• Structural Engineering and Mechanics
• /
• v.74 no.4
• /
• pp.567-576
• /
• 2020

Considerable controversy surrounds the choice of the best abutment type for implant prosthetics. The two most common structures are hex and non-hex abutments. The non-hex abutment typically furnishes a larger contact area between itself and the implant than that provided by a hex structure. However, when a hex abutment is loaded, the position of its contact area may be deeper than that of a non-hex abutment. Hence, the purpose of this study is to determine the different biomechanical behaviors of an internal bone-level implant based on the abutment type-hex or non-hex-and clinical crown length under static and cyclic loadings using finite element analysis (FEA). The hex structure was found to increase the implant and abutment stability more than the nonhex structure among several criteria. The use of the hex structure resulted in a smaller volume of bone tissues being at risk of hypertrophy and fatigue failure. It also reduced micromovement (separation) between the implant components, which is significantly related to the pumping effect and possible inflammation. Both static and fatigue analyses, used to examine short- and long-term stability, demonstrated the advantages of the hex abutment over the non-hex type for the stability of the implant components. Moreover, although its impact was not as significant as that of the abutment type, a large crown-implant ratio (CIR) increased bone strain and stress in the implant components, particularly under oblique loading.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.38 no.3
• /
• pp.274-279
• /
• 2010

The present work is to analyze the longitudinal static stability and the drop trajectory of fighter aircraft's external fuel tank, of which horizontal fin is modified as the 20% scale down size compared with the original one. The analytical results to the pitching stability of external fuel tank using a thin airfoil's aerodynamic force data show the corresponding tendency to results of wind tunnel experiment. Results of trajectory simulation by the 6 degree of freedom equations of motion, comparing with drop trajectories of wind tunnel experiment, are shown that aircraft's attitude affects strongly on horizontal movement but not on the vertical movement. Those results give the reliability to aircraft safety when the external fuel tank with the 20% reduced horizontal fins is released from aircraft based on the flight manual.

• Restorative Dentistry and Endodontics
• /
• v.35 no.4
• /
• pp.246-256
• /
• 2010

The purpose of this study was to evaluate a rotational stability of endodontic electronic motors by comparing the changes of rotational speed, depending on the number of usages and with/without static load. Twelve new endodontic electronic motors were used in this study. Non contact type digital tachometer was used for measuring the rotational speed of handpiece. True RMS Multimeter was used for measuring the voltages and the electric currents. All measurements were recorded every 10 seconds during 10 minutes and repeated 9 times. Five repetition was done per each electronic motor. To statistical analysis, student t-test, repeated measures and Scheffe's post-hoc tests were performed. In the same motor group, there was no significant difference in all measurements. In all groups, there was no significant difference in the amount of rotational speed changes depending on the number of usages and with/without static load. In the limitation of this study, the results showed that all kinds of endodontic electronic motors in this study had an established rotational stability. Therefore they could be safely used in root canal treatment with a reliable maintenance of rotational speed, regardless of the number of usages and with/without load.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.40 no.5
• /
• pp.385-394
• /
• 2012

A computer program that can estimate static, dynamic stability and control derivatives using a subsonic-supersonic panel method is developed. The panel method uses subsonic-supersonic source and elementary horse shoe vortex distributions, and their strengths are determined by solving the boundary condition approximated with a thin body assumption. In addition, quasi-steady analysis on the body fixed coordinate system allows the estimation of damping coefficients of aircraft 3 axes. The code is validated by comparing the neutral point, roll and pitch damping of delta wings with published analysis results. Finally, the static, dynamic stability and control derivatives of F-18 are compared with experimental data as well as other numerical results to show the accuracy and the usefulness of the code.

• Journal of Ocean Engineering and Technology
• /
• v.27 no.6
• /
• pp.43-55
• /
• 2013

In general, huge caissons for breakwaters have been constructed on land or a floating dock. In the case of the construction on a floating dock, a 4 step installation procedure is involved: i) construction on a floating dock, ii) transportation by the floating dock to an area near the target sea, iii) launching from the floating dock, and iv) transference by tug-boats to the installation site. It is especially important to pay attention to the dynamic stability of the floating dock against the conditions in the sea during steps i) and iii). In this paper, the static and dynamic stabilities of a caisson on a floating dock are evaluated based on IMO rules during the construction and launching of the caisson on a floating dock by using independent commercial S/Ws such as NAPA, WAMIT, and CHARM3D.

• Geomechanics and Engineering
• /
• v.13 no.6
• /
• pp.929-946
• /
• 2017

Composite foundation treated with compaction piles can eliminate collapsibility and improve the bearing capacity of foundation in loess area. However, the large number of piles in the composite foundation leads to difficulties in the analysis of such type of engineering works. This paper proposes two simplified methods to quantify the stability of composite foundation treated with a large number of compaction piles. The first method is based on the principle of making the area replacement ratios of the simplified model as the same time as the practical engineering situation. Then, discrete piles arranged in a triangular shape can be simplified in the model where the annular piles and compacted soil are arranged alternately. The second method implements equivalent continuous treatment in the pile-soil area and makes the whole treated region equivalent to a type of composite material. Both methods have been verified using treated foundation of an oil storage tank. The results have shown that the differences in the settlement values obtained from the water filled test in the field and those calculated by the two simplified methods are negligible. Using stability analysis, the difference ratios of the static and dynamic safety factors of the composite foundation treated with compaction piles calculated by these two simplified methods are found to be 3.56% and 5.32%, respectively. At the same time, both static and dynamic safety factors are larger than the general safety factor, which should be greater than or equal to 2.0 according to the provisions in civil engineering. This indicates that after being treated with compaction piles, the bearing capacity of the composite foundation is effectively improved and the foundation has enough safety reserve.

• Journal of Aerospace System Engineering
• /
• v.13 no.5
• /
• pp.32-38
• /
• 2019

The flying wing configuration with high sweep angles and rounded leading edge represent a complex flow of structures by the leading edge vortex. For control of the tailless flying wing configuration with unstable directional stability, flaperon is used. In this study, we conducted numerical simulations for a non-slender flying wing configuration with a rounded leading edge and analyzed the effect of the sideslip angle and flaperon. Through aerodynamic coefficient analysis, it was found that the effect of AoS on lift and drag coefficient was minimal and the side force and moment coefficient were markedly influenced by AoS. As the sideslip angle increased, the pitch break, which is related to the pitching moment coefficient, was delayed. Through stability analysis, the directional and lateral static stability of the flying wing configuration were increased by flaperon. Also, the structure and behavior of the leading edge vortex were analyzed by observing the contour of the pressure coefficient and the skin friction line.

• Korean Journal of Agricultural Science
• /
• v.47 no.4
• /
• pp.963-978
• /
• 2020

Earthquakes can induce a large number of landslides and cause very serious property damage and human casualties. There are two issues in study on earthquake-induced landslides: (1) slope stability analysis under seismic loading and (2) debris flow run-out analysis. This study aims to review technical studies related to the development and application of earthquake-induced landslide models (seismic slope stability analysis). Moreover, a pilot application of a physics-based slope stability model to Mt. Umyeon, in Seoul, with several earthquake scenarios was conducted to test regional scale seismic landslide mapping. The earthquake-induced landslide simulation model can be categorized into 1) Pseudo-static model, 2) Newmark's dynamic displacement model and 3) stress-strain model. The Pseudo-static model is preferred for producing seismic landslide hazard maps because it is impossible to verify the dynamic model-based simulation results due to lack of earthquake-induced landslide inventory in Korea. Earthquake scenario-based simulation results show that given dry conditions, unstable slopes begin to occur in parts of upper areas due to the 50-year earthquake magnitude; most of the study area becomes unstable when the earthquake frequency is 200 years. On the other hand, when the soil is in a wet state due to heavy rainfall, many areas are unstable even if no earthquake occurs, and when rainfall and 50-year earthquakes occur simultaneously, most areas appear unstable, as in simulation results based on 100-year earthquakes in dry condition.

• Journal of Korean Physical Therapy Science
• /
• v.27 no.3
• /
• pp.35-44
• /
• 2020

Background: This study was to confirm the effect and feasibility of knee extension assist orthosis (KEAO) on balance and gait in subacute stroke patients. Design: Case study. Methods: The subjects of the study were 4 subacute stroke patients, who had an onset period of less than 6 months. The limit of stability (LOS) and berg balance scale (BBS), timed up and go test (TUG) were used to verify the dynamic balance ability, static balance ability, and gait ability pre and post and after wearing the knee extension assist orthosis (KEAO). In addition, the satisfaction survey was to confirm the feasibility of the knee extension assist orthosis (KEAO) through the to Korean quebec user evaluation of satisfaction assistive technology 2.0 (K-QUEST 2.0). Results: After the wearing on KEAO, the distance for the limit of stability decreased by mean 541.25±240.46 mm2, and the score on the berg balance scale improved by mean 5±2.71 point, and the time for the timed up and go test deceased by mean 3.75±1.71 second. The stability and durability were found to be full score, and the control, ease, effectiveness were some high score, and the size, weight, comfort were some low score in the satisfaction and feasibility. Conclusion: The knee extension assist orthosis (KEAO) produce in this study was improved the static balance ability, dynamic balance ability and gait ability of subacute stroke patients, and the satisfaction and feasibility were high in the stability, durability and effectiveness of the user.

• Fisheries and Aquatic Sciences
• /
• v.27 no.5
• /
• pp.265-275
• /
• 2024

The success of establishing the Indonesian growing fast hybrid carp, namely "Permata", on a controlled environmental test must be followed up with a large-scale test. This study aims to evaluate the phenotypic performance of the Permata hybrid carp in multi-locations with different cultivation systems. The test sites consisted of floating net cages, running-water ponds, semi-concrete ponds, earthen ponds, fully concrete ponds, and static net cages. For 90 days, fish were fed commercial pellets with a 28%-30% protein content. At the end of the test, all fish were harvested and counted. Data on length, weight, survival rate, and harvested biomass were used to analyze the effect of genotype, environment, and their interaction on the phenotypic performance. The growth based on final weight is used to analyze the stability performance in each test location. The results showed that the length and weight of common carp were significantly affected by genotype and the environment, but not by the interaction of both. The genotype, environment, and the interaction of both factors affected common carp's survival and harvested biomass. Common carp reared in floating net cages generally had the best performance, while carp reared in fully concrete tanks and static net cages had the lowest. The growth stability analysis showed that the common carp in this study were unstable genotypes but have a broad adaptability in term of different environments.