• Particle and aerosol research
• /
• v.13 no.1
• /
• pp.1-10
• /
• 2017

Accurate prediction of size, shape and velocity of a bubble rising through a liquid pool is very important for predicting the particulate removal efficiency in pool scrubbing, for designing engineering safety features to prepare for severe accidents in nuclear power plants, and for predicting the emission of fission products from MCCI (molten core-concrete interaction) process during severe accidents. In this review article, previous studies on the determination of the size, shape and rising velocity of a bubble in liquid are reviewed. Various theoretical and parameterization formulas calculating the bubble size, shape and velocity from physical properties of liquid and gas flowrate are compared. Recent studies tend to suggest simple parameterizations that can easily determine the bubble shape and rising velocity without iteration, whereas iteration has to be performed to determine the bubble shape and velocity in old theories. The recent parameterizations show good agreement with measured data obtained from experiments conducted using different liquid materials with very diverse physical properties, proving themselves to be very useful tools for researchers in related fields.

• Steel and Composite Structures
• /
• v.24 no.2
• /
• pp.191-200
• /
• 2017

Impact resistance and weight are important features for ballistic materials. Kevlar fibres are the most widely reinforcement for military and civil systems due to its excellent impact resistance and high strength-to-weight ratio. Kevlar fibres or spectra fiber composites are used for designing personal body armour to avoid perforation. In this study, the ballistic impact behaviour of Kevlar/filled epoxy matrix is investigated. Three different fillers, nanoclay, nanocalcite and nanocarbon, were used in order to increase the ballistic impact performance of Kevlar-epoxy composite at lower weight. The filler, nanoclay and nanocalcite, content employed was 1 wt.% and 2 of the epoxy resin-hardener mixture while the nanocarbon were dispersed into the epoxy system in a 0.5%, 1% and 2% ratio in weight relating to the epoxy matrix. Specimens were produced by a hand lay-up process. The results obtained from ballistic impact experiments were discussed in terms of damage and perforation. The experimental tests revealed a number of damage mechanisms for composite laminated plates. In the ballistic impact test, it was observed whether the target was perforated completely penetrated at the back or not. The presence of small amounts of nanoclay and nanocalcite dispersed into the epoxy system improved the impact properties of the Kevlar/epoxy composites. The laminates manufactured with epoxy resin filled by 1 wt.% of nanoclay and 2 wt% nanocalcite showed the best performance in terms of ballistic performance. The addition of nanocarbon reduced ballistic performance of Kevlar-epoxy composites when compared the results obtained for laminates with 0% nanoparticles concentration.

• Journal of the Ergonomics Society of Korea
• /
• v.36 no.1
• /
• pp.9-21
• /
• 2017

Objective: The objective of this study is to understand the effect of angle and curvature of push-return switches, which are external factors in the operation environment inside the cars, on the feel of operation and to propose optimum alternatives. Background: Customers' needs for products are changing from functional and performance aspects to customer-led type where customers can reflect on their needs on the products. The operation inside cars is executed by HMI. The push-return switch is utilized as the most intuitive mode of HMI; therefore, this push-return switch, which is widely used, has to be developed by assessing the preference and satisfaction of the customer. Method: The angle and curvatures, which are external factors that affect the feel of operation, are drawn through surveying the preceding research literatures. The stages to construct alternatives in experiments are as follows: (1) the tactile switch is replaced after dismantling the switch assembly to evaluate the internal characteristics proposed by preceding researches, (2) a drawing is prepared by using a design software, is printed using 3D printer, and then it is attached on the switch assembly, and (3) evaluation for satisfaction of operation is carried out by using a driving simulator. Results: Both the angle and curvature that are external factors of switch significantly affect the feel of operation. However, interaction between the two factors is found insignificant. Therefore, an optimum alternative is proposed considering the experimental outcomes. Conclusion: This study evaluates the satisfaction in operation that affects the feel of operation environment inside the cars. Based on the study results, a guideline for switch design in the center fascia is proposed. Application: This study is expected to be used as basic data for designing automotive switches, as well as switches in the industries similar with the operation environments of cars.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.53 no.11
• /
• pp.123-129
• /
• 2016

Disturbance Observer(DOB) based control is considered for the purpose of the balancing performance enhancement in a single-wheel robot. Design of DOB can be folded into two parts, the inverse model of the plant and the Q-filter. The inverse model is derived from the inverted stick model and a Q-filter is designed to stabilize the inverse model. In this paper, a Q31 filter is designed and its effect is evaluated by experimental studies. The time constant provides a complimentary characteristic between the disturbance suppression and the sensor noise immunity. Therefore, suitable selection of the time-constant must be considered. Comparative experiments are conducted to investigate the control performances when three different Q filters are respectively applied in the DOB. Through the analysis of the experimental results, a time constant is designed to have a proper value in the design of DOB for balancing control of a single-wheel robot.

• Composites Research
• /
• v.31 no.3
• /
• pp.83-87
• /
• 2018

An object in the Low Earth Orbit (LEO) is affected by many environmental conditions unlike earth's surface such as, Atomic oxygen (AO), Ultraviolet Radiation (UV), thermal cycling, High Vacuum and Micrometeoroids and Orbital Debris (MMOD) impacts. The effect of all these parameters have to be carefully considered when designing a space structure, as it could be very critical for a space mission. Polybenzimidazole (PBI) is a high performance thermoplastic polymer that could be a suitable material for space missions because of its excellent resistance to these environmental factors. A thin coating of PBI polymer on the carbon epoxy composite laminate (referred as CFRP) was found to improve the energy absorption capability of the laminate in event of a hypervelocity impact. However, the overall efficiency of the shield also depends on other factors like placement and orientation of the laminates, standoff distances and the number of shielding layers. This paper studies the effectiveness of using a PBI coating on the front bumper in a multi-shock shield design for enhanced hypervelocity impact resistance. A thin PBI coating of 43 micron was observed to improve the shielding efficiency of the CFRP laminate by 22.06% when exposed to LEO environment conditions in a simulation chamber. To study the effectiveness of PBI coating in a hypervelocity impact situation, experiments were conducted on the CFRP and the PBI coated CFRP laminates with projectile velocities between 2.2 to 3.2 km/s. It was observed that the mass loss of the CFRP laminates decreased 7% when coated by a thin layer of PBI. However, the study of mass loss and damage area on a witness plate showed CFRP case to have better shielding efficiency than PBI coated CFRP laminate case. Therefore, it is recommended that PBI coating on the front bumper is not so effective in improving the overall hypervelocity impact resistance of the space structure.

• The Journal of the Korea Contents Association
• /
• v.9 no.12
• /
• pp.212-221
• /
• 2009

In this thesis, for analysis of efficient semantics flow frameworks with creative designing of interaction, we propose three elements: coincidence with intuition and common sense, self-leading activeness, and diversity of control parameters. Through analysis of my interactive art works, it is shown that the three proposed qualitative measures for interactive flow analysis are very useful evaluation measures for efficient semantics flows of interactive art works. In the experiments for this analysis, we measured the duration of each action-response feedback, the enjoyment duration of each entire art work, and the number of different types of interactions. The proposed qualitative measures can be used to design models for new interactive art works, as well as for the evaluating framework for existing art works.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.25 no.3
• /
• pp.248-253
• /
• 2015

In order to adapt to human's life and perform missions, a humanoid robot needs a height at least similar with children's. In this paper, we proposed a humanoid robot which is like a child who is taller than 1m. We presented showing the humanoid robot's kinematics, designing of a three-dimensional model, developing mechanisms, and the hardware structures using servo motors and compact size PC. Through this process, we designed and manufactured child humanoid robot 'CHARLES(Cognitive Humanoid Autonomous Robot with Learning and Evolutionary Systems)' that is robot is 1m 10cm tall and 8.16kg in weight. For robot's walking, we applied to ZMP-based walking technique and the creation algorithm is applied for walking patterns. Through experiments, we analyzed walking patterns according to the creation and changing parameter values.

• JSTS:Journal of Semiconductor Technology and Science
• /
• v.15 no.1
• /
• pp.48-59
• /
• 2015

In recent years, there are increasing threats of rootkits that undermine the integrity of a system by manipulating OS kernel. To cope with the rootkits, in Vigilare, the snoop-based monitoring which snoops the memory traffics of the host system was proposed. Although the previous work shows its detection capability and negligible performance loss, the problem is that the proposed design is not acceptable in recent commodity mobile application processors (APs) which have become de facto the standard computing platforms of smart devices. To mend this problem and adopt the idea of snoop-based monitoring in commercial products, in this paper, we propose a snoop-based monitor design called S-Mon, which is designed for the AP platforms. In designing S-Mon, we especially consider two design constraints in the APs which were not addressed in Vigilare; the unified memory model and the crossbar switch interconnect. Taking into account those, we derive a more realistic architecture for the snoop-based monitoring and a new hardware module, called the region controller, is also proposed. In our experiments on a simulation framework modeling a productionquality device, it is shown that our S-Mon can detect the rootkit attacks while the runtime overhead is also negligible.

• The Journal of Engineering Geology
• /
• v.7 no.2
• /
• pp.91-99
• /
• 1997

In general, there are various approaches available in literature to model discontinuous rock masses and engineers are often confused which one to use for designing structures in rock masses. Modelling rock masses can be classified mainly into two approaches. One is discrete modelling of intact rock and discontinuities and the other is the equivalent continuum modelling. In this study five models are selected ;(1) Crack tensor model, (2) Equivalent volume defect model, (3) Damage model, (4) Micro - structure model (Parallel model and Series model), and (5) Homogenization model. Most of these models are mainly concerned with how to define additional strain due to discontinuities over the representative elementary volume (REV) and how to relate the stress field of discontinuities to that acting on the REV. The characteristics of these models are clarified by comparing with results of some laboratory tests.

• Journal of the Korea Computer Industry Society
• /
• v.10 no.4
• /
• pp.167-176
• /
• 2009

In this paper, we propose an improved SHACAL-1 of the same encryption and decryption with a simple symmetric layer. SHACAL-1 has 4 rounds, and each round has 20 steps. Decryption is becoming inverse function of encryption, In this paper, we proposed SHACAL-1 are composed of the first half, symmetry layer and the last half. The first half with SHACAL-1 encryption algorithm 1 round does with 10 steps and composes of 4 round. The last half identically with SHACAL-1 decryption algorithm, has a structure. On the center inserts a symmetry layer, encryption and decryption algorithm identically, composes. In the experiments, the proposed SHACAL-1 algorithm showed similar execution time to that of the SHACAL-1. Thanks to the symmetric layer, the proposed algorithm makes it difficult for the attacks which take advantages of high probability path such as the linear cryptanalysis, differential cryptanalysis. The proposed algorithm can be applicable to the other block cipher algorithms which have different encryption and decryption and useful for designing a new block cipher algorithm.