• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.26 no.11
• /
• pp.2457-2465
• /
• 2002

Numerical modeling of a nondestructive testing system plays an important role in many aspects of quantitative nondestructive evaluation (QNDE). The ultimate goal of a model is to predict test results for a specific flaw in a material. Thus, in ultrasonic testing, a system model should include the transducer, its radiation pattern, the beam reflection and propagation, and scattering from defects. In this paper attention is focused on the scattering model and the scattered fields by defects are observed by an elastodynamic boundary element method. Flaw types addressed are void-like and crack-like flaws. When transverse ultrasonic waves are obliquely incident on the flaw, the angular distribution of far-field scattered displacements are calculated and presented in the form of A-scan mode. The component signals obtained from each scattering problem are identified and their differences are addressed. The numerical results are also compared with those obtained by high frequency approximate solutions.

• Journal of Mechanical Science and Technology
• /
• v.16 no.9
• /
• pp.1147-1155
• /
• 2002

Discharge flows from a centrifugal pump impeller with a specific speed of 150 [rpm, m$^3$/min, m] were experimentally investigated. A large axisymmetric collector instead of a volute casing was installed to obtain circumferentially uniform flow, i.e. without interaction of the impeller and the volute. The unsteady flow was measured at the impeller exit and vaneless diffuser using a hot film probe and a pressure transducer. The flow at impeller exit showed pronounced jet-wake flow patterns. The wake, which was on the suction/hub side at high flow rate, became enlarged pitchwisely on both the hub and the shroud side as the flow rate decreases. The pitchwise non-uniformity of the flow rapidly decreased along the downstream and the non-uniformity almost disappeared at radius ratio of 1.18 for medium flow rate. The mean vaneless diffuser flow was reasonably predicted using a one dimensional analysis when an empirical constant was used to specify the skin friction coefficient. The data can be used for a centrifugal pump impeller design and validation of CFD codes and flow modeling.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2008.04a
• /
• pp.218-223
• /
• 2008

Cell-phone becomes a necessary communication device in modern society. However, a paging signal by a sound transducer often acts as an unpleasant noise, thus necessitating a paging signal by a vibration motor. The conventional flat type vibration motor uses three-phase windings with three phase coils. In this article, a new design of a vibration motor using a V connection with two phase coils is presented, increasing mass productivity. For electromagnetic field analysis, due to the motor symmetry, two-dimensional modeling can be implemented for fast computation, and performance is predicted by the finite element method. The winding distribution angle turns out to be the most important design parameter for the elimination of dead points, and a new coil configuration is suggested which has no adverse effect on motor size and weight. Experimental tests of vibration confirm the validity of the proposed design.

• International Journal of Automotive Technology
• /
• v.6 no.2
• /
• pp.133-139
• /
• 2005

In this study, a three-dimensional transient simulation with a knock model was performed to predict knock occurrence and autoignition site in a heavy-duty LPG engine. A FAE (Flame Area Evolutoin) premixed combustion model was applied to simulate flame propagation. The coefficient of the reduced kinetic model was adjusted to LPG fuel and used to simulate autoignition in the unburned gas region. Engine experiments using a single-cylinder research engine were performed to calibrate the reduced kinetic model and to verify the results of the modeling. A pressure transducer and a head-gasket type ion-probe circuit board were installed in order to detect knock occurrences, flame arrival angles, and autoignition sites. Knock occurrence and position were compared for different piston bowl shapes. The simulation concurred with engine experimental data regarding the cylinder pressure, flame arrival angle, knock occurrence, and autoignition site. Furthermore, it provided much information about in-cylinder phenomena and solutions that might help reducing the knocking tendency. The knock simulation model presented in this paper can be used for a development tool of engine design.

• Smart Structures and Systems
• /
• v.12 no.2
• /
• pp.97-119
• /
• 2013

This paper presents numerical and experimental results on the use of guided waves for structural health monitoring (SHM) of crack growth during a fatigue test in a thick steel plate used for civil engineering application. Numerical simulation, analytical modeling, and experimental tests are used to prove that piezoelectric wafer active sensor (PWAS) can perform active SHM using guided wave pitch-catch method and passive SHM using acoustic emission (AE). AE simulation was performed with the multi-physic FEM (MP-FEM) approach. The MP-FEM approach permits that the output variables to be expressed directly in electric terms while the two-ways electromechanical conversion is done internally in the MP-FEM formulation. The AE event was simulated as a pulse of defined duration and amplitude. The electrical signal measured at a PWAS receiver was simulated. Experimental tests were performed with PWAS transducers acting as passive receivers of AE signals. An AE source was simulated using 0.5-mm pencil lead breaks. The PWAS transducers were able to pick up AE signal with good strength. Subsequently, PWAS transducers and traditional AE transducer were applied to a 12.7-mm CT specimen subjected to accelerated fatigue testing. Active sensing in pitch catch mode on the CT specimen was applied between the PWAS transducers pairs. Damage indexes were calculated and correlated with actual crack growth. The paper finishes with conclusions and suggestions for further work.

• 제어로봇시스템학회:학술대회논문집
• /
• 2004.08a
• /
• pp.614-619
• /
• 2004

The line-of-sight (LOS) stabilization system is a precision electro-mechanical gimbals assembly for rejecting vibration to isolate the load from its environment and point toward the target in a desired direction. This paper describes the design of gimbals system to reject the disturbance and to improve stabilization. To generate movement commands for the actuators in the stabilization system, the control system uses a sensor of angular rotation. The controller is a DSP with transducer and actuator interfaces. Unknown parameters of the gimbals are estimated using the signal compression method. The cross-correlation coefficient between the impulse response from the assumed model and the one from model of the gimbals is used to obtain the better estimation. And SMCPE (sliding mode control with perturbation estimation) is used to control the gimbals. SMCPE provides robustness of the control against the modeling deficiencies and unknown disturbances. In order to compare the performance of SMCPE with the classical SMC, a sample test result is presented.

• Smart Structures and Systems
• /
• v.26 no.6
• /
• pp.735-751
• /
• 2020

Identification of structure parameters is crucial in Structural Health Monitoring (SHM) context for activities such as model validation, damage assessment and signal processing of structure response. In this paper, guided waves generated by piezoelectric transducers are used for in-situ and non-destructive structural parameter estimation based on Bayesian approach. As Bayesian approach needs iterative process, which is computationally expensive, this paper proposes a method in which an analytical model is selected and developed in order to decrease computational time and complexity of modeling. An experimental set-up is implemented to estimate three target elastic and geometrical parameters: Young's modulus, Poisson ratio and thickness of aluminum and steel plates. Experimental and simulated data are combined in a Bayesian framework for parameter identification. A significant accuracy is achieved regarding estimation of target parameters with maximum error of 8, 11 and 17 percent respectively. Moreover, the limitation of analytical model concerning boundary reflections is addressed and managed experimentally. Pulse excitation is selected as it can excite the structure in a wide frequency range contrary to conventional tone burst excitation. The results show that the proposed non-destructive method can be used in service for estimation of material and geometrical properties of structure in industrial applications.

• The Korean Journal of Physiology and Pharmacology
• /
• v.12 no.5
• /
• pp.267-274
• /
• 2008

Since first discovered in chick skeletal muscles, stretch-activated channels (SACs) have been proposed as a probable mechano-transducer of the mechanical stimulus at the cellular level. Channel properties have been studied in both the single-channel and the whole-cell level. There is growing evidence to indicate that major stretch-induced changes in electrical activity are mediated by activation of these channels. We aimed to investigate the mechanism of stretch-induced automaticity by exploiting a recent mathematical model of rat atrial myocytes which had been established to reproduce cellular activities such as the action potential, $Ca^{2+}$ transients, and contractile force. The incorporation of SACs into the mathematical model, based on experimental results, successfully reproduced the repetitive firing of spontaneous action potentials by stretch. The induced automaticity was composed of two phases. The early phase was driven by increased background conductance of voltage-gated $Na^+$ channel, whereas the later phase was driven by the reverse-mode operation of $Na^+/Ca^{2+}$ exchange current secondary to the accumulation of $Na^+$ and $Ca^{2+}$ through SACs. These results of simulation successfully demonstrate how the SACs can induce automaticity in a single atrial myocyte which may act as a focus to initiate and maintain atrial fibrillation in concert with other arrhythmogenic changes in the heart.

• Geophysics and Geophysical Exploration
• /
• v.13 no.4
• /
• pp.307-314
• /
• 2010

Although conventional seismic data processing is based on the assumption that the media are isotropic, the subsurface is often anisotropy in shale formation or carbonate with cracks and fractures. This paper presents the anisotropic parameter and seismic modeling in transversely isotropic media with a vertical symmetry axis using seismic physical modeling. The experiment was successfully carried out with VTI media, laminated bakelite material, using contact transducer of p and s-wave transmission. The variation of velocities with angle of incidence was clearly shown in anisotropic material. Comparing these velocities with the calculated phase velocities, the (P) and (S)-wave velocity observed in anisotropic material was a very good agreement with the calculated values. Anisotropic parameter ${\varepsilon}$, ${\delta}$, ${\gamma}$ was estimated by using Lame's constant calculated from the observed velocity. For the purpose of testing (S)-wave polarization, a birefringence experiment was carried out. The higher velocity was associated with the polarization parallel to the fracture, and the lower velocity was associated with the polarization perpendicular to the fracture.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.11a
• /
• pp.731-734
• /
• 2005

Generally, characteristics of electromechanical actuators are coupled with the mechanical and the electrical properties. Important mechanical parameters of these actuators are the achievable force and displacement in the presence of electric field. These mechanical parameters are related to the stress and strain of the materials and the actuator geometry. This paper presents how to measure the blocked force by using the micro-balance. The blocked force is defined as the force produced by the transducer under an applied voltage when the tip is constrained to zero motion. Also, a theoretical force by using the cantilever beam model is calculated under elastic domain. From the sample of 4 cm $\times$ 1 cm $\times$ 20 $\mu$m, the blocked farce measured from the equipment is 20.3 $\mu$N at 8 V$_{DC}$. By comparing it with the theoretical value, 24.9 $\mu$N, the blocked force measurement is acceptable. The furce measurement is also investigated with different AC electric fields and the frequency.