The delay compensation method plays an essential role in maintaining the stability and achieving accurate real-time hybrid simulation results. The effectiveness of various compensation methods in different test scenar...The delay compensation method plays an essential role in maintaining the stability and achieving accurate real-time hybrid simulation results. The effectiveness of various compensation methods in different test scenarios, however, needs to be quantitatively evaluated. In this study, four compensation methods （i.e., the polynomial extrapolation, the linear acceleration extrapolation, the inverse compensation and the adaptive inverse compensation） are selected and compared experimentally using a frequency evaluation index （FEI） method. The effectiveness of the FEI method is first verified through comparison with the discrete transfer fimction approach for compensation methods assuming constant delay. Incomparable advantage is further demonstrated for the FEI method when applied to adaptive compensation methods, where the discrete transfer function approach is difficult to implement. Both numerical simulation and laboratory tests with predefined displacements are conducted using sinusoidal signals and random signals as inputs. Findings from numerical simulation and experimental results demonstrate that the FEI method is an efficient and effective approach to compare the performance of different compensation methods, especially for those requiring adaptation of compensation parameters.展开更多
Reducing the power and energy required by the device/circuit to operate is the main aim of this paper. Here the new design is implemented to reduce the power consumption of the device using the triggering pulses. The ...Reducing the power and energy required by the device/circuit to operate is the main aim of this paper. Here the new design is implemented to reduce the power consumption of the device using the triggering pulses. The proposed triggering method uses a complementary MOS transistor (pMOS and nMOS) as a voltage divider and ground leakage suppressor (i.e.);these designs are named as Trig01 and Trig10 designs. In Trig01 design the pair of CMOS is placed in the voltage divider part;similarly in Trig10 design the pair of CMOS is placed at the ground leakage suppressor part. Standard CMOS gates like NOT, NAND, NOR, EX-OR etc. are designed with these technologies and these gates are designed with 180 nm technology file in the cadence tool suite;compared to the normal CMOS gates, the Bi-Trig gate contains 4 inputs and 2 outputs. The two extra inputs are used as Bi-Trig control signaling inputs. There are 2 control inputs and thus 2<sup>2</sup> = 4 combination of controlling is done (i.e.);both pMOS and nMOS are ON, both pMOS and nMOS are OFF, pMOS ON and nMOS OFF and pMOS ON and nMOS ON. Depending on the usage of the circuit, the mode of operation is switched to any one of the combination. If the output of the circuit is not used anywhere in the total block, that specified circuit can be switched into idle mode by means of switched OFF both the pMOS and nMOS transistor in the control unit. This reduces the leakage current and also the power wastage of the circuits in the total block. Bi-Trig controlled circuit reduces the power consumption and leakage power of the circuit without affecting a performance of the circuits.展开更多
We conducted experiments in a wind tunnel with Mach number 2 to explore the evolution of a transverse plasma jet and its modification effect on a shock wave induced by a ramp with an angle of 24°. The transverse ...We conducted experiments in a wind tunnel with Mach number 2 to explore the evolution of a transverse plasma jet and its modification effect on a shock wave induced by a ramp with an angle of 24°. The transverse plasma jet was created by arc discharge in a small cylindrical cavity with a 2 mm diameter orifice. Three group tests with different actuator arrangements in the spanwise or streamwise direction upstream from the ramp were respectively studied to compare their disturbances to the shock wave. As shown by a time-resolved schlieren system, an unsteady motion of the shock wave by actuation was found： the shock wave was significantly modified by the plasma jet with an upstream motion and a reduced angle. Compared to spanwise actuation, a more intensive impact was obtained with two or three streamwise actuators working together. From shock wave structures, the control effect of the plasma jet on the shock motion based on a thermal effect, a potential cause of shock modification, was discussed. Furthermore, we performed a numerical simulation by using the Improved Delayed Detached Eddy Simulation（IDDES） method to simulate the evolution of the transverse plasma jet plume produced by two streamwise actuators. The results show that flow structures are similar to those identified in schlieren images. Two streamwise vortices were recognized, which indicates that the higher jet plume is the result of the overlap of two streamwise jets.展开更多
Considered as the building blocks,vortex structures with variety of sizes and intensity are widely recognized in the viscous flow field around ship.In this paper,the computational fluid dynamics(CFD)solver,naoe-FOAM-S...Considered as the building blocks,vortex structures with variety of sizes and intensity are widely recognized in the viscous flow field around ship.In this paper,the computational fluid dynamics(CFD)solver,naoe-FOAM-SJTU,coupled with delayed detached-eddy simulation(DDES)is adopted to analyze the vortex structures around the benchmark model Yupeng Ship in dynamic pure yaw tests,which are captured by third generation of vortex identification method.The good agreement of the predicted force/moment by DDES method with the experimental data indicates that the present numerical schemes are reliable and robust.Three vortex identification methods,Q-criteria,Ω_(R) and Liutex,are used to capture the vortex structures around the hull.The large separated flow is able to be investigated by these three methods,in which more vortex structures are captured byΩ_(R) approach and Liutex method with scalar,vector and tensor form seems to be more suitable for analyzing the flow mechanism around the hull in dynamic pure yaw test.In general,each vortex structure corresponds to a dominant positive/negative axial Liutex and a bound vortex pair.The streamlines are spiral in the large separated flow,indicating that the flow in corresponding region is rotational.But the rotation of the flow is not directly related to the intensity of Liutex.展开更多
The precision in predicting cavitation noise critically depends on the accuracy of flow field simulations.In the present work,we employ the improved delayed detached eddy simulation(IDDES),coupled with Spalart-Allmara...The precision in predicting cavitation noise critically depends on the accuracy of flow field simulations.In the present work,we employ the improved delayed detached eddy simulation(IDDES),coupled with Spalart-Allmaras(SA)turbulence model and Schnerr-Sauer cavitation model,to simulate the cavitating flow around a three-dimension twisted hydrofoil.The accuracy of simulation is accessed by examining the power spectral density of pressure fluctuations and the percentage of resolved turbulent kinetic energy.The simulated cavitation behavior is compared with experimental observation in terms of shedding patterns and frequencies.The cavitation-radiated noise,computed via the porous Ffowcs-Williams and Hawkings(PFWH)method,is subsequently calculated.Strategies for setting different integral surfaces are discussed.An analysis of sound pressure and cavity evolution patterns for a typical cycle elucidates the correlation between the dynamic characteristics of the cavity and the noise properties.The simulation addresses the lack of experimental data,which poses challenges due to the need for numerous hydrophones and the elimination of tunnel wall effects.The combination of the PFWH source surface and the original FW-H source surface facilitates the investigation of various noise sources.The results indicate that the pseudo-thickness term approximates a monopole noise associated with cavity volume acceleration,the loading term resembles a dipole,and the quadrupole term can be obtained by subtracting from the total sound pressure.The sound pressure levels at the monitoring points reveal that the monopole term predominates,followed by the quadrupole term,with the dipole term registering the lowest values.展开更多
We present an approximation method for the non-stationary nonlinear in- compressible Navier-Stokes equations in a cylindrical domain （0, T） x G, where G C ]R3 is a smoothly bounded domain. Our method is applicable t...We present an approximation method for the non-stationary nonlinear in- compressible Navier-Stokes equations in a cylindrical domain （0, T） x G, where G C ]R3 is a smoothly bounded domain. Our method is applicable to general three-dimensional flow without any symmetry restrictions and relies on existence, uniqueness and rep- resentation results from mathematical fluid dynamics. After a suitable time delay in the nonlinear convective term v. ~7v we obtain globally （in time） uniquely solvable equations, which - by using semi-implicit time differences - can be transformed into a finite number of Stokes-type boundary value problems. For the latter a boundary element method based on a corresponding hydrodynamical potential theory is carried out. The method is reported in short outlines ranging from approximation theory up to numerical test calculations.展开更多
Ship bow wave breaking contains complex flow mechanism,which is very important for ship performance.In this study,a practical numerical simulation scheme for bow wave breaking is proposed and the scheme is applied to ...Ship bow wave breaking contains complex flow mechanism,which is very important for ship performance.In this study,a practical numerical simulation scheme for bow wave breaking is proposed and the scheme is applied to the simulation of bow wave breaking of KCS ship model with Fr=0.26,0.30,0.35,0.40,analyzing the impact of speed on the bow wave breaking.The results indicate that an increase in speed leads to a significant rise in viscous pressure resistance and more pronounced bow wave breaking.Moreover,it is found that the traditional wave height function in OpenFOAM is not suitable for detailed studies of bow wave breaking.This study extracts different free surfaces through top and bottom views to further analyze the free surface overturning,droplet splashing,and cavity entrainment in bow wave breaking.Additionally,the spatial and temporal distribution of cavities at Fr=0.40 is analyzed,revealing that cavity distribution is closely related to vortex structures and exhibits a periodic pulsation characteristic of approximately 12 s.展开更多
基金National Natural Science Foundation of China under Grant No.51378107the Fundamental Research Funds for the Central Universities and Priority Academic Program Development of Jiangsu Higher Education Institutions under Grant No.KYLX-0158the National Natural Science Foundation under Grant No.CMMI-1227962
文摘The delay compensation method plays an essential role in maintaining the stability and achieving accurate real-time hybrid simulation results. The effectiveness of various compensation methods in different test scenarios, however, needs to be quantitatively evaluated. In this study, four compensation methods （i.e., the polynomial extrapolation, the linear acceleration extrapolation, the inverse compensation and the adaptive inverse compensation） are selected and compared experimentally using a frequency evaluation index （FEI） method. The effectiveness of the FEI method is first verified through comparison with the discrete transfer fimction approach for compensation methods assuming constant delay. Incomparable advantage is further demonstrated for the FEI method when applied to adaptive compensation methods, where the discrete transfer function approach is difficult to implement. Both numerical simulation and laboratory tests with predefined displacements are conducted using sinusoidal signals and random signals as inputs. Findings from numerical simulation and experimental results demonstrate that the FEI method is an efficient and effective approach to compare the performance of different compensation methods, especially for those requiring adaptation of compensation parameters.
文摘Reducing the power and energy required by the device/circuit to operate is the main aim of this paper. Here the new design is implemented to reduce the power consumption of the device using the triggering pulses. The proposed triggering method uses a complementary MOS transistor (pMOS and nMOS) as a voltage divider and ground leakage suppressor (i.e.);these designs are named as Trig01 and Trig10 designs. In Trig01 design the pair of CMOS is placed in the voltage divider part;similarly in Trig10 design the pair of CMOS is placed at the ground leakage suppressor part. Standard CMOS gates like NOT, NAND, NOR, EX-OR etc. are designed with these technologies and these gates are designed with 180 nm technology file in the cadence tool suite;compared to the normal CMOS gates, the Bi-Trig gate contains 4 inputs and 2 outputs. The two extra inputs are used as Bi-Trig control signaling inputs. There are 2 control inputs and thus 2<sup>2</sup> = 4 combination of controlling is done (i.e.);both pMOS and nMOS are ON, both pMOS and nMOS are OFF, pMOS ON and nMOS OFF and pMOS ON and nMOS ON. Depending on the usage of the circuit, the mode of operation is switched to any one of the combination. If the output of the circuit is not used anywhere in the total block, that specified circuit can be switched into idle mode by means of switched OFF both the pMOS and nMOS transistor in the control unit. This reduces the leakage current and also the power wastage of the circuits in the total block. Bi-Trig controlled circuit reduces the power consumption and leakage power of the circuit without affecting a performance of the circuits.
基金supported by the National Natural Science Foundation of China(Nos.51522606,51507187,51276197,51407197,and 11472306)
文摘We conducted experiments in a wind tunnel with Mach number 2 to explore the evolution of a transverse plasma jet and its modification effect on a shock wave induced by a ramp with an angle of 24°. The transverse plasma jet was created by arc discharge in a small cylindrical cavity with a 2 mm diameter orifice. Three group tests with different actuator arrangements in the spanwise or streamwise direction upstream from the ramp were respectively studied to compare their disturbances to the shock wave. As shown by a time-resolved schlieren system, an unsteady motion of the shock wave by actuation was found： the shock wave was significantly modified by the plasma jet with an upstream motion and a reduced angle. Compared to spanwise actuation, a more intensive impact was obtained with two or three streamwise actuators working together. From shock wave structures, the control effect of the plasma jet on the shock motion based on a thermal effect, a potential cause of shock modification, was discussed. Furthermore, we performed a numerical simulation by using the Improved Delayed Detached Eddy Simulation（IDDES） method to simulate the evolution of the transverse plasma jet plume produced by two streamwise actuators. The results show that flow structures are similar to those identified in schlieren images. Two streamwise vortices were recognized, which indicates that the higher jet plume is the result of the overlap of two streamwise jets.
基金supported by the National Natural Science Foundation of China(Grant Nos.51909160,51879159,52131102)the National Key Research and Development Program of China(Grant No.2019YFB1704200).
文摘Considered as the building blocks,vortex structures with variety of sizes and intensity are widely recognized in the viscous flow field around ship.In this paper,the computational fluid dynamics(CFD)solver,naoe-FOAM-SJTU,coupled with delayed detached-eddy simulation(DDES)is adopted to analyze the vortex structures around the benchmark model Yupeng Ship in dynamic pure yaw tests,which are captured by third generation of vortex identification method.The good agreement of the predicted force/moment by DDES method with the experimental data indicates that the present numerical schemes are reliable and robust.Three vortex identification methods,Q-criteria,Ω_(R) and Liutex,are used to capture the vortex structures around the hull.The large separated flow is able to be investigated by these three methods,in which more vortex structures are captured byΩ_(R) approach and Liutex method with scalar,vector and tensor form seems to be more suitable for analyzing the flow mechanism around the hull in dynamic pure yaw test.In general,each vortex structure corresponds to a dominant positive/negative axial Liutex and a bound vortex pair.The streamlines are spiral in the large separated flow,indicating that the flow in corresponding region is rotational.But the rotation of the flow is not directly related to the intensity of Liutex.
基金Project supported by the Fundamental Research Project(Grant No.909120103),the National Natural Science Foundation of China(Grant Nos.92252205,11802275 and 12172219).
文摘The precision in predicting cavitation noise critically depends on the accuracy of flow field simulations.In the present work,we employ the improved delayed detached eddy simulation(IDDES),coupled with Spalart-Allmaras(SA)turbulence model and Schnerr-Sauer cavitation model,to simulate the cavitating flow around a three-dimension twisted hydrofoil.The accuracy of simulation is accessed by examining the power spectral density of pressure fluctuations and the percentage of resolved turbulent kinetic energy.The simulated cavitation behavior is compared with experimental observation in terms of shedding patterns and frequencies.The cavitation-radiated noise,computed via the porous Ffowcs-Williams and Hawkings(PFWH)method,is subsequently calculated.Strategies for setting different integral surfaces are discussed.An analysis of sound pressure and cavity evolution patterns for a typical cycle elucidates the correlation between the dynamic characteristics of the cavity and the noise properties.The simulation addresses the lack of experimental data,which poses challenges due to the need for numerous hydrophones and the elimination of tunnel wall effects.The combination of the PFWH source surface and the original FW-H source surface facilitates the investigation of various noise sources.The results indicate that the pseudo-thickness term approximates a monopole noise associated with cavity volume acceleration,the loading term resembles a dipole,and the quadrupole term can be obtained by subtracting from the total sound pressure.The sound pressure levels at the monitoring points reveal that the monopole term predominates,followed by the quadrupole term,with the dipole term registering the lowest values.
文摘We present an approximation method for the non-stationary nonlinear in- compressible Navier-Stokes equations in a cylindrical domain （0, T） x G, where G C ]R3 is a smoothly bounded domain. Our method is applicable to general three-dimensional flow without any symmetry restrictions and relies on existence, uniqueness and rep- resentation results from mathematical fluid dynamics. After a suitable time delay in the nonlinear convective term v. ~7v we obtain globally （in time） uniquely solvable equations, which - by using semi-implicit time differences - can be transformed into a finite number of Stokes-type boundary value problems. For the latter a boundary element method based on a corresponding hydrodynamical potential theory is carried out. The method is reported in short outlines ranging from approximation theory up to numerical test calculations.
基金Project supported by the National Natural Science Foundation of China(Grant No.52131102).
文摘Ship bow wave breaking contains complex flow mechanism,which is very important for ship performance.In this study,a practical numerical simulation scheme for bow wave breaking is proposed and the scheme is applied to the simulation of bow wave breaking of KCS ship model with Fr=0.26,0.30,0.35,0.40,analyzing the impact of speed on the bow wave breaking.The results indicate that an increase in speed leads to a significant rise in viscous pressure resistance and more pronounced bow wave breaking.Moreover,it is found that the traditional wave height function in OpenFOAM is not suitable for detailed studies of bow wave breaking.This study extracts different free surfaces through top and bottom views to further analyze the free surface overturning,droplet splashing,and cavity entrainment in bow wave breaking.Additionally,the spatial and temporal distribution of cavities at Fr=0.40 is analyzed,revealing that cavity distribution is closely related to vortex structures and exhibits a periodic pulsation characteristic of approximately 12 s.
