• Title/Summary/Keyword: 상하동요

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Study on the Shape of Appendage for the Reduction of Motion of Floating Wind Turbine Platforms (부유식 풍력 하부구조물의 운동 저감을 위한 부가물 형상 연구)

  • Dae-Won Seo;Jaehyeon Ahn;Jungkeun Oh
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.28 no.7
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    • pp.1201-1208
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    • 2022
  • In general, to maximize the supply and efficiency of floating offshore wind power generation energy, the motion caused by wave attenuation of the substructure must be reduced. According to previous studies, the motion response was reduced due to the vortex viscosity generated by the damping plate installed in the lower structure among the waves. In this study, a 5 MW semi-submersible OC5 platform and two platforms with attenuation plates were designed, and free decay experiments and numerical calculations were performed to confirm the effect of reducing motion due to vortex viscosity. As a result of the model test, when the heave free decay tests were conducted at drop heights of 30 mm, 40 mm, and 50 mm, compared with the OC5 platform, the platform with two types of damping plates attached had relatively improved motion damping performance. In the model test and numerical calculation results, the damping plate models, KSNU Plate 1 and KSNU Plate 2, were 1.1 times and 1.3 times lower than OC5, respectively, and the KSNU Plate 2 platform showed about two times better damping performance than OC5. This study shows that the area of the damping plate and the vortex viscosity are closely related to the damping rate of the heave motion.

Calculation of Nonlinear Interactions between Hydrofoil and Free-Surface by the High-Order Spectral/Boundary-Integral Method (고차 스펙트럴 / 경계적분법에 의한 수중익과 자유표면의 비선형 상호작용 계산)

  • 김용직;하영록
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.39 no.1
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    • pp.27-32
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    • 2003
  • Under the assumption of potential flow, free-surface flow around a hydrofoil is calculated by the high-order spectra1!boundary-integral method, This method is one of the most efficient numerical methods by which the nonlinear interactions between hydrofoil and free-surface can be simulated in time-domain. In this method. the wave potential which represents the nonlinear evolution of free-surface is solved by the high-order spectral method and the body potential which provides the effects of hydrofoil and shed vortex is solved by the boundary-integral method. The calculated free-surface profiles which are generated by a uniformly translating hydrofoil are compared with other experimental results. And they show relatively good agreements each other. As another example, free-surface flow generated by a heaving and translating hydrofoil is calculated and discussed.

Short-term clinical outcome of intentionally replanted posterior molars (의도적 재식술을 시행한 대구치의 단기간의 임상 평가)

  • Choi, Yong-Hoon
    • Restorative Dentistry and Endodontics
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    • v.36 no.1
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    • pp.12-18
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    • 2011
  • Objectives: This retrospective study evaluated the therapeutic effects of the intentional replantation (IR) procedure performed on the maxillary and mandibular molars of 35 patients. Materials and Methods: For the subjects, IR was performed due to difficulties in anatomically accessing the lesions and/or close proximity to the thick cortical bone, inferior alveolar nerve, or maxillary sinus, which rendered the ordinary periradicular surgery impossible. The patients'progress was followed for a year and up to 2 years and 4 months. The success of the procedure was evaluated in terms of clinical and radiographic success (%). Results: The results revealed the following: (a) 1 case (3%) of failed tooth extraction during IR; (b) 2 cases (6%) of extraction due to periodontal diseases and inflammatory root resorption; (c) 3 cases (9%) of normally functioning teeth in the oral cavity with minor mobility and apical root resorption, and; (d) 29 cases (82%) of normally functioning teeth without obvious problems. Conclusions: IR was confirmed to be a reliably repeatable, predictable treatment option for those who cannot receive conventional periradicular surgery because of anatomic limitations or patient factors.

Full mouth rehabilitation of fully edentulous patient using implant hybrid prosthesis (완전무치악 환자에서 임플란트 하이브리드보철물을 이용한 전악 수복 증례)

  • Park, Sang-Yong;Kim, Yoon-Young;Park, Won-Hee;Lee, Young-Soo
    • The Journal of Korean Academy of Prosthodontics
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    • v.53 no.3
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    • pp.228-233
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    • 2015
  • Loss of teeth may not only imply impaired oral function and loss of alveolar bone but is also often accompanied by reduced self-confidence. This results in a larger problem with the fully edentulous patient. The patient introduced in this study showed multiple missing teeth and mobility of remaining teeth and wanted to have fixed dental prosthesis using implants. Remaining teeth were extracted because of periodontally bad prognosis. This article reports a satisfactory clinical and esthetic outcome of full mouth rehabilitation using implant hybrid prosthesis in fully edentulous patient.

The success rate of Mg-incorporated oxidized implants in partially edentulous patients: a prospective clinical study (부분 무치악 환자에서 마그네슘 이온주입 임플란트의 성공률에 대한 전향적 임상연구)

  • Choi, Su-Jung;Yoo, Jung-Ho;Lee, Ku-Bok;Kim, Jin-Wook
    • The Journal of Korean Academy of Prosthodontics
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    • v.50 no.3
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    • pp.176-183
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    • 2012
  • Purpose: This study examined the clinical success rate of Mg titanate implants (M Implant system, Shinhung, Korea), which employ a Mg coating method, by evaluating the marginal bone loss and implant stability using radiographs and Osstell$^{(R)}$, over a 1 year. Materials and methods: The locations of the implants placement were divided into 4 areas; the maxillary and mandibular premolars and molars. In the maxilla, 8 and 9 implants were inserted in the premolar and molar areas, respectively. In the mandible, 11 and 51 implants were inserted in the premolar and molar areas. Marginal bone loss and ISQ of all implants (79) were measured after insertion, mounting the prosthetic appliance, and 1, 3, 6, and 12 months after loading. The marginal bone loss was measured from the radiograph using XCP bite, which was customized, and the implant stability measured using Osstell$^{(R)}$. Fisher's exact test (${\alpha}$=.05) was used to compare the success rates of each region. Results: The mean marginal bone loss for the upper and lower jaws were 1.537 mm and 1.172 mm. The mobility showed a non-significant reduction or increase according with time. The success rates were accounted for 94.12% and 98.39% in the upper and lower jaws; the premolars and molars were accounted for 100% and 96.67%. The two cases of early failure resulted from failure of primary stability during implant insertion. The late failures were not observed for 1 year after adding a loading to the implants. Conclusion: The Mg titanate implant showed good primary stability and good clinical results in both healing and function.

PERIODONTAL DISEASE CAUSED BY TRAUMA FROM OCCLUSION IN A CHILD (외상성 교합으로 인한 어린이의 치주질환)

  • Choi, Byung-Jai;Ko, Dong-Hyun;Kim, Seong-Oh;Lee, Jae-Ho;Son, Heung-Kyu
    • Journal of the korean academy of Pediatric Dentistry
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    • v.31 no.3
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    • pp.448-452
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    • 2004
  • Trauma from occlusion(TFO) is injury to the periodontal tissue as a result of occlusal forces. Mobility is a common clinical sign of occlusal trauma. In acute occlusal trauma, this may be accomanied by pain, tenderness to percussion, thermal sensitivity, and pathologic tooth migration. Chronic occlusal trauma may be marked by excessive wear and gingival recession. Radiographic finding include a widened periodontal ligament space, radiolucence and condensation of the alveolar bone and root resorption. TFO is related to the pathogenesis of periodontal disease. It can cause increased tooth mobility TFO itself does not initate or aggravate marginal gingivitis or initiate periodontal pockets. Active trauma can accelerate bone loss, pocket formation and gingival recession depending on the presence of local irritants and inflammation. Gingival recession associated with occlusal forces includes traumatic crescent, McCall's festoon and Stillman's cleft. TFO plays a minor role in the pathogenesis of early to moderate periodontitis. A 5-year-old male visited Yonsei University Pedodontics clinic with a chief complaint about gingival recession. Mobility, excessive wear, gingival recession were detected by clinical exam on the both mandibular deciduous ca nine. On the radiographic view, vertical alveolar bone loss was observed on both mandibular deciduous canine.

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Clinical Report by using hybrid telescopic double crown Removable Partial Denture on a few remaining teeth with severe periodontal disease (치주적으로 불리한 소수 잔존치에서 하이브리드 텔레스코픽 이중관 국소의치를 이용한 임상증례)

  • Seo, Jang-Won;Lee, Cheong-Hee
    • The Journal of Korean Academy of Prosthodontics
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    • v.57 no.1
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    • pp.24-30
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    • 2019
  • The successful results of the treatment using a double crown denture have been reported in several papers for some of the few remaining teeth in patient. In particular, double crown dentures may be an alternative to treatment in cases where the periodontal status is poor and clasp type removable partial dentures are inappropriate (crown/root ratio > 1). In this case, the patient visited clinic with a chief complaint of difficulty in mastication due to loss of posterior teeth and overall teeth mobility. After teeth with severe periodontitis were extracted, treatment plan of mandible is Kennedy class I removable partial denture (RPD) and treatment plan of maxilla is hybrid telescopic double crown RPD with a friction pin. Patient is well adapted after the prosthetic treatment and we report due to achieving satisfactory results in pronunciation, mastication, retention and aesthetics.

Study on the Applicability of a New Multi-body Dynamics Program Through the Application to the Heave Compensation System (상하동요 감쇠장치 적용을 통한 새로운 다물체동역학 프로그램의 적용성 검토)

  • Ku, Nam-Kug;Ha, Sol;Roh, Myung-Il
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.26 no.4
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    • pp.247-254
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    • 2013
  • In this paper, dynamic response analysis of a heave compensation system is performed for offshore drilling operations based on multibody dynamics. With this simulation, the efficiency of the heave compensation system can be virtually confirmed before it is applied to drilling operations. The heave compensation system installed on a semi-submersible platform consists of a passive and an active heave compensator. The passive and active heave compensator are composed of several bodies that are connected to each other with various types of joints. Therefore, to carry out the dynamic response analysis, the dynamics kernel was developed based on mutibody dynamics. To construct the equations of motion of the multibody system and to determine the unknown accelerations and constraint forces, the recursive Newton-Euler formulation was adapted. Functions of the developed dynamics kernel were verified by comparing them with other commercial dynamics kernels. The hydrostatic force with nonlinear effects, the linearized hydrodynamic force, and the pneumatic and hydraulic control forces were considered as the external forces that act on the platform of the semi-submersible rig and the heave compensation system. The dynamic simulation of the heave compensation system of the semi-submersible rig, which is available for drilling operations with a 3,600m water depth, was carried out. From the results of the simulation, the efficiency of the heave compensation system were evaluated before they were applied to the offshore drilling operations. Moreover, the calculated constraint forces could serve as reference data for the design of the mechanical system.

The effect of early loading on the direct bone-to-implant surface contact of the orthodontic osseointegrated titanium implant (교정력이 골유착성 티타니움 임프란트의 초기 고정에 미치는 영향에 관한 실험적 연구)

  • Chung, Kyu-Rhim;Lee, Sung-Ja
    • The korean journal of orthodontics
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    • v.31 no.2 s.85
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    • pp.173-185
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    • 2001
  • The orthodontic osseointegrated titanium implant, a kind of intraoral skeletal anchorage can be an alternative to tooth-borne anchorage, in case that the conventional tooth-borne anchorage is not available or the anchorage is critical. This study was conducted to elucidate the effect of early loading on the osseointegration of the orthodontic titanium implant and the healing process of the impaired bone at the site of implant after removing it. In two adult beagle dogs24 osseointegrated titanium implants were inserted into the alveolar bone, with 12 implants placed in each dog. In dog1, 6 out of 12 implants were loaded with 200-300gm of force immediately after placing, and the remaining 6 implants were not loaded for 4weeks. In dog2, all 12 implants had healing period of 4weeks, and then were loaded with 200-300gm of force for another 4weeks. Following an observation period of 4 and 8 weeks, the animals were sacrificed. Then the implants and the surrounding bone of dog1 and dog2 were removed, respectively. Undecalcified sections along the long axis of implant were made and the degree of osseointegration was examined under the light microscope. The results were as follows. 1. In the histologic features of tissues around implants anchored in dog1, there was no difference between immediately loaded implants and unloaded implants. Immature woven bone was ingrowing into the thread spaces from the original compacta and in direct contact with the implant surface in part. 2. The premature loading just after 4weeks healing period did not halt the progress of the osseointegration between bone and implant surface. The woven bone around the implants was maturing into the lamellar bone which resembled the structure of the original compacta at the end of 8weeks observation period. 3. Most implants with the inflammed surrounding mucosa were lost or mobile. The mobile implants were encapsulated by fibrous connective tissue which separated the implant surface from the bone. 4. The impaired bone at the site of the implant failed to anchor was showing recovery without inflammatory reaction 2weeks after removing, with the immaure woven bone lined by active osteoblasts and osteoid. Based on the results of this study, the integration of this orthodontic implant seemed to be impaired by the inflammation of the tissue surrounding the Implant rather than by early loading on implant, and increased with time lapsed after placing the implant. The use of implant described in this report can be recommended as an orthodontic anchorage unit immediately after insertion under the careful control of orthodontic force applied and plaque.

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AN INVESTIGATION OF TRAUMATIC DENTAL INJURIES IN CHILDREN (소아의 치아와 지지조직 외상에 관한 분석)

  • Baik, Byeong-Ju;Yang, Yeon-Mi;Yang, Cheol-Hee;Kim, Jae-Gon
    • Journal of the korean academy of Pediatric Dentistry
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    • v.28 no.4
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    • pp.600-612
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    • 2001
  • The purpose of this study is concerned with an investigation of the actual condition of traumatic injuries of teeth and supporting structures in children to set up possible criteria for prevention and treatment of injured teeth. The materials consisted of the clinical records of 431 traumatically injured teeth of 212 children, accumulated during two years from the first of April in 1998 to the end of March in 2000, supplied from the Dept. of Pediatric Dentistry, Chonbuk National University Hospital. The incidence of injuries in boys was extremely high for permanent teeth, twice as high as in girls. Accidents to primary teeth were most common from 1 to 2 years of age and to permanent teeth were most from 8 to 9 years of age. The most common cause of trauma was a fall for both primary and permanent teeth, followed by collision. The anterior teeth in maxilla was most frequently affected by trauma in both the primary and permanent teeth. The most common type of trauma were loosening for the primary teeth, followed by luxation types which included the intrusion, displacement and extrusion and complete avulsion types. For the permanent teeth, the most common type of trauma were tooth fracture. The most common trauma of soft tissue was laceration of upper lip, lower lip and gingiva of maxilla Concerning treatment at the first visit, primary teeth with only loosening and concussion were not usually treated. Permanent teeth were often treated by crown restorations for crown fractures and by endodontic procedures for pulpal exposure. Though we could elucidate actual condition of traumatic injuries of teeth in children, we should make a follow-up survey to ensure the prognosis of injured teeth and establish the most desirable criteria for traumatized teeth in children.

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