The Experts below are selected from a list of 7914 Experts worldwide ranked by ideXlab platform
Riccardo Panciroli - One of the best experts on this subject based on the ideXlab platform.
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Live monitoring of the distributed strain field in impulsive events through fiber Bragg gratings
Journal of Fluids and Structures, 2016Co-Authors: Riccardo Panciroli, Giacomo Falcucci, Elio Jannelli, Chiara Biscarini, Stefano UbertiniAbstract:Abstract In this paper, we propose a measurement technique based on local strain measurements to perform real-time reconstruction of the overall structural deformation and the distributed stress field produced by the impact of a body on a water free surface. In particular, we seek establishing a measurement chain capable of acquiring and elaborating the signals at high frequency, so that it can be utilized to study rapidly varying strain fields, such as those occurring in impulsive events. Fiber Bragg gratings are utilized to sense the local structural deformation. Experiments are conducted on flexible plastic wedges with variable deadrise angles impacting on a quiescent fluid surface. The experimental tests are performed in free fall and we explore variations of the Entry Velocity by varying the drop height. The structural deformation is reconstructed from point-wise strain measurements utilizing a modal reconstruction methodology. The impact dynamics are analysed through accelerometers and linear position sensors. Results show that the impact behaviour of the flexible body is characterized by a main overall deformation where the structure is distorted in the direction of the loading, whereby marked vibrations, whose amplitude increase with the Entry Velocity, dominate the dynamic response. The influence of the mode shapes considered in the present analysis on the accuracy of the results is also observed. The proposed methodology allows for a fairly high acquisition frequency, which translates into a real-time structural reconstruction technique. Results show that the proposed methodology can be a valuable tool for the live monitoring of structures undergoing impact events.
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Fluid-structure interaction during the water Entry of flexible cylinders
2015Co-Authors: Riccardo Panciroli, Giacomo Falcucci, G. Erme, E. De Santis, Elio JannelliAbstract:In this work, we experimentally study the water Entry of flexible cylinders. Experiments are performed in free fall and we explore variations of the Entry Velocity by varying the drop height. High speed imaging is utilized to study the fluid kinematics, the pile-up evolution, the cavity formation, and the overall structural deflection. The impact dynamics is analyzed through accelerometers, whereby fibre bragg gratings (FBG) measure the punctual deformation at characteristic locations on the cylinder surface. A modal decomposition approach is utilized to reconstruct the overall structural deflection from the punctual strain measurements. The proposed reconstruction methodology is compared against high-speed images. Results show that during the water Entry the cylinder mainly deforms in the direction of the hydrodynamic loading, whereby marked vibrations whose amplitude increase with the Entry Velocity dominate the dynamic response.
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Experiments on the water Entry of curved wedges: High speed imaging and particle image velocimetry
Ocean Engineering, 2015Co-Authors: Riccardo Panciroli, Adel Shams, Maurizio PorfiriAbstract:Abstract In this work, we experimentally study the water Entry of curved rigid wedges. Experiments are performed on two groups of rigid wedges comprising five specimens each. Each group has a fixed mean deadrise angle (25° and 35°) and varying radius of curvature. Drop tests are conducted in free-fall, and the drop height is parametrically varied to investigate the effect of the Entry Velocity on the pile-up evolution, the impact dynamics, and the energy transferred to the fluid. Specifically, high speed imaging is utilized to simultaneously measure the penetration depth of the wedge and its wetted surface. Experimental results are used to compute the pile-up coefficient, which is found to be largely independent of both the wedge geometry and the Entry Velocity, while exhibiting modest variations as a function of the penetration depth. In addition, particle image velocimetry is used to investigate the flow physics generated by the water Entry, and especially dissect the energy absorbed by the risen water during impact. Results show that between 60 and 80% of the impact energy is consistently transferred to the risen water, which accounts for the formation of the pile-up and the spray jets.
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Evaluation of the pressure field on a rigid body entering a quiescent fluid through particle image velocimetry
Experiments in Fluids, 2013Co-Authors: Riccardo Panciroli, Maurizio PorfiriAbstract:The objective of this work is to verify the accuracy of indirect pressure measurement from particle image velocimetry in water Entry problems. The pressure is evaluated by solving the incompressible Navier–Stokes equations, whose kinematic components are estimated from particle image velocimetry. We focus on the water Entry of a rigid wedge, for which we explore variations of the Entry Velocity. Experimental results are verified through comparison with well-established analytical formulations based on potential flow theory. Our findings demonstrate the feasibility of accurately reconstructing the hydrodynamic pressure field over the entire duration of the impact. Along with a thorough experimental validation of the method, we also offer insight into experimentally relevant factors, such as the maximum resolved fluid Velocity and the required spatial integration area.
Devendra Sharma - One of the best experts on this subject based on the ideXlab platform.
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Multiple species plasma boundary criterion with non-degenerate Entry flows
2015Co-Authors: Prabhat Kumar Dubey, Nishchhal Yadav, Devendra SharmaAbstract:The structure and spatial scaling of a collective electrostatic sheath forming in multiple-ion-species plasmas flowing into an absorbing boundary is examined using generalized criterion allowing non-degenerate Entry flows. The sheath thickness is characterized with respect to the relative velocities of Entry between individual ion species. Using the dispersion relation of multiple ion species plasma it is shown that while the smaller sheath thickness corresponds to the Entry velocities of the incident ion species far exceeding the effective ion acoustic Velocity. The plasma Debye length remains the limiting value of the sheath thickness beyond which the Entry Velocity solutions are lost as the individual ion velocities must ideally approach infinity for the sheath dimension approaching the Debye length.
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Valid flow combinations for stable sheath in a magnetized multiple ion species plasma
Physics of Plasmas, 2012Co-Authors: Devendra Sharma, Predhiman KawAbstract:Theoretical study is done of the Entry criterion for the plasma flow into the electrostatic boundary layer, or sheath, forming in a magnetized multiple ion species plasma. Finding valid Entry Velocity combinations in a magnetized set up requires a magnetized equivalent of the generalized Bohm criterion. A magnetized generalized Entry criterion is obtained with the scale length distribution in a region of validity for the stable solutions. The analysis finds that the valid Entry flow Velocity combinations with distinct values of individual ion species can correspond to a unique system phase Velocity. Magnetization effects govern the region of validity whose boundaries collapse to the unmagnetized sheath criterion in the limit of normal incidence, independent of the strength of the magnetic field. Considerably smaller Entry velocities, in comparison to the unmagnetized system sound Velocity, are recovered for the species in appropriate regime of magnetization in the cases of oblique incidences.
Predhiman Kaw - One of the best experts on this subject based on the ideXlab platform.
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Valid flow combinations for stable sheath in a magnetized multiple ion species plasma
Physics of Plasmas, 2012Co-Authors: Devendra Sharma, Predhiman KawAbstract:Theoretical study is done of the Entry criterion for the plasma flow into the electrostatic boundary layer, or sheath, forming in a magnetized multiple ion species plasma. Finding valid Entry Velocity combinations in a magnetized set up requires a magnetized equivalent of the generalized Bohm criterion. A magnetized generalized Entry criterion is obtained with the scale length distribution in a region of validity for the stable solutions. The analysis finds that the valid Entry flow Velocity combinations with distinct values of individual ion species can correspond to a unique system phase Velocity. Magnetization effects govern the region of validity whose boundaries collapse to the unmagnetized sheath criterion in the limit of normal incidence, independent of the strength of the magnetic field. Considerably smaller Entry velocities, in comparison to the unmagnetized system sound Velocity, are recovered for the species in appropriate regime of magnetization in the cases of oblique incidences.
Robert D Braun - One of the best experts on this subject based on the ideXlab platform.
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Mission design options for human Mars missions
The Mars Journal, 2007Co-Authors: Paul D. Wooster, Robert D Braun, Zachary R. PutnamAbstract:Background: Interplanetary trajectory selection will be a significant driver for the design of human Mars missions, impacting propulsive, habitation, and atmospheric Entry system requirements. Conjunction-class interplanetary trajectories are the leading candidate for human Mars missions, due to their short in-space durations, long surface stays, and lower propulsion requirements, in contrast to the long in-space durations, short surface stays, and high propulsion requirements characteristic of opposition-class missions. Within conjunction-class mission trajectories, considerations for providing an abort option to return the crew to Earth without stopping at Mars are also worthwhile. Approach: This paper presents Earth-Mars and Mars-Earth conjunction trajectories across a series of mission opportunities and transfer times in order to provide human Mars mission designers with an option space of possible crew and cargo transfer trajectories. For the specific case of crew transfer from Earth to Mars, the potential for aborting the mission without capture into Mars orbit is also examined. Two additional sub-classes of trajectories are thus presented: free return trajectories, where the outbound trajectory would return the crew to Earth after a fixed period of time without major propulsive maneuvers; and propulsive-abort trajectories, where the propulsive capability of the transfer vehicle is used to modify the trajectory during a Mars swing-by. Beyond propulsive requirements, trajectory selection also has a significant impact on the Entry Velocity and therefore the aeroassist system requirements, which are also examined in this paper. Results: Conjunction-class interplanetary trajectory data across a range of mission and architecture options is provided for use by designers of human Mars missions. Our investigation suggests potential constraints for Entry velocities at Earth and Mars due to aeroassist considerations and describes feasible trajectories within these constraints. Based upon Mars Entry Velocity, the 2-year period free return abort trajectory is found to be less desirable for many mission opportunities than previously considered.
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trajectory options for human mars missions
AIAA AAS Astrodynamics Specialist Conference and Exhibit, 2006Co-Authors: Paul D. Wooster, Robert D Braun, Zachary R. PutnamAbstract:This paper explores trajectory options for the huma n exploration of Mars, with an emphasis on conjunction-class missions. Conjunction-class missions are characterized by short in-space durations with long surface stays, a s opposed to the long in-space durations and short surface stays characteristic of oppositio n-class missions. Earth-Mars and Mars- Earth trajectories are presented across a series of mission opportunities and transfer times in order to explore the space of possible crew and cargo transfer trajectories. In the specific instance of crew transfer from Earth to Mars, the p otential for aborting the mission without capture into Mars orbit is also of interest. As suc h two additional classes of trajectories are considered: free-return trajectories, where the tra jectory would return the crew to Earth after a fixed period of time; and propulsive-abort trajectories, where the propulsive capability of the transfer vehicle is used to modif y the trajectory during a Mars swing-by. The propulsive requirements of a trajectory, due to their associated impact on spacecraft mass, are clearly of interest in assessing trajecto ries for human Mars missions. Beyond the propulsive requirements, trajectory selection can h ave a significant impact on the Entry Velocity and therefore the aeroassist system requir ements. The paper suggests potential constraints for Entry velocities at Earth and Mars. Based upon Mars Entry Velocity, the 2- year period free-return abort trajectory is shown t o be less desirable than previously considered for many mission opportunities.
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Influence of interplanetary trajectory selection on Mars atmospheric Entry Velocity
Journal of Spacecraft and Rockets, 1993Co-Authors: Scott A. Striepe, Robert D Braun, Richard W. Powell, Wallace T. FowlerAbstract:Many current manned Mars mission studies are using low lift-to-drag ratio (L/D) vehicles to aerobrake at both Mars and Earth. The use of these low L/D vehicles could limit the allowable Velocity at the atmospheric interface. This paper will demonstrate that if Entry Velocity constraints are incorporated into the interplanetary analysis of aerobraking Mars missions, many opportunities can be achieved for a small increase in initial mass in low-Earth orbit (IMLEO). These opportunities result from varying the initial launch date and the encounter dates and possibly using a powered Venus swingby on either the inbound or outbound transfer. This paper demonstrates this technique by using three atmospheric Entry Velocity ranges at Mars arrival (6.0-8.5, 6.4-8.1, and 7.2-7.3 km/s), unconstrained Mars Entry velocities, and an Earth return Entry Velocity below 14 km/s. The results indicate that, by carefully selecting the interplanetary trajectory, an optimum IMLEO mission can be found for even highly restrictive Entry Velocity missions in practically all of the 15 yr studied.
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Influence of Interplanetary Trajectory Selection on Earth Atmospheric Entry Velocity of Mars Missions
Journal of Spacecraft and Rockets, 1993Co-Authors: Scott A. Striepe, Robert D Braun, Richard W. Powell, Wallace T. FowlerAbstract:Many current manned Mars mission studies are using low lift-to-drag ratio vehicles to aerobrake at both Mars and Earth. This paper will demonstrate that if Entry Velocity constraints are incorporated into the interplanetary analysis of aerobraking Mars missions, more opportunities can be achieved for only a small increase in initial mass in low-Earth orbit (IMLEO). These additional opportunities result from varying the initial launch date and the encounter dates and possibly using a powered Venus swingby on either the inbound or outbound transfer. This paper not only presents unconstrained Entry Velocity missions but also includes results for Entry velocities below 12.5 and 14 km/s on Earth return and between 6.0-8.5 km/s at Mars arrival. The results indicate that, regardless of the Mars Entry Velocity range selected, an Earth Entry Velocity below 14 km/s is easily attainable for a minimal IMLEO increase. Although there are fewer 12.5 km/s Earth Entry Velocity missions possible, both Mars Entry Velocity constraint cases have over 50 percent of their missions requiring a negligible IMLEO increase.
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Earth aerobraking strategies for manned return from Mars
Journal of Spacecraft and Rockets, 1992Co-Authors: Robert D Braun, Richard W. Powell, James Evans LyneAbstract:Earth-return Entry corridor analyses are performed to evaluate the atmospheric flight environment of manned return from Mars. Trajectory and performance differences between aerocapture and direct Entry are assessed and quantified in terms of the required aerobrake lift-drag ratio (L/D), stagnation-point heating, and the significance of off-nominal atmospheric conditions. The Earth-return aerobraking scenarios compared are 1) aerocapture into a phasing orbit with a 24-h period, 2) aerocapture into a 500-km circular orbit, 3) and direct Entry to splashdown. No significant differences between aerocapture to a 500-km circular orbit and direct Entry were observed in terms of aerobrake L /D requirements, maximum deceleration, or peak stagnation-point heat rate. The importance of parking orbit selection is demonstrated for low Entry Velocity Earth-return missions from Mars and missions returning from the Moon. Additionally, a stagnation-point heating analysis revealed that in all cases the peak heat rate is large enough to require an ablative thermal protection system for manned return from Mars. However, for Entry velocities of 12.5 km/s and less, the heating environment is of the same order of magnitude as that experienced during the Apollo program. To perform the Entry analysis, two predictor-corrector guidance design strategies were developed. Use of a predictor-corrector technique was shown to provide adequate flight margin for managing off-nominal atmospheric conditions.
G H Su - One of the best experts on this subject based on the ideXlab platform.
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full scale numerical study on the flow characteristics and mal distribution phenomena in sg steam water separation system of an advanced pwr
Progress in Nuclear Energy, 2020Co-Authors: Di Fang, Mingjun Wang, Yuangang Duan, Jun Li, Wenxi Tian, G H SuAbstract:Abstract The steam-water separation system is of great importance to ensuring the steam quality in a PWR UTSG. In the present work, the full-scale three-dimensional CFD analysis is performed to study the mal-distribution steam flow in the system using ANSYS-FLUENT platform. A full-scale model of newly-designed PWR is established and all the sophisticated structures of 19 swirl-vane separators are modeled. Besides, the porous medium model is adopted to simplify the steam flow inside the dryers because of the complex structure of wave-type vanes. Employing CFD methodologies, detailed flow characteristics in the whole system are captured, especially the Velocity fields of steam at inlets of 7 dryer units. The outcomes show that the maximum unit-area mass-flow rate appears at the entrance of #4 dryer which is in the central part of dryers. In addition, the maximum Entry Velocity is 2.136 m/s, while the Velocity is decreased to 1.049 m/s, lower than the critical Velocity, with the application of an orifice plate assembly with the perforation in different calibers on the plate. Also, the effect of the separator down-comer on the mal-distribution phenomenon is also analyzed. In general, the current work could be expected to be a basis for the future optimization on moisture separation components in the steam generator.