• The Journal of Engineering Geology
• /
• v.7 no.2
• /
• pp.139-149
• /
• 1997

Electrical resistivity monitoring methods were adopted to detect groundwater table change in alluvium. Numerical modelling test using finite element method(FEM) and field resisfivity monitoring were conducted in the study. The field monitoring data were acquired in the alluvium deposit site in Jeong-Dong Ri, Geum River where pumping test had been conducted continuously for 20 days to make artificial changes of groundwater table. The unit distance of the electrode array was 4m and 21 fixed electrodes were applied in numerical calculation and field data acquisition. "Modified Wenner" and dipole-dipole array configurations were used in the study. The models used in two-dimensional numerical test were designed on the basis of the simplifving geological model of the alluvium in Jeong Dong Ri, Geum River. Numerical test results show that the apparent resistivity pseudosections were changed in the vicinity of the pootion where groundwater table was changed. Furthermore, there are some apparent resistivity changes in the boundary between aquifer and crystalline basement rock which overlays the aquifer. The field monitoring data also give similar results which were observed in numerical tests. From the numerical test using FEM and field resistivity monitoring observations in alluvium site of Geum River, the electrical monitoring method is proved to be a useful tool for detecting groundwater behavior including groundwater table change. There are some limitations, however, in the application of the resistivity method only because the change of groundwater table does not give enough variations in the apparent resistivity pseudosections to estimate the amount of groundwater table change. For the improved detection of groundwater table changes, it is desirable to combine the resistivity method with other geophysical methods that reveal the underground image such as high-resolution seismic and/or ground penetrating radar surveys.

• Korean Journal of Environmental Agriculture
• /
• v.18 no.1
• /
• pp.18-23
• /
• 1999

A numerical model of flow velocity in the standing water system is presented. This model(RMA-2), based on the 2-dimensional unsteady momentum and continuity equations, uses finite element techniques to simulate the distribution of velocity over a spatial location of lakes. The present model represents an improvement over existing numerical water quality models in that it can model the unsteady state and can, therefore, cope with time with a spatial location of standing waters such as lakes and large reservoirs. The model thus allows the engineer to do more accurate estimation of water flows and thus water qualities in standing waters where directions and velocities of the flow become more important for the simulation of the water quality than in running waters. Tests for the data collected in the lake "Paldang" indicates that the model works well under limited circumstances. However, to be more accurate estimation of velocity with the present model, accumulation of data for the measurement of velocities and renovation of geometrical conditions of the lake would be needed.

• Tunnel and Underground Space
• /
• v.20 no.4
• /
• pp.267-276
• /
• 2010

In modern rock engineering practice, fully grouted rock bolting is actively employed as a major supporting system, so that understanding the behavior of fully grouted rock bolts is essential for the precise design of rock bolting. Despite its importance, the supporting mechanism of rock bolts has not been fully understood yet. Since most of existing analytical models for rock bolts were developed by drastically simplifying their boundary conditions, they are not suitable for the bolts of in-situ condition. In this study, 3-D elastic FE analysis of fully grouted rock bolts has been conducted to provide insight into the supporting mechanism of the bolt. The distribution of shear and axial stresses along the bolt are investigated with the consideration of different boundary conditions including three different displacement boundary conditions at the bolt head, the presence of intersecting rock joints, and the variation of elastic modulus of adjacent rock. The numerical result reveals that installation of the faceplate at the bolt head plays an important role in mobilizing the supporting action and enhancing the supporting capabilities of the fully grouted rock bolts.

• Journal of the Korea Convergence Society
• /
• v.6 no.4
• /
• pp.99-105
• /
• 2015

In order to prevent the environmental pollution nowadays, the mobile device for one person of cruiser board not used with the fossil oil has been noticed. This study aims to analyze the property of cruiser board due to the shape by carrying out the structural analysis for the safe design of cruiser board. Two models of the existing cruiser board and the cruiser board with new configuration are designed. As the structural analysis was carried out by using the finite element analysis program, the durability by deformation, stress and fatigue life was investigated. In the study result, the model of cruiser board with new configuration has the maximum deformation of 0.000971mm, the maximum stress of 0.936MPa and the fatigue life from 1827.7Cycle to $1.887{\times}105Cycle$. As all study result values at the new model became better than the existing model, the new model was seen to become more adequate at using than the existing model. This study result can be contributed to the safer and durable design of cruiser board. And it is possible to be grafted onto the convergence technique at design and show the esthetic sense.

• Journal of Energy Engineering
• /
• v.20 no.2
• /
• pp.90-95
• /
• 2011

This study was conducted to judge requalification of cylinders by assessing composite flaws such as scratches, cuts, and gouges damaging on the composite of Type III cylinders for compressed natural gas vehicles. As a result of the flaw tolerance test, all specimens have satisfied with minimum requirement cycles according to damage levels based on ISO 19078 and cyclic performance for pressure showed beyond twenty thousands in damage level 1 and 2, and did eighteen thousands to twenty-one thousands in damage level 3. Eight of twelve specimens failed the test due to composite flaws and the rest of the cylinders failed regardless of flaws. The results of Finite Element Method followed by the computer simulation indicated that the stress of 79.5 MPa calculated on the flaw model of $1.25\;mm{\times}200\;mm$ and the stress of 66.6 MPa on the non-flaw model when the service pressure applied to inside of cylinder. The difference between the models is about 19.37%. We concluded that this difference influences fatigue life and this flaw model is a critical value affecting cyclic performance of cylinders.

• Journal of Biomedical Engineering Research
• /
• v.26 no.2
• /
• pp.123-127
• /
• 2005

Compression Hip Screw (CHS) is one of the most widely-used prostheses for the treatment of intertrochanteric fractures because of its strong fixation capability. Fractures at the neck and screw holes are frequently noted as some of its clinical drawbacks, which warrant more in-depth biomechanical analysis on its design variables. The purpose of this study was to evaluate changes in the strength with respect to the changes in design such as the plate thickness and the number of screw holes. Both mechanical test and FEM analysis were used to systematically investigate the sensitivities of the above-mentioned design variables. For the first part of the mechanical test, CHS (n=20) were tested until failure. The CHS specimens were classified into four groups: Group Ⅰ was the control group with the neck thickness of 6-㎜ and 5 screw holes on the side plate, Group Ⅱ 6-㎜ thick and 8 holes, Group Ⅲ 7.5-㎜ thick and 5 holes, and Group Ⅳ 7.5-㎜ thick and 8 holes. Then, the fatigue test was done for each group by imparting 50% and 75% of the failure loads for one million cycles. For the FEM analysis, FE models were made for each group. Appropriate loading and boundary conditions were applied based on the failure test results. Stresses were assessed. Mechanical test results indicated that the failure strength increased dramatically by 80% with thicker plate. However, the strength remained unchanged or decreased slightly despite the increase in number of holes. These results indicated the higher sensitivity of plate thickness to the implant strength. No fatigue failures were observed which suggested the implant could withstand at least one million cycles of fatigue load regardless of the design changes. Our FEM results also supported the above results by showing a similar trend in stress as those of mechanical test. In summary, our biomechanical results were able to show that plate thickness could be a more important variable in design for reinforcing the strength of CHS than the number of screw holes.

• Journal of Aerospace System Engineering
• /
• v.14 no.1
• /
• pp.21-27
• /
• 2020

Aircraft should be equipped with various external stores for mission performance. Since these external stores may cause structural instability of aircraft, an evaluation of the effects between the aircraft and the external stores is required. For this purpose, an aircraft dynamic characteristics analysis reflecting an external store was performed, and the finite element model for the analysis of aircraft dynamic characteristics should simulate the dynamic characteristics of the component as accurately as possible while using a minimum of the nodes and elements. In this study, a stick model was constructed for dynamic characteristics analysis of the external fuel tank and installation pylon using MSC Patran/Nastran. For the calculation of the equivalent stiffness of the stick model, a simple beam theory was applied to construct the stick model of each part, and the validity of each stick models was confirmed by mode comparison with the fine model. Additionally, the model analysis of the stick model assembly, simulating a pylon equipped with an external fuel tank was performed to confirm that the basic modes required for the analysis of aircraft dynamic characteristics are well extracted. Finally, it was confirmed that the developed stick model assembly could be used for analysis of aircraft dynamic characteristics by comparing the errors in modes between the fine model assembly and the stick model assembly.

• Tribology and Lubricants
• /
• v.36 no.2
• /
• pp.105-115
• /
• 2020

This paper presents a numerical study on the rotordynamic analysis of a dual-spool turbofan engine in the context of blade defect events. The blades of an axial-type aeroengine are typically well aligned during the compressor and turbine stages. However, they are sometimes exposed to damage, partially or entirely, for several operational reasons, such as cracks due to foreign objects, burns from the combustion gas, and corrosion due to oxygen in the air. Herein, we designed a dual-spool rotor using the commercial 3D modeling software CATIA to simulate blade defects in the turbofan engine. We utilized the rotordynamic parameters to create two finite element Euler-Bernoulli beam models connected by means of an inter-rotor bearing. We then applied the unbalanced forces induced by the mass eccentricities of the blades to the following selected scenarios: 1) fully balanced, 2) crack in the low-pressure compressor (LPC) and high pressure compressor (HPC), 3) burn on the high-pressure turbine (HPT) and low pressure compressor, 4) corrosion of the LPC, and 5) corrosion of the HPC. Additionally, we obtained the transient and steady-state responses of the overall rotor nodes using the Runge-Kutta numerical integration method, and employed model reduction techniques such as component mode synthesis to enhance the computational efficiency of the process. The simulation results indicate that the high-vibration status of the rotor commences beyond 10,000 rpm, which is identified as the first critical speed of the lower speed rotor. Moreover, we monitored the unbalanced stages near the inter-rotor bearing, which prominently influences the overall rotordynamic status, and the corrosion of the HPC to prevent further instability. The high-speed range operation (>13,000 rpm) coupled with HPC/HPT blade defects possibly presents a rotor-case contact problem that can lead to catastrophic failure.

• Journal of the Korea Concrete Institute
• /
• v.15 no.6
• /
• pp.769-777
• /
• 2003

The strengthening of concrete structures in situ with externally bonded carbon fiber is increasingly being used for repair and rehabilitation of existing structures. Because carbon fiber is attractive for this application due to its good tensile strength, resistances to corrosion, and low weight. Generally bond strength and behavior between concrete and carbon fiber mesh(CFM) is very important, because of enhancing bond of CFM. Therefore if bond strength is sufficient, it will be expect to enhance reinforcement effect. Unless sufficient, expect not to enhance reinforcement effect, because of occuring bond failure between concrete and CFM. In this study, the bond strength and load-displacement response of CFM to the concrete by the direct pull-out test(the tensile-shear test method) were investigated using the experiment and the finite element method analysis with ABAQUS. The key variables of the experiment are the location of clip, number of clips and thickness of cover mortar. The general results indicate that the clip anchorage technique for increasing bond strength with CFM appear to be effective to maintain the good post-failure behavior.

• Composites Research
• /
• v.29 no.2
• /
• pp.45-52
• /
• 2016

An understanding of the failure mechanisms of the adhesive layer is decisive in interpreting the performance of a particular adhesive joint because the delamination is one of the most common failure modes of the laminated composites such as the fiber metal laminates. The interface between different materials, which is the case between the metal and the composite layers in this study, can be loaded through a combination of fracture modes. All loads can be decomposed into peel stresses, perpendicular to the interface, and two in-plane shear stresses, leading to three basic fracture mode I, II and III. To determine the load causing the delamination growth, the energy release rate should be identified in corresponding criterion involving the critical energy release rate ($G_C$) of the material. The critical energy release rate based on these three modes will be $G_{IC}$, $G_{IIC}$ and $G_{IIIC}$. In this study, to evaluate the fracture behaviors in the fracture mode I and II of the adhesive layer in fiber metal laminates, the double cantilever beam and the end-notched flexure tests were performed using the reference adhesive joints. Furthermore, it is confirmed that the experimental results of the adhesive fracture toughness can be applied by the comparison with the finite element analysis using cohesive zone model.