• Steel and Composite Structures
• /
• v.30 no.6
• /
• pp.567-576
• /
• 2019

Time-dependent creep analysis of a rotating functionally graded cantilever beam with trapezoidal longitudinal cross section subjected to thermal and inertia loading is investigated using first-order shear deformation theory (FSDT). The model described in this paper is a simple simulation of a turbine blade working under creep condition. The material is a metal based composite reinforced by a ceramic where the creep properties of which has been described by the Sherby's constitutive model. All mechanical and thermal properties except Poisson's ratio are assumed to be variable longitudinally based on the volume fraction of constituent. The principle of virtual work as well as first order shear deformation theory is used to derive governing equations. Longitudinal distribution of displacements and stresses are investigated for various volume fractions of reinforcement. Method of successive elastic solution is employed to obtain history of stresses and creep deformations. It is found that stresses and displacements approach their steady state values after 40000 hours. The results presented in this paper can be used for selection of appropriate longitudinal distribution of reinforcement to achieve the desired stresses and displacements.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2006.11a
• /
• pp.801-804
• /
• 2006

The purpose of this paper is to investigate the stability of stepped cantilever columns with a tip mass of rotatory inertia and a translational spring at one end. The column model is based on the Bernoulli-Euler theory which neglects the effects of rotatory inertia and shear deformation. The governing differential equation for the free vibration of columns with stepwise variable cross-section and subjected to a subtangential follower force is solved numerically using the corresponding boundary conditions. And the bisection method is used to calculate the critical divergence/flutter load. The frequency and critical divergence/flutter load for the stepped column with a single step are presented as functions of various non-dimensional system parameters: the segmental length parameter, the section ratio, the subtangential parameter, the mass, the moment of inertia of the mass, and the spring parameter.

• Structural Engineering and Mechanics
• /
• v.9 no.2
• /
• pp.169-180
• /
• 2000

An optimization procedure has been prescribed for the minimum weight design of symmetrical parabolic arches subjected to arbitrary loading. The cross section is assumed to be a symmetrical box section with variable depth and flange areas. The webs are unstiffened and have constant thickness. The proposed sequential, iterative search technique determines the optimum geometrical configuration of the parabolic arch which includes the optimum depth profile and the optimum lengths and areas of the required flange plates corresponding to the prescribed number of curtailments. The study shows that the optimum value of rise to span ratio (h/L) of a parabolic arch is maximum at 0.41 for uniformly distributed loading over the entire span. For any other loading, the optimum value of h/L is less than 0.41.

• Proceedings of the Korea Association of Crystal Growth Conference
• /
• 1999.06a
• /
• pp.209-225
• /
• 1999

Detailed description of the crystal growth methods permitting one to obtain complicated shape crystals from the melt is given. The variable shaping technique provides the growth of crystals with a discrete altering cross-section configuration during crystallization. The dynamic local shaping technique enables one to grow items with a continuous alteration of the side surface profile by a preset program.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.9 no.4
• /
• pp.417-423
• /
• 1999

Detailed description of the crystal growth methods permitting one to obtain complicated shape crystals from the melt is given. The variable shaping technique provides the growth of crystals with a discrete altering cross-section configuration during crystallization. The dynamic local shaping technique enables one to grow items with a continuous alteration of the side surface profile by a preset program.

• Structural Engineering and Mechanics
• /
• v.8 no.3
• /
• pp.243-256
• /
• 1999

Using appropriate transformations, the differential equation for flexural free vibration of a cantilever bar with variably distributed mass and stiffness is reduced to a Bessel's equation or an ordinary differential equation with constant coefficients by selecting suitable expressions, such as power functions and exponential functions, for the distributions of stiffness and mass. The general solutions for flexural free vibration of one-step bar with variable cross-section are derived and used to obtain the frequency equation of multi-step cantilever bars. The new exact approach is presented which combines the transfer matrix method and closed form solutions of one step bars. Two numerical examples demonstrate that the calculated natural frequencies and mode shapes of a 27-storey building and a television transmission tower are in good agreement with the corresponding experimental data. It is also shown through the numerical examples that the selected expressions are suitable for describing the distributions of stiffness and mass of typical tall buildings and high-rise structures.

• Structural Engineering and Mechanics
• /
• v.73 no.2
• /
• pp.109-121
• /
• 2020

This study aims to estimate crack location and crack length in damaged beam structures using transfer matrix formulations, which are based on analytical solutions of governing equations of motion. A single variable shear deformation theory (SVSDT) that considers parabolic shear stress distribution along beam cross-section is used, as well as, Timoshenko beam theory (TBT). The cracks are modelled using massless rotational springs that divide beams into segments. In the forward problem, natural frequencies of intact and cracked beam models are calculated for different crack length and location combinations. In the inverse approach, which is the main concern of this paper, the natural frequency values obtained from experimental studies, finite element simulations and analytical solutions are used for crack identification via plots of rotational spring flexibilities against crack location. The estimated crack length and crack location values are tabulated with actual data. Three different beam models that have free-free, fixed-free and simple-simple boundary conditions are considered in the numerical analyses.

• Structural Engineering and Mechanics
• /
• v.46 no.2
• /
• pp.153-177
• /
• 2013

Pendulums can be used as passive vibration control devices in several structures and machines. In the present work, the nonlinear behavior of a pendulum-tower system is studied. The tower is modeled as a bar with variable cross-section with concentrated masses. First, the vibration modes and frequencies of the tower are obtained analytically. The primary structure and absorber together constitute a coupled system which is discretized as a two degrees of freedom nonlinear system, using the normalized eigenfunctions and the Rayleigh-Ritz method. The analysis shows the influence of the geometric nonlinearity of the pendulum absorber on the response of the tower. A parametric analysis also shows that, with an appropriate choice of the absorber parameters, a pendulum can decrease the vibration amplitudes of the tower in the main resonance region. The results also show that the pendulum nonlinearity cannot be neglected in this type of problem, leading to multiplicity of solutions, dynamic jumps and instability. In order to improve the effectiveness of the control during the transient response, a hybrid control system is suggested. The added control force is implemented as a non-linear variable stiffness device based on position and velocity feedback. The obtained results show that this strategy of nonlinear control is attractive, has a good potential and can be used to minimize the response of slender structures under various types of excitation.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.32 no.9
• /
• pp.733-739
• /
• 2008

The X-ring is a elastomer with X-shaped cross-section used as a mechanical seal or gasket. Such a X-ring was equipped in a groove and compressed between two or more parts, acts as a seal on the interface. This study aims to detect contact stress and deformed shape of a X-shaped ring shell under various compressive contact conditions. A contact stress analysis was carried out by finite element analysis. The effect of compression rates and thickness design variable was analyzed. X-ring kept up the double seal until a compression rate of 20%. The maximum stresses of the X-ring was occurred at the top and bottom corner. The maximum contact stress of X-ring was rapidly increased according with the compression rate. The X-rings with thickness design variable from 1.3 mm to 1.5 mm had comparative low stress levels.

• Journal of the Korean Institute of Navigation
• /
• v.25 no.1
• /
• pp.45-52
• /
• 2001

The purpose of this study is the optimum modification of dynamic characteristics of stiffened plate structure. In the method of the optimization, finite element method(FEM), sensitivity analysis and optimum structural modification method are used. To begin with, using FEM, the dynamic characteristics of stiffened plate structure is analyzed. Next, rate of change of dynamic characteristics by the change of design variable is calculated using the sensitivity analysis. Then, amount of change of design variable is calculated using this sensitivity value and optimum structural modification method. The change of natural frequency is made to be an objective function. Thickness of plate and cross section moment become a design variable. It is shown that the results are effective in the optimum modification for dynamic characteristics of the stiffened plate structure.