• Geomechanics and Engineering
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• v.37 no.3
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• pp.243-251
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• 2024

In the current work, a poro-thermoelastic half-space issue with temperature-dependent characteristics and an inclined load is examined in the framework of the three-phase-lag model (3PHL) while taking into account the effects of magnetic and gravity fields. The resulting coupled governing equations are non-dimensional and are solved by normal mode analysis. To investigate the impacts of the gravitational field, magnetic field, inclined load, and an empirical material constant, numerical findings are graphically displayed. MATLAB software is used for numerical calculations. Graphs are used to visualize and analyze the computational findings. It is found that the physical quantities are affected by the magnetic field, gravity field, the nonlocal parameter, the inclined load, and the empirical material constant.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.211-216
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• 1997

The mode localization phenomenon in non-periodic multispan beam is theoretically investigated. When localization occurs, the free vibration amplitude of a normal mode becomes confined to a local region of the structure. It is well known that the weakly coupled periodic structures are sensitive to certain types of periodicity-breaking disorder, resulting in the mode localization. The results of this study indicate that the mode localization occurs also in nonperiodic structures and the degrees of mode localization of some modes are very sensitive to system parameters. Free vibration analysis of simply supported two-span beams of arbitrary span lengths is performed. Degrees of mode localization and their sensitivities to system parameters are appraised by considering the characteristic graph and the structural line defined in this study first.

• Smart Structures and Systems
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• v.26 no.2
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• pp.157-174
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• 2020

The guided wave technique is commonly used in structural health monitoring as the guided waves can propagate far in the structures without much energy loss. The guided waves are conventionally generated by the surface-mounted piezoelectric wafer active sensor (PWAS). However, there is still lack of understanding of the wave propagation in layered structures, especially in structures made of anisotropic materials such as carbon fiber reinforced polymer (CFRP) composites. In this paper, the Rayleigh-Lamb wave strain tuning curves in a PWAS-mounted unidirectional CFRP plate are analytically derived using the normal mode expansion (NME) method. The excitation frequency spectrum is then multiplied by the tuning curves to calculate the frequency response spectrum. The corresponding time domain responses are obtained through the inverse Fourier transform. The theoretical calculations are validated through finite element analysis and an experimental study. The PWAS responses under the free, debonded and bonded CFRP conditions are investigated and compared. The results demonstrate that the amplitude and travelling time of wave packet can be used to evaluate the CFRP bonding conditions. The method can work on a baseline-free manner.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.197-198
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• 2011

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.6
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• pp.993-1000
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• 2002

The objective of this work is to develop the capability to analyze accurately the mixed-mode propagation of a crack in composite structures with elastic orthotropic material stiffness properties and anisotropic material strength characteristics. In order to develop the capability to fully analyze fracture growth and failure in anisotropic structures, we examined the fundamental problem of mixed mode fracture by carrying out the analysis on orthotropic materials with an inclined crack subject to biaxial loading. Our goal here is to include an additional term in the asymptotic expansion of the crack tip stress field and to show that the direction of crack initiation can be significantly affected by that term. We employ the normal stress ratio theory to predict the direction of crack extension. It is shown that the angle of crack extension can be altered by horizontal loads and the use of second order term in the series expansion is important f3r the accurate determination of crack growth direction.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.31 no.5
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• pp.57-72
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• 1999

Traditional theories of the tensile failure of paper have assumed that uniform strain progresses throughout the sheet until an imperfection within the structure causes a catastrophic break. The resistance to tensile elongation is assumed to be elastic , at first, throughout the structure, followed by an overall plastic yield. However, linear image strain analysis (LISA) has demonstrated that the yield in tensile loading of paper is quite non-uniform throughout the structure, Traditional theories have failed to define the flaws that trigger catastrophic failure. It was assumed that a shive or perhaps a low basis weight area filled that role. Studies of the fracture mechanics of paper have typically utilized a well-defined flaw around which yield and failure could be examined . The flaw was a simple razor cut normal to the direction of tensile loading. Such testing is labeled mode I analysis. The included fla in the paper was always normal to the tensile loading direction, never at another orientation . However, shives or low basis weight zones are likely to be at random angular orientations in the sheet. The effects of angular flaws within the tensile test were examined. The strain energy density theory and experimental work demonstrate the change in crack propagation from mode I to mode IIas the initial flaw angle of crack propagation as a function of the initial flaw angle is predicted and experimentally demonstrated.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.9
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• pp.2173-2180
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• 1995

This paper presents free vibration analysis method using the characteristics of the rotationally periodic structures and includes the analysis results of a tire as an example. The normal modes of the rotationally periodic structures are the kind of standing waves, so all sectors have the same deflection shapes, and only different phases. This property makes it possible to derive the analysis method called sector method. The sector method can give the accurate natural frequencies and the corresponding mode shapes of the rotationally periodic structure with information of only one sector. When the free vibration analysis is performed to find the dynamic characteristics of the rotationally periodic structure by using the sector method, the computer memory spaces and the CPU times can be saved. We obtained much economic benefits by using the sector method in the analysis of dynamic characteristics of a tire made of non-linear materials.

• Fire Science and Engineering
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• v.20 no.3 s.63
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• pp.9-14
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• 2006

In this study boundary velocity which is one of the important boundary conditions for numerical simulation for subway station on fire are experimentally obtained. The tests were conducted according to its operating mode of the ventilation systems in the platform: smoke extraction ventilation mode in occurrence of fire and normal ventilation mode for air conditioning. Velocities are measured at various points on the platform. To examine smoke extraction and air supply capacity in the platform level, air velocities were checked on opening vents. Numerical analysis under normal ventilation mode without fire is conducted by using measured boundary conditions, and the numerical results are compared with the measured velocities on the platform.

• Journal of Mechanical Science and Technology
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• v.20 no.8
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• pp.1224-1231
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• 2006

The stability and control derivatives of DURUMI-lI UAV using the flight test are obtained. The flight test data is gathered from the normal flight condition (normal mode) and the flight condition assumed as the right elevator fixed (fault mode). Using real-time parameter estimation techniques, applied to Fourier transform regression method, simulates the aircraft motion. From the result, the fault of control surface is to be detected. In this paper, the results of the real- time parameter estimation techniques are compared with the results of the Advanced Aircraft Analysis (AAA). Using the aerodynamic derivatives, it provides the base line of normal/failure for the control surface by using the on-line parameter estimation of Fourier transform regression. In flight, this approach maybe helpful to detect and isolate the fault of primary control surface. It is explained how to perform the flight condition assumed as the right elevator fixed in the flight test. Also, it is mentioned how to switch between the normal flight condition and the assumed fault flight condition.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.51-56
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• 1998

This paper presents modal contribution method to reduce vehicle vibration. Normal mode analysis is performed to obtain modal vector matrix. The proposed method uses this modal vector matrix to evaluate forced response of an active mode to the applied engine forces and the rotating force due to wheel unbalance mass. Comparing the responses, of the specific active mode with one another, it can be easily done to determine most contributed mode in the interesting frequency band. Then we can find dominant bushes by the strain energy distribution of the mode. Vibration response is decrease with modification of those bushes.