Harvey B Manbeck

Elastoplastic finite element model development and validation for low pressure uniaxial compaction of dry cohesive powders

A basic elastoplastic model (modified Cam-clay) was applied to wheat flour, a dry cohesive powder. Five constitutive parameters for the modified Cam-clay model have been previously determined for wheat flour using triaxial tests. To apply the elastoplastic constitutive model, a test cylinder was built that uniaxially compacted the wheat flour under constant axial displacement. Hoop and vertical strains in the cylinder wall were measured at three levels while the flour inside was compacted. Predicted vertical strains, using a finite element model (FEM), were within 25% (worst case error) of average measured values for all three levels up to 59.4 kPa axial pressure. Predicted hoop strains, at the cylinder bottom, were within 45% (worst case error) of average measured values up to 59.4 kPa. Along with predicting strains in the cylinder wall, the FEM also predicted stress distribution in the powder mass. Stress distribution proved useful in identifying potential regions of stress concentration and large shear stresses in the powder mass.

Computational Fluid Dynamics Modeling of Ventilation of Confined-Space Manure Storage Facilities: Applications

Fatalities associated with entry into on-farm confined-space manure storage tanks occur each year The fatalities are due to asphyxiation or poisoning by exposure to high concentrations of hydrogen sulfide, methane, and carbon dioxide. Forced ventilation has been shown to be an effective way to reduce concentrations of these noxious gases to levels that are safe for human entry into these storage tanks. Hydrogen sulfide (H2S) was used as an indicator gas to investigate the effectiveness of forced ventilation strategies for eliminating the toxic and oxygen-deficient atmospheres in confined-space manure tanks. Validated computational fluid dynamics (CFD) modeling protocols were used to simulate H2S evacuation from fan-ventilated manure tanks. The simulation studies were conducted for rectangular and circular manure tanks, and the effects of pollutant source, inter-contamination (process by which a portion of exhausted contaminant gas enters a ventilated confined airspace through the fresh air intake), storage size (i.e., length, diameter), and air exchange rate on H2S removalfrom fan-ventilated manure tanks were investigated. For the same air exchange rate, as the size (i.e., length, diameter) of the tank increased, the rate of evacuation of the H2S from the confined space decreased. For rectangular and circular manure tanks, the higher the air exchange rate, the higher the rate of evacuation of the H2S from the confined space. For the rectangular tank geometries and ventilation system layouts simulated, evacuation times decreased exponentially with air exchange rate. Evacuation times for the circular tanks simulated decreased linearly with air exchange rate.

Simulation and Validation of Hydrogen Sulfide Removal from Fan Ventilated Confined-space Manure Storages

Confined-space manure storage entry is a major safety concern in the agricultural industry. Oxygen-deficient atmospheres as well as toxic and/or explosive gases (i.e., NH3, H2S, CH4, and CO2) often result from fermentation and accumulation of the stored manure in confined areas. These gases may create very hazardous conditions to farm workers who may need to enter these confined-space manure storages to work or perform maintenance. Hydrogen sulfide (H2S), a highly toxic and irritating gas, was used as a tracer gas to investigate the effectiveness of forced ventilation strategies for eliminating the toxic and oxygen deficient atmospheres in confined-space manure storages. Validated Computational Fluid Dynamics (CFD) modeling protocols were used to simulate H2S evacuation from fan ventilated confined-space manure storages. The simulation studies were conducted for rectangular and round confined-space manure storages and the effects of pollutant source, inter-contamination, storage size (i.e., length, diameter), and air exchange rate on H2S removal from fan ventilated confined-space manure storages were investigated. For the same air exchange rate, as the size (i.e., length, diameter) of manure storage increased, the rate of evacuation of the H2S from the confined space decreased. For rectangular and round manure storages, the higher the air exchange rate, the higher the rate of evacuation of the H2S from the confined space. For the geometries and ventilation system layouts simulated, evacuation times decreased exponentially with air exchange rate for the rectangular tanks. Evacuation times for the round tanks simulated decreased linearly with air exchange rate.

Screening Ventilation Strategies for Confined-Space Manure Storage Facilities

Fatalities associated with entry into on-farm confined-space manure storage facilities occur each year. The fatalities are due to asphyxiation or poisoning by exposure to high concentrations of hydrogen sulfide, methane, and carbon dioxide. Forced ventilation has been shown to be an effective way to reduce concentrations of noxious gases to levels that are safe for human entry into these storage facilities. Hydrogen sulfide (H2S) was used as an indicator gas to investigate the effectiveness of forced-air ventilation strategies for eliminating the toxic and oxygen-deficient atmosphere in confined-space manure storage facilities. This article focuses on experimental methods for identifying ventilation strategies that effectively reduce toxic gas (i.e., H2S) concentrations in a fan-ventilated confined-space manure tank to the OSHA permissible exposure limit (PEL) (H2S PEL = 10 ppm) and to 25% of the initial gas concentration. Typical H2S concentration reduction curves during forced-air ventilation were identified in the tank as well. Based on the experimental tests conducted in this research, the most promising candidate ventilation strategies were identified for this rectangular confined-space manure tank with solid, fully slotted, and partially slotted covers. In addition, based on the results of experimental tests, a field-based database was developed for future validation of computational fluid dynamics modeling protocols.

Online Design Aid for Evaluating Manure Pit Ventilation Systems to Reduce Entry Risk

On-farm manure storage pits contain both toxic and asphyxiating gases such as hydrogen sulfide, carbon dioxide, methane, and ammonia. Farmers and service personnel occasionally need to enter these pits to conduct repair and maintenance tasks. One intervention to reduce the toxic and asphyxiating gas exposure risk to farm workers when entering manure pits is manure pit ventilation. This article describes an online computational fluid dynamics-based design aid for evaluating the effectiveness of manure pit ventilation systems to reduce the concentrations of toxic and asphyxiating gases in the manure pits. This design aid, developed by a team of agricultural engineering and agricultural safety specialists at Pennsylvania State University, represents the culmination of more than a decade of research and technology development effort. The article includes a summary of the research efforts leading to the online design aid development and describes protocols for using the online design aid, including procedures for data input and for accessing design aid results. Design aid results include gas concentration decay and oxygen replenishment curves inside the manure pit and inside the barns above the manure pits, as well as animated motion pictures of individual gas concentration decay and oxygen replenishment in selected horizontal and vertical cut plots in the manure pits and barns. These results allow the user to assess (1) how long one needs to ventilate the pits to remove toxic and asphyxiating gases from the pit and barn, (2) from which portions of the barn and pit these gases are most and least readily evacuated, and (3) whether or not animals and personnel need to be removed from portions of the barn above the manure pit being ventilated.

An Educational Program to Reduce Risk when Entering Confined-Space Manure Storages

This paper presents the goals and components of a comprehensive educational program designed to teach participants how to reduce risk of serious injury or death from entering on-farm, confined-space manure storage facilities. The educational program is based upon manure storage ventilation research and a manure storage ventilation standard which are summarized in this paper. The educational program objectives include: (a) identification of confined-space manure storage hazards, (b) effective mitigation of toxic gas hazards through forced air ventilation, (c) use and maintenance of gas monitoring equipment, and (d) recommended procedures for planned and emergency entry. Fact sheets, pamphlets, demonstrations, lecture presentations and interactive web-based training materials are being developed. These materials and presentations are primarily based upon the proposed X607 ASABE standard. This proposed standard outlines specific requirements for the design of confined-space manure storage ventilation systems. Delivery of the educational program will include presentations for a variety of audience groups including farm families, operators of confined-space manure storage systems, agricultural educators and agricultural emergency service providers. Technical design and construction details will be presented to designers, manufactures, and regulatory personnel. The educational program will deliver important safety information and research results in an attempt to decrease risks associated with entering confined-space manure storage facilities.

Computational Fluid Dynamics Simulations of Gas Evacuation and O2 Recovery Times for Fan Ventilated Confined-Space Manure Pits

Fatalities associated with entry into on-farm confined-space manure storage facilities occur each year. The fatalities are due to asphyxiation or poisoning by exposure to high concentrations of hydrogen sulfide, methane, carbon dioxide or oxygen deficiency. Forced ventilation has been identified previously as an effective way to reduce concentrations of these noxious gases to levels that are safe for human entry into these facilities. Previously validated computational fluid dynamics (CFD) modeling protocols were used to identify the influence of several key initial conditions and modeling techniques on gas evacuation or oxygen recovery times for fan ventilated confined-space manure pits. This paper includes an extensive literature review to define the maximum expected initial concentrations and emission rates of primary manure gases in manure pits. The effect of the initial condition, the maximum initial concentrations of contaminant gases, on simulated contaminant gas evacuation time is explored. The influence of boundary conditions (i.e., emission rate (ER), inter-contamination (INC): process by which a portion of exhausted contaminant gas re-enters a ventilated confined airspace through the fresh air intake) on CFD outcomes is also explored. Simulation results showed that evacuation times increased as inter-contamination strength (the ratio of contaminant concentration at the fan intake to the concentration in the air exhausted from the manure pit, INC-strength) increased from 0 to 0.40; however, no further increase in evacuation times was predicted for inter-contamination strengths above 0.40. Simulations on oxygen recovery (from 0 % to 20.0 % by volume) in the confined airspace initially filled completely with a contaminant gas (i.e. H2S, NH3, CH4, and CO2) showed little difference (< 5 %) in recovery time by gas. Additionally, for a confined airspace (domain) filled with a gas mixture of contaminant gases, simulations showed that time to reduce H2S concentration from a documented high level (10,000 ppm) to the OSHA PEL level (10 ppm) was equal to or greater than evacuation times for other gases from their documented highest initial levels to their safe exposure levels. Also, an initial gaseous mixture including H2S and CO2 at their highest documented concentrations was the critical initial atmospheres in manure pits for performing CFD simulations.

Ventilating Confined Manure Storages: Progress Report

Confined manure storage entry is identified as a major safety concern in the agricultural industry. Oxygen-deficient atmospheres as well as toxic and/or explosive gases (e.g., NH3, H2S, CH4 and CO2) coming from fermentation and agitation may create very hazardous conditions to farmers who may need to enter these confined manure storages to work or perform maintenance. The goal of the research is to develop effective ventilation design recommendations for confined manure storages to reduce the risk coming from entry into confined manure storage facilities. The research is divided into two phases: experimental screening of ventilation strategies and Computational Fluid Dynamic (CFD) model simulation for effective ventilation design recommendations. Adequate experimental data for NH3 and H2S concentrations during ventilation have been collected to identify the most promising candidate ventilation strategies. Meanwhile, preliminary measurements of gas emission rate from manure during agitation and during ventilation after agitations are being conducted. The identified ventilation strategies and the measured emission rates obtained will be used to set up CFD simulations. The experimental data will be applied to validate and verify the CFD model.