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  • Title/Summary/Keyword: closure method

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Investigation of Turbulence Structures and Development Turbulence Model Based upon a Higher Order Averaging Method (고차평균법에 의한 난류구조의 규명 및 난류모델의 개발)

  • 여운광;편종근
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.4 no.4
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    • pp.201-207
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    • 1992
  • The averaged non-linear term in the turbulence equations, suggested by Yeo (1987), is analyzed theoretically and experimentally. It was formulated by applying the filtering concepts to the convolution integral average definition with the Gaussian response function. This filtering approach seems to be superior to the conventional averaging methods in which all four terms at the doubly average vol must be defined separately, and it also gives a very useful tool in understanding the turbulence structures. By theoretically analyzing the newly derived description for the averaged non-linear terms, it is found that the vortex stretching can be explicitly accounted for. Furthermore, comparisons of the correlation coefficients based on the experimental data show that the vortex stretching acts most significantly on the turbulence residual stress. Thus, it strongly supports the claim that the vortex stretching is essential in the transfer of turbulence. In addition. a general form of turbulent energy models in LES is derived, by which it is recognized that the Smagorinsky, the vorticity and the SGS energy models are not distinctive.

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The Surgical Treatment of Esophageal Perforation (식도 파열의 수술적 치료)

  • Hwang Jung Joo;Joung Eun Kyu;Lee Doo Yun;Paik Hyo Chae
    • Korean Journal of Bronchoesophagology
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    • v.11 no.1
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    • pp.15-20
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    • 2005
  • Background : It is well-known that esophageal perforation (EP) is difficult in diagnosis and has high mortality rate despite proper management. There are disputes in regarding the reatment in cases of delayed diagnosis although in the early diagnosed cases, operation is recommended without arguments. Methods: From April, 2001 to December, 2004, nine patients who were diagnosed as EP in our hospital were analyzed retrospectively about the causes, the interval between the cause and the treatment, and operation methods. Results: There were 8 male and one female with men age of 49.3 years (range: 25-67 years). The causes of EP included perforations following operations of corvical spine in three cases, spontaneous perforation(Boehaave syndrome) in two cases, foreign bodies in two cases, operation of esophageal diverticulum in one case and blunt trauma bytraffic accident in one case. Mean interval between the first treatments and the causes was 11.6 days (range: 2-30 days). The sites of perforation were upper third of esophagus in three cases, middle third in three cases and lower third in three cases. All except two cervical cases presented as mediastinitis or empyema at the time of diagnosis. Primary repair and irrigation had been performed in 7 cases but five cases out of them required more than two procedures. Conclusions : More than one procedure wasrequired in the treatment of EP because of contaminations and infections which had been spread at the time of initial manifestatios, howeverprimary closure and massive irrigation is the best method in order to preserve esophagus unless the remaining esophagus is extensively damaged.

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Individual Tree Growth Models for Natural Mixed Forests in Changbai Mountains, Northeast China

  • Lu, Jun;Li, Fengri
    • Journal of Korean Society of Forest Science
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    • v.96 no.2
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    • pp.160-169
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    • 2007
  • The data used to develop distance-independent individual models for natural mixed forests were collected from 712 remeasured permanent sample plots (25,526 trees) of 10-year periodic from 1990 to 2000 in Baihe Forest Bureau of Changbai Mountains, northeast China. Based on analyzing relationship between diameter increment of individual trees with tree size, competitive status, and site condition, the diameter growth models for individual trees of 15 species growing in mixed-species uneven-aged forest stands, that have simple form, good predicting precision, and easily applicable, were developed using stepwise regression method. The main variables influencing on diameter increment of individual trees were tree size and competition, however, the site conditions were not significantly related with diameter increment. The tree size variables (lnDBH and DBH2) were the most significant and important predictors of diameter growth existing in all 15 growth models. The diameter increment was directly proportional to tree diameter for each species. For the competitive factors in growth model, the relative diameter (RD), canopy closure (P), and the ratio of diameter of subject tree with maximum diameter (DDM) were contributed to the diameter increment at a certain extent. Other measures of stand density, such as basal area of stand (G) and stand density index (SDI), were not significantly influenced on diameter increment. Site factors, such as site index, slope and aspect were not important to diameter increment and excluded in the final models. The total variance explained by the final models of squared diameter increment (R2) for all 15 species ranged from 35% to 72% and these results compared quit closely with those of Wykoff (1990) for mixed conifer stands. Using independent data set, validation measures were evaluated for predicting models of diameter increment developed in this study. The result indicated that the estimated precision was all greater than 94% and the models were suitable to describe diameter increment.

A Comparison of the Epidural Nalbuphine to Epidural Morphine in Post-Cesarean Section Patients (제왕절개술후 통증치료를 위해 경막외강에 투입된 Morphine과 Nalbuphine의 비교 연구)

  • Moon, Bong-Kee;Lee, Youn-Woo;Lee, Ja-Won;Yoon, Duck-Mi;Oh, Hung-Kun
    • The Korean Journal of Pain
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    • v.6 no.1
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    • pp.60-66
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    • 1993
  • The clinical effects of epidural nalbuphine were compared to those of epidural morphine in sixty Cesarean delivery. They were physical status 1 or 2 by ASA classification and randomly divided into three groups. They were administered nalbuphine 5 mg(Group N5), nalbuphine 10 mg(Group N10) or morphine 3 mg(Group M3) through an indwelling epidural catheter at the time of peritoneal closure. During the first postoperative 24 hours, their analgesic effects were evaluated by visual analogue scale(0-10), respiration rates and Trieger dot test. The severity of side effects(0-2) was also evaluated. The results were as follows ; 1) The number of patients who needed additional epidural analgesics was least in group M3 (p<0.05). There was no significant difference between group N5 and group N10. 2) The duration between the first and second epidural administration was ; 19.2 hours in group M3, 8.6 hours in group N10 and 5.4 hours in group N5. There was a significant difference each group (p<0.05). 3) From the fourth post operative hour, both groups receiving nalbuphine showed a higher VAS score compared to group M3(p<0.05). 4) The incidence of pruritus, nausea, vomiting and voiding difficulty were more severe in group M3 compared with the other groups. However the severity did not increase with increasing nalbuphine dosage. 5) There were no patients showing objective sedation or low respiration rate(10 times/minute). We concluded that epidural administration of nalbuphine 5 mg or 10 mg is one way of post operative pain control. Its side effects were less than epidural morphine, but it is a less convenient in the method of analgesia.

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Treatment of Partial Thickness Skin Defect with Cultured Allogenic Keratinocytes (Kaloderm®) (동종유래각질세포(Cultured Allogenic Keratinocytes, Kaloderm®)를 이용한 부분층 피부 결손의 치료)

  • Seo, Sang Won;Chang, Choong Hyun;Cho, Min Su;Hong, Yoon Gi;Jeon, Sae Wha
    • Journal of Trauma and Injury
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    • v.20 no.1
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    • pp.1-5
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    • 2007
  • Purpose: Grafting with autograft skin remains the most effective method for treating skin defects. When insufficient donor sites are present or patients are afraid of the operation, a skin graft is impossible. Cultured allogenic keratinocytes speed wound healing by providing cover and by producing growth factors and extracellular matrix protein. We report an application of cultured allogenic keratinocytes (Kaloderm(R), Tegoscience, Seoul, Korea) in the treatment of an acute partial thickness skin defect. Methods: From March 2005 to January 2006, 20 patients with a partial thickness skin defect were treated with cultured allogenic keratinocytes. The wound was covered with a sheet of cultured allogenic keratinocytes and ointment with Bactigras(R) gauze. The wound was inspected every two or three days. We regarded completion of epithelialization as wound healing. Results: The mean period between time of injury and time of Kaloderm(R) application was 7.5 days. The time taken from application of Kaloderm(R) to complete closure of the wounds was 7.2 days. Conclusion: In view of the favorable outcome, cultured allogenic keratinocytes are safe and effective biologic dressing materials for use in the treatment of open wounds.

A Numerical Study of Turbulent Flow Around a Twin-Skeg Container Ship Model with Appendages

  • Kim, Hyoung-Tae;Lee, Pyung-Kuk;Kim, Hee-Taek
    • Journal of Ship and Ocean Technology
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    • v.10 no.4
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    • pp.12-23
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    • 2006
  • In this paper, a numerical study is carried out to investigate the turbulent flow around a twin-skeg container ship model with rudders including propeller effects. A commercial CFD code, FLUENT is used with body forces distributed on the propeller disk to simulate the ship stem and wake flows with the propeller in operation. A multi-block, matching, structured grid system has been generated for the container ship hull with twin-skegs in consideration of rudders and body-force propeller disks. The RANS equations for incompressible fluid flows are solved numerically by using a finite volume method. For the turbulence closure, a Reynolds stress model is used in conjunction with a wall function. Computations are carried out for the bare hull as well as the hull with appendages of a twin-skeg container ship model. For the bare hull, the computational results are compared with experimental data and show generally a good agreement. For the hull with appendages, the changes of the stem flow by the rudders and the propellers have been analyzed based on the computed result since there is no experimental data available for comparison. It is found the flow incoming to the rudders has an angle of attack due to the influence of the skegs and thereby the hull surface pressure and the limiting streamlines are changed slightly by the rudders. The axial velocity of the propeller disk is found to be accelerated overall by about 35% due to the propeller operation with the rudders. The area and the magnitude of low pressure on the hull surface enlarge with the flow acceleration caused by the propeller. The propellers are found to have an effect on up to the position where the skeg begins. The propeller slipstream is disturbed strongly by the rudders and the flow is accelerated further and the transverse velocity vectors are weakened due to the flow rectifying effect of the rudder.

Numerical Analysis of the Wake of a Surface Ship Model Mounted in KRISO Large Cavitation Tunnel (KRISO 대형 캐비테이션터널 시험조건의 함정 모형선 반류에 대한 수치해석적 연구)

  • Park, Il-Ryong;Kim, Je-In;Kim, Ki-Sup;Ahn, Jong-Woo;Park, Young-Ha;Kim, Myoung-Soo
    • Journal of the Society of Naval Architects of Korea
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    • v.53 no.6
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    • pp.494-502
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    • 2016
  • The accurate assessment of hull-appendage interaction in the early design stage is important to control the inflow to the propeller plane, which can cause undesirable hydrodynamic effects in terms of cavitation phenomenon. This paper describes a numerical analysis for the flow around a fully appended surface ship model for which KRISO has carried out a model test in the Large Cavitation Tunnel(LCT). This numerical study was performed with the LCT model test in a complementary manner for a good reproduction of the wake distribution of surface ships. A second order accurate finite volume method provided by a commercial computational fluid dynamics(CFD) program was used to solve the governing Reynolds Averaged Navier-Stokes(RANS) equations, where the SST kω model was used for turbulence closure. The numerical results were compared to available LCT experimental data for validation. The calculations gave good predictions for the boundary layer profiles on the walls of the empty cavitation tunnel and the wake at the propeller plane of the fully appended hull model in the LCT.

Development and CFD Analysis of a New Type Pre-Swirl Duct for 176k Bulk Carrier (176k Bulk Carrier에 대한 신개념 타입의 Pre-Swirl Duct의 개발 및 CFD 해석)

  • Yoo, Gwang Yeol;Kim, Moon Chan;Shin, Yong Jin;Shin, Irok;Kim, Hyun Woong
    • Journal of the Society of Naval Architects of Korea
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    • v.56 no.4
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    • pp.373-382
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    • 2019
  • This paper shows numerical results for the estimation of the propulsor efficiency of Pre-Swirl Duct for 176k bulk carrier as well as its design method. Reynolds averaged Navier-Stokes equations have been solved and the k-epsilon model applied for the turbulent closure. The propeller rotating motion is determined using a sliding mesh technique. The design process is divided into each part of Pre-Swirl Duct, duct and Pre-Swirl Stator. The design of duct was performed first because it is located further upstream than Pre-Swirl Stator. The distribution of velocity through the duct was analyzed and applied for the design of Pre-Swirl Stator. The design variables of duct include duct angle, diameter, and chord length. Diameter, chord length, equivalent angle are considered when designing the Pre-Swirl Stator. Furthermore, a variable pitch angle stator is applied for the final model of Pre-Swirl Duct. The largest reduction rate of the delivered power in model scale is 7.6%. Streamlines, axial and tangential velocities under the condition that the Pre-Swirl Duct is installed were reviewed to verify its performance.

A Study on Development of Men's Formal Jacket Pattern by 3D Human Body Scan Data -A Focus on Men's in their Late 30s- (3D 인체데이터를 활용한 남성 정장재킷 패턴개발 연구 -30대 후반 남성을 중심으로-)

  • Shin, Kyung-hee;Suh, Chuyeon
    • Journal of the Korean Society of Clothing and Textiles
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    • v.43 no.3
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    • pp.440-458
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    • 2019
  • Based on a 3D body data and pattern comparison analysis, this study developed a formal jacket pattern for men in their late 30s. In order to select the representative type of men in their late 30s, factor analysis and cluster analysis were conducted on data form 319 men, 35 to 39 years old using the anthropometric data from The 7th Size Korea (2015) as the representative body type. The surface of the body surface was developed using a 3D human shape of a male in his 30s in The 6th Size Korea (2010). Then the shape was changed to a flat pattern that confirmed the necessary elements for setting the shape and dimension. Cluster analysis revealed type B as the representative type because it showed the best shape characteristics for men in the late 30s. The drafting method of the final research pattern is as follows. Jacket length: stature/2.5cm, back length: stature/5+8.5cm (constant)], armhole depth: [stature/ 7-1.5cm (constant)], back width: [C/9+9.5cm (constant)]+1cm (ease), front width: [C/9+8.5cm (constant)]+1cm (ease), armscye depth: C/8, front waist darts: 1cm, front closure amount: 2cm.

Reliability of Early Ambulation after Intradural Spine Surgery : Risk Factors and a Preventive Method for Cerebrospinal Fluid Leak Related Complications

  • Lee, Subum;Cho, Dae-Chul;Kim, Kyoung-Tae;Lee, Young-Seok;Rhim, Seung Chul;Park, Jin Hoon
    • Journal of Korean Neurosurgical Society
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    • v.64 no.5
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    • pp.799-807
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    • 2021
  • Objective : Cerebrospinal fluid leakage related complications (CLC) occasionally occur after intradural spinal surgery. We sought to investigate the effectiveness of early ambulation after intradural spinal surgery and analyze the risk factors for CLC. Methods : For this retrospective cohort study, we enrolled 314 patients who underwent intradural spinal surgery at a single institution. The early group contained 79 patients who started ambulation after 1 day of bedrest without position restrictions, while the late group consisted of 235 patients who started ambulation after at least 3 days of bed rest and were limited to the prone position after surgery. In the early group, Prolene 6-0 was used as the dura suture material, while black silk 5-0 was used as the dura suture material in the late group. Results : The overall incidence rate of CLC was 10.8%. Significant differences between the early and late groups were identified in the rate of CLC (2.5% vs. 13.6%), surgical repair required (1.3% vs. 7.7%), and length of hospital stay (2.99 vs. 9.29 days) (p<0.05). Logistic regression analysis revealed that CLC was associated with practices specific to the late group (p=0.011) and the revision surgery (p=0.022). Conclusion : Using Prolene 6-0 as a dura suture material for intradural spinal surgery resulted in lower CLC rates compared to black silk 5-0 sutures despite a shorter bed rest period. Our findings revealed that suture - needle ratio related to dura defect was the most critical factor for CLC. One-day ambulation after primary dura closure using Prolene 6-0 sutures appears to be a costeffective and safe strategy for intradural spinal surgery.