Papers by Keyword: Modal Analysis

Abstract: This paper deals with static and dynamic analysis of asymmetric high-rise building. Two alternatives have been analysed – without dilatation and with dilatation. Then, the influence of the dilatation was discussed. The building was located in 4^th seismic area in Slovakia (Bratislava). The description of the building, applied load, considered soil-structure interaction, created calculating models, used analysis and obtained results are mentioned here. The conclusions and the photos of defective repairs of real structures are depicted at the end of the paper.

Abstract: This article focuses on the estimation of a proper logarithmic damping decrement in industrial boilers when flue gases travel in the vertical direction. The structure for this type of facility is quite unified worldwide. The structural conception is rather simple, and the response to any static loading is predictable. Nevertheless, with regard to dynamics and damping, some specifics in the detailed solution make this system unique. For the purpose of this analysis, a Plexiglas scale model was prepared at a geometric scale of 1:20. A set of experimental modal analyses was performed on the model. Each test focused on the damping effect of specific details and compared it with the common structure without a damping effect. Finally, a site modal analysis was conducted on an actual boiler located in the CHP Torun Plant in Poland. The upper part of the structure was reinforced to have a horizontal deflection of 8 mm and was suddenly released. The resulting movement was recorded with an HD camera linked to a theodolite. Experimental results on the scale model of the actual structure confirmed that damping of this type of structure is significantly higher than that considered for common steel structures.

Abstract: CNG driven three wheeler vehicles is seen to carrying passenger around Bangladesh and vary favorable as public or private hired vehicle. Its drive shaft is a vital component for transmitting power from engine to wheel rotates at around 4000-5000 rpm. Most shafts undergo varying range of loads including bending, torsion and axial simultaneously. Therefore, the shaft fails frequently. But the problem of its replacement is difficult. It is imported from abroad; usually from the origin country of a specific model which makes its interchangeability exorbitant to the owner but also time consuming due to unavailability throughout the country. Substituting high cost unoriginal drive shaft by locally made shaft is an important criterion for lowering the maintenance cost. In this work an attempt has been made to estimate the deflection, stresses under subjected loads using FEA in ANSYS. The static structural analysis gives deflection and stresses. Modal analysis shows the nature of frequency and the maximum permissible rotating speed.

Abstract: The calculation of fundamental time period of vibration is a crucial step in seismic design and analysis of the structures to assess global response of the structure. Different international code proposed empirical expressions considering only height for bare frame structures and height and width of the buildings with infill to estimate the fundamental time period. This paper summaries the effect of the following parameters of building height, bay width, number of bays, cracked or un-cracked section of the structural member and support condition at the base on the fundamental time period of reinforced concrete bare frame and buildings with infill. Modal analysis of 360 building models with selected parameters is investigated in this study. A new equation, which is a function of the selected parameters (building height, bay width, number of bays, type of support condition, cracked or un-cracked sections and type of frame chosen for analysis) is also proposed using multiple linear regression analysis for predicting the fundamental period of buildings. The proposed simple model, including the building height, bay width, number of bays, type of support condition, cracked or un-cracked sections and type of frame chosen for analysis, showed better estimate in predicting the fundamental period of buildings compared to the code equations.

Abstract: In this study, an effective method based on wavelet transform, for identification of damage on rotating shafts is proposed. The nodal displacement data of damaged rotor is processed to obtain wavelet coefficients to detect, localise and quantify damage severity. Because the wavelet coefficients are calculated with various scaled indices, local disturbances in the mode shape data can be found out in the finer scales that are positioned at local disturbances. In the present work the displacement data are extracted from the MATLAB model at a particular speed. Damage is represented as reduction in diameter of the shaft. The difference vectors between damaged and undamaged shafts are used as input vectors for wavelet analysis. The measure of damage severity is estimated using a parameter formulated from the distribution of wavelet coefficients with respect to the scales. Diagnosis results for different damage cases such as single and multiple damages are presented.

Abstract: Piezoelectric energy harvesting has applications in aircraft technology, where the piezoelectric patches are attached to the wings of the aircraft to convert the mechanical vibrations into useful electrical energy, which further is used to power the sensors of Aircraft Health Monitoring System, inflight operations like lighting and onboard entertainment. In this article, the performance of vibration based piezoelectric energy harvester (PEH) for a given frequency range is studied. A piezoelectric material that has a maximum piezoelectric coefficient (PZT-G1195) is chosen to increase the effective power output. The output power generated by the harvester due to transverse and longitudinal vibrations are compared. Finally parametric studies are performed on the PEH to analyze the design parameters influencing its performance.

Abstract: Mixed flow pumps applications have been exploited in a large number of diversified fields of engineering. They find applications as an important component in waste water treatment systems, power stations, irrigation systems etc. User requirements make these pumps to work very close to the functioning requirements and therefore under these conditions the vibrations are bound to occur in different moving components of the pump. It would be difficult to analyse the pump vibrations, considering the pump as a single system. Analysing vibrations in different moving components of the pump will not only be easier but also will aid in reducing the vibrations at the microscopic level. As a subject of the present paper, the mixed flow pump impeller blade has been designed using sparingly used yet accurate mean stream line theory. Modal analysis of the pump blade has been carried out at different modes of frequency. Total deformation for different modes of frequencies has also been determined. Stainless steel has been used as the construction material of the impeller blade.

Abstract: The most recent studies about the seismic behavior of the leaning Tower of Pisa that consider the soil-foundation-structure interaction date back to twenty years ago. From 1999 to 2001, the foundation of the monument was consolidated by means of under-excavation and the "Catino" at the basement was rigidly connected to the foundation. Meanwhile, significant progresses have been made in the field of earthquake engineering. Therefore, the need exists to assess the dynamic behavior of the Tower in light of the novelties occurred in the past decades. In the present study, the mechanical characteristics of the foundation have been calibrated comparing the outcomes of the experimental dynamic monitoring with the results of the finite element analysis performed on a simple but effective model. The scenario earthquakes for return periods equal to 130 years and 500 years are also presented.

Abstract: As the premise, exploring aero-engine structure parts damage accurately can guarantee safety of the aero-engine structure parts, which are restricted by the working condition under the high temperature, high pressure and high speed. Analyzed the structure parts modal parameters by the modal theory, and researched the facts how to influence the modal parameters based on the different damage extent of the structure parts. Then construct the different damage extent structure models on the structure junctions with the finite element analysis method. At last, constructed and verified seven models with the example of aero-engine turbine structure damage in the constant temperature. The results were shown that the characteristic parameters with the inherent frequency and the inherent frequency deviation square can explore the structure damage accurately, but have no significant influence on the structural damages. So it will be important for us to ensure reliable operation and structure damage identification timely by the proposing the structure damage parameters.

Abstract: This paper presented a numerical model of a grinding wheel hub to analyze the dynamic behavior between CFRP hub and steel hub. Natural frequencies of the two different hubs were extracted with the help of finite element software ABAQUS. In addition, the vibration attenuation procedure in the process of free vibration of the hubs was also compared. The numerical results obtained from the model demonstrated that natural frequency of the CFRP hub is much higher than that made of steel owing to the great ratio of elastic modulus to density of carbon fiber. The CFRP hub has a better damping vibration characteristic which allows it to absorb vibration in grinding process to achieve a finer surface roughness.