Graphitized carbon foams(GFms)were prepared using mesophase pitch(MP)as a raw material by foaming(450℃),pre-oxidation(320℃),carbonization(1000℃)and graphitization(2800℃).The differences in structure and properties...Graphitized carbon foams(GFms)were prepared using mesophase pitch(MP)as a raw material by foaming(450℃),pre-oxidation(320℃),carbonization(1000℃)and graphitization(2800℃).The differences in structure and properties of GFms prepared from different MP precursors pretreated by ball milling or liquid phase extraction were investigated and compared,and semi-quantitative calculations were conducted on the Raman and FTIR spectra of samples at each preparation stage.Semi-quantitat-ive spectroscopic analysis provided detailed information on the structure and chemical composition changes of the MP and GFm de-rived from it.Combined with microscopic observations,the change from precursor to GFm was analyzed.The results showed that ball milling concentrated the distribution of aromatic molecules in the pitch,which contributed to uniform foaming to give a GFm with a uniform pore distribution and good properties.Liquid phase extraction helped remove light components while retaining large aromatics to form graphitic planes with the largest average size during post-treatment to produce a GFm with the highest degree of graphitization and the fewest open pores,giving the best compression resistance(2.47 MPa),the highest thermal conductivity(64.47 W/(m·K))and the lowest electrical resistance(13.02μΩ·m).Characterization combining semi-quantitative spectroscopic ana-lysis with microscopic observations allowed us to control the preparation of the MP-derived GFms.展开更多
The preparation of a synthetic pitch from aromatic monomers could easily regulate structure orientation at the molecu-lar level,which would be useful in fabrication.An isotropic synthetic pitch was prepared by a chlor...The preparation of a synthetic pitch from aromatic monomers could easily regulate structure orientation at the molecu-lar level,which would be useful in fabrication.An isotropic synthetic pitch was prepared by a chlorine-and/or nitrogen-induced sub-stitution polymerization reaction method using aromatic hydrocarbon precursors containing Cl and N,which for this study were chloromethyl naphthalene and quinoline.This method was verified by investigating the structural changes under different synthesis conditions,and the synthesis mechanism induced by aromatics containing Cl was also probed.The result shows that the pyridinic N in quinoline contains a lone pair of electrons,and is an effective active site to induce the polymerization reaction by coupling with aromatic hydrocarbons containing Cl.The reaction between such free radicals causes strong homopolymerization and oligomeriza-tion.A higher reaction temperature and longer reaction time significantly increased the degree of polymerization and thus increased the softening point of the pitch.A linear molecular structure was formed by the Cl substitution reaction,which produced a highly spinnable pitch with a softening point of 258.6℃,and carbon fibers with a tensile strength of 1163.82 MPa were obtained.This study provides a relatively simple and safe method for the preparation of high-quality spinnable pitch.展开更多
Because of its high purity and excellent orientation, mesophase pitch is a superior precursor for high-performance car-bon materials. However, the preparation of top-notch mesophase pitch faces challenges. Catalytic p...Because of its high purity and excellent orientation, mesophase pitch is a superior precursor for high-performance car-bon materials. However, the preparation of top-notch mesophase pitch faces challenges. Catalytic polycondensation at low temperat-ures is more favorable for synthesizing mesophase pitch, because it circumvents the high-temperature free radical reaction of other thermal polycondensation approaches. The reaction is gentle and can be easily controlled. It has the potential to significantly im-prove the yield of mesophase pitch and easily introduce naphthenic characteristics into the molecules, catalytic polycondensation is therefore a preferred method of synthesizing highly spinnable mesophase pitch. This review provides a synopsis of the selective pre-treatment of the raw materials to prepare different mesophase pitches, and explains the reaction mechanism and associated research advances for different catalytic systems in recent years. Finally, how to manufacture high-quality mesophase pitch by using a cata-lyst-promoter system is summarized and proposed, which may provide a theoretical basis for the future design of high-quality pitch molecules.展开更多
This paper describes the experimental analysis and preliminary investigation of the predictability of pitch angle scattering(PAS) events through the electron cyclotron emission(ECE)radiometer signals at the ADITYA-Upg...This paper describes the experimental analysis and preliminary investigation of the predictability of pitch angle scattering(PAS) events through the electron cyclotron emission(ECE)radiometer signals at the ADITYA-Upgrade(ADITYA-U) tokamak. For low-density discharges at ADITYA-U, a sudden abnormal rise is observed in the ECE signature while other plasma parameters are unchanged. Investigations are done to understand this abrupt rise that is expected to occur due to PAS. The rise time is as fast as 100 μs with a single step and/or multiple step rise in ECE radiometer measurements. This event is known to limit the on-axis energy of runaway electrons. Being a repetitive event, the conditions of its repetitive occurrence can be investigated, thereby exploring the possibility of it being triggered and surveyed as an alternate runaway electron mitigation plan. Functional parameterization of such events with other discharge parameters is obtained and the possibility to trigger these events is discussed.PREDICT code is used to investigate the possible interpretations for the PAS occurrence through modeling and supporting the ECE observations. The trigger values so obtained experimentally are set as input criteria for PAS occurrence. Preliminary modeling investigations provide reliable consistency with the findings.展开更多
A terminal ballistic analysis of the effects of 7.62 mm × 51 AP P80 rounds on inclined high-strength armor steel plates is the focus of the presented study.The findings of an instrumented ballistic testing combin...A terminal ballistic analysis of the effects of 7.62 mm × 51 AP P80 rounds on inclined high-strength armor steel plates is the focus of the presented study.The findings of an instrumented ballistic testing combined with 3D advanced numerical simulations performed using the IMPETUS Afea? software yielded the conclusions.The experimental verification proved that slight differences in the pitch-andyaw angles of a projectile upon an impact caused different damage types to the projectile’s core.The residual velocities predicted numerically were close to the experimental values and the calculated core deviations were in satisfactory agreement with the experimental results.An extended matrix of the core deviation angles with combinations of pitch-and-yaw upon impact angles was subsequently built on the basis of the numerical study.The presented experimental and numerical investigation examined thoroughly the influence of the initial pitch and yaw angles on the after-perforation projectile’s performance.展开更多
Short pitch corrugation has been a problem for railways worldwide over one century.In this paper,a parametric investigation of fastenings is conducted to understand the corrugation formation mechanism and gain insight...Short pitch corrugation has been a problem for railways worldwide over one century.In this paper,a parametric investigation of fastenings is conducted to understand the corrugation formation mechanism and gain insights into corrugation mitigation.A three-dimensional finite element vehicle-track dynamic interaction model is employed,which considers the coupling between the structural dynamics and the contact mechanics,while the damage mechanism is assumed to be differential wear.Various fastening models with different configurations,boundary conditions,and parameters of stiffness and damping are built up and analysed.These models may represent different service stages of fastenings in the field.Besides,the effect of train speeds on corrugation features is studied.The results indicate:(1)Fastening parameters and modelling play an important role in corrugation formation.(2)The fastening longitudinal constraint to the rail is the major factor that determines the corrugation formation.The fastening vertical and lateral constraints influence corrugation features in terms of spatial distribution and wavelength components.(3)The strengthening of fastening constraints in the longitudinal dimension helps to mitigate corrugation.Meanwhile,the inner fastening constraint in the lateral direction is necessary for corrugation alleviation.(4)The increase in fastening longitudinal stiffness and damping can reduce the vibration amplitudes of longitudinal compression modes and thus reduce the track corrugation propensity.The simulation in this work can well explain the field corrugation in terms of the occurrence possibility and major wavelength components.It can also explain the field data with respect to the small variation between the corrugation wavelength and train speed,which is caused by frequency selection and jump between rail longitudinal compression modes.展开更多
Adynamic pitch strategy is usually adopted to improve the aerodynamic performance of the blade of awind turbine.The dynamic pitch motion will affect the linear vibration characteristics of the blade.However,these infl...Adynamic pitch strategy is usually adopted to improve the aerodynamic performance of the blade of awind turbine.The dynamic pitch motion will affect the linear vibration characteristics of the blade.However,these influences have not been studied in previous research.In this paper,the influences of the rigid pitch motion on the linear vibration characteristics of a wind turbine blade are studied.The blade is described as a rotating cantilever beam with an inherent coupled rigid-flexible vibration,where the rigid pitch motion introduces a parametrically excited vibration to the beam.Partial differential equations governing the nonlinear coupled pitch-bend vibration are proposed using the generalized Hamiltonian principle.Natural vibration characteristics of the inherent coupled rigid-flexible system are analyzed based on the combination of the assumed modes method and the multi-scales method.Effects of static pitch angle,rotating speed,and characteristics of harmonic pitch motion on flexible natural frequencies andmode shapes are discussed.It shows that the pitch amplitude has a dramatic influence on the natural frequencies of the blade,while the effects of pitch frequency and pith phase on natural frequencies are little.展开更多
Aiming at the influence of blade pitch Angle on aerodynamic noise of wind turbines, the sound field and flow field distribution at 0˚, 5˚, 10˚ and 15˚ are calculated by numerical simulation. Then, through the distribu...Aiming at the influence of blade pitch Angle on aerodynamic noise of wind turbines, the sound field and flow field distribution at 0˚, 5˚, 10˚ and 15˚ are calculated by numerical simulation. Then, through the distribution of pressure field and velocity field calculated by flow field, the influence of different pitch angles on wind turbine blade aerodynamic noise and the reasons for its influence are analyzed. The results show that when the pitch Angle increases within 0˚ - 10˚, the aerodynamic noise pressure level of the blade decreases. However, the sound pressure level of aerodynamic noise increases in the range of 10˚ - 15˚. The changes of static pressure gradient and pressure pulsation on the blade surface make the aerodynamic noise change, and the changes of the two are positively correlated. At the same time, the fluid velocity and fluid motion state on the blade surface are closely related to the aerodynamic noise of the blade. The greater the fluid velocity, the more complex the fluid motion state and the greater the turbulent kinetic energy of the wind turbine blade, and the aerodynamic noise of the wind turbine blade will also increase.展开更多
Tetrahydrofuran(THF) extract of coal tar pitch(CTP) was used instead of blending CTP with pretreated pyrolysis fuel oil to prepare an isotropic pitch precursor with excellent spinnability for general-purpose carbon fi...Tetrahydrofuran(THF) extract of coal tar pitch(CTP) was used instead of blending CTP with pretreated pyrolysis fuel oil to prepare an isotropic pitch precursor with excellent spinnability for general-purpose carbon fibre through bromination-dehydrobromination. The feasibility and effectiveness of synthesising an isotropic pitch precursor derived from THF-soluble(CTP-THFs) is demonstrated in this study.The results show that CTP-THFs contains more light components than CTP;CTP-THFs and CTP monomer proportions were 62.52% and 45.32%, respectively. However, based on comparisons of CTP-THFsBr0 and CTPBr0 characterisations, CTP-THFs exhibits better polycondensation than CTP. Bromination-dehydrobro mination promotes polycondensation of pitch precursors, leading to greater carbon aromaticity in CTP-THFsBr5, CTP-THFsBr10, and CTP-THFsBr15 than that in CTP-THFsBr0 and CTPBr0. CTP-THFsBr5 and CTP-THFsBr10 have excellent spinnability even with softening points as high as 230 ℃. The pericondensed carbon and carbon aromaticity of CTP-THFsBr5 and CTP-THFsBr10 are high owing to the higher degree of polycondensation;however, they still possess a more linear molecular structure. The as-prepared carbon fibre exhibits homogeneity and uniformity, and the mechanical performance is comparable with that of commercial general-purpose carbon fibre products.展开更多
The microstructures of carbon precursors significantly affect the electrochemical performance of Si/C composite anodes.However,the interaction between Si and carbon materials with different structures is still unclear...The microstructures of carbon precursors significantly affect the electrochemical performance of Si/C composite anodes.However,the interaction between Si and carbon materials with different structures is still unclear.Pitch-based materials undergoing different thermal treatments are superior sources for synthesizing carbons with different structures.Herein,different types of mesophase pitch(domain,flow-domain and mosaic structure) obtained from controllable thermal condensation are utilized to prepare Si/C composite materials and the corresponding models are established through finite element simulation to explore the correlation between the lithium storage properties of Si/C composites and the structures of carbon materials.The results indicate that the flow-domain texture pitch P2 has a better ability to buffer the volume expansion of silicon particles for its highly ordered arrangement of carbon crystallites inside could disperse the swelling stress uniformly alongside the particle surface.The sample Si@P2 exhibits the highest capacity of 1328 mA h/g after 200 cycles at a current density of 0.1 A/g as well as the best rate performance and stability.While sample Si@P3 in which the mosaic texture pitch P3 composed of random orientation of crystallites undergoes the fastest capacity decay.These findings suggest that highly ordered carbon materials are more suitable for the synthesis of Si/C composite anodes and provide insights for understanding the interaction between carbon and silicon during the charging/discharging process.展开更多
The pitch angle distributions of ions and electrons can be affected by various processes;thus,they can serve as an important indicator of the physical mechanisms driving the dynamics of space plasmas.From observations...The pitch angle distributions of ions and electrons can be affected by various processes;thus,they can serve as an important indicator of the physical mechanisms driving the dynamics of space plasmas.From observations from the Mars Ion and Neutral Particle Analyzer onboard the Tianwen-1 orbiter,we calculated the pitch angle distributions of protons in the Martian induced magnetosphere by using information from the magnetohydrodynamically simulated magnetic field,and we statistically analyzed the spatial occurrence pattern of different types of pitch angle distributions.Even though no symmetrical features were seen in the dataset,we found the dominance of the field-aligned distribution type over the energy range from 188 to 6232 eV.Maps of the occurrence rate showed the preferential presence of a trapped-like distribution at the lower altitudes of the surveyed nightside region.Although our results are more or less restricted by the adopted magnetic field,they indicate the complexity of the near-Mars proton pitch angle distributions and infer the possibility of wave–particle interactions in the Martian induced magnetosphere.展开更多
In order to obtain the microwave absorption(MA)materials with light weight,high efficiency and tunable properties,the carbonized mesophase pitch(CMP)with the variation in carbonization temperatures and particle sizes ...In order to obtain the microwave absorption(MA)materials with light weight,high efficiency and tunable properties,the carbonized mesophase pitch(CMP)with the variation in carbonization temperatures and particle sizes were prepared and characterized.The carbonization temperature mainly controlled the graphitization degree of the CMP to affect their conductive loss.The carbon residues were generated on the CMP surface when the temperature was higher than 700℃,which contributed significantly to the polarization loss of the CMP.For scale regulation,the segregation between the particles in the paraffin ring caused by the reduction particles of CMP carbonization at 750℃(750 CMP)resulted in a significant reduction in conductive losses while improving their impedance matching.The 750 CMP over 300 mesh sieved had the strongest MA properties of-53 d B at 3.4 GHz within 5.5 mm.Moreover,the prepared CMPs were multi-layer compounded and optimized by CST microwave studio.The synergistic effect derived from the improved impedance matching and the enhanced interfacial polarization resulted in significant reflection loss in multi-layer CMP.Overall,these findings lead to the systematically regulation of carbon-based materials for MA,showing an attractive application prospect for the preparation of high-performance MA materials.展开更多
To improve the electrochemical performance of graphite anode materials,pitches with various softening points(150℃,180℃,200℃,and 250℃)were prepared from ethylene tar and used to coat graphite through a liquid coati...To improve the electrochemical performance of graphite anode materials,pitches with various softening points(150℃,180℃,200℃,and 250℃)were prepared from ethylene tar and used to coat graphite through a liquid coating process.The effects of the softening point of the pitch and the coating amount on the microstructure and electrochemical properties of graphite were studied by methods including thermogravimetric analysis,X-ray diffraction,Raman spectroscopy,surface area analysis,scanning electron microscopy,transmission electron microscopy,and electrochemical testing.The graphite particles were coated uniformly by the pyrolytic carbon in the pitch.The coating changed the degree of graphitization,decreased the average specific surface area,and improved the electrochemical performance significantly.The best battery anode performance was obtained when the mass ratio of pitch to graphite was 10%,the heat treatment temperature was 1100℃,and the softening point of the pitch was 250℃.Under the optimum conditions,the irreversible capacity loss in the first cycle at 0.1 C was only 23 mAh/g,and the first Coulombic efficiency reached 94.2%.The capacity retention rate was 98.3%after 100 charge-discharge cycles at 0.1 C.展开更多
To ensure wind turbine(WT)safe operations and improve the utilization rate of wind energy,effective evaluation of the operation state of the pitch system is critical.Therefore,a new method was proposed to evaluate the...To ensure wind turbine(WT)safe operations and improve the utilization rate of wind energy,effective evaluation of the operation state of the pitch system is critical.Therefore,a new method was proposed to evaluate the operation state of the pitch system of WT based on fuzzy comprehensive evaluation.Firstly,based on SCADA data,the working state of the pitch system under rated power state and power state of WT were analyzed.Secondly,through the analysis of characteristic parameters and physical mechanism of the pitch system,the consistency principle of characteristic parameters,the stability principle of power under rated state,and the stability principle of blade angle underpowered state were obtained.Next,based on the aforementioned principles,the evaluation indexes were established,and the fuzzy comprehensive evaluation method was used to establish the operation state evaluation model of the pitch system under rated power state and under power state of the WT.Finally,an example was provided to verify the effectiveness of the method.The evaluation model established in this study can be used as a technical reference for the online monitoring of WT pitch systems to ensure the safe and stable operation of WTs.展开更多
There are numerous methods and additives available to improve the durability and quality of road bitumen. A coal tar obtained by coal coking was distilled in a laboratory into fractions of initial boiling point IBP-18...There are numerous methods and additives available to improve the durability and quality of road bitumen. A coal tar obtained by coal coking was distilled in a laboratory into fractions of initial boiling point IBP-180℃ (gasoline-like fuel), 180℃ - 360℃ (diesel-like fuel), and >360℃ (residue or coal tar pitch). The coal tar pitch was added into road bitumen by up to 1 - 5 wt% and investigated the alteration of physical and chemical properties. The physico-mechanical properties of coal tar pitch and bitumen blends, as well as the chemical group composition, were determined using standard techniques (MNS) and the SARA method, respectively. Results of 3% coal tar pitch addition into bitumen enhanced ductility by 12.4% and softening point by 1.6℃. We found that blending with bitumen coal tar pitch as a modifier could improve bitumen properties.展开更多
The underlying principle of pitch determination based on the mean shift algorithm is studied, and the cause of pitch error propagation in the original pseudo code is analyzed. The problem of error propagation is solve...The underlying principle of pitch determination based on the mean shift algorithm is studied, and the cause of pitch error propagation in the original pseudo code is analyzed. The problem of error propagation is solved by choosing an appropriate initial pitch candidate F00. The theoretical choice guideline in a pitch epoch is obtained as ensuring the true pitch F0 satisfying F00/2 〈 F0 〈 3F00/2. The validity of the choice guideline is verified by the F00 experiment. Meanwhile, the algorithm is extended to the pitch determination in the noisy case and compared with the method of subharmonic-to-harmonic ratio （SHR）. The experimental results show that the improved algorithm bears comparison with SHR and it runs much faster than SHR.展开更多
The thrust coefficients and propulsive efficiency of a two-dimensional flexible fin with heaving and pitching motion were computed using FLUENT. The effect of different locations of the pitching axis on propulsive per...The thrust coefficients and propulsive efficiency of a two-dimensional flexible fin with heaving and pitching motion were computed using FLUENT. The effect of different locations of the pitching axis on propulsive performance was examined using three deflexion modes which are respectively, modified Bose mode, cantilever beam with uniformly distributed load and cantilever beam with non-uniformly distributed load. The results show that maximum thrust can be achieved with the pitching axis at the trailing edge, but the highest propulsive efficiency can be achieved with the pitching axis either 1/3 of the chord length from the leading edge in modified Bose mode, or 2/3 of the chord length from the leading edge in cantilever beam mode. At the same time, the effects of the Strouhal number and maximal attack angle on the hydrodynamics performance of the flexible fin were analyzed. Parameter interval of the maximum thrust coefficient and the highest propulsive efficiency were gained. If the Strouhal number is low, high propulsive efficiency can be achieved at low αmax , and vice versa.展开更多
In this paper, hydrodynamic analysis of vertical axis tidal turbine （both fixed pitch ＆ variable pitch） is numerically analyzed. Two-dimensional numerical modeling ＆ simulation of the unsteady flow through the bla...In this paper, hydrodynamic analysis of vertical axis tidal turbine （both fixed pitch ＆ variable pitch） is numerically analyzed. Two-dimensional numerical modeling ＆ simulation of the unsteady flow through the blades of the turbine is performed using ANSYS CFX, hereafter CFX, which is based on a Reynolds-Averaged Navier-Stokes （RANS） model. A transient simulation is done for fixed pitch and variable pitch vertical axis tidal turbine using a Shear Stress Transport turbulence （SST） scheme. Main hydrodynamic parameters like torque T, combined moment CM, coefficients of performance Cp and coefficient of torque Cr, etc. are investigated. The modeling and meshing of turbine rotor is performed in ICEM-CFD. Moreover, the difference in meshing schemes between fixed pitch and variable pitch is also mentioned. Mesh motion option is employed for variable pitch turbine. This article is one part of the ongoing research on tm＇bine design and developments. The numerical simulation results are validated with well reputed analytical results performed by Edinburgh Design Ltd. The article concludes with a parametric study of turbine performance, comparison between fixed and variable pitch operation for a four-bladed turbine. It is found that for variable pitch we get maximum Ce and peak power at smaller revolution per minute N and tip sped ratio 2.展开更多
Collective pitch control and individual pitch control algorithms were present for straight-bladed vertical axis wind turbine to improve the self-starting capacity.Comparative analysis of straight-bladed vertical axis ...Collective pitch control and individual pitch control algorithms were present for straight-bladed vertical axis wind turbine to improve the self-starting capacity.Comparative analysis of straight-bladed vertical axis wind turbine(SB-VAWT) with or without pitch control was conducted from the aspects of aerodynamic force,flow structure and power coefficient.The computational fluid dynamics(CFD) prediction results show a significant increase in power coefficient for SB-VAWT with pitch control.According to the aerodynamic forces and total torque coefficient obtained at various tip speed ratios(TSRs),the results indicate that the blade pitch method can increase the power output and decrease the deformation of blade;especially,the total torque coefficient of blade pitch control at TSR 1.5 is about 2.5 times larger than that of fixed pitch case.Furthermore,experiment was carried out to verify the feasibility of pitch control methods.The results show that the present collective pitch control and individual pitch control methods can improve the self-starting capacity of SB-VAWT,and the former is much better and its proper operating TSRs ranges from 0.4 to 0.6.展开更多
A combined experimental and numerical investigation is carried out to study the performance of a vertical-axis eccentric-disc variable-pitch turbine(VEVT).A scheme of eccentric disc pitch control mechanism based on do...A combined experimental and numerical investigation is carried out to study the performance of a vertical-axis eccentric-disc variable-pitch turbine(VEVT).A scheme of eccentric disc pitch control mechanism based on doubleblock mechanism is proposed.The eccentric control mechanism and the deflection angle control mechanism in the pitch control structure are designed and optimized according to the functional requirements of the turbine,and the three-dimensional model of the turbine is established.Kinematics analysis of the eccentric disc pitch control mechanism is carried out.Kinematics parameters and kinematics equations which can characterize its motion characteristics are derived.Kinematics analysis and simulation are carried out,and the motion law of the corresponding mechanical system is obtained.By analyzing the force and motion of blade of VEVT,the expressions of the important parameters such as deflection angle,attack angle and energy utilization coefficient are obtained.The lateral induced velocity coefficient is acquired by momentum theorem,the hydrodynamic parameters such as energy utilization coefficient are derived,and the hydrodynamic characteristics of VEVT are also obtained.The experimental results show that the turbine has good energy capture capability at different inflow velocities of different sizes and directions,which verifies that VEVT has good self-startup performance and high energy capture efficiency.展开更多
文摘Graphitized carbon foams(GFms)were prepared using mesophase pitch(MP)as a raw material by foaming(450℃),pre-oxidation(320℃),carbonization(1000℃)and graphitization(2800℃).The differences in structure and properties of GFms prepared from different MP precursors pretreated by ball milling or liquid phase extraction were investigated and compared,and semi-quantitative calculations were conducted on the Raman and FTIR spectra of samples at each preparation stage.Semi-quantitat-ive spectroscopic analysis provided detailed information on the structure and chemical composition changes of the MP and GFm de-rived from it.Combined with microscopic observations,the change from precursor to GFm was analyzed.The results showed that ball milling concentrated the distribution of aromatic molecules in the pitch,which contributed to uniform foaming to give a GFm with a uniform pore distribution and good properties.Liquid phase extraction helped remove light components while retaining large aromatics to form graphitic planes with the largest average size during post-treatment to produce a GFm with the highest degree of graphitization and the fewest open pores,giving the best compression resistance(2.47 MPa),the highest thermal conductivity(64.47 W/(m·K))and the lowest electrical resistance(13.02μΩ·m).Characterization combining semi-quantitative spectroscopic ana-lysis with microscopic observations allowed us to control the preparation of the MP-derived GFms.
文摘The preparation of a synthetic pitch from aromatic monomers could easily regulate structure orientation at the molecu-lar level,which would be useful in fabrication.An isotropic synthetic pitch was prepared by a chlorine-and/or nitrogen-induced sub-stitution polymerization reaction method using aromatic hydrocarbon precursors containing Cl and N,which for this study were chloromethyl naphthalene and quinoline.This method was verified by investigating the structural changes under different synthesis conditions,and the synthesis mechanism induced by aromatics containing Cl was also probed.The result shows that the pyridinic N in quinoline contains a lone pair of electrons,and is an effective active site to induce the polymerization reaction by coupling with aromatic hydrocarbons containing Cl.The reaction between such free radicals causes strong homopolymerization and oligomeriza-tion.A higher reaction temperature and longer reaction time significantly increased the degree of polymerization and thus increased the softening point of the pitch.A linear molecular structure was formed by the Cl substitution reaction,which produced a highly spinnable pitch with a softening point of 258.6℃,and carbon fibers with a tensile strength of 1163.82 MPa were obtained.This study provides a relatively simple and safe method for the preparation of high-quality spinnable pitch.
文摘Because of its high purity and excellent orientation, mesophase pitch is a superior precursor for high-performance car-bon materials. However, the preparation of top-notch mesophase pitch faces challenges. Catalytic polycondensation at low temperat-ures is more favorable for synthesizing mesophase pitch, because it circumvents the high-temperature free radical reaction of other thermal polycondensation approaches. The reaction is gentle and can be easily controlled. It has the potential to significantly im-prove the yield of mesophase pitch and easily introduce naphthenic characteristics into the molecules, catalytic polycondensation is therefore a preferred method of synthesizing highly spinnable mesophase pitch. This review provides a synopsis of the selective pre-treatment of the raw materials to prepare different mesophase pitches, and explains the reaction mechanism and associated research advances for different catalytic systems in recent years. Finally, how to manufacture high-quality mesophase pitch by using a cata-lyst-promoter system is summarized and proposed, which may provide a theoretical basis for the future design of high-quality pitch molecules.
文摘This paper describes the experimental analysis and preliminary investigation of the predictability of pitch angle scattering(PAS) events through the electron cyclotron emission(ECE)radiometer signals at the ADITYA-Upgrade(ADITYA-U) tokamak. For low-density discharges at ADITYA-U, a sudden abnormal rise is observed in the ECE signature while other plasma parameters are unchanged. Investigations are done to understand this abrupt rise that is expected to occur due to PAS. The rise time is as fast as 100 μs with a single step and/or multiple step rise in ECE radiometer measurements. This event is known to limit the on-axis energy of runaway electrons. Being a repetitive event, the conditions of its repetitive occurrence can be investigated, thereby exploring the possibility of it being triggered and surveyed as an alternate runaway electron mitigation plan. Functional parameterization of such events with other discharge parameters is obtained and the possibility to trigger these events is discussed.PREDICT code is used to investigate the possible interpretations for the PAS occurrence through modeling and supporting the ECE observations. The trigger values so obtained experimentally are set as input criteria for PAS occurrence. Preliminary modeling investigations provide reliable consistency with the findings.
文摘A terminal ballistic analysis of the effects of 7.62 mm × 51 AP P80 rounds on inclined high-strength armor steel plates is the focus of the presented study.The findings of an instrumented ballistic testing combined with 3D advanced numerical simulations performed using the IMPETUS Afea? software yielded the conclusions.The experimental verification proved that slight differences in the pitch-andyaw angles of a projectile upon an impact caused different damage types to the projectile’s core.The residual velocities predicted numerically were close to the experimental values and the calculated core deviations were in satisfactory agreement with the experimental results.An extended matrix of the core deviation angles with combinations of pitch-and-yaw upon impact angles was subsequently built on the basis of the numerical study.The presented experimental and numerical investigation examined thoroughly the influence of the initial pitch and yaw angles on the after-perforation projectile’s performance.
文摘Short pitch corrugation has been a problem for railways worldwide over one century.In this paper,a parametric investigation of fastenings is conducted to understand the corrugation formation mechanism and gain insights into corrugation mitigation.A three-dimensional finite element vehicle-track dynamic interaction model is employed,which considers the coupling between the structural dynamics and the contact mechanics,while the damage mechanism is assumed to be differential wear.Various fastening models with different configurations,boundary conditions,and parameters of stiffness and damping are built up and analysed.These models may represent different service stages of fastenings in the field.Besides,the effect of train speeds on corrugation features is studied.The results indicate:(1)Fastening parameters and modelling play an important role in corrugation formation.(2)The fastening longitudinal constraint to the rail is the major factor that determines the corrugation formation.The fastening vertical and lateral constraints influence corrugation features in terms of spatial distribution and wavelength components.(3)The strengthening of fastening constraints in the longitudinal dimension helps to mitigate corrugation.Meanwhile,the inner fastening constraint in the lateral direction is necessary for corrugation alleviation.(4)The increase in fastening longitudinal stiffness and damping can reduce the vibration amplitudes of longitudinal compression modes and thus reduce the track corrugation propensity.The simulation in this work can well explain the field corrugation in terms of the occurrence possibility and major wavelength components.It can also explain the field data with respect to the small variation between the corrugation wavelength and train speed,which is caused by frequency selection and jump between rail longitudinal compression modes.
基金supported by the University Outstanding Youth Researcher Support Program of the Education Department of Anhui Province,the National Natural Science Foundation of China(Grant Nos.11902002 and 51705002)the Sichuan Provincial Natural Science Foundation(Grant No.2022NSFSC0275)+1 种基金the Science and Technology Research Project of Chongqing Municipal Education Commission(Grant No.KJQN201901146)the Special Key Project of Technological Innovation and Application Development in Chongqing(Grant No.cstc2020jscx-dxwtBX0048).
文摘Adynamic pitch strategy is usually adopted to improve the aerodynamic performance of the blade of awind turbine.The dynamic pitch motion will affect the linear vibration characteristics of the blade.However,these influences have not been studied in previous research.In this paper,the influences of the rigid pitch motion on the linear vibration characteristics of a wind turbine blade are studied.The blade is described as a rotating cantilever beam with an inherent coupled rigid-flexible vibration,where the rigid pitch motion introduces a parametrically excited vibration to the beam.Partial differential equations governing the nonlinear coupled pitch-bend vibration are proposed using the generalized Hamiltonian principle.Natural vibration characteristics of the inherent coupled rigid-flexible system are analyzed based on the combination of the assumed modes method and the multi-scales method.Effects of static pitch angle,rotating speed,and characteristics of harmonic pitch motion on flexible natural frequencies andmode shapes are discussed.It shows that the pitch amplitude has a dramatic influence on the natural frequencies of the blade,while the effects of pitch frequency and pith phase on natural frequencies are little.
文摘Aiming at the influence of blade pitch Angle on aerodynamic noise of wind turbines, the sound field and flow field distribution at 0˚, 5˚, 10˚ and 15˚ are calculated by numerical simulation. Then, through the distribution of pressure field and velocity field calculated by flow field, the influence of different pitch angles on wind turbine blade aerodynamic noise and the reasons for its influence are analyzed. The results show that when the pitch Angle increases within 0˚ - 10˚, the aerodynamic noise pressure level of the blade decreases. However, the sound pressure level of aerodynamic noise increases in the range of 10˚ - 15˚. The changes of static pressure gradient and pressure pulsation on the blade surface make the aerodynamic noise change, and the changes of the two are positively correlated. At the same time, the fluid velocity and fluid motion state on the blade surface are closely related to the aerodynamic noise of the blade. The greater the fluid velocity, the more complex the fluid motion state and the greater the turbulent kinetic energy of the wind turbine blade, and the aerodynamic noise of the wind turbine blade will also increase.
基金the financial support provided by the National Natural Science Foundation of China (22008254)the Fundamental Research Funds for the Central Universities (2020XJHH01)+1 种基金the National Training Program of Innovation and Entrepreneurship for Undergraduates (C202003309)China University of Mining and Technology (Beijing) Yueqi Outstanding Scholar Project (2020JCB02)。
文摘Tetrahydrofuran(THF) extract of coal tar pitch(CTP) was used instead of blending CTP with pretreated pyrolysis fuel oil to prepare an isotropic pitch precursor with excellent spinnability for general-purpose carbon fibre through bromination-dehydrobromination. The feasibility and effectiveness of synthesising an isotropic pitch precursor derived from THF-soluble(CTP-THFs) is demonstrated in this study.The results show that CTP-THFs contains more light components than CTP;CTP-THFs and CTP monomer proportions were 62.52% and 45.32%, respectively. However, based on comparisons of CTP-THFsBr0 and CTPBr0 characterisations, CTP-THFs exhibits better polycondensation than CTP. Bromination-dehydrobro mination promotes polycondensation of pitch precursors, leading to greater carbon aromaticity in CTP-THFsBr5, CTP-THFsBr10, and CTP-THFsBr15 than that in CTP-THFsBr0 and CTPBr0. CTP-THFsBr5 and CTP-THFsBr10 have excellent spinnability even with softening points as high as 230 ℃. The pericondensed carbon and carbon aromaticity of CTP-THFsBr5 and CTP-THFsBr10 are high owing to the higher degree of polycondensation;however, they still possess a more linear molecular structure. The as-prepared carbon fibre exhibits homogeneity and uniformity, and the mechanical performance is comparable with that of commercial general-purpose carbon fibre products.
基金financial support from the National Key Research and Development Programme (2018YFC1801901)the National Natural Science Foundation of China (21808115, 22108309, 52172093)+1 种基金the Key Research and Development Project (Major Project of Scientific and Technological Innovation) of Shandong Province (2020CXGC010308)the Taishan Scholar Program of Shandong (ts20190919)。
文摘The microstructures of carbon precursors significantly affect the electrochemical performance of Si/C composite anodes.However,the interaction between Si and carbon materials with different structures is still unclear.Pitch-based materials undergoing different thermal treatments are superior sources for synthesizing carbons with different structures.Herein,different types of mesophase pitch(domain,flow-domain and mosaic structure) obtained from controllable thermal condensation are utilized to prepare Si/C composite materials and the corresponding models are established through finite element simulation to explore the correlation between the lithium storage properties of Si/C composites and the structures of carbon materials.The results indicate that the flow-domain texture pitch P2 has a better ability to buffer the volume expansion of silicon particles for its highly ordered arrangement of carbon crystallites inside could disperse the swelling stress uniformly alongside the particle surface.The sample Si@P2 exhibits the highest capacity of 1328 mA h/g after 200 cycles at a current density of 0.1 A/g as well as the best rate performance and stability.While sample Si@P3 in which the mosaic texture pitch P3 composed of random orientation of crystallites undergoes the fastest capacity decay.These findings suggest that highly ordered carbon materials are more suitable for the synthesis of Si/C composite anodes and provide insights for understanding the interaction between carbon and silicon during the charging/discharging process.
基金supported by the National Natural Science Foundation of China(Grant No.42241143)the pre-research projects on Civil Aerospace Technologies(No.D020104)funded by the China National Space Administration.
文摘The pitch angle distributions of ions and electrons can be affected by various processes;thus,they can serve as an important indicator of the physical mechanisms driving the dynamics of space plasmas.From observations from the Mars Ion and Neutral Particle Analyzer onboard the Tianwen-1 orbiter,we calculated the pitch angle distributions of protons in the Martian induced magnetosphere by using information from the magnetohydrodynamically simulated magnetic field,and we statistically analyzed the spatial occurrence pattern of different types of pitch angle distributions.Even though no symmetrical features were seen in the dataset,we found the dominance of the field-aligned distribution type over the energy range from 188 to 6232 eV.Maps of the occurrence rate showed the preferential presence of a trapped-like distribution at the lower altitudes of the surveyed nightside region.Although our results are more or less restricted by the adopted magnetic field,they indicate the complexity of the near-Mars proton pitch angle distributions and infer the possibility of wave–particle interactions in the Martian induced magnetosphere.
基金supported by Sichuan Science and Technology Program,Grant No.2022YFG0111the Postdoctoral Innovative Talent Support Program(Grant No.BX20190220)the State Key Laboratory of Polymer Materials Engineering(Grant No.sklpme2019-2-02)for financial support。
文摘In order to obtain the microwave absorption(MA)materials with light weight,high efficiency and tunable properties,the carbonized mesophase pitch(CMP)with the variation in carbonization temperatures and particle sizes were prepared and characterized.The carbonization temperature mainly controlled the graphitization degree of the CMP to affect their conductive loss.The carbon residues were generated on the CMP surface when the temperature was higher than 700℃,which contributed significantly to the polarization loss of the CMP.For scale regulation,the segregation between the particles in the paraffin ring caused by the reduction particles of CMP carbonization at 750℃(750 CMP)resulted in a significant reduction in conductive losses while improving their impedance matching.The 750 CMP over 300 mesh sieved had the strongest MA properties of-53 d B at 3.4 GHz within 5.5 mm.Moreover,the prepared CMPs were multi-layer compounded and optimized by CST microwave studio.The synergistic effect derived from the improved impedance matching and the enhanced interfacial polarization resulted in significant reflection loss in multi-layer CMP.Overall,these findings lead to the systematically regulation of carbon-based materials for MA,showing an attractive application prospect for the preparation of high-performance MA materials.
基金This work was financially supported by the Research Program of China Petrochemical Corporation(SINOPEC 121023).
文摘To improve the electrochemical performance of graphite anode materials,pitches with various softening points(150℃,180℃,200℃,and 250℃)were prepared from ethylene tar and used to coat graphite through a liquid coating process.The effects of the softening point of the pitch and the coating amount on the microstructure and electrochemical properties of graphite were studied by methods including thermogravimetric analysis,X-ray diffraction,Raman spectroscopy,surface area analysis,scanning electron microscopy,transmission electron microscopy,and electrochemical testing.The graphite particles were coated uniformly by the pyrolytic carbon in the pitch.The coating changed the degree of graphitization,decreased the average specific surface area,and improved the electrochemical performance significantly.The best battery anode performance was obtained when the mass ratio of pitch to graphite was 10%,the heat treatment temperature was 1100℃,and the softening point of the pitch was 250℃.Under the optimum conditions,the irreversible capacity loss in the first cycle at 0.1 C was only 23 mAh/g,and the first Coulombic efficiency reached 94.2%.The capacity retention rate was 98.3%after 100 charge-discharge cycles at 0.1 C.
基金supported by National Natural Science Foundation of China(Nos.51875199 and 51905165)Hunan Natural Science Fund Project(2019JJ50186)the Key Research and Development Program of Hunan Province(No.2018GK2073).
文摘To ensure wind turbine(WT)safe operations and improve the utilization rate of wind energy,effective evaluation of the operation state of the pitch system is critical.Therefore,a new method was proposed to evaluate the operation state of the pitch system of WT based on fuzzy comprehensive evaluation.Firstly,based on SCADA data,the working state of the pitch system under rated power state and power state of WT were analyzed.Secondly,through the analysis of characteristic parameters and physical mechanism of the pitch system,the consistency principle of characteristic parameters,the stability principle of power under rated state,and the stability principle of blade angle underpowered state were obtained.Next,based on the aforementioned principles,the evaluation indexes were established,and the fuzzy comprehensive evaluation method was used to establish the operation state evaluation model of the pitch system under rated power state and under power state of the WT.Finally,an example was provided to verify the effectiveness of the method.The evaluation model established in this study can be used as a technical reference for the online monitoring of WT pitch systems to ensure the safe and stable operation of WTs.
文摘There are numerous methods and additives available to improve the durability and quality of road bitumen. A coal tar obtained by coal coking was distilled in a laboratory into fractions of initial boiling point IBP-180℃ (gasoline-like fuel), 180℃ - 360℃ (diesel-like fuel), and >360℃ (residue or coal tar pitch). The coal tar pitch was added into road bitumen by up to 1 - 5 wt% and investigated the alteration of physical and chemical properties. The physico-mechanical properties of coal tar pitch and bitumen blends, as well as the chemical group composition, were determined using standard techniques (MNS) and the SARA method, respectively. Results of 3% coal tar pitch addition into bitumen enhanced ductility by 12.4% and softening point by 1.6℃. We found that blending with bitumen coal tar pitch as a modifier could improve bitumen properties.
基金The National Basic Research Program of China (973Program) (No2002CB312102)
文摘The underlying principle of pitch determination based on the mean shift algorithm is studied, and the cause of pitch error propagation in the original pseudo code is analyzed. The problem of error propagation is solved by choosing an appropriate initial pitch candidate F00. The theoretical choice guideline in a pitch epoch is obtained as ensuring the true pitch F0 satisfying F00/2 〈 F0 〈 3F00/2. The validity of the choice guideline is verified by the F00 experiment. Meanwhile, the algorithm is extended to the pitch determination in the noisy case and compared with the method of subharmonic-to-harmonic ratio （SHR）. The experimental results show that the improved algorithm bears comparison with SHR and it runs much faster than SHR.
基金Supported by the National Natural Science Foundation of China under Grant No.50879031
文摘The thrust coefficients and propulsive efficiency of a two-dimensional flexible fin with heaving and pitching motion were computed using FLUENT. The effect of different locations of the pitching axis on propulsive performance was examined using three deflexion modes which are respectively, modified Bose mode, cantilever beam with uniformly distributed load and cantilever beam with non-uniformly distributed load. The results show that maximum thrust can be achieved with the pitching axis at the trailing edge, but the highest propulsive efficiency can be achieved with the pitching axis either 1/3 of the chord length from the leading edge in modified Bose mode, or 2/3 of the chord length from the leading edge in cantilever beam mode. At the same time, the effects of the Strouhal number and maximal attack angle on the hydrodynamics performance of the flexible fin were analyzed. Parameter interval of the maximum thrust coefficient and the highest propulsive efficiency were gained. If the Strouhal number is low, high propulsive efficiency can be achieved at low αmax , and vice versa.
基金financially supported by National "863" Program (Grant No.2007AA05Z450, No. 200805040)National S&T Program (No.2008BAA15B04)+2 种基金2010 National Ocean Special Funds(No.ZJME2010GC01, No. ZJME2010CY01, No.GHME2010GC02)supported by the Fundamental Research Funds of the Universities(No.HEUCF130105)supported by "111 project" foundation(No. B07019) from State Administration of Foreign Experts Affairs of China and Ministry of Education of China
文摘In this paper, hydrodynamic analysis of vertical axis tidal turbine （both fixed pitch ＆ variable pitch） is numerically analyzed. Two-dimensional numerical modeling ＆ simulation of the unsteady flow through the blades of the turbine is performed using ANSYS CFX, hereafter CFX, which is based on a Reynolds-Averaged Navier-Stokes （RANS） model. A transient simulation is done for fixed pitch and variable pitch vertical axis tidal turbine using a Shear Stress Transport turbulence （SST） scheme. Main hydrodynamic parameters like torque T, combined moment CM, coefficients of performance Cp and coefficient of torque Cr, etc. are investigated. The modeling and meshing of turbine rotor is performed in ICEM-CFD. Moreover, the difference in meshing schemes between fixed pitch and variable pitch is also mentioned. Mesh motion option is employed for variable pitch turbine. This article is one part of the ongoing research on tm＇bine design and developments. The numerical simulation results are validated with well reputed analytical results performed by Edinburgh Design Ltd. The article concludes with a parametric study of turbine performance, comparison between fixed and variable pitch operation for a four-bladed turbine. It is found that for variable pitch we get maximum Ce and peak power at smaller revolution per minute N and tip sped ratio 2.
基金Project (E201216) supported by Heilongjiang Provincial Natural Science Foundation,China
文摘Collective pitch control and individual pitch control algorithms were present for straight-bladed vertical axis wind turbine to improve the self-starting capacity.Comparative analysis of straight-bladed vertical axis wind turbine(SB-VAWT) with or without pitch control was conducted from the aspects of aerodynamic force,flow structure and power coefficient.The computational fluid dynamics(CFD) prediction results show a significant increase in power coefficient for SB-VAWT with pitch control.According to the aerodynamic forces and total torque coefficient obtained at various tip speed ratios(TSRs),the results indicate that the blade pitch method can increase the power output and decrease the deformation of blade;especially,the total torque coefficient of blade pitch control at TSR 1.5 is about 2.5 times larger than that of fixed pitch case.Furthermore,experiment was carried out to verify the feasibility of pitch control methods.The results show that the present collective pitch control and individual pitch control methods can improve the self-starting capacity of SB-VAWT,and the former is much better and its proper operating TSRs ranges from 0.4 to 0.6.
基金the National Natural Science Foundation of China(Grant Nos.U1706227 and 51979063)the Harbin Applied Technology Research and Development Project(Grant No.2015RQXXJ016)the Basic Research and Cutting-Edge Technology Projects of State Administration of Science(Grant No.JCKY2019604C003).
文摘A combined experimental and numerical investigation is carried out to study the performance of a vertical-axis eccentric-disc variable-pitch turbine(VEVT).A scheme of eccentric disc pitch control mechanism based on doubleblock mechanism is proposed.The eccentric control mechanism and the deflection angle control mechanism in the pitch control structure are designed and optimized according to the functional requirements of the turbine,and the three-dimensional model of the turbine is established.Kinematics analysis of the eccentric disc pitch control mechanism is carried out.Kinematics parameters and kinematics equations which can characterize its motion characteristics are derived.Kinematics analysis and simulation are carried out,and the motion law of the corresponding mechanical system is obtained.By analyzing the force and motion of blade of VEVT,the expressions of the important parameters such as deflection angle,attack angle and energy utilization coefficient are obtained.The lateral induced velocity coefficient is acquired by momentum theorem,the hydrodynamic parameters such as energy utilization coefficient are derived,and the hydrodynamic characteristics of VEVT are also obtained.The experimental results show that the turbine has good energy capture capability at different inflow velocities of different sizes and directions,which verifies that VEVT has good self-startup performance and high energy capture efficiency.
