• International Journal of Aeronautical and Space Sciences
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• v.14 no.4
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• pp.356-368
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• 2013

The Korea Aerospace Research Institute plans to launch a lunar module by 2025, and so is carrying out a preliminary study. Landing stability on the lunar surface is a key design factor of a lunar module. In this paper, a 1/6 scale model of a lunar module is investigated, for its landing stability on non-level surfaces. The lunar module has four tripod legs, with aluminum honeycomb shock absorbers in each leg strut. ADAMS$^{TM}$, the most widely used multi-body dynamics and motion analysis software, is used to simulate the module's lunar landing. Three types of dampers in the struts (rigid, viscous, and aluminum honeycomb dampers), and two types of lunar surfaces (rigid and elastic) are considered. The Sforce function is adopted, to model the aluminum honeycomb dampers. Details on the modeling and analysis of the landing stability of the 1/6 scale lunar module and the simulation results are provided in this paper.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.6
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• pp.31-39
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• 1998

The role of bushing elements linked between suspension parts is to enhance ride quality and handling stability by the spring and damping effect from the elastic deformation. In this paper, a theoretical derivation and computer implementation off a bushing element are proposed. Three different vehicle models are generated to test the developed bushing module. The developed bushing module is implemented as a bushing module in the vehicle dynamic analysis program AUTODYN7.

• IEMEK Journal of Embedded Systems and Applications
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• v.16 no.6
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• pp.259-266
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• 2021

Edge Computing enables real-time big data processing by performing computing close to the physical location of the user or data source. However, in an edge computing environment, various situations that affect big data processing performance may occur depending on temporary service requirements or changes of physical resources in the field. In this paper, we proposed a BigCrawler system that dynamically configures the computing module and storage module according to the big data collection status and computing resource usage status in the edge computing environment. And the feature of big data processing workload according to the arrangement of computing module and storage module were analyzed.

• Nuclear Engineering and Technology
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• v.55 no.9
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• pp.3229-3240
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• 2023

Due to neutron radiation, atomic displacement has a significant effect on material in nuclear reactors. A range of secondary displacement models, including the Kinchin-Pease (K-P), Lindhard, Norgett-Robinson-Torrens (NRT), and athermal recombination-corrected displacement per atom (arc-dpa) have been suggested to calculate the number of displacement per atom (dpa). As neutron elastic interaction is the main cause of displacement damage, the focus of the current study is to calculate the atomic displacement caused by the neutron elastic interaction in order to estimate the exact amount of yield strength in a WWER-1000 reactor pressure vessel. To achieve this purpose, the reactor core is simulated by MCNPX code. In addition, a program is developed to calculate the elastic radiation damage induced by the incident neutron flux (RADIX) based on different models using Fortran programming language. Also, due to non-elastic interaction, the displacement damage is calculated by the HEATR module of the NJOY code. ASME E-693-01 standard, SPECTER, NJOY codes, and other pervious findings have been used to validate RADIX results. The results showed that the RADIX(arc-dpa)/HEATR outputs have appropriate accuracy. The relative error of the calculated dpa resulting from RADIX(arc-dpa)/HEATR is about 8% and 46% less than NJOY code, respectively in the ¼ and ¾ vessel wall.

• Geomechanics and Engineering
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• v.29 no.3
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• pp.207-218
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• 2022

In submerged floating tunnels (SFTs), a next-generation maritime transportation infrastructure, the tunnel module floats in water due to buoyancy. For the effective and economical use of SFTs, connection with the ground is inevitable, but the stability of the shore connection is weak due to stress concentration caused by the displacement difference between the subsea bored tunnel and the SFT. The use of an elastic joint has been proposed as a solution to solve the stability problem, but it changes the dynamic characteristics of the SFT, such as natural frequency and mode shape. In this study, the finite element method (FEM) was used to simulate the elastic joints in shore connections, assuming that the ground is a hard rock without displacement. In addition, a small-scale model test was performed for FEM model validation. A parametric study was conducted on the resonance behavior such as the natural frequency change and velocity, stress, and reaction force distribution change of the SFT system by varying the joint stiffness under loading conditions of various frequencies and directions. The results indicated that the natural frequency of the SFT system increased as the stiffness of the elastic joint increased, and the risk of resonance was the highest in the low-frequency environment. Moreover, stress concentration was observed in both the SFT and the shore connection when resonance occurred in the vertical mode. The results of this study are expected to be utilized in the process of quantitative research such as designing elastic joints to prevent resonance in the future.

• Nuclear Engineering and Technology
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• v.31 no.6
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• pp.631-637
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• 1999

The module LEAPR of NJOY data processing system has been improved to have the capability of computing the thermal elastic scattering cross sections for silicon, which has a diamond-like structure. Silicon lattice was assumed as an fcc lattice with two atoms at each lattice point. The calculation formulas for thermal neutron elastic scattering by silicon were introduced and incorporated into LEAPR, and then the scattering cross sections for silicon were computed. The results were compared with experimental data, and they were found to give a good agreement with experimental data.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.1
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• pp.79-88
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• 2014

Enhancing the working speed and positional accuracy of high-speed press machines is essential for improving the parts accuracy and productivity. However it is known that the positional accuracy decreases and the risk of parts failure increases as the working speed of press machine increases. Therefore predicting such problems during the stage of press structure design is necessary for precise design of high-speed press machines. In the present investigation, the dynamic-elastic deformation of press drive module parts with eccentric masses was examined by finite element analysis and experiment. Then the positional accuracy and parts failure of high-speed press machines was evaluated.

• Smart Structures and Systems
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• v.29 no.1
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• pp.1-16
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• 2022

Despite recent breakthroughs in deep learning and computer vision fields, the pixel-wise identification of tiny objects in high-resolution images with complex disturbances remains challenging. This study proposes a modified U-net for tiny crack segmentation in real-world steel-box-girder bridges. The modified U-net adopts the common U-net framework and a novel Self-Attention-Self-Adaption (SASA) neuron as the fundamental computing element. The Self-Attention module applies softmax and gate operations to obtain the attention vector. It enables the neuron to focus on the most significant receptive fields when processing large-scale feature maps. The Self-Adaption module consists of a multiplayer perceptron subnet and achieves deeper feature extraction inside a single neuron. For data augmentation, a grid-based crack random elastic deformation (CRED) algorithm is designed to enrich the diversities and irregular shapes of distributed cracks. Grid-based uniform control nodes are first set on both input images and binary labels, random offsets are then employed on these control nodes, and bilinear interpolation is performed for the rest pixels. The proposed SASA neuron and CRED algorithm are simultaneously deployed to train the modified U-net. 200 raw images with a high resolution of 4928 × 3264 are collected, 160 for training and the rest 40 for the test. 512 × 512 patches are generated from the original images by a sliding window with an overlap of 256 as inputs. Results show that the average IoU between the recognized and ground-truth cracks reaches 0.409, which is 29.8% higher than the regular U-net. A five-fold cross-validation study is performed to verify that the proposed method is robust to different training and test images. Ablation experiments further demonstrate the effectiveness of the proposed SASA neuron and CRED algorithm. Promotions of the average IoU individually utilizing the SASA and CRED module add up to the final promotion of the full model, indicating that the SASA and CRED modules contribute to the different stages of model and data in the training process.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.4
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• pp.295-306
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• 2010

Contrary to an intact rock, the jointed rock mass shows strain-dependent deformation characteristics (elastic modulus and damping ratio). The maximum elastic modulus of a rock mass can be obtained from an elastic wave-based exploration in a small strain level and applied to seismic analyses. However, the assessment and application of the non-linear characteristics of rock masses in a small to medium strain level ($10^{-4}{\sim}0.5%$) have not been carried out yet. A non-linear dynamic analysis module is newly developed for FLAC3D to simulate strain-dependent shear modulus degradation and damping ratio amplification characteristics. The developed module is verified by analyzing the change of the Ricker wave propagation. Strain-dependent non-linear characteristics are obtained from disks of cored samples using a rock mass dynamic testing apparatus which can evaluate wave propagation characteristics in a jointed rock column. Using the experimental results and the developed non-linear dynamic module, seismic analyses are performed for the intersection of a shaft and an inclined tunnel. The numerical results show that vertical and horizontal displacements of non-linear analyses are larger than those of linear analyses. Also, non-linear analyses induce bigger bending compressive stresses acting on the lining. The bending compressive stress concentrates at the intersection part. The fundamental understanding of a strain-dependent jointed rock mass behavior is achieved in this study and the analytical procedure suggested can be effectively applied to field designs and analyses.

• Journal of The Korean Society of Agricultural Engineers
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• v.61 no.2
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• pp.41-50
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• 2019

Stiffness characteristic of subgrade is one of the most important aspects for the design and evaluation of pavement and railway. However, adequate field testing methods for evaluating the stiffness characteristics of the subgrade have not been developed yet. In this study, an in-situ dynamic stiffness analyzer (IDSA) is developed to evaluate the characteristics of subgrade stiffness along the depth, and its performance is evaluated in elastic materials and a compacted soil. The IDSA consists of a falling hammer system, a connecting rod, and a tip module. Four strain gauges and an accelerometer are installed at the tip of the rod to analyze the dynamic response of the tip generated by the drop of hammer. Based on the Boussinesq's method, the stiffness and Young's modulus of the specimens can be calculated. The performance of IDSA was tested on three elastic materials with different hardness and a compacted soil. For the repeatability of test performance, the dynamic signals for force and displacement of the tip are averaged from the hammer impact tests performed five times at the same drop height. The experimental results show that the peak force, peak displacement, and the duration depend on the hardness of the elastic materials. After calculating the stiffness and elastic modulus, it is revealed that as the drop height of hammer increases, the stiffness and elastic moduli of MC nylon and the compacted soil rapidly increase, while those of urethanes less increase.