• Journal of the Korean Society for Precision Engineering
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• v.29 no.7
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• pp.770-777
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• 2012

This paper deals with the design and modal characteristics analysis of a drive-train for a paralleltype hybrid electric vehicle (HEV). The function of the drive-train system (DTS) in the HEV combines or divides the torque and velocity from the internal combustion engine along with the induction motor. The system consists of a compound planetary gear and unit's electromagnetic clutch to provide the operation modes such as Engine Only (EO), Electric Vehicle (EV), and Hybrid Electric Vehicle (HEV) modes. In order to investigate the characteristics of the velocity and torque flow for the system, dynamic models of the HEV with DTS are derived from the prototype DTS. The performance of the derived dynamic models is evaluated by both computer simulations and experiments according to each mode.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.10
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• pp.87-97
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• 2020

In general, tires require various sensors and power supply devices, such as batteries, to obtain information such as pressure, temperature, acceleration, and the friction coefficient between the tire and the road in real time. However, these sensors have a size limitation because they are mounted on a tire, and their batteries have limited usability due to short replacement cycles, leading to additional replacement costs. Therefore, vibration energy harvesting technology, which converts the dynamic strain energy generated from the tire into electrical energy and then stores the energy in a power supply, is advantageous. In this study, the output voltage and power generated from piezoelectric elements are predicted through finite element analysis under static state and transient state conditions, taking into account the dynamic characteristics of tires. First, the tire and piezoelectric elements are created as a finite element model and then the natural frequency and mode shapes are identified through modal analysis. Next, in the static state, with the piezoelectric element attached to the inside of the tire, the voltage distribution at the contact surface between the tire and the road is examined. Lastly, in the transient state, with the tire rotating at the speeds of 30 km/h and 50 km/h, the output voltage and power characteristics of the piezoelectric elements attached to four locations inside the tire are evaluated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.4A
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• pp.375-382
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• 2010

This paper presents the extraction of natural frequencies and mode shapes of a cable-stayed bridge using data acquired from GNSS. The response signals of 6 GNSS measuring points installed at the Seohae cable-stayed bridge are used for analysis of dynamic characteristics. Using normalization process and a third order Butterworth filter for the measured signals, the related pass band's signals have been isolated. Then, the acceleration data by double differentiation for these signals are obtained. Total five natural frequencies have been extracted by the fast Fourier transform and compared to the results of different studies. For the acceleration obtained from GNSS signals, the mode shapes of the bridge have been successfully extracted by TDD technique.

• Smart Structures and Systems
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• v.16 no.5
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• pp.891-918
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• 2015

In many of microdevices a part of a microbeam is covered by a piezoelectric layer. Depend on the application a DC or AC voltage is applied between upper and lower side of the piezoelectric layer. A common method in many of previous works for evaluating the response of these structures is discretizing by Galerkin method. In these works often single mode shape of a uniform microbeam i.e. the microbeam without piezoelectric layer has been used as comparison function, and so the convergence of the solution has not been verified. In this paper the Galerkin method is used for discretization, and a comprehensive analysis on the convergence of solution of equation that is discretized using this comparison function is studied for both clamped-clamped and clamped-free microbeams. The static and dynamic solution resulted from Galerkin method is compared to the modal expansion solution. In addition the static solution is compared to an exact solution. It is denoted that the required numbers of uniform microbeam mode shapes for convergence of static solution due to DC voltage depends on the position and thickness of deposited piezoelectric layer. It is shown that when the clamped-clamped microbeam is coated symmetrically by piezoelectric layer, then the convergence for static solution may be obtained using only first mode. This result is valid for clamped-free case when it is covered by piezoelectric layer from left clamped side to the right. It is shown that when voltage is AC then the number of required uniform microbeam shape mode for convergence is much more than the number of required mode in modal expansion due to the dynamic effect of piezoelectric layer. This difference increases by increasing the piezoelectric thickness, the closeness of the excitation frequency to natural frequency and decreasing the damping coefficient. This condition is often indefeasible in microresonator system. It is concluded that discreitizing the equation of motion using one mode shape of uniform microbeam as comparison function in many of previous works causes considerable errors.

• Computational Structural Engineering
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• v.6 no.1
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• pp.127-135
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• 1993

This paper summarizes a study on the application of viscoelastic dampers as an energy dissipation device in the frame structure. It can be concluded that, even at high temperatures, the viscoelastically damped structure can achieve a significant reduction of structural response as compared to the case with no dampers added. Empirical formulae for estimating the dynamic properties of the viscoelastic damper are established based on the regression analysis using data obtained from component tests of the damper. The structural damping with added dampers can be satisfactorily estimated by the modal strain energy method and the derived empirical formulae. Numerical simulations using conventional modal analysis methods are also carried out to predict the dynamic response of viscoelastically damped structures under seismic excitations. Comparison between numerical simulations and test results shows very good agreement. Based on the above studies, a design procedure for viscoelastically damped structures is present . This design procedure fits naturally into the conventional structural design flow-chart by including damping ratio an additional design parameter.

• Smart Structures and Systems
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• v.29 no.3
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• pp.499-512
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• 2022

This work proposes a novel contactless vibration damping and thermal isolation tripod platform based on Superconducting Magnetic Levitation (SML). This prototype is suitable for cryogenic environments, where classical passive, semi active and active vibration isolation techniques may present tribological problems due to the low temperatures and/or cannot guarantee an enough thermal isolation. The levitating platform consists of a Superconducting Magnetic Levitation (SML) with inherent passive static stabilization. In addition, the use of Operational Modal Analysis (OMA) technique is proposed to characterize the transmissibility function from the baseplate to the platform. The OMA is based on the Stochastic Subspace Identification (SSI) by using the Expectation Maximization (EM) algorithm. This paper contributes to the use of SSI-EM for SML applications by proposing a step-by-step experimental methodology to process the measured data, which are obtained with different unknown excitations: ambient excitation and impulse excitation. Thus, the performance of SSI-EM for SML applications can be improved, providing a good estimation of the natural frequency and damping ratio without any controlled excitation, which is the main obstacle to use an experimental modal analysis in cryogenic environments. The dynamic response of the 510 g levitating platform has been characterized by means of OMA in a cryogenic, 77 K, and high vacuum, 1E-5 mbar, environment. The measured vertical and radial stiffness are 9872.4 N/m and 21329 N/m, respectively, whilst the measured vertical and radial damping values are 0.5278 Nm/s and 0.8938 Nm/s. The first natural frequency in vertical direction has been identified to be 27.39 Hz, whilst a value of 40.26 Hz was identified for the radial direction. The determined damping values for both modes are 0.46% and 0.53%, respectively.

• Earthquakes and Structures
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• v.22 no.1
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• pp.1-13
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• 2022

When a building suffers damages under moderate to severe loading condition, its physical properties such as damping and stiffness parameters will change. There are different practical methods besides various numerical procedures that have successfully detected a range of these changes. Almost all the previous proposed methods used to work with translational components of mode shapes, probably because extracting these components is more common in vibrational tests. This study set out to investigate the influence of using both rotational and translational components of mode shapes, in detecting damages in 3-D steel structures elements. Three different sets of measured components of mode shapes are examined: translational, rotational, and also rotational/translational components in all joints. In order to validate our assumptions two different steel frames with three damage scenarios are considered. An iterative model updating program is developed in the MATLAB software that uses the OpenSees as its finite element analysis engine. Extensive analysis shows that employing rotational components results in more precise prediction of damage location and its intensity. Since measuring rotational components of mode shapes still is not very convenient, modal dynamic expansion technique is applied to generate rotational components from measured translational ones. The findings indicated that the developed model updating program is really efficient in damage detection even with generated data and considering noise effects. Moreover, methods which use rotational components of mode shapes can predict damage's location and its intensity more precisely than the ones which only work with translational data.

• Smart Structures and Systems
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• v.32 no.1
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• pp.1-7
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• 2023

In modal analysis, the mode shape reflects the vibration characteristics of the structure, and thus it is widely performed for finite element model updating and structural health monitoring. Generally, the acceleration-based mode shape is suitable to express the characteristics of structures for the translational vibration; however, it is difficult to represent the rotational mode at boundary conditions. A tilt sensor and gyroscope capable of measuring rotational mode are used to analyze the overall behavior of the structure, but extracting its mode shape is the major challenge under the small vibration always. Herein, we conducted a feasibility study on a multi-mode shape estimating approach utilizing a single physical quantity signal. The basic concept of the proposed method is to receive multi-metric dynamic responses from two sensors and obtain mode shapes through bridge loading test with relatively large deformation. In addition, the linear transformation matrix for estimating two mode shapes is derived, and the mode shape based on the gyro sensor data is obtained by acceleration response using ambient vibration. Because the structure's behavior with respect to translational and rotational mode can be confirmed, the proposed method can obtain the total response of the structure considering boundary conditions. To verify the feasibility of the proposed method, we pre-measured dynamic data acquired from five accelerometers and five gyro sensors in a lab-scale test considering bridge structures, and obtained a linear transformation matrix for estimating the multi-mode shapes. In addition, the mode shapes for two physical quantities could be extracted by using only the acceleration data. Finally, the mode shapes estimated by the proposed method were compared with the mode shapes obtained from the two sensors. This study confirmed the applicability of the multi-mode shape estimation approach for accurate damage assessment using multi-dimensional mode shapes of bridge structures, and can be used to evaluate the behavior of structures under ambient vibration.

• Journal of the Korean Society of Industry Convergence
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• v.26 no.6_3
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• pp.1341-1347
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• 2023

This study proposes to ensure the seismic stability of an existing switchboard for emergency diesel generator by applying mode analysis, static analysis and dynamic analysis. First, a three dimensional model for the swithboard was made with simplification for mode analysis. Next, The mode analysis for the finite element model of the existing switchboard was performed. The 1st natural frequency below 33 Hz, the seismic safety cutoff frequency, was calculated to be 21.943 Hz. Finally, based on the seismic stability theory, the von-Mises equivalent stresses derived by structural analysis and response spectrum analysis under the normal and faulted conditions were 74.179 MPa and 49.769 MPa, respectively. These are less than specified allowable stresses. So seismic stability was confirmed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.4
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• pp.301-307
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• 2013

MRU(motor reduction unit) for KTX is a assembled complex structure that is equipped with a lot of parts at the express train KTX and that is the core power source operating variable speeds. This study is recorded the dynamic characteristics analysis results tested by EMA which is done through the parts and assembly test, transient analysis and stoped train test in order to design the online monitoring system for KTX MRU. And the mode shapes result from critical vibration frequency explain the relation with variable speeds of express train over 250 km/hr. Also these variable speeds make variable operational frequencies at pinion, axle gear mesh frequency and normal bearing fault frequencies. As the specified speed can make resonance with natural frequencies of the MRU, for the train operating stability, this study also presents the MRU's critical speeds calculated by the each train speed.