression tests and resonant column tests were performed for sand specimens reinforced with vinyl strips and cement to investigate their reinforcing effects on static and dynamic behaviors. The changes in the uniaxial compressive strength (UCS), the shear modulus and the damping ratio according to the mixing ratio of vinyl strips and cements were analysed for sand specimens, having 40% and 60% relative densities, under various mixing conditions. As a result, both the static and dynamic reinforcing effects of vinyl strip-cement mixture were confirmed and the optimum mixing ratio was proposed.

• The KSFM Journal of Fluid Machinery
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• v.10 no.2 s.41
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• pp.41-45
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• 2007

The shutoff unit was designed to provide rapid insertion of neutron absorbing material into the reactor core to shutdown the reactor quickly and also to withdraw the absorber slowly to avoid a log-rate trip. Four shutoff units were installed on the HANARO reactor but the half-core test facility was equipped with one shutoff unit. The reactor trip or shutdown is accomplished by four shutoff units by insertion of the shutoff rods. The shutoff rod(SOR) is actuated by a directly linked hydraulic cylinder on the reactor chimney, which is pressurized by a hydraulic pump. The rod is released to drop by gravity, when triplicate solenoid valves are de-energized to vent the cylinder. The hydraulic pump, pipe and air supply system are provided to be similar with the HANARO reactor. The shutoff rod drops for 647mm stroke within 1.13 seconds to shut down the reactor and it is slowly inserted to the full down position, 700mm, with a damping. We have conducted the drop test of the shutoff rod in order to show the performance and the structural integrity of operating system of the shutoff unit. The present paper deals with the 647mm drop time and the withdrawal time according to variation of the pool water temperature, the water level and the core flow.

• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.687-694
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• 2005

In current design practice, the thickness of the floor slab has been determined to satisfy requirement for deflection control. However, previous study shows that the floor thicknesses in residential buildings may not satisfy the floor vibration criteria, even though the thickness is determined by the serviceability requirements in current design provisons. Thus it is necessary to develop the procedure to determine slab thickness that satisfies the floor vibration criteria. This study attempts to propose slab thickness for flat plate slab systems that satisfies floor vibration criteria against occupant induced floor vibration(heel drop load). Two boundary conditions(simple and fixed support), three square flat plates(4, 6, 8m), and five concrete strength($18\~30$ MPa) are considered. Since there are large uncertainties in loading and material properties, probabilistic approach is adopted using Monte-Carlo simulation procedures.

• Journal of Mechanical Science and Technology
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• v.19 no.3
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• pp.778-791
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• 2005

A novel pneumatic artificial muscle actuator (PAM actuator), which has achieved increased popularity to provide the advantages such as high strength and high power/weight ratio, low cost, compactness, ease of maintenance, cleanliness, readily available and cheap power source, inherent safety and mobility assistance to humans performing tasks, has been regarded during the recent decades as an interesting alternative to hydraulic and electric actuators. However, some limitations still exist, such as the air compressibility and the lack of damping ability of the actuator bring the dynamic delay of the pressure response and cause the oscillatory motion. Then it is not easy to realize the performance of transient response of pneumatic artificial muscle manipulator (PAM manipulator) due to the changes in the external inertia load with high speed. In order to realize satisfactory control performance, a variable damper-Magneto­Rheological Brake (MRB), is equipped to the joint of the manipulator. Superb mixture of conventional PID controller and a phase plane switching control method brings us a novel controller. This proposed controller is appropriate for a kind of plants with nonlinearity, uncertainties and disturbances. The experiments were carried out in practical PAM manipulator and the effectiveness of the proposed control algorithm was demonstrated through experiments, which had proved that the stability of the manipulator can be improved greatly in a high gain control by using MRB with phase plane switching control method and without regard for the changes of external inertia loads.

• Earthquakes and Structures
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• v.18 no.2
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• pp.215-222
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• 2020

In this paper, slit steel rubber bearing is presented as an innovative seismic isolator device. In this type of isolator, slit steel damper is an energy dissipation device. Its advantages in comparison with that of the lead rubber bearing are its simplicity in manufacturing process and replacement of its yielding parts. Also, slit steel rubber bearing has the same ability to dissipate energy with smaller value of displacement. Using finite element method in ABAQUS software, a parametric study is done on the performance of this bearing. Three different kinds of isolator with three different values of strut width, 9, 12 and 15 mm, three values of thickness, 4, 6 and 8 mm and two steel types with different yield stress are assessed. Effects of these parameters on the performance characteristics of slit steel rubber bearing are studied. It is shown that by decreasing the thickness and strut width and by selecting the material with lower yield stress, values of effective stiffness, energy dissipation capacity and lateral force in the isolator reduce but equivalent viscous damping is not affected significantly. Thus, by choosing appropriate values for thickness, strut width and slit steel damper yield stress, an isolator with the desired behavior can be achieved. Finally, the performance of an 8-storey frame with the proposed isolator is compared with the same frame equipped with LRB. Results show that SSRB is successful in base shear reduction of structure in a different way from LRB.

• The Journal of the Acoustical Society of Korea
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• v.34 no.3
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• pp.210-218
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• 2015

When the driving voltage of an ultrasound transducer is increased to improve the quality of ultrasound images, heat is generated inside the transducer that can cause patient's skin burn and degradation of transducer performance. Hence, in this paper, a method to disperse the heat of the transducer has been studied. The phased array transducer having 3 MHz center frequency and 32 channels was selected for analyses of the thermal dispersion. First, mechanism of the heat generation was investigated in relation to the transducer operation through theoretical analysis, and material damping and sound pressure amplitude were confirmed to be influential on the heat generation. Further, we investigated the effects of the properties of the materials constituting the transducer on the thermal dispersion through finite element analysis. Based on the analysis results, we determined the thermal properties of the constituent materials that could facilitate the thermal dispersion inside the transducer. The determined thermal properties were applied to the finite element model, and the results showed that the maximum temperature at an acoustic lens contacting with a patient was decreased to 51 % of its initial value.