CFD-Based Optimization of a Shell-and-Tube Heat Exchanger

The main objective of this study is the technical optimization of a Shell-and-Tube Heat Exchanger(STHE).In order to do so,a simulation model is introduced that takes into account the related gas-phase circulation.Then,simulation verification experiments are designed in order to validate the model.The results show that the tem-peraturefield undergoes strong variations in time when an inlet wind speed of 6 m/s is considered,while the heat transfer error reaches a minimum of 5.1%.For an inlet velocity of 9 m/s,the heat transfer drops to the lowest point,while the heat transfer error reaches a maximum,i.e.,9.87%.The pressure drop increasesfirst and then decreases with an increase in the wind speed and reaches a maximum of 819 Pa under the 9 m/s wind speed con-dition.Moreover,the pressure drops,and the heat transfer coefficient increases with the Reynolds number.

Threshold Dynamics of a Vector-Borne Epidemic Model for Huanglongbing with Impulsive Control

In this paper, the basic reproduction number is calculated for Huanglongbing (HLB) model with impulses which is a vector-borne epidemic model with impulses. For controlling HLB, farmers’ experience is replanting of healthy plants and removing infected plants. To reflect the real world, we construct an impulsive control model which considers replanting of healthy plants and removing infected plants at one fixed time. By analyzing the model, we conclude that the disease-free equilibrium is globally asymptotically stable if the basic reproduction number Ro 1, and we prove that the HLB is permanence if the basic reproduction number Ro > 1.

Optimization of a Heat Exchanger Using an ARM Core Intelligent Algorithm

In order to optimize heat transfer in a heat exchanger using an ARM(advanced RISC machine)core intelligent computer algorithm,a new type of controller has been designed.The whole control structure of the heat exchange unit has been conceived on the basis of seven functional modules,including data processing and output,human-computer interaction,alarm,and data communication.The main controller and communication controller have been used in a combined fashion and a new MCU(micro control unit)system scheme has been proposed accordingly.A fuzzy controller has been designed by using a fuzzy control algorithm,and a new mode of heat transfer for the heat exchanger has been implemented by combining the fuzzy controller and the PID(proportioning integral derivative)controller.Finally,the model has been applied to an actual heat exchange station to test and verify the performances of the new approach.

A Simulation of the Response of a Sounding Temperature Sensor Based on the Combination of a Genetic Algorithm and Computational Fluid Dynamics

The present study aims at improving the accuracy of weather forecast by providing useful information on the behavior and response of a sounding temperature sensor.A hybrid approach relying on Computational Fluid Dynamics and a genetic algorithm(GA)is used to simulate the system represented by the bead thermistor and the surrounding air.In particular,the influence of different lead angles,sensor lead length,and lead number is considered.The results have shown that when the length of the lead wire of the bead thermistor is increased,the radiation temperature rise is reduced;when the number of lead wire is four and the angle between the lead wires is 180°,the solar radiation angle has a scarce influence on the radiation temperature rise of the sounding temperature sensor.

Optimal Scheduling of Electrical Energy Systems Using a Fluid Dynamic Analogy

The electricity-gas transformation problem and related intrinsic mechanisms are considered.First,existing schemes for the optimization of electricity-gas integrated energy systems are analyzed through consideration of the relevant literature,and an Electricity Hub(EH)for electricity-gas coupling is proposed.Then,the distribution mechanism in the circuit of the considered electricity-gas integrated system is analyzed.Afterward,a mathematical model for the natural gas pipeline is elaborated according to the power relationship,a node power flow calculation method,and security requirements.Next,the coupling relationship between them is implemented,and dedicated simulations are carried out.Through experimental data,it is found that after 79 data iterations,the optimization results of power generation and gas purchase cost in the new system converge to$54,936 in total,which is consistent with the data obtained by an existing centralized optimization scheme.However,the new proposed optimization scheme is found to be more flexible and convenient.

Dynamics of a Nonautonomous Plant Disease Model with General Nonlinear Incidence Rate and Time-Varying Impulse

In this paper, for controlling the spread of plant diseases, a nonautonomous SEIS (Susceptible → Exposed → Infectious → Susceptible) epidemic model with a general nonlinear incidence rate and time-varying impulsive control strategy is proposed and investigated. This novel model could result in an objective criterion on how to control plant disease transmission by replanting of healthy plants and removal of infected plants. Using the method of small amplitude perturbation, the sufficient conditions under which guarantee the globally attractive of the disease-free periodic solution and the permanence of the disease are obtained, that is, the disease dies out if R12>1.

Investigation and Research on the Psychological Status of Children and Adolescents During the Epidemic Period of COVID-19

Objective:The paper was to analyze the investigation and study of the psychological status of children and adolescents during the epidemic period of COVID-19.Methods:From March 5th to 11th,2020,1766 students from 8 to 18 years old in Yan'an area were taken as the research objects,and the psychological characteristics of this group of people during the epidemic period of COVID-19 were analyzed by the online questionnaires.Results:In the questionnaire,all children and adolescents were in good psychological conditions,and they had not shown serious negative psychological emotions,and they attached great importance to COVID-19.Conclusion:The psychological changes of children and adolescents during the epidemic period of COVID-19 are diverse.Most children and adolescents have a good mental state,and a few have negative psychological emotions.It can strengthen the psychological management of children and adolescents during the epidemic,and promote the healthy growth of children and adolescents clinically.

Fiber‑Shaped Soft Actuators:Fabrication,Actuation Mechanism and Application

As mechanical devices for moving or controlling mechanisms or systems,actuators have attracted increasing attention in various fields.Compared to traditional actuators with rigid structures,soft actuators made up of stimulus-responsive soft materials are more adaptable to complex working conditions due to soft bodies and diverse control styles.Different from plate-shaped soft actuators,which have the limited deformations between two dimensional(2D)and 3D-configurations such as bending and twisting,fiber-shaped soft actuators(FSAs)own intriguing deformation modes to satisfy diverse practical applications.In this mini review,the recent progress on the controlled fabrication of the FSAs is presented.The advantages and disadvantages of each fabrication method are also demonstrated.Subsequently,the as-developed actuation mechanisms of the FSAs are displayed.Additionally,typical examples of the related applications of the FSAs in different fields have been discussed.Finally,an outlook on the development tendency of the FSAs is put forward as well.

中国海的极端海浪强度变化及归因分析

海浪作为海洋上主要的动力过程,其极端强度的时空变化正在得到越来越多的关注.为了获得中国海的极端海浪强度的长期时空变化趋势,并研究导致该变化的主要原因,采用欧洲中期天气预报中心最新发布的ERA-5海浪和大气再分析资料,使用Sen斜率估计和Mann-Kendall趋势检测方法,分析中国海的极端海浪强度(此处用有效波高的99.5%百分位数表征)在年际、台风浪和冷空气浪盛行期的历史40 a(1979~2018年)变化趋势.并通过对极端风速以及热带气旋数量和强度的变化趋势分析,研究导致中国海极端海浪变化的原因.分析结果表明,东海南部海域的极端海浪存在十分显著的年际增强趋势,幅度可达+5 cm/a,与其在台风浪盛行期的增强趋势及幅度一致,而极端风速在年际和台风浪盛行期的增强趋势是直接原因.此外,影响东海南部的强台风和超强台风的数量也存在显著增加趋势,这也导致了该海域极端海浪的恶劣程度加剧.同时,南海南部的极端海浪在年际、台风浪和冷空气浪盛行期均存在增强趋势,幅度最大+3 cm/a,而极端风速的增强是直接原因.

Climate and extrema of ocean waves in the East China Sea

Wave climate plays an important role in the air-sea interaction over marginal seas. Extreme wave height provides fundamental information for various ocean engineering practices, such as hazard mitigation, coastal structure design, and risk assessment. In this paper, we implement a third generation wave model and conduct a high-resolution wave hindcast over the East China Sea to reconstruct a 15-year wave field from 1988 to 2002 for derivation of monthly mean wave parameters and analysis of extreme wave conditions. The numerical results of the wave field are validated through comparison with satellite altimetry measurements, low-resolution reanalysis, and the ocean wave buoy record. The monthly averaged wave height and wave period show seasonal variation and refined spatial patterns of surface waves in the East China Sea. The climatological significant wave height and mean wave period decrease from the open ocean in the southeast toward the continental area in the northwest, with the pattern generally following the bathymetry. Extreme analysis on the significant wave height at the buoy station indicates the hindcast data underestimate the extreme values relative to the observations. The spatial pattern of extreme wave height shows single peak emerges at the southwest of Ryukyu Island although a wind forcing with multi-core structure at the extreme is applied.

Hierarchical ferric-cobalt-nickel ternary oxide nanowire arrays supported on graphene fibers as high-performance electrodes for flexible asymmetric supercapacitors

基于纤维的 supercapacitors (FSC ) 是精力存储家庭的新成员。他们现在的优秀灵活性并且在小、灵活、便携的设备有有希望的应用。当保留灵活性时， FSC 的存在挑战之一正在提高他们的精力密度。我们开发了一个灵巧、划算的方法基于层次 ferric-cobalt-nickel 制作一个高度电容的积极电极第三的氧化物 nanowire arrays/graphene 纤维和一个否定电极基于导出 polyaniline 的碳 nanorods/graphene 纤维。漂亮微观结构和两个电极的优秀电气化学的表演使我们能构造 highperformance 灵活不对称的 graphene 有 1.4 V 的操作电压的基于纤维的 supercapacitor 设备，一个特定的电容直到 61.58 mF ??摔??圠敔????猯'T??????????????猯'T???????猯'T???

Achieving high dielectric energy-storage properties through a phase coexistence design and viscous polymer process in BNT-based ceramics

In the last few decades,dielectric capacitors have gotten a lot of attention because they can store more power and charge and discharge very quickly.But it has a low energy-storage density(Wrec),efficiency(h),and temperature stability.By adding Pb(Mg1/3Nb2/3)O3(PMN)and(Bi0$1Sr0.85)TiO3(BST)to a nonstoichiometric(Bi0$51Na0.5)TiO3(BNT)matrix,the goal is to change the phase transition properties and make the material more relaxor ferroelectric(RFE)by lowering the remnant polarization Pr and keeping the maximum polarization Pmax.A viscous polymer process(VPP)is used to improve the electric breakdown strength,which is also a key part of being able to store energy.By working together,ceramics with the formula 0.79[0.85BNT-0.15PMN]-0.21BST(BP-0.21BST)are made.The phase structure has been changed from a rhombohedral phase to a rhombohedral-tetragonal coexisted phase.This is beneficial for RFE properties and gives a Wrec of 6.45 J/cm^(3) and a h of 90%at 400 kV/cm.Also,the energy-storage property is very temperature stable between 30 and 150
C.These results show that process optimization and composition design can be used to improve the energy storage properties,and that the dielectric ceramic materials made can be used in high-powder pulse dielectric capacitors.