Journal of Engineering and Thermal Sciences
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Nonlinear filtering and identification algorithms for correlation-extremum dynamic systems with random structure
Get PDFThe problem of adaptive estimation using spatial-time-varying filtering in dynamic systems with random structure is investigated. The proposed approach of the extension of state estimation in the classical stochastic dynamic systems with deterministic structure to the case of signal processing and parameter identification in stochastic systems with random structure or with switching parameters using the correlation-extremum methods and the theory of Markov processes provides the system operation in varying and uncertain external conditions
Studying the effects of earthquakes near and far fault region on seismic behavior of dual frame equipped with viscous damper
Get PDFThe effects of strong earthquakes in the past years show that the acceleration of near fault earthquake, for having impact motion with long periods at the beginning of the record, “exerted” have significant differences with far-fault earthquakes. Adverse effects of such earthquakes increases by approaching the main time of period of structures to period of these earthquakes. Nowadays using energy dissipation systems, in order to reduce the vibrations of the structure has been very common. Such these energy dissipation systems can be noted viscose dampers that by having hysteresis loops of fat greatly increase energy loss in buildings. In this study, the number of dual-steel frames equipped with nonlinear viscous dampers and by applying records seismic near and far fault to the frames of 4, 6, 8 and 10 floors, behavior and response of these types of frames by nonlinear analysis and in Perform 3D software is evaluated
Experimental research and numerical simulation of influence of pre-stress values on the natural vibration frequency of concrete simply supported beams
Get PDFTo study the relationship between the fundamental frequencies and pre-stress values, based on experiments and numerical simulation, the simply supported was excited under different pre-stress values through using the hammering method. The collected acceleration signals in the mid-span of the beam were processed and analyzed to obtain the relationship between the fundamental frequency and pre-stress values. As shown from the analyzed result, the relationship between the fundamental frequency and pre-stress values could not be explained better based on the traditional “Euler-Bernoulli Beam Equation” theory. The fundamental frequency of the pre-stressed beam with the hammering method would be increased with the increasing pre-stress value. When the hammering method was introduced into the numerical simulation, its analysis result and the experimental result were very approximate and presented a small error, which indicated the feasibility and accuracy of the analyzed method. When the pre-stress value was a constant, the fundamental frequency of the beam would be increased with the increasing eccentric distance of the pre-stressing tendon. When other conditions were constant, the fundamental frequency of the beam presented a decreasing trend with the counterweight at the upper part of the beam
Dynamic response prediction of non-obstructive particle damping using principles of gas-solid flows
Get PDFParticle damping is a kind of passive and strongly nonlinear damping for energy dissipation. Many researchers have expended huge amounts of effort and time to study internal mechanism of particle damping. However, there is not a systematic and feasible approach for estimating damping performance of non-obstructive particle damping (NOPD). In this paper, we performed studies to mathematically evaluate the damping effect of particle damping based on principles of gas-solid flows. In consideration of the structural characteristics of NOPD which granular materials should be filled into sealed cavity of vibrating structure and the damping act on lateral and bottom of holes in NOPD technology, the gross damping is divided into lateral damping and bottom damping by Janson's theory of stress change direction. And the damping coefficients are compiled into a plug-in by MATLAB and are invoked in FEM software by enterprise integration kits of COMSOL. Meanwhile the frequency domain and time domain analysis of the experiment are used to verify the prediction accuracy of dynamic vibration response of an aluminium cantilever beam which ONPD is imposed at the free end with different packing rate and granular material, the result indicate that the mathematical model has excellent performance to predict the dynamic vibration response of NOPD. Then, the relationship damping effect with the particle filling ratio, particle density and length-diameter ratio of the hole is also researched using co-simulation, it should be noted that larger packing rate and particle density, smaller length-diameter ratio of the hole can play excellent damping effects in NOPD
The effect of accelerometer mass in mechanomyography measurements
Get PDFMechanomyography (MMG) signals record and quantify low-frequency lateral oscillations of active skeletal muscles. These oscillations reflect the ‘‘mechanical counterpart’’ of the motor unit activity measured by electromyography (EMG). Accelerometers have been commonly used to measure MMG. However, the accelerometer mass can affect the MMG signal. The purpose of this paper was to investigate the relationship of the accelerometer mass and the MMG signal. Thirty-two normal volunteers conducted the maximum voluntary contraction of leg extension. MMG signals were obtained from the rectus femoris muscle using an accelerometer. For each subject, the accelerometer mass was varied from 3, 8, 13, 18, 23 and 28 g. The signals were measured for three seconds with a sampling rate of 1kHz. Results showed that the MMG signal amplitude increased as the accelerometer mass increased. However, the median frequency (MF) of the MMG signal decreased with the increased accelerometer mass. When the accelerometer mass increased from 8 g to 13 g, the amplitude of the MMG signal increased the most, and the MF of the MMG signal decreased the most. However, for accelerometers heavier than 13 g, no significant change was observed in both the amplitude and MF. Based on the present study, the mass of the accelerometer is recommended to not exceed 13 g to properly measure MMG signals
Cyclic testing of reinforced concrete columns with double or one-side headed shear reinforcement
Get PDFThe effectiveness of single-leg crossties that were anchored by heads in reinforced concrete columns was assessed. Seven reinforced concrete columns were tested under reversed cyclic loading with a 10 % axial load of the nominal axial capacity of the columns. Four columns were designed to fail in a flexural mode, and three columns were designed to fail in a shear mode. The main variable was the anchorage type of crossties: conventional crossties that were anchored with 135° and 90° hooks, crossties that were anchored with one-side head and one-side 180° hook, and crossties that were anchored with double heads. The test results indicate that the hysteretic behavior of the columns with crossties that were anchored by double heads or one-side head was similar or superior to the columns with conventional crossties anchored by hooks in terms of ductility and energy dissipation. After the cover concrete spalled, the 90° hooks inevitably opened and the column longitudinal bars buckled. However, the heads could delay the buckling of the column bars and the columns could maintain their capacities until 8 % drift ratio for the columns that were designed to fail in a flexural mode. For the columns that were designed to fail in a shear mode, all columns showed similar behaviors and had identical strengths. The columns with the headed crossties had smaller crack widths than the columns with conventional crossties because the headed crossties well confined the core concrete under severe shear deformation. The test results show that headed crossties can effectively confine the column bars and core concrete of the columns: therefore, the ductility and energy dissipation capacity of the columns were improved
Sliding mode control of a 2-DOF manipulator with random base vibration based on modified exponential reaching law
Get PDFTo solve the precise position control problem of a two degree of freedom (2-DOF) manipulator with random base vibration, a sliding mode control method based on modified exponential reaching law is studied. The dynamic model of manipulator is established by using the second kind Lagrange equation. The nonlinear term generated by base random vibration is presented as external disturbance term. Based on dynamic models, the sliding mode control using improved exponential reaching law is applied in the manipulator system. It is verified by the simulation result that the control method can effectively suppress the influence of base random vibration, and bring the manipulator from a given initial state to a prescribed terminal state rapidly and precisely
Vibration suppression of rotating nonlinear beam by nonlinear energy sink
Get PDFIn this paper, vibration suppression of a rotating nonlinear beam under the action of an external harmonic force is studied by a Nonlinear Energy Sink (NES). Dynamic model of the rotating nonlinear beam coupled with a NES is obtained by using quasi-Hamilton’s principle and Galerkin method. Then, harmonic balance method is used to acquire the analytic solution of the vibration amplitude of beam. In addition, the influences of rotating speed and NES parameters (mass, damping, nonlinear stiffness, and position of NES) are investigated in details
The fuzzy model of the emergency level assessment at sea
Get PDFThis paper presents the model based on a fuzzy set theory, designed to assess the level of emergency situations at sea. The model consists of three linguistic input variables and one single output. To determine the emergency level at sea, the following was taken into account: information about the dangers to human health and life (group of persons), the extent of damage to the ship and the level of environmental pollution. The paper presents the fuzzy sets corresponding to the term of these linguistic variables and their analytical and graphical representation. The fuzzy product base of fuzzy model contains 80 rules
Research model robot-hexapod under static and dynamic loads
Get PDFIn the paper the stress-strain state of hexapod robot is considered in order to clarify its dynamical characteristics. Full-size model of hexapod robot is built in the SolidWorks program complex. The state of the robot was analyzed in an extremely dangerous location at static loading. Dynamic analysis was conducted to clarify oscillation of the support unit in the robot’s construction. The results of the survey show that such robot design cannot be used in the environments with the vibrating background below 5 Hz