• 한국안전학회지
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• 제21권3호
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• pp.38-44
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• 2006

The majority of both small and large-scale experiments on gas explosion have been carried out in the explosion instruments with cylindrical tubes of a high length/diameter ratio and vessels of a high height/length ratio, focusing on investigating the interaction between propagating flame and obstacles inside the tubes or vessels. The results revealed that there is a strong interaction between the propagating flame and turbulence formed after the flame passes the obstacle. However this paper focuses on analyzing the pressure impact or profile outside the vent in vented gas explosion in a partially confined chamber by performing gas explosion experiments in a reduced-scale experimental assembly properly constructed. This study has considered eight different cases in gas explosion based on variation of three kinds of parameters such as height of vessel, shape of the vent and vent size, and reveals that the large vessel with big size circle vent is more danger to the target than others because the overpressure is spread out faraway horizontally and vertically.

• 한국해양공학회지
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• 제20권4호
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• pp.9-16
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• 2006

A new wave-absorbing system, called the liquefied sandbed wave barrier (LSWB) system, is currently under development at the Port and Airport Research Institute (PARI) of Japan. The wave damping effect by the LSWB system is substantial, as confirmed by small-scale experiments and FEM numerical calculations, i.e., the wave transmission coefficient of the system is less than 0.2. Here, the results of large-scale experiments arediscussed in view of practical application. Although the LSWB system provides high wave damping, nearly equal to theoretical values, difficulty exists in obtaining a homogeneously liquefied sandbed, due to the occurrence of liquefied sandbed compaction by cyclic wave loading, which in turn, reduces excess pare pressure and the wave damping effect. These two phenomena primarily occur when the sandbed is composed of fine sand with small permeability. Based on experimental results, we propose a design method that includes countermeasures against such problems, and a prototype LSWB system is constructed in a very large wave flume at PARI. Wave damping by the prototype LSWB system is confirmed to be quite stable and high, as predicted by theoretical calculations.

• Nuclear Engineering and Technology
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• 제53권10호
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• pp.3182-3195
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• 2021

The implementation and validation of multi-dimensional (multi-D) features in thermal-hydraulic system codes aims to extend the application of these codes towards multi-scale simulations. The main goal is the simulation of large-scale three-dimensional effects inside large volumes such as piping or vessel. This novel approach becomes especially relevant during the simulation of accidents with strongly asymmetric flow conditions entailing density gradients. Under such conditions, coolant mixing is a key phenomenon on the eventual variation of the coolant temperature and/or boron concentration at the core inlet and on the extent of a local re-criticality based on the reactivity feedback effects. This approach presents several advantages compared to CFD calculations, mainly concerning the model size and computational efforts. However, the range of applicability and accuracy of the newly implemented physical models at this point is still limited and needs to be further extended. This paper aims at contributing to the validation of the multi-D features of the system code ATHLET based on the simulation of the Tests 1.1 and 2.1, conducted at the test facility ROCOM. Overall, the multi-D features of ATHLET predict reasonably well the evolution from both experiments, despite an observed overprediction of coolant mixing at the vessel during both experiments.

• 대한임베디드공학회논문지
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• 제19권2호
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• pp.73-81
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• 2024

Recently, mobile manipulators have been utilized in agriculture industry for weed removal and harvest automation. This paper proposes a domain adaptive fruit detection method for harvest automation, by utilizing OWL-ViT model which is an open-vocabulary object detection model. The vision-language model can detect objects based on text prompt, and therefore, it can be extended to detect objects of undefined categories. In the development of deep learning models for real-world problems, constructing a large-scale labeled dataset is a time-consuming task and heavily relies on human effort. To reduce the labor-intensive workload, we utilized a large-scale public dataset as a source domain data and employed a domain adaptation method. Adversarial learning was conducted between a domain discriminator and feature extractor to reduce the gap between the distribution of feature vectors from the source domain and our target domain data. We collected a target domain dataset in a real-like environment and conducted experiments to demonstrate the effectiveness of the proposed method. In experiments, the domain adaptation method improved the AP50 metric from 38.88% to 78.59% for detecting objects within the range of 2m, and we achieved 81.7% of manipulation success rate.

• Nuclear Engineering and Technology
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• 제56권1호
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• pp.19-33
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• 2024

In nuclear thermal-hydraulic system codes, most correlations used for vertical pipes, under downward two-phase flow, have been developed considering small pipes or pool systems. This suggests that there could be uncertainties in applying the correlations to accident scenarios involving large vertical pipes owing to the difference in the characteristics of two-phase flows, or flow conditions, between large and small pipes. In this study, we modified the Multi-dimensional Analysis of Reactor Safety KINS Standard (MARS-KS) code using correlations, such as the drift-flux model and two-phase multiplier, developed in a plant-scale air-inflow experiment conducted for a pipe of diameter 600 mm under downward two-phase flow. The results were then analyzed and compared with those based on previous correlations developed for small pipes and pool conditions. The modified code indicated a good estimation performance in two plant-scale experiments with large pipes. For the siphon-breaking experiment, the maximum errors in water flow for modified and original codes were 2.2% and 30.3%, respectively. For the air-inflow accident experiment, the original code could not predict the trend of frictional pressure gradient in two-phase flow as / increased, while the modified MARS-KS code showed a good estimation performance of the gradient with maximum error of 3.5%.

• 한국대기환경학회지
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• 제11권2호
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• pp.145-152
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• 1995

Predictability of a Gaussian model, ISCST2 was assessed by scaling up wind tunnel experiments with a 1/3,000 terrain model to the real scale. Concentration profiles obtained from the flat-terrain experiment in the neutral condition were estimated to be in agreement with the calculated ones from ISCST2 in the stability class A, but the difference between the two was still large. Concentration profiles from the mountainous-terrain experiments were better fitted to the calculated ones primarily because in the experiment, concentration behind the source was raised due to the effect of a hill in the upstream side. Model prediction was improved with including the downwash effect of buildings and the hill, but overall concentration profiles were not much different from a typical Gaussian profile. While concentration profiles in the experiments were changed with local flows by varying the wind direction and the topography, those from the Gaussian modeling were mot freely changed together with these variations.

• 상하수도학회지
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• 제19권5호
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• pp.572-581
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• 2005

This research is conducted to develop predictable method of real scale nanofiltration treatability with small scale nanofiltration experiments. As a result of comparing calculated values with measured values, they are in a good agreement for the concentrations in filtered water and concentrated water. The results of that are not affected by change of system recovery from 20% to 95%. The proposed method is produced using constant recovery of elements, that is, no considering the pressure change. we can predict filtrated flux and contaminant concentrations with the method. The method has the following steps. (1) Calculate recovery of each element with water quality level after fixing recovery elements, (2) Predict system recovery with recovery of elements in 1, 2, 3, and 4 banks, (3) Run small scale nanofiltration experiments in predicted water quality and (4) Simulate large scale nanofiltration system for forecasting actual water quality. As the cost for nanofiltration pretest will reduced if we use the proposed method, it will be a promising method for introducing nanofiltration to supply safe drinking water.

• 수산해양기술연구
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• 제47권1호
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• pp.1-9
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• 2011

In order to investigate the cause and magnitude of scale effect occurring in the model experiments of fishing nets, five pairs of Nylon pyramid nets and one pair of PE ones in which all the two nets paired were equal each other in the factors determining their flow resistance, i. e., the ratio d/l of diameter d to length l of bars, the angle f between two adjacent bars, the attack angle q of nettings to the water flow, and the wall area S of nets, and different in the values of d and l were prepared. Then, the nets were attached to the circular steel frame alternately and their flow resistances with shapes in water were measured on the sea ascribing no turbulent flows by using the tension meter made of a block bearing for the experiment. All the Nylon nets were spreads out easily in water to form a circular cone at relatively low velocity of water and showed the resistance smaller a little in the nets with larger d and l than them with smaller d and l, because the filtration of water through meshes become easier in nets especially with larger l. But PE nettings were not spread out sufficiently on account of their small flexibility and showed higher resistance especially in them with thicker twines. Therefore, the difference in bar length or mesh size and flexibility of nettings between prototype and model nets are regarded to become factors ascribing scale effect. Especially the influence of the difference in mesh size may become large significantly in actual model experiments because the mesh size of model nets is decided at much larger value than that given by scale ratio and so the difference of mesh size between the two nets become much larger than that between nets used in this experiment.

• 산업기술연구
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• 제21권B호
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• pp.27-30
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• 2001

For the development of a large-scale dialysis process for silk fibroin solution, a batch and continuous dialysis chamber was designed and built, which are to be used as a unit module for the process. A series of dialysis experiments were carried out to estimate the kinetic parameters for dialysis using the solutions of salt-solubilized silk fibroin. The solution was dialyzed by distilled water either batch-wise or continuously. Dialysis kinetics was monitored by measuring refractometery at high salt concentration and conductivity at lower salt concentration. The apparent dialysis coefficients were $5.4g/m^2-hr$ and $1.8g/m^2-hr$, for well mixed batch and continuous dialysis, respectively. The alteration of molecular weight distribution of dialyzed silk fibroin solution was monitored.

• 제어로봇시스템학회논문지
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• 제16권4호
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• pp.335-338
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• 2010

A new method that improves the performance of large scale voice dialling system is presented using speaker adaptation. Since SI (Speaker Independent) based speech recognition system with phoneme HMM uses only the phoneme string of the input sentence, the storage space could be reduced greatly. However, the performance of the system is worse than that of the speaker dependent system due to the mismatch between the input utterance and the SI models. A new method that estimates the phonetic string and adaptation vectors iteratively is presented to reduce the mismatch between the training utterances and a set of SI models using speaker adaptation techniques. For speaker adaptation the stochastic matching methods are used to estimate the adaptation vectors. The experiments performed over actual telephone line shows that proposed method shows better performance as compared to the conventional method. with the SI phonetic recognizer.