Ilwook Park

Bio: Ilwook Park is an academic researcher from Inha University. The author has contributed to research in topics: Finite element method & Spectral element method. The author has an hindex of 8, co-authored 18 publications receiving 194 citations.

Dynamic analysis of smart composite beams by using the frequency-domain spectral element method †

Abstract: To excite or measure the dynamic responses of a laminated composite structure for the active controls of vibrations or noises, wafer-type piezoelectric transducers are often bonded on the surface of the composite structure to form a multi-layer smart composite structure. Thus, for such smart composite structures, it is very important to develop and use a very reliable mathematical and/or computational model for predicting accurate dynamic characteristics. In this paper, the axial-bending coupled equations of motion and boundary conditions are derived for two-layer smart composite beams by using the Hamilton’s principle with Lagrange multipliers. The spectral element model is then formulated in the frequency domain by using the variation approach. Through some numerical examples, the extremely high accuracy of the present spectral element model is verified by comparing with the solutions by the conventional finite element model provided in this paper. The effects of the lay-up of composite laminates and surface-bonded wafer-type piezoelectric (PZT) layer on the dynamics and wave characteristics of smart composite beams are investigated. The effective constraint forces at the interface between the base beam and PZT layer are also investigated via Lagrange multipliers.

Forced Vibration of a Timoshenko Beam Subjected to Stationary and Moving Loads Using the Modal Analysis Method

Abstract: The modal analysis method (MAM) is very useful for obtaining the dynamic responses of a structure in analytical closed forms. In order to use the MAM, accurate information is needed on the natural frequencies, mode shapes, and orthogonality of the mode shapes a priori. A thorough literature survey reveals that the necessary information reported in the existing literature is sometimes very limited or incomplete, even for simple beam models such as Timoshenko beams. Thus, we present complete information on the natural frequencies, three types of mode shapes, and the orthogonality of the mode shapes for simply supported Timoshenko beams. Based on this information, we use the MAM to derive the forced vibration responses of a simply supported Timoshenko beam subjected to arbitrary initial conditions and to stationary or moving loads (a point transverse force and a point bending moment) in analytical closed form. We then conduct numerical studies to investigate the effects of each type of mode shape on the long-term dynamic responses (vibrations), the short-term dynamic responses (waves), and the deformed shapes of an example Timoshenko beam subjected to stationary or moving point loads.

Dynamics of two-layer smart composite Timoshenko beams: Frequency domain spectral element analysis

Abstract: Ultrasonic guided waves in a laminated composite structure can be excited or measured using piezoelectric transducers (PZTs). In this study, we propose a spectral element model for two-layer smart composite Timoshenko beams that consist of a host composite beam and a PZT layer. Contrary to the previous study (2012) where the Bernoulli-Euler beam theory was applied to the host composite beam, the Timoshenko beam theory and the Mindlin-Herrmann rod theory were applied in this study. The proposed spectral element model was evaluated first by comparison with standard finite element analyses, and it was then used to investigate the guided waves in some laminated composite beams.

Structural damage identification using damping: a compendium of uses and features

Abstract: The vibration responses of structures under controlled or ambient excitation can be used to detect structural damage by correlating changes in structural dynamic properties extracted from responses with damage. Typical dynamic properties refer to modal parameters: natural frequencies, mode shapes, and damping. Among these parameters, natural frequencies and mode shapes have been investigated extensively for their use in damage characterization by associating damage with reduction in local stiffness of structures. In contrast, the use of damping as a dynamic property to represent structural damage has not been comprehensively elucidated, primarily due to the complexities of damping measurement and analysis. With advances in measurement technologies and analysis tools, the use of damping to identify damage is becoming a focus of increasing attention in the damage detection community. Recently, a number of studies have demonstrated that damping has greater sensitivity for characterizing damage than natural frequencies and mode shapes in various applications, but damping-based damage identification is still a research direction ‘in progress’ and is not yet well resolved. This situation calls for an overall survey of the state-of-the-art and the state-of-the-practice of using damping to detect structural damage. To this end, this study aims to provide a comprehensive survey of uses and features of applying damping in structural damage detection. First, we present various methods for damping estimation in different domains including the time domain, the frequency domain, and the time-frequency domain. Second, we investigate the features and applications of damping-based damage detection methods on the basis of two predominant infrastructure elements, reinforced concrete structures and fiber-reinforced composites. Third, we clarify the influential factors that can impair the capability of damping to characterize damage. Smart Materials and Structures Smart Mater. Struct. 26 (2017) 043001 (14pp) doi:10.1088/1361-665X/aa550a 3 Author to whom any correspondence should be addressed. 4 Present address: Nanoscale Materials Science, Empa-Swiss Federal Laboratories for Materials Science and Technology, Dubendorf, Switzerland. Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. 0964-1726/17/043001+14$33.00 © 2017 IOP Publishing Ltd Printed in the UK 1 Finally, we recommend future research directions for advancing damping-based damage detection. This work holds the promise of (a) helping researchers identify crucial components in damping-based damage detection theories, methods, and technologies, and (b) leading practitioners to better implement damping-based structural damage identification.

Finite-element structural analysis

Abstract: Computer program aids in reduction and analysis of data. It determines critical loading conditions for critical values of reactions, applied loads, deflections, stresses, internal loads, etc. Input to program must be in one of specified three-part format.