The aerodynamic performances of a passenger car and a box car with different heights of windbreak walls under strong wind were studied using the numerical simulations, and the changes of aerodynamic side force, lift f...The aerodynamic performances of a passenger car and a box car with different heights of windbreak walls under strong wind were studied using the numerical simulations, and the changes of aerodynamic side force, lift force and overturning moment with different wind speeds and wall heights were calculated. According to the principle of static moment balance of vehicles, the overturning coefficients of trains with different wind speeds and wall heights were obtained. Based on the influence of wind speed and wall height on the aerodynamic performance and the overturning stability of trains, a method of determination of the load balance ranges for the train operation safety was proposed, which made the overturning coefficient have nearly closed interval. A min(|A1|+|A2|), s.t. |A1|→|A2|(A1 refers to the downwind overturning coefficient and A2 refers to the upwind overturning coefficient)was found. This minimum value helps to lower the wall height as much as possible, and meanwhile, guarantees the operation safety of various types of trains under strong wind. This method has been used for the construction and improvement of the windbreak walls along the Lanzhou–Xinjiang railway(from Lanzhou to Urumqi, China).展开更多
The traditional matched field processing localization need complicated computation to get the replica field and has high dependence on environment parameters and acoustic field model. To overcome the shortcoming, virt...The traditional matched field processing localization need complicated computation to get the replica field and has high dependence on environment parameters and acoustic field model. To overcome the shortcoming, virtual receiver technique is used for source ranging. A virtual receiver is constructed by correlating the two signals of the guide source and the objective source received by a vertical line array. Then, the slope of the interference striation of the virtual field is estimated using relevant signal processing method. Combining with the waveguide invariant/3, the range of the objective source is determined. Through the numerical simulations and data processing collected from the experiment carried out in the South China Sea in 2004, the virtual receiver technique for broadband source ranging under the slope- bottom shallow water environment is discussed. As the frequency increases, the frequency bands should be broadened to obtain complete interference striation for good ranging results. In data processing, the receiving array spacing is too large to promise the orthogonality of the modes as the frequency increases and ranging results become worse.展开更多
In this study,aerodynamic behaviors of swept and leaned blades were investigated.Axial and tangential blade curvatures impacts on compressor's operating parameters were analyzed separately.A commercial CFD program...In this study,aerodynamic behaviors of swept and leaned blades were investigated.Axial and tangential blade curvatures impacts on compressor's operating parameters were analyzed separately.A commercial CFD program which solves the Reynolds-averaged Navier-Stokes equations was used to find out the mentioned impact and the complicated flow field of transonic compressor-rotors.The CFD method that was used for solving flow field's equation was validated by experimental data of NASA Rotor 67.The results showed that the compressor with curved rotors had higher efficiency,rotor pressure ratio and stable operating range compared to the compressor with un-curved rotors.Using curved rotors mostly had higher impact on the overall stable operating range compared to the other operating parameters.Operating range involves choking point and stall point that were changed separately by using of bended blade.For finding the detailed impact of sweep and lean angle on transonic blades,various forms of lean and sweep angles were exerted to basic rotor.It was found that sweep angles increased overall operating range up to 30%,efficiency up to 2%and pressure ratio up to 1%.Leaning the blades increased the safe operating range,the pressure ratio and efficiency by 14%,4%and 2%respectively.展开更多
Autonomous underwater vehicles(AUVs)have various applications in both military and civilian fields.A wider operation area and more complex tasks require better overall range performance of AUVs.However,until recently,...Autonomous underwater vehicles(AUVs)have various applications in both military and civilian fields.A wider operation area and more complex tasks require better overall range performance of AUVs.However,until recently,there have been few unified criteria for evaluating the range performance of AUVs.In the present work,a unified range index,i.e.,L^(*),considering the cruising speed,the sailing distance,and the volume of an AUV,is proposed for the first time,which can overcome the shortcomings of previous criteria using merely one single parameter,and provide a uniform criterion for the overall range performance of various AUVs.After constructing the expression of the L^(*)index,the relevant data of 49 AUVs from 12 countries worldwide have been collected,and the characteristics of the L^(*)range index in different countries and different categories were compared and discussed.Furthermore,by analyzing the complex factors affecting the range index,methods to enhance the L^(*)range index value,such as efficiency enhancement and drag reduction,have been introduced and discussed.Under this condition,the work proposes a unified and scientific criterion for evaluating the range performance of AUVs for the first time,provides valuable theoretical insight for the development of AUVs with higher performance,and then arouses more attention to the application of the cutting-edge superlubricity technology to the field of underwater vehicles,which might greatly help to accelerate the coming of the era of the superlubricitive engineering.展开更多
基金Project(U1334203) supported by the National Natural Science Foundation of China
文摘The aerodynamic performances of a passenger car and a box car with different heights of windbreak walls under strong wind were studied using the numerical simulations, and the changes of aerodynamic side force, lift force and overturning moment with different wind speeds and wall heights were calculated. According to the principle of static moment balance of vehicles, the overturning coefficients of trains with different wind speeds and wall heights were obtained. Based on the influence of wind speed and wall height on the aerodynamic performance and the overturning stability of trains, a method of determination of the load balance ranges for the train operation safety was proposed, which made the overturning coefficient have nearly closed interval. A min(|A1|+|A2|), s.t. |A1|→|A2|(A1 refers to the downwind overturning coefficient and A2 refers to the upwind overturning coefficient)was found. This minimum value helps to lower the wall height as much as possible, and meanwhile, guarantees the operation safety of various types of trains under strong wind. This method has been used for the construction and improvement of the windbreak walls along the Lanzhou–Xinjiang railway(from Lanzhou to Urumqi, China).
基金supported by the National Natural Science Foundation of China(10774156)
文摘The traditional matched field processing localization need complicated computation to get the replica field and has high dependence on environment parameters and acoustic field model. To overcome the shortcoming, virtual receiver technique is used for source ranging. A virtual receiver is constructed by correlating the two signals of the guide source and the objective source received by a vertical line array. Then, the slope of the interference striation of the virtual field is estimated using relevant signal processing method. Combining with the waveguide invariant/3, the range of the objective source is determined. Through the numerical simulations and data processing collected from the experiment carried out in the South China Sea in 2004, the virtual receiver technique for broadband source ranging under the slope- bottom shallow water environment is discussed. As the frequency increases, the frequency bands should be broadened to obtain complete interference striation for good ranging results. In data processing, the receiving array spacing is too large to promise the orthogonality of the modes as the frequency increases and ranging results become worse.
文摘In this study,aerodynamic behaviors of swept and leaned blades were investigated.Axial and tangential blade curvatures impacts on compressor's operating parameters were analyzed separately.A commercial CFD program which solves the Reynolds-averaged Navier-Stokes equations was used to find out the mentioned impact and the complicated flow field of transonic compressor-rotors.The CFD method that was used for solving flow field's equation was validated by experimental data of NASA Rotor 67.The results showed that the compressor with curved rotors had higher efficiency,rotor pressure ratio and stable operating range compared to the compressor with un-curved rotors.Using curved rotors mostly had higher impact on the overall stable operating range compared to the other operating parameters.Operating range involves choking point and stall point that were changed separately by using of bended blade.For finding the detailed impact of sweep and lean angle on transonic blades,various forms of lean and sweep angles were exerted to basic rotor.It was found that sweep angles increased overall operating range up to 30%,efficiency up to 2%and pressure ratio up to 1%.Leaning the blades increased the safe operating range,the pressure ratio and efficiency by 14%,4%and 2%respectively.
文摘Autonomous underwater vehicles(AUVs)have various applications in both military and civilian fields.A wider operation area and more complex tasks require better overall range performance of AUVs.However,until recently,there have been few unified criteria for evaluating the range performance of AUVs.In the present work,a unified range index,i.e.,L^(*),considering the cruising speed,the sailing distance,and the volume of an AUV,is proposed for the first time,which can overcome the shortcomings of previous criteria using merely one single parameter,and provide a uniform criterion for the overall range performance of various AUVs.After constructing the expression of the L^(*)index,the relevant data of 49 AUVs from 12 countries worldwide have been collected,and the characteristics of the L^(*)range index in different countries and different categories were compared and discussed.Furthermore,by analyzing the complex factors affecting the range index,methods to enhance the L^(*)range index value,such as efficiency enhancement and drag reduction,have been introduced and discussed.Under this condition,the work proposes a unified and scientific criterion for evaluating the range performance of AUVs for the first time,provides valuable theoretical insight for the development of AUVs with higher performance,and then arouses more attention to the application of the cutting-edge superlubricity technology to the field of underwater vehicles,which might greatly help to accelerate the coming of the era of the superlubricitive engineering.
