Investigation on Unsteady Cavitation Flow and Excited Pressure Fluctuations in Regulating Valve

A multi-field synchronous measurement system for the cavitation flow in a regulating valve was established. The system combines a high-speed full-flow field display system with a pressure measurement system to realize the simultaneous acquisition of cavitation shapes and pressure pulsations. Cavitation flow occurs near the throttle orifice, which is obviously a quasi-periodic behavior. The unsteady cavitation flow mainly includes three stages: the growth of the attached cavity, the fracture and shedding of the attached cavity and the growth and collapse of the free cavity. The time evolution of the cavitation behaviors is highly related with excited pressure fluctuations. With the increasing attached cavity area, the corresponding pressure in the flow field decreases slowly. When the attached cavity falls off and develops downstream, the cavity area decreases gradually, and the pressure increases gradually. When the free cavity shrinks and collapses, the pressure in the flow field reaches the peak value. The pressure pulsation and the change of cavity area have the same dominant frequency, around 2000 Hz, at the monitoring point in the upstream, throat and expansion monitoring points. Furthermore, with increasing inlet pressure, the mean and variance values of cavitation area become larger, and the excited pressure fluctuation at each measuring point becomes more intense. The mean value of pulsating pressure at the throat gradually increases, while the pressure in the expansion section presents a downward trend. The variance of pressure pulsation and the maximum pressure also increase gradually with the increase in inlet pressure. The change of cavitation area and the pressure pulsation in the regulating valve complement each other. The results in this paper could provide experimental guidance on optimizing the structure of the valve, inhibiting cavitation occurrence and prolonging the service life of the valve.

Study on Seismic Performance of UHV Transformer Based on Soil-structure Interaction

At present, the seismic performance of UHV transformers is mostly studied without considering the interaction between soil and superstructure. In practical engineering, the transformer is installed on the foundation slab buried in the soil. Under the action of earthquake, the interaction between the soil and the structure changes the earthquake response of the upper electrical structure. In order to study the influence of the interaction between soil and structure on the seismic performance of the transformer, the shaking table test method of simulated earthquake is used, and the shaking table test of UHV transformer with scale ratio of 1:4 is carried out in class I field conditions. The dynamic characteristics of the equipment and the seismic response of the bushing under different test conditions are obtained respectively. The test results show that when the peak acceleration is 1.2g, the acceleration response at each measuring point on the box is 1.63-1.92 times that when the peak acceleration is 0.4g. With the increase of seismic peak acceleration, the acceleration and strain increase of high voltage bushing are greater than that of medium and low voltage bushing, which has a great influence on the seismic response of high voltage bushing. The research conclusion can provide reference for substation engineering design.

Analysis of the Influence of Transmission Housing Elasticity on the Vibration Characteristics of Gear Shafting under Coupling Effect

The influences of transmission housing elastic deformations on the vibration gear shafting characteristics are studied. The vibration model of the vehicle transmission system in consideration of the dynamics coupling of the housing and the gear shafting is constructed. Aiming at a vehicle transmission, the mathematical model of the bending and torsional gear shafting vibrations is established based on the lumped mass method. Following the elastic treatment of the box, a comprehensive stiffness model at the bearing considering the housing deformation is proposed to achieve the dynamic coupling between the box and the gear shafting system. Furthermore, the gear shafting vibration characteristics considering housing deformations are obtained by integrating multisource dynamic excitation, which is solved using an iterative method. The results are verified through a bench test. And, it shows that the elastic deformation of the housing aggravates the gear shafting vibration (bending and torsional coupled vibration). The peak frequency mostly remains the same. The maximum speed changes amplitude and associated root mean square value (calculated at the gear position) increase by 55.5% and 59.6%, respectively. Next, the maximum bearing support force and its root mean square value are increased by 63.7% and 97.6%, respectively. Finally, the largest increase in maximum vibration acceleration at the measuring point and the simulated root mean square value are 90% and 63.1%, respectively. It is concluded that the research results provide a theoretical basis for the study of transmission dynamic reliability.

Curvature Detection with an Optoelectronic Measurement System Using a Self-Made Calibration Profile

So far, no studies of material deformations (e.g., bending of sports equipment) have been performed to measure the curvature (w″) using an optoelectronic measurement system OMS. To test the accuracy of the w″ measurement with an OMS (Qualisys), a calibration profile which allowed to: (i) differentiates between three w″ (0.13˙ m−1, 0.2 m−1, and 0.4 m−1) and (ii) to explore the influence of the chosen infrared marker distances (50 mm, 110 mm, and 170 mm) was used. The profile was moved three-dimensional at three different mean velocities (vzero = 0 ms−1, vslow = 0.2 ms−1, vfast = 0.4 ms−1) by an industrial robot. For the accuracy assessment, the average difference between the known w″ of the calibration profile and the detected w″ from the OMS system, the associated standard deviation (SD) and the measuring point with the largest difference compared to the defined w″ (=maximum error) were calculated. It was demonstrated that no valid w″ can be measured at marker distances of 50 mm and only to a limited extent at 110 mm. For the 170 mm marker distance, the average difference (±SD) between defined and detected w″ was less than 1.1 ± 0.1 mm−1 in the static and not greater than −3.8 ± 13.1 mm−1 in the dynamic situations. The maximum error in the static situation was small (4.0 mm−1), while in the dynamic situations there were single interfering peaks causing the maximum error to be larger (−30.2 mm−1 at a known w″ of 0.4 m−1). However, the Qualisys system measures sufficiently accurately to detect curvatures up to 0.13˙ m−1 at a marker distance of 170 mm, but signal fluctuations due to marker overlapping can occur depending on the direction of movement of the robot arm, which have to be taken into account.

Comparison of Static Model, Adaptation Study, and CFD Simulation in Evaluating Thermal Comfort Based on Köppen Climate Classification System in Churches in Indonesia

This research examined thermal comfort in church buildings in Indonesia by making a comparison between three different Indonesian climatic regions using three different research models. A static model, an adaptation study model and a CFD simulation were used to find the similarities and differences between the results generated from determining thermal comfort in church buildings in the three regions. The comparison revealed that church buildings had different PMV scores at each measuring point that were inversely proportional to the subjects’ response on thermal comfort inside the buildings, i.e. points adjoining with openings affect a low PMV score and a high perceived thermal sensation, and vice versa. The CFD simulation showed that changing the conditions of the openings affects air velocity and flow into the building, which influences the subjects’ thermal comfort response inside the churches.

Real-time evaluation method of turbine rotor’s thermal stress with governing stage partial admission condition at low-load

In order to ensure the safety and stability of the new energy power system, many power units will be maintained at low-load state for a long time during peak-load regulation in China. However, the partial arc admission of the nozzle governing mode will cause uneven temperature distribution in the circumferential direction after GS, which will affect real-time thermal stress of the rotor. Toward this end, this paper proposes a real-time evaluation method of thermal stress for rotors in low-load conditions. First of all, the solution boundary conditions of thermal stress model can be obtained by designing the measuring points arrangement after GS, which comprehensively takes into account the uneven temperature distribution of GS under low-load conditions. In the meantime, various punching schemes are analyzed by ANSYS, which used to analyze the influence of cylinder structure strength caused by the new measuring point punching of each scheme. The result shows that the punching impact on the stress and deformation of cylinder is not obvious, which has a great significance to reduce minimum technical output and improve peak governing capability of thermal power unit.

Operation analysis of C3-MR process cold box by grey system theory

In this paper, the problems of high refrigerant line differential pressure and uneven distribution of cold energy in cold box regulation under C3-MR process are studied. Five reasons are predicted by engineering performance. Using gas chromatography experiment and grey system pure mathematics analysis, it is determined that the main causes of the problem are unreasonable distribution ratio of each group of mixed refrigerants and disordered latent heat of vaporization of refrigerants. Furthermore, the grey system model is used to study: 1. grey relation analysis model shows that the correlation degree of T3 temperature measuring point is 0.8552, which is the only main factor. The abnormal working condition is determined by the project to be caused by incorrect proportion of N2 components. 2. According to GM(1,N) model, the driving term of T3 temperature measuring point is 3.8304, which needs to be supplemented with N2 component to eliminate the problem. 3. After adding N2 to 10% (mol component), abnormal working conditions disappeared. The GM(1,N) model is used again to verify that the difference of driving results is small, the average relative error is 24.91%, and the accuracy of the model is in compliance.

Experimental Investigation on the Influence of Ambient Temperature on the Test Accuracy for the Differential Pressure Hydrostatic Levelling System

Hydrostatic levelling system (HLS) is widely used to monitor the settlement of major projects, such as high-speed railways, bridges, tunnels, dams, and nuclear power plants; ambient temperature is the most important influencing factor in the actual engineering settlement detection process. In order to systematically study the influence of ambient temperature TA on the test accuracy of the HLS, a test platform was built in the ambient temperature laboratory, and the influence of factors, including the amount of TA change, the rate of increase/decrease of TA, the expansion coefficient of the connecting pipe, and the distance of the measuring point, on the HLS test accuracy was quantitatively analyzed. The test results show that the elevation of a single HSL case has a linear correlation with the ambient temperature; when the temperature rise rate is greater than 0.1°C/min, the measured data are distorted due to incomplete development of material expansion. The temperature influence coefficient of a single HSL case is linearly related to the expansion coefficient deviation between the refrigerant and pipe; the test error of the double HLS case caused by TA is attributed to the expansion coefficient deviation of the pipe and the refrigerant between the base station and the measuring point. The relative temperature influence coefficient increases as distance measurement increases, and the HLS test error caused by TA will maintain a constant value when the distance measurement exceeds a certain value.

Improving CPT-InSAR Algorithm with Adaptive Coherent Distributed Pixels Selection

The Coherent Pixels Technique Interferometry Synthetic Aperture Radar (CPT-InSAR) method of inverting surface deformation parameters by using high-quality measuring points possesses the flaw inducing sparse measuring points in non-urban areas. In this paper, we propose the Adaptive Coherent Distributed Pixel InSAR (ACDP-InSAR) method, which is an adaptive method used to extract Distributed Scattering Pixel (DSP) based on statistically homogeneous pixel (SHP) cluster tests and improves the phase quality of DSP through phase optimization, which cooperates with Coherent Pixel (CP) for the retrieval of ground surface deformation parameters. For a region with sparse CPs, DSPs and its SHPs are detected by double-layer windows in two steps, i.e., multilook windows and spatial filtering windows, respectively. After counting the pixel number of maximum SHP cluster (MSHPC) in the multilook window based on the Anderson–Darling (AD) test and filtering out unsuitable pixels, the candidate DSPs are selected. For the filtering window, the SHPs of MSHPC’ pixels within the new window, which is different compared with multilook windows, were detected, and the SHPs of DSPs were obtained, which were used for coherent estimation. In phase-linking, the results of Eigen decomposition-based Maximum likelihood estimator of Interferometric phase (EMI) results are used as the initial values of the phase triangle algorithm (PTA) for the purpose of phase estimation (hereafter called as PTA-EMI). The DSPs and estimated phase are then combined with CPs in order to retrievesurface deformation parameters. The method was validated by two cases. The results show that the density of measuring points increased approximately 6–10 times compared with CPT-InSAR, and the quality of the interferometric phase significantly improved after phase optimization. It was demonstrated that the method is effective in increasing measuring point density and improving phase quality, which increases significantly the detectability of the low coherence region. Compared with the Distributed Scatterer InSAR (DS-InSAR) technique, ACDP-InSAR possesses faster processing speed at the cost of resolution loss, which is crucial for Earth surface movement monitoring at large spatial scales.