• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.772-785
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• 2021

Container ships has a transverse section in the form of an open profile, making it very sensitive to torsion phenomena. To minimize this effect, a structure known as a torsion box exists, which is subject to high stresses influenced by the fatigue phenomenon and the existence of cut-outs, for the passage of the longitudinal stiffeners, acting as stress concentrators. The aim of this study is to propose a two-stage design methodology to aid designers in satisfying the structural requirements and contribute with to a better understanding of the considered structure. The transverse webs of a torsional box structure are examined by comparing different cut-out geometries from numerical models with different regular load conditions to obtain the variables of the fatigue safety factor through linear regression models. The most appropriate geometry of the torsion box is established in terms of minimum weight, from nonlinear multivariable optimization models.

• Steel and Composite Structures
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• 제41권6호
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• pp.787-803
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• 2021

The size-dependent nonlinear thermomechanical vibration analysis of pre- and post-buckled tapered two-directional functionally graded (2D-FG) microbeams is presented in this study. In the context of the modified couple stress theory, the formulations are derived based on the parabolic shear deformation beam theory and von Karman nonlinear strains. Different thermomechanical material properties are assumed to be temperature-dependent and smoothly vary in both length and thickness directions using the power law and the physical neutral axis concept is employed. The nonlinear governing equations are derived using the Hamilton principle and the resulting variable coefficient equations of motion are solved using the differential quadrature method (DQM) and iterative Newton's method for clamped-clamped and simply supported boundary conditions. Comparison studies are presented to validate the derived model and solution procedure. The impacts of induced thermal moments, temperature power index, two gradient indices, nonuniform cross-section, and microstructure length scale parameter on the frequency-temperature configurations are explored for both clamped and simply supported microbeams.

• Structural Engineering and Mechanics
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• 제81권4호
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• pp.523-527
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• 2022

The objective of this study is to simulate the flow in pipes with various boundary conditions. Free-pressure fluid model, is used in the pipe based on Navier-Stokes equation. The models are solved by using the numerical method. A problem called "stability of pipes" is used in order to compare frequency and critical fluid velocity. When the initial conditions of problem satisfied the instability conditions, the free-pressure model could accurately predict discontinuities in the solution field. Employing nonlinear strains-displacements, stress-strain energy method the governing equations were derived using Hamilton's principal. Differential quadrature method (DQM) is used for obtaining the frequency and critical fluid velocity. The results of this paper are analyzed by hyperbolic numerical method. Results show that the level of numerical diffusion in the solution field and the range of well-posedness are two important criteria for selecting the two-fluid models. The solutions for predicting the flow variables is approximately equal to the two-pressure model 2. Therefore, the predicted pressure changes profile in the two-pressure model is more consistent with actual physics. Therefore, in numerical modeling of gas-liquid two-phase flows in the vertical pipe, the present model can be applied.

• The Plant Pathology Journal
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• 제38권5호
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• pp.432-448
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• 2022

Planthopper infestation in rice causes direct and indirect damage through feeding and viral transmission. Host microbes and small RNAs (sRNAs) play essential roles in regulating biological processes, such as metabolism, development, immunity, and stress responses in eukaryotic organisms, including plants and insects. Recently, advanced metagenomic approaches have facilitated investigations on microbial diversity and its function in insects and plants, highlighting the significance of microbiota in sustaining host life and regulating their interactions with the environment. Recent research has also suggested significant roles for sRNA-regulated genes during rice-planthopper interactions. The response and behavior of the rice plant to planthopper feeding are determined by changes in the host transcriptome, which might be regulated by sRNAs. In addition, the roles of microbial symbionts and sRNAs in the host response to viral infection are complex and involve defense-related changes in the host transcriptomic profile. This review reviews the structure and potential functions of microbes and sRNAs in rice and the associated planthopper species. In addition, the involvement of the microbiota and sRNAs in the rice-planthopper-virus interactions during planthopper infestation and viral infection are discussed.

• 한국항만학회지
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• 제9권2호
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• pp.25-38
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• 1995

The wind generated circulation model describes the phenomenon based on the following physical assumptions: a) As the horizontal dimension of the flow domain is several orders of magnitude larger than vertical dimension, nearly horizontal flow is realistic. b) The time taken for circulation to develop may effect on the flow domain of the earth's rotation, the contribution of the Coriolis force. c) A flow domain of large dimension results in quite large Reynolds number and the Reynolds stresses are approximated by the turbulent mean velocity gradient. d) The circulation is forced by the shear stresses on the water surface exercised by the wind. Modification made to the depth average approximation of the convective terms and the bed shear stress terms by adopting a certain distribution of current over the depth and laboratory measurements for the bed shear expression. Modification circulation patterns, energy evolution and surface profile gave the significant differences comparing with the classical model results. The modified model results in higher free surface gradients balancing both the free surface shear and the bed shear and consequently to higher surface profiles along the coast.

• 한국정밀공학회지
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• 제12권8호
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• pp.63-72
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• 1995

Closed-die forging of spur gears with hollow cylindrical billet has been analysed by using the upper-bound method. A kinematically admissible velocity field has been developed, wherein, an involute curve has been introduced to represent the forging die profile. In the analysis, the deformation region has been divided into nine zones. A constant frictional stress has been assumed on the contacting surfaces. Utilizing the formulated velocity field, numerical calculations have been carried out to investigate the effects of various parameters, such as module, number of teeth and friction factor, on the forging of spur gears. Hardness and accuracy of forged gears are measured. The following results have been obtained: (1) It is verified that an axisymmetric deformation zone exists between root circle and center of gear through forged gears. (2) The average relative forging pressure is predominantly dependent on the number of teeth and increases near the final filling stage as the addendum modification coefficient increases. (3) Close agreement was found between the predicted values of forging load and those obtained from experimental results.

• Structural Engineering and Mechanics
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• 제90권5호
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• pp.435-446
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• 2024

The use of cold-formed steel members is increasing day by day, especially in regions where earthquake effects are intensively experienced. Among cold-formed steel members (CFS), "channel" members are used more than other crosssectional members, especially in buildings or industrial structures. In recent years, several studies have been carried out on the axial load and flexural performance of these members under monotonic loading. In this study, CFS beam-column members were cyclically and monotonically loaded under combined axial load and biaxial bending moments, and their buckling behavior, load bearing capacity, stiffness, ductility, and energy absorption capacity were determined. For this purpose, monotonic and cyclic loading experiments were carried out on 30 CFS channel members at 15 different eccentricities. Then, material properties were determined by axial monotonic tensile and very low cycle fatigue tests for use in numerical studies. From the experimental results, the buckling modes, bearing capacities, ductility, stiffness, and energy absorption capacities of the members were obtained. The characteristics of the members were compared according to the stress state of the lips. According to the data obtained from the displacement transducer placed on the lips and on the back of the web, information about the buckling mode and curvature of the members was obtained. Finally, monotonic, and cyclic loading results were compared to determine the differences in the buckling behavior of the members.

• 대한간호학회지
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• 제24권1호
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• pp.58-69
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• 1994

In order to see the development of Nursing related research activities in Korea over the last three decades, abstracts of almost all of the Master and Ph.D theses that appeared from 1961 up to August 1991 were collected. The number of theses was 2354, from which an index of key words has been constructed. Key words were defined as those terms in each thesis title that convey major objectives of the given thesis study and the important nursing concepts dealt with in the thesis. Although all the key words were picked from the thesis title only, full use was made of the abstracts in deciding the principal objectives and essential contents of the thesis studies and their important concepts as well. In total, 539 kinds of key words were identified from the 2354 titles, and the identified words were all found to be in the International Nursing Index. On an average each title has two key words. Which key words were most frequently used, how they have changed with time, what kind of concept is preferably dealt with by each graduate school, and the concepts to which a given key word is likely to be connected were examined. The results are summerized below : 1) For each decade the theses numbers were as follows : 54(2.3%) from the 60’s, 413(17.5%) from the 70’s, 1523(64.7%) from the 80’s, and 364(15.5%) from the 90’s. Master’s thesis contributed 96% (2252) of the papers and Ph. D’s theses filled the remaining 4%(102). 2) A total of 539 key words were used, averaging about 2 for each thesis. The most frequently used key words were ‘Nurse’, ‘Anxiety’, ‘Knowledge / Attitude /Practice’, ‘Stress /Stressor’, ‘Attitude’, ‘Job-Satisfaction’, ‘Mental Disorder’, ‘Operation’, ‘Elderly’, ‘Nursing Role’. 3) Each decades key words can be classified as : the 60’s : ‘Nursing Education’, ‘Pulmonary Tuberculosis’, ‘Mother-Child Health’, ‘Growth & Development’, ‘Public Facilities’, ‘Mental Disorder’ : the 70’s : ‘Nurse’, ‘Family Planning’, ‘Attitude’ / ‘Knowledge, Attitude / Practice’, ‘Curriculum in Nursing Education’, ‘Clinical Practice in Nursing’, ‘Analysis of the Work of the Nurse’, ‘Health Education of School’, : the 80’s : ‘Nurse’, ‘Anxiety’, ‘Stress /Stressor’, ‘Operation’, ‘Nursing Role’, ‘Job Satisfaction’ : the 90’s : ‘Nurse’, ‘Elderly’, ‘Family-Support’, ‘Stress /Stressor’, ‘Home Care’. Key word ‘Nurse’ appears continuously and most frequently through the years, which indicates that there has been active study of the characteristics of nurses and related fields. The concept ‘Anxiety’ has been studied steadly from the 80’s and it shows that interest in health and disease are increasing Which comes as a result of society changing to an industrial and informational community. 4) Looking into each graduate school’s study area key words ‘Anxiety’, ‘Nurse’, ‘Mental Disorder’, ‘Stress /Stressor’, ‘Operation’, ‘Attitude’, ‘Hemo-dialysis’, were studied in the regular graduate school : ‘Family Planning /Contraception’, ‘Knowledge / Attitude /Practice’, ‘Physical Health-State /Physical Health Examination’, ‘Nurse’, ‘Using Clinical Facilities’, ‘Health Education of School’, were studied in the Graduate School of Public Health’ ; ‘Nurse’, ‘Anxiety’, ‘Stress / Stressor’, ‘Job-Satisfaction’, ‘Clinical Practice Education’, ‘Nursing Education’, were studied in the Graduate School of Education : ‘Nurse’, ‘Job Satisfaction’, ‘Nursing Role’, ‘Administration - Employment /Employment Management’, ‘Leadership’, ‘Personnel Profile’, ‘Nursing Manpower / Changing Working Place’, were studied in the Graduate School of Public Administration. 5) The Connection between key words were : ‘Nurse Job Satisfaction’, ‘Stress / Stressor ⇔ Coping / Ajustment’, ‘Nurse ⇔ Nursing Role’, ‘Anxiety ⇔ Giving Information’, ‘Nurse ⇔ Stress / Stressor’, ‘Anxiety ⇔ Operation’, ‘Nurse ⇔ Burnout’, ‘Knowledge, Attitude, Practice ⇔ Family Planning’, ‘Nurse Administration ⇔ Employment’, ‘Anxiety Muscle ⇔ Relaxation Technic’, ‘Anxiety ⇔ Mental Disorder’. From the above it can be noted that many nursing concepts were handled in the thesis titles. But there were more than enough papers on the characteristics of the nurse. It is suggested that in depth research be made on ‘Nursing Accidents’, t-‘Ethics’, ‘Nurse - Patient Interactions’, ‘Spritual Care’, ‘Dying’, ‘Hospice’, ‘Resident Helper’ and that there should be in depth research relating to the physical and mental development of youth and in particular physical concepts like ‘Drug - Abuse’, ‘Child -Abuse and Teaching’.

• 한국산림과학회지
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• 제108권3호
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• pp.440-453
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• 2019

본 연구는 평면 숲동영상 및 VR 숲동영상 시청이 성인의 스트레스 감소에 미치는 영향을 밝히기 위해 수행되었다. 실험은 인공기후실에서 진행되었으며, 피험자는 40명이 참가하였다. 피험자의 스트레스를 유발한 후 2D 회색동영상, 2D 숲동영상, VR 숲동영상을 5분 동안 시청하게 하였다. 실험하는 동안 연속적으로 심박변동성을 측정하여 자율신경계 활동을 평가하였으며, 각 실험 후 설문지를 이용하여 심리 상태를 평가하였다. 생리적 측정 결과 2D 숲동영상은 2D 회색동영상보다 스트레스 지수 감소효과가 크고, HF 증가효과가 크며, 심장박동수 감소효과가 크다는 사실을 확인하였다. 또한 VR 숲동영상은 2D 회색동영상 시청보다 스트레스 지수 감소효과가 크고, LF/HF 증가효과가 크며, 심장박동수 감소효과가 크다는 사실을 확인하였다. 심리적 측정 결과 피험자들은 2D 회색동영상보다 2D 숲동영상과 VR 숲동영상을 더 쾌적하고, 자연적이며, 진정된다고 느꼈다는 사실을 확인하였다. 그리고 2D 숲동영상과 VR 숲동영상이 2D 회색동영상보다 긍정적인 정서를 증가시키고 부정적인 정서를 감소시킨다는 사실을 확인하였다. 이상의 결과를 바탕으로 2D 숲동영상과 VR 숲동영상의 시청은 스트레스 상황을 벗어나 2D 회색동영상을 시청하는 것보다 더 스트레스 지수를 감소시키고, 심장박동수를 감소시키는 것으로 판단된다. 또한 2D 숲동영상은 부교감 신경계의 활동을 증가시키고 VR 숲동영상은 교감 신경계의 활동을 증가시키는 차이점이 있는 것으로 판단된다. 마지막으로 VR 숲동영상의 교감 신경계의 활동 증가는 스트레스, 긴장 등의 부정적 교감신경 활성이 아닌 신기함, 호기심 등의 긍정적 교감신경 활성으로 판단된다. 이러한 연구의 결과가 산림치유의 시각적 효과에 대한 기반이 되길 기대하고, 임업분야에서 4차 산업혁명의 기술인 VR의 활용이 넓어지는 기반이 되길 기대한다.

• 한국가스학회지
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• 제14권2호
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• pp.1-6
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• 2010

고압가스 압력용기의 강도안전성을 FEM으로 해석하였다. 본 연구에서 고려한 강재용기의 내압은 서비스 충전압력 $9kg/cm^2$, 가스충전 최고압력 $18.6kg/cm^2$, 안전변 작동 최고압력 $24.5kg/cm^2$, 수압시험압력 $34.5kg/cm^2$이다. FEM 해석결과에 의하면, 서비스 충전압력 $9kg/cm^2$와 충전최고압력 $18.6kg/cm^2$에 대한 강도안전성은 가스용기에 걸리는 응력이 강재의 항복강도 이내에 있기 때문에 안전한 것으로 나타났다. 그러나 수압시험압력 $34.5kg/cm^2$을 가하였을 때에 발생하는 응력은 항복강도를 충분히 넘어서기 때문에 불안전하지만, 인장강도 이내에 존재하기 때문에 아직은 안전하다. 수압시험압력을 용기에 자주 공급하면 용기는 소성변형에 의한 피로잔류응력이 특히 하단반구부에 축적되므로 파손될 수 있다. 계산결과에 의하면, 스커트 지역에 작용하는 집중하중은 하단반구부에 영향을 미치지 않지만, 용기에 서 가장 취약한 부분은 용기의 몸체와 스커트 사이에 위치한 하단반구부의 중간부분임을 알 수 있다. 따라서 하단반구부의 형상은 고압가스 저장용기 설계에서 중요한 요소라는 것을 보여주는 FEM 해석결과를 제공하고 있다.