Daniel Kirk

Biomarkers of blast-induced neurotrauma: profiling molecular and cellular mechanisms of blast brain injury.

The nature of warfare in the 21st century has led to a significant increase in primary blast or over-pressurization injuries to the whole body and head, which manifest as a complex of neuro-somatic damage, including traumatic brain injury (TBI). Identifying relevant pathogenic pathways in reproducible experimental models of primary blast wave exposure is therefore vital to the development of biomarkers for diagnostics of blast brain injury. Comparative analysis of mechanisms and putative biomarkers of blast brain injury is complicated by a deficiency of experimental studies. In this article, we present an overview of current TBI biomarkers, as well as outline experimental strategies to investigate molecular signatures of blast neurotrauma and to develop a pathway network map for novel biomarker discovery. These biomarkers will be effective for triaging and managing both combat and civilian casualities.

Neuro-Glial and Systemic Mechanisms of Pathological Responses in Rat Models of Primary Blast Overpressure Compared to “Composite” Blast

A number of experimental models of blast brain injury have been implemented in rodents and larger animals. However, the variety of blast sources and the complexity of blast wave biophysics have made data on injury mechanisms and biomarkers difficult to analyze and compare. Recently, we showed the importance of rat position toward blast generated by an external shock tube. In this study, we further characterized blast producing moderate traumatic brain injury and defined “composite” blast and primary blast exposure set-ups. Schlieren optics visualized interaction between the head and a shock wave generated by external shock tube, revealing strong head acceleration upon positioning the rat on-axis with the shock tube (composite blast), but negligible skull movement upon peak overpressure exposure off-axis (primary blast). Brain injury signatures of a primary blast hitting the frontal head were assessed and compared to damage produced by composite blast. Low to negligible levels of neurodegeneration were found following primary blast compared to composite blast by silver staining. However, persistent gliosis in hippocampus and accumulation of GFAP/CNPase in circulation was detected after both primary and composite blast. Also, markers of vascular/endothelial inflammation integrin alpha/beta, soluble intercellular adhesion molecule-1, and L-selectin along with neurotrophic factor nerve growth factor-beta were increased in serum within 6 h post-blasts and persisted for 7 days thereafter. In contrast, systemic IL-1, IL-10, fractalkine, neuroendocrine peptide Orexin A, and VEGF receptor Neuropilin-2 (NRP-2) were raised predominantly after primary blast exposure. In conclusion, biomarkers of major pathological pathways were elevated at all blast set-ups. The most significant and persistent changes in neuro-glial markers were found after composite blast, while primary blast instigated prominent systemic cytokine/chemokine, Orexin A, and Neuropilin-2 release, particularly when primary blast impacted rats with unprotected body.

Real-Time Estimation of Time-Varying Bending Modes Using Fiber Bragg Grating Sensor Arrays

An important challenge in launch vehicle simulation and control is created by the time-varying mass and inertia of the vehicle, as well as the consequent changes in modal frequencies and modal shapes of the structure as propellant is exhausted. Estimating modal information from a limited number of onboard sensors is inadequate for attitude control of a launch vehicle in real time, and the use of additional conventional sensors is unwarranted because of the mass penalty and complexity. This limitation has forced mission planners to base vehicle control schemes on pre-calculated modal information from finite element models. Recent advances in fiber Bragg grating (FBG) sensor technology enable locating a large number of sensing elements along a rockets structure with a negligible mass penalty. This opens the path for real-time modal estimation and control. This paper presents a novel approach for the real-time estimation of mode shapes on a variable mass structure using FBG sensor arrays. The method is vali...

Analytical Model for Cryogenic Stratification in a Rotating and Reduced-Gravity Environment

Modeling the thermal behavior of cryogenic propellants within the upper stages of a launch vehicle is necessary for successful mission planning. During orbital transfer, the upper stage may coast for several hours, during which the propellants are heated by solar radiation and undergo thermal stratification. At the end of a coast, the propellant temperature and pressure must be within a narrowly defined range to ensure engine restart. This work develops a thermal stratificationmodel that includes the thermal conditioning spin of the stage. Themodelmay be used to assess the impact of thermal stratificationwithin propellant tanks over a range of axial accelerations, spin rates, heat fluxes, and tank geometries. The parabolic dishing effect from spinning the tank results in an increased stratum thickness, due to the larger length of the free-convection boundary layer along the tank wall. However, due to the balance between the increased wall-heating area and increased free-surface area, stratum temperatures may be cooler or warmer, depending on the spin rate.

Experimental and Numerical Investigation of Liquid Slosh Behavior Using Ground-Based Platforms

Liquid-propellant slosh events occurring during orbital maneuvers of a rocket’s upper stage may adversely affect vehicle performance. Mission planners require accurate and validated simulation tools to understand and predict the effects of slosh on the intended trajectory of the vehicle, as well as for propellant and tank thermal management. A coupledrigid-bodyandfluid-dynamicsnumerical tool is presentedwhich canbeused topredict the effect of internalfluid slosh on a tank’s trajectory. To benchmark the numerical tool, a novel experimental framework is presented which examines the influence of liquid slosh on the trajectory of moving tanks with multiple degrees of freedom. The motion history of the tank is measured along with synchronized camera images of the liquid distribution within the tank. The acquiredexperimentaldataareused toassess the accuracyof thenumerical tool.Thepredictions fromthenumerical tool are in excellent agreement with the experimentally measured data over a wide range of tank motion profiles.

Update on SPHERES Slosh for Acquisition of Liquid Slosh Data aboard the ISS

A current problem that severely affects the performance of spacecraft is related to slosh dynamics in liquid propellant tanks under microgravity conditions. The confidence in computational fluid dynamics (CFD) predictions are low because of the lack of benchmark against experimental data. The goal of the SPHERES Slosh Experiment (SSE) is to acquire long-duration, low-gravity liquid slosh data aboard the International Space Station. The proposed experimental platform consists of a tank, partially filled with fluid, cameras, and inertial sensors to monitor the fluid distribution in the tank. Currently the SSE has passed NASA’s Critical Design Review (CDR) and Phase 0/I-II Flight Safety Review (FSR). The manufacture and qualification testing of the flight article has been completed. The Slosh payload is scheduled to be launched in December 2013 with on-orbit experiments to begin shortly thereafter.

Parametric Study of a Propellant Tank Slosh Baffle

A current problem that severely affects the performance of spacecraft is related to slosh dynamics in liquid propellant tanks under microgravity conditions. Accurate prediction of the slosh dynamics is critical for successful mission planning and may impact vehicle control and positioning during rendezvous, docking, and reorientation maneuvers. The purpose of this work is to assess the performance of various sloshmitigating baffle designs and configurations using computational fluid dynamics. This work develops metrics, including wall wetting, peak slosh amplitude, and bulk fluid motion, to assess the relevance of a particular baffle geometry and placement within the tank for a prescribed bulk fluid motion over a range of acceleration levels. The twoand three-dimensional studies are used to assess the slosh model’s sensitivity to grid resolution, laminar versus turbulent flow models, and Bond number scaling. The results are used to develop a foundation on which to build a full six-degree-of-freedom dynamic mesh model, allowing for fluidforce interaction with a propellant tank, which will be benchmarked against low-gravity slosh flight data.

Effect of Isogrid-Type Obstructions on Thermal Stratification in Upper-Stage Rocket Propellant Tanks

Analytical models for propellant thermal stratification are typically based on smooth wall flow correlations. However, many propellant tank walls have a mass-saving isogrid, which alters the boundary layer. This work investigates the boundary-layer behavior over walls with obstruction elements that are representative of isogrid or internal stiffener rings. The experimental studies reveal that the thickness of the velocity boundary layer over an isogrid wall is more than 200% thicker than a smooth wall at full-scale upper-stage tank Reynolds numbers. For buoyancy-induced free convection flows, the computational-fluid-dynamics models demonstrate that the velocity boundary layer over a wall lined with obstruction elements may be thicker or thinner than the equivalent boundary layer over a smooth wall, whereas the thermal boundary layer is always thicker for the rough wall. A Rayleigh number scaling analysis is presented for a range of fluids, tank and obstruction sizes, heat loads, and acceleration levels. W...

Design of an Experimental Platform for Acquisition of Liquid Slosh Data aboard the International Space Station

Liquid propellant slosh occurring during orbital maneuvers of a rocket’s upper-stage may adversely affect vehicle performance. During orbital maneuvers the acceleration levels of an upper-stage vary substantially and significant liquid sloshing events may occur which can affect the intended trajectory of the vehicle as well as influence propellant and tank thermal management. Mission planners require accurate and validated simulation tools to understand and predict the effects of slosh on a mission and therefore there is a need to better understand and model liquid slosh in micro-gravity. This work aims to bridge the gap of missing data by designing a Slosh Platform capable of acquiring long-duration low-gravity slosh data on the International Space Station. The slosh data acquired will facilitate calibration and validation of CFD models. The proposed experimental platform consists of a tank partially filled with water, inertial measurement units to measure the dynamics of the system, as well as cameras to image the fluid distribution in the tank. The Slosh Platform utilizes the existing ISS SPHERES apparatus, which will be used to maneuver the tank through a variety of trajectories. To mimic the motions of actual upper-stage rocket maneuvers, a scaling analysis based on relevant nondimensional parameters is performed and applied to the design and operation of the Slosh platform onboard ISS. The proposed motion profiles to be conducted by the Slosh Platform on ISS were verified using a CFD tool to assess the magnitude of fluid slosh and its impact on the attitude change of the platform. The CFD tools predict that the liquid slosh within the tank of the Slosh Platform will cause the trajectory of the apparatus to deviate in a measurable way as compared with a rigid, non-sloshing system. Currently the experimental design has passed NASA’s Critical Design Review and manufacture of the first test article is in progress. The Slosh experiment is scheduled to fly to the ISS in July of 2013 with on-orbit experiments to begin shortly thereafter.

Electromagnetic launch by linear quadrupole field

This paper presents a novel electromagnetic launch concept based on a DC linear quadrupole field with no axial component. The proposed design enables contact-free power transfer to the launch vehicle while removing the need of switching power or AC induction. Passive damping windings are proposed to provide radial stability during launch. The 6-DOF dynamics of the launch vehicle, including the coupling of electromagnetic propulsion and damping, has been simulated. The result shows that the proposed method provides sufficient thrust for the proposed mission while providing satisfactory radial stability during launch.