• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.1
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• pp.13-20
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• 1994

Determination of the number of modes to be included in the mode superposition method(MSM) is very important and difficult. Mode acceleration method(MAM) is recommended recently with the intention to overcome the problem. But the solution of the MAM is complex and complicate in frequency domain analysis. In this paper, advanced mode acceleration method(AMAM) is formulated and examined. The results from example analyses show that AMAM is a simple, accurate and reliable method compared with the MSM and the MAM.

• International Journal of Automotive Technology
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• v.5 no.4
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• pp.311-319
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• 2004

There are many methods to test engine emissions depending on the regulations used such as FTP-75(CYS-75) mode, 10-15 mode and ECE-15 mode. Most of these modes consist of transient conditions such as cranking, rapid acceleration or deceleration modes. In this experimental research, the transient characteristics including cranking and accelerating mode in SI engines were studied to compare pure gasoline with methanol-reformulated fuels for performance and exhaust emissions. The results show that methanol-reformulated fuels have a better emissions reduction rate than that of pure gasoline especially for HC, CO and NOx emissions during cranking mode. The acceleration performances conform to the results of the distillation curve and the CO concentration for RM50 varies slightly in acceleration mode.

• Computers and Concrete
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• v.25 no.3
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• pp.273-282
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• 2020

A new seismic design methodology for precast concrete diaphragms has been developed and incorporated into the current American seismic design code. This design methodology recognizes that diaphragm inertial forces during earthquakes are highly influenced by higher dynamic vibration modes and incorporates the higher mode effect into the diaphragm seismic design acceleration determination using a first mode reduced method, which applies the response modification coefficient only to the first mode response but keeps the higher mode response unreduced. However the first mode reduced method does not consider effects of diaphragm flexibility, which plays an important role on the diaphragm seismic response especially for the precast concrete diaphragm. Therefore this paper investigated the effect of diaphragm flexibility on the diaphragm seismic design acceleration for precast concrete shear wall structures through parametric studies. Several design parameters were considered including number of stories, diaphragm geometries and stiffness. It was found that the diaphragm flexibility can change the structural dynamic properties and amplify the diaphragm acceleration during earthquakes. Design equations for mode contribution factors considering the diaphragm flexibility were first established through modal analyses to modify the first mode reduced method in the current code. The modified first mode reduced method has then been verified through nonlinear time history analyses.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.549-555
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• 2000

The improved mode superposition methods for non-classically damped systems are presented in this paper. Generally, the mode superposition method uses a relatively small subset of the normal modes of structures. The mode acceleration method and the modal truncation augmentation method improve the results of the mode superposition method by considering effects of truncated high modes. For using these methods to analyze non-classically damped systems, the systems are approximated to the classically damped systems and thereby the errors are induced. In this paper, the mode acceleration method and the modal truncation augmentation method are expanded to analyze the non-classically damped systems. The applicability of the expanded methods is verified by closed form solutions and numerical examples. The expanded modal truncation augmentation method is conditionally stable depending on the pattern of the external loading in the non-classically damped systems whereas the expanded mode acceleration method is stable for the all cases of loading. In the stable case, the results are the same with those of the expanded mode acceleration method.

• 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.

• Wind and Structures
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• v.16 no.2
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• pp.157-178
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• 2013

Output-only modal parameter identification is based on the assumption that external forces on a linear structure are white noise. However, harmonic excitations are also often present in real structural vibrations. In particular, it has been realized that the use of forced acceleration responses without knowledge of external forces can pose a problem in the modal parameter identification, because an external force is imparted to its impulse acceleration response function. This paper provides a three-stage identification procedure as a solution to the problem of harmonic and white noise excitations in the acceleration responses of a linear dynamic system. This procedure combines the uses of the mode indicator function, the complex mode indication function, the enhanced frequency response function, an iterative rational fraction polynomial method and mode shape inspection for the correlation-related functions of the force-embedded acceleration responses. The procedure is verified via numerical simulation of a five-floor shear building and a two-dimensional frame and also applied to ambient vibration data of a large-span roof structure. Results show that the modal parameters of these dynamic systems can be satisfactorily identified under the requirement of wide separation between vibration modes and harmonic excitations.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.5 no.4
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• pp.65-73
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• 1985

A stochastic dynamic analysis using Mode-Acceleration Method was formulated and examined in this paper. A computer program was developed using this theory and model offshore structure was analyzed by the program. Results show that the stochastic dynamic analysis using the Mode-Acceleration Method is superior to that using Mode Displacement Method. The method using the theory developed in this paper was proved to be very reliable, economic and potential.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1997.10a
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• pp.223-230
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• 1997

A method of stochastic dynamic analysis of suspension bridge subjected to random wind loads has been developed in this paper. Example analyses are carried out by mode superposition method(MSM), mode acceleration method(MAM) and advanced mode acceleration method(AMAM) in frequency domain for the Nam-Hae Bridge. In this study the statistical characterics of random wind loads we assumed to be Gaussian stationary zero mean processes. The considered structural response quanties are displacements, shear forces and bending moments. The mean extreme responses are approximately calculated by three times of standard deviations. The followings are the conclusions from this study. 1. Numerical results which obtained by three methods of computer program developed in this paper agree reasonably well when the numbers of modes increase. 2. AMAM is simple, accurate, economic and reliable method compared with the MSM and the MAM.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2008.10a
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• pp.62-65
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• 2008

In this paper, we estimated the D147 mode test, which is introduced as a new emission test mode for the driving car using diesel fuel. And we compared the D147 test mode, Lug-Down3 test mode and no load acceleration test mode. And the exhaust gas concentration between the three modes was compared. The exhaust concentration at the D147 mode is lower than the exhause concentration at the Lug-Down 3 mode and higher than that at the no load acceleration test mode. Also the correlation factor was estimated between the D147 mode and Lug-Down 3 mode.

• Smart Structures and Systems
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• v.15 no.3
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• pp.645-663
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• 2015

Recently, an indirect displacement estimation method using data fusion of acceleration and strain (i.e., acceleration-strain-based method) has been developed. Though the method showed good performance on beam-like structures, it has inherent limitation in applying to more general types of bridges that may have complex shapes, because it uses assumed analytical (sinusoidal) mode shapes to map the measured strain into displacement. This paper proposes an improved displacement estimation method that can be applied to more general types of bridges by building the mapping using the finite element model of the structure rather than using the assumed sinusoidal mode shapes. The performance of the proposed method is evaluated by numerical simulations on a deck arch bridge model and a three-span truss bridge model whose mode shapes are difficult to express as analytical functions. The displacements are estimated by acceleration-based method, strain-based method, acceleration-strain-based method, and the improved method. Then the results are compared with the exact displacement. An experimental validation is also carried out on a prestressed concrete girder bridge. The proposed method is found to provide the best estimate for dynamic displacements in the comparison, showing good agreement with the measurements as well.