• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1996.10a
• /
• pp.295-300
• /
• 1996

In this study, the dynamic instabilities of a nonlinear elastic system subjected to follower force are investigated. The two-degree-of-freedom double pendulum model with nonlinear geometry, cubic spring, and linear viscous damping is used for the study. The constant and periodic follower forces are considered. The chaotic nature of the system is identified using the standard methods, such as time histories, phase portraits, and Poincare maps, etc.. The responses are chaotic and unpredictable due to the sensitivity to initial conditions. The sensitivities to parameters, such as geometric initial imperfections, magnitude of follower force, and viscous damping, etc. is analysed. The strange attractors in Poincare map have the self-similar fractal geometry. Dynamic buckling loads are computed for various parameters, where the loads are changed drastically for the small change of parameters.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1996.10a
• /
• pp.422-430
• /
• 1996

The automated scanning laser Doppler vibrometer (LDV) has been designed, and built to measure in-plane displacements associated with waves propagating on vibrating structures. Use of optical fibers allows the compact design of a laser probe head which can be scanned over the vibrating structures. An algorithm for automated self-alignment of the laser probe is developed. The system is completely automated for scanning over the structures, focusing two laser beams at each data point until the detected vibration signal is stable, and for recording and transferring the data to a system computer. The automated system allows one to get extensive data of the vibration field over the structures. The system is tested by scanning a piezoelectric cylindrical shell and a plate excited by a continuous signal and by a pulse signal, respectively. Results show that the automated scanning LDV system can be a useful tool to measure the in-plane vibration field and to detect the elastic waves propagating on the vibrating structures.

• Coupled systems mechanics
• /
• v.4 no.2
• /
• pp.191-209
• /
• 2015

Hybrid girders can be constructed in different geometrical forms and from different materials. Selection of beam's effective constellation represents a complex process considering the variations of geometrical parameters, changes of built in material characteristics and their mutual relations, which has important effect on the behavior of the girder. This paper presents the theoretical and experimental research on behavior of the timber-steel hybrid girders' different geometrical constellation with external prestressing and in different conditions of timber moisture. These researches are based on linear elastic analysis, and further refine by using the plasticity and damage models.

• Journal of Korean Society of Steel Construction
• /
• v.15 no.2
• /
• pp.219-229
• /
• 2003

The extended tangent stiffness matrices and force-deformation relations of the elastic catenary element were initially derived through the addition of the unstrained length of cables to unknown nodal 'displacements. A beam-column element was then introduced to model the deck and pylon of cable-stayed bridges. The conventional geometric nonlinear analysis, initial force method, and TCUD method were summarized, with an effective method combining two methods presented to determine the initial shapes of cable-stayed bridges with dead loads. In this combined method, TCUD method was applied to eliminate vertical and horizontal displacements at cable-supported points of decks and on top of pylons, respectively. The initial force method was also adopted to eliminate horizontal and vertical displacements of decks and pylons. Finally, the accuracy and validity of the proposed combined method were demonstrated through numerical examples.

• Physical Therapy Rehabilitation Science
• /
• v.6 no.4
• /
• pp.159-163
• /
• 2017

Objective: Persons with stroke have a tendency to exhibit asymmetric weight-bearing during sit-to-stand because due to the attempt to support themselves with the non-paretic foot. However, there are few devices that can assist with sit-to-stand (STS) performance. This study was designed to investigate the use of the elastic band with rings (EBR) in improving weight-bearing effectively in persons with stroke during STS training. Design: Cross-sectional study. Methods: Thirteen stroke survivors participated in the study. An EBR was applied onto the patient during STS activity. The foot pressure was measured before and after wearing the EBR, with a 5-minute rest period between measurements. Subjects were asked to perform each test twice with and without the EBR. Bilateral feet pressures were measured with standing posture being divided into the forward and backward aspects. The foot contact pressure during STS activity was measured with the CONFORMat System. Results: With EBR, the forward pressure of the affected foot significantly increased while the less-affected forward foot pressure significantly decreased (p=0.015 and p=0.023, respectively). The backward foot pressure did not differ significantly in the two limbs, and there was no difference with and without the EBR in terms of the total pressure of the affected foot. There was a significant difference with and without the EBR in the total pressure of the less-affected foot (p<0.05). Conclusions: STS training with the EBR has been shown to improve weight-bearing of both feet while decreasing the total pressure of the less-affected foot in stroke survivors. Therefore, we suggest that the EBR is a useful tool for STS training for persons with stroke in the clinic.

• Fashion & Textile Research Journal
• /
• v.17 no.4
• /
• pp.646-656
• /
• 2015

This study investigates the conditions of Korean naval duty and combat uniforms to develop a new design. Survey participants consisted of, 723 Sailors ($25.3{\pm}6.9yr$ in age, $43{\pm}53$ months in work experience, $174{\pm}6cm$ in height, $71{\pm}9kg$ in body mass) serving in the Korean Navy for over 12 months. The questionnaire consisted of 72 questions about anthropometric characteristics, preferred design, textiles, wear mobility, and subjective perceptions. The results showed that the preferred colors for future naval duty uniforms were blue in summer (69%) and black in winter (62%). Digital camouflage pattern (60%) and darker colors on the inside of shirt collar (87%) and the edge of sleeves (84%) were preferred. They favored more than one pocket on the upper arm and chest of the shirts (58%), narrower width around pant legs and hems than the current clothing (63%), self-controlled elastic waist (55%) and no cargo type pocket on the pants (45%). There were requirements to alleviate excessive heat stress in summer and to protect from the cold and wind in winter. Wrinkle-free (85%), anti-bacterial (78%), water-proof (75%), oil-proof (90%), and elastic (67%) textiles were preferred for Korean navy uniforms. These results will be applied to develop the next generation Korean navy uniforms.

• Women's Health Nursing
• /
• v.10 no.4
• /
• pp.301-310
• /
• 2004

Purpose: The purpose of this study was to develop an exercise program for postmastectomy patients. Method: This study was conducted from October, 2003 to June, 2004. The exercise program was developed based on literature review and needs assessment using focus group interviews. The subjects for the focus group interview consisted of 11 patients, 13 recovering patients, and 20 nurses from 3 hospitals. Development of the program was proceeded with analysusm design and development steps. Result: The results of the needs assessment using the focus group interview showed that the exercise program was imperative for postmastectomy patients. Based on the results, a home video tape containing 3 steps, was developed. Each step includes warming-up, stretching, the main exercise, and cool-down. Steps 2 and 3 include exercises with an elastic band, and an elastic ball. The program was modified after conducting a pre-test. A self-checklist including shoulder mobility, hand strength, arm volume and subjective comments on how they feel will be used before and after the exercise program. Conclusion: The exercise program will improve breast cancer patients' quality of life and their physical well-being. Further studies are recommended to test the effectiveness of the exercise program.

• International Journal of Highway Engineering
• /
• v.11 no.4
• /
• pp.87-94
• /
• 2009

Volume of concrete slab changes by variations of temperature and moisture after its placement. Shrinkage due to evaporation causes tensile stress in the slab when contraction of the slab is restrained by its self weight, friction with subbase, and etc. Actual tensile stress caused by the shrinkage was less than theoretically predicted stress according to previous studies. It was the stress reduction due to visco-elastic property of the early-age concrete slab partially restrained. In this study, strains of restrained circumferential, unrestrained circumferential, and unrestrained square pillar concrete specimens were measured to investigate stress reduction of the specimens with age of concrete. Elastic modulus of the concrete was measured at the age of 1, 3, 7, 14, 28 days and penetration test was performed. The stress reduction was calculated by input the test results into theoretical equations suggested by previous researchers. The stress reduction of the restrained concrete specimens will be applied to design of concrete pavements based on results of the study.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.13 no.5
• /
• pp.820-830
• /
• 1989

The tire inflation and contact problem has been solved by a finite element method. The finite element formulation is derived from the equilibrium equations by the principle of virtual work in the form of an updated Lagrangian formulation for incremental analysis. Then, a contact formulation is added to the finite element formulation to calculate stress state of tire in contact with flat rigid road under the load due to the self-weight of a vehicle. In the finite element analysis, equations of effective material properties are introduced to analyze a plane strain model of the shell-like tire by considering the bending effect of reinforced steel cords. The proposed equations of effective material properties produced stress concentration around the edge of belt layers, which does not appear when other well-known equations of material properties are adopted. The result from the above algorithm demonstrates the validity of the formulation and the proposed equations for the effective elastic constants. The result fully interprets the cause of separation between belt layers by showing the stress concentration.

• The Journal of Advanced Prosthodontics
• /
• v.16 no.2
• /
• pp.91-104
• /
• 2024

PURPOSE. The objectives of the current study were to estimate the influence of self-reinforced hollow structures with a graded density on the dimensional accuracy, weight, and mechanical properties of Co-Cr objects printed with the direct metal laser sintering (DMLS) technique. MATERIALS AND METHODS. Sixty-five dog-bone samples were manufactured to evaluate the dimensional accuracy of printing, weight, and tensile properties of DMLS printed Co-Cr. They were divided into Group 1 (control) (n = 5), Group 2, 3, and 4 with incorporated hollow structures based on (spherical, elliptical, and diamond) shapes; they were subdivided into subgroups (n = 5) according to the volumetric reduction (10%, 15%, 20% and 25%). Radiographic imaging and microscopic analysis of the fractographs were conducted to validate the created geometries; the dimensional accuracy, weight, yield tensile strength, and modulus of elasticity were calculated. The data were estimated by one-way ANOVA and Duncan's tests at P < .05. RESULTS. The accuracy test showed an insignificant difference in the x, y, z directions in all printed groups. The weight was significantly reduced proportionally to the reduced volume fraction. The yield strength and elastic modulus of the control group and Group 2 at 10% volume reduction were comparable and significantly higher than the other subgroups. CONCLUSION. The printing accuracy was not affected by the presence or type of the hollow geometry. The weight of Group 2 at 10% reduction was significantly lower than that of the control group. The yield strength and elastic modulus of the Group 2 at a 10% reduction showed means equivalent to the compact objects and were significantly higher than other subgroups.