Papers by Keyword: Structural Dynamics

Abstract: The structures are prone to dynamic loads such as earthquake as they often generate uncomfortable movement into existing structures. In order to reduce extreme vibration generated by dynamic or operational loads passive, active or hybrid controlling devices are used. And the advantages of passive systems are well accepted due to their inexpensiveness and simplicity. This study investigates the performance of a newly developed uniaxial tuned mass damper (TMD). The novelty of the developed device is that the properties of the damper are adjustable based on the structural requirements. And most importantly, another key design criterion is to make a low-cost affordable device. To do this end, a toy two degree of freedom (2-DOF) system is considered and the experiments are conducted. The experimental tests and numerical simulations are carried out on the structure without and with TMD along with extra masses of 25 kg, 30 kg and 35 kg on the floors to observe the effect of floor mass changes. The scaled El Centro 1940 earthquake data is used as input excitation. In order to determine the optimal performance of the damper, it is tuned to modal mass of 0% (i.e., without TMD), 5%, 7.5%, 10%, 12.5%, and 17.5%. The experimental results have shown that the structure without TMD has pronounced vibration (i.e., displacement) as compared to the structure with TMD. As the percentage of modal mass increases, the vibration of the structure decreases. It is observed that up to 12.5% of modal mass for both 20 and 25 sec excitation duration could be the optimum amount that minimizes the vibration of the structure. The overall performance of this device is capable of reducing vibration in a reasonable manner and has the possibility to use it for the real engineering application.

Abstract: Within the framework of structural dynamics, the article deals with the problem ofdetermining at a given moment the probability density function of certain quantities of interest,based on the uncertainties about the initial data, the structure characteristics and the applied loads.The proposed method uses the so-called principle of preservation of probability, and leads towriting a linear partial differential equation for any quantity whose probability density function hasto be determined.

Abstract: Base Isolation systems have been implemented on civil engineering structures subject to earthquakes worldwide for a number of years because of their simplicity, reliability, and effectiveness; passive isolators usually consist of members located in between the foundations and the super-structure and characterised by high damping capacity and relatively low stiffness. Devices are available typically coupling elements endowed with large translating deformability, mainly aimed at shifting the structural frequency band, with components devoted to dissipate and/or absorb the filtered transmitted energy. Although characterized by stability and low energy demand, BI devices are limited in their ability to adapt themselves to changing demands for structure response reduction. The performance of such devices may fail expectations under special, like in case of soft soil, or unexpected conditions, and, in order to optimize the overall performance of the control system, the isolated system should be embedded in a more complex system able to possibly activate some corrective actions. In the paper, with reference to steel structures, a strategy is outlined to this purpose, devoted to existing, or not, isolated constructions.

Abstract: The unmanned aerial vehicle (UAV) is a light weight flight system that can carry sensors and cameras for data collection. Tremendous excitement surrounds the use of UAVs because they can be deployed easily and rapidly for data collection; they also can be programmed to execute missions with high degrees of autonomy. For these reasons, UAVs hold promise in accelerating the collection of data in geophysical explorations. In this study, a UAV platform is explored for the collection of data from geophones deployed to measure the vibrations of a concrete slab foundation. The UAV is designed to drop a weight as a controlled energy source. Both the energy and location of the impulsive load are adjustable by the flight parameters of the UAV. The study adopts a time-domain analysis for source localization using the dense array of geophones

Abstract: Wind energy technology is an integrated technology, which involves aerodynamics, structural dynamics, meteorology, mechanical engineering, electrical engineering, control multiple disciplines technology, materials science, environmental science and other areas. This paper studies the structural dynamics of the wind turbine. On one hand, modern wind turbine is composed of various interacting components and subsystems, and its aerodynamic rotor design technique involves controlling a wide range of areas systems, mechanical systems, electrical systems. On the other hand, the wind turbine has characteristics different from the usual mechanical systems. Wind turbine power source is natural randomness of strong wind, The leaves are often run in a stall condition. The system has a strong stochastic dynamic process. The transmission system irregular power input is abnormal . The main structural components exposed to several times higher than normal rotating mechanical fatigue loading. Thus the unique characteristic of dynamics of the wind turbine is formed . Analysis of wind turbine blade load dynamics of basic research carried out in this article by means of an appropriate structure coordinates.

Abstract: With the increasing complexity of the products, engineers face a higher level of uncertainty in both simulation and test. Correlation between numerical and experimental analysis using model updating techniques helps engineers to asses uncertainty. Present research efforts focus to combine finite element analysis and testing in one common framework. Experimental and operational modal analysis and simulation make benefit from common databases. Some applications presented emphasize the advantages of these techniques.

Abstract: Reinforced concrete beams are widely employed in civil engineering structures. To reduce the maintenance financial cost, structure damages have to be detected early. To this end, one needs robust monitoring techniques. The paper deals with the identification of mechanical parameters, useful for Structural Health Monitoring, in a 2D beam using inverse modeling technique. The optimal control theory is employed. As an example, we aim to identify a reduction of the steel bar cross-section and a decrease of the concrete Young modulus in damaged areas. In our strategy, the beam is instrumented with strain sensors, and a known dynamic load is applied. In the inverse technique, two space discretizations are considered: a fine dicretization (h) to solve the structural dynamic problem and a coarse discretization (H) for the beam parameter identification. To get the beam parameters, we minimize a classical data misfit functional using a gradient-like algorithm. A low-cost computation of the functional gradient is performed using the adjoint equation. The inverse problem is solved in a general way using engineer numerical tools: Python scripts and the free finite element software Code_Aster. First results show that a local reduction of the steel bar cross-section and a local decrease of concrete Young modulus can be detected using this inverse technique.

Abstract: The structural integrity of a jet pump assembly of a boiling water reactor (BWR) under hydrodynamic loading was evaluated. This arrangement, which has a riser joined with a couple of jet pumps by the transition piece, is part of the reactor recirculation system. It is submerged in water under pressure. The main function is to induce forced flow through the core of the reactor. A dynamic structural analysis was carried out with the finite element method. The first ten modes of vibration and their natural frequencies were calculated. The first five natural frequencies are in the range between 25 Hz and 40 Hz. In this analysis, it was considered that the jet pump assembly is supported at the riser brace. The restrainer bracket keeps together the riser with the two jet pumps and there is free movement at the slip joints.

Abstract: Laser Doppler Vibrometry (LDV) is a well established technique able to accurately measure vibration velocity of any kind of structure in remote, i.e. non-intrusive way, this allowing to overcome the problem of mass loading, typical of contact sensors as accelerometers and strain-gauges, which has strong influence in case of lightweight structures. Moreover, the possibility of driving automatically the laser beam, by means of moving mirrors controlled with galvanometer servo-actuators, permits to perform scanning measurements at different locations with high spatial resolution and reduced testing time and easily measure the operational deflection shapes (ODS) of the scanned surface. The exploitation of the moving mirrors has allowed to drive the laser beam in a continuous way making it to scan continuously over the structure surface and cover it completely. This way of operation, named Continuous Scanning LDV, permits to perform full-field measurements, the LDV output carrying simultaneously the time-and spatial-dependent information related to the structural vibration. A complementary strategy making use of the LDV coupled with moving mirrors is the so called Tracking LDV, where the laser beam is driven to follow a moving object whose trajectory must be known a priori or measured during operation (e.g. via an encoder in the case of rotating structures). In this paper some applications of the Tracking Laser Doppler Vibrometry (TLDV) and Continuous Scanning Laser Doppler Vibrometry (CSLDV) will be described they concerning, specifically modal and vibrational analysis of rotating structures.

Abstract: Wind energy industry has been growing tremendously in recent years. Tubular steel towers are currently dominant supporting structures for wind turbines. With the increase of the converter capacity, there is a great demand for higher supporting towers. However, structural vibrations in extreme wind events tend to become a major concern during tower design. To study wind turbine tower dynamics, an existing tubular steel tower was tested. Vibrational frequencies and damping ratios were identified. To avoid unexpected dynamic problems, a space frame steel tower has been proposed for supporting larger wind turbines. It is a structural system that can be assembled on-site by using prefabricated beams, columns, and brace members. A typical space frame steel tower was designed in this paper. Static loading, modal and buckling analyses of the tower were presented. It is expected to introduce engineers and designers more options for wind turbine tower design.