• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.3
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• pp.194-199
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• 2010

Based on the idea of eigen-mode expansion, a method to analyze the reflection of Lamb wave from a finite vertical discontinuity of plate is theoretically derived and verified by experiment. The theoretical prediction is in good agreement with the experimental result, and this strongly suggests that eigen-mode expansion method could be used for solution of inverse scattering problem for ultrasonic testing using Lamb wave.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.6
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• pp.748-754
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• 1999

The acoustic performance of reactive type single expansion chamber can be calculated theoretically by plane wave theory. But higher order modes should be considered to widen the frequency range. Munjal has suggested the method for analyzing the acoustic properties of simple expansion chamber with taking into consideration of higher order mode of inlet/outlet. But his method cannot predict the acoustic properties exactly when the dimensions of inlet/outlet and expansion chamber have not integer multiples. In this paper the new method was suggested to overcome the shortcomings of Munjal's method The predictions by this method were also compared with those by the finite element method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.5 s.176
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• pp.1314-1322
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• 2000

The acoustic property of reactive type single expansion chamber can be analyzed by traditional plane wave theory. This theory can be applied in low frequency range and has good performance. But this theory can't include higher order modes, therefore another method is essential to analyze acoustic filter in high frequency range. Many researcher suggested the method that can concern higher order modes, and their methods are using mode matching technique. But there is no method that can be applied to the analysis of single expansion chamber with arbitrary inlet/outlet duct position and numbers of higher order modes of inlet/outlet duct and middle chamber. In this paper, the method which can analyze single expansion chamber with arbitrary inlet/outlet duct position and numbers of higher order modes of inlet/outlet duct and middle chamber using fundamental mode matching technique, was suggested and the predictions by this method was compared with those by the finite element method, and the influence of inlet/outlet location to acoustic performance of single expansion chamber is investigated and explained by higher order mode effects.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.778-785
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• 2006

In this paper, two possible ways for mode shape expansion are proposed and opened for discussion for future use. The first method minimizes the modal flexibility error between the experimental and analytical mode shapes corresponding to the measured DOFs to find the multiplication matrix which can be treated as the least-squares minimization problem. In the second method, Normalized Modal Difference (NMD) is used to calculate multiplication matrix using the analytical DOFs corresponding to measured DOfs. This matrix is then used to expand the measured mode shape to unmeasured DOFs. A simulated simply supported beam is used to demonstrate the performance of the methods. These methods are then compared with two most promising existing methods namely Kidder dynamic expansion and Modal expansion methods. It is observed that the performance of the modal flexibility method is comparable with existing methods. NMD also have the potential to expand the mode shapes though it is seen more sensitive to the distribution of error between FEM and actual test data.

• Journal of KSNVE
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• v.9 no.2
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• pp.340-347
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• 1999

The acoustic performance of reactive type single expansion chamber can be calculated theoretically by plane wave theory. But higher order model should be considered to widen the frequency range. Mode matching method has been developed to consider higher order modes, but very complicated algebra should be used. Munjal suggested a numerical collocation method, which can overcome the shortcomings of mode matching method, using the compatibility conditions for acoustic pressure and particle velocity at the junctions of area discontinuities. But the restriction of Munjal's method is that the ratio between the area of inlet(or outlet) pipe and that of chamber must be natural number. In this paper, the new method was suggested to overcome the shortcomings of Munjal's method. The predictions by this method was also compared with those by the finite element method and Munjal's method in order to demonstrate the accuracy of the modified method presented here.

• The Journal of the Acoustical Society of Korea
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• v.19 no.1
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• pp.54-60
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• 2000

There are many works to analyze a simple expansion chamber involving higher order modes. These works are classified to mode matching method, velocity potential method and finite element method. Among these methods, mode matching method has good performance at analyzing a concentric expansion chamber. Generally inlet/outlet pipe cross section area is smaller than middle chamber cross section area. So the number of higher order modes of inlet/outlet pipe can be fewer than that of middle chamber. But mode matching method must use the same number of higher order modes at inlet pipe, middle chamber and outlet pipe. Therefore the redundant modes of inlet/outlet pipe makes the computation time of mode matching method longer. In this paper, the new method, which can select number of each higher order modes of inlet pipe, middle chamber and outlet pipe, was suggested. And this method was compared to conventional mode matching method and finite element method in order to demonstrate the accuracy of the new method and to show that the new method can reduce a calculating time.

• Journal of KSNVE
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• v.9 no.5
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• pp.914-921
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• 1999

There are many theoretical investigations to analyze higher order mode of reactive type single expansion chambers with offset inlet/outlet locations. But the conventional method has the restriction that the ratio between the area of inlet(or outlet) pipe and that of chamber must be natural number. In the paper, a new method was suggested to apply the Kim's method to silencer with circular cross-section. Not only the offset location but also the magnitude of cross-section area of inlet/outlet pipe can be considered by the suggested method. The predictions by this new method also compared with those by the finite element method and Munjal's method in order to verify the accuracy of the suggested method presented here.

• Journal of Mechanical Science and Technology
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• v.16 no.11
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• pp.1379-1394
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• 2002

In case of a single input single output (SISO) system with a nonlinear term, a signal compression method is useful to identify a system because the equivalent impulse response of linear part from the system can be extracted by the method. However even though the signal compression method is useful to estimate uncertain parameters of the system, the method cannot be directly applied to a unique system with hysteresis characteristics because it cannot estimate all of the two different dynamic properties according to its motion direction. This paper proposes a signal compression method with a pre-processor to identify a unique system with two different dynamics according to its motion direction. The pre-processor plays a role of separating expansion and retraction properties from the system with hysteresis characteristics. For evaluating performance of the proposed approach, a simulation to estimate the assumed unknown parameters for an arbitrary known model is carried out. A motion platform with several single-rod cylinders is a representative unique system with two different dynamics, because each single-rod cylinder has expansion and retraction dynamic properties according to its motion direction. The nominal constant parameters of the motion platform are experimentally identified by using the proposed method. As its application, the identified parameters are applied to a design of a sliding mode controller for the simulator.

• 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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.10 s.181
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• pp.2487-2495
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• 2000

The acoustic characteristics of expansion chamber will be changed with the variation of inlet/outlet location due to the higher order acoustic mode in a high frequency in which the plane wave theory is not available. In this paper, the acoustic performance of reactive type expansion chamber with circular cross-section is analyzed by using the modified mode matching theory. The sensitivity analysis of four-pole parameters with respect to the location of inlet and outlet is also suggested to increase the acoustic performance. The acoustic power transmission coefficient is used as cost function, and the location of inlet and outlet is used as design variables. The steepest descent method and SUMT algorithm are used for optimization technique. Several results showed that the expansion chamber with optimally located inlet/outlet had better acoustic performance than concentric expansion chamber.