Kuldeep R. Prasad

Direct and Indirect Measurements and Modeling of Methane Emissions in Indianapolis, Indiana

This paper describes process-based estimation of CH4 emissions from sources in Indianapolis, IN and compares these with atmospheric inferences of whole city emissions. Emissions from the natural gas distribution system were estimated from measurements at metering and regulating stations and from pipeline leaks. Tracer methods and inverse plume modeling were used to estimate emissions from the major landfill and wastewater treatment plant. These direct source measurements informed the compilation of a methane emission inventory for the city equal to 29 Gg/yr (5% to 95% confidence limits, 15 to 54 Gg/yr). Emission estimates for the whole city based on an aircraft mass balance method and from inverse modeling of CH4 tower observations were 41 ± 12 Gg/yr and 81 ± 11 Gg/yr, respectively. Footprint modeling using 11 days of ethane/methane tower data indicated that landfills, wastewater treatment, wetlands, and other biological sources contribute 48% while natural gas usage and other fossil fuel sources contribute 52% of the city total. With the biogenic CH4 emissions omitted, the top-down estimates are 3.5-6.9 times the nonbiogenic city inventory. Mobile mapping of CH4 concentrations showed low level enhancement of CH4 throughout the city reflecting diffuse natural gas leakage and downstream usage as possible sources for the missing residual in the inventory.

Behavior of Full-scale Frames with Slim Floor Slab Construction under Exposure in a Fire Resistance Furnace

In recent years, there has been increasing interest in developing and designing slim floor systems in steel-framed buildings. This article describes the results of a furnace test conducted on two full-scale composite steel frames with slim floor slab construction to understand their performance under fire loading. In one frame, the beam-to-column connections were protected, while in the second frame, the columns as well as the beam-to-column connections were protected. During the test, the furnace temperature, the steel and concrete temperature, as well as the horizontal and vertical displacements were recorded. The complete deformation process of the test frame observed during the heating phase and the cooling phase, including failure of the frame, is described in this article. A comparison of the data obtained from the two tests indicates that the fire resistance of a composite beam is significantly better than that of a steel column. Fire resistance of composite frames with slim floor slabs is compared...

Experiments and Modeling of Unprotected Structural Steel Elements Exposed to a Fire

A large-scale fire experiment was conducted to assess the accuracy of a combination of gas and solid-phase models designed to predict the temperatures of structural steel elements exposed to a fire. The experiment involved a 2 MW heptane spray fire in a compartment that was nominally 4 m by 7 m by 4 m tall. The compartment openings were designed such that natural ventilation flowed into the compartment from one side and flowed out through the opposing side. Measurements included the surface temperature of uninsulated steel elements and the temperature of the upper layer gases in the compartment. The measurements were compared to predictions made by a computational fluid dynamics model of the fire coupled with a finite-element model of the steel. The numerical predictions of the steel surface temperatures were within 8% of the measurements on-average. An analysis showed that the uncertainty in the prediction could be attributed to the uncertainty in the prescribed heat release rate in the fire model.

Tower-based greenhouse gas measurement network design—The National Institute of Standards and Technology North East Corridor Testbed

The North–East Corridor (NEC) Testbed project is the 3rd of three NIST (National Institute of Standards and Technology) greenhouse gas emissions testbeds designed to advance greenhouse gas measurements capabilities. A design approach for a dense observing network combined with atmospheric inversion methodologies is described. The Advanced Research Weather Research and Forecasting Model with the Stochastic Time-Inverted Lagrangian Transport model were used to derive the sensitivity of hypothetical observations to surface greenhouse gas emissions (footprints). Unlike other network design algorithms, an iterative selection algorithm, based on a k-means clustering method, was applied to minimize the similarities between the temporal response of each site and maximize sensitivity to the urban emissions contribution. Once a network was selected, a synthetic inversion Bayesian Kalman filter was used to evaluate observing system performance. We present the performances of various measurement network configurations consisting of differing numbers of towers and tower locations. Results show that an overly spatially compact network has decreased spatial coverage, as the spatial information added per site is then suboptimal as to cover the largest possible area, whilst networks dispersed too broadly lose capabilities of constraining flux uncertainties. In addition, we explore the possibility of using a very high density network of lower cost and performance sensors characterized by larger uncertainties and temporal drift. Analysis convergence is faster with a large number of observing locations, reducing the response time of the filter. Larger uncertainties in the observations implies lower values of uncertainty reduction. On the other hand, the drift is a bias in nature, which is added to the observations and, therefore, biasing the retrieved fluxes.摘要东北走廊(NEC, North-East Corridor)测试平台项目是美国国家标准与技术研究所(NIST, National Institute of Standards and Technology)的第三个温室气体排放源测试平台. 本项目旨在提高温室气体测量能力. 本文介绍了这个项目的与大气反演方法相结合的密集观测网络的设计方法. 这种方法应用 WRF(ARW 版本) 模式(Advanced ResearchWeather Research and Forecasting Model)与STILT模式(Stochastic Time-Inverted Lagrangian Transport model)相耦合来计算假定的观测对地表温室气体排放源的敏感性(足迹). 和其他观测网的设计算法的不同之处在于, 这个密集观测网络应用一个基于 k-means 聚类方法的迭代挑选算法, 以最小化每个站点的时间响应之间的相似性, 并最大化城市排放源贡献的敏感性. 一旦选择了某种配置的观测网, 将使用综合反演贝叶斯卡尔曼滤波来评估它的性能. 我们展示了由不同数量的塔和不同的位置的塔组成的不同配置的多个观测网的性能. 结果表明, 由于附加到每个站点的空间信息不能最理想的覆盖最大可能的区域, 过度密集的观测网的空间覆盖范围会减小, 而过度分散的观测网则会失去约束通量不确定性的能力. 此外, 我们还探讨了使用带有较低成本和具有较大不确定性和时间偏移的性能传感器的高密度网络的可能性. 当观测站点较多时, 分析收敛速度变快, 减少了滤波的响应时间. 观测中的较大不确定性意味着较少的不确定性的减少值. 另一方面, 自然界中存在的偏差被带入到观测中, 从而使得反演通量有偏差.

Fire Induced Thermal and Structural Response of the World Trade Center Towers.

Over the past several years, there has been a resurgence of interest in studying the response of building structures to fires. Simulations of the effects of severe fires on the structural integrity of buildings requires a close coupling between the gas phase energy release and transport phenomena and the stress analysis in the load bearing materials. A methodology has been developed for coupling CFD simulations of fire growth with finite element models for thermal analysis and for using the thermal data to compute the demand-to-capacity ratio in a multi-story structure. A simple radiative transport model that assumes the compartment is divided locally into a hot, soot laden upper layer and a cool, relatively clear lower layer is employed to predict radiative fluxes incident on sub-grid scale structural members. Thermal response coupled with realistic fire simulations of various steel structural components on floors of World Trade Center Tower 1 that were subjected to aircraft impact damage and fires are presented. The thermal response was used to compute the reduction in load carrying capacity of the structural components as a function of time, which ultimately results in global collapse of the towers.