Overtime, reduction in the amount of heat generated in engineering systems in operations have been of great concern and have continuously been under study. It is in line with the above that this research work develope...Overtime, reduction in the amount of heat generated in engineering systems in operations have been of great concern and have continuously been under study. It is in line with the above that this research work developed a mathematical model of an evaporative cooling pad using sintered Nigerian clay. A physical model of the evaporative cooling phenomenon was developed followed by the derivation of the governing equations describing the energy and mass transfer for the clay model from the laws of conservation of continuum mechanics. A set of reasonable and appropriate as-sumptions were imposed upon the physical model. Constitutive relationships were also developed for further analysis of the developed equations. The finite element model of numerical methods was used to analyse the energy transfer governing equations which resulted in the determination of the temperature of the exposed boundary surface at any given time, t2 after the commencement of the evaporative cooling processes. In this paper, it was found out that surface temperature differences could be as much as 6?C in the first cycle of evaporative cooling with the potential of further reduction. Further, an equation for the prediction of the effectiveness of an evaporative cooling system using clay modeled cooling pads was developed. The findings in this research work can be applied in the design, construction and maintenance of evaporative coolers used to dissipate waste heat when a large amount of natural water is not readily available or if for environmental and safety reasons the large water body can no longer absorb waste heat.展开更多
Traditional model for calculating performance parameters of a fix-pad journal bearing leads to heavy workload, complicated and changeable formulae as it requires deriving various geometric formulae with different bear...Traditional model for calculating performance parameters of a fix-pad journal bearing leads to heavy workload, complicated and changeable formulae as it requires deriving various geometric formulae with different bearing types such as circular journal bearing, dislocated bearing and elliptic bearing. Considering different pad preload ratios for non-standard bearing, traditional model not only becomes more complicated but also reduces scalability and promotion of the calculation programs. For the complexly case of traditional model while dealing with various fix-pad journal bearings, unified coordinate system model for performance calculation of fix-pad journal bearing is presented in the paper. A unified coordinate system with the bearing center at the origin is established, and the eccentricity ratio and attitude angle of axis relative to each pad are calculated through the coordinates of journal center and each pad center. Geometric description of fix-pad journal bearing is unified in this model, which can be used for both various standard bearing and non-standard bearing with different pad preload ratios. Validity of this model is verified with an elliptical bearing. Performance of a non-standard four-leaf bearing with different pad preload ratios is calculated based on this model. The calculation result shows that increasing preload ratio of the pad 1 and keeping that of the left three pads constant improves bearing capacity, stiffness and damping coefficients. This research presents a unified coordinate system model unifies performance calculation of fix-pad journal bearings and studied a non-standard four-leaf bearing with different pad preload ratios, the research conclusions provides new methods for performance calculation of fix-pad journal bearings.展开更多
The modelling results from numerical simulations of the Early Cretaceous, Mannville coal measures with anisotropic permeability provide insights into development strategies not readily visualized or otherwise intuitiv...The modelling results from numerical simulations of the Early Cretaceous, Mannville coal measures with anisotropic permeability provide insights into development strategies not readily visualized or otherwise intuitive. The complex relationships between water and gas production, the contribution from multiple coal seams as well as from organic rich shales, and the impact of well interference combined with anisotropic fracture permeability are investigated through a series of numerical simulations of four well-pads (on the corners of a square mile of land with decreasing well spacing from 1, 3, to 4 laterals per pad). After 25 years of production, the two pads with optimally-oriented laterals with respect to the fracture permeability anisotropy produce 61% of the recovered gas for the 1 lateral/pad model, 52% for the 3 laterals/pad model, and 50% for the 4 laterals/pad model. Downspacing has a greater impact on increasing the gas production from pads with the poorly-oriented main laterals than from the pads with the optimally-oriented main laterals. The cumulative gas production at the end of the 25 year history is 4.2% higher for an optimally-oriented pad (pad1) and 1.1× higher for a poorly-oriented pad (pad3) for a model with 4 laterals/pad than 3 laterals/pad and an optimally-oriented pad is 1.1% higher for an optimally-oriented pad and 1.5× higher for a poorly-oriented pad for a model with 3 laterals/pad than 1 lateral/pad. Although downspacing from 3 to 4 laterals/pad has a greater impact on increasing the cumulative gas production from optimally-oriented pads than downspacing from 1 to 3 laterals/pad, the lower impact on poorly-oriented pads results in a lower total increase the cumulative gas production from the four pads. At the end of the 25-year production history, 9.0% more gas is recovered for the 4 lateral/pad model than the 3 lateral/pad model, which predicts 1.2× more gas than the 1 lateral/pad model. The recovered shale gas exceeds the recovered coal gas after ~7 years of production. The higher contribution of produced coal gas predicted due to downspacing results from a higher contribution of recovered gas from the main coal seam, while the contribution from the minor coal seams is lower. Downspacing has a minimal impact on the cumulative water production;after 25 years of production a difference of 1.0% is predicted between models with 4 and 3 laterals/pad and 1.7% between models with 1 and 3 laterals/pad. While downspacing increases the cumulative water production for the poorly-oriented pads (1.1× for 3 to 4 laterals/pad and 1.3× for 3 to 1 lateral/pad after 25 years), the cumulative water production for the optimally-oriented pads is lower over the majority of the production history (after ~4 years and 3.2% lower after 25 years for 3 to 4 laterals/pad and after ~6 months and 1.1× lower after 25 years for 1 to 3 laterals/pad).展开更多
为准确表征扣件弹性垫板的非线性动力学性能,将超弹性本构和线性黏弹性本构相结合,同时考虑垫板塑性,建立扣件弹性垫板非线性黏弹性-塑性本构模型;以中国高速铁路WJ-8B型扣件弹性垫板为研究对象,根据垫板的材料特性,结合各种本构模型的...为准确表征扣件弹性垫板的非线性动力学性能,将超弹性本构和线性黏弹性本构相结合,同时考虑垫板塑性,建立扣件弹性垫板非线性黏弹性-塑性本构模型;以中国高速铁路WJ-8B型扣件弹性垫板为研究对象,根据垫板的材料特性,结合各种本构模型的优缺点,分别采用Yeoh模型、Berg摩擦模型和高阶分数阶导数模型(Fraction Voigt and Maxwell model in Parallel,FVMP)对垫板的超弹性、黏弹性和塑性特性进行表征;利用配有高低温试验箱的MFT-250加载系统分别对垫板进行变温静载试验、低频大振幅试验和定频变温试验,求取各本构模型中的参数;通过前述3种试验探究温度对垫板超弹性、黏弹性和塑性的影响。结果表明:当温度高于-40℃时,垫板非线性性质较显著,且垫板所受荷载越大,位移非线性增大趋势越明显;各温度下垫板动态塑性力-位移滞回曲线主刚度与静态力学试验结果变化趋势一致;垫板储能刚度随温度降低逐渐增大,而耗能刚度则随温度降低先增后减,峰值处温度为-46℃;损耗因子在-42℃时达到峰值,约为玻璃化转变温度;非线性黏弹性-塑性模型相较于线性黏弹性-塑性模型拟合效果更好,能全面反映垫板非线性动力学特性;该组合模型可进一步嵌入车辆-轨道耦合动力学仿真平台,为车辆-轨道系统动力学性能优化、减振降噪技术研发提供模型支撑。展开更多
文摘Overtime, reduction in the amount of heat generated in engineering systems in operations have been of great concern and have continuously been under study. It is in line with the above that this research work developed a mathematical model of an evaporative cooling pad using sintered Nigerian clay. A physical model of the evaporative cooling phenomenon was developed followed by the derivation of the governing equations describing the energy and mass transfer for the clay model from the laws of conservation of continuum mechanics. A set of reasonable and appropriate as-sumptions were imposed upon the physical model. Constitutive relationships were also developed for further analysis of the developed equations. The finite element model of numerical methods was used to analyse the energy transfer governing equations which resulted in the determination of the temperature of the exposed boundary surface at any given time, t2 after the commencement of the evaporative cooling processes. In this paper, it was found out that surface temperature differences could be as much as 6?C in the first cycle of evaporative cooling with the potential of further reduction. Further, an equation for the prediction of the effectiveness of an evaporative cooling system using clay modeled cooling pads was developed. The findings in this research work can be applied in the design, construction and maintenance of evaporative coolers used to dissipate waste heat when a large amount of natural water is not readily available or if for environmental and safety reasons the large water body can no longer absorb waste heat.
基金Supported by National Natural Science Foundation of China(Grant No.51275395)Major National Basic Research Development Program of China(973 Program,Grant Nos.2009CB724304-2,2009CB724404)
文摘Traditional model for calculating performance parameters of a fix-pad journal bearing leads to heavy workload, complicated and changeable formulae as it requires deriving various geometric formulae with different bearing types such as circular journal bearing, dislocated bearing and elliptic bearing. Considering different pad preload ratios for non-standard bearing, traditional model not only becomes more complicated but also reduces scalability and promotion of the calculation programs. For the complexly case of traditional model while dealing with various fix-pad journal bearings, unified coordinate system model for performance calculation of fix-pad journal bearing is presented in the paper. A unified coordinate system with the bearing center at the origin is established, and the eccentricity ratio and attitude angle of axis relative to each pad are calculated through the coordinates of journal center and each pad center. Geometric description of fix-pad journal bearing is unified in this model, which can be used for both various standard bearing and non-standard bearing with different pad preload ratios. Validity of this model is verified with an elliptical bearing. Performance of a non-standard four-leaf bearing with different pad preload ratios is calculated based on this model. The calculation result shows that increasing preload ratio of the pad 1 and keeping that of the left three pads constant improves bearing capacity, stiffness and damping coefficients. This research presents a unified coordinate system model unifies performance calculation of fix-pad journal bearings and studied a non-standard four-leaf bearing with different pad preload ratios, the research conclusions provides new methods for performance calculation of fix-pad journal bearings.
文摘The modelling results from numerical simulations of the Early Cretaceous, Mannville coal measures with anisotropic permeability provide insights into development strategies not readily visualized or otherwise intuitive. The complex relationships between water and gas production, the contribution from multiple coal seams as well as from organic rich shales, and the impact of well interference combined with anisotropic fracture permeability are investigated through a series of numerical simulations of four well-pads (on the corners of a square mile of land with decreasing well spacing from 1, 3, to 4 laterals per pad). After 25 years of production, the two pads with optimally-oriented laterals with respect to the fracture permeability anisotropy produce 61% of the recovered gas for the 1 lateral/pad model, 52% for the 3 laterals/pad model, and 50% for the 4 laterals/pad model. Downspacing has a greater impact on increasing the gas production from pads with the poorly-oriented main laterals than from the pads with the optimally-oriented main laterals. The cumulative gas production at the end of the 25 year history is 4.2% higher for an optimally-oriented pad (pad1) and 1.1× higher for a poorly-oriented pad (pad3) for a model with 4 laterals/pad than 3 laterals/pad and an optimally-oriented pad is 1.1% higher for an optimally-oriented pad and 1.5× higher for a poorly-oriented pad for a model with 3 laterals/pad than 1 lateral/pad. Although downspacing from 3 to 4 laterals/pad has a greater impact on increasing the cumulative gas production from optimally-oriented pads than downspacing from 1 to 3 laterals/pad, the lower impact on poorly-oriented pads results in a lower total increase the cumulative gas production from the four pads. At the end of the 25-year production history, 9.0% more gas is recovered for the 4 lateral/pad model than the 3 lateral/pad model, which predicts 1.2× more gas than the 1 lateral/pad model. The recovered shale gas exceeds the recovered coal gas after ~7 years of production. The higher contribution of produced coal gas predicted due to downspacing results from a higher contribution of recovered gas from the main coal seam, while the contribution from the minor coal seams is lower. Downspacing has a minimal impact on the cumulative water production;after 25 years of production a difference of 1.0% is predicted between models with 4 and 3 laterals/pad and 1.7% between models with 1 and 3 laterals/pad. While downspacing increases the cumulative water production for the poorly-oriented pads (1.1× for 3 to 4 laterals/pad and 1.3× for 3 to 1 lateral/pad after 25 years), the cumulative water production for the optimally-oriented pads is lower over the majority of the production history (after ~4 years and 3.2% lower after 25 years for 3 to 4 laterals/pad and after ~6 months and 1.1× lower after 25 years for 1 to 3 laterals/pad).
文摘为准确表征扣件弹性垫板的非线性动力学性能,将超弹性本构和线性黏弹性本构相结合,同时考虑垫板塑性,建立扣件弹性垫板非线性黏弹性-塑性本构模型;以中国高速铁路WJ-8B型扣件弹性垫板为研究对象,根据垫板的材料特性,结合各种本构模型的优缺点,分别采用Yeoh模型、Berg摩擦模型和高阶分数阶导数模型(Fraction Voigt and Maxwell model in Parallel,FVMP)对垫板的超弹性、黏弹性和塑性特性进行表征;利用配有高低温试验箱的MFT-250加载系统分别对垫板进行变温静载试验、低频大振幅试验和定频变温试验,求取各本构模型中的参数;通过前述3种试验探究温度对垫板超弹性、黏弹性和塑性的影响。结果表明:当温度高于-40℃时,垫板非线性性质较显著,且垫板所受荷载越大,位移非线性增大趋势越明显;各温度下垫板动态塑性力-位移滞回曲线主刚度与静态力学试验结果变化趋势一致;垫板储能刚度随温度降低逐渐增大,而耗能刚度则随温度降低先增后减,峰值处温度为-46℃;损耗因子在-42℃时达到峰值,约为玻璃化转变温度;非线性黏弹性-塑性模型相较于线性黏弹性-塑性模型拟合效果更好,能全面反映垫板非线性动力学特性;该组合模型可进一步嵌入车辆-轨道耦合动力学仿真平台,为车辆-轨道系统动力学性能优化、减振降噪技术研发提供模型支撑。
