More than 90%of natural gas hydrates(hereinafter,hydrate for short)in the South China Sea are non-diagenetic ore bodies,so they cannot be exploited easily by means of the conventional methods.In this paper,the solid f...More than 90%of natural gas hydrates(hereinafter,hydrate for short)in the South China Sea are non-diagenetic ore bodies,so they cannot be exploited easily by means of the conventional methods.In this paper,the solid fluidization method,as one of the revolutionary technologies in efficient exploitation of non-diagenetic natural gas hydrates,was,for the first time,put forward by Academician Zhou Shouwei.And it is successfully applied in the Shenhu Area of the South China Sea based on the technologies,equipment and processes which rely on domestic independent intellectual property rights.During the production test of fluidization,the ore bodies of hydrates are broken by the jet at the bottom hole into fine particles and carried upward by the drilling fluid.When the phase equilibrium state is reached with the increase of temperature and the decrease of pressure affected by the operation parameters,which is different from conventional phase equilibrium state,the hydrates bearing solid particles are decomposed,and consequently liquid-solid flow in the annulus becomes complex gas-liquid-solid multiphase flow.Therefore,it is necessary to optimize the construction parameters design so as to meet the high-level requirements of well control safety.In this paper,the engineering parameters are optimally designed based on the engineering geological characteristics of the target block,combined with the analysis on complex multiphase flow in the wellbore.Then,a theoretical model and a numerical calculation method for the multiphase flow,temperature and pressure of complex media in wellbores and the phase equilibrium and decomposition of natural gas hydrates were established.And the multiphase flow in the wellbore during the production test of fluidization was analyzed under different operating parameters by means of numerical simulation,software emulation and experimental verification.And thus,the design optimization scheme of on-site engineering parameters of production test of marine natural gas hydrate fluidization was prepared.It is pointed out that the diameter of jet fluidization well section shall not be excessively large;and that it is necessary to increase the flow rate and density of drilling fluid and apply wellhead back pressure to ensure the cutting carrying safety and to mitigate well control risks.The results of this basic theoretical study can provide significant support to field operation and improvement of output in production tests.展开更多
To efficiently link the continuum mechanics for rocks with the structural statistics of rock masses,a theoretical and methodological system called the statistical mechanics of rock masses(SMRM)was developed in the pas...To efficiently link the continuum mechanics for rocks with the structural statistics of rock masses,a theoretical and methodological system called the statistical mechanics of rock masses(SMRM)was developed in the past three decades.In SMRM,equivalent continuum models of stressestrain relationship,strength and failure probability for jointed rock masses were established,which were based on the geometric probability models characterising the rock mass structure.This follows the statistical physics,the continuum mechanics,the fracture mechanics and the weakest link hypothesis.A general constitutive model and complete stressestrain models under compressive and shear conditions were also developed as the derivatives of the SMRM theory.An SMRM calculation system was then developed to provide fast and precise solutions for parameter estimations of rock masses,such as full-direction rock quality designation(RQD),elastic modulus,Coulomb compressive strength,rock mass quality rating,and Poisson’s ratio and shear strength.The constitutive equations involved in SMRM were integrated into a FLAC3D based numerical module to apply for engineering rock masses.It is also capable of analysing the complete deformation of rock masses and active reinforcement of engineering rock masses.Examples of engineering applications of SMRM were presented,including a rock mass at QBT hydropower station in northwestern China,a dam slope of Zongo II hydropower station in D.R.Congo,an open-pit mine in Dexing,China,an underground powerhouse of Jinping I hydropower station in southwestern China,and a typical circular tunnel in Lanzhou-Chongqing railway,China.These applications verified the reliability of the SMRM and demonstrated its applicability to broad engineering issues associated with jointed rock masses.展开更多
The effects of Sr addition and pressure increase on the microstructure and casting defects of a low-pressure die cast （LPDC） AISi7Mg0.3 alloy have been studied. Metallographic and image analysis techniques have been...The effects of Sr addition and pressure increase on the microstructure and casting defects of a low-pressure die cast （LPDC） AISi7Mg0.3 alloy have been studied. Metallographic and image analysis techniques have been used to quantitatively examine the microstructural changes and the amount of porosity occurring at different Sr levels and pressure parameters. The results indicate that an increase in the filling pressure induces lower heat dissipation of the liquid close to the die/core surfaces, with the formation of slightly greater dendrite arms and coarser eutectic Si particles. On the other hand, the increase in the Sr level leads to finer microstructural scale and eutectic Si. The analysed variables, within the experimental conditions, do not affect the morphology of eutectic Si particles. Higher applied pressure and Sr content generate castings with lower amount of porosiW. However, as the filling pressure increases the flow of metal inside the die cavity is more turbulent, leading to the formation of oxide films and cold shots. In the analysed range of experimental conditions, the design of experiment methodology and the analysis of variance have been used to develop statistical models that accurately predict the average size of secondary dendrite arm spacing and the amount of porosity in the low-pressure die cast AISiTMg0.3 alloy.展开更多
Performance based design becomes an effective method for estimating seismic demands of buildings. In asymmetric plan tall building the effects of higher modes and torsion are crucial. The consecutive modal pushover （...Performance based design becomes an effective method for estimating seismic demands of buildings. In asymmetric plan tall building the effects of higher modes and torsion are crucial. The consecutive modal pushover （CMP） procedure is one of the procedures that consider these effects. Also in previous studies the influence of soil-structure interaction （SSI） in pushover analysis is ignored. In this paper the CMP procedure is modified for one-way asymmetric plan mid and high-rise buildings considering $SI. The extended CMP （ECMP） procedure is proposed in order to overcome some limitations of the CMP procedure. In this regard, 10, 15 and 20 story buildings with asymmetric plan are studied considering SSI assuming three different soil conditions. Using nonlinear response history analysis under a set of bidirectional ground motion; the exact responses of these buildings are calculated. Then the ECMP procedure is evaluated by comparing the results of this procedure with nonlinear time history results as an exact solution as well as the modal pushover analysis procedure and FEMA 356 load patterns. The results demonstrate the accuracy of the ECMP procedure.展开更多
This paper investigates the performance of different configurations of gas turbine engines.A full numerical model for the engine is built.This model takes into account the variations in specific heat and the effects o...This paper investigates the performance of different configurations of gas turbine engines.A full numerical model for the engine is built.This model takes into account the variations in specific heat and the effects of turbine cooling flow.A lso,the model considers the efficiencies of all component,effectiveness of heat exchangers and the pressure drop in relevant components.The model is employed to compare the engine performances in cases of employing intercooler,recuperation and reheat on a single spool gas turbine engine.A comparison is made between single-spool engine and two-spool engine with free power turbine.Also,the performance of the eng ine with inter-stage turbine burner is investigated and compared with engine employing the nominal reheat concept.The engine employing inter-stage turbine bumers produces superior improvements in both net work and efficiency over all other configurations.The effects of ignoring the variations on specific heat of gases and turbine cooling flow on engine performance are estimated.Ignoring the variation in specific heat can cause up to 30%difference in net specific work.The optimum locations of the intercooler and the reheat combustor are detemined using the numerical model of the engine.The maximum net specific work is obtained if the reheat combustor is placed at 40%of the expansion section.On the other hand,to get maximum efficiency the reheat combustor has to be placed at nearly 10%-20%of the expansion section.The optimum location of the intercooler is almost at 50%of the compression section for both maximum net specific work and efficiency.展开更多
基金Project supported by National Key Research and Development Program“New Technology for Marine Gas Hydrate Fluidization Test”(No.:2016YFC0304008)National Natural Science Foundation of China Key Program“Research on the Theoretical Aspects and Key Issues in Managed Pressure Drilling Measuring and Controlling”(No.:51334003).
文摘More than 90%of natural gas hydrates(hereinafter,hydrate for short)in the South China Sea are non-diagenetic ore bodies,so they cannot be exploited easily by means of the conventional methods.In this paper,the solid fluidization method,as one of the revolutionary technologies in efficient exploitation of non-diagenetic natural gas hydrates,was,for the first time,put forward by Academician Zhou Shouwei.And it is successfully applied in the Shenhu Area of the South China Sea based on the technologies,equipment and processes which rely on domestic independent intellectual property rights.During the production test of fluidization,the ore bodies of hydrates are broken by the jet at the bottom hole into fine particles and carried upward by the drilling fluid.When the phase equilibrium state is reached with the increase of temperature and the decrease of pressure affected by the operation parameters,which is different from conventional phase equilibrium state,the hydrates bearing solid particles are decomposed,and consequently liquid-solid flow in the annulus becomes complex gas-liquid-solid multiphase flow.Therefore,it is necessary to optimize the construction parameters design so as to meet the high-level requirements of well control safety.In this paper,the engineering parameters are optimally designed based on the engineering geological characteristics of the target block,combined with the analysis on complex multiphase flow in the wellbore.Then,a theoretical model and a numerical calculation method for the multiphase flow,temperature and pressure of complex media in wellbores and the phase equilibrium and decomposition of natural gas hydrates were established.And the multiphase flow in the wellbore during the production test of fluidization was analyzed under different operating parameters by means of numerical simulation,software emulation and experimental verification.And thus,the design optimization scheme of on-site engineering parameters of production test of marine natural gas hydrate fluidization was prepared.It is pointed out that the diameter of jet fluidization well section shall not be excessively large;and that it is necessary to increase the flow rate and density of drilling fluid and apply wellhead back pressure to ensure the cutting carrying safety and to mitigate well control risks.The results of this basic theoretical study can provide significant support to field operation and improvement of output in production tests.
基金The authors are grateful to the financial support from the National Natural Science Foundation of China(Grant No.41831290)the Key R&D Project from Zhejiang Province,China(Grant No.2020C03092).
文摘To efficiently link the continuum mechanics for rocks with the structural statistics of rock masses,a theoretical and methodological system called the statistical mechanics of rock masses(SMRM)was developed in the past three decades.In SMRM,equivalent continuum models of stressestrain relationship,strength and failure probability for jointed rock masses were established,which were based on the geometric probability models characterising the rock mass structure.This follows the statistical physics,the continuum mechanics,the fracture mechanics and the weakest link hypothesis.A general constitutive model and complete stressestrain models under compressive and shear conditions were also developed as the derivatives of the SMRM theory.An SMRM calculation system was then developed to provide fast and precise solutions for parameter estimations of rock masses,such as full-direction rock quality designation(RQD),elastic modulus,Coulomb compressive strength,rock mass quality rating,and Poisson’s ratio and shear strength.The constitutive equations involved in SMRM were integrated into a FLAC3D based numerical module to apply for engineering rock masses.It is also capable of analysing the complete deformation of rock masses and active reinforcement of engineering rock masses.Examples of engineering applications of SMRM were presented,including a rock mass at QBT hydropower station in northwestern China,a dam slope of Zongo II hydropower station in D.R.Congo,an open-pit mine in Dexing,China,an underground powerhouse of Jinping I hydropower station in southwestern China,and a typical circular tunnel in Lanzhou-Chongqing railway,China.These applications verified the reliability of the SMRM and demonstrated its applicability to broad engineering issues associated with jointed rock masses.
文摘The effects of Sr addition and pressure increase on the microstructure and casting defects of a low-pressure die cast （LPDC） AISi7Mg0.3 alloy have been studied. Metallographic and image analysis techniques have been used to quantitatively examine the microstructural changes and the amount of porosity occurring at different Sr levels and pressure parameters. The results indicate that an increase in the filling pressure induces lower heat dissipation of the liquid close to the die/core surfaces, with the formation of slightly greater dendrite arms and coarser eutectic Si particles. On the other hand, the increase in the Sr level leads to finer microstructural scale and eutectic Si. The analysed variables, within the experimental conditions, do not affect the morphology of eutectic Si particles. Higher applied pressure and Sr content generate castings with lower amount of porosiW. However, as the filling pressure increases the flow of metal inside the die cavity is more turbulent, leading to the formation of oxide films and cold shots. In the analysed range of experimental conditions, the design of experiment methodology and the analysis of variance have been used to develop statistical models that accurately predict the average size of secondary dendrite arm spacing and the amount of porosity in the low-pressure die cast AISiTMg0.3 alloy.
文摘Performance based design becomes an effective method for estimating seismic demands of buildings. In asymmetric plan tall building the effects of higher modes and torsion are crucial. The consecutive modal pushover （CMP） procedure is one of the procedures that consider these effects. Also in previous studies the influence of soil-structure interaction （SSI） in pushover analysis is ignored. In this paper the CMP procedure is modified for one-way asymmetric plan mid and high-rise buildings considering $SI. The extended CMP （ECMP） procedure is proposed in order to overcome some limitations of the CMP procedure. In this regard, 10, 15 and 20 story buildings with asymmetric plan are studied considering SSI assuming three different soil conditions. Using nonlinear response history analysis under a set of bidirectional ground motion; the exact responses of these buildings are calculated. Then the ECMP procedure is evaluated by comparing the results of this procedure with nonlinear time history results as an exact solution as well as the modal pushover analysis procedure and FEMA 356 load patterns. The results demonstrate the accuracy of the ECMP procedure.
文摘This paper investigates the performance of different configurations of gas turbine engines.A full numerical model for the engine is built.This model takes into account the variations in specific heat and the effects of turbine cooling flow.A lso,the model considers the efficiencies of all component,effectiveness of heat exchangers and the pressure drop in relevant components.The model is employed to compare the engine performances in cases of employing intercooler,recuperation and reheat on a single spool gas turbine engine.A comparison is made between single-spool engine and two-spool engine with free power turbine.Also,the performance of the eng ine with inter-stage turbine burner is investigated and compared with engine employing the nominal reheat concept.The engine employing inter-stage turbine bumers produces superior improvements in both net work and efficiency over all other configurations.The effects of ignoring the variations on specific heat of gases and turbine cooling flow on engine performance are estimated.Ignoring the variation in specific heat can cause up to 30%difference in net specific work.The optimum locations of the intercooler and the reheat combustor are detemined using the numerical model of the engine.The maximum net specific work is obtained if the reheat combustor is placed at 40%of the expansion section.On the other hand,to get maximum efficiency the reheat combustor has to be placed at nearly 10%-20%of the expansion section.The optimum location of the intercooler is almost at 50%of the compression section for both maximum net specific work and efficiency.
