The picture presents a liquid metal soft pump induced by alternating electric field. When applying AC signal on a pair of electrodes positioned at two sides of the liquid metal droplet which is immersed in a closed channel filled with alkaline solution, violent surface flow of the liquid metal droplet was actuated. It then induced circular flow of the electrolyte and thus the pumping effect. The power consumption of such liquid metal pump is extremely small, say about dozens of milli-watt. This pump is straightforward to fabricate and its pumping performance can be easily controlled even programmable. Further, some fundamental phenomena were also revealed, including re ...
Two-dimensional numerical manifold method with multilayer covers Hot!
In order to reach the best numerical properties with the numerical manifold method (NMM), uniform finite element meshes are always favorite while constructing mathematical covers, where all the elements are congruent. In the presence of steep gradients or strong singularities, in principle, the locally-defined special functions can be added into the NMM space by means of the partition of unity, but they are not available to those complex problems with heterogeneity or nonlinearity, necessitating local refinement on uniform meshes. This is believed to be one of the most important open issues in NMM. In this study multilayer covers are proposed to solve this issue. In addition to the first layer cover which is the global cover and covers the whole problem domain, the second and higher layer covers with smaller elements, called local covers, are used to cover those local regions with steep gradients or strong singularities. The global cover and the local covers have their own partition of unity, and they all participate in the approximation to the solution. Being advantageous over the existing procedures, the proposed approach is easy to deal with any arbitrary-layer hanging nodes with no need to construct super-elements with variable number of edge nodes or introduce the Lagrange multipliers to enforce the continuity between small and big elements. With no limitation to cover layers, meanwhile, the creation of an even error distribution over the whole problem domain is significantly facilitated. Some typical examples with steep gradients or strong singularities are analyzed to demonstrate the capacity of the proposed approach.
Numerical simulation of the separation between concrete face slabs and cushion layer of Zipingpu dam during the Wenchuan earthquake Hot!
The Zipingpu concrete-faced rockfill dam (CFRD) experienced strong ground motion from the 2008 Wenchuan earthquake. Separation between concrete face slabs and the cushion layer was observed after the earthquake. The separation voids under the stage III slabs make up 55% of the total area of the stage III slabs. The observed maximum height of the separation voids was nearly 23 cm at the top of the stage III slabs. Separation voids were also observed locally below the top of stage II slabs near the left abutment, with a maximum height of 7 cm. In this study, a static and dynamic elasto-plastic finite element analysis on Zipingpu CFRD was conducted to capture the separation during the Wenchuan earthquake. The rockfill materials were described using a state-dependent elasto-plastic model that considered particle breakage. The model parameters of rockfill materials were obtained from feedback analysis. The numerical results were largely consistent with the field measurements during construction and after the Wenchuan earthquake. A three-dimensional state-dependent elasto-plastic model that can trace the separation and re-contact of a soil-structure interface was employed to investigate the interaction between concrete face slabs and a cushion layer. The analysis showed the distribution of separation voids observed in the Zipingpu CFRD has a close relationship to the water level and slab dislocations at the time of the earthquake. The phenomenon of the separation from the Wenchuan earthquake was successfully captured by the proposed numerical procedure.
Statistical analysis of one Chinese sun-synchronous satellite anomalies Hot!
Based on the data from the Medium-Energy Proton and Electron Detector (MEPED) onboard NOAA-17, 141 anomalies of a Chinese Sun-Synchronous satellite (SSO-X) that occurred between 02/01/2010 and 09/31/2012 were studied statistically. About 26 out of the 52 anomalies that occurred outside the South Atlantic Anomaly (SAA) were accompanied by energetic electron storms. Superposed Epoch Analysis (SEA) was used to analyze the properties of the anomalies and the dynamics of the space environments during these 26 events. Then, a Monte Carlo method was utilized to simulate the electron deposition and the interactions of the injected electrons with an aluminum shield and polyethylene dielectric. The average, median, and 75th percentile values of the maximum electric field strength inside the dielectric were calculated. The results showed the following. (1) SSO-X anomalies are more likely to occur within the SAA, as 89 out of 141 anomalies (63%) occurred there. (2) Twenty-six of the anomalies that occurred outside the SAA during energetic electron storms were located near the outer boundaries of the outer radiation belts, and these were more frequent in the Southern Hemisphere than in the Northern Hemisphere. (3) Electron flux enhancements occurred around the failure time at all energy levels but were more profound in the lower energy channels. The maximum fluxes of electrons >30 keV, >100 keV, and >300 keV were 106, 3.5×105, and 1.2×106 cm-2 s-1 sr-1, respectively. (4) The average, median, and 75th percentile values of the maximum electric field strengths inside the dielectric for the aforementioned 26 events remained in the range from 106 to 107 V/m for long time periods, which suggests that the ‘potential hazards’ of internal discharges cause SSO-X anomalies. The above results can provide useful information for the design and protection of sun-synchronous spacecraft.
Quasi-periodic variations of low energy cosmic rays
Cosmic rays (CR) play an important role in space weather-related studies. Their temporal variability, both of a quasi-periodic character as well as an irregular one, has been studied from ground-based direct measurements, as well as from cosmogenic nuclides, over a long time. We attempt to describe the current knowledge of selected quasi-periodicities in CR flux in the energy range above the atmospheric threshold, from direct measurements. The power spectrum density (PSD) of the CR time series as measured by neutron monitors (NMs) and by muon detectors has a rather complicated character. Along with the shape (slope) of the PSD, knowledge of the contribution of quasi-periodic variations (q-per) to the CR signal is of importance for the modulation, as well as for checking the links of CR to space weather, and/or to space climate effects. The rotation of the Earth and solar rotation cause two types of mechanisms behind the certain q-per observed in secondary CR on the Earth's surface. Solar activity and solar magnetic field cyclicities contribute to the q-per signals in CR if studied over a longer time. The complexity of the spatial structure of the interplanetary magnetic field (IMF) and its evolution within the heliosphere, in addition to the changes in the geomagnetic field, cause variability in contributions of the q-per in CR. Wavelet spectra are useful tools for checking the fine structure of q-per and their temporal behaviour. Over a long time NMs and muon telescopes provide information about q-per in CR.
New high-accuracy spacecraft VLBI tracking using high data-rate signal: A demonstration with Chang'E-3
As the scientific data volume in deep-space exploration rapidly grows, spacecraft heavily relies on high data-rate signals that span several megahertz to transmit data back to Earth. Employing high data-rate signals for high-accuracy radiometric interferometry can simultaneously deal with data transmission and spacecraft navigation. We demonstrate very long baseline interferometry (VLBI) tracking of the Chang'E-3 lander and rover to determine their relative lunar-surface position using downlink high data-rate signals. A new method based on the VLBI phase-referencing technique is proposed to obtain the differential phase delay, which is much more accurate than the differential group delay acquired by conventional VLBI approaches. The systemic errors among different signal channels have been well calibrated using the new method. The data from the Chang'E-3 mission were then processed, and meter-level accuracy positions of the rover with respect to the lander have been obtained. This demonstration shows the feasibility of high-accuracy radiometric interferometry using high data-rate signals. The method proposed in this paper can also be applied to future deep-space navigation.
A new type of leak-floor flip bucket
Flip buckets are commonly used to discharge flow away from a hydraulic structure into the downstream to dissipate energy. A new leak-floor flip bucket is presented, making the ski-jump water jet a typical long-narrow nappe. Based on the model experiments and numerical simulation, the flow pattern, formation process and mechanism of the leak-floor flip bucket are studied. The results show that cross section flow shape develops from the "Y-type" to "|-type", and this is because the natural pressure difference is generated when water flows through the leak-floor area and moves transversely from both sides to the center. Different from the slit-type flip bucket with sidewall contraction, the leak-floor flit bucket makes the water jet narrow and long without high pressure on the side walls of the flip bucket. Under the same jet length condition, the maximum sidewall pressure of the slit-type is 4.67 times that of the leak-floor flip bucket. The effects of flow discharge on the jet length are less significant for the leak-floor bucket than for the slit-type bucket.
Constructing confidence intervals of extreme rainfall quantiles using Bayesian, bootstrap, and profile likelihood approaches
Hydrological risk is highly dependent on the occurrence of extreme rainfalls. This fact has led to a wide range of studies on the estimation and uncertainty analysis of the extremes. In most cases, confidence intervals (CIs) are constructed to represent the uncertainty of the estimates. Since the accuracy of CIs depends on the asymptotic normality of the data and is questionable with limited observations in practice, a Bayesian highest posterior density (HPD) interval, bootstrap percentile interval, and profile likelihood (PL) interval have been introduced to analyze the uncertainty that does not depend on the normality assumption. However, comparison studies to investigate their performances in terms of the accuracy and uncertainty of the estimates are scarce. In addition, the strengths, weakness, and conditions necessary for performing each method also must be investigated. Accordingly, in this study, test experiments with simulations from varying parent distributions and different sample sizes were conducted. Then, applications to the annual maximum rainfall (AMR) time series data in South Korea were performed. Five districts with 38-year (1973-2010) AMR observations were fitted by the three aforementioned methods in the application. From both the experimental and application results, the Bayesian method is found to provide the lowest uncertainty of the design level while the PL estimates generally have the highest accuracy but also the largest uncertainty. The bootstrap estimates are usually inferior to the other two methods, but can perform adequately when the distribution model is not heavy-tailed and the sample size is large. The distribution tail behavior and the sample size are clearly found to affect the estimation accuracy and uncertainty. This study presents a comparative result, which can help researchers make decisions in the context of assessing extreme rainfall uncertainties.
Effect of total phosphorous pollution on cavitation pressure characteristics of working water used in turbines
Many experiments have proven that with increasing silt and gas (out-of-phase media) content in water, the cavitation characteristics change and the cavitation pressure increases. Currently, many large reservoirs in China are polluted by total phosphorus (TP) and other chemical contaminants because of the use of phosphate fertilizer runoff from agriculture. However, research regarding how chemical pollutants (in the form of out-of-phase media) affect the cavitation pressure characteristics of water is sparse. In this paper, the Goupitan Hydropower Station, the largest hydropower reservoir on the Wujiang River, which is heavily polluted by TP, is taken as an example to evaluate the effects of chemical pollution on water cavitation pressure characteristics. In this study, the cavitation pressure characteristics of polluted and clean water are compared. The results show that the cavitation pressure of water polluted by chemicals is larger than that of clean water. In a hydraulic power generation system, cavitation and cavitation erosion are likely to occur earlier in runners when the fluid is polluted. These results are of great importance to further studies of cavitation theory and can directly influence the arrangement of turbines in practical engineering.
Influence of laser geometric morphology type on SiC surface wettability
To obtain effective surface morphology to control surface wettability, this work investigated the influence of protuberant and concave morphology, which are respectively represented by circle-dimpled and micro-square-convex morphology, on surface wettability. The geometric morphologies were processed on silicon carbide (SiC) surfaces by a laser-marking machine, and surface wettability was monitored by the measurement of contact angles using the sessile drop method. Correlation analysis between contact angles and morphology parameters was conducted to determine the extent of influence. The results showed that the circle-dimpled diameter had a significant influence on surface wettability, whereas grooved width did not. Additionally, the depth of dimples and grooves exerted less influence on controlling wetting behaviors. In addition, surface wettability transformed from a superhydrophilic state to a hydrophobic state on micro-square-convex surfaces; contact angles on circle-dimpled surfaces showed a relatively slow transformation, though the surface wettability also underwent the state change.
Alternating electric field actuated oscillating behavior of liquid metal and its application
As a class of newly emerging functional material, Gallium based liquid metals have attracted increasing attentions in many fields, such as chip cooling, printed electronics and microfluidics, etc. Particularly, the motion control of liquid metal droplet has been recently tried for its importance in microelectromechanical system (MEMS), microfluidics and potential use in micro-machine or reconfigurable soft robot. This paper is dedicated to explore the motion behavior of liquid metal droplet under AC electric field. The quickly induced oscillation phenomena of liquid metal droplet and surrounding electrolyte solution were observed and the major factors to influence such behaviors are theoretically interpreted and experimentally investigated, including the size of the liquid metal droplet, electrode voltage, electrolyte solution concentration and AC signal frequency etc. Moreover, some typical features to distinguish AC filed actuation with DC field are observed, such as intensive fluid waving induced by the resonance stimulation, and the efficient inhibition of solution electrolysis. Finally, two important applications of adopting AC induced surface oscillation of liquid metal droplet to develop solution mixer as well as fluidic pump were demonstrated which successfully avoid gas generation inside electrolyte environment. The bulk oscillation effects of liquid metal as clarified here could be very useful in a variety of areas such as solution disturbance and mixing, and fluid oscillator or pump etc.
Complex network theory-based condition recognition of electromechanical system in process industry
In order to recognize the different operating conditions of a distributed and complex electromechanical system in the process industry, this work proposed a novel method of condition recognition by combining complex network theory with phase space reconstruction. First, a condition-space with complete information was reconstructed based on phase space reconstruction, and each condition in the space was transformed into a node of a complex network. Second, the limited penetrable visibility graph method was applied to establish an undirected and un-weighted complex network for the reconstructed condition-space. Finally, the statistical properties of this network were calculated to recognize the different operating conditions. A case study of a real chemical plant was conducted to illustrate the analysis and application processes of the proposed method. The results showed that the method could effectively recognize the different conditions of electromechanical systems. A complex electromechanical system can be studied from the systematic and cyber perspectives, and the relationship between the network structure property and the system condition can also be analyzed by utilizing the proposed method.
Powertrain design and energy management of a novel coaxial series-parallel plug-in hybrid electric vehicle
For a series plug-in hybrid electric vehicle, higher working efficiency can be achieved by the drive system with two small motors in parallel than that with one big motor alone. However, the overly complex structure will inevitably lead to a substantial increase in the development cost. To improve the system price-performance ratio, a new kind of series-parallel hybrid system evolved from the series plug-in hybrid system is designed. According to the technical parameters of the selected components, the system model is established, and the vehicle dynamic property and pure electric drive economy are evaluated. Based on the dynamic programming, the energy management strategy for the drive system under the city driving cycle is developed, and the superiority validation of the system is completed. For the studied vehicle driven by the designed series-parallel plug-in hybrid system, compared with the one driven by the described series plug-in hybrid system, the dynamic property is significantly improved because of the multi-power coupling, and the fuel consumption is reduced by 11.4% with 10 city driving cycles. In a word, with the flexible configuration of the designed hybrid system and the optimized control strategy of the energy management, the vehicle performance can be obviously improved.
Constructal optimization of cylindrical heat sources with forced convection based on entransy dissipation rate minimization
Based on constructal theory and entransy theory, the optimal designs of constant- and variable-cross-sectional cylindrical heat sources are carried out by taking dimensionless equivalent resistance minimization as optimization objective. The effects of the cylindrical height, the cylindrical shape and the ratio of thermal conductivity of the fin to that of the heat source are analyzed. The results show that when the volume of the heat source is fixed, there exists an optimal ratio of the center-to-centre distance of the fin and the heat source to the cylinder radius which leads to the minimum dimensionless equivalent thermal resistance. With the increase in the height of the cylindrical heat source and the ratio of thermal conductivity, the minimum dimensionless equivalent thermal resistance decreases gradually. For the heat source model with inverted variable-cross-sectional cylinder, there exist an optimal ratio of the center-to-centre distance of the fin and the heat source to the cylinder radius and an optimal radius ratio of the smaller and bigger circles of the cylindrical fin which lead to a double minimum dimensionless equivalent thermal resistance. Therefore, the heat transfer performance of the cylindrical heat source is improved by adopting the cylindrical model with variable-cross-section. The optimal constructs of the cylindrical heat source based on the minimizations of dimensionless maximum thermal resistance and dimensionless equivalent thermal resistance are different. When the thermal security is ensured, the optimal construct of the cylindrical heat source based on minimum equivalent thermal resistance can provide a new alternative scheme for the practical design of heat source. The results obtained herein enrich the work of constructal theory and entransy theory in the optimal design field of the heat sources, and they can provide some guidelines for the designs of practical heat source systems.
A novel natural circulation evaporative cooling system for super-high power intensity ECR ion sources
Cooling is very important for the safe operation of an electron cyclotron resonance ion source (ECRIS), especially when the window current density is very high (up to 11 A/mm2). We proposed an innovative cooling method using evaporative cooling technology. A demonstration prototype was designed, built and tested. The on-site test results showed that the temperature of the solenoids and permanent magnets maintains well in the normal operational range of 14-18 GHz. A simple computational model was developed to predict the characteristics of the two-phase flow. The predicted temperatures agreed well with the on-site test data within 2 K. We also proposed useful design criteria. The successful operation of the system indicates the potential for broad application of evaporative cooling technology in situations in which the power intensity is very high.
Evolved clustering analysis of 300 MW boiler furnace pressure sequence based on entropy characterization
The furnace process is very important in boiler operation, and furnace pressure works as an important parameter in furnace process. Therefore, there is a need to analyze and monitor the pressure signal in furnace. However, little work has been conducted on the relationship with the pressure sequence and boiler's load under different working conditions. Since pressure sequence contains complex information, it demands feature extraction methods from multi-aspect consideration. In this paper, fuzzy c-means analysis method based on weighted validity index (VFCM) has been proposed for the working condition classification based on feature extraction. To deal with the fluctuating and time-varying pressure sequence, feature extraction is taken as nonlinear analysis based on entropy theory. Three kinds of entropy values, extracted from pressure sequence in time-frequency domain, are studied as the clustering objects for work condition classification. Weighted validity index, taking the close and separation degree into consideration, is calculated on the base of Silhouette index and Krzanowski-Lai index to obtain the optimal clustering number. Each time FCM runs, the weighted validity index evaluates the clustering result and the optimal clustering number will be obtained when it reaches the maximum value. Four datasets from UCI Machine Learning Repository are presented to certify the effectiveness in VFCM. Pressure sequences got from a 300 MW boiler are then taken for case study. The result of the pressure sequence case study with an error rate of 0.5332% shows the valuable information on boiler's load and pressure sequence in furnace. The relationship between boiler's load and entropy values extracted from pressure sequence is proposed. Moreover, the method can be considered to be a reference method for data mining in other fluctuating and time-varying sequences.
OWC air chamber performance prediction under impulse turbine damping effects
Oscillating water columns (OWCs) are most widely used in coastal wave energy conversion. The air duct opens into the atmosphere through the air turbine, which is the power take-off device, and this results in a pressure drop across the air chamber. However, because of the complex configure of the impulse turbine and its high rotation speed, it is difficult to install it in the experimental simulator and numerical model. Therefore, the turbine damping effects on the operation of the OWC air chamber are induced to predict its performance more accurately. Orifice plates are used as a substitute for the impulse turbine as it generates a similar pressure drop and power output; the experimental and numerical pressure drops and output powers are compared. A 3D numerical wave tank based on the two-phase VOF model is established using the commercial CFD code Fluent, which can predict air flow and pressure variations in the chamber and duct. Water surface elevations, air flow velocity and pressure variation inside the chamber with the orifice plate are studied numerically, and validated by the corresponding experimental data. The air chamber of the Yongsoo OWC pilot plant is used as the engineering project case. The operating performance of the air chamber installed with a 0.428D orifice plate as the substitute for the designed impulse turbine is computed and analyzed. It is found that the turbine damping effects will cause around 30% reduction in the peak values of the pneumatic energy output of the OWC air chamber in the resonant wave domain.
Effects of polydopamine modification on self-grown CuO cube anodes in lithium-ion batteries
We report the synthesis of CuO cubes with well-defined size and shape by thermal treatments of Cu2O cubes. Polydopamine (PDA) is introduced to modify the CuO cubes by the in-situ polymerization of the dopamine precursor. The initial specific capacity of the lithium-ion batteries using the CuO cubes as anodes increases about 10 times at a 0.5 C rate as a result of the modification of PDA. The overall specific capacity for 100 cycles also increases effectively due to the introduction of PDA. So PDA as surface modifying agent significantly improves the electrochemical performance of the CuO anodes.
Electron backscatter diffraction investigation of duplex-phase microstructure in a forged Zr-2.5Nb alloy
Microstructural features of a duplex-phase Zr-2.5Nb alloy were investigated in detail using electron channeling contrast (ECC) imaging and electron backscatter diffraction (EBSD) technique in an emission gun scanning electron microscope (FEGSEM). The excellent resolution provided by the FEGSEM promises the combined utilization of both techniques to be quite adequate for characterizing the duplex-phase microstructures. Results show that the microstructure of the Zr-2.5Nb alloy is composed of bulk α grains (majority) in equiaxed or plate shape and thin β films (minority) surrounding the bulk grains, with their average grain size and thickness measured to be 1.4 μm and 72 nm, respectively. Analyses on α-grain boundaries reveal a number of low angle boundaries, most of which belong to deformation-induced dislocation boundaries. Measurements on relative proportions of various Burgers boundaries suggest very weak (if any) variant selection during β→α cooling, which should be related to deformation-induced higher nucleation rate of α phases. Compared to earlier attempts, more satisfactory indexing of fine β phases (down to nanoscale) is attained by the FEGSEM-based EBSD. Examples are presented to clearly reveal well-obeyed Burgers orientation relationships between adjacent α and β phases. Finally, it is deduced that continuing application of the FEGSEM-based EBSD to duplex-phase Zr alloys could help clarify controversies like the deformation priority of the two phases.
Robust adaptive cross-coupling position control of biaxial motion system
The stability and synchronous performance are usually hard to be improved simultaneously in the biaxial cross-coupling position motion control system. Based on analyzing the characteristics of the cross-coupling control system, a robust adaptive cross-coupling control strategy is proposed. To restrict influences of destabilizing factors and improve both of stability and synchronous performance, the strategy forces dual axes to track the same reference model using Narendra adaptive control theory. And then, a robust parameters adaptive law is proposed. The stability analysis of the proposed strategy is conducted by applying Lyapunov stability theory. Related simulations and experiments indicate that the proposed strategy can improve synchronous performance and stability simultaneously.