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Numerical simulation of herringbone gear abrasive flow machining
Get PDFThe Eulerian-Eulerian method is used to numerically simulate herringbone teeth using the precision machining technique of abrasive flow. The effects of inlet velocity and abrasive concentration factors on abrasive flow machining are investigated separately for numerical analysis to reveal the effects of dynamic pressure and wall shear on abrasive flow machining under different machining parameters. The simulation results show that increasing the inlet velocity can improve the processing efficiency and the processing effect of abrasive flow processing. Increasing the abrasive concentration increases the processing cost and predicts a weakening of the abrasive flow, allowing for the use of lower concentrations of abrasive flow for actual processing
Experimental investigation of bi-modular material coating to enhance damping
Get PDFHard coatings can be used to increase damping when applied on the surface of the components of turbomachinery. This can be effective to reduce the resonant vibration level of components working in a high cycle fatigue environment due to the extremely high operational speed. This paper discusses the experimental investigation of a bi-modular material hard coating to enhance damping in structural steel elements. Firstly, a hard coating (Al2O3+MgO) is applied on AISI 304L stainless steel substrate by plasma spraying. After that, a layer of chrome is deposited by chrome plating. Dynamic responses of both coated and uncoated samples are measured. The damping ratio of the test specimen is extracted from the time response by the logarithmic decrement method. Improved damping capacity of the coated steel sample is observed and is mainly attributed to the thin coating of chrome on the steel structure. The natural frequency of coated specimen showed 8 to 10 % improvement, the forced response showed a 30 to 35 % decrement in displacement, the damping ratio showed a 200 % increment, and the time of decaying showed a 20 % decrement. The results of the present study provide new ideas for the development of high-damping structural elements
Simulation test of transformer short-circuit impedance based on equivalent model at different frequencies
Get PDFA distribution transformer is one of the most important equipments in the power grid, and its operational status is directly related to the security and stability of the entire power system. The performance of transformer windings determines the service life of the transformer. It is of great significance to evaluate the performance of transformer windings accurately, reliably, and effectively after the short-circuit test of the transformer. Aiming at the problem that the natural vibration frequency of the transformer measured before and after the short circuit may not be the same under the impact of the short circuit of the transformer, this paper puts forward the evaluation method for the performance evaluation of the winding of the transformer after the short circuit test and adopts the method of combining the analytic hierarchy process with the fuzzy evaluation method to quantitatively obtain the score for the performance evaluation of the winding. And that evaluation language is given according to the score. Finally, the evaluation of the transformer winding performance after the short-circuit test is realized. The evaluation results show that this method can effectively get the performance index of the transformer winding, without the need for hanging cover inspection, and solve the subjectivity of human eye observation to objectively, accurately, and quantitatively describe the performance state of the transformer winding. The method is favorable for power grid monitoring and maintenance personnel to accurately evaluate the operation stability of the transformer and has very positive significance for improving the short-circuit impact resistance of the transformer and ensuring the safety and stability of the operation of a power system
The importance of a realistic leakage evaluation to support public awareness and acceptance for carbon capture and storage
Get PDFCarbon Capture and Storage is not only highly recommended by the IPCC as a mechanism to significantly lower carbon emissions to the atmosphere, it is now also gaining traction in terms of large-scale implementation. Its importance is increasing in many parts of the world to directly decrease emissions from industrial sources, but also to lower the carbon footprint of blue hydrogen production. With most CCS projects being planned for offshore locations, public acceptance is less of a determining factor than it used to be 10-20 years ago, where discussions were rather for onshore locations. CO2 leakage has always been a risk highlighted in the public debate, while no or minimal leakage has been reported for current CCS projects worldwide. However, as scientific community, we need to realistically highlight the risk of leakage across sealing units for CO2 stored to inform various stakeholders like regulators, the public and of course also operating companies. Caprock leakage needs to be studied across various length and time scales, considering the undisturbed matrix as well as fracture networks and faults; we need to consider advective and diffusive flow and transport and incorporate mineral alterations, potentially leading to changes in hydraulic or mechanical properties. This talk will highlight the current state of research, advancements and future research required for a realistic evaluation of caprock leakage. It will be based on past research related to matrix transport as well as current research focusing on single and multiphase flow along faults and fractures
Study on vibration characteristics of ship mining system under composite load
Get PDFThe load that borne by ship mining system is very complex. The vibration of lifting pipe can be significantly affected by ocean current and wind load, which has a key impact on material lifting, ore bin storage and ship towing. Considering the composite load condition, the vibration control equation of mining ship is established based on the transverse swing mechanism of ship hull, and the variation law of transverse disturbance is obtained. The dynamic equation is constructed according to the bearing characteristics of the lifting system and the D’Alembert principle. The Wilson method is used to analyze and obtain the transverse vibration spectrum response of the lifting pipe under different wind loads, hull disturbance velocity and water depth. Based on the analogy method and hammering method, the vibration feedback test-bed of the lifting system is built, and the time-domain and frequency-domain vibration characteristics of the lifting pipe model under different water depths are obtained. The results show that in shallow water, the disturbance of mining ship and the composite load of ocean current are the key factors affecting the vibration amplitude of lifting pipe respectively. With the increase of water depth, the characteristic frequency and amplitude of the system decrease, and the amplitude gradually presents a discontinuous phenomenon
Experimental study of the lap motion trajectory of vibratory finishing machine
Get PDFVibratory equipment is widely used for performing various finishing processes, machining and forcing of different parts and materials. Numerous researchers and technologists pay specific attention to the possibilities of implementing vibration-driven machinery for conducting the lapping and polishing operations on flat surfaces. The present paper is dedicated to studying the laps kinematic parameters of the vibratory finishing machine actuated by six electromagnets. The paper’s scientific novelty consists in the experimental verification of the previously modelled and simulated circular trajectories of the laps under different operational conditions. The methodology of research contains two basic stages: changing the excitation frequency at the constant traction force and changing the traction force at the constant excitation frequency. The improved 3D-design of the vibratory finishing machine was developed in the SolidWorks software. The experimental prototype was implemented in practice, and full-scale tests were carried out using the WitMotion sensors and software. Based on the obtained experimental data, the trajectories of the machine’s laps were constructed and analyzed in the MathCad software. The research results substantiate the possibilities of providing circular oscillations of the laps at different operational conditions. The results can be used by technologists and engineers while choosing the appropriate design and control parameters for similar vibratory equipment intended for lapping and polishing of flat surfaces
Research on online monitoring and early warning system of transmission line galloping based on multi-source data
Get PDFWhen the conductor is covered with ice on a non-circular section, and there is low-frequency, large-amplitude motion under wind excitation, it is usually called the transmission line galloping phenomenon. Due to the large amplitude, the galloping of the transmission line will lead to line fatigue, increase in tension, damage to hardware, or toppling of towers. In addition, it will also lead to flashover, tripping, and other transmission accidents caused by the short phase distance, which is not conducive to the safe operation of power grids. In order to improve the safety of power grid operation, this paper designed an online monitoring and early warning system for transmission line galloping on the basis of multi-source data and verified the system through implementation. It was found that the safety factor was 1.568, which determines its early warning level and affirms the feasibility of this study. This research has a positive role in improving the safe operation of the power grid
Solitons in a cold electron beam plasma
Get PDFNecessary and sufficient conditions for the existence of dissipative electron-acoustic solitons in a cold electron beam plasma with superthermal trapped electrons described by the Schamel equation are derived in this paper. Soliton solutions to the Schamel equation are constructed using formal analytical techniques which yield counter-intuitive conditions for the existence of these solutions. The existence conditions are derived in terms of system parameters and initial conditions. Computational experiments are used to validate the obtained results
Analysis and optimization of seismic performance of high-rise residential building
Get PDFIn order to improve the seismic performance of high-rise buildings, a friction damper installation scheme was proposed in the paper. Through numerical simulation and experimental testing, the vibration reduction effect was compared and verified. Herringbone structure was applied to install friction damper in the bearing wall. Based on this vibration reduction scheme, the finite element model of high-rise building was established, and the influence of damper on the modal characteristics of building frame was analyzed. It can be known that the damper has little influence on the natural frequency, but has a great influence on the amplitude range of the excitation response. In the finite element model, two kinds of seismic waves were applied, the strength and dynamic response was simulated and calculated, and the maximum deformation and stress results were obtained. Compared with the initial model, it can be known that the more intense the vibration is, the more obvious the damping effect of the damper is. A seismic excitation simulation system based on acceleration sensor detection is designed and applied to the wall vibration test. The results show that the maximum vibration acceleration of the measured point is reduced by 26.3 % by the damper, and the stable seismic effect can still be maintained during the impact of extension. Compared with the traditional hardness and volume reinforcement scheme, the friction damper can reduce the production cost and improve the adaptability to seismic wave excitation, which provides an important basis for seismic research in other fields
Handheld Micro tiller time-frequency characteristic and vibration isolation measures
Get PDFThe handheld micro tiller is a typical small agricultural machine. It vibrates severely during the rotary tillage process, which harms the users’ health. It is necessary to study its vibration characteristics and propose vibration isolation measurements. Firstly, the external forces applied on various components of the micro-tiller were analyzed. The main components of the handheld micro tiller were simplified. And then the micro-tiller vibration model was built. The time-frequency domain characteristics of the micro-tiller were analyzed. The main components’ RMS values were calculated. It shows that the excitation force of the engine is the main source of vibration of the micro-tiller. The simulated RMS values of the frame and the gearbox were compared to the tested values. The errors indicate the established model is to some extent reasonable. In order to reduce the vibration transmitted to the handrail, firstly, the ordinary bolts connecting the engine and the frame were replaced with rubber bolts. And then the RMS value was analyzed and calculated. The results showed that this method could not effectively reduce the vibration of other main components. Furthermore, it is considered to install a vibration isolator between the engine and the frame of the tiller. Time-frequency domain simulation results show that after adding the vibration isolator, the vibration RMS value of each component was much smaller than before. It shows that it isolates the engine vibration effectively. The research in this paper laid the foundation for designing a reasonable vibration isolator and reducing the vibration of the main components of the tiller