A typical summer weather event in the mid-west starts with a cool dry wind moving south near the Rocky Mountains and an equal mass of warm moist air moving north to the east of it in a side by side arrangement. Argume...A typical summer weather event in the mid-west starts with a cool dry wind moving south near the Rocky Mountains and an equal mass of warm moist air moving north to the east of it in a side by side arrangement. Arguments supporting this proposition include observa<span style="font-family:Verdana;">tions, theory and one assumption. Observations are an awareness of the predominately </span><span style="font-family:Verdana;">north/south wind directions at one point in northwest Iowa for more than 30 consecutive summers as well as knowledge of the eastward flourishing vegetation distribution throughout the mid-west starting at the Rockies. The theory is the expectation that in geophysical flows the configuration most likely to persist and be observed has the least amount of friction among all possibilities. One assumption is that only a single southward cold wind takes place at one time to initiate the weather “cycle”.</span>展开更多
Surface gravity waves continually come to the beach but rarely go back to sea. They bring excess mass to shore which must be returned offshore. Rip currents do that job because there is less overall friction in the ne...Surface gravity waves continually come to the beach but rarely go back to sea. They bring excess mass to shore which must be returned offshore. Rip currents do that job because there is less overall friction in the nearshore region than there is in the only other imagined circulation, a two-layer scheme, which has in fact never been seen. An argument is presented to support this proposal. If correct, rip currents join a group of geophysical flow phenomena that persist, probably because there is zero friction associated with them, which include surface gravity waves, tornadoes and hurricanes, individually promoted recently.展开更多
The identification of maximum road friction coefficient and optimal slip ratio is crucial to vehicle dynamics and control.However,it is always not easy to identify the maximum road friction coefficient with high robus...The identification of maximum road friction coefficient and optimal slip ratio is crucial to vehicle dynamics and control.However,it is always not easy to identify the maximum road friction coefficient with high robustness and good adaptability to various vehicle operating conditions.The existing investigations on robust identification of maximum road friction coefficient are unsatisfactory.In this paper,an identification approach based on road type recognition is proposed for the robust identification of maximum road friction coefficient and optimal slip ratio.The instantaneous road friction coefficient is estimated through the recursive least square with a forgetting factor method based on the single wheel model,and the estimated road friction coefficient and slip ratio are grouped in a set of samples in a small time interval before the current time,which are updated with time progressing.The current road type is recognized by comparing the samples of the estimated road friction coefficient with the standard road friction coefficient of each typical road,and the minimum statistical error is used as the recognition principle to improve identification robustness.Once the road type is recognized,the maximum road friction coefficient and optimal slip ratio are determined.The numerical simulation tests are conducted on two typical road friction conditions（single-friction and joint-friction）by using CarSim software.The test results show that there is little identification error between the identified maximum road friction coefficient and the pre-set value in CarSim.The proposed identification method has good robustness performance to external disturbances and good adaptability to various vehicle operating conditions and road variations,and the identification results can be used for the adjustment of vehicle active safety control strategies.展开更多
文摘A typical summer weather event in the mid-west starts with a cool dry wind moving south near the Rocky Mountains and an equal mass of warm moist air moving north to the east of it in a side by side arrangement. Arguments supporting this proposition include observa<span style="font-family:Verdana;">tions, theory and one assumption. Observations are an awareness of the predominately </span><span style="font-family:Verdana;">north/south wind directions at one point in northwest Iowa for more than 30 consecutive summers as well as knowledge of the eastward flourishing vegetation distribution throughout the mid-west starting at the Rockies. The theory is the expectation that in geophysical flows the configuration most likely to persist and be observed has the least amount of friction among all possibilities. One assumption is that only a single southward cold wind takes place at one time to initiate the weather “cycle”.</span>
文摘Surface gravity waves continually come to the beach but rarely go back to sea. They bring excess mass to shore which must be returned offshore. Rip currents do that job because there is less overall friction in the nearshore region than there is in the only other imagined circulation, a two-layer scheme, which has in fact never been seen. An argument is presented to support this proposal. If correct, rip currents join a group of geophysical flow phenomena that persist, probably because there is zero friction associated with them, which include surface gravity waves, tornadoes and hurricanes, individually promoted recently.
基金Supported by National Hi-tech Research and Development Program of China(863 Program,Grant No.2006AA110101)
文摘The identification of maximum road friction coefficient and optimal slip ratio is crucial to vehicle dynamics and control.However,it is always not easy to identify the maximum road friction coefficient with high robustness and good adaptability to various vehicle operating conditions.The existing investigations on robust identification of maximum road friction coefficient are unsatisfactory.In this paper,an identification approach based on road type recognition is proposed for the robust identification of maximum road friction coefficient and optimal slip ratio.The instantaneous road friction coefficient is estimated through the recursive least square with a forgetting factor method based on the single wheel model,and the estimated road friction coefficient and slip ratio are grouped in a set of samples in a small time interval before the current time,which are updated with time progressing.The current road type is recognized by comparing the samples of the estimated road friction coefficient with the standard road friction coefficient of each typical road,and the minimum statistical error is used as the recognition principle to improve identification robustness.Once the road type is recognized,the maximum road friction coefficient and optimal slip ratio are determined.The numerical simulation tests are conducted on two typical road friction conditions（single-friction and joint-friction）by using CarSim software.The test results show that there is little identification error between the identified maximum road friction coefficient and the pre-set value in CarSim.The proposed identification method has good robustness performance to external disturbances and good adaptability to various vehicle operating conditions and road variations,and the identification results can be used for the adjustment of vehicle active safety control strategies.
基金The National Natural Science Foundation of China(No.61273236)the Natural Science Foundation of Jiangsu Province(No.BK2010239)the Ph.D. Programs Foundation of Ministry of Education of China(No.200802861061)
