• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.30 no.6
• /
• pp.929-935
• /
• 1997

The total energy of fish movement and the maximum burst swimming speed were estimated and formulated in accordance with body length and water temperature for several species in fisheries by empirical methods and also by using published results. Under the assumption of swimming energy reserve of a fish at the initial rest state, the swimming endurance of fish with different body lengths, swimming speeds and angular velocity was calculated using the relevant equations under similar conditions in tank experiments as well as natural conditions in field. Relative swimming energy efficiency or the transition swimming speed between red and white muscle for energy consumption was represented as a trigonometric function of swimming speed ratio. Therefore, this model does closely approach the actual swimming abilities and their limits especially in relation to the fishing gear operation and allow for the greater vitality of the wild fish in the fields.

• International Journal of Railway
• /
• v.2 no.4
• /
• pp.131-138
• /
• 2009

Static tensile and fatigue tests were conducted using tensile-shear specimens to evaluate the fatigue strength of a SPCC sheet clinch joint. The maximum tensile strength of the specimen produced at the optimal punching force was 1750 kN. The fatigue endurance limit (=760 N) approached 43% of the maximum tensile load (=1750 N) at a load ratio of 0.1, suggesting that the fatigue limit is approximately half of the value of the maximum tensile strength. The FEM analysis showed that at the fatigue endurance limit, the maximum von-Mises stress of 373 MPa is very close to the ultimate tensile strength of the SPCC sheet (=382 MPa).

• Journal of Electrical Engineering and Technology
• /
• v.12 no.4
• /
• pp.1641-1648
• /
• 2017

Many researchers had examined the validity of using the high-to-low ratio between two fixed frequency band amplitudes (H/L-FFB) from the surface electromyography of a face and body as the first spectral index to assess muscle fatigue. Despite these studies, the disadvantage of this index is the lack of a criterion for choosing the optimal border frequency. We tested the potential of using the high-to-low ratio between two signal spectral moments (H/L-SSM), without fixed border frequencies, to evaluate muscle fatigue and predict endurance time ($T_{end}$), which was determined when the subject was exhausted and could no longer follow the fixed contraction cycle. Ten healthy participants performed five sets of voluntary isotonic contractions until they could only produce 10% and 20% of their maximum voluntary contraction (MVC). The $T_{end}$ values for all participants were $138{\pm}35s$ at 10% MVC and $69{\pm}20s$ at 20% MVC. Changes in conventional spectral indices, such as the mean power frequency (MPF), Dimitrov spectral index (DSI), H/L-FFB, and H/L-SSM, were extracted from surface EMG signals and were monitored using the initial slope computed every 10% of $T_{end}$ as a statistical indicator and compared as a predictor of $T_{end}$. Significant correlations were found between $T_{end}$ and the initial H/L-SSM slope as computed over 30% of $T_{end}$. In conclusion, initial H/L-SSM slope can be used to describe changes in the spectral content of surface EMG signals and can be employed as a good predictor of $T_{end}$ compared to that of conventional spectral indices.

• Journal of the Korean Applied Science and Technology
• /
• v.5 no.2
• /
• pp.39-54
• /
• 1988

The effects of exercise and selenium added high fat diet on edurance and serum lipid components were studied in rats. A total of 72 male Sprague-Dawley ($150{\pm}35g$, body weight) were divided into trained group and untrained group and were bred for 7 weeks. Each group had 6 different dietary subgroups; namely, basal diet, 20％ shortening and 20％ soybean oil subgroup and selenium (0.01mg％) added each subgroups. Exercises of 8-min treadmill running and 10-min swimming were given to the trained group every other day during the experimental period while only treadmill running was given to the untrained group during the last week. The amounts of food intake, changes in body weight and endurance were determined once a week and serum lipid components were measured before and after experimental period. Following are the results obtained : 1) The untrained group took a slightly larger amount of food than that in the trained group. The food efficiency is, however, higher in the trained group. Body weight increased more in untrained group, while high fat diet resulted in greater increment in body weight than that in normal diet groups. 2) The trained group showed remarkably longer endurance than the untrained group and selenium added high fat diet enhanced the effect. 3) The trained group showed lower blood level of T-chol., TG and TG/PL than the untrained group. All the other blood values of HDL-chol., PL, MDL-chol./T-chol., HDL/LDL and A/G ratio were higher in trained group. 4) Soybean oil added dietary groups exibited lower blood levels of T-chol., TG, TG/PL and A/G than those in shortening added dietary groups. On the contrary, the former groups showed higher blood HDL-chol., PL., HDL, HDL-chol. and HDL/LDL ratio than those of soybean oil added dietary groups. 5) $LDH_5$ was the most abundant one among serum LDH isozymes. The electrophoretic pattern of serum LDH isozymes was not changed by exercise training and selenium added high fat diet. 6) Exercise training lowered blood GOT and TBA. These effects were enhanced by soybean oil added diets. From the above results it was concluded that a regular and long term exercise training as well as a small amount of selenium added high fat diet result in reduction of body weight and TBA and improve dietary efficiency and physical endurance in rats.

• Proceedings of the Korean Society of Marine Engineers Conference
• /
• 2005.11a
• /
• pp.224-225
• /
• 2005

The lightness of components required on marine and shipbuilding industry is requiring high strength of components. In particular, fatigue failure phenomena, which happen in metal, bring on danger in human life and property. Therefore, antifatigue failure technology takes an important part of current industries. In this study, it was investigated about endurance and fatigue crack propagation rate of according to stress ratio of SMAW commonly using for welding structures in present. Fatigue crack propagation rate(da/dN) of low load(R=0.1) was lower than of high load(R=0.6) for piping weld. And in stage I, ${\Delta}$Kth, the threshold stress intensity factor of the weld under heavy load is higher than under small load. Fatigue life shows more improvement in the weld of stress ratio R=0.l than in the weld of stress ratio R=0.6.

• The Journal of Korean Physical Therapy
• /
• v.31 no.6
• /
• pp.339-345
• /
• 2019

Purpose: The purpose of this study was to identify changes in knee muscle strength after reconstruction of the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL). Methods: Thirteen subjects (males) with anterior ligament injury and ten subjects (males) with posterior ligament injury voluntarily participated in this study. Both groups were evaluated at the pre-and post-reconstruction stages using an isokinetic dynamometer. Peak torque, total work, and the hamstrings to quadriceps (H/Q) peak torque ratio were calculated at angular velocities of 60°/sec and 180°/sec. Statistical analysis was conducted on SPSS 18.0 for Windows using t-tests to compare mean differences. Results: At an angular velocity of 60°/sec, both the ACL and PCL groups showed a significant increase in muscle strength in the flexors and extensors. Muscle strength in the extensors was significantly increased in the PCL group compared to the ACL group. At an angular velocity of 180°/sec, the ACL group showed a significant increase in muscle endurance in the flexors and extensors, and the PCL group showed a significant increase in muscle endurance in the flexors. At angular velocities of 60°/sec and 180°/sec, the H/Q peak torque ratio increased in the ACL group but decreased in the PCL group. Consequently, the H/Q peak torque ratio was significantly different for the two groups. Conclusion: The results suggest that the patients with ACL injury should focus on strengthening the knee extensors and that the patients with PCL injury need to strengthen the knee flexors.

• Journal of Ocean Engineering and Technology
• /
• v.5 no.2
• /
• pp.58-66
• /
• 1991

Not only difference of fatigue crack growth and propagation behavior resulted from the grain size, the hardness ratio and volume fraction in M.E.F. dual phase steel composed of martensite in hard phase and ferrite in soft phase, but also the effects of the plastic constraint were investigated by fracture mechanics and microstructural method. The main results obtained are as follows: 1) The fatigue endurance of M.E.F. steel increases with decreasing the grain size, increasing the ratio of hardness and volume fraction. 2) The initiation of slip and crack occures faster as the stress level goes higher. These phenomena result from the plastic constraint effect of the second phase. 3) The crack propagation rate in the constant stress level is faster as the grain size gets larger, the ratio of hardness lower and volume fraction smaller.

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.207-212
• /
• 2003

Recently there has been a remarkable increase in the number of high speed and large ships, and the high power involved for propulsion of above ships have brought high pitch ratio and high skew propeller. The recent tendency toward highly skewed propeller has increased the load on propeller blades and the fatigue strength of propeller blades has become the critical point in design of propellers for above ships. In this paper fatigue tests in sea water were carried out on propeller material of Ni-Al bronze. The stress and environmental conditions of the test were selected to be close to those of full size propellers in use. The effect of stress ratio, stress frequency, revolution number of propeller for above ships numbers and so on were discussed.

• Proceedings of the KSME Conference
• /
• 2001.06a
• /
• pp.603-608
• /
• 2001

Recently, cold expansion of fastener holes is commonly used in the aerospace industry to increase the fatigue endurance of airframes. Cold expansion process is used as the retardation of crack initiation in the hole. This treatment leads to an improvement of fatigue behavior due to the compressive residual stresses developed on the hole surface. The residual stress profile depends on the cold expansion ratio. In the present paper, it is shown that residual stress is redistributed due to the application of cold expansion process for CT specimen. It is further shown that residual stress increases in proportion to cold expansion ratio. It is thought that crack growth rate increases as cold expansion ratio.

• International Journal of Aeronautical and Space Sciences
• /
• v.7 no.1
• /
• pp.99-105
• /
• 2006

In this study, nonlinear static and dynamic aeroelastic analyses for a high-aspect-ratio wing have been performed. To achieve these aims, the transonic small disturbance (TSD) theory for the aerodynamic analysis and the large deflection beam theory considering a geometrical nonlinearity for the structural analysis are applied, respectively. For the coupling between fluid and structure, the transformation of a displacement from the structural mesh to the aerodynamic grid is performed by a shape function which is used for the finite element and the inverse transformation of force by work equivalent load method. To validate the current method, the present analysis results of a high-aspect-ratio wing are compared with the experimental results. Static deformations in the vertical and torsional directions caused by an angle of attack and gravity loading are compared with experimental results. Also, static and dynamic aeroelastic characteristics are investigated. The comparisons of the flutter speed and frequency between a linear and nonlinear analysis are presented.