• Structural Engineering and Mechanics
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• v.59 no.6
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• pp.1139-1153
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• 2016

Elastic constraints are usually simplified as "spring forces" exerted on beam ends without considering the "spring deformation". The partial differential equation governing the free vibrations of a cantilever Bernoulli-Euler beam considering the deformation of elastic constraints is firstly established, and is nondimensionalized to obtain two dimensionless factors, $k_v$ and $k_r$, describing the effects of elastically vertical and rotational end constraints, respectively. Then the frequency equation for the above Bernoulli-Euler beam model is derived using the method of separation of variables. A numerical analysis method is proposed to solve the transcendental frequency equation for the continuous change of the frequency with $k_v$ and $k_r$. Then the mode shape functions are given. Finally, effects of $k_v$ and $k_r$ on free vibration characteristics of the beam with different slenderness ratios are calculated and analyzed. The results indicate that the effects of $k_v$ are larger on higher-order free vibration characteristics than on lower-order ones, and the impact strength decreases with slenderness ratio. Under a relatively larger slenderness ratio, the effects of $k_v$ can be neglected for the fundamental frequency characteristics, while cannot for higher-order ones. However, the effects of $k_r$ are large on both higher- and lower-order free vibration characteristics, and cannot be neglected no matter the slenderness ratio is large or small.

• Journal of Advanced Marine Engineering and Technology
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• v.18 no.2
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• pp.113-121
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• 1994

Since two oil shocks in 1970s, all of engine makers have persevered in their efforts to reduce specific fuel consumption and to increase engine power rate as much as possible in marine diesel engines. As a result, the maximum pressure in cylinders of these engines has been continuously increased. It causes direct axial vibration. The axial stiffness of crank shaft is low compared to old types of engine models by increasing the stroke/bore ratio and its major critical speed might occur within engine operation range. An axial damper, therefore, needs to be installed in order to reduce the axial vibration amplitude of the crankshaft. Usually the main critical speed of axial vibration for the propulsion shafting system with a 4-8 cylinder engine exists near the maximum continuous revolution(MCR). In this case, when the damping coefficient of the damper is increased within the allowance of the structural strength, its stiffness coefficient is also increased. Therefore, the main critical speed of axial vibration can be moved beyond the MCR. It has the same function as a conventional detuner. However, in the case of a 9-12 cylinder engine, the main critical speed of axial vibration for the propulsion shafting system exists below the MCR and thus the critical speed cannot be moved beyond the MCR by using an axial damper. In this case, the damping coefficient of an axial damper should be adjusted by considering the range of engine revolution, the location and vibration amplitude of the critical speed, the fore and aft vibration of the hull super structure. It needs to clarify the dynamic characteristics of the axial vibration damper to control the axial vibration appropriately. Therefore authors suggest the calculation method to analyse the dynamic characteristics of axial vibration damper. To confirm the calculation method proposed in this paper, it is applied to the propulsion shafting system of the actual ships and satisfactory results are obtained.

• Journal of Digital Convergence
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• v.15 no.2
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• pp.519-525
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• 2017

The purpose of this study is to elaborate the factors and strategies to revitalize the policies of elderly-friendly care industry. The analysis was carried out using the method called DEMATEL. The analytical method is based on the DEMATEL technique. The purpose of this study is to clarify the complexity and unclear relationship between activation factors and factors that constitute the elderly friendly-care industry through the prioritization of policy strengthening. As the result of analysis, it was analyzed that the most intensive activation intensity was the highest total strength of meal service(22.095). Followed by health promotion facilities(19.97) and health care(17.726). The lowest factor is sport(15.896). Therefore, in order to improve and promote these factors, continuous policy measures should be sought that are closely related to facility care services, home care services, and preventive support services.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.4
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• pp.95-104
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• 1999

Use of the ultra thick plate is being continuously increased in large off-shore structures, ships, bridges and skyscraper construction, due to increasingly large-sized steel structures and it seems that this trend will be maintained. But, occurrence of the lamella tearing has been reported in ultra thick plate used for construction. It is reportedly caused by impurities such S(sulfur), P(phosphorus) and others accumulated in the ultra thick plate's centerline in the thickness direction with strip shape or by restraint residual stress caused by the welding. In the ultra thick plate made by continuous casting method, occurrence of lamination is difficult to avoid because of the properties of production procedure. Therefore, with a view to reducing the lamella properties, this report tries tearing in the steel structure in the view of welding strength rather than metallic properties, this report tries to seek the optimum groove and welding procedure by using the computer simulation based on FEM(Finite Element Method).

• Journal of the Korean GEO-environmental Society
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• v.2 no.1
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• pp.91-101
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• 2001

This paper investigates the effectiveness of quick lime piles for soft ground improvement. The field tests based on the results of the laboratory test were performed, and the results of field tests were compared with those of numerical analyses(FEM). The results of the field test showed that the domestic quick lime was very effective in reducing the water contents of the surrounding ground quickly due to its characteristics such as digestion, absorption, and exothermic reactions. Accordingly, consolidation occurred without any additional load increment and the shear strength of surrounding ground was increased more than twice. Therefore the quick lime pile method could be considered as an excellent improvement technique reducing the improvement period for soft ground. For the practical applications of the quick lime pile method, issues such as hydration heat, particulation and equipment enhancement should be solved through continuous research and development.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.4
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• pp.521-528
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• 2021

The high-density fiber composite manufacturing method by the extrusion molding method has the characteristic that continuous production is possible, and the product is molded through a mold forming a specific cross-section. OPC is used as a defect material, an appropriate amount of SiO₂ is supplied for CaO reaction activity, and high density and high strength are expressed through steam and autoclave curing. However, due to the use of organic reinforcing fibers, the flame duration exceeds the regulations during the non-combustible performance test, making it difficult to secure performance. In this study, the product was produced by mixing alkali-resistant organic fiber and fly ash having voids as a binder by replacing the existing polypropylene fiber. appeared to be possible.

• Journal of Oral Medicine and Pain
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• v.35 no.1
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• pp.75-81
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• 2010

By repeating nocturnal bruxism occlusal appliance's wearing condition that is used to cure temporomandibular disorders into the vitro experiment, research aims to find out how moisture infiltrated and drying cycle process affects on the surface microhardness of the resin for occlusal appliance and flexural strength. By utilizing resin for occlusal appliance which is the main component of poly methyl methacrylate, bar shaped sample was produced. For the resin sample utilized as the controlled group 1, the sample was infiltrated in the moisture for 7 days in the temperature of 37C. Then, the resin sample of the controlled group 2 was maintained in a dry condition for 7 days in the normal temperature. After that, each sample's surface microhardness and flexural strength were measured. For the resin sample that is utilized as the experimental sample, the sample was infiltrated in the moisture for 7 days in the temperature of 37C. Then, it was inundated for 8 hours a day and dried in the normal temperature for 16 hours with the continuous process of moisture infiltration and dry cycle process for 30 days. During this cycle process, sample's surface and flexural strength were measured in the 1st day, 7th day, and 30th day. Then, it was statistically analyzed to find out the difference of controlled and experiment group's surface microhardness and flexural strength. Results are 1. For the experimental and controlled group's surface microhardness of the resin for the occlusal appliance, it did not show any significant differences after moisture infiltration and dry cycle process repetition. 2. In case of the flexural strength for resin for the occlusal appliance, experimental group with moisture infiltration and dry cycle for 30 day process had greater effect than the experimental group at the 1st day and controlled group These results can be considered to be utilized from the patients of the temporomandibular disorders towards occlusal appliance used and maintained method.

• Composites Research
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• v.31 no.4
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• pp.139-144
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• 2018

Long Fiber-reinforced composites have advantages of excellent production efficiency and formability of complex shapes compared to conventional continuous fiber reinforced composite materials. However, if we need to make complicated composite shapes or to assemble parts made of different materials, a variety of joining methods are needed. In general, long fiber prepreg sheet (LFPS) contains mold release agent to facilitate demolding after thermoforming. Therefore, mechanical fastening is required in addition to the adhesive bonding to get proper joining strength. In this study, we proposed a stainless steel insert for co-cure bonding which cures LFPS and bonds the stainless steel insert through thermoforming process. The wing of the insert which is spread during the thermoforming process induces adhesion and mechanical wedging effect and serves as a hook to resist the pulling force. The burn-out method was used to confirm the unfolded state of the stainless steel insert wings inserted into the composite material. The static pull-out test was performed to quantitatively evaluate the joining strength. From these experimental results, the condition which guarantees the most appropriate joining strength was derived.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.3
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• pp.212-219
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• 2015

This study focuses evaluating the efficiency and performance evaluation of composite type sheet-membrane waterproofing method that utilizes a separation behavior inducement system designed to resolve the chronic problems of disintegration and damage of overlap areas of waterproofing layers. As the result of the test, the tensile strength value was at 13.8N/mm and elongation rate at 587% for the separation behavior inducement type specimen, and the compared specimens had 14.2N/mm for tensile strength and 335% for elongation rate. For the separation behavior adhesion method specimen, when tensile stress or displacement occurred, the Zero-Span tension occurrence did not follow, which resulted in that the bottom sheet layer and the top membrane layer did not simultaneously becoming damaged. When undergoing the top and bottom layers were separated through separation behavior due to lack of flexibility, the bottom layer began to damage at the primary stage, and with the allowed boundary the upper membrane layer began to display flexibility and showed continuous displaced resulting in secondary phase damaging.

• Journal of Korean Society of Steel Construction
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• v.15 no.1
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• pp.77-85
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• 2003

The lifting and lowering supports method makes up for the weak points in the classical method and provides makes construction economical effect to construction. The application of pre-compression to continuous steel box girder bridges makes it possible to reduce the amount of steel, the height of girders and consequently, the cost consequentlyof the bridges' construction by through the process of concrete filling- up and the lifting-lowering of the inner supports. The lifting and lowering supports method is apt to cause local buckling in the lower flange and web plates by due to the process of the lifting of the inner supports. Therefore iln this study, therefore, the possibility of local buckling could be decreased, in consideration of the lifting force and the buckling strength of stiffened plates, by increasing the number of longitudinal stiffeners and the installation of extended longitudinal stiffeners on the lower flange and the web plates in the range of positive moment.