Journal of Vibroengineering
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Secondary frequency regulation scheme based on improved virtual synchronous generator in an islanded microgrid
Get PDFTo aim at the defects of the traditional VSG (virtual synchronous generator) control schemes to only complete the primary frequency regulation equivalent to droop control, and not to realize the secondary frequency regulation, this paper proposes a new control scheme to realize the secondary frequency regulation of the VSG, such that system frequency can return to the rated value. In this method, the torque change process of the rotor of synchronous generator is firstly analyzed when the system active power fluctuates. And then, a novel secondary frequency regulation control strategy of the VSG is proposed, where the small-signal model of power transmission of the VSG is established and transfer function is analyzed, and parameters design and stability analysis of the control system are conducted. Finally, simulation experiments show the correctness and effectiveness of the proposed method
Hybrid spectral speed determination method for rotary machines
Get PDFAccurate rotational speed determination for rotary machines tends to be allocated high priority in technical applications. In some cases, it is not easy to measure shaft speed directly. Vibration diagnostic tools can offer an alternative solution to the problem posed by direct rotational speed measurement. Using calculated spectra and cepstra can help to determine the rotational speed easily and accurately. This paper examines the comparison of the spectrum and cepstrum based methods in terms of their applicable ranges and rotational speed estimation accuracy. Most papers which present similar comparisons state that the speed of rotary machines can be determined better with cepstrum calculation. However, this argument does not entirely stand up to scrutiny. This paper explains how to calculate the possible speed estimation error which arises out of the resolution of the discrete output data produced by the methodologies. The novel hybrid speed estimation logic uses these equations to decide which method results in the most accurate output. Numerous vibration measurements were made to test the usability of this hybrid method. It was successfully tested on electromotive drive trains, as well as spark- and compression-ignition internal combustion engines with different cylinder numbers and arrangements
Dynamic simulation analysis of elastic overpressure fluctuation on silo wall for the arch action
Get PDFIn this research, the concept of elastic overpressure fluctuation is introduced on the basis of the overpressure theory in the arch action, the formation of overpressure in the arch action is investigated with the elastic fluctuation on the silo wall. The formation and elastic fluctuation of overpressure in arch action is analyzed systematically with the laboratory experiment and the PFC simulation which were established on the basic of a project example, the models achieve the arch action by changing factors such as the physical parameters of grain and cone half angle of the silo hopper. The results obtained indicate that the increment of pressure and the overpressure coefficient all decrease with height. And the overpressure started from the arch feet, propagated upward in the form of fluctuation on the silo wall. In addition, the overpressure fluctuations propagate uniformly which is illustrated by observing the time step of when the pressure fluctuations amplitude occur at each monitoring points. The results reveal the formation mechanism of the overpressure in arching, and the relevant research conclusions would be of great reference significance for the design of silo
Analyses on deformation and fracture evolution of zonal disintegration during axial overloading in 3D geomechanical model tests
Get PDFTo investigate the formation of zonal disintegration phenomenon in deep rock mass under high axial geostress, 3D geomechanical model tests for two rock strengths are carried out via capacity of deep rock breakage mechanics and supporting technique model test. Considering the maximum principal stress along the tunnel axis, 3D geomechanical model tests are carried out in a loading procedure of first loading to initial geostress, then excavating the tunnel with blasting construction, and finally overloading the stress along the tunnel. Due to unloading effect, radial strain is tensile and tangential strain is compressive around excavated tunnel after excavation complete, which indicates a radial tension and circumferential compression stress state. With continuous overloading of axial stress, values of both radial tensile strain and tangential compressive strain increase, then ring fracture appears due to large radial tensile strain. After axial overloading, an interval distribution of peaks and troughs is shown in radial tensile strain distribution around excavated tunnel, which indicates a formation of zonal disintegration. By cutting the rectangular cemented sand model, a distinct zonal disintegration phenomenon emerges, and an apparent shrinkage of excavated tunnel is also shown due to radial deformation towards excavated tunnel. The larger the rock strength is, the less the tunnel shrinkage is, the smaller the radius of fracture zone. After statistical analyses of three ring tensile fracture zones, the radius scale factor of fracture zone in zonal disintegration is about 1.28
Experimental study on dynamic deformation properties of muck soil under low frequency cyclic loading
Get PDFA series of dynamic triaxial tests were performed to investigate the dynamic deformation properties of the muck soil, in the Pearl River Delta region of Shenzhen, China, under different consolidation ratios, loading frequencies and cyclic stress with SPAX-2000 triaxial testing system. The results showed that the initial stress-strain hysteresis curve of the muck soil under the low-frequency cyclic loading developed rapidly and the curve shape changes from sparse to tight and to slightly sparse. The cumulative plastic strain of muck soil increased nonlinearly with the dynamic stress amplitude, and there was a critical dynamic stress. As the dynamic stress amplitude reached its critical value, the strain increased sharply and the soil microstructure was destroyed. There was a frequency threshold between 0.25 Hz and 0.5 Hz, and the cumulative plastic strain development mode was from stable model to over-destructive model. The stiffness of the muck decreased gradually, and the plastic deformation increased as the number of cycles increased. Therefore, the lower the loading frequency developed, the greater the plastic deformation would be. The dynamic elastic modulus decreased as the plastic deformation increased, while the dynamic elastic modulus increased as the consolidation stress increased. Moreover, the empirical formulas of dynamic elastic modulus and plastic strain index were established with the consolidation stress ratio as the parameter, and the validity was verified by experimental data
Dynamical analysis of wind turbine blades based on harmonic response
Get PDFAs the forces applied on the wind turbine blade are irregular, the deformation and concentrated stress of the blade may vary with the load and excitation. And the lamination of composite materials is critical to blade design, it directly affects the performance and power of wind power plants. In this paper, the response characteristics of the wind turbine blade is analyzed by the application of the harmonic response method under different ply angles. Through the simulation results, the performance of the actual blade is estimated, and the rationality of this design is judged. The results demonstrate that the blade displacement response amplitude is the minimum when ply angle is 45°. It is also found that the maximum displacement response occurs in the Y direction (i.e. parallel to the flow direction) by analyzing the displacement of each section in the blade, while the maximum stress is located at blade root
Numerical simulation of vehicle movement on rigid roadway pavement with discontinuities
Get PDFA numerical simulation of a moving vehicle on the rigid roadway pavement with discontinuities is presented in this paper by using the data from one of the toll road segments in Indonesia. The analysis procedure considers the dynamic interaction between the vehicle and the rigid pavement. The rigid roadway pavement is modeled using the Kirchhoff theory of thin slab on elastic foundations. The aim of the numerical analysis is to obtain the vertical deflection in the middle of the slab, to obtain the time history of the slab deflection; and to identify the parameters of the sub-grade that has a significant effect on the dynamic response of the rigid roadway pavement. The equations of motion are derived in the form of partial differential equations of the fourth order. The mode shapes of the slab deflection are determined from the method of first and the second auxiliary equations of Levy-type in the x- and y-directions, which is also known as the Modified Bolotin Method (MBM). The equations of motion are solved numerically by using Mathematica. The influence of various parameters including the peak vertical velocity due to the moving vehicle, the stiffness of subgrade, the slab thickness and the road profile to the dynamic behavior of the rigid roadway pavement are studied in detail. The results obtained from the plate computing model in this paper are then compared and analyzed with the results computed using the finite element method by Strand 7 to show that the solution obtained using the MBM method is accurate. In addition, the paper aims to show that the thickness of the plate plays a significant role in the distribution of the bending stresses in plate discontinuities and is necessary for engineers to design rigid roadway pavements
Fault diagnosis method for energy storage mechanism of high voltage circuit breaker based on CNN characteristic matrix constructed by sound-vibration signal
Get PDFAiming at the problem that some traditional high voltage circuit breaker fault diagnosis methods were over-dependent on subjective experience, the accuracy was not very high and the generalization ability was poor, a fault diagnosis method for energy storage mechanism of high voltage circuit breaker, which based on Convolutional Neural Network (CNN) characteristic matrix constructed by sound-vibration signal ,was proposed. In this paper, firstly, the morphological filtering was used for background noise cancellation of sound signal, and the time scale alignment method based on kurtosis and envelope similarity were proposed to ensure the synchronism of the sound-vibration signal. Secondly, the Pearson correlation coefficient was used to construct two-dimensional image characteristic matrix for the expanded sound-vibration signal. Finally, the characteristic matrix was trained by utilizing CNN. Local Response Normalization (LRN) and core function decorrelation were utilized to improve the structure of CNN model, which reduced the bad impact of large data fluctuation of energy storage process on the diagnostic accuracy of circuit breaker energy storage mechanism. Compared with the traditional method, the proposed method has obvious advantages, whose total accurate rate up to 98.2 % and generalization performance is excellent
Influence of ultrasonic vibration on discrete media filled tubes during forward extrusion
Get PDFThe coupled deformation of composite structures of discrete media filled thin-walled tubes under the action of forces is a complicate mechanical process, especially when it is superimposed with external vibration. A Jenike shear cell connected with an ultrasonic exciting system was used to test the friction angles of the aggregations of ferric powder and steel ball under quasi-static and high frequency vibration conditions; then forward extrusion of Al6061 tubes filled with these discrete materials under different conditions were examined by experiment and numerical simulation. The results showed that the friction angles of both the discrete materials decreased under vibration, and those of the powders were reduced more, indicating that the “surface effect” of vibration on the particles with smaller granularity is more obvious. Under the combining action of “volume” and “surface” effects of vibration, the extrusion loads of the structures significantly decrease with the superposition of vibration, meanwhile the loads of the tubes filled with powders reduced more. With the imposed vibration, the density of fillers after forming are higher and the tube wall thickness distribution is more uniform
Selection of ground motion prediction equations for probabilistic seismic hazard analysis based on an improved fuzzy logic
Get PDFThe fuzzy logic method has been used widely in civil and earthquake engineering, but there is no comprehensive point of view for utilizing fuzzy approach in order to obtain ground motion prediction equations (GMPEs) for probabilistic seismic hazard analysis (PSHA). Hence, fuzzy magnitude–distance method as a new approach for choosing GMPEs in the process of PSHA, is developed in this research through the selection of the ruling peak ground acceleration (PGA) of each common cell (the combined cell of earthquake intensity and site to source distance). The presented method reduces the need for engineering judgments in seismic analysis based on a newly developed benchmark. It enables designers to not only determine the range of acceptable fuzzy results but also introduces a concept which ensures the selection of initial well-suited GMPEs for the analysis