A tunneled planing hull has unique hybrid hydrodynamic and aerodynamic characteristics due to the presence of a tunnel.In this paper,experimental and numerical investigations on hydrody namic analysis of a tunneled pl...A tunneled planing hull has unique hybrid hydrodynamic and aerodynamic characteristics due to the presence of a tunnel.In this paper,experimental and numerical investigations on hydrody namic analysis of a tunneled planing hull are carried out.The resistance tests of models with three dif ferent masses(127.4 kg,159.5 kg,202.9 kg)are conducted for the Froude number in the range of 0.761≤Fn≤1.925.The results of resistance measured by towing tank imply that the tunneled planing hull with a larger displacement has a superior resistance performance.The numerical simulation of Reynolds Average Navier Stokes(RANS)equations based on the finite volume method is performed to analyze the hull characteristics in calm water(M=159.5 kg)with two degrees of freedom(sinkage and trim).The numerical results are compared with the experimental data,which shows good agreement.Pressure distribution,wave profiles and lift forces obtained by SST k-ωand Realizable k-εturbulence models are compared and discussed.Finally,the local fluid flow of streamline around the hull can be divided into four regions due to the presence of a tunnel,which is different from the behaviors of the conventional planing monohull with prismatic form.展开更多
Several parameter identification methods of thermal response test were evaluated through numerical and experimental study.A three-dimensional finite-volume numerical model was established under the assumption that the...Several parameter identification methods of thermal response test were evaluated through numerical and experimental study.A three-dimensional finite-volume numerical model was established under the assumption that the soil thermal conductivity had been known in the simulation of thermal response test.The thermal response curve was firstly obtained through numerical calculation.Then,the accuracy of the numerical model was verified with measured data obtained through a thermal response test.Based on the numerical and experimental thermal response curves,the thermal conductivity of the soil was calculated by different parameter identification methods.The calculated results were compared with the assumed value and then the accuracy of these methods was evaluated.Furthermore,the effects of test time,variable data quality,borehole radius,initial ground temperature,and heat injection rate were analyzed.The results show that the method based on cylinder-source model has a low precision and the identified thermal conductivity decreases with an increase in borehole radius.For parameter estimation,the measuring accuracy of the initial temperature of the deep ground soil has greater effect on identified thermal conductivity.展开更多
The hot compression test of 6063 Al alloy was performed on a Gleeble-1500 thermo-simulation machine, and the forming of 6063 rod cxtrudate in low-temperature high-speed extrusion was simulated with extrusion ratio of ...The hot compression test of 6063 Al alloy was performed on a Gleeble-1500 thermo-simulation machine, and the forming of 6063 rod cxtrudate in low-temperature high-speed extrusion was simulated with extrusion ratio of 25 on the platform of DEFORM 2D successfully. From the compression experimental results, the flow stress model of this Al alloy is obtained which could be the constitutive equation in the simulation of low-temperature high-speed extrusion process. From the numerical simulation results, there is a higher strain concentration at the entrance of the die and the exit temperature reaches up to 522 ℃ in low-temperature high-speed extrusion, which approaches to the quenching temperature of the 6063 Al alloy. The results show that the low-temperature high-speed extrusion method as a promsing one can reduce energy consumption effectively.展开更多
The mechanical properties of outwash deposits which are taken as unconsolidated geo-materials with the characteristics of non-uniformity, heterogeneity and multiphase have attracted much attention in engineering. Acco...The mechanical properties of outwash deposits which are taken as unconsolidated geo-materials with the characteristics of non-uniformity, heterogeneity and multiphase have attracted much attention in engineering. According to the results of laboratory direct shear test on the remolded samples, the soil particle parameters of numerical model based on in-situ particle size cumulative curves and 3D granular discrete element method were determined. Then, numerical experiments on different lithology, stone content and gradation composition were conducted. The results show that it is not a flat surface but a shear band that yields in the sample. The curve of particle velocity vs distance from the designed shear surface of test model that is taken as a datum plane in the vertical section of sample shows in "S" shape. The shear disturbance area is about twice the maximum diameter of stone blocks. The greater the stiffness of stone is, the rougher the shear surface is. The shear strength of outwash deposits is largely controlled by lithology and stone content, and the bite force between stone blocks is the root reason of larger friction angle. It is also shown that strain hardening and low shear dilatancy occur under high confining pressure as well as possibility of shear shrinkage. But it is easy to behave shear dilatation and strain softening under low confining pressure. The relationship between particle frictional coefficient and stone content presents an approximately quadratic parabola increase. The strain energy first increases and then drops with the increase of frictional energy. The cohesion increases with soil stiffness increasing but decreases with stone stiffness increasing. Numerical results are consistent with the laboratory test results of remolded samples, which indicate that this method can be a beneficial supplement to determine the parameters of engineering deposit bodies.展开更多
Combined with the kinetic model of liquid film spreading, a new numerical method of solid-liquid-gas three-phase flow was developed for the moving of contact line, which was a hybrid method of computational fluid dyna...Combined with the kinetic model of liquid film spreading, a new numerical method of solid-liquid-gas three-phase flow was developed for the moving of contact line, which was a hybrid method of computational fluid dynamics and lattice Boltzmalm method （LBM）. By taking the effect of molecule force in droplet and the wall surface on liquid film into account, the changing law of contact angle with different surface tensions was analyzed on glass and aluminum foil surfaces. Compared with experimental results, the standard deviation by using LBM is less than 0.5°, which validates the feasibility of LBM simulation on the dynamic process of liquid film spreading. In addition, oscillations are discovered both at the initial and end phases. The phenomenon of retraction is also found and the maximum retraction angle is 7.58°. The obtained result shows that the retraction is proved to be correlative with precursor film by tracking the volume change of liquid film contour. Furthermore, non-dimensional coefficient 2 is introduced to measure the liquid film retraction capacity.展开更多
In order to maintain vibration performances within the limits of the design, a vibration-based feature extraction method for dynamic characteristic using empirical mode decomposition （EMD） and wavelet analysis was p...In order to maintain vibration performances within the limits of the design, a vibration-based feature extraction method for dynamic characteristic using empirical mode decomposition （EMD） and wavelet analysis was proposed. The proposed method was verified experimentally and numerically by implementing the scheme on engine block. In the implementation process, the following steps were identified to be important： 1） EMD technique in order to solve the feature extraction of vibration signals; 2） Vibration measurement for the purpose of confirming the structural weak regions of engine block in experiment; 3） Finite element modeling for the purpose of determining dynamic characteristic in time region and frequency region to affirm the comparability of response character corresponding to improvement schemes; 4） Adopting a feature index oflMF for structural improvement based on EMD and wavelet analysis. The obtained results show that IMF of signal is more sensitive to response character corresponding to improvement schemes. Finally, examination of the results confirms that the proposed vibration-based feature extraction method is very robust, and focuses on the relative merits of modification and full-scale structural optimization of engine, together with the creation of new low-vibration designs.展开更多
In order to numerically simulate the failure process of rock and concrete under uniaxial tension,an improved method of selecting the mechanical properties of materials was presented for the random mechanic parameter m...In order to numerically simulate the failure process of rock and concrete under uniaxial tension,an improved method of selecting the mechanical properties of materials was presented for the random mechanic parameter model based on the mesoscopic damage mechanics.The product of strength and elastic modulus of mesoscale representative volume element was considered to be one of the mechanical property parameters of materials and assumed to conform to specified probability distributions to reflect the heterogeneity of mechanical property in materials.With the improved property parameter selection method,a numerical program was developed and the simulation of the failure process of the rock and concrete specimens under static tensile loading condition was carried out.The failure process and complete stress-strain curves of a class of rock and concrete in stable fracture propagation manner under uniaxial tension were obtained.The simulated macroscopic mechanical behavior was compared with the available laboratory experimental observation,and a reasonable agreement was obtained.Verification shows that the improved parameter selection method is suitable for mesoscopic numerical simulation in the failure process of rock and concrete.展开更多
文摘A tunneled planing hull has unique hybrid hydrodynamic and aerodynamic characteristics due to the presence of a tunnel.In this paper,experimental and numerical investigations on hydrody namic analysis of a tunneled planing hull are carried out.The resistance tests of models with three dif ferent masses(127.4 kg,159.5 kg,202.9 kg)are conducted for the Froude number in the range of 0.761≤Fn≤1.925.The results of resistance measured by towing tank imply that the tunneled planing hull with a larger displacement has a superior resistance performance.The numerical simulation of Reynolds Average Navier Stokes(RANS)equations based on the finite volume method is performed to analyze the hull characteristics in calm water(M=159.5 kg)with two degrees of freedom(sinkage and trim).The numerical results are compared with the experimental data,which shows good agreement.Pressure distribution,wave profiles and lift forces obtained by SST k-ωand Realizable k-εturbulence models are compared and discussed.Finally,the local fluid flow of streamline around the hull can be divided into four regions due to the presence of a tunnel,which is different from the behaviors of the conventional planing monohull with prismatic form.
基金Project(xjj20100078) supported by the Fundamental Research Funds for the Central Universities in China
文摘Several parameter identification methods of thermal response test were evaluated through numerical and experimental study.A three-dimensional finite-volume numerical model was established under the assumption that the soil thermal conductivity had been known in the simulation of thermal response test.The thermal response curve was firstly obtained through numerical calculation.Then,the accuracy of the numerical model was verified with measured data obtained through a thermal response test.Based on the numerical and experimental thermal response curves,the thermal conductivity of the soil was calculated by different parameter identification methods.The calculated results were compared with the assumed value and then the accuracy of these methods was evaluated.Furthermore,the effects of test time,variable data quality,borehole radius,initial ground temperature,and heat injection rate were analyzed.The results show that the method based on cylinder-source model has a low precision and the identified thermal conductivity decreases with an increase in borehole radius.For parameter estimation,the measuring accuracy of the initial temperature of the deep ground soil has greater effect on identified thermal conductivity.
基金Project(2008A09030004) supported by the Major Science and Technology Project of Guangdong Province,ChinaProject(30815009) supported by the Foundation of State Key Laboratory of Advanced Design and Manufacture for Vehicle Body
文摘The hot compression test of 6063 Al alloy was performed on a Gleeble-1500 thermo-simulation machine, and the forming of 6063 rod cxtrudate in low-temperature high-speed extrusion was simulated with extrusion ratio of 25 on the platform of DEFORM 2D successfully. From the compression experimental results, the flow stress model of this Al alloy is obtained which could be the constitutive equation in the simulation of low-temperature high-speed extrusion process. From the numerical simulation results, there is a higher strain concentration at the entrance of the die and the exit temperature reaches up to 522 ℃ in low-temperature high-speed extrusion, which approaches to the quenching temperature of the 6063 Al alloy. The results show that the low-temperature high-speed extrusion method as a promsing one can reduce energy consumption effectively.
基金Project(2011CB013504) supported by the National Basic Research Program of ChinaProjects(50911130366, 11172090) supported by the National Natural Science Foundation of ChinaProject supported by Central University Basic Research Special Fund, China
文摘The mechanical properties of outwash deposits which are taken as unconsolidated geo-materials with the characteristics of non-uniformity, heterogeneity and multiphase have attracted much attention in engineering. According to the results of laboratory direct shear test on the remolded samples, the soil particle parameters of numerical model based on in-situ particle size cumulative curves and 3D granular discrete element method were determined. Then, numerical experiments on different lithology, stone content and gradation composition were conducted. The results show that it is not a flat surface but a shear band that yields in the sample. The curve of particle velocity vs distance from the designed shear surface of test model that is taken as a datum plane in the vertical section of sample shows in "S" shape. The shear disturbance area is about twice the maximum diameter of stone blocks. The greater the stiffness of stone is, the rougher the shear surface is. The shear strength of outwash deposits is largely controlled by lithology and stone content, and the bite force between stone blocks is the root reason of larger friction angle. It is also shown that strain hardening and low shear dilatancy occur under high confining pressure as well as possibility of shear shrinkage. But it is easy to behave shear dilatation and strain softening under low confining pressure. The relationship between particle frictional coefficient and stone content presents an approximately quadratic parabola increase. The strain energy first increases and then drops with the increase of frictional energy. The cohesion increases with soil stiffness increasing but decreases with stone stiffness increasing. Numerical results are consistent with the laboratory test results of remolded samples, which indicate that this method can be a beneficial supplement to determine the parameters of engineering deposit bodies.
基金Project(U1261107)supported by the National Natural Science Foundation of China
文摘Combined with the kinetic model of liquid film spreading, a new numerical method of solid-liquid-gas three-phase flow was developed for the moving of contact line, which was a hybrid method of computational fluid dynamics and lattice Boltzmalm method （LBM）. By taking the effect of molecule force in droplet and the wall surface on liquid film into account, the changing law of contact angle with different surface tensions was analyzed on glass and aluminum foil surfaces. Compared with experimental results, the standard deviation by using LBM is less than 0.5°, which validates the feasibility of LBM simulation on the dynamic process of liquid film spreading. In addition, oscillations are discovered both at the initial and end phases. The phenomenon of retraction is also found and the maximum retraction angle is 7.58°. The obtained result shows that the retraction is proved to be correlative with precursor film by tracking the volume change of liquid film contour. Furthermore, non-dimensional coefficient 2 is introduced to measure the liquid film retraction capacity.
基金Project(50975192) supported by the National Natural Science Foundation of ChinaProject(10YFJZJC14100) supported by Tianjin Municipal Natural Science Foundation of China
文摘In order to maintain vibration performances within the limits of the design, a vibration-based feature extraction method for dynamic characteristic using empirical mode decomposition （EMD） and wavelet analysis was proposed. The proposed method was verified experimentally and numerically by implementing the scheme on engine block. In the implementation process, the following steps were identified to be important： 1） EMD technique in order to solve the feature extraction of vibration signals; 2） Vibration measurement for the purpose of confirming the structural weak regions of engine block in experiment; 3） Finite element modeling for the purpose of determining dynamic characteristic in time region and frequency region to affirm the comparability of response character corresponding to improvement schemes; 4） Adopting a feature index oflMF for structural improvement based on EMD and wavelet analysis. The obtained results show that IMF of signal is more sensitive to response character corresponding to improvement schemes. Finally, examination of the results confirms that the proposed vibration-based feature extraction method is very robust, and focuses on the relative merits of modification and full-scale structural optimization of engine, together with the creation of new low-vibration designs.
基金Project(50679006) supported by the National Natural Science Foundation of ChinaProject(NCET-06-0270) supported by the Program for New Century Excellent Talents in University
文摘In order to numerically simulate the failure process of rock and concrete under uniaxial tension,an improved method of selecting the mechanical properties of materials was presented for the random mechanic parameter model based on the mesoscopic damage mechanics.The product of strength and elastic modulus of mesoscale representative volume element was considered to be one of the mechanical property parameters of materials and assumed to conform to specified probability distributions to reflect the heterogeneity of mechanical property in materials.With the improved property parameter selection method,a numerical program was developed and the simulation of the failure process of the rock and concrete specimens under static tensile loading condition was carried out.The failure process and complete stress-strain curves of a class of rock and concrete in stable fracture propagation manner under uniaxial tension were obtained.The simulated macroscopic mechanical behavior was compared with the available laboratory experimental observation,and a reasonable agreement was obtained.Verification shows that the improved parameter selection method is suitable for mesoscopic numerical simulation in the failure process of rock and concrete.
