Journal of Engineering and Thermal Sciences
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Seismic performance evaluation and improvement for damaged reinforcement concrete piers using a fiber steel composite plate
Get PDFThe seismic performance evaluation and retrofit process are very important in damaged bridges. If the result is not appropriate, then retrofit process are required. In this paper, to validate the seismic performance of retrofitted bridge experimentally, an experimental study was conducted to verify the application and efficiency of the jacket retrofit method to ensure seismic performance of damaged reinforcement concrete (RC) bridge piers. A total of 4 RC bridge piers was made and then 3 piers were pre-loaded under the range of service load to be damaged. These piers were retrofitted and repaired using a carbon fiber reinforced polymer (CFRP), steel plate, and fiber steel composite (FSC) plates. These retrofitted and repaired piers were subjected to monotonic loading. Hysteresis and ultimate behaviors of the 3 RC piers were evaluated and compared with those of 1 non-damaged pier (standard specimen). As a test result, the retrofitted and repaired RC bridge piers applied by the jacket retrofit method were ensured under the targeted displacement ductility and ultimate load. The ultimate load and displacement ductility of the pier retrofitted and repaired by FSC plate were higher than those of other piers by CFRP and steel plates and also the pier by FSC plate showed better energy dissipation capacity than others. Generally, RC bridge pier retrofitted and repaired with the jacket retrofit method has low ductility but it was found that the pier retrofitted and repaired by FSC plate combined with CFRP and steel wire had overcome effectively this disadvantage through ductility evaluation based on the concept of energy numerically. This experiment showed that one could improve the safety margin and targeted ductility by repairing the cracks, spalls, etc. of the damaged RC bridge piers appropriately and then retrofitting them with the high ductile materials. The responses of existing damage bridges are compared with those of retrofitted bridge by jacket method for earthquake of target level, and also seismic performances are evaluated. By the test and analysis results it can be concluded that the proposed seismic retrofit method was found to be valid
Identification of viscoelastic material properties based on Big Bang-Big Crunch optimization method
Get PDFAn efficient identification method of the dynamic properties of viscoelastic damping materials using an optimization technique is proposed. A Zener fractional derivative model is used to describe the frequency-dependent dynamic characteristics of materials. In this study, the viscoelastic material is used in a Passive Constrained Layer Damping (PCLD) configuration in order to increase the shear deformation in the material. Mean Square Velocities (MSVs) of a clamped-free beam covered with a PCLD patch are measured in an environmental chamber at different frequencies and used as reference MSVs. The excitation force is performed thinks to a low mass magnet fixed on the beam and placed inside a coil subjected to an electrical current. Numerical MSVs are calculated using an equivalent single layer plate model with warping functions chosen to ensure continuity of transverse shear stresses and displacements layer's interfaces
A novel method for detecting bearing defects based on EMD and fractal dimension
Get PDFBearings are widely used in rotating machines. Its health status is a significant index to indicate whether machines run continually or not. Detecting the bearing defects timely is very important for the maintenance decision making. In this paper, a novel bearing defects detection method based on EMD and Fractal Dimension is developed. The original data is decomposed into a set of intrinsic mode functions (IMFs) using EMD, and the fractal dimension of IMFs which contains bearing fault characteristic information are calculated, and these characteristic parameters are used to identify bearing fault types. The effectiveness of this methodology is demonstrated using experimental data
Investigation on a collapse accident of guyed portal towers caused by strong wind
Get PDFA collapse of 3 guyed portal towers in a 220 kV transmission power system were caused by short period of strong wind. In order to unmask accident, various methods are used, such as scene investigation, material test and FE method. The reasons caused the collapse accident are obtained in this paper, and some improvement measures are recommended for sake of continuing maintenance
Modeling and analysis of the vibration characteristics of a new type of in-arm hydropneumatic suspension of a tracked vehicle
Get PDFWe investigated the nonlinear elastic characteristic of an in-arm hydropneumatic suspension unit (ISU) as well as the damping characteristic of the controllable vane absorber. Due to the strong nonlinear characteristic of the ISU, simplify is needed to accurately model the vehicle. Based on the theory of multibody dynamics, a virtual prototype of the tracked vehicle was built, which includes the hydraulic system, the multi-dynamics of running gears and a road surface model. The virtual prototype is validated using both a static balancing test and a stiffness characteristics test. By simulating the road impact loading of the tracked vehicle when travelling on a trapezoidal US military road, the changes of the pitch angle and the acceleration of seats and centroid of the tracked vehicle was analyzed for two different damping ratios. We also determined key ride indicators for different speeds. The stiffness and damping characteristics of the ISU were tested in a bench experiment
Modal and dynamic responses of the human head-neck complex for impact applications
Get PDFThe human head-neck is the most complex structure in the human body and its behavior under vibration remain poorly understood. Therefore, a comprehensive theoretical or experimental analysis is needed. This study is mainly based on an available finite element human head-neck complex and concentrates on its modal and dynamic responses. Resonance frequencies and responses of the human head-neck complex’s finite element model in impact simulations have been analyzed. These dynamic responses show a very good agreement with the previous studies. The fundamental frequency of modal analysis of finite element model is 35.25 Hz which is reasonably close to existing literatures. However, our modal dynamic analysis of an elaborated human head-neck complex introduces supplementary dynamic responses like nasal sideward cartilages’ “flipping” modes and the mandible’s “mastication” modes. Modal validation is performed which indicates a requirement for elaborated modeling to make out all the extra resonance frequencies. Moreover, the influence of damping factor on biomechanical response or natural frequencies is also investigated. It can be found that damping factor has got an inverse proportionality between damping factor effect on natural frequency and that on biomechanical responses. This demonstrates the significance of identification of the suitable damping factor evaluating biomechanical response in modal dynamic analysis and validation
Vibration characteristics of stators of bearingless switched reluctance motors
Get PDFThe vibration characteristics of stators of bearingless switched reluctance motors (BSRMs) are analyzed based on finite-element method (FEM) in this paper. Aiming at to overcome the limitations of the previous modal analysis in which the influence of stator windings on the natural frequencies of switched reluctance motors (SRMs) stators is treated simply as an additional mass, the finite-element (FE) model of a 12/8-pole BSRM stator which takes torque windings and suspension windings in account is constructed based on its real structural model. In this paper, a kind of method is proposed to connect the windings and stator core as well as torque windings and suspension windings through the contact whose type is bonded. The validity of the connection method is proved by three-dimension (3D) finite-element analysis (FEA) and experimental modal analysis results of the SRM prototype
Research on fault diagnosis method of rolling bearing based on AMD and LabVIEW
Get PDFAiming at the problem of rolling bearing fault diagnosis, a fault diagnosis method of rolling bearing is proposed based on analytical mode decomposition (AMD) and LabVIEW. For the fault feature frequency of rolling bearing is predictable, the AMD method can be used to extract the signal in the frequency band of fault characteristic frequency in rolling bearing signal, and seek frequency spectrum of vibration signal. If the spectrum contains fault characteristic frequency, then the rolling bearing fault can be diagnosed by vibration signal. A rolling bearing fault diagnosis system is developed based on LabVIEW and AMD, and the application of AMD algorithm is realized. The validity of the method is proved by the analysis of actual fault signal of rolling bearing
Affection of the technology of multiple-input and multiple-output to the vibratory testing
Get PDFThe model of SIMO or SISO is usually used in the traditional vibration testing while the test item is always excited by multiple excitations in the field. The dynamic characteristics of structure (such as resonant frequency, mode shapes and modal damping) which will provide the basis for further analysis are obtained by vibration testing. Since the shaker needs to be mechanically attached to the structure under test, it is nearly inevitable that some sort of interaction will occur between them. It means that the traditional vibration testing or simulation don't have the ability to completely replicate the environment of test structure in the field which will lead to inaccurate results or even incorrect results. This paper offers differences between traditional SIMO vibration testing and MIMO vibration testing and presents some advantage of MIMO vibration testing which will distinctly improve the situation in laboratory and make boundary in the laboratory more similar to the environment in the field. Compared to traditional SIMO vibration testing, the MIMO vibration testing in the laboratory not only can significantly minimize the phenomenon of drops in the excitation forces close to resonant frequencies but also can replicate the boundary situations of the test item in the field
A remaining useful life prediction and maintenance decision optimal model based on Gamma process
Get PDFAiming at the practical problem of maintenance decision-making, the remaining useful life (RUL) prediction method and the maintenance decision optimization model are studied emphatically. Firstly, the condition space model based on Gamma degradation process is established, according to the characteristics of the degradation process of the equipment condition. Then the RUL expectancy is predicted by this model, and the RUL probability density function of the equipment can be got. Finally, this model is validated by the data obtained from the roller bearing life test. The maintenance decision model is established with the minimum cost as the objective, the maintenance decision is optimized, and the RUL prediction and maintenance decision are realized. the example proves the validity and feasibility of this model