Simulation of the flow of an explosive atmosphere exposed to a hot surface

The accidental ignition of combustible atmospheres by hot surfaces is of great concern for chemical and process plant safety. In this paper, we present our research regarding the evolution of thermal plumes originating from hot hemispheres and discs. In particular, we focus on the effect of the orientation of the surface on the ignition process. The auto-ignition temperatures and ignition locations were studied experimentally. To get further insight, we conducted detailed numerical simulations and validated them with measurements. Three-dimensional simulations were performed on hot hemispheres and hot discs for different orientations ranging from 0° to 180°. The solver employs a transient, implicit scheme which is based on the coupled heat transfer and flow equations. The mesh in the vicinity of the hot surfaces is refined to resolve the steep temperature gradients and to capture the boundary layer separation. The influence of the orientation on critical hot spots in the gas mixture is analysed by examining the flow structures and the temperature evolution of the buoyancy-driven flow. Using the obtained results, we discuss the change of the onset and location of the ignition.     

Review of hydrogen safety during storage,transmission, and applications processes

Hydrogen is considered an excellent clean fuel with potential applications in several fields. There are serious safety concerns associated with the hydrogen process. These concerns need to be thoroughly understood and addressed to ensure its safe operation. To better understand the safety challenges of hydrogen use, application, and process, it is essential to undertake a detailed risk analysis. This can be achieved by performing detailed consequence modellings and assessing risk using the computational fluid dynamics (CFD) approach. This study comprehensively reviews and analyses safety challenges related to hydrogen, focusing on hydrogen storage, transmission, and application processes. Range of release and dispersion scenarios are investigated to analyse associated hazards. Approaches to quantitative risk assessment are also briefly discussed.     

Seismic fragility analysis of a coupled tank-piping system based on artificial ground motions and surrogate modeling

The catastrophic consequences of recent NaTech events triggered by earthquakes highlighted the inadequacy of standard approaches to seismic risk assessment of chemical process plants. To date, the risk assessment of such facilities mainly relies on historical data and focuses on uncoupled process components. As a consequence, the dynamic interaction between process equipment is neglected. In response to this gap, researchers started a progressive integration of the Pacific Earthquake Engineering Research Center (PEER) Performance-Based Earthquake Engineering (PBEE) risk assessment framework. However, a few limitations still prevent a systematic implementation of this framework to chemical process plants. The most significant are: (i) the computational cost of system-level simulations accounting for coupling between process equipment; (ii) the experimental cost for component-level model validation; (iii) a reduced number of hazard-consistent site-specific ground motion records for time history analyses.In response to these challenges, this paper proposes a recently developed uncertainty quantification-based framework to perform seismic fragility assessments of chemical process plants. The framework employs three key elements: (i) a stochastic ground-motion model to supplement scarcity of real records; (ii) surrogate modeling to reduce the computational cost of system-level simulations; (iii) a component-level model validation based on cost-effective hybrid simulation tests. In order to demonstrate the potential of the framework, two fragility functions are computed for a pipe elbow of a coupled tank-piping system.     

新型矿用圆弧形薄壁防冲吸能装置屈曲特性数值分析*

为解决支架面对冲击地压产生的强冲作用容易失效、失稳的难题,针对现有矿用防冲吸能装置存在的不足,提出1种新型矿用圆弧形薄壁防冲吸能装置。采用ABAQUS有限元数值模拟方法对新型防冲吸能装置与原有方形预折纹薄壁装置进行对比分析,同时研究新型防冲吸能装置在不同壁厚和不同轴向模块堆积个数情况下的屈曲特性。结果表明:圆弧形薄壁装置相比于方形折纹薄壁装置在相同厚度情况下其总吸能提升近20%,比吸能提高63%,装置防冲优势明显;在装置高度不变的情况下增加模块轴向堆积个数可有效降低压溃峰值荷载、荷载波动系数,增加平均压溃荷载;随着装置薄壁厚度降低,压溃峰值荷载、压溃平均荷载、总吸能与比吸能均降低,荷载波动系数增加,曲线波动性变大。     

Simulating Soil Water Content,Evapotranspiration, and Yield of Variably Irrigated Grain Sorghum Using AquaCrop

Use of models to simulate crop production has become important in optimizing irrigation management in arid and semiarid regions. However, applicability and performance of these models differ across regions, due to differences in environmental and management factors. The AquaCrop model was used to simulate soil water content (SWC), evapotranspiration (ET), and yield for grain sorghum under different irrigation regimes and dryland conditions at two sites in Central and Southern High Plains. Prediction error (P_e), estimated as the difference between simulated and measured divided by measured, for SWC ranged from ?17% to 4% in fully irrigated, ?3% to ?10% in limited irrigated, and ?16% to 25% in dryland treatments. The P_e within ±4%, ?5%, and ?17% to 24% were attained for seasonal ET under fully irrigated, limited irrigated, and dryland conditions, respectively. P_e values for grain yield were within those previously reported and ranged from ?10% to 12%, ?12% to 7%, and 9% to 17% for fully irrigated, limited irrigated and dryland conditions, respectively. Overall performance of the AquaCrop model showed it could be used as an effective tool for evaluating the impacts of variable crop and irrigation managements on the production of grain sorghum in the study area. Finally, the application of the model in the study area revealed planting date has a significant impact on sorghum yield and irrigation requirements, but the impact of planting density was negligible. Editor's note : This paper is part of the featured series on Optimizing Ogallala Aquifer Water Use to Sustain Food Systems. See the February 2019 issue for the introduction and background to the series.     

Modeling Hydrological and Environmental Consequences of Climate Change and Urbanization in the Boise River Watershed,Idaho

The potential impacts driven by climate variability and urbanization in the Boise River Watershed (BRW), located in southwestern Idaho, are evaluated. The outcomes from Global Circulation Models (GCMs) and land use and land cover (LULC) analysis have been incorporated into a hydrological and environmental modeling framework to characterize how climate variability and urbanization can affect the local hydrology and environment at the BRW. The combined impacts of future climate and LULC change are also evaluated relative to the historical baseline conditions. For modeling exercises, Hydrological Simulation Program‐Fortran (HSPF) is used in parallel computing and statistical techniques, including spatial downscaling and bias correlation, are employed to evaluate climate consequences derived from GCMs as well. The implications of climate variability and land use change driven by urbanization are then observed to evaluate how these overall global challenges can affect water quantity and quality conditions at the BRW. The results show the combined impacts of both climate change and urbanization can lead to more seasonal variability of streamflow (from ?27.5% to 12.5%) and water quality, including sediment (from ?36.5% to 49.3%), nitrogen (from ?24% to 124.2%), and phosphorus (from ?13.3% to 21.2%) during summer and early fall over the next several decades.     

Evaluation of SWAT Impoundment Modeling Methods in Water and Sediment Simulations

Worldwide studies show 80%–90% of all sediments eroded from watersheds is trapped within river networks such as reservoirs, ponds, and wetlands. To represent the impact of impoundments on sediment routing in watershed modeling, Soil and Water Assessment Tool (SWAT) developers recommend to model reservoirs, ponds, and wetlands using impoundment tools (ITs). This study evaluates performance of SWAT ITs in the modeling of a small, agricultural watershed dominated by lakes and wetlands. The study demonstrates how to incorporate impoundments into the SWAT model, and discusses and evaluates involved parameters. The study then recommends an appropriate calibration sequence, i.e., landscape parameters calibration, followed by pond/wetlands calibration, then channel parameter calibrations, and lastly, reservoir parameter calibration. Results of this study demonstrate not following SWAT recommendation regarding modeling water land use as an impoundment depreciates SWAT performance, and may lead to misplaced calibration efforts and model over‐calibration. Further, the chosen method to model impoundments’ outflow significantly impacts sediment loads in the watershed, while streamflow simulation is not very sensitive. This study also allowed calculation of mass accumulation rates in modeled impoundments where the annual mass accumulation rate in wetlands (2.3 T/ha/yr) was 39% higher than mass accumulation rate in reservoirs (1.4 T/ha/yr).     

Green energy generation through PEHF – a blueprint of alternate energy harvesting

In this work, an attempt has been made to harvest green energy from piezoelectric material using fluid flow in a conduit. Piezoelectric Energy Harvesting using Fluid Flow (PEHF) experimental model has been designed and the outputs obtained are compared with results obtained from simulations using ANSYS (computational fluid dynamics) and also with the mathematical modeling. The PEHF model has been utilized to analyze the effect of flow rate of water with reference to energy extracted. The full wave bridge rectifier and voltage doubler circuits have been used to obtain the direct current (DC) from the PEHF model. It is observed that the output obtained using experiments holds good in agreement with the results retrieved through simulations and mathematical results. The increase in flow rate of fluid leads to initially increase and then decrease in output of PEHF model as the maximum energy generated when flow rates (external force) matches with the frequency of excitation of the systems, i.e., at its resonance. The maximum energy output is generated at its resonance frequencies. It is observed that the full wave bridge rectifier circuit gives greater output as compared to a voltage doubler circuit.     

Extrinsic modeling and simulation of helio-photovoltaic system: a case of single diode model

Simulation of helio-photovoltaic system is continuously undergoing revolution through diverse parameter modifications which closely mimic the experimental data. In retrospect, the current work has presented a nonlinear modification of equivalent circuit parameters and simulated the same for different semiconductors (crystalline and thin films); furthermore, established a mathematical relation between the coefficients of solar irradiance and module temperature (SIMT); moreover, investigated the influence of SIMT on the model parameters. The simulation upshot reveals that increment in solar irradiance (SI) intensifies the output current whereas an increase in module temperature (MT) diminishes the output voltage; the SIMT coefficients developed validated well with the manufacturers data; the influence of SI was evident on the photon current, diode current, and shunt resistance whereas the effect of MT was pronounced on the diode current, ideality factor, and shunt resistance. Thus, the provision made by this work is essential for advanced design and simulation of helio-photovoltaic systems.     

Modeling and simulation of biogas-fueled power system

The main objective of this paper is to develop a complete model that fully simulate a biogas-fueled power plant which can be used to supply a rural farm with sufficient electricity. The reactor is fed with animal manure of the farm. The proposed model consists of three main parts; a biogas reactor, a microturbine (MT) coupled to a permanent magnet synchronous generator, and a storage system. The model describes the dynamics of an MT and it is suitable for both steady state and transient simulation and analysis. The volume of biogas output delivered from the Anaerobic Digester depends on the reactor volume, reactor temperature, and animal manure type. The storage system is used to store the excess value of biogas if any. It is composed of two parts: a comparator and a storage tank. The comparator compares the volume of biogas produced by the reactor with that needed to supply the load. An adaptive controller is developed to withstand the system against any transient condition such as suddenly load increase/decrease. The proposed model is implemented for chemical and physical behaviors of the biogas production process, as well as for different variables of MT-generator operations. The model is implemented in Matlab/Simulink environment and tested under different operating conditions in both steady state and transient status to study the impacts of different variables on the system output. The output results prove its applicability and effectiveness under different operating conditions.