Multi-point discharge model: study on corona discharge of double-ended needle in large space

Corona discharge, as a common means to obtain non-equilibrium plasma, can generally obtain high-concentration plasma by increasing discharge points to meet production needs. However,the existing numerical simulation models used to study multi-point corona discharge are all calculations of small-scale space models, which cannot obtain the distribution characteristics of plasma in large space. Based on our previous research, this paper proposes a hybrid model for studying the distribution of multi-point discharge plasma in large-scale spaces, which divides the computational domain and computes separately with the hydrodynamic model and the ion mobility model. The simulation results are verified by a needle–ball electrode device. Firstly, the electric field distribution and plasma distribution of the needle electrodes with single tip and double tips are compared and discussed. Secondly, the plasma distribution of the needle electrode with the double tip at different voltages is investigated. Both computational and experimental results indicate that the charged particle concentration and current of the needle electrode with double tips are both twice as high as those of the needle electrode with a single tip. This model can extend the computational area of the multi-point corona discharge finite element model to the sub-meter(25 cm) or meter level, which provides an effective means to study the plasma distribution generated by multiple discharge points in large-scale space.

Design Schemes and Comparison Research of the End-effector of Large Space Manipulator

The end-effector of the large space manipulator is employed to assist the manipulator in handling and manipulating large payloads on orbit.Currently,there are few researches about the end-effector,and the existing end-effectors have some disadvantages,such as poor misalignment tolerance capability and complex mechanical components.According to the end positioning errors and the residual vibration characters of the large space manipulators,two basic performance requirements of the end-effector which include the capabilities of misalignment tolerance and soft capture are proposed.And the end-effector should accommodate the following misalignments of the mechanical interface.The translation misalignments in axial and radial directions and the angular misalignments in roll,pitch and yaw are ±100 mm,100 mm,±10°,±15°,±15°,respectively.Seven end-effector schemes are presented and the capabilities of misalignment tolerance and soft capture are analyzed elementarily.The three fingers-three petals end-effector and the steel cable-snared end-effector are the most feasible schemes among the seven schemes,and they are designed in detail.The capabilities of misalignment tolerance and soft capture are validated and evaluated,through the experiment on the micro-gravity simulating device and the dynamic analysis in ADAMS software.The results show that the misalignment tolerance capabilities of these two schemes could satisfy the requirement.And the translation misalignment tolerances in axial and radial directions and the angular misalignment tolerances in roll,pitch and yaw of the steel cable-snared end-effector are 30mm,15mm,6°,3° and 3° larger than those of the three fingers-three petals end-effector,respectively.And the contact force of the steel cable-snared end-effector is smaller and smoother than that of the three fingers-three petals end-effector.The end-effector schemes and research methods are beneficial to the developments of the large space manipulator end-effctor and the space docking mechanism.

The Turbulent Schmidt Number for Transient Contaminant Dispersion in a Large Ventilated Room Using a Realizable k-εModel

Buildings with large open spaces in which chemicals are handled are often exposed to the risk of explosions.Computational fluid dynamics is a useful and convenient way to investigate contaminant dispersion in such large spaces.The turbulent Schmidt number(Sc_(t))concept has typically been used in this regard,and most studies have adopted a default value.We studied the concentration distribution for sulfur hexafluoride(SF_(6))assuming different emission rates and considering the effect of Sc_(t).Then we examined the same problem for a light gas by assuming hydrogen gas(H_(2))as the contaminant.When SF_(6) was considered as the contaminant gas,a variation in the emission rate completely changed the concentration distribution.When the emission rate was low,the gravitational effect did not take place.For both low and high emission rates,an increase in S_(ct) accelerated the transport rate of SF_(6).In contrast,for H_(2) as the contaminant gas,a larger S_(ct) could induce a decrease in the H_(2) transport rate.

Investigation of natural ventilation performance of large space circular coal storage dome

Large space circular coal storage dome(LSCCSD)offers an environmental and dependable alternative to open stockpiles,and it has been consequently widely applied in China.However,due to the lack of scientific guidelines,its natural ventilation performance is lower than expected.Natural ventilation potential strongly depends on the roof geometry and opening mode,which have not yet been investigated for LSCCSD.This paper presents a detailed evaluation of the impact of dome geometry(rise span ratio),opening height,and opening modes on the ventilation performance of LSCCSD.The evaluation is based on computational fluid dynamics(CFD)methods and is validated by available wind tunnel testing.We employed three evaluation indicators,which are wind pressure coefficient,effective ventilation rate,and wind speed ratio.The results demonstrate that the rise span ratio has a significant effect on the wind pressure difference and the effective ventilation rate increases by approximately 9%–42%with a single-annular opening.When double-annular openings are set in a strong positive pressure zone,the effective ventilation rate increases by 100%and the average wind speed ratio increases by 50%.When it is compared with single one with similar opening height,the effective ventilation rate increases by 25%.The optimum natural ventilation performance for LSCCSD is achieved at a rise span ratio of 0.37.In addition,the lateral middle opening is kept higher than the ridge top of the coal pile.The proposed evaluation approach and design parameters provided instructive information in the building design and ventilation control for LSCCSDs.

Zoning strategy of zonal modeling for thermally stratified large spaces

Large space buildings play a significant role in modern society because of their environmental advantages and market value.While the zonal model is promising for the efficient and rapid evaluation of the stratified thermal environment,there is a lack of a reasonable and convenient zoning strategy with the advent of modern computing.This paper presents a universal and practical zonal model,in which a simplified momentum equation is applied to consider air momentum preservation,transformation,and dissipation.Hence,the zoning structure is generalized and flexible.Moreover,limiting the dimensionless temperature constraint between adjacent zones establishes the connection between thermal nonuniformity and zoning results automatically.Simultaneously,the dimension and number of zones should be restricted within reasonable ranges to satisfy the characteristics of zonal simulation and reach the criteria of convergence.To further explore and validate the zonal model,a reduced-scale experimental model was constructed to replicate the thermal stratification in a mechanically ventilated large space by considering many crucial realistic factors.A particle image velocimetry(PIV)measurement was then conducted to visualize the airflow pattern and support the partition of zones.The results showed that the zonal simulation with adaptive zoning method can realize a similar accuracy with fewer zones and exhibit a better tolerance for zoning results compared to the conventional empirical zoning method.Furthermore,a case study of an atrium was performed to demonstrate the practicality and efficiency of the method for long-term dynamic simulations of complex thermal environments and building energy use.

The Hjek-Rnyi Inequlity For Banach Space Valued Random Variable Sequences and Its Application

In this paper we prove the following Hajek Renyi inequality:Let 0<p≤1 ,then for any Banach space B , any L p integrable B valued random variable sequence {D n,n≥1} ,any real number sequence {b n,n≥1} with 0<b n↑∞ ,any integer n≥1 ,there exits a constant C=C p>0 (only depending on p ) such thatP( sup j≥nji=1D ib j≥ε)≤Cε -p (∞j=n+1E‖D j‖ pb p j+nj=1E‖D j‖ pb p n) In the other direction,we prove some strong laws of large numbers and the integrability of the maximal functions for B valued random variable sequences by using this inequality and the Hajeck Renyi inequality we have obtained recently.Some known results are extended and improved.

Analysis and Evaluation of Thermal-cooling Loads of Office Buildings Using Carrier Software in Iran

The importance and necessity of energy saving in the world have been dis­cussed for many years,but achieving a logical and transparent solution is still one of the main challenges and problems of the world’s economy.The rapid growth of energy consumption in the last two decades has caused the security of the domestic energy supply of buildings to face serious prob­lems.In this research,first by entering parameters such as the type of mate­rials,doors and windows,and the type of soil on the floor connected to the ground,etc.in the heat and cold load calculation software(HAP Carrier)as the design calculations and then in the second step entering the specifica­tions inferred from the Iran’s national building code as a reference for ener­gy saving calculations,calculations are performed and compared as the first criterion,and finally these two outputs are compared.The actual energy consumption and determination of the building energy consumption index are determined as another criterion,as well as the degree of deviation from the actual consumption.The results showed that the theoretical method and the thermal and refrigeration load calculations of the Zanjan Gas Company building have 6%difference in cooling load but the heating load is about 34%different,which means for cooling loads,the theoretical model can be used with high accuracy but for heating loads,the national building code needs fundamental changes.

Enhanced Reversible Zinc Ion Intercalation in Deficient Ammonium Vanadate for High-Performance Aqueous Zinc-Ion Battery

Ammonium vanadate with bronze structure(NH_(4)V_(4)O_(10))is a promising cathode material for zinc-ion batteries due to its high specific capacity and low cost.However,the extraction of NH^(+)_(4) at a high voltage during charge/discharge processes leads to irreversible reaction and structure degradation.In this work,partial NH^(+)_(4) ions were pre-removed from NH_(4)V_(4)O_(10) through heat treatment;NH_(4)V_(4)O_(10) nanosheets were directly grown on carbon cloth through hydrothermal method.Defi-cient NH_(4)V_(4)O_(10)(denoted as NVO),with enlarged interlayer spacing,facilitated fast zinc ions transport and high storage capacity and ensured the highly reversible electrochemical reaction and the good stability of layered structure.The NVO nanosheets delivered a high specific capac-ity of 457 mAh g^(−1) at a current density of 100 mA g^(−1) and a capacity retention of 81%over 1000 cycles at 2 A g^(−1).The initial Coulombic efficiency of NVO could reach up to 97%compared to 85%of NH_(4)V_(4)O_(10) and maintain almost 100%during cycling,indicating the high reaction reversibility in NVO electrode.

Electrolyte Concentration Regulation Boosting Zinc Storage Stability of High-Capacity K0.486V2O5 Cathode for Bendable Quasi-Solid-State Zinc Ion Batteries

Vanadium-based cathodes have attracted great interest in aqueous zinc ion batteries(AZIBs)due to their large capacities,good rate performance and facile synthesis in large scale.However,their practical application is greatly hampered by vanadium dissolution issue in conventional dilute electrolytes.Herein,taking a new potassium vanadate K0.486V2O5(KVO)cathode with large interlayer spacing(~0.95 nm)and high capacity as an example,we propose that the cycle life of vanadates can be greatly upgraded in AZIBs by regulating the concentration of ZnCl2 electrolyte,but with no need to approach“water-in-salt”threshold.With the optimized moderate concentration of 15 m ZnCl2 electrolyte,the KVO exhibits the best cycling stability with ~95.02% capacity retention after 1400 cycles.We further design a novel sodium carboxymethyl cellulose(CMC)-moderate concentration ZnCl2 gel electrolyte with high ionic conductivity of 10.08 mS cm^-1 for the first time and assemble a quasi-solid-state AZIB.This device is bendable with remarkable energy density(268.2 Wh kg^−1),excellent stability(97.35% after 2800 cycles),low self-discharge rate,and good environmental(temperature,pressure)suitability,and is capable of powering small electronics.The device also exhibits good electrochemical performance with high KVO mass loading(5 and 10 mg cm^-2).Our work sheds light on the feasibility of using moderately concentrated electrolyte to address the stability issue of aqueous soluble electrode materials.

Nitrogen/sulphur dual-doped hierarchical carbonaceous fibers boosting potassium-ion storage

The carbon materials as anode electrodes have been widely studied for potassium ion batteries(PIBs).However,the large size of potassium ions prevents their intercalation/deintercalation,resulting in poor storage behaviors.Herein,a novel design of N/S codoped hierarchical carbonaceous fibers(NSHCF)formed from nanosheets self-assembled by catalyzing Aspergillus niger with Sn is reported.The asprepared NSHCF at 600℃(NSHCF-600)exhibits a high reversible capacity of 345.4 m Ah g^(-1) at 0.1 A g^(-1) after 100 cycles and an excellent rate performance of 124.5 m Ah g^(-1) at 2 A g^(-1).The excellent potassium storage performance can be ascribed to the N/S dual-doping,which enlarges interlayer spacing(0.404 nm)and introduces more defects.The larger interlayer spacing and higher pyridinic N active sites can promote K ions diffusion and storage.In addition,the ex situ transmission electron microscopy reveals the high reversibility of potassiation/depotassiation process and structural stability.

Corrosion damage assessment and monitoring of large steel space structures

Large steel space structures,when exposed to a harsh corrosive environment,are inevitably subjected to atmospheric corrosion and stress corrosion cracking.This paper proposes a framework for assessing the corrosion damage of large steel space structures subjected to both stress corrosion cracking and atmospheric corrosion.The empirical model for estimating atmospheric corrosion based on measured information is briefly introduced.The proposed framework is applied to a real large steel space structure built in the southern coastal area in China to assess its corrosion damage and investigate the effects of atmospheric corrosion on stress corrosion cracking.Based on the results,the conceptual design of the corrosion monitoring system of large steel space structures is finally conducted as the first step for a real corrosion monitoring system.

A parallel scheduling algorithm for reinforcement learning in large state space

The main challenge in the area of reinforcement learning is scaling up to larger and more complex problems. Aiming at the scaling problem of reinforcement learning, a scalable reinforcement learning method, DCS-SRL, is proposed on the basis of divide-and-conquer strategy, and its convergence is proved. In this method, the learning problem in large state space or continuous state space is decomposed into multiple smaller subproblems. Given a specific learning algorithm, each subproblem can be solved independently with limited available resources. In the end, component solutions can be recombined to obtain the desired result. To ad- dress the question of prioritizing subproblems in the scheduler, a weighted priority scheduling algorithm is proposed. This scheduling algorithm ensures that computation is focused on regions of the problem space which are expected to be maximally productive. To expedite the learning process, a new parallel method, called DCS-SPRL, is derived from combining DCS-SRL with a parallel scheduling architecture. In the DCS-SPRL method, the subproblems will be distributed among processors that have the capacity to work in parallel. The experimental results show that learning based on DCS-SPRL has fast convergence speed and good scalability.

A review of structures,verification,and calibration technologies of space robotic systems for on-orbit servicing

Recently,with the rapid development of aerospace technology,an increasing number of spacecraft is being launched into space.Additionally,the demands for on-orbit servicing(OOS)missions are rapidly increasing.Space robotics is one of the most promising approaches for various OOS missions;thus,research on space robotics technologies for OOS has attracted increased attention from space agencies and universities worldwide.In this paper,we review the structures,ground verification,and onorbit kinematics calibration technologies of space robotic systems for OOS.First,we systematically summarize the development of space robotic systems and OOS programs based on space robotics.Then,according to the structures and applications,these systems are divided into three categories:large space manipulators,humanoid space robots,and small space manipulators.According to the capture mechanisms adopted,the end-effectors are systematically analyzed.Furthermore,the ground verification facilities used to simulate a microgravity environment are summarized and compared.Additionally,the on-orbit kinematics calibration technologies are discussed and analyzed compared with the kinematics calibration technologies of industrial manipulators with regard to four aspects.Finally,the development trends of the structures,verification,and calibration technologies are discussed to extend this review work.

Numerical study on indoor environment and thermal comfort in train station waiting hall with two different air-conditioning modes

With the increasing size of the waiting hall,the large-area use of transparent envelope materials makes the interior surface temperature of the envelope too high,which puts forward higher requirements for the control of environment and thermal comfort indoors.In this paper,the characteristics of indoor temperature distribution,relative humidity distribution and thermal comfort under the all air system(AAs)and the radiant floor cooling and wall cooling combined with air supply system(RC/ASs)were investigated in the large spaces.The computational fluid dynamics(CFD)method was used,and the performance of the CFD model was validated by comparing the measured results with CFD simulation results in the AAs.The numerical results clearly showed that the temperature and relative humidity indoors could satisfy the design requirement both in the AAs and RC/ASs.The indoor air distribution in most areas under the RC/ASs was more uniform based on the indoor heat and humidity requirements under the cooling load of measured day.In the AAs,the total cooling capacity of air conditioning unit was the highest when indoor thermal comfort was the best,that meant that to achieve the best working condition,the air-conditioning system need high energy consumption.Meanwhile,the RC/ASs addressed the problem that the temperature around the seated passengers in the waiting area was relatively high in the AAs.This paper will provide reference for the air conditioning system design in the similar large spaces in the future.

Application of Computer Integration Technology for Fire Safety Analysis

With the development of information technology, the fire safety assessment of whole structure or region based on the computer simulation has become a hot topic. However, traditionally, the concerned studies are performed separately for different objectives and difficult to perform an overall evaluation. A new multi-dimensional integration model and methodology for fire safety assessment were presented and two newly developed integrated systems were introduced to demonstrate the function of integration simulation technology in this paper. The first one is the analysis on the fire-resistant behaviors of whole structure under real fire loads. The second one is the study on fire evaluation and emergency rescue of campus based on geography information technology (GIS). Some practical examples are presented to illuminate the advantages of computer integration technology on fire safety assessment and emphasize some problems in the simulation. The results show that the multi-dimensional integration model offers a new way and platform for the integrating fire safety assessment of whole structure or region, and the integrated software developed is the useful engineering tools for cost-saving and safe design.

A numerical study on the effect of column layout on air distribution and performance of column attachment ventilation

Based on the structural characteristics of existing buildings and the disadvantages of current mixed ventilation mode in the application to large space buildings,an original column attachment ventilation(CAV)has been proposed.In this study,the experiment utilized a room space with four columns uniformly distributed in the space to visualize the movement of attached airflow along the cylinder surface and the floor,the numerical technique was employed to study the effects of the column layout(i.e.,uniform,centralized,dispersed,and crossed distribution)on the air distribution of CAV mode in a standard four-column full scale model of a shopping mall.Seven indices,including airflow pattern,air diffusion performance index(ADPI),air temperature distribution,heat removal effectiveness,draught rate(DR),predicted mean vote(PMV),and carbon dioxide(CO2)concentration,were used to assess the ventilation performance.In the CAV mode with a uniform column layout scheme,the experimental results indicated that the air supply flows downward along the wall surface,forming a secondary attachment with the ground and spreading along the floor in a fan radiation flow mode.Further,an“air lake”-like speed and temperature distribution similar to displacement ventilation(DV)was formed in the occupied zone.In all simulation cases,it was found that the average air velocity was less than 0.25 m/s in occupied zone,the effectiveness for heat removal was more significant than 1.0,DR value was less than 20%,the PMV level can also satisfy most people.The average CO2 concentration was around 470 ppm in the occupied breathing zone.These results indicated that the CAV mode could be an efficient air distribution method.They demonstrated the technical feasibility of applying the CAV in the space under different column layout schemes.