• Steel and Composite Structures
• /
• v.3 no.4
• /
• pp.261-275
• /
• 2003

Truss members built-up with double angles back-to-back have monosymmetric cross-section and twisting always accompanies flexion upon the onset of buckling about the axis of symmetry. Approximate formulae for calculating the buckling capacity are presented in this paper for routine design purpose. For a member susceptible only to flexural buckling, its optimal cross-section should consist of slender plate elements so as to get larger radius of gyration. But, occurrence of twisting changes the situation owing to the weakness of thin plates in resisting torsion. Criteria for limiting the leg slenderness are discussed herein. Truss web members in compression are usually considered as hinged at both ends for out-of-plane buckling. In case one (or both) end of member is not supported laterally by bracing member, its adjoining members have to provide an elastic support of adequate stiffness in order not to underdesign the member. The stiffness provided by either compression or tension chords in different cases is analyzed, and the effect of initial crookedness of compression chord is taken into account. Formulae are presented to compute the required stiffness of chord member and to determine the effective length factor for inadequately constrained compressive diagonals.

• Journal of Magnetics
• /
• v.21 no.3
• /
• pp.431-436
• /
• 2016

In the design of transformer winding, natural vibration frequency is an important parameter. This paper presents a 2D model to calculate axial vibration natural frequency of power transformer winding based on the elastic dynamics theory, and according to the elastic support equivalent principle of radial pressboards. The 3D model to calculate natural vibration frequency can be simplified as a 2D one as the support of pressboards on the winding is same. It is verified that results of the 2D model are consistent with those of 3D one, but the former can achieve much higher calculation efficiency. It shows that increasing the width and number of pressboards can improve axial natural frequency through formula analysis and simulation, and also the relations between the changes of axial pre-compression and axial natural vibration frequency on the windings are investigated. Finally, the proposed 2D model's effectiveness is proved when compared with tested ones.

• Smart Structures and Systems
• /
• v.13 no.1
• /
• pp.1-24
• /
• 2014

The present study deals with two dimensional electro-elastic analysis of a functionally graded piezoelectric (FGP) cylinder under internal pressure. Energy method and first order shear deformation theory (FSDT) are employed for this purpose. All mechanical and electrical properties except Poisson ratio are considered as a power function along the radial direction. The cylinder is subjected to uniform internal pressure. By supposing two dimensional displacement and electric potential fields along the radial and axial direction, the governing differential equations can be derived in terms of unknown electrical and mechanical functions. Homogeneous solution can be obtained by imposing the appropriate mechanical and electrical boundary conditions. This proposed solution has capability to solve the cylinder structure with arbitrary boundary conditions. The previous solutions have been proposed for the problem with simple boundary conditions (simply supported cylinder) by using the routine functions such as trigonometric functions. The axial distribution of the axial displacement, radial displacement and electric potential of the cylinder can be presented as the important results of this paper for various non homogeneous indexes. This paper evaluates the effect of a local support on the distribution of mechanical and electrical components. This investigation indicates that a support has important influence on the distribution of mechanical and electrical components rather than a cylinder with ignoring the effect of the supports. Obtained results using present method at regions that are adequate far from two ends of the cylinder can be compared with previous results (plane elasticity and one dimensional first order shear deformation theories).

• Nuclear Engineering and Technology
• /
• v.33 no.5
• /
• pp.547-555
• /
• 2001

In pressurized light water reactor fuel assembly, spacer grids support nuclear fuel rods both laterally and vertically. The fuel rods are supported by spacer grid springs and grid dimples that are located in the grid cell. The support system allows for some thermal expansion and imbalance of the fuel rods. The imbalance is absorbed by elastic energy to prevent coolant flow- induced vibration damage. Design requirements are defined and a design process is established. The design process includes mathematical optimization as well as practical design method. The shape of the grid spring is designed to maintain its function during the lifetime of the fuel assembly. A structural optimization method is employed for the shape design. Since the optimization is carried out in the linear range of finite element analysis, the optimum solution is verified by nonlinear analysis. A good design is found and the final design is compared with the initial conceptual design. Commercial codes are utilized for structural analysis and optimization.

• Journal of Bio-Environment Control
• /
• v.7 no.3
• /
• pp.181-190
• /
• 1998

An elastic analysis under wind load was performed for the double layered plastic greenhouse model developed particularly for minimizing damages under typhoons at Cheju Citrus Research institute in Seagipo city. General EVA film was used for the inner covering and the developed special film which would break the wind pressure down was used for the outer covering. The wind tunnel test showed this special film reduced the wind speed up to 86 to 98% under well controlled situation. Based on the elastic analysis performed in the study, the behavior of the greenhouse was changed significantly due to the boundary conditions. Not like other researchers before we applied dead load of the concrete support to the ground pipe and fixed support boundary conditions at the 4 corner pipes. The analysis shows that the greenhouse was lifted and pulled the pipe out of the ground due to the sucking wind pressure. The behavior of the greenhouse was quite similar to that one real greenhouse failure. Therefore, not only we need to find the realistic boundary conditions for the supports, but also need to find how to rest the pipe supports on the ground without economic loss.

• Journal of the Society of Naval Architects of Korea
• /
• v.43 no.4 s.148
• /
• pp.512-520
• /
• 2006

The effects of flexibilities of supporting structures on shaft alignment are growing as ship sizes are Increasing mainly for container carrier and LNG carrier. But, most of classification societies not only do not suggest any quantitative guidelines about the flexibilities but also do not have shaft alignment design program considering the flexibility of supporting structures. A newly developed program, which is based on innovative shaft alignment technologies including nonlinear elastic multi-support bearing concept and hull deflection database approach, has S basic modules : 1)fully automated finite element generation module, 2) hull deflection database and it's mapping module on bearings, 3) squeezing and oil film pressure calculation module, 4) optimization module and 5) gap & sag calculation module. First module can generate finite element model including shafts, bearings, bearing seats, hull and engine housing without any misalignment of nodes. Hull deflection database module has built-in absolute deflection data for various ship types, sizes and loading conditions and imposes the transformed relative deflection data on shafting system. The squeezing of lining material and oil film pressures, which are relatively solved by Hertz contact theory and built-in hydrodynamic engine, can be calculated and visualized by pressure calculation module. One of the most representative capabilities is an optimization module based on both DOE and Hooke-Jeeves algorithm.

• Journal of the Korean Society for Advanced Composite Structures
• /
• v.1 no.2
• /
• pp.1-13
• /
• 2010

Delamination reduces an elastic buckling load of the laminated composite structures and lead to global structural failure at loads below the design level. Therefore, the problem of the delamination buckling of laminated composite structures has generated significant research interest and has been the subject of many theoretical and experimental investigations. However, questions still remain regarding a complete understanding and details of the phenomena involved. In this paper an efficient finite element model is presented for analyzing the elastic buckling behavior of laminated composite plates with square embedded delamination using a solid element based on a three-dimensional theory. The solid finite element, named by EAS-SOLID8, based on an enhanced assumed strain method is developed. The study for elastic buckling behavior of laminated composite plates with embedded square delaminations are focused on various parameters, such as support condition and width-to-thickness ratio. Both graphs and buckling modes in this paper are good guide for design of the laminated composite plates with embedded square delamination.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.35 no.2
• /
• pp.101-106
• /
• 2007

The optical performance of the mirror for satellite camera is highly dependent on the adhesive properties between the mirror and its support. Therefore, in order to design a mirror with high optical performance, the mechanical properties of adhesives should be well defined. In this paper, the mechanical properties of three kinds of space adhesives are studied. Elastic moduli of the adhesives are determined by tensile tests. Stress-strain relation is obtained by using exponential curve fitting for the adhesive which shows non-linear behavior. In case of the linear behavior material, elastic modulus is calculated through linear curve fitting. For the tensile tests, several points have been selected in the operating temperature range of the adhesive. The elastic modulus of each adhesive is expressed as a function of temperature. Characteristics of the adhesives are discussed regarding their temperature sensitivity.

• Korean Journal of Applied Biomechanics
• /
• v.18 no.4
• /
• pp.49-57
• /
• 2008

The purpose of this study was to determine the effects of 12-week elastic resistance exercise for the elderly on the magnitude of frequency and variability of ground reaction force signals. To this aim, total 12 elderly women aged in their 70 were participated in this study and asked to do a 12-week elastic resistance exercise program. FFT(fast Fourier Transform) was used to analyze the frequency domain analysis of the ground reaction forces's signals and an accumulative PSD (power spectrum density) normalized by support phase of walking was calculated to reconstruct the certain signals. To estimate the gait stability between the before and after exercise, values of variability were determined in a coefficient of variance. The magnitude of frequency and variability analysis for media-lateral signal revealed significantly less after exercise (p<.05). In contrast, variability of this signal's frequency that have used to evaluate the local stability during walking exhibited significantly greater after exercise(p<.05). In summary, magnitude frequency and variability of media-lateral ground reaction force's signal were significantly changed after a 12-week elastic resistance exercise.

• Physical Therapy Korea
• /
• v.24 no.1
• /
• pp.19-29
• /
• 2017

Background: Patients after rotator cuff (RC) surgery experienced pain, weakness and limited of motion of the shoulder. Physical therapists have used heat therapy, electrotherapy, range of motion (ROM) exercise and other methods to treat patients after RC surgery. In addition, functional taping is also used to support joint movement and to increase shoulder joint stability. Objects: The purpose of this study was to determine the initial effects of functional taping using non-elastic tape on pain, strength and ROM of the shoulder following RC surgery. Methods: Forty-eight patients with who underwent RC surgery volunteered for this study. The subjects were randomly divided into an experimental group (EG, $n_1=25$) and a control group (CG, $n_2=23$). First, non-allergic tape was applied to the shoulder to prevent skin irritation. The EG applied functional taping using non-elastic tape and the CG applied sham taping using elastic tape. Assessment tools included the shoulder pain and disability index for functional activity score, visual analog scale for level of pain, shoulder muscle strength, hand grip strength and ROM testing. Results: Pain score in the both group significantly decreased (p<.05), and change in pain score of in the EG increased significantly than in the CG (p<.05). Shoulder strength and ROM in the both group significantly increased (p<.05). Especially external rotation and extension of the shoulder ROM in the EG increased significantly more than in the CG (p<.05), but the rate of change in the two groups showed no significant difference. Conclusion: These results suggest that functional taping using non-elastic tape was initially effective in decreasing pain score level in patients with RC surgery.