• Journal of Ocean Engineering and Technology
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• v.27 no.4
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• pp.83-89
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• 2013

A numerical scheme based on a mode superposition method is presented for the dynamic response analysis of a top-tensioned riser (TTR) under sheared current loads. The natural frequencies and mode shapes of the TTR have been calculated analytically for a beam with a slowly varying tension and pinned-pinned boundary conditions at the top and bottom ends. The lift coefficients and corresponding amplitudes used to estimate the vortex-induced modal force and damping for each mode were predicted via iterative calculations based on the input and output power balancing concept. Here, the power-in regions were controlled by the normal distribution function, for which the center was coincident with the lock -in location by local vortex-shedding, and the range was defined by the constant standard deviation for the reduced velocity by the local current speed. Finally, dynamic responses such as root-mean-squared displacement and stress were calculated using the mode superposition technique. In order to verify the presented scheme, a numerical calculation was performed for a TTR under an arbitrary linearly sheared current and linearly varying tension. A comparison with the results of the existing software showed that the presented scheme could give reliable and feasible solutions. Case studies were performed to investigate the effects of various current loads and tensions.

• Journal of the Korean Institute of Telematics and Electronics T
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• v.36T no.2
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• pp.32-41
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• 1999

The design method that the structure of double actuators of read-only or read-writable DVD optical pick-up of high density can be compact into the structure of one actuator, is proposed. The designed actuator has the structure of the shaft sliding type in which the moving part can be rotated about the shaft accord to a used optical disc and an objective lens can be switched, and is suspended with magnetic spring. In this actuator, Coulomb's friction is used as damping force and the moving part is designed by finite element method so that the second natural vibration mode can not occur within the servo band. The mock-up of the actuator designed in this paper is made, and its dynamic characteristics is measured and estimated.

• Wind and Structures
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• v.17 no.6
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• pp.609-627
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• 2013

The Yingxian wooden tower in China is currently the tallest wooden tower in the world. It was built in 1056 AD and is 65.86 m high. Field measurements of wind speed and wind-induced response of this tower are conducted. The wind characteristics, including the average wind speed, wind direction, turbulence intensity, gust factor, turbulence integral length scale and velocity spectrum are investigated. The power spectral density and the root-mean-square wind-induced acceleration are analyzed. The structural modal parameters of this tower are identified with two different methods, including the Empirical Mode Decomposition (EMD) combined with the Random Decrement Technique (RDT) and Hilbert transform technique, and the stochastic subspace identification (SSI) method. Results show that strong wind is coming predominantly from the West-South of the tower which is in the same direction as the inclination of the structure. The Von Karman spectrum can describe the spectrum of wind speed well. Wind-induced torsional vibration obviously occurs in this tower. The natural frequencies identified by EMD, RDT and Hilbert Transform are close to those identified by SSI method, but there is obvious difference between the identified damping ratios for the first two modes.

• Advances in aircraft and spacecraft science
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• v.6 no.6
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• pp.443-461
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• 2019

This communication investigates exact and distorted similitudes and the related scaling laws for the analysis of both dynamic response and radiated power of rectangular plates. The response of a given panel in similitude from another one is determined from a generalization of the modal approach, allowing the use of mode shapes, natural frequencies and finally radiation functions in order to establish appropriate scaling laws. Analytical models of simply supported rectangular plates are used to produce both original and replica model responses under point mechanical excitation. Emphasis is then especially put on laboratory experiments which are performed on baffled simply supported aluminum panels under mechanical excitations. All the six possible scaling directions, i.e. predicting a plate vibroacoustic reponse from another plate, are reported. All obtained results show that structural response or radiated sound power of a given plate can be both recovered with satisfactory accuracy by using the related scaling laws, even if parent models are used.

• Advances in concrete construction
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• v.9 no.6
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• pp.557-568
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• 2020

In this study, the impact of ring supports around the shell circumferential has been examined for their various positions along the shell axial length using Rayleigh-Ritz formulation. These shells are stiffened by rings in the tangential direction. For isotropic materials, the physical properties are same everywhere where the laminated and functionally graded materials, they vary from point to point. Here the shell material has been taken as functionally graded material. The influence of the ring supports is investigated at various positions. These variations have been plotted against the locations of ring supports for three values of length-to-diameter ratios. Effect of ring supports with middle layer thickness is presented using the Rayleigh-Ritz procedure with three different conditions. The influence of the positions of ring supports for clamped-clamped is more visible than simply supported and clamped-free end conditions. The frequency first increases and gain maximum value in the midway of the shell length and then lowers down. The Lagrangian functional is created by adding the energy expressions for the shell and rings. The axial modal deformations are approximated by making use of the beam functions. The comparisons of frequencies have been made for efficiency and robustness for the present numerical procedure. Throughout the computation, it is observed that the frequency behavior for the boundary conditions follow as; clamped-clamped, simply supported-simply supported frequency curves are higher than that of clamped-simply curves. To generate the fundamental natural frequencies and for better accuracy and effectiveness, the computer software MATLAB is used.

• Fashion & Textile Research Journal
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• v.11 no.2
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• pp.337-343
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• 2009

This study systematically investigated a method for extraction of safflower (Carthamus tinctorius Linnaeus) colorants by ultrasonic treatment. Compared to pigments productivity and cell wall structures of safflower after general and ultrasonic method, the ultrasonic method showed high extraction efficiency of safflower pigments due to destruction of safflower cell wall caused by high vibration energies. Microscopic analysis confirmed the hypothesis that the ultrasonic treatment of safflower caused its cell wall structure loosened and made efficient extraction of safflower pigments. And also, LC-MS/MS analysis revealed that productivities of the yellow and red safflower pigments by ultrasonic method were 21.9% and 14.6% higher, respectively, than those of pigments extracted by general method. The ultrasonic extracted yellow and red colorants could be used to dye not only natural fibers like cotton, silk and wool, but also synthetic fiber like nylon, and generally gave a better color tone than the general extracted colorants from safflower due to the affinities of red and yellow colorant on different fibers. As the yellow and red colorant were extracted by ultrasonic treatment in water, the K/S value on of 550/440nm of cotton and rayon was increased but in the case of silk and wool the change of this value was almost not detected. Finally, this technique might provide a solution to establish reproducibility and standardization for the extraction and dyeing methods on fabrics.

• Composites Research
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• v.13 no.6
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• pp.9-22
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• 2000

The Rayleigh-Ritz procedure based on energy method is used to present analytically the natural frequencies and the critical buckling loads for four types of loading conditions: (1) uniaxial, (2) biaxial, (3) positive shear and (4) negative shear, of the rectangular, composite plates unidirectionally stiffened with box beam type stiffeners. In analysis the discrete stiffener theory is adopted to present the effect of stiffeners in the plate structure. The convergence study is presented to demonstrate the accuracy of the results. Contour plots of the vibrated and buckled mode shapes are shown for some examples. The effect of various parameters such as numbers, position, aspect ratio of stiffener and layer angle, aspect ratio of plate are focused.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.11
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• pp.1815-1823
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• 2003

The vibrational system of this study consists of a cantilever pipe conveying fluid, the moving masses upon it and having an attached tip mass. The equation of motion is derived by using Lagrange's equation. The influences of the velocity and the inertia force of the moving mass and the velocities of fluid flow in the pipe have been studied on the dynamic behavior and the natural frequency of a cantilever pipe by numerical method. The deflection of the cantilever pipe conveying fluid is increased due to the tip mass and rotary Inertia. After the moving mass passed upon the cantilever pipe, the amplitude of pipe is influenced by energy variation when the moving mass fall from the cantilever pipe. As the moving mass increase, the frequency of the cantilever pipe conveying fluid is increased. The rotary inertia of the tip mass influences much on the higher frequencies and vibration mode.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.9
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• pp.895-902
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• 2015

In this paper, finite element analysis of a cycloidal pitch reducer for a 2 MW-class wind turbine is reviewed. The system is composed of one cycloid set, one spur gear set, an input shaft, an output shaft, and a housing. The system was also evaluated for stability by analyzing spur gear strength according to ISO 6336. An analysis of the natural vibration characteristics of the 2 MW-class wind turbine cycloid pitch reducer was performed with attention to critical speed with input mass unbalance, output mass unbalance, spur gear transmission error, cycloid gear transmission error, and excitation frequency.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.18 no.2
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• pp.162-169
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• 2009

This paper describes a study on dynamic characteristics analysis and dynamic compliance evaluation of a 5-axis multi-tasking machine tool of ram-head type. Structural dynamics analysis and evaluation are necessary to machine tool design and development to secure good machine tool performance against tough and harsh machining conditions. In this study, natural frequencies and corresponding vibration modes of the machine tool structure were analyzed by using both F.E.M. modal analysis and impulse hammer test. Furthermore, dynamic compliance of the machine tool was analyzed by using F.E.M. and also measured by using a hydraulic exciter test. Both the theoretical analysis and experimental test results showed good agreement with each other.