氢和氨作为清洁能源受到广泛关注,为深入探究氢-氨混燃的燃烧特性和影响因素,本文借助Chemkin仿真平台建立相关反应模型,以氢-氨混合气体为燃料,空气作为助燃剂,采用Otomo等人提出的一种氨氧化机理对其燃烧过程进行模拟计算,并模拟研究...氢和氨作为清洁能源受到广泛关注,为深入探究氢-氨混燃的燃烧特性和影响因素,本文借助Chemkin仿真平台建立相关反应模型,以氢-氨混合气体为燃料,空气作为助燃剂,采用Otomo等人提出的一种氨氧化机理对其燃烧过程进行模拟计算,并模拟研究了混合气体的点火延迟时间、层流燃烧速度、绝热燃烧温度、NO排放等燃烧特性随当量比、初始压力以及燃料中H_(2)比例的具体变化规律,对不同工况下的层流火焰结构、H和OH自由基的产率(rate of production,ROP)、NO生成的敏感度进行了化学动力学分析。结果表明:纯氨气体的点火延迟时间长、层流燃烧速度慢,掺氢后燃烧特性均有所改善,且提高了火焰的绝热燃烧温度,但掺氢比例越大,NO排放越多。NO摩尔分数随当量比变化的趋势先增后减,在当量比为0.8左右达到峰值。综合考虑氢-氨混燃的一系列燃烧特性以及掺氢、加压的成本和收益情况,推荐H_(2)占比15%、当量比φ=1.1、压力P=0.2 MPa为氢-氨混合燃烧的最优条件。展开更多
Person re-identification is a prevalent technology deployed on intelligent surveillance.There have been remarkable achievements in person re-identification methods based on the assumption that all person images have a...Person re-identification is a prevalent technology deployed on intelligent surveillance.There have been remarkable achievements in person re-identification methods based on the assumption that all person images have a sufficiently high resolution,yet such models are not applicable to the open world.In real world,the changing distance between pedestrians and the camera renders the resolution of pedestrians captured by the camera inconsistent.When low-resolution(LR)images in the query set are matched with high-resolution(HR)images in the gallery set,it degrades the performance of the pedestrian matching task due to the absent pedestrian critical information in LR images.To address the above issues,we present a dualstream coupling network with wavelet transform(DSCWT)for the cross-resolution person re-identification task.Firstly,we use the multi-resolution analysis principle of wavelet transform to separately process the low-frequency and high-frequency regions of LR images,which is applied to restore the lost detail information of LR images.Then,we devise a residual knowledge constrained loss function that transfers knowledge between the two streams of LR images and HR images for accessing pedestrian invariant features at various resolutions.Extensive qualitative and quantitative experiments across four benchmark datasets verify the superiority of the proposed approach.展开更多
大规模风电接入电网给电网安全运行和管理带来了较大的挑战,新的电网导则要求风电机组应保证具备低电压穿越能力。考虑到动态电压恢复器(Dynamic Voltage Restorer,DVR)具有在短时间内快速准确进行电压补偿的优势,提出了基于动态电压恢...大规模风电接入电网给电网安全运行和管理带来了较大的挑战,新的电网导则要求风电机组应保证具备低电压穿越能力。考虑到动态电压恢复器(Dynamic Voltage Restorer,DVR)具有在短时间内快速准确进行电压补偿的优势,提出了基于动态电压恢复器的风电机组低电压穿越方案。针对DVR中滤波器带来的检测延时和衰减,采用基于瞬时无功功率理论的积分检测法,降低滤波器带来的延迟和衰减。根据DVR的控制特性,提出一种基于坐标变换的双Q-P理论的DVR控制算法,该算法可以补偿瞬时电压扰动,并且能有效改善动态电压恢复器的补偿性能。利用PSCAD/EMTDC仿真软件建立仿真模型,仿真结果表明,电网发生短路故障时,DVR能快速检测电压变化并且准确补偿所需电压,获得理想的瞬态特性,协助改善风电机组的低电压穿越性能。展开更多
文摘氢和氨作为清洁能源受到广泛关注,为深入探究氢-氨混燃的燃烧特性和影响因素,本文借助Chemkin仿真平台建立相关反应模型,以氢-氨混合气体为燃料,空气作为助燃剂,采用Otomo等人提出的一种氨氧化机理对其燃烧过程进行模拟计算,并模拟研究了混合气体的点火延迟时间、层流燃烧速度、绝热燃烧温度、NO排放等燃烧特性随当量比、初始压力以及燃料中H_(2)比例的具体变化规律,对不同工况下的层流火焰结构、H和OH自由基的产率(rate of production,ROP)、NO生成的敏感度进行了化学动力学分析。结果表明:纯氨气体的点火延迟时间长、层流燃烧速度慢,掺氢后燃烧特性均有所改善,且提高了火焰的绝热燃烧温度,但掺氢比例越大,NO排放越多。NO摩尔分数随当量比变化的趋势先增后减,在当量比为0.8左右达到峰值。综合考虑氢-氨混燃的一系列燃烧特性以及掺氢、加压的成本和收益情况,推荐H_(2)占比15%、当量比φ=1.1、压力P=0.2 MPa为氢-氨混合燃烧的最优条件。
基金supported by the National Natural Science Foundation of China(61471154,61876057)the Key Research and Development Program of Anhui Province-Special Project of Strengthening Science and Technology Police(202004D07020012).
文摘Person re-identification is a prevalent technology deployed on intelligent surveillance.There have been remarkable achievements in person re-identification methods based on the assumption that all person images have a sufficiently high resolution,yet such models are not applicable to the open world.In real world,the changing distance between pedestrians and the camera renders the resolution of pedestrians captured by the camera inconsistent.When low-resolution(LR)images in the query set are matched with high-resolution(HR)images in the gallery set,it degrades the performance of the pedestrian matching task due to the absent pedestrian critical information in LR images.To address the above issues,we present a dualstream coupling network with wavelet transform(DSCWT)for the cross-resolution person re-identification task.Firstly,we use the multi-resolution analysis principle of wavelet transform to separately process the low-frequency and high-frequency regions of LR images,which is applied to restore the lost detail information of LR images.Then,we devise a residual knowledge constrained loss function that transfers knowledge between the two streams of LR images and HR images for accessing pedestrian invariant features at various resolutions.Extensive qualitative and quantitative experiments across four benchmark datasets verify the superiority of the proposed approach.
文摘大规模风电接入电网给电网安全运行和管理带来了较大的挑战,新的电网导则要求风电机组应保证具备低电压穿越能力。考虑到动态电压恢复器(Dynamic Voltage Restorer,DVR)具有在短时间内快速准确进行电压补偿的优势,提出了基于动态电压恢复器的风电机组低电压穿越方案。针对DVR中滤波器带来的检测延时和衰减,采用基于瞬时无功功率理论的积分检测法,降低滤波器带来的延迟和衰减。根据DVR的控制特性,提出一种基于坐标变换的双Q-P理论的DVR控制算法,该算法可以补偿瞬时电压扰动,并且能有效改善动态电压恢复器的补偿性能。利用PSCAD/EMTDC仿真软件建立仿真模型,仿真结果表明,电网发生短路故障时,DVR能快速检测电压变化并且准确补偿所需电压,获得理想的瞬态特性,协助改善风电机组的低电压穿越性能。
