Browsing by Author "Gokoglu, Suleyman"
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Item A Comparison of CFD and Lumped Capacity Analyses of Fires in Spacecraft(49th International Conference on Environmental Systems, 2019-07-07) Brooker, John; Dietrich, Dan; Gokoglu, Suleyman; Ruff, Gary; Urban, DavidComputational fluid dynamics (CFD) simulations of flows inside a spacecraft offer a high level of detail and fidelity and are invaluable tools in the design of spacecraft environmental control and life support systems (ECLSS). They are, however, time and resource intensive and not efficient for large scale sensitivity analyses over a range of possible design parameters. Lumped capacity analysis (LCA) treatments are simple and fast, but lack the detailed treatment of flow and heat transfer that CFD simulations offer. Their speed and low level of required resources, however, make them more convenient for large sensitivity analyses. Both approaches have the potential to be design tools to assess the impact that an accidental fire will have on a spacecraft. This paper compares the results of CFD and LCA simulations for a given volume approximately the size of the Orion spacecraft. The CFD model uses the open source Fire Dynamics Simulator for the simulation and includes, as sensitivity parameters, changes in ECLSS ventilation (direction and speed), fire location, and wall boundary condition. The results show that the LCA model can reasonably predict pressure rise in a spacecraft if the prescribed fire scenario approximates the model assumptions. The sensitivity studies show how variations in parameters not captured directly in the LCA model (e.g., direction of ventilation flow) influence the results and provide limits on the predictive capability of the LCA. We also demonstrate how CFD simulations can improve LCA predictions by providing more realistic estimates of heat transfer coefficients between the gas and various cabin walls.Item Development and Validation of a Model to Account for Gaseous HCl and Aluminum Surface Interactions for Spacecraft Fire Safety Applications(49th International Conference on Environmental Systems, 2019-07-07) Niehaus, Justin; Gokoglu, Suleyman; Mazumder, Sandip; Berger, Gordon; Easton, JohnExperiments and modeling were performed to determine the surface kinetics of gaseous hydrogen chloride (HCl) with aluminum surfaces subjected to various treatments. HCl and other acid gases are a spacecraft fire safety concern as they are commonly found in products from electrical wire pyrolysis. Three types of aluminum surfaces were considered: surface with chromate conversion coating (iridite), anodized, and untreated. A test cell made of Teflon was used to measure the difference in HCl from the inlet to the outlet. Inlet and outlet sensors were used to measure HCl concentrations. A simple one-step global surface reaction model was proposed, and an Arrhenius surface kinetics expression that accounts for active surface sites was employed. The kinetic constants were determined (calibrated) using the measured data. The calibrated model was validated against experiments with different flow rates and HCl inlet concentrations. The results showed that anodized aluminum had the most HCl uptake, followed by the iridite and then the untreated aluminum. The amount of HCl uptake seems to correlate well with the thickness of the oxide layer on aluminum. The relevance of these findings are discussed with respect to the design of large-scale fire safety experiments in space and various fire safety application scenarios.Item Effect of Humidity on Surface Interactions of Gaseous HCl and Aluminum for Spacecraft Fire Safety Applications(2020 International Conference on Environmental Systems, 2020-07-31) Niehaus, Justin; Gokoglu, Suleyman; Mazumder, Sandip; Berger, Gordon; Easton, JohnExperiments were performed to understand the interaction of gaseous hydrogen chloride (HCl) with aluminum surfaces in the presence of water vapor. The results show that increasing levels of relative humidity, tested for 10, 25, and 50 percent in air, increase the capacity of HCl adsorption compared to results previously published with dry air flow. A series of tests were performed on individual aluminum samples after they had been saturated with a fixed concentration of HCl in dry air conditions with the goal of determining how their HCl uptake capacity change after various treatments with water relative to the original saturation run. HCl-saturated aluminum samples subjected to a second dry air flow at the same HCl concentration as the original test had an uptake of 23.5% of the original sample. Saturated aluminum samples subjected to an in-between clean-up relative humidity of 90% air flow had an uptake of 35.6% of the original. Saturated aluminum samples submerged in distilled water for 12 hours had an uptake of 82.2% of the original sample. Saturated aluminum subjected to 50% humid air resulted in similar uptake characteristics in multiple repeated tests. These small-scale tests were run in parallel to a large-scale ground duct test used to mimic the stand-off in the Cygnus spacecraft during a Saffire experiment. Conclusions of this testing will be used in the design of large-scale spacecraft fire safety experiments and to develop a model to account for the interactions of HCl and aluminum surfaces in the presence of water in those tests.Item Modeling the Uptake of Hydrogen Chloride onto Interior Spacecraft Materials(50th International Conference on Environmental Systems, 7/12/2021) Niehaus, Justin; Mazumder, Sandip; Gokoglu, Suleyman; Berger, Gordon; Easton, JohnHydrogen chloride (HCl) is a major combustion product from the pyrolysis of polyvinyl chloride (PVC) insulated electrical wires, a common spacecraft fire safety concern. Models at two different scales were developed to predict HCl uptake on anodized, chromate conversion coated (Iridite), and bare aluminum surfaces, as well as on Nomex fabric: a macroscopic one-step global surface reaction model where all the active sites are on the exterior surface, and a pore model where the interior active sites deeper into the oxide layer can also be accessed by HCl. Experiments were performed to calibrate kinetic and diffusion constants in the models. A cast acrylic test cell was used to measure the differences between the inlet and outlet concentration of HCl after inserting a sample rod of the test material. For the materials with a thin (< 200 �m) or no oxide layer, the macroscopic surface reaction model adequately predicts the experimental measurements. For the anodized aluminum with a thicker oxide layer, the pore model provided a better match to experimental results. The results will be discussed with respect to the spacecraft fire safety project (Saffire).Item Strategy for Risk Quantification of Spaceflight Crew Health and Performance Using Dynamic Probabilistic Risk Assessment(2024 International Conference on Environmnetal Systems, 2024-07-21) Munster, Drayton; Matar, Mona; Gokoglu, Suleyman; Lewandowski, Beth; McIntyre, Lauren; Myers, JerryAt NASA, the Crew Health and Performance (CHP) system represents the span of countermeasures, capabilities, interventions, and tested processes and procedures that in combination work to mitigate the human component of spaceflight mission risk. Across the varying NASA mental models of the CHP system, the different functionalities needed to meet human flight systems standards can be broken down into specific categories (i.e. medical capability, environmental health, behavioral health). These categories can be further broken down into specific subgroups generally associated with the CHP functionalities meant to mitigate or buy down individual human system risks. Taking a similar development approach used by the NASA Human Research Program for modeling risk in the spaceflight medical system, we seek to leverage dynamic probabilistic risk assessment as a means to quantify and relatively assess the human risk state within the crew health and performance domain.12 By utilizing existing tools as integrators, we propose a rapid development strategy for incorporating research and operational data that represent the influence of the CHP system functionalities, in order to provide order of magnitudes estimates of the influence on most human system risks outcomes. By taking a modest cumulative risk approach and limiting scope to primary paths of influence between the CHP functionalities and human system risks, we can quickly prototype the integrative effects of CHP functional combinations to solicit valuable feedback from stakeholders and customers on the data, relationship, and structure of the integration. In this presentation, we will introduce the initial concept and development timeline for this tool and demonstrate a proof-of-concept through an application to the exercise device as a countermeasure in an Artemis-like design reference mission.