To investigate the effect of ambient temperature on the mechanical properties of rubber bearings,high-speed compression shear apparatus is used to conduct a series of compression-shear tests at varying temperatures(-20,0,23 ℃),frequencies(0.2,0.25,0.3 Hz),and shear strains(50%,100%,250%)on rubber bearings(LRB700 and LNR700).Given that the significant inertial and frictional forces generated by the high-speed and high-pressure(15 MPa vertial compressive stress),this paper firstly proposes correction methodologies for accurately determining the performance indexes of bearings under conditions of high-speed and high-pressure loading.Test results indicate that with an increasing number of loading circles,the temperature variation within the internal lead core of LRB700 is more pronounced and exhibits symmetry with respect to the height of the lead core,whereas the temperature variation on the inner wall of LNR700 is minimal.In addition,the primary mechanical indexes of LRB700 and LNR700(such as characteristic strength,post-yield horizontal stiffness,and horizontal equivalent stiffness)exhibit varying degrees of an upward trend as ambient temperature decreases.Specifically,the characteristic strength of LRB700 increases by 15%to 32%,the post-yield stiffness of LRB700 increases by 7%to 16%,and the horizontal equivalent stiffness of LRB700 and LNR700 increases by 12%to 23%and 5%to 16%,respectively.Finally,this research concludes by proposing mechanical performance adjustment coefficients for LRB700 and LNR700 that account for the effect of ambient temperature based on the aforementioned results and in accordance with relevant standards.
To solve the problem of scattering and dose-rate setting for on-site calibration of fixed X,gamma radiation dosimeter,and to ensure the safe and stable operation of nuclear facilities,a portable X-ray irradiation device and self-shielded X-ray irradiation device were established based on X-ray machine.Based on Monte Carlo simulation,machine learning algorithms and experimental methods,the scattering radiation correction of X-ray radiation field was completed and the radiation field dose rate setting technology was studied.Firstly,MCNP was used to simulate the radiation characteristics of portable X-ray reference radiation field and self-shielded X-ray reference radiation field,such as uniformity,scattered radiation and energy spectrum distribution.The obtained results were compared with experimental data to validate the effectiveness of the numerical simulation method and the feasibility of applying the device to field calibration.Secondly,an ambient scattered radiation correction system for on-site calibration was built based on machine learning algorithm,and the mean absolute error(MAE)was used to evaluate the performance of the machine learning model.Finally,on-site calibration experiments were carried out by combining the irradiation device and secondary ionization chamber with the ambient scattered radiation correction system built.The results show that both the portable X-ray irradiation device and self-shielded X-ray irradiation device can provide reference radiation field meeting the requirements of GB/T 12162.1-2000.The relative error of calibration factor and laboratory calibration factor of fixed X,gamma radiation dosimeter calibration based on environmental scattered radiation correction system is less than 6.2％,meeting the requirements of on-site calibration work.
Standard platinum cobalt resistance thermometers(SPCRTs)are important temperature sensors used in low-temperature region especially from 0.65 K to 24.556 1 K(triple point of neon),and high-stability ones have the potential to be used as the data carrier for temperature calibration and international comparison.Based on our previous research,this article establishes a low-temperature assessment system with temperature control stabilities of 13 μK at 5 K and 27 μK at 24.556 1 K.It is currently the most stable low-temperature assessment systems reported in the world.Based on the system,stability of the developed SPCRTs is investigated under hundred low-temperature cycling from 5 K to 24.556 1 K,and five high-stability SPCRTs are obtained.Among them,the stability of four 50 Ω SPCRTs is better than 0.2 mK and the stability of one 100 Ω SPCRT is better than 0.5 mK at 24.556 1 K,which is the best international result for low temperature stability of SPCRTs.In the future,the high stability SPCRTs selected in this article will be used in the relevant applications and research of temperature calibration and international comparison at low temperatures.
To investigate the fretting wear of the contact parts of electrical connectors caused by random vibrations during operation,resulting in decreased contact performance due to wear debris,stepped stress and constant stress random vibration tests were conducted.Electrical capacitance tomography technology was used to detect the wear debris between the contact parts of the electrical connectors during fretting wear.The effects of vibration period,direction,magnitude,and load current on wear debris accumulation and distribution were studied.Surface morphology and energy spectrum analysis were conducted on the specimens after testing,and fractal dimension was used to study the uniformity of debris distribution,quantifying the extent of wear on the contact surfaces.Results of the tests show that vibration period,direction,and magnitude have a positive cumulative effect on the generation and accumulation of wear debris between contact parts.The coupling effect of load current,leading to heating and stress relaxation,delays the performance degradation process.Axial vibration causes the most severe wear,with the root of the pin being the area of severe wear.The degradation patterns of the electrical connectors under stepped stress random vibration are similar to those under constant stress,with wear debris characteristic values under stepped stress showing a certain step-change feature.Significant changes occur in contact surface morphology during fretting wear of the connectors.The results of surface morphology and spectrum analysis align with the characteristics of wear debris and the variation in contact resistance.
In order to investigate the feasibility and adaptability of a type of combined seismic isolation system in high-speed railway simply supported bridges in nine-degree seismic regions, a series of shaking table tests with a 1/10-scaled model are carried out in this paper. Firstly, a type of combined seismic isolation system is presented on the basis of seismic prevention principles of high-speed railway bridges in nine-degree seismic regions. Then, a 1/10-scaled full-bridge model with combined seismic isolation systems is designed and constructed by using a three-span high-speed railway simple supported box girder bridge as a prototype. Finally, fifteen near-fault seismic waves are input to obtain and analyze the damage state and seismic responses of the key components on the bridge model under different seismic waves. The test results show that the bridge model is in the elastic state under frequent seismic waves. The transverse and vertical accelerations of the main girders are within 0.375 g and 0.625 g. Under design seismic waves, the relative displacements of the piers and main girders and the displacement ductility ratios of the piers are less than 20 mm and 1.5. Under rare seismic waves, the main girders do not drop, and the displacement ductility ratios of the piers are less than 3.0. Therefore, the combined seismic isolation system meets the seismic prevention principles. It is expected to be an effective seismic isolation measure for high-speed railway simply supported bridges in nine-degree seismic regions.
In this work, an actuate membrane and an electrode membrane were prepared by a sol-gel method. And then, they were physically pressed to form a chitosan-based ion actuator（CSIA）. Importantly, the effect of sodium chloride on CSIA was investigated.The mechanical properties of CSIA were tested by establishing an output force test platform and a displacement test platform while testing its porosity. And, the electrochemical performance was tested by electrochemical workstation. At the end, the surface morphology and functional groups were measured by scanning electron microscopy and infrared spectrogram, respectively. The results indicated that the molar concentration of the sodium chloride was the best at 0.06836 mol·L -1 for CSIA. Its mechanical properties could reach an output force of 2.939 mN and a deflection displacement of 4.025 mm, and the maximum porosity of 12.98 % at the same time. The specific capacitance of the electrochemical performance was up to 0.07719 F·g -1 , and the minimum resistance reached 13.48 Ω. From the surface morphology and functional groups, the appropriate doping ratio of NaCl into CSIA was helpful for increasing the transport space of internal ions. The effective internal ion concentration and significantly reduced internal stress provided excellent performances under the appropriate voltage conditions. The doping of inorganic ion sodium chloride improved the internal electron transport efficiency of chitosan ion actuator, and it advanced the mechanical properties of the actuator. Hence the enhancement of NaCl output force in CSIA had a good significance for the development of inorganic salt ion strengthened ion actuator.
Diabetes mellitus is associated with foot ulcers,which frequently pave the way to lower-extremity amputation.Neuropathy,trauma,deformity,high plantar pressures,and peripheral vascular disease are the most common underlying causes.Around 15%of diabetic patients are affected by diabetic foot ulcer in their lifetime.64 million people are affected by diabetics in India and 40000 amputations are done every year.Foot ulcers are evaluated and classified in a systematic and thorough manner to assist in determining the best course of therapy.This paper proposes a novel model which predicts the threat of diabetic foot ulcer using independent agents for various input values and a combination of fuzzy expert systems.The proposed model uses a classification system to distinguish between each fuzzy framework and its parameters.Based on the severity levels necessary prevention,treatment,and medication are recommended.Combining the results of all the fuzzy frameworks derived from its constituent parameters,a risk-specific medication is recommended.The work also has higher accuracy when compared to other related models.
Recently, a description on a practicability of the Wöhler Curve Method for LCF of metallic materials was given by Yan. By the description and the low-cycle fatigue test data of 16MnR steel, it is important to illustrate that, for LCF of the metallic material, such a way that a “stress quantity” calculated based on the linear-elastic analysis is taken to be the stress intensity parameter, S , to establish a relationship between the stress intensity parameter, S, and the fatigue life, N , is practicable. In this study, many examples from the literature are given to illustrate that the Wöhler Curve Method is well suitable for LCF analysis of metallic materials
Over the past decades, many advances have occurred for theories on large-strain nonlinear consolidation of soft soils with regard to traditional drainage boundaries, which are completely permeable and impermeable cases and which may not truly reflect the whole process of drainage boundary. Thus, some further considerations related to a time-dependent drainage boundary are adopted in the analysis of soft soil consolidation by incorporating biologarithmic compressibility and permeability models. Also, the analytical solutions are obtained by means of variable substitution and Laplace transform. Additionally, the proposed solution is degenerated and compared with the existing solution and the laboratory tests to validate its correctness and feasibility. Finally, the soil consolidation behavior is analyzed under different values of the interface parameter, nonlinear compressibility and permeability, and external loading. The results indicate that the drainage boundary permeability is largely determined by the interface parameter; the larger the interface parameter, the better the boundary permeability. Besides, the consolidation rate decreases with the increasing value of I-c(alpha - 2) when the external loading remains constant. While the parameter I-c(alpha - 2) is a constant value, the consolidation rate varies with the external loading. Therefore, appropriate parameter values are more conducive to the full consolidation of soft soil foundations.
This study aims to improve the mechanical properties of cement-steel slag mortar by the addition of alkaline activators (NaOH, Na2CO3/NaOH and water glass) to promote the optimal utilization of steel slag. In this paper, the setting time, flexural and compressive strength, early-age hydration kinetics and microstructure are investigated to explore how the alkaline activators influence the hydration of cement-steel slag system. The results indicate that the incorporation alkaline activators shortens the setting time and enhances the mechanical strength of cement-steel slag composite binder, which are ranked from large to small in the order of water glass >Na2CO3/NaOH > NaOH. Moreover, the hydration exothermic action of cement-steel slag activated by alkaline activators is significantly accelerated in comparison to cement-steel slag. Furthermore, the incorporation of alkaline activators promotes the formation of amorphous gel products, such as C-S-H and C-A-S-H gel, of cement-steel slag system, which can fill the capillary pores and convert them into gel pores with a smaller pore size, leading to a denser microstructure. Based on the outcome of different analytical techniques, it is observed that alkaline activators can facilitate disintegration of steel slag's vitreous structure and can be applied to enhance the reactivity of steel slag in the cement-steel slag system to develop a sustainable composite cement.
Existing studies on columns with a stay-in-place formwork mostly focus on those with integrated formwork. A few researchers have mainly studied the axial compression performance or eccentric compression performance of composite columns with stay-in-place formwork. However, existing research on the seismic performance of composite columns is quite limited. This paper presents an experimental study to investigate the seismic per-formance of composite columns with an assembled UHPC stay-in-place formwork. Six column specimens with various assembly methods and surface treatments of a UHPC stay-in-place formwork and one reference specimen for reinforced concrete (RC) columns built by temporary formworks were designed. The seismic performances of the composite columns were investigated through quasi-static tests, and the results were analyzed in terms of seismic performance indices, such as failure mode, hysteresis curve, bearing capacity, energy dissipation ca-pacity, and ductility. The damage evolution process of the composite columns was analyzed by using the seismic damage assessment model suitable for cyclic loading. The results show that the assembled formwork with greater flexibility is more convenient for fabrication and transport. It is possible to form an integrated stressed member with the composition of the UHPC stay-in-place formwork and post-cast concrete that jointly provides structural resistance. The UHPC stay-in-place formwork can effectively improve the ductility and bearing capacity of the members. Compared with the RC specimen, the ductility coefficient and bearing capacity of the composite columns were improved by 28 -84 % and 30 -43 %, respectively. The damage assessment model can reflect the damage state of the specimen during loading and is suitable for engineering applications.
In this article, we consider the attitude tracking control problem for rigid spacecraft with bounded external disturbances. We propose a predefined-time predefined-bounded attitude tracking control scheme based on a nonsingular predefined-time sliding-mode manifold. The proposed controller is continuous and it can achieve predefined-time predefined-bounded stability. That is, the attitude tracking errors are driven to a predefined-bounded region around the origin within a predefined time, which can be set as a tuning parameter during the controller design, independently of initial conditions. Finally, numerical simulations are carried out to evaluate the performance of the proposed control law.
针对局部异常因子(local outlier factor,LOF)异常检测算法时间空间复杂度高、对交叉异常及低密度簇周围异常点不敏感等局限,提出了基于近邻搜索空间提取的LOF异常检测算法(isolation-based data extracting LOF,iDELOF),将基于隔离思想的近邻搜索空间提取(isolation-based KNN search space extraction,iKSSE)前置于LOF算法,以高效剪切掉大量无用以及干扰数据,获得更加精准的搜索空间.基于此完成了理论以及4 组实验分析,每组实验分别进行iDELOF算法与LOF、iForest、iNNE等多种典型算法的对比分析.结果表明:iDELOF算法通过拉大正异常点局部离群因子的差距,增强了对交叉异常以及低密度簇周围异常点的识别能力,提升了LOF的检测效果;iDELOF算法在识别轴平行异常方面与LOF同样具有明显优越性;iDELOF算法通过iKSSE所获数据子集显著小于原数据集,多数子集数据量小于原数据集的 1%,因此iDELOF的时间空间复杂度显著降低,且原数据集数据量越大,优越性越明显,当数据量足够大时,iDELOF算法的运行时间将低于IF算法.
The molecular dynamics method is used to investigate decomposition of methane hydrate at different temperatures,pressures and concentrations of inhibitor.By analyzing the parameters of system conformation,mean square displacement and radial distribution function,the decomposition of hydrate in the presence of alcohol inhibitors ethylene glycol and glycerol is explored.The results show that the hydroxyl groups in alcohol molecules can destroy the cage structure of hydrate,and form hydrogen bonds with nearby water molecules to effectively prevent the reformation of hydrate.Therefore,ethylene glycol and glycerol serve as inhibitors of methane hydrate,furthermore,in terms of inhibition effect,glycerol is better than ethylene glycol by comparing rate of hydrate decomposition.
This study explored the concurrent scheduling of machines,tools,and tool transporter(TT)with alternative machines in a multi-machine flexible manufacturing system(FMS),taking into mind the tool transfer durations for minimization of the makespan(MSN).When tools are expensive,just a single copy of every tool kind is made available for use in the FMS system.Because the tools are housed in a central tool magazine(CTM),which then distributes and delivers them to many machines,because there is no longer a need to duplicate the tools in each machine,the associated costs are avoided.Choosing alternative machines for job operations(jb-ons),assigning tools to jb-ons,sequencing jb-ons on machines,and arranging allied trip activities,together with the TT's loaded trip times and deadheading periods,are all challenges that must be overcome to achieve the goal of minimizing MSN.In addition to a mixed nonlinear integer programming(MNLIP)formulation for this simultaneous scheduling problem,this paper suggests a symbiotic organisms search algorithm(SOSA)for the problem's solution.This algorithm relies on organisms'symbiotic interaction strategies to keep living in an ecosystem.The findings demonstrate that SOSA is superior to the Jaya algorithm in providing solutions and that using alternative machines for operations helps bring down MSN.
In this current work,aluminum alloy grade 2024 is adopted as a plate material that is used in the rolling process with three different parameters including thickness reduction,forming temperature,and density of lubrication type.The experimental procedure of the rolling process is performed using the design of the experiment based on the Taguchi technique(L27),then surface roughness,surface hardness,and surface residual stresses are measured.The results showed that the lubrication density has a significant impact on the surface roughness which depends on the lubrication properties(mineral oil type,natural fat,and kinematic viscosity)while surface hardness and surface residual stresses were strongly affected by thickness reduction.On the other side,the augment in forming temperature can decrease the quality of the final surface finish and the surface hardness but reduce the induced residual stresses.The best surface finish is obtained based on the optimum condition of the rolling factors are(R％3,T1,and ρ3)while the optimum condition of rolling parameters that generate higher hardness and compressive residual stresses are(R％3T1ρ1).
A fourth generation single crystal(SC)nickel based cast superalloy DD15 with 1％Ru,3％Ru,5％Ru was prepared using vacuum induction single crystal furnace in order to optimize the properties and cost of DD15 alloy.The exposure experiment of three alloys was conducted at 1100 ℃ for 1000 h.The stress rupture properties tests were performed at 1100 ℃ temperature and 137 MPa pressure.The composition optimization of Ru element in DD15 alloy had been studied.It was found that the alloys with different Ru contents all consist of cuboidal γ'phase embedded coherent in γ phase.The γ'phase of the alloy all has a size of about 300-500 nm and a volume content of more than sixty percent.The dimension of γ'precipitates is reduced and uniform with increase of Ru content.Ru element can reduce the distribution ratio of high melting point element,so the microstructural stability is enhanced with Ru content increasing.No topologically close-packed(TCP)phase precipitated in the 5％Ru alloy even after 1000 h exposure.The stress rupture life of the alloy is significantly improved as Ru content rising.The raft breadth decreases slightly as Ru content increases.The specimen with 1％Ru and 3％Ru exhibits the presence of TCP phases and without TCP phases precipitated in fracture specimen with 5％Ru.The density and integrity of γ/γ'interfacial dislocation network increase as Ru content of the alloy rises.
To examine and investigate the impact of nanofluid on heat exchanger performance,including the total heat transfer,the effect of friction factor,the average Nusselt number,and the thermal efficiency,the output heat transfers of a shell and tube heat exchanger using ZnO nanoparticles suspended in water has been conducted numerically.The governing equations were solved using finite volume techniques and CFD simulations with ANSYS/FLUENT Solver 2021.The nanoparticles volume fractions adopted are 0.2％and 0.35％that used in numerical computations under 200 to 1400 Reynolds numbers range.The increasing of temperature is approximately 13％from the bottom to the top of heat exchanger,while the maximum enhancement of Nusselt number is about 10％,19％for volume fractions 0.2％and 0.35％respectively.The elevated values of the friction factor at the volumetric ratios of 0.2％and 0.35％are 0.25％and 0.47％respectively.The findings demonstrate that the performance efficiency of shell and tube heat exchanger is enhanced due to the increase in Nusselt number.
Efficient routing protocols are crucial for enabling secure communication among the highly mobile and self-configurable nodes in Vehicular Ad-Hoc Networks(VANETs).In this work,we present a performance evaluation of different routing protocols in VANETs based on the currently available research.Our study focuses on analyzing the strength and weaknesses of the routing protocols,namely,Ad-Hoc On-demand Distance Vector(AODV),Dynamic Source Routing(DSR),and Destination-Sequenced Distance-Vector(DSDV),under varying network conditions.We examine the protocols'performance based on key metrics such as throughput,delay,and energy consumption.We also highlight the advantages and limitations of each protocol in different scenarios,such as varying vehicular densities and mobility patterns.Our results show that AODV outperforms DSR and DSDV in terms of throughput and delay,while DSR consumes the least energy.We also observe that the performance of the routing protocols varies with the density of vehicles and the mobility patterns of the nodes.Our study highlights the importance of conducting real-world experiments to evaluate the performance of routing protocols in VANETs,as they provide more realistic and accurate results than simulation-based studies.Our findings can help in the selection and design of efficient and secure routing protocols for VANETs.
Industrial robot which can acquire high accuracy has been widely used in automatic assembly.Usually,the geometric parameter of industrial robot should be inspected during manufacturing and application.High precision measurement equipment was utilized to acquire the position and orientation of robot's end-effector,when calibrating the geometric parameter of robot.A kind of measurement system based on a draw-wire encoder was presented,since the current measurement equipment has some disadvantages,such as the cost and the requirements of working environment are high.According to this kind of measurement system,a sort of geometric calibration method of robot was presented including position and orientation parameters.The uncertain arc length of the cable length between robot end-effector and the measurement can be exactly acquired according to the position and orientation parameters.The pose-solving model of robot end-effector was associated with the kinematic model of robot,and robot's geometric parameter can be computed by using the least-squares methods.Validate instance was conducted,the result showed that the optimal number of the calibration pose was 47 with little improvement in accuracy,even if increasing the number of calibration pose.Robot calibration experiment was performed and the results showed that the absolute accuracy of robot decreased from 4.32 mm to 0.87 mm after calibration,which improved the robot's absolute accuracy effectively.
