• Structural Engineering and Mechanics
• /
• v.7 no.4
• /
• pp.387-400
• /
• 1999

Damage detection in civil engineering structures using the change in dynamic system parameters has gained a lot of scientific interest during the last decade. By repeating a dynamic test on a structure after a certain time of use, the change in modal parameters can be used to quantify and qualify damages. To be able to use the modal parameters confidentially for damage evaluation, the effect of other parameters such as excitation type, ambient conditions,... should be considered. In this paper, the influence of excitation type on the dynamic system parameters of a highway prestressed concrete bridge is investigated. The bridge, B13, lies between the villages Vilvoorde and Melsbroek and crosses the highway E19 between Brussels and Antwerpen in Belgium. A drop weight and ambient vibration are used to excite the bridge and the response at selected points is recorded. A finite element model is constructed to support and verify the dynamic measurements. It is found that the difference between the natural frequencies measured using impact weight and ambient vibration is in general less than 1%.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 1998.04a
• /
• pp.291-300
• /
• 1998

This paper demonstrates how ambient vibration measurements at a limited number of locations can be effectively utilized to estimate parameters of a finite element model of a large-scale structural system involving a large number of elements. System identification using ambient vibration measurements presents a challenge requiring the use of special identification techniques, which ran deal with very small magnitudes of ambient vibration contaminated by noise without the knowledge of input farces. In the present study, the modal parameters such as natural frequencies, damping ratios, and mode shapes of the structural system were estimated by means of appropriate system identification techniques including the random decrement method. Moreover, estimation of parameters such as the stiffness matrix of the finite element model from the system response measured by a limited number of sensors is another challenge. In this study, the system stiffness matrix was estimated by using the quadratic optimization involving the computed and measured modal strain energy of the system, with the aid of a sensitivity relationship between each element stiffness and the modal parameters established by the second order inverse modal perturbation theory. The finite element models thus identified represent the actual structural system very well, as their calculated dynamic characteristics satisfactorily matched the observed ones from the ambient vibration test performed on a large-scale structural system subjected primarily to ambient wind excitations. The dynamic models identified by this study will be used for design of an active mass damper system to be installed on this structure fer suppressing its wind vibration.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.8 no.2
• /
• pp.27-32
• /
• 2000

The main objective of this work is to investigate the effect of ambient conditions on the spray behavior and spray characteristics of high-pressure fuel injector. For this purpose, the effects of ambient pressure and temperature on the spray characteristics have been studied by applying the analysis of visualization system and phase Doppler particle analyzer. In this experiment, the visualization of spray behavior was performed under various ambient gas conditions and injection parameters such as gas temperature, ambient pressure, injection pressure of injector, and axial distance from the nozzle tip. Based on the investigation results, the spray tip penetration and spray width decrease with the increase of ambient gas pressure in the spray chamber. The effects of the spray parameters on the microscopic characteristics of gasoline spray were discussed.

• Earthquakes and Structures
• /
• v.4 no.3
• /
• pp.325-339
• /
• 2013

A number of structural and modal parameters are derived from the strong motion records of an instrumented G + 9 storeyed RC building during Bhuj earthquake, 26 Jan. 2001 in India. Some of the extracted parameters are peak floor accelerations, storey drift and modal characteristics. Modal parameters of the building are also compared with the values obtained from ambient vibration survey of the instrumented building after the occurrence of earthquake. These parameters are further used for calibrating the accuracy of fixed-base Finite Element (FE) models considering structural and non-structural elements. Some conclusions are drawn based on theoretical and experimental results obtained from strong motion records and time history analysis of FE models. An important outcome of the study is that strong motion peak acceleration profile in two horizontal directions is close to FE model in which masonry infill walls are modeled.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.39 no.8
• /
• pp.689-701
• /
• 2011

The relations between ambient conditions and ice accretion shapes are quantitatively analyzed by employing self-organization maps and analysis of variance. Liquid water contents(LWC), mean volumetric droplet diameter(MVD), ambient temperature and free-stream velocity are chosen as ambient conditions which change ice accretion shapes. The parameters of ice accretion shape are selected as maximum thickness, icing limits, ice heading, and ice accretion area. Qualitative analysis was conducted by employing self-organization maps which show the qualitative relations between ice shapes and ambient conditions. The quantitative results of analysis of variance yield intensity of ambient conditions to the parameters of ice accretion shapes.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.47 no.6
• /
• pp.860-868
• /
• 2014

The study was performed to investigate changes in hematological responses and antioxidative enzyme activities (superoxide dismutase, SOD; catalase, CAT) of Japanese eel Anguilla japonica following exposure to 0 (control), 2.33, 4.60, 6,64 and 8.78 mM nitrite-N in fresh water for 48 h. Hematological parameters such as plasma nitrite, electrolytes, cortisol, glucose, glutamate oxaloacetate transaminase (GOT), glutamate pyruvate transaminase (GPT), hemoglobin (Hb), methemoglobin (metHb) and NADH-methemoglobin reductase (NMR) were measured. Plasma nitrite, cortisol, metHb and NMR increased directly with increasing ambient nitrite concentration, while Hb content showed a progressive decline. Levels of plasma potassium, GOT and GPT of the eel exposed to 6.64 mM ambient nitrite were significantly higher than the control fish. The activity of SOD and CAT in plasma, gill and liver of the eel following exposure to nitrite were augmented by increasing ambient nitrite. Levels of plasma nitrite, metHb, NMR, cortisol, glucose and antioxidative enzyme activities of the eel exposed to 2.33 mM ambient nitrite were significantly higher than the control fish. This study suggested that the eel acutely exposed to elevated ambient nitrite causes nitrite-induced stress responses, changes in antioxidative enzyme activities and hematological parameters.

• Structural Engineering and Mechanics
• /
• v.22 no.1
• /
• pp.53-70
• /
• 2006

The paper summarizes the dynamic-based assessment of a reinforced concrete arch bridge, dating back to the 50's. The outlined approach is based on ambient vibration testing, output-only modal identification and updating of the uncertain structural parameters of a finite element model. The Peak Picking and the Enhanced Frequency Domain Decomposition techniques were used to extract the modal parameters from ambient vibration data and a very good agreement in both identified frequencies and mode shapes has been found between the two techniques. In the theoretical study, vibration modes were determined using a 3D Finite Element model of the bridge and the information obtained from the field tests combined with a classic system identification technique provided a linear elastic updated model, accurately fitting the modal parameters of the bridge in its present condition. Hence, the use of output-only modal identification techniques and updating procedures provided a model that could be used to evaluate the overall safety of the tested bridge under the service loads.

• 한국가시화정보학회:학술대회논문집
• /
• 2003.11a
• /
• pp.111-114
• /
• 2003

Drop size is one of the most important parameters which are control the performance of the engine using liquid fuel/oxidizer and drop formation is mainly controlled by aerodynamic force caused by ambient gas. Because of this, empirical data and correlation acquired under standard ambient condition are not valid. So experiments under high ambient pressure condition to measure the drop size using image processing method And find the empirical correlation between SMD and chamber pressure(density), injection velocity.

• Structural Engineering and Mechanics
• /
• v.50 no.2
• /
• pp.137-149
• /
• 2014

In this study, modal parameters such as natural frequencies, mode shapes and damping ratios of RC frames with low strength are determined for different construction stages using ambient vibration test. For this purpose full scaled, one bay and one story RC frames are produced and tested for plane, brick in-filled and brick in-filled with plaster conditions. Measurement time, frequency span and effective mode number are determined by considering similar studies and literature. To obtain experimental dynamic characteristics, Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification techniques are used together. It is shown that the ambient vibration measurements are enough to identify the most significant modes of RC frames. The results indicate that modal parameters change significantly depending on the construction stages. In addition, Infill walls increase stiffness and change the mode shapes of the RC frame. There is a good agreement between mode shapes obtained from brick in-filled and in-filled with plaster conditions. However, some differences are seen in plane frame, like expected. Dynamic characteristics should be verified using finite element analysis. Finally, inconsistency between experimental and analytical dynamic characteristics should be minimize by finite element model updating using some uncertain parameters such as material properties, boundary condition and section properties to reflect the current behavior of the RC frames.

• Ocean and Polar Research
• /
• v.28 no.4
• /
• pp.459-465
• /
• 2006

Ambient noise as a background noise in the ocean has been well known for its the various and irregular signal characteristics. Generally, these signals we treated as noise and they are analyzed through stochastical level if they don't include definite sinusoidal signals. This study is to see how ocean ambient noise can be analyzed by the chaotic analysis technique. The chaotic analysis is carried out with underwater ambient noise obtained in areas near the Korean Peninsula. The calculated physical parameters of time series signal are as follows: histogram, self-correlation coefficient, delay time, frequency spectrum, sonogram, return map, embedding dimension, correlation dimension, Lyapunov exponent, etc. We investigate the chaotic pattern of noises from these parameters. From the embedding dimensions of underwater noises, the assesment of underwater noise by chaotic analysis shows similar results if they don't include a definite sinusoidal signal. However, the values of Lyapunov exponent (divergence exponent) are smaller than that of random noise signal. As a result we confirm the possibility of classification of underwater noise using Lyapunov analysis.