Faculty Research and Data

Permanent URI for this collectionhttps://digital.lib.washington.edu/handle/1773/43472

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Now showing 1 - 11 of 11

Tuning body shape and stiffness to reduce water slamming forces
(Ocean Engineering, 2025) Boom, Bart; Truscott, Tadd; Fish, Frank E.; Habtour, Ed
This paper reveals how plunge-diving seabirds control impact energy during high-velocity water entry to hunt fish in deep waters without breaking their necks. Previous research has shown that the aerodynamic shape of the head or the structural compliance in the neck can reduce slamming forces. However, the physics governing their combined effects combined on the dive performance are is not well understood. The paper addresses this gap by demonstrating analytically and experimentally why the combined effect of shape and compliance is key for controlling the energy transmission during impact, passively. The impact forces at varying velocities are measured experimentally using a simple projectile design— to emulate seabirds’ dives —with different head shapes (cone angles) and spring stiffnesses (compliance). The experiments are utilized to develop a semi-analytical model to estimate the amount and duration of the stored, released, and dissipated energy. Our findings show that the slamming forces can be passively reduced by tuning the compliance to increase the amount of impact energy stored in the system and delay its release and dissipation. While decreasing the cone angle reduces the slamming forces for a rigid system, the effect of compliance on reducing these forces is more pronounced in projectiles with half-cone angles larger than 30°. Modeling the interplay between cone angle and neck compliance offers physical insights into how diving seabirds mitigate mechanical stresses during impacts, thereby avoiding catastrophic damage. Conversely, these insights can be exploited to engineer mechanical systems with passive control of dynamic loads such as impact, shock, or vibrations with minimal energy losses.
Mechanics of Solids
(2024-09-21) Arshad, Muzammil
The primary purpose of the book is to provide review material for the graduate courses of AE 540 or AA 530 Mechanics of Solids taught at William E. Boeing Department of Aeronautics & Astronautics, University of Washington. For the students to achieve a good understanding of the advanced concepts for the graduate course in Mechanics of Solids, the entire book is designed with classroom lecture notes. The book and lecture notes can also be used by undergraduate students for the courses of Mechanics of Materials and Solid Mechanics.
Turbine blade cooling using Coulomb repulsion
(2023-03-13) Colannino, Joseph; Breidenthal, Robert E
In order to preserve the integrity of the film cooling layer on a turbine blade, it is proposed that the blade is raised to a positive voltage with respect to a nearby negative electrode. The positive ions within the hot combustion products are repulsed from the blade, transferring that force to the surrounding neutrals. The neutral gas within the film cooling layer experiences no such body force. Therefore the boundary between the two fluids acts as a stably-stratified interface, analogous to the surface of the ocean. The flatness of the interface is determined by a Richardson number, the ratio of the potential energy of the Coulomb force to the kinetic energy of the turbulence. If Ri is greater than unity, the interface is relatively flat and the film cooling layer remains preserved.
A simple model of the hypersonic boundary layer
(2023-03-13) Breidenthal, Robert E
A simple model of the hypersonic boundary layer is proposed. There are three assumptions: The mean velocity profile is linear, the total enthalpy is uniform, and turbulent transport is controlled by sonic eddies, whose rotational Mach number is unity. The model predicts that turbulent transport is slowest at the outer edge of the layer, consistent with the formal assumption of a linear velocity profile. The concentration profile of any conserved scalar is uniform across the boundary layer, matching the boundary condition at the wall. Any difference with the free stream concentration is accommodated by a jump at the outer edge of the layer.
Design Considerations for the Implementation of a High-Field Side Transient CHI System on QUEST
(2022-08) Raman, Roger; Kuroda, K.; Hanada, K.; Ono, Masayuki; Hasegawa, M.; Onchi, T.; Ikezoe, R.; Idei, H.; Ido, T.; Rogers, John A.
Transient Coaxial Helicity Injection, a method first developed on the small HIT-II experiment and then validated on the much larger NSTX device, is a method to initiate an inductive-like tokamak plasma discharge without reliance on the central solenoid. A CHI discharge is initiated by driving current along magnetic flux that connects the inner and outer divertor plates on one end of the tokamak. To permit this, on both HIT-II and NSTX, toroidal ceramic insulators were used to electrically separate the inner and outer vessel components. The use of such large toroidal vacuum insulators may not be easy to implement in reactors. To address this issue, the QUEST ST is developing a reactor-relevant CHI configuration in which one of the divertor plates is electrically insulated from the rest of the vessel. The first application of transient CHI on QUEST biased the CHI electrode to the outer vessel. While the CHI discharges could be easily generated, it was found that as the discharge filled the vessel, the separation distance between the injector magnetic flux footprints widened, a condition that is not favorable for the generation of closed flux surfaces. Biasing the electrode to the inner wall is a configuration similar to that used on NSTX and HIT-II, but initial testing in this configuration has proved to be challenging. The design described here overcomes the present limitation by locating the CHI electrode much closer to the CHI injector flux coil and using an NSTX-like gas injection manifold to enable high-field side transient CHI startup on QUEST. The concepts described in this paper should also benefit the future implementation of transient CHI systems in other tokamaks and spherical tokamaks.
Transient CHI system design studies for PEGASUS-III
(2022-08-03) Raman, Roger; Morgan, Kyle; Reusch, Joshua A.; Rogers, John A.; Diem, Stephanie J.; Ebrahimi, Fatima; Jardin, Stephen C.; Nelson, Brian A.; Ono, Masayuki; Weberski, Justin D.
Transient Coaxial Helicity Injection (transient CHI) first developed on the Helicity Injected Torus-II and later on the National Spherical Torus Experiment (NSTX) for implementing solenoid-free plasma current startup capability in a Spherical Tokamak (ST), is now planned to be tested on the PEGASUS-III ST using a novel double biased configuration. Such a configuration is likely needed for transient CHI deployment in a reactor. The transient CHI system optimization will be studied on PEGASUS-III to enable startup toroidal persisting currents at the limits permitted by the external poloidal field coils. A transient CHI discharge is generated by driving injector current along magnetic field lines that connect the inner and outer divertor plates on one end of the ST. Simulations using the Tokamak Simulation Code (TSC) are used to assess the transient CHI toroidal current generation potential and electrode gap location on PEGASUS-III. While past transient CHI systems have used high voltage oil-filled capacitors for driving the injector current, for improved safety, PEGASUS-III will use a high-current capacitor bank based on low voltage electrolytic capacitors. The designed and fabricated system is capable of over 32 kA. The modular design features permit the system to be upgraded to higher currents, as needed, to meet the future needs of the PEGASUS-III facility.
Highly Sensitive Nonlinear Identification to Track Early Fatigue Signs in Flexible Structures
(Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems, 2022-05) Habtour, Ed M; Di Maio, Dario; Masmeijer, Thijs; Gonzalez, Laura Cordova; Tinga, Tiedo
This study describes a physics-based and data-driven nonlinear system identification (NSI) approach for detecting early fatigue damage due to vibratory loads. The approach also allows for tracking the evolution of damage in real-time. Nonlinear parameters such as geometric stiffness, cubic damping, and phase angle shift can be estimated as a function of fatigue cycles, which are demonstrated experimentally using flexible aluminum 7075-T6 structures exposed to vibration. NSI is utilized to create and update nonlinear frequency response functions, backbone curves and phase traces to visualize and estimate the structural health. Findings show that the dynamic phase is more sensitive to the evolution of early fatigue damage than nonlinear parameters such as the geometric stiffness and cubic damping parameters. A modified Carrella–Ewins method is introduced to calculate the backbone from nonlinear signal response, which is in good agreement with the numerical and harmonic balance results. The phase tracing method is presented, which appears to detect damage after approximately 40% of fatigue life, while the geometric stiffness and cubic damping parameters are capable of detecting fatigue damage after approximately 50% of the life-cycle.
Damage precursor detection for structures subjected to rotational base vibration
(International Journal of Non-Linear Mechanics, 2016-03-04) Habtour, Ed M; Cole, Daniel P; Stanton, Samuel C; Sridharan, Raman; Dasgupta, Abhijit
This paper presents a nonlinear dynamic methodology for monitoring precursors of fatigue damage in metallic structures under variable rotational base excitation. The methodology accounts for important nonlinearities due to the complex loading generated by variable rotation and structural degradation. The sources of the nonlinearities include: structural stiffening due to gyroscopic motion and high-response amplitude at the fundamental mode, softening due to inertial forces and gyroscopic loads, and localized microscopic material damage and micro-plasticity. The loading intensity and number of vibration cycles increase the influence of these effects. The change in the dynamic response due to fatigue damage accumulation is experimentally investigated by exciting a cantilever beam at variable rotational base motions. The observed fatigue evolution in the material microstructure at regions of large stresses (and the resulting progressive structural softening) is tracked by quantifying the growth in the tip response, the change in the fundamental natural frequency of the beam and the skewedness of the stepped-sine response curve. Previous understanding of the structural dynamic behavior is necessary to ascertain the damage precursor location and evolution. Nanoindentation studies near the beam clamped boundary are conducted to confirm the gradual progression in the local mechanical properties as a function of loading cycles, and microstructural studies are conducted to obtain qualitative preliminary insights into the microstructure evolution. This study demonstrates that careful monitoring of the nonlinearities in the structural dynamic response can be a sensitive parameter for detection of damage precursors.
Quantifying Information without Entropy: Identifying Intermittent Disturbances in Dynamical Systems
(Entropy, 2020-10-23) Montoya, Angela; Habtour, Ed M; Moreu, Fernando
A system’s response to disturbances in an internal or external driving signal can be characterized as performing an implicit computation, where the dynamics of the system are a manifestation of its new state holding some memory about those disturbances. Identifying small disturbances in the response signal requires detailed information about the dynamics of the inputs, which can be challenging. This paper presents a new method called the Information Impulse Function (IIF) for detecting and time-localizing small disturbances in system response data. The novelty of IIF is its ability to measure relative information content without using Boltzmann’s equation by modeling signal transmission as a series of dissipative steps. Since a detailed expression of the informational structure in the signal is achieved with IIF, it is ideal for detecting disturbances in the response signal, i.e., the system dynamics. Those findings are based on numerical studies of the topological structure of the dynamics of a nonlinear system due to perturbated driving signals. The IIF is compared to both the Permutation entropy and Shannon entropy to demonstrate its entropy-like relationship with system state and its degree of sensitivity to perturbations in a driving signal.
Structural state awareness through integration of global dynamic and local material behavior
(2019) Habtour, Ed M; Cole, Daniel P; Kube, Christopher M; Henry, Todd C; Haynes, Robert A; Gardea, Frank; Sano, Tomoko; Tinga, Tiedo
Structural health monitoring and nondestructive inspection techniques typically assess the lifecycle and reliability of high- value aerospace, mechanical, and civil systems. Maintenance and inspection intervals are typically time-based and depen- dent on the structural health monitoring/nondestructive inspection technique to detect macroscale damage resulting from fatigue or environmental damage. The current work proposes an integrated materials-structures-dynamics approach for providing state awareness of structural health. The proposed approach shifts the conventional structural health monitoring/nondestructive inspection focus of searching for cracks to a health state awareness based on tracking changes in the energetics of the materials-structures-dynamics states. Energy variations are tracked in a cantilevered structure exposed to nonlinear harmonic oscillation, where the strain energy of the beam was derived and used to determine a health state index. Nanoindentation was used to probe the near-surface mechanical properties of the beam to characterize local material variations as a function of fatigue cycles. A nonlinear ultrasonic approach was considered in order to connect the local material behavior changes to the variations in the dynamic performance of the beam. The intent of the investigation was to connect the traditionally detached materials, structural, and dynamics approaches to structural health monitoring/nondestructive inspection, while providing a framework for enabling damage precursor detection.
Physics-Based-Adaptive Plasma Model for High-Fidelity Numerical Simulations
(Frontiers in Physics, 2018-09-21) Ho, Andrew; Datta, Iman Anwar Michael; Shumlak, Uri
A physics-based-adaptive plasma model and an appropriate computational algorithm are developed to numerically simulate plasma phenomena in high fidelity. The physics-based-adaptive plasma model can be dynamically refined based on the local plasma conditions to increase model fidelity uniformity throughout the domain at all times of the simulation. The adaptive plasma model uses continuum representations of the plasma, which include a kinetic Vlasov model for the highest fidelity, multi-fluid 5N-moment plasma model, and single-fluid MHD model for the lowest fidelity. The models include evolution equations for the electromagnetic fields, electron species, ion species, and neutral species. A nodal discontinuous Galerkin finite element method is implemented and is coupled with various implicit and explicit Runge-Kutta methods. Various model coupling techniques are investigated for a 5N-moment multi-fluid models with a Vlasov-Maxwell model, and a 5N-moment two-fluid model with an MHD model. Continuum plasma models using consistent normalizations and identical spatial representations provide straightforward and accurate coupling between the models. The solution approach offers high-order accuracy and computational efficiency. Target compute platforms are heterogeneous computer architectures using a compute model that minimizes data movement.

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