• Advances in concrete construction
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• v.6 no.3
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• pp.269-283
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• 2018

This study presents the effects of geometrical dimensions of concrete gravity dams on the seismic response considering different base width/dam height (L/H) ratios. In the study, a concrete gravity dam with the height of 200 m is selected and finite element models of the dam are constituted including five different L/H ratios such as 0.25, 0.5, 0.75, 1.00, 1.25. All dams are modeled in ANSYS software considering dam-reservoir-foundation interaction. 1989 Loma Prieta earthquake records are applied to models in upstream-downstream direction and linear time history analyses are performed. Dynamic equilibrium equations of motions obtained from the finite element models of the coupled systems are solved by using Newmark time integration algorithm. The seismic response of the models is evaluated from analyses presenting natural frequencies, mode shapes, displacements and principal stresses. The results show that the L/H ratios considerably affect the seismic response of gravity dams. Also, the model where L/H ratio is 1.00 has more desirable results and most appropriate representation of the seismic response of gravity dams.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.711-716
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• 2008

A circular tube undergoes bucking behavior when it is subjected to axial loading. An upper bound analysis can be an attractive approach to predict the buckling load and energy absorption efficiently. The upper bound analysis obtains the load or energy absorption by means of assumption of the kinematically admissible velocity fields. In order to obtain an accurate solution, kinematically admissible velocity fields should be defined by considering many factors such as geometrical parameters, dynamic effect, etc. In this study, experiments and finite element analyses are carried out for circular tubes with various dimensions and loading conditions. As a result, the kinematically admissible velocity field is newly proposed in order to consider various dimensions and the strain rate effect of material. The upper bound analysis with the suggested velocity field accurately estimates the mean load and energy absorption obtained from results of experiment and finite element analysis.

• 한국금형공학회:학술대회논문집
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• 2008.06a
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• pp.155-158
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• 2008

Flow imbalance among the cavities was often observed in multi-cavity mold. The flow imbalance affects on the dimensions and physical properties of molded articles. First of all, the origin of flow imbalance is geometrical imbalance of delivery system. However, even the geometry of delivery system is balanced the cavity imbalance is being developed. This comes from the temperature distribution in the cross-section of runner, which is affected by the operational conditions. In this study, experimental study of flow imbalance has been conducted for various injection speeds. This study also suggests new runner design to eliminate flow imbalance in multi-cavity injection mold. Simulation and experimental results showed suggested new designed runner could eliminate or reduce flow imbalance in multi-cavity injection mold.

• Smart Structures and Systems
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• v.26 no.3
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• pp.391-401
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• 2020

The present article reports the feasibility of the electrical energy generation from ambient low-frequency vibration using a piezoelectric material mounted on a bimorph cantilever beam actuator. A corresponding higher-order analytical model is developed using MATLAB in conjunction with finite element method under low-frequency with both damped and undamped conditions. An alternate model is also developed to check the material and dimensional viability of both piezoelectric materials (mainly focussed to PVDF and PZT) and the base material. Also, Genetic Algorithm is implemented to find the optimum dimensions which can produce the higher values of voltage at low-frequency frequencies (≤ 100 Hz). The delamination constraints are employed to avoid inter-laminar stresses and to increase the fracture toughness. The delamination has been done using a Teflon sheet sandwiched in between base plates and the piezo material is stuck to the base plate using adhesives. The analytical model is tested for both homogenous and isotropic material characteristics of the base material and extended to investigate the effect of the different geometrical parameters (base plate dimensions, piezo layer dimensions and placement, delamination thickness and placement, excitation frequency) on the model responses of the bimorph cantilever beam. It has been observed that when the base material characteristics are homogenous, the efficiency of the model remains higher when compared to the condition when it is of isotropic material. The necessary convergence behaviour of the current numerical model has been established and checked for the accuracy by comparing with available published results. Finally, using the results obtained from the model, a prototype is fabricated for the experimental validation via a suitable circuit considering Glass fibre and Aluminium as the bimorph material.

• Steel and Composite Structures
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• v.35 no.5
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• pp.659-670
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• 2020

This paper proposes the use of a porous core between layers of laminated composite plates to examine its effect on the natural frequencies of the resulted porous laminated composite sandwich plate (PLCSP) resting on a two-parameter elastic foundation. Moreover, it has been suggested that the dispersion of porosity has two different functionally graded (FG) patterns which are compared with a uniformly dispersed (UD) profile to find their best vibrational efficiency in the proposed PLCSPs. In FG patterns, two types of dispersions, including symmetric (FG-S) and asymmetric (FG-A) patterns have been considered. To derive the governing Eigen value equation of such structures, the first order shear deformation theory (FSDT) of plates has been employed. Accordingly, a finite element method (FEM) is developed to solve the derived Eigen value equation. Using the mentioned theory and method, the effects of porosity parameters, fiber orientation of laminated composite, geometrical dimensions, boundary conditions and elastic foundation on the natural frequencies of the proposed PLCSPs have been studied. It is observed that embedding porosity in core layer leads to a significant improvement in the natural frequencies of PLCSPs. Moreover, the natural frequencies of PLCSPs with FG porous core are higher than those with UD porous core.

• Advances in aircraft and spacecraft science
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• v.10 no.1
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• pp.51-65
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• 2023

In this paper, the effect of deepness on in-plane free vibration behavior of a curved functionally graded (FG) nanobeam based on nonlocal elasticity theory has been investigated. Differential equations and boundary conditions have been developed based on Hamilton's principle. In order to figure out the size effect, nonlocal theory has been adopted. Properties of material vary in radial direction. By using Navier solution technique, the amount of natural frequencies has been obtained. Also, to take into account the deepness effect on vibrations, thickness to radius ratio has been considered. Differences percentage between results of cases in which deepness effect is included and excluded are obtained and influences of power-law exponent, nonlocal parameter and arc angle on these differences percentage are studied. Results show that arc angle and power law exponent parameters have the most influences on the amount of the differences percentage due to deepness effect. It has been observed that the inclusion of geometrical deep term and material distribution results in an increase in sensitivity of dimensionless natural frequency about variation of aforementioned parameters and a change in variation range of natural frequency. Finally, several numerical results of deep and shallow curved functionally graded nanobeams with different geometry dimensions are presented, which may serve as benchmark solutions for the future research in this field.

• Geophysics and Geophysical Exploration
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• v.9 no.2
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• pp.148-154
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• 2006

The effect of small-scale near surface inhomogeneity on Rayleigh wave propagation and dispersion has been investigated in this study using two-dimensional FEM elastic modeling. Various inhomogeneity models with a variety of geometrical shape and embedment depth which exist in homogeneous half-space and two-layered media are considered. Results show that any near surface inhomogeneity greater than one wavelength in terms of minimum wavelength of Rayleigh wave shows dispersion characteristics. Such dispersion effect become stronger as the dimensions of the inhomogeneity increase. The effect of horizontal dimension is more dominant factor governing the dispersion characteristics than vertical dimension. However, the dispersion effect can not be identifiable in seismogram if the horizontal dimension is not wide enough. Nonetheless, even in this case, the existence of inhomogeneity can be inferred by the reflection or transmission event of Rayleigh wave. The results can be expected to provide insights on the behavior of Rayleigh wave which may be helpful for designating field work or new processing scheme to detect near surface inhomogeneity by surface wave method.

• Steel and Composite Structures
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• v.18 no.6
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• pp.1541-1555
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• 2015

In this paper mechanical behavior of the functional gradient materials (FGM) micro-gripper under thermal load and DC voltage is numerically investigated taking into account the effect of intermolecular forces. In contrary to the similar previous works, which have been conducted for homogenous material, here, the FGM material has been implemented. It is assumed that the FGM micro-gripper is made of metal and ceramic and that material properties are changed continuously along the beam thickness according to a given function. The nonlinear governing equations of the static and dynamic deflection of microbeams have been derived using the coupled stress theory. The equations have been solved using the Galerkin based step-by-step linearization method (SSLM). The solution procedure has been evaluated against available data of literature showing good agreement. A parametric study has been conducted, focusing on the combined effects of important parameters included DC voltage, temperature variation, geometrical dimensions and ceramic volume concentration on the dynamic response and stability of the FGM micro-gripper.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.3 no.4
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• pp.95-100
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• 2004

Plastics is used to produce precise parts with an inclusion of a reinforcement material such as glass fiber or carbon fiber to improve the dimension accuracy. The plastic goods can be produced with inaccurate dimensions, low mechanical strength, or residual stress due to the over packing of cavity inside, if the filling balance of melt resin is not accomplished. To overcome this problem, it is necessary to design the runner system with the geometrical balance at the mold design stage. However, even if the balanced runner system is achieved, a severe filling imbalance is observed practically in a multi-cavity mold. In this study, experiments were performed with Taguchi method to achieve the filling balance in multi-cavity mold with a symmetric runner system, by the use of pure PA and PA with glass fiber 33%. The experimental results were investigated to understand the effect of related molding factors on the filling imbalance for two resins.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.5
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• pp.259-264
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• 2000

In this paper, the characteristics of piezoelectric transformer is studied for driving CCFL(Cold Cathode Fluorescent Lamp). In order to investigate the effects of geometrical dimensions, λvibration-mode type piezoelectric transformers with different sizes in the length(l), width$(\omega)$ and thickness(t) are made of ceramics with PZT-PMWS compositions. The increases in temperature and aging effect are also measured in the transformer of PT-3 sample under the condition of operation continuously for 10 hrs. As the results of dimensional effects, the output power and voltage step-up ratio are largely affected by the ratio of length to thickness(l/t) rather than that of length to $width(l/\omega)$. The output power and step-up ratio are increased with increasing l/t. On case of PT-3, the output voltages are 510[Vrms] at 36[Vrms] in input voltage, $100[k\Omega]$ in load resistance. Temperature increases and variation of output voltages are $10[^{\circ}C]$ and less than 5[%], respectively.