Research is scarce on non-financial characteristics, including owner characteristics and their influences on capital structure in the establishment phase. The objective of this study is to examine the factors affectin...Research is scarce on non-financial characteristics, including owner characteristics and their influences on capital structure in the establishment phase. The objective of this study is to examine the factors affecting firms＇ availability of external finance, utilizing a sample of Finnish start-up micro firms. The overall purpose is not to produce a comprehensive model for capital structure, but to illustrate the importance of non-accounting characteristics in explaining the attractiveness of the new venture from the lender＇s point of view. The results show that a founder who has prior work experience from the same sector and has little or no personal financial property seems to have higher leverage. After splitting the data into survived and failed firms, lenders viewed work experience positively only in the sample of failed firms. In addition, limited liability companies, firms located in bigger cities, and firms with good demand evaluated by the lender have a lower level of leverage.展开更多
This research paper investigates the role of Italian venture capital in supporting innovative start-ups in their early-stage process,which is usually focused on the creation of a new product or the development of a ne...This research paper investigates the role of Italian venture capital in supporting innovative start-ups in their early-stage process,which is usually focused on the creation of a new product or the development of a new service.The aim of the study is to observe and assess the key economic features of innovative start-ups funded at the beginning of the early-stage by venture capital funds and thereafter analyze the level of development of target companies at four years since the capital injection.The sample of deals created to describe this dynamic process is composed by investments realized between 1996 and 2012 and,in this way,according to the chosen methodology,it is representative of Italian venture capital role and contribution in the years from 1996 to 2016.The authors used for their empirical study a proprietary database,Venture Capital Monitor—VeMTM.Through the analysis of collected data,the paper describes the strategic importance of venture capital investments in early-stage opportunities both for target companies and the Italian socio-economic environment,and finds aggregate values of reference to quantitatively define the socio-economic outcome of this kind of operations.A final further contribution is provided by comparing the present results to the ones of two previous studies conducted by the authors.展开更多
Financial resilience refers to a start-up's capacity to anticipate,plan for,respond to,and adapt to gradual change and abrupt unforeseen shocks to survive and thrive by enacting appropriate economic policies to de...Financial resilience refers to a start-up's capacity to anticipate,plan for,respond to,and adapt to gradual change and abrupt unforeseen shocks to survive and thrive by enacting appropriate economic policies to decrease budget deficits.Economic history tells us that more companies fail to emerge from a downturn than go into or during it.Many studies have been done on financial resilience in many dimensions,but no one has studied start-ups’organizational readiness for financial resilience.This gap inspires the current research,which uses the Total Interpretive Structural Modelling(TISM)approach to identify financial resilience factors and analyze hierarchical interrelationships start-ups’organizational readiness factors for financial resilience.This article aims to identify,assess,and categorize start-up organizational preparation elements for financial resilience.The result shows that the first importance should be given to digital financial innovation,liquidity planning,going concern consideration,financial strategy of CFOs,and cyberthreats.Managers of start-ups can utilize the findings of this study to prepare for financial resilience professionally.In a fast-paced environment,start-ups may use financial resilience to gain a competitive edge.展开更多
A nonlinear mathematical model of the low-frequency dynamics of the clustered multi-engine rocket propulsion system has been developed and the computations of the engine transient processes during the start-ups of the...A nonlinear mathematical model of the low-frequency dynamics of the clustered multi-engine rocket propulsion system has been developed and the computations of the engine transient processes during the start-ups of the four-engine propulsion system with a shared feed system have been made applied.Based on propulsion system start-up modeling the influence of the connectivity of engines in a cluster on the starting characteristics of individual engines is shown.In particular,an advanced nonlinear mathematical model of the pump cavitation phenomena is a distinctive feature of the mathematical model.The computation results showed that the asynchronous engines start-ups during rocket lift-off lead to severely nonlinear engine transients and clustered engine thrust misbalance.The influence of the rocket engines asynchronous start-ups on the clustered feed system transients depends on many factors,mainly on from the clustered feed system low-frequency dynamics,the magnitude of the disturbance and the phase difference between disturbances acting on different branches of the feed system.The deep lingering dips in the flow rate and pressure transients are possible due to the nonlinear dynamic interaction of the engines.In case of great pressure dips at the pump inlet(up to the pressure of saturated vapors during significant periods of start-up time)the cavitation breakdowns of the pumps of one or more engines from the cluster are possible.This can disrupt the operation of the entire propulsion system and leads to the failure of the launch vehicle mission.展开更多
According to the physics of tokamak start-up,this study constructs a zero-dimensional(0D)model applicable to electron cyclotron(EC)wave assisted start-up in NCST spherical torus(spherical tokamak)and CN-H1 stellarator...According to the physics of tokamak start-up,this study constructs a zero-dimensional(0D)model applicable to electron cyclotron(EC)wave assisted start-up in NCST spherical torus(spherical tokamak)and CN-H1 stellarators.Using the constructed 0D model,the results obtained in this study under the same conditions are compared and validated against reference results for pure hydrogen plasma start-up in tokamak.The results are in good agreement,especially regarding electron temperature,ion temperature and plasma current.In the presence of finite Ohmic electric field in the spherical tokamak,a study on the EC wave assisted start-up of the NCST plasma at frequency of 28 GHz is conducted.The impact of the vertical magnetic field B_(v)on EC wave assisted start-up,the relationship between EC wave injection power P_(inj),Ohmic electric field E,and initial hydrogen atom density n_(H0)are explored separately.It is found that under conditions of Ohmic electric field lower than ITER(~0.3 V m^(-1)),EC wave can expand the operational space to achieve better plasma parameters.Simulating the process of28 GHz EC wave start-up in the CN-H1 stellarator plasma,the plasma current in the zerodimensional model is replaced with the current in the poloidal coil of the stellarator.Plasma startup can be successfully achieved at injection powers in the hundreds of kilowatts range,resulting in electron densities on the order of 10^(17)-10^(18)m^(-3).展开更多
Solid rocket motors have important applications in the propulsion of trans-media vehicles and underwater launched rockets.In this paper,the ignition start-up process of an underwater solid rocket motor across a wide d...Solid rocket motors have important applications in the propulsion of trans-media vehicles and underwater launched rockets.In this paper,the ignition start-up process of an underwater solid rocket motor across a wide depth range has been numerically studied.A novel multi-domain integrated model has been developed by combining the solid propellant ignition and combustion model with the volume of fluid multiphase model.This integrated model enables the coupled simulation of the propellant combustion and gas flow inside the motor,along with the gas jet evolution in the external water environment.The detailed flow field developments in the combustion chamber,nozzle,and wake field are carefully analyzed.The variation rules of the internal ballistics and thrust performance are also obtained.The effects of environmental medium and operating depth on the ignition start-up process are systematically discussed.The results show that the influence of the operating environment on the internal ballistic characteristics is primarily reflected in the initial period after the nozzle closure opens.The development of the gas jet in water lags significantly compared with that in air.As the water depth increases,the ignition delay time of the motor is shortened,and the morphology evolution of the gas jet is significantly compressed and accelerated.Furthermore,the necking and bulging of the jet boundary near the nozzle outlet and the consequent shock oscillations are intensified,resulting in stronger fluctuations in the wake pressure field and motor thrust.展开更多
The biotreatment of mine drainage containing dissolved manganese(Mn)using Mn(II)-oxidizing bacteria is challenging.Sequencing-batch(SBRs)and continuous-flow reactors(CFRs)packed with limestones and inoculated with the...The biotreatment of mine drainage containing dissolved manganese(Mn)using Mn(II)-oxidizing bacteria is challenging.Sequencing-batch(SBRs)and continuous-flow reactors(CFRs)packed with limestones and inoculated with the mine-drainage microbial communitywere compared to determine the removal efficiency of Mn(II)from mine drainage.Mn(II)removal in CFRs was 11.4%±0.0%(mean±standard deviation)in the first two weeks and;it slightly increased to 13.6%±0.0%after four weeks,and more than 94%of Mn(II)was removed under the steady-state treatment phase.The performance of SBRs was more effective,wherein 24.4%±0.1%of Mn was removed in the first two weeks,and in four weeks,surpassed 66.6%±0.2%.Rapid Mn(II)removal observed in the start-up of SBR resulted from higher microbial metabolic activities.The adenosine triphosphate(ATP)content of the microbial community was four-fold more than in CFR,but comparable during the steady-state phase.The Mn-oxide deposits occurring in the SBR and CFR at steady-state were mixed phases of birnessite and woodruffite,and the average Mn oxidation valence in the SBR(+3.73)was slightly higher than that in the CFR(+3.54).During the start-up treatment,the closest relatives of Methyloversatilis,Methylibium,and Curvibacter dominated the SBR,whereas putative Mn oxidizers were associated with Hyphomicrobium,Pedobacter,Pedomicrobium,Terricaulis sp.,Sulfuritalea,and Terrimonas organisms.The growth of potential Mnoxidizing genera,including Mesorhizobium,Rhodococcus,Hydrogenophaga,Terricaulis sp.,and‘Candidatus Manganitrophus-noduliformans’was observed under the steady state.The SBR operation was effective as a prior start-up treatment for mine drainage-containing Mn(II),through which the CFR performed well as posterior bio-treatment.展开更多
To address the excessive complexity of monthly scheduling and the impact of uncertain net load on the chargeable energy of storage,a reduced time-period monthly scheduling model for thermal generators and energy stora...To address the excessive complexity of monthly scheduling and the impact of uncertain net load on the chargeable energy of storage,a reduced time-period monthly scheduling model for thermal generators and energy storage,incorporating daily minimum chargeable energy constraints,was developed.Firstly,considering the variations in the frequency of unit start-ups and shutdowns under different levels of net load fluctuation,a method was proposed to reduce decision time periods for unit start-up and shut-down operations.This approach,based on the characteristics of net load fluctuations,minimizes the decision variables of units,thereby simplifying the monthly schedulingmodel.Secondly,the relationship between energy storage charging and discharging power,net load,and the total maximum/minimum output of units was analyzed.Based on this,daily minimum chargeable energy constraints were established to ensure the energy storage system meets charging requirements under extreme net load scenarios.Finally,taking into account the operational costs of thermal generators and energy storage,load loss costs,and operational constraints,the reduced time-period monthly schedulingmodel was constructed.Case studies demonstrate that the proposedmethod effectively generates economical monthly operation plans for thermal generators and energy storage,significantly reduces model solution time,and satisfies the charging requirements of energy storage under extreme net load conditions.展开更多
The problems including excessive flow of attemperating water for boiler, failure of butterfly valve at the outlet of circulating water pump, burnt-out of thyristor for excitation regulator, load variation rate of CCS ...The problems including excessive flow of attemperating water for boiler, failure of butterfly valve at the outlet of circulating water pump, burnt-out of thyristor for excitation regulator, load variation rate of CCS not complying with the contract target, etc. occurred during start-up and debugging of two 600 MW generating units in Yangzhou No.2 Thermal Power Plant. Through analysis on these problems. the remedial measures were put forward, to which can be referred for similar units.展开更多
The anaerobic ammonia oxidation(Anammox) bioreactor was successfully started up with the nitrifying activated sludge. After anaerobically operated for 105 d, the bioreactor reached a good performance with removal perc...The anaerobic ammonia oxidation(Anammox) bioreactor was successfully started up with the nitrifying activated sludge. After anaerobically operated for 105 d, the bioreactor reached a good performance with removal percentage of both ammonia and nitrite higher than 95% and volumetric total nitrogen removal as high as 149.55 mmol/(L·d). The soft padding made an important contribution to the high efficiency and stability because it held a large amount of biomass in the bioreactor.展开更多
N-dodecanoyl homoserine lactone（C（12）-HSL）was detected in the supernatant of an anammox granular sludge reactor（AGSR）.C（12）-HSL could enhance the specific anammox activity of anammox biomass.Adding C（12）-HSL...N-dodecanoyl homoserine lactone（C（12）-HSL）was detected in the supernatant of an anammox granular sludge reactor（AGSR）.C（12）-HSL could enhance the specific anammox activity of anammox biomass.Adding C（12）-HSL-containing AGSR supernatant into the continuously stirred tank reactors reduced the start-up time of the anammox process from80 to 66 days.Moreover,the nitrogen loading rate was also enhanced to 1.6 times that of the control reactor.AHLs could increase the secretion of extracellular polymeric substances and anammox obtained better enrichment with the addition of AHLs-containing AGSR supernatant.Denaturing gradient gel electrophoresis analysis further revealed that AHLs played a role in mediating microbial community parameters.In conclusion,adding AHL-containing supernatant could be an effective and economical way to accelerate the start-up of anammox.展开更多
The start-up current control of the high-speed brushless DC（HS-BLDC） motor is a challenging research topic. To effectively control the start-up current of the sensorless HS-BLDC motor, an adaptive control method is ...The start-up current control of the high-speed brushless DC（HS-BLDC） motor is a challenging research topic. To effectively control the start-up current of the sensorless HS-BLDC motor, an adaptive control method is proposed based on the adaptive neural network（ANN）inverse system and the two degrees of freedom（2-DOF） internal model controller（IMC）. The HS-BLDC motor is identified by the online least squares support vector machine（OLS-SVM） algorithm to regulate the ANN inverse controller parameters in real time. A pseudo linear system is developed by introducing the constructed real-time inverse system into the original HS-BLDC motor system. Based on the characteristics of the pseudo linear system, an extra closed-loop feedback control strategy based on the 2-DOF IMC is proposed to improve the transient response performance and enhance the stability of the control system. The simulation and experimental results show that the proposed control method is effective and perfect start-up current tracking performance is achieved.展开更多
As an efficient method for ammonium（NH4~＋）removal,contact catalytic oxidation technology has drawn much attention recently,due to its good low temperature resistance and short start-up period.Two identical filters ...As an efficient method for ammonium（NH4~＋）removal,contact catalytic oxidation technology has drawn much attention recently,due to its good low temperature resistance and short start-up period.Two identical filters were employed to compare the process for ammonium removal during the start-up period for ammonium removal in groundwater（Filter-N）and surface water（Filter-S）treatment.Two types of source water（groundwater and surface water）were used as the feed waters for the filtration trials.Although the same initiating method was used,Filter-N exhibited much better ammonium removal performance than Filter-S.The differences in catalytic activity among these two filters were probed using X-ray diffraction（XRD）,scanning electron microscopy（SEM）,X-ray photoelectron spectroscopy（XPS）,and compositional analysis.XRD results indicated that different manganese oxide species were formed in Filter-N and Filter-S.Furthermore,the Mn3p XPS spectra taken on the surface of the filter films revealed that the average manganese valence of the inactive manganese oxide film collected from Filter-S（FS-MnOx）was higher than in the film collected from Filter-N（FN-MnOx）.Mn（IV）was identified as the predominant oxidation state in FS-MnOxand Mn（III）was identified as the predominant oxidation state in FN-MnOx.The results of compositional analyses suggested that polyaluminum ferric chloride（PAFC）used during the surface water treatment was an important factor in the mineralogy and reactivity of MnOx.This study provides the theoretical basis for promoting the wide application of the technology and has great practical significance.展开更多
Starting the cracking gas compressor and precooling the refrigeration system are keys to start-up of an ethylene plant and accounts for up to 50% of the total start-up time and plant flare emissions. Premature feeding...Starting the cracking gas compressor and precooling the refrigeration system are keys to start-up of an ethylene plant and accounts for up to 50% of the total start-up time and plant flare emissions. Premature feeding of cracking furnaces can be avoided if the cracking gas compressor is started and the refrigeration system is precooled in advance using mixed gas as the start-up working medium(SWM). Start-up scenario with mixed gas as SWM could significantly reduce the emission loss and shorten the precooling time. Research shows that making appropriate start-up scheme is important not only to ensure operational safety and feasibility, but also to reduce energy consumption. In this paper, a method is proposed to select suitable start-up operational parameters of compression and refrigeration system with sufficient safe operating ranges and short precooling time. The complex interrelation among key parameters of start-up is analyzed. It is found that higher energy consumption, especially for super high-pressure steam(SS), can promote operational safety and shorten the precooling time during start-up.Based on steady-state and dynamic simulation, appropriate operating parameter ranges are determined with reasonable SS consumption. A real case study demonstrates that an appropriate start-up scheme will optimize the operation.展开更多
The start-up process of Stokes＇ second problem of a viscoelastic material with fractional element is studied. The fluid above an infinite flat plane is set in motion by a sudden acceleration of the plate to steady os...The start-up process of Stokes＇ second problem of a viscoelastic material with fractional element is studied. The fluid above an infinite flat plane is set in motion by a sudden acceleration of the plate to steady oscillation. Exact solutions are obtained by using Laplace transform and Fourier transform. It is found that the relationship between the first peak value and the one of equal-amplitude oscillations depends on the distance from the plate. The amplitude decreases for increasing frequency and increasing distance.展开更多
Expanded granular sludge bed （EGSB） reactor and bioaugmentation were employed to investigate biohydrogen production with molasses wastewater. The start-up experiments consisted of two stages. In the first stage （0 ...Expanded granular sludge bed （EGSB） reactor and bioaugmentation were employed to investigate biohydrogen production with molasses wastewater. The start-up experiments consisted of two stages. In the first stage （0 - 24d） seeded with activated sludge, the butyric acid type-fermentation formed when the initial expanding rate, organic loading rate （OLR）, the initial redox potential （ORP） and hydraulic retention time （HRT） were 10%, 10.0 kg COD/（m^3·d）, -215 mV and 6.7 h, respectively. At the beginning of the second stage on day 25, the novel hydrogen-producing fermentative bacterial strain B49 （AF481148 in EMBL） were inoculated into the reactor under the condition of OLR 16. 0 kg COD/（m^3·d）, ORP and HRT about - 139 mV and 6.7 h, respectively, and then the reaction system transformed to ethanol-type fermentation gradually with the increase in OLR. When OLR, ORP and HRT were about 94.3 kg COD/（m^3·d）, -250 mV and 1.7 h, respectively, the system achieved the maximum hydrogen-producing rate of 282.6 mL H2/L reactor·h and hydrogen percentage of 51% -53% in the biogas.展开更多
A novel anaerobic reactor, jet biogas inter-loop anaerobic fluidized bed （JBILAFB）, was designed and constructed. The start-up and performance of the reactor was investigated in the Process. of .artificial glucose w...A novel anaerobic reactor, jet biogas inter-loop anaerobic fluidized bed （JBILAFB）, was designed and constructed. The start-up and performance of the reactor was investigated in the Process. of .artificial glucose wastewater treatment. With the wastewater recycle ratio of 2.5 ： 1, the recycled wastewater with biogas could mix sludge and wastewater in the JBILAFB reactor completely. The start-up of the JBILAFB reactor could be completed in less than 70 d through maintenance of hydraulic retention time （HR^I＂） and stepwise increase of feed total organic carbon （TOC） concentration. After the start-up, with the volumetric TOC loadings of 14.3 kg·m ^-3·d^-1, the TOC removal ratio, the effluent pH, and the volatile fatty acids （VFA）/alkalinity of the JBILAFB reactor were more than 80%, close to 7.0 and less than 0.4, respectively. Moreover, CH4 was produced at more than 70% of the theoretical value, The reactor exhibited high stability under the condition of high volumetric TOC loading. Sludge granules in the JBILAFB reactor were developed during the start-up and their sizes were enlarged with the stepwise increase of volumetric TOC loadings from 0.8 kg.m^-3.d ^-1 to 14.3 kg.m^-3.d^-1. Granules, an offwhite color and a similar spherical shape, were mainly comprised of global-like bacteria. These had good methanogenic activity and settleability, which were formed probably through adhesion of the bacteria. Some inorganic metal compounds such as Fe, Ca, Mg, Al, etc. were advantageous to the formation of the granules.展开更多
In order to research start-up pressure wave propagation mechanism and determine pressure wave speed in gelled crude oil pipelines accurately,experiment of Large-scale flow loop was carried out.In the experiment,start-...In order to research start-up pressure wave propagation mechanism and determine pressure wave speed in gelled crude oil pipelines accurately,experiment of Large-scale flow loop was carried out.In the experiment,start-up pressure wave speeds under various operation conditions were measured,and effects of correlative factors on pressure wave were analyzed.The experimental and theoretical analysis shows that thermal shrinkage and structural properties of gelled crude oils are key factors influencing on start-up pressure wave propagation.The quantitative analysis for these effects can be done by using volume expansion coefficient and structural property parameter of gelled crude oil.A new calculation model of pressure wave speed was developed on the basis of Large-scale flow loop experiment and theoretical analysis.展开更多
This paper analyses the issue of accelerated start-up of a marine steam turbine,which is an important problem because the start-up of a steam machine involves the combustion of fuel that is not transformed into useful...This paper analyses the issue of accelerated start-up of a marine steam turbine,which is an important problem because the start-up of a steam machine involves the combustion of fuel that is not transformed into useful energy.To find novel technologies that offer improvements in this aspect is essential due to restrictions on reducing ship emissions.Thus,the shorter the start-up time,the better for the environment and economy.High-pressure(HP)part of the turbine originally located on the Queen Elizabeth II unit was analysed.Advanced numerical calculations by thermal fluid-solid-interaction(Thermal FSI)were carried out.A series of simulations were performed for the accelerated start-up with controlled steam injection.A description of the chosen calculation methodology and the results obtained by simulation are included in this paper.The stress occurring during the accelerated start-up are approximately 40 MPa higher than those during the reference start-up.The relative elongations between the rotor and the hull during accelerated start-up reach a maximum value of 0.89 mm(0.83 mm for ultra-fast start-up).Reducing the steam turbine start-up time by 75%results in a 36.7 tons reduction in fuel consumption for start-up,resulting in an annual savings of 5372 USD.In conclusion,the concept proposed by the authors is safe,less expensive and does not affect the life of the turbine.In addition,results and applications from Siemens prove that additional injection of cooling steam is possible.展开更多
文摘Research is scarce on non-financial characteristics, including owner characteristics and their influences on capital structure in the establishment phase. The objective of this study is to examine the factors affecting firms＇ availability of external finance, utilizing a sample of Finnish start-up micro firms. The overall purpose is not to produce a comprehensive model for capital structure, but to illustrate the importance of non-accounting characteristics in explaining the attractiveness of the new venture from the lender＇s point of view. The results show that a founder who has prior work experience from the same sector and has little or no personal financial property seems to have higher leverage. After splitting the data into survived and failed firms, lenders viewed work experience positively only in the sample of failed firms. In addition, limited liability companies, firms located in bigger cities, and firms with good demand evaluated by the lender have a lower level of leverage.
文摘This research paper investigates the role of Italian venture capital in supporting innovative start-ups in their early-stage process,which is usually focused on the creation of a new product or the development of a new service.The aim of the study is to observe and assess the key economic features of innovative start-ups funded at the beginning of the early-stage by venture capital funds and thereafter analyze the level of development of target companies at four years since the capital injection.The sample of deals created to describe this dynamic process is composed by investments realized between 1996 and 2012 and,in this way,according to the chosen methodology,it is representative of Italian venture capital role and contribution in the years from 1996 to 2016.The authors used for their empirical study a proprietary database,Venture Capital Monitor—VeMTM.Through the analysis of collected data,the paper describes the strategic importance of venture capital investments in early-stage opportunities both for target companies and the Italian socio-economic environment,and finds aggregate values of reference to quantitatively define the socio-economic outcome of this kind of operations.A final further contribution is provided by comparing the present results to the ones of two previous studies conducted by the authors.
文摘Financial resilience refers to a start-up's capacity to anticipate,plan for,respond to,and adapt to gradual change and abrupt unforeseen shocks to survive and thrive by enacting appropriate economic policies to decrease budget deficits.Economic history tells us that more companies fail to emerge from a downturn than go into or during it.Many studies have been done on financial resilience in many dimensions,but no one has studied start-ups’organizational readiness for financial resilience.This gap inspires the current research,which uses the Total Interpretive Structural Modelling(TISM)approach to identify financial resilience factors and analyze hierarchical interrelationships start-ups’organizational readiness factors for financial resilience.This article aims to identify,assess,and categorize start-up organizational preparation elements for financial resilience.The result shows that the first importance should be given to digital financial innovation,liquidity planning,going concern consideration,financial strategy of CFOs,and cyberthreats.Managers of start-ups can utilize the findings of this study to prepare for financial resilience professionally.In a fast-paced environment,start-ups may use financial resilience to gain a competitive edge.
文摘A nonlinear mathematical model of the low-frequency dynamics of the clustered multi-engine rocket propulsion system has been developed and the computations of the engine transient processes during the start-ups of the four-engine propulsion system with a shared feed system have been made applied.Based on propulsion system start-up modeling the influence of the connectivity of engines in a cluster on the starting characteristics of individual engines is shown.In particular,an advanced nonlinear mathematical model of the pump cavitation phenomena is a distinctive feature of the mathematical model.The computation results showed that the asynchronous engines start-ups during rocket lift-off lead to severely nonlinear engine transients and clustered engine thrust misbalance.The influence of the rocket engines asynchronous start-ups on the clustered feed system transients depends on many factors,mainly on from the clustered feed system low-frequency dynamics,the magnitude of the disturbance and the phase difference between disturbances acting on different branches of the feed system.The deep lingering dips in the flow rate and pressure transients are possible due to the nonlinear dynamic interaction of the engines.In case of great pressure dips at the pump inlet(up to the pressure of saturated vapors during significant periods of start-up time)the cavitation breakdowns of the pumps of one or more engines from the cluster are possible.This can disrupt the operation of the entire propulsion system and leads to the failure of the launch vehicle mission.
基金supported by the National Key Research and Development Program of China(Nos.2022YFE03070000 and 2022YFE03070003)National Natural Science Foundation of China(Nos.12375220 and 12075114)。
文摘According to the physics of tokamak start-up,this study constructs a zero-dimensional(0D)model applicable to electron cyclotron(EC)wave assisted start-up in NCST spherical torus(spherical tokamak)and CN-H1 stellarators.Using the constructed 0D model,the results obtained in this study under the same conditions are compared and validated against reference results for pure hydrogen plasma start-up in tokamak.The results are in good agreement,especially regarding electron temperature,ion temperature and plasma current.In the presence of finite Ohmic electric field in the spherical tokamak,a study on the EC wave assisted start-up of the NCST plasma at frequency of 28 GHz is conducted.The impact of the vertical magnetic field B_(v)on EC wave assisted start-up,the relationship between EC wave injection power P_(inj),Ohmic electric field E,and initial hydrogen atom density n_(H0)are explored separately.It is found that under conditions of Ohmic electric field lower than ITER(~0.3 V m^(-1)),EC wave can expand the operational space to achieve better plasma parameters.Simulating the process of28 GHz EC wave start-up in the CN-H1 stellarator plasma,the plasma current in the zerodimensional model is replaced with the current in the poloidal coil of the stellarator.Plasma startup can be successfully achieved at injection powers in the hundreds of kilowatts range,resulting in electron densities on the order of 10^(17)-10^(18)m^(-3).
基金supported by the National Level Project of China.
文摘Solid rocket motors have important applications in the propulsion of trans-media vehicles and underwater launched rockets.In this paper,the ignition start-up process of an underwater solid rocket motor across a wide depth range has been numerically studied.A novel multi-domain integrated model has been developed by combining the solid propellant ignition and combustion model with the volume of fluid multiphase model.This integrated model enables the coupled simulation of the propellant combustion and gas flow inside the motor,along with the gas jet evolution in the external water environment.The detailed flow field developments in the combustion chamber,nozzle,and wake field are carefully analyzed.The variation rules of the internal ballistics and thrust performance are also obtained.The effects of environmental medium and operating depth on the ignition start-up process are systematically discussed.The results show that the influence of the operating environment on the internal ballistic characteristics is primarily reflected in the initial period after the nozzle closure opens.The development of the gas jet in water lags significantly compared with that in air.As the water depth increases,the ignition delay time of the motor is shortened,and the morphology evolution of the gas jet is significantly compressed and accelerated.Furthermore,the necking and bulging of the jet boundary near the nozzle outlet and the consequent shock oscillations are intensified,resulting in stronger fluctuations in the wake pressure field and motor thrust.
基金funded by the JOGMEC Research Grant and JSPS KAKENHI(No.JP21H03636).
文摘The biotreatment of mine drainage containing dissolved manganese(Mn)using Mn(II)-oxidizing bacteria is challenging.Sequencing-batch(SBRs)and continuous-flow reactors(CFRs)packed with limestones and inoculated with the mine-drainage microbial communitywere compared to determine the removal efficiency of Mn(II)from mine drainage.Mn(II)removal in CFRs was 11.4%±0.0%(mean±standard deviation)in the first two weeks and;it slightly increased to 13.6%±0.0%after four weeks,and more than 94%of Mn(II)was removed under the steady-state treatment phase.The performance of SBRs was more effective,wherein 24.4%±0.1%of Mn was removed in the first two weeks,and in four weeks,surpassed 66.6%±0.2%.Rapid Mn(II)removal observed in the start-up of SBR resulted from higher microbial metabolic activities.The adenosine triphosphate(ATP)content of the microbial community was four-fold more than in CFR,but comparable during the steady-state phase.The Mn-oxide deposits occurring in the SBR and CFR at steady-state were mixed phases of birnessite and woodruffite,and the average Mn oxidation valence in the SBR(+3.73)was slightly higher than that in the CFR(+3.54).During the start-up treatment,the closest relatives of Methyloversatilis,Methylibium,and Curvibacter dominated the SBR,whereas putative Mn oxidizers were associated with Hyphomicrobium,Pedobacter,Pedomicrobium,Terricaulis sp.,Sulfuritalea,and Terrimonas organisms.The growth of potential Mnoxidizing genera,including Mesorhizobium,Rhodococcus,Hydrogenophaga,Terricaulis sp.,and‘Candidatus Manganitrophus-noduliformans’was observed under the steady state.The SBR operation was effective as a prior start-up treatment for mine drainage-containing Mn(II),through which the CFR performed well as posterior bio-treatment.
基金This study was supported by State Grid Corporation headquarters technology project(4000-202399368A-2-2-ZB).
文摘To address the excessive complexity of monthly scheduling and the impact of uncertain net load on the chargeable energy of storage,a reduced time-period monthly scheduling model for thermal generators and energy storage,incorporating daily minimum chargeable energy constraints,was developed.Firstly,considering the variations in the frequency of unit start-ups and shutdowns under different levels of net load fluctuation,a method was proposed to reduce decision time periods for unit start-up and shut-down operations.This approach,based on the characteristics of net load fluctuations,minimizes the decision variables of units,thereby simplifying the monthly schedulingmodel.Secondly,the relationship between energy storage charging and discharging power,net load,and the total maximum/minimum output of units was analyzed.Based on this,daily minimum chargeable energy constraints were established to ensure the energy storage system meets charging requirements under extreme net load scenarios.Finally,taking into account the operational costs of thermal generators and energy storage,load loss costs,and operational constraints,the reduced time-period monthly schedulingmodel was constructed.Case studies demonstrate that the proposedmethod effectively generates economical monthly operation plans for thermal generators and energy storage,significantly reduces model solution time,and satisfies the charging requirements of energy storage under extreme net load conditions.
文摘The problems including excessive flow of attemperating water for boiler, failure of butterfly valve at the outlet of circulating water pump, burnt-out of thyristor for excitation regulator, load variation rate of CCS not complying with the contract target, etc. occurred during start-up and debugging of two 600 MW generating units in Yangzhou No.2 Thermal Power Plant. Through analysis on these problems. the remedial measures were put forward, to which can be referred for similar units.
文摘The anaerobic ammonia oxidation(Anammox) bioreactor was successfully started up with the nitrifying activated sludge. After anaerobically operated for 105 d, the bioreactor reached a good performance with removal percentage of both ammonia and nitrite higher than 95% and volumetric total nitrogen removal as high as 149.55 mmol/(L·d). The soft padding made an important contribution to the high efficiency and stability because it held a large amount of biomass in the bioreactor.
基金supported by the Major State Science and Technology Water Projects (No. 2013ZX07202010)
文摘N-dodecanoyl homoserine lactone（C（12）-HSL）was detected in the supernatant of an anammox granular sludge reactor（AGSR）.C（12）-HSL could enhance the specific anammox activity of anammox biomass.Adding C（12）-HSL-containing AGSR supernatant into the continuously stirred tank reactors reduced the start-up time of the anammox process from80 to 66 days.Moreover,the nitrogen loading rate was also enhanced to 1.6 times that of the control reactor.AHLs could increase the secretion of extracellular polymeric substances and anammox obtained better enrichment with the addition of AHLs-containing AGSR supernatant.Denaturing gradient gel electrophoresis analysis further revealed that AHLs played a role in mediating microbial community parameters.In conclusion,adding AHL-containing supernatant could be an effective and economical way to accelerate the start-up of anammox.
基金co-supported by the National Major Project for the Development and Application of Scientific Instrument Equipment of China (No. 2012YQ040235)
文摘The start-up current control of the high-speed brushless DC（HS-BLDC） motor is a challenging research topic. To effectively control the start-up current of the sensorless HS-BLDC motor, an adaptive control method is proposed based on the adaptive neural network（ANN）inverse system and the two degrees of freedom（2-DOF） internal model controller（IMC）. The HS-BLDC motor is identified by the online least squares support vector machine（OLS-SVM） algorithm to regulate the ANN inverse controller parameters in real time. A pseudo linear system is developed by introducing the constructed real-time inverse system into the original HS-BLDC motor system. Based on the characteristics of the pseudo linear system, an extra closed-loop feedback control strategy based on the 2-DOF IMC is proposed to improve the transient response performance and enhance the stability of the control system. The simulation and experimental results show that the proposed control method is effective and perfect start-up current tracking performance is achieved.
基金supported by the National Key Research and Development Program of China (No. 2016YFC0400706)the National Natural Science Foundation of China (Nos. 51278409, 51608431, 51408469)the Key Laboratory of Education Department of Shaanxi province (Nos. 15JS046, 16JS060)
文摘As an efficient method for ammonium（NH4~＋）removal,contact catalytic oxidation technology has drawn much attention recently,due to its good low temperature resistance and short start-up period.Two identical filters were employed to compare the process for ammonium removal during the start-up period for ammonium removal in groundwater（Filter-N）and surface water（Filter-S）treatment.Two types of source water（groundwater and surface water）were used as the feed waters for the filtration trials.Although the same initiating method was used,Filter-N exhibited much better ammonium removal performance than Filter-S.The differences in catalytic activity among these two filters were probed using X-ray diffraction（XRD）,scanning electron microscopy（SEM）,X-ray photoelectron spectroscopy（XPS）,and compositional analysis.XRD results indicated that different manganese oxide species were formed in Filter-N and Filter-S.Furthermore,the Mn3p XPS spectra taken on the surface of the filter films revealed that the average manganese valence of the inactive manganese oxide film collected from Filter-S（FS-MnOx）was higher than in the film collected from Filter-N（FN-MnOx）.Mn（IV）was identified as the predominant oxidation state in FS-MnOxand Mn（III）was identified as the predominant oxidation state in FN-MnOx.The results of compositional analyses suggested that polyaluminum ferric chloride（PAFC）used during the surface water treatment was an important factor in the mineralogy and reactivity of MnOx.This study provides the theoretical basis for promoting the wide application of the technology and has great practical significance.
基金Supported by the National Basic Research Program of China(2012CB720500)the National Natural Science Foundation of China(U1462206)
文摘Starting the cracking gas compressor and precooling the refrigeration system are keys to start-up of an ethylene plant and accounts for up to 50% of the total start-up time and plant flare emissions. Premature feeding of cracking furnaces can be avoided if the cracking gas compressor is started and the refrigeration system is precooled in advance using mixed gas as the start-up working medium(SWM). Start-up scenario with mixed gas as SWM could significantly reduce the emission loss and shorten the precooling time. Research shows that making appropriate start-up scheme is important not only to ensure operational safety and feasibility, but also to reduce energy consumption. In this paper, a method is proposed to select suitable start-up operational parameters of compression and refrigeration system with sufficient safe operating ranges and short precooling time. The complex interrelation among key parameters of start-up is analyzed. It is found that higher energy consumption, especially for super high-pressure steam(SS), can promote operational safety and shorten the precooling time during start-up.Based on steady-state and dynamic simulation, appropriate operating parameter ranges are determined with reasonable SS consumption. A real case study demonstrates that an appropriate start-up scheme will optimize the operation.
文摘The start-up process of Stokes＇ second problem of a viscoelastic material with fractional element is studied. The fluid above an infinite flat plane is set in motion by a sudden acceleration of the plate to steady oscillation. Exact solutions are obtained by using Laplace transform and Fourier transform. It is found that the relationship between the first peak value and the one of equal-amplitude oscillations depends on the distance from the plate. The amplitude decreases for increasing frequency and increasing distance.
文摘Expanded granular sludge bed （EGSB） reactor and bioaugmentation were employed to investigate biohydrogen production with molasses wastewater. The start-up experiments consisted of two stages. In the first stage （0 - 24d） seeded with activated sludge, the butyric acid type-fermentation formed when the initial expanding rate, organic loading rate （OLR）, the initial redox potential （ORP） and hydraulic retention time （HRT） were 10%, 10.0 kg COD/（m^3·d）, -215 mV and 6.7 h, respectively. At the beginning of the second stage on day 25, the novel hydrogen-producing fermentative bacterial strain B49 （AF481148 in EMBL） were inoculated into the reactor under the condition of OLR 16. 0 kg COD/（m^3·d）, ORP and HRT about - 139 mV and 6.7 h, respectively, and then the reaction system transformed to ethanol-type fermentation gradually with the increase in OLR. When OLR, ORP and HRT were about 94.3 kg COD/（m^3·d）, -250 mV and 1.7 h, respectively, the system achieved the maximum hydrogen-producing rate of 282.6 mL H2/L reactor·h and hydrogen percentage of 51% -53% in the biogas.
基金Supported by the National Natural Science Foundation of China （No.50278036）, the Natural Science Foundation of Guangdong Province （No.04105951） and the National High Technology Research and Development Program of China （No.2006AA06Z378）.
文摘A novel anaerobic reactor, jet biogas inter-loop anaerobic fluidized bed （JBILAFB）, was designed and constructed. The start-up and performance of the reactor was investigated in the Process. of .artificial glucose wastewater treatment. With the wastewater recycle ratio of 2.5 ： 1, the recycled wastewater with biogas could mix sludge and wastewater in the JBILAFB reactor completely. The start-up of the JBILAFB reactor could be completed in less than 70 d through maintenance of hydraulic retention time （HR^I＂） and stepwise increase of feed total organic carbon （TOC） concentration. After the start-up, with the volumetric TOC loadings of 14.3 kg·m ^-3·d^-1, the TOC removal ratio, the effluent pH, and the volatile fatty acids （VFA）/alkalinity of the JBILAFB reactor were more than 80%, close to 7.0 and less than 0.4, respectively. Moreover, CH4 was produced at more than 70% of the theoretical value, The reactor exhibited high stability under the condition of high volumetric TOC loading. Sludge granules in the JBILAFB reactor were developed during the start-up and their sizes were enlarged with the stepwise increase of volumetric TOC loadings from 0.8 kg.m^-3.d ^-1 to 14.3 kg.m^-3.d^-1. Granules, an offwhite color and a similar spherical shape, were mainly comprised of global-like bacteria. These had good methanogenic activity and settleability, which were formed probably through adhesion of the bacteria. Some inorganic metal compounds such as Fe, Ca, Mg, Al, etc. were advantageous to the formation of the granules.
基金Project(2008B-2901) supported by China National Petroleum Corporation
文摘In order to research start-up pressure wave propagation mechanism and determine pressure wave speed in gelled crude oil pipelines accurately,experiment of Large-scale flow loop was carried out.In the experiment,start-up pressure wave speeds under various operation conditions were measured,and effects of correlative factors on pressure wave were analyzed.The experimental and theoretical analysis shows that thermal shrinkage and structural properties of gelled crude oils are key factors influencing on start-up pressure wave propagation.The quantitative analysis for these effects can be done by using volume expansion coefficient and structural property parameter of gelled crude oil.A new calculation model of pressure wave speed was developed on the basis of Large-scale flow loop experiment and theoretical analysis.
文摘This paper analyses the issue of accelerated start-up of a marine steam turbine,which is an important problem because the start-up of a steam machine involves the combustion of fuel that is not transformed into useful energy.To find novel technologies that offer improvements in this aspect is essential due to restrictions on reducing ship emissions.Thus,the shorter the start-up time,the better for the environment and economy.High-pressure(HP)part of the turbine originally located on the Queen Elizabeth II unit was analysed.Advanced numerical calculations by thermal fluid-solid-interaction(Thermal FSI)were carried out.A series of simulations were performed for the accelerated start-up with controlled steam injection.A description of the chosen calculation methodology and the results obtained by simulation are included in this paper.The stress occurring during the accelerated start-up are approximately 40 MPa higher than those during the reference start-up.The relative elongations between the rotor and the hull during accelerated start-up reach a maximum value of 0.89 mm(0.83 mm for ultra-fast start-up).Reducing the steam turbine start-up time by 75%results in a 36.7 tons reduction in fuel consumption for start-up,resulting in an annual savings of 5372 USD.In conclusion,the concept proposed by the authors is safe,less expensive and does not affect the life of the turbine.In addition,results and applications from Siemens prove that additional injection of cooling steam is possible.
