• Wind and Structures
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• 제30권2호
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• pp.211-217
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• 2020

Vibrations of a wind turbine blade have a negative impact on its performance and result in failure of the blade, therefore an approach to effectively control vibration in turbine blades are sought by wind industry. The small domestic horizontal axis wind turbine blades induce flap wise (out-of-plane) vibration, due to varying wind speeds. These flap wise vibrations are transferred to the structure, which even causes catastrophic failure of the system. Shape memory alloys which possess physical property of variable stiffness across different phases are embedded into the composite blades for active vibration control. Previously Shape memory alloys have been used as actuators to change their angles and orientations in fighter jet blades but not used for active vibration control for wind turbine blades. In this work a GFRP blade embedded with Shape Memory Alloy (SMA) and tested for its vibrational and material damping characteristics, under martensitic and austenite conditions. The embedment portrays 47% reduction in displacement of blade, with respect to the conventional blade. An analytical model for the actuated smart blade is also proposed, which validates the harmonic response of the smart blade.

• Transactions of the Korean Society of Mechanical Engineers
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• 제13권1호
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• pp.40-47
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• 1989

Alternator noises are composed of magnetic noise, mechanical noise, and ventilation noise. These noises depend on the design of magnetic parts and fans, the machining accuracy of each element, and assembled conditions. In running alternator there are various exciting forces which can generate noises and vibrations. In order to identify the noise sources of the alternator, the characteristics of noises and vibrations are analyzed as rotating speed is increased. And the experiment for structural vibration is carried out. From results of experimental study, the noise sources are identified and their contributions to the overall noise level are investigated. Their results can lead the instruction to the noise reduction on the alternator.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권4호
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• pp.1041-1063
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• 2014

Some results on the hydroelasticity of ultra large container ships related to the beam structural model and restoring stiffness achieved within EU FP7 Project TULCS are summarized. An advanced thin-walled girder theory based on the modified Timoshenko beam theory for flexural vibrations with analogical extension to the torsional problem, is used for formulation of the beam finite element for analysis of coupled horizontal and torsional ship hull vibrations. Special attention is paid to the contribution of transverse bulkheads to the open hull stiffness, as well as to the reduced stiffness of the relatively short engine room structure. In addition two definitions of the restoring stiffness are considered: consistent one, which includes hydrostatic and gravity properties, and unified one with geometric stiffness as structural contribution via calm water stress field. Both formulations are worked out by employing the finite element concept. Complete hydroelastic response of a ULCS is performed by coupling 1D structural model and 3D hydrodynamic model as well as for 3D structural and 3D hydrodynamic model. Also, fatigue of structural elements exposed to high stress concentration is considered.

• Structural Engineering and Mechanics
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• 제42권2호
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• pp.131-152
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• 2012

In-plane free vibrations of circular beams with stepped cross-sections are investigated by using the exact analytical solution. The axial extension, transverse shear deformation and rotatory inertia effects are taken into account. The stepped arch is divided into a number of arches with constant cross-sections. The exact solution of the governing equations is obtained by the initial value method. Several examples of arches with different step ratios, different locations of the steps, boundary conditions, opening angles and slenderness ratios for the first few modes are presented to illustrate the validity and accuracy of the method. The effects of the geometric parameters on the natural frequencies are investigated in details. Several examples in the literature are solved and the results are given in tables. The agreement of the results is good for all examples considered. The mode transition phenomenon is also observed for the stepped arches. Some examples are solved also numerically by using the commercial finite element program ANSYS.

• Steel and Composite Structures
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• 제24권2호
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• pp.141-149
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• 2017

In this study, vibration analysis of fluid conveying microbeams under non-ideal boundary conditions (BCs) is performed. The objective of the present paper is to describe the effects of non-ideal BCs on linear vibrations of fluid conveying microbeams. Non-ideal BCs are modeled as a linear combination of ideal clamped and ideal simply supported boundary conditions by using the weighting factor (k). Non-ideal clamped and non-ideal simply supported beams are both considered to show the effects of BCs. Equations of motion of the beam under the effect of moving fluid are obtained by using Hamilton principle. Method of multiple scales which is one of the perturbation techniques is applied to the governing linear equation of motion. Approximate solutions of the linear equation are obtained and the effects of system parameters and non-ideal BCs on natural frequencies are presented. Results indicate that, natural frequencies of fluid conveying microbeam changed significantly by varying the weighting factor k. This change is more remarkable for clamped microbeams rather than simply supported ones.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제32권7호
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• pp.541-548
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• 2008

To improve the operational stability of the 100 Watts class Micro Gas Turbine, the air foil bearing with additional damping material has been investigated. The key of structure is that a viscoelastic material is coated under the top foil. The compliant foil journal bearing and thrust bearing are designed to withstand high load of vibrations at the operational speed 870,000 rpm. Test is executed in room temperature. Rotor has stably operated above 480,000 rpm. It is over 55% of the designed speed 870,000 rpm. Synchronous and subsynchronous vibrations are both well controlled. Vibration amplitude diminished over 50%. With the help of increased damping resulting from the viscoelasticity, the rotor stability of Micro turbocharger has been improved.

• Steel and Composite Structures
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• 제35권6호
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• pp.765-777
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• 2020

In the context of classic conical shell formulation, nonlinear forced vibration analysis of truncated conical shells and annular plates made of multi-scale epoxy/CNT/fiberglass composites has been presented. The composite material is reinforced by carbon nanotube (CNT) and also fiberglass for which the material properties are defined according to a 3D Mori-Tanaka micromechanical scheme. By utilizing the Jacobi elliptic functions, the frequency-deflection curves of truncated conical shells and annular plates related to their forced vibrations have been derived. The main focus is to study the influences of CNT amount, fiberglass volume, open angle, fiber angle, truncated distance and force magnitude on forced vibrational behaviors of multi-scale truncated conical shells and annular plates.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• 제26권7호
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• pp.865-874
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• 2016

This research is concerned with the experimental investigation on the vibrations of a flexible two-link system for verifying the theoretical result from simplified equations of motion for the system along with the kinematical synthesis are proposed to simulate the elastic vibrations of a previous study. The structure consists of flexible two-links; The link 2 is attached to the end of the link 1. The link 1 is made of composite fiber reinforced polymer and the link 2 is an aluminum beam. In order to verify the theoretical result, a flexible two-link system operated by the AC and RC servo motors was constructed. Experimental results show that the dynamic modeling approach and the kinematical synthesis proposed in this paper are effective.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제27권6호
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• pp.857-863
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• 2003

In rotating machinery, unbalance and misalignment are major concerns in vibration. Unbalance can be eliminated by balancing procedure to some degree. but little work has been done on the vibrations that occur in a misaligned rotor system. Currently, no generalized theoretical model based on a rotor system with flexible coupling is available to describe the vibrations caused by misalignment. As a part of systematic investigation on the misalignment, first of all, the study on flexible coupling with misalignment should be preceded. In this study, the geometry and reaction force and moment of a gear coupling with misalignment was investigated, also the theoretical model of a gear coupling with misalignment was presented by using the relationship between geometry and moment of gear coupling. It is expected that the proposed procedure can be applied to derive the theoretical model of other couplings.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제24권8호
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• pp.1978-1990
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• 2000

In this study, the free vibrations of the cantilever plate, which is one of the most frequently used elements in various machine structures, are analyzed and further the results are utilized to develop the methodology to predict and control the natural frequencies for designing stabilized systems. The proposed method has three major steps. The first step is the frequency response test to investigate the natural frequencies of some plates, then the database is constituted from experiments and the FEM, and finally the natural frequencies are predicted using the database to be cross-checked by the identification test. The result of this study will help design many different stable structures without any complicated calculations.