Free-fall of a sphere in fluid is investigated at a Galileo number of 204 by direct numerical simulations(DNS). We mainly focus on the effects of different degrees-of-freedom(DOFs) of the sphere motion during free-fal...Free-fall of a sphere in fluid is investigated at a Galileo number of 204 by direct numerical simulations(DNS). We mainly focus on the effects of different degrees-of-freedom(DOFs) of the sphere motion during free-fall. The characteristics of free-fall are compared with those of flow past a fixed sphere. Additional numerical tests are conducted with constraints placed on the translational or rotational DOFs of the sphere motion to analyze different DOFs of sphere motion. The transverse motion contributes significantly to the characteristics of free-fall; it results in the retardation of the vortex shedding, leading to the decrease of the Strouhal number. In addition, the transversal sphere motion exhibits the tendency to promote the sphere rotation. On the contrary, the effects of the sphere rotation and vertical oscillations during free-fall are negligible.展开更多
The nonholonomic motion planning of a free-falling cat is investigated. Nonholonomicity arises in a free-falling cat subject to nonintegrable angle velocity constraints or nonintegrable conservation laws. When the tot...The nonholonomic motion planning of a free-falling cat is investigated. Nonholonomicity arises in a free-falling cat subject to nonintegrable angle velocity constraints or nonintegrable conservation laws. When the total angular momentum is zero, the motion equation of a free-falling cat is established based on the model of two symmetric rigid bodies and conservation of angular momentum. The control of system can be converted to the problem of nonholonomic motion planning for a free-falling cat. Based on Ritz approximation theory, the Gauss-Newton method for motion planning by a falling cat is proposed. The effectiveness of the numerical algorithm is demonstrated through simulation on model of a free-falling cat.展开更多
In this study,the optical flow method is used to measure the velocity distribution of a granular flow in a rectangular quasi-two-dimensional silo.Using the velocity gradient,a free-fall arch(FFA)is obtained and its ge...In this study,the optical flow method is used to measure the velocity distribution of a granular flow in a rectangular quasi-two-dimensional silo.Using the velocity gradient,a free-fall arch(FFA)is obtained and its geometric characteristics are calculated.A parabola-shaped FFA structure is discovered above the orifice in the steady flow state.The shape of the FFA affects the flow rate through the orifice.Furthermore,as jamming begins to occur,the geometry of the FFA disappears gradually from both sides and then from the middle;finally,the FFA disappears completely in the state of jamming.As the boundary between finite-stress and stress-free regions,the FFA facilitates further studies regarding the discontinuity of the stress area above the orifice.展开更多
Recently,laser pre-sowing treatment of seed is attracting a great attention of scientific community for its positive influence to enhance germination,seedling and growth of plants,vegetables and crops.In this study,ef...Recently,laser pre-sowing treatment of seed is attracting a great attention of scientific community for its positive influence to enhance germination,seedling and growth of plants,vegetables and crops.In this study,effect of laser pre-sowing treatment of rice seeds was given,which was implemented by free-falling transport method.Test has been processed in Unzon district(DPRK)in 2017.Two kinds of Korean rice seeds(namely Pyongyang-53 and Dongsung-1)were irradiated by semiconductor laser with wavelength of 650 nm,which was controlled in PWM mode.Each group was irradiated using exposure time of 0.28 s and duty ratio of 50 percent.In result,a considerable improvement has been observed in germination,growth and final productivity.Using laser pre-sowing treatment of rice seed,total productivities have been increased by 7.7%and 21%for “Pyongyang-53”and “Dongsung-1”,respectively.Results show that laser pre-sowing treatment of seed can significantly enhance germination,seedling and growth,and thus can improve the productivity of rice.In future research,laser pre-sowing treatment by free-falling transport method should be processed for other kinds of plants,vegetables and cereal crops to find out appropriate parameters,such as mechanical structure of device,wave length and power of laser,frequency and duty cycle of PWM control signal and exposure time,etc.展开更多
Dimensionless variable groups(DGs)of free-fall grain dryer were developed by using the characteristic scaling method and engineering intuition.These DGs were intended for the analyses of drying characteristics and siz...Dimensionless variable groups(DGs)of free-fall grain dryer were developed by using the characteristic scaling method and engineering intuition.These DGs were intended for the analyses of drying characteristics and sizes of this dryer.Experiments of the free-fall rough rice dryer were carried out using different drying chambers(small and medium scales),drying air temperatures(100°C-150°C),and drying air speeds(1-3 m/s).Experimental data were used to study relationships and to validate similarities among these DGs.The results of the study showed the five appropriate dimensionless variables representing and describing the drying mechanism of the free-fall dryer.These DGs could be applied to design and analyze scaling up the dryer.In addition,the dimensionless correlation was established to predict the moisture contents of rough rice while being dried by the free-fall dryer.The predicted values from this correlation were in relatively good agreement with the experimental data under the proposed drying conditions(R2=0.989,MRD=1.82%and RMSE=0.0168).展开更多
The effects of three factors （i.e., drop height h, hopper outlet diameter do, and material temperature T] on the dust generation rate derived from a free falling particle stream were investigated via filll factorial ...The effects of three factors （i.e., drop height h, hopper outlet diameter do, and material temperature T] on the dust generation rate derived from a free falling particle stream were investigated via filll factorial experiments. The correlation between the three factors and dust generation rate was also analysed. Results show that Tand h affect the first fugitive dust rate largely, whereas the second fugitive dust rate is mainly dominated by h and do. Through analysing the first fugitive dust percentage data, it is found that h and T should be considered first for higher temperatures and lower flow rates, whereas h and do can be considered under contrasting conditions, and h should be controlled in the remaining two sets of conditions. Relationships between the influencing factors and total and first fugitive dust rates were developed via multiple regression to quantify the dust emission rates for different contact surfaces （rigid or water）.展开更多
This paper presents a novel experiment to observe the whole water entry process of a free-falling sphere into a regular wave.A time-accurate synchronizing system modulates the moment elaborately to ensure the sphere i...This paper presents a novel experiment to observe the whole water entry process of a free-falling sphere into a regular wave.A time-accurate synchronizing system modulates the moment elaborately to ensure the sphere impacting onto the water surface at the desirable wave phase.Four high-speed cameras focus locally to measure the high-precision size of the cavity evolution.Meanwhile,the aggregated field view of the camera array covers both the splash above the free surface and the entire cavity in the wave.The detailed methodologies are described and verified for the hardware set-up and the image post-processing.The theoretical maximum deviation is 1.7%on the space scale.The integral morphology of the cavity is captured precisely in the coordinate system during the sphere penetrates through the water at four representative wave phases and the still water.The result shows that the horizontal velocity of the fluid particle in the wave impels the cavity and changes the shape distinctly.Notably,the wave motion causes the cavity to pinch offearlier at the wave trough phase and later at the wave crest phase than in the still water.The wave motion influences the falling process of the sphere slightly in the present parameters.展开更多
基金financially supported by the National Key Research and Development Program of China(Grant No.2016YFC0304103)the National Natural Science Foundation of China(Grant No.51509152)
文摘Free-fall of a sphere in fluid is investigated at a Galileo number of 204 by direct numerical simulations(DNS). We mainly focus on the effects of different degrees-of-freedom(DOFs) of the sphere motion during free-fall. The characteristics of free-fall are compared with those of flow past a fixed sphere. Additional numerical tests are conducted with constraints placed on the translational or rotational DOFs of the sphere motion to analyze different DOFs of sphere motion. The transverse motion contributes significantly to the characteristics of free-fall; it results in the retardation of the vortex shedding, leading to the decrease of the Strouhal number. In addition, the transversal sphere motion exhibits the tendency to promote the sphere rotation. On the contrary, the effects of the sphere rotation and vertical oscillations during free-fall are negligible.
基金Project supported by the National Natural Science Foundation of China (No.10372014)the Natural Science Foundation of Beijing (No.1072008)
文摘The nonholonomic motion planning of a free-falling cat is investigated. Nonholonomicity arises in a free-falling cat subject to nonintegrable angle velocity constraints or nonintegrable conservation laws. When the total angular momentum is zero, the motion equation of a free-falling cat is established based on the model of two symmetric rigid bodies and conservation of angular momentum. The control of system can be converted to the problem of nonholonomic motion planning for a free-falling cat. Based on Ritz approximation theory, the Gauss-Newton method for motion planning by a falling cat is proposed. The effectiveness of the numerical algorithm is demonstrated through simulation on model of a free-falling cat.
基金This study was supported by the National Natural Science Foundation of China(Grant Nos.91634202,12072200,12002213)the Natural Science Foundation of Shanghai(20ZR1438800)Science and Technology Commission of Shanghai Municipality(19142201500).
文摘In this study,the optical flow method is used to measure the velocity distribution of a granular flow in a rectangular quasi-two-dimensional silo.Using the velocity gradient,a free-fall arch(FFA)is obtained and its geometric characteristics are calculated.A parabola-shaped FFA structure is discovered above the orifice in the steady flow state.The shape of the FFA affects the flow rate through the orifice.Furthermore,as jamming begins to occur,the geometry of the FFA disappears gradually from both sides and then from the middle;finally,the FFA disappears completely in the state of jamming.As the boundary between finite-stress and stress-free regions,the FFA facilitates further studies regarding the discontinuity of the stress area above the orifice.
基金This work was supported by the National Natural Science Foundation of Korea(Grant No.54289562).
文摘Recently,laser pre-sowing treatment of seed is attracting a great attention of scientific community for its positive influence to enhance germination,seedling and growth of plants,vegetables and crops.In this study,effect of laser pre-sowing treatment of rice seeds was given,which was implemented by free-falling transport method.Test has been processed in Unzon district(DPRK)in 2017.Two kinds of Korean rice seeds(namely Pyongyang-53 and Dongsung-1)were irradiated by semiconductor laser with wavelength of 650 nm,which was controlled in PWM mode.Each group was irradiated using exposure time of 0.28 s and duty ratio of 50 percent.In result,a considerable improvement has been observed in germination,growth and final productivity.Using laser pre-sowing treatment of rice seed,total productivities have been increased by 7.7%and 21%for “Pyongyang-53”and “Dongsung-1”,respectively.Results show that laser pre-sowing treatment of seed can significantly enhance germination,seedling and growth,and thus can improve the productivity of rice.In future research,laser pre-sowing treatment by free-falling transport method should be processed for other kinds of plants,vegetables and cereal crops to find out appropriate parameters,such as mechanical structure of device,wave length and power of laser,frequency and duty cycle of PWM control signal and exposure time,etc.
基金This research is sponsored by the Royal Golden Jubilee(RGJ)Ph.D.Program of the Thailand Research Fund(TRF).
文摘Dimensionless variable groups(DGs)of free-fall grain dryer were developed by using the characteristic scaling method and engineering intuition.These DGs were intended for the analyses of drying characteristics and sizes of this dryer.Experiments of the free-fall rough rice dryer were carried out using different drying chambers(small and medium scales),drying air temperatures(100°C-150°C),and drying air speeds(1-3 m/s).Experimental data were used to study relationships and to validate similarities among these DGs.The results of the study showed the five appropriate dimensionless variables representing and describing the drying mechanism of the free-fall dryer.These DGs could be applied to design and analyze scaling up the dryer.In addition,the dimensionless correlation was established to predict the moisture contents of rough rice while being dried by the free-fall dryer.The predicted values from this correlation were in relatively good agreement with the experimental data under the proposed drying conditions(R2=0.989,MRD=1.82%and RMSE=0.0168).
文摘The effects of three factors （i.e., drop height h, hopper outlet diameter do, and material temperature T] on the dust generation rate derived from a free falling particle stream were investigated via filll factorial experiments. The correlation between the three factors and dust generation rate was also analysed. Results show that Tand h affect the first fugitive dust rate largely, whereas the second fugitive dust rate is mainly dominated by h and do. Through analysing the first fugitive dust percentage data, it is found that h and T should be considered first for higher temperatures and lower flow rates, whereas h and do can be considered under contrasting conditions, and h should be controlled in the remaining two sets of conditions. Relationships between the influencing factors and total and first fugitive dust rates were developed via multiple regression to quantify the dust emission rates for different contact surfaces （rigid or water）.
基金sponsored by the National Natural Sci-ence Foundation of China(Grant Nos.12102262,U22136010 and 11632012).
文摘This paper presents a novel experiment to observe the whole water entry process of a free-falling sphere into a regular wave.A time-accurate synchronizing system modulates the moment elaborately to ensure the sphere impacting onto the water surface at the desirable wave phase.Four high-speed cameras focus locally to measure the high-precision size of the cavity evolution.Meanwhile,the aggregated field view of the camera array covers both the splash above the free surface and the entire cavity in the wave.The detailed methodologies are described and verified for the hardware set-up and the image post-processing.The theoretical maximum deviation is 1.7%on the space scale.The integral morphology of the cavity is captured precisely in the coordinate system during the sphere penetrates through the water at four representative wave phases and the still water.The result shows that the horizontal velocity of the fluid particle in the wave impels the cavity and changes the shape distinctly.Notably,the wave motion causes the cavity to pinch offearlier at the wave trough phase and later at the wave crest phase than in the still water.The wave motion influences the falling process of the sphere slightly in the present parameters.
