scholarly journals An Alternative Ballistic Limit Equation for the Whipple Shield in the Shatter Regime, Based on Characteristics of the Large Central Fragment

2021 ◽  
Vol 2021 (2) ◽  
pp. 12-29
Author(s):  
Ken Wen ◽  
De-ning Di ◽  
Xiao-wei Chen
Keyword(s):  
Significant Contribution ◽  
Experimental Results ◽  
Limit Equation ◽  
Ballistic Limit ◽  
Central Fragment ◽  
Alternative Approach ◽  
Debris Cloud ◽  
Whipple Shield

Abstract In the shatter regime of a Whipple shield, a large central fragment makes a significant contribution to the damage-causing capacity of the debris cloud. Herein we present a feasible scheme for the identification and measurement of this large central fragment and propose an alternative approach to the ballistic limit equation (BLE) for the Whipple shield, deducing an alternative ballistic limit in the shatter regime based on the large central fragment’s characteristics. This alternative BLE is compared with the phenomenological Whipple BLE, the JSC Whipple BLE and the Ryan curve. Our alternative BLE, modified at the incipient fragmentation and completed fragmentation point, is shown to agree well with experimental results.

Numerical modeling of high velocity impact in sandwich panels with honeycomb core and composite skin including composite progressive damage model

2018 ◽  
Vol 22 (8) ◽  
pp. 2768-2795 ◽  
Author(s):  
Meysam Khodaei ◽  
Mojtaba Haghighi-Yazdi ◽  
Majid Safarabadi
Keyword(s):  
Numerical Model ◽  
Sandwich Panel ◽  
Material Model ◽  
Absorption Capacity ◽  
Numerical Results ◽  
Ballistic Impact ◽  
Experimental Results ◽  
Ballistic Limit ◽  
Honeycomb Core ◽  
Damage Initiation

In this paper, a numerical model is developed to simulate the ballistic impact of a projectile on a sandwich panel with honeycomb core and composite skin. To this end, a suitable material model for the aluminum honeycomb core is used taking the strain-rate dependent properties into account. To validate the ballistic impact of the projectile on the honeycomb core, numerical results are compared with the experimental results available in literature and ballistic limit velocities are predicted with good accuracy. Moreover, to achieve composite skin material model, a VUMAT subroutine including damage initiation based on Hashin’s seven failure criteria and damage evolution based on MLT approach modulus degradation is used. To validate the composite material model VUMAT subroutine, the ballistic limit velocities of the projectile impact on the composite laminates are predicted similar to the numerical results presented by other researchers. Next, the numerical model of the sandwich panel ballistic impact at different velocities is compared with the available experimental results in literature, and energy absorption capacity of the sandwich panel is predicted accurately. In addition, the numerical model simulated the sandwich panel damage mechanisms in different stages similar to empirical observations. Also, the composite skin damages are investigated based on different criteria damage contours.

A Predictive Non-Dimensional Scaling Law for the Plate Perforation of Several Aluminum Alloys by Fragment-Simulating Projectiles

2019 ◽  
Author(s):  
Weinong Chen ◽  
Zherui Guo
Keyword(s):  
Aluminum Alloys ◽  
Scaling Law ◽  
Limit Equation ◽  
Ballistic Limit ◽  
Limit Velocity ◽  
Dimensional Scaling ◽  
Material Problem ◽  
Plate Perforation ◽  
Ballistic Limit Velocity ◽  
Aluminum Armor Plates

Abstract An equation was previously-presented to predict the ballistic-limit velocity for the perforation of aluminum armor plates by fragment-simulating projectiles (FSP). The ballistic-limit equation was presented in terms of dimensionless parameters so that the geometric and material problem scales are identified. Previously published predictions and data for two different FSP projectile calibers (12.7 mm and 20 mm) and two different strength aluminum alloys show the scaling law to be accurate. In this paper we extend the same concept to several other alloys and show that this scaling law is predictive.

scholarly journals The Measurement of Dynamic Tidal Contribution to Apsidal Motion in Heartbeat Star KIC 4544587

2021 ◽  
Vol 922 (1) ◽  
pp. 37
Author(s):  
Jian-Wen Ou ◽  
Cong Yu ◽  
Ming Yang ◽  
Chen Jiang ◽  
Bo Ma ◽  
...  
Keyword(s):  
Significant Contribution ◽  
Tidal Effect ◽  
Photometric Data ◽  
Apsidal Motion ◽  
Analysis Method ◽  
Alternative Approach ◽  
Orbital Phase ◽  
Long Time ◽  
General Relativistic ◽  
The Impact

Abstract Apsidal motion is a gradual shift in the position of periastron. The impact of dynamic tides on apsidal motion has long been debated, because the contribution could not be quantified due to the lack of high-quality observations. KIC 4544587 with tidally excited oscillations has been observed by Kepler high-precision photometric data based on long-time-baseline and short-cadence schema. In this paper, we compute the rate of apsidal motion that arises from the dynamic tides as 19.05 ± 1.70 mrad yr−1 via tracking the orbital phase shifts of tidally excited oscillations. We also calculate the procession rate of the orbit due to the Newtonian and general relativistic contribution as 21.49 ± 2.8 and 2.4 ± 0.06 mrad yr−1, respectively. The sum of these three factors is in excellent agreement with the total observational rate of apsidal motion 42.97 ± 0.18 mrad yr−1 measured by eclipse timing variations. The tidal effect accounts for about 44% of the overall observed apsidal motion and is comparable to that of the Newtonian term. Dynamic tides have a significant contribution to the apsidal motion. The analysis method mentioned in this paper presents an alternative approach to measuring the contribution of the dynamic tides quantitatively.

An Alternative Approach for Teaching Turbulent Flow

2007 ◽  
Author(s):  
Ahmad Fakheri
Keyword(s):  
Turbulent Flow ◽  
Pipe Flow ◽  
Numerical Solutions ◽  
Experimental Results ◽  
Mixing Length ◽  
Law Of The Wall ◽  
Alternative Approach ◽  
Logarithmic Law ◽  
Basic Concepts ◽  
Moody Diagram

Teaching of turbulence in undergraduate and early graduate level fluid mechanics and heat transfer courses is a difficult undertaking. The approach taken in typical texts requires the students to accept a number of basic concepts without much quantitative justifications. This paper presents an alternative approach, one in which most of the salient features of the turbulent flow are derived by using numerical solutions and experimental results, as opposed to simply having them presented. In this approach, Prandtl’s mixing length model is used to obtain the velocity distribution for fully developed pipe flow. By comparing the numerical calculations with the experimental results, students determine the value of κ that best fits the experimental data on their own. In addition, deficiency of the mixing length in the transition region is shown. It is also shown that other models like Van Driest’s do a better job. The Logarithmic Law of the wall as well as 7th power law are also proven. The different models are used to determine the friction factor for pipe flow and the results are compared with the values obtained from the Moody diagram.

scholarly journals Numerical Simulation of Ti-Based Metallic Glasses as Whipple Shield Bumper by Smoothed Particle Hydrodynamics Methods

2020 ◽  
Vol 993 ◽  
pp. 826-835
Author(s):  
Wei Qi Tang ◽  
Kun Zhang ◽  
Yan Sen Li ◽  
Yang Wang ◽  
Ya Ting Zhang ◽  
...  
Keyword(s):  
Metallic Glasses ◽  
Smoothed Particle Hydrodynamics ◽  
Areal Density ◽  
Hypervelocity Impacts ◽  
Al 6061 ◽  
Ejection Angle ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Debris Cloud ◽  
Whipple Shield

The debris clouds produced by hypervelocity impacts on Ti-based metallic glasses (Ti-MGs) and Al-6061-T6 bumper were studied by smoothed particle hydrodynamics (SPH) methods. The change of the vanguard shape, dispersion and ejection angle were also obtained with the same bumper thickness to the projectile-diameter ratio (h/d). For the same h/d valve, the debris cloud of Ti-MGs bumper had a more widely dispersion and ejection angle than with Al-6061-T6 bumper; the vanguard velocity of Ti-MGs bumper was also lower than Al-6061-T6 bumper. Moreover, for the same bumper areal density, the vanguard of the debris cloud in MGs bumper was plane-shaped. This study demonstrates that Ti-MGs exhibit an excellent bumper protection performance, which asset can pave new paths for their further applications.

Moving sensors for improved estimation of dynamic structures: Experimental validation

2020 ◽  
pp. 107754632096501
Author(s):  
Maria Chierichetti ◽  
Michael Demetriou
Keyword(s):  
Laser Scanning ◽  
Estimation Error ◽  
Experimental Results ◽  
State Estimator ◽  
Estimation Errors ◽  
Nonlinear Beam ◽  
Sensor Position ◽  
Alternative Approach ◽  
Lyapunov Redesign ◽  
Dynamic Structures

In the monitoring of structural systems, the use of multiple high-end sensors may prove to be economically prohibitive. The alternative approach would be to use fewer devices capable of moving across the span of the structural system. In the proposed approach, a velocity sensor that is able to move across the spatial domain and obtain point-wise velocity measurements is combined to a novel dynamic observer. Based on the measured velocities, a state estimator is developed, the gain of which depends on the motion of the sensor. The motion of the sensor is defined using Lyapunov redesign methods and depends only on the estimation error at the current sensor position. The guidance policy is performance based and steers the sensor to spatial regions of the structure with larger estimation errors. The proposed approach is validated with a one-dimensional flexible structure, mathematically described by an Euler–Bernoulli partial differential equation. The moving sensor is realized through the use of a laser scanning vibrometer that provides both the moving measurements and additional measurements against which the proposed approach will be validated. Once measurements over a large number of locations are acquired, the experimental results are fed to the algorithm that selects the instantaneous sensor location. Experimental results for linear and nonlinear beam cases are presented to show the feasibility and robustness of the proposed approach.

scholarly journals New forms of checks and balances are needed to improve research integrity

F1000Research ◽  
2014 ◽  
Vol 3 ◽  
pp. 119 ◽  
Author(s):  
Elizabeth Iorns ◽  
Christin Chong
Keyword(s):  
Scientific Discovery ◽  
Research Misconduct ◽  
Research Integrity ◽  
The Self ◽  
Experimental Results ◽  
Checks And Balances ◽  
Publishing Process ◽  
Technical Review ◽  
Alternative Approach ◽  
Highly Cited

Recent attempts at replicating highly-cited peer-reviewed studies demonstrate that the “reproducibility crisis” is indeed upon us. However, punitive measures against individuals committing research misconduct are neither sufficient nor useful because this is a systemic issue stemming from a lack of positive incentive. As an alternative approach, here we propose a system of checks and balances for the publishing process that involves 1) technical review of methodology by publishers, and 2) incentivizing direct replication of key experimental results. Together, these actions will help restore the self-correcting nature of scientific discovery.

Investigation on Response of an Aluminum Honeycomb Subjected to Hypervelocity Impacts using Lagrange and SPH for Numerical Modeling

2019 ◽  
Author(s):  
Kumi Nitta ◽  
Masumi Higashide ◽  
Mirai Sueki ◽  
Atushi Takeba
Keyword(s):  
Numerical Modeling ◽  
High Strain ◽  
Hypervelocity Impact ◽  
Numerical Results ◽  
Experimental Results ◽  
Ballistic Limit ◽  
Limit Curve ◽  
Material Models ◽  
Hypervelocity Impacts ◽  
Aluminum Honeycomb

Abstract Numerical modeling has been conducted with the commercial code AUTODYN 2D, using the Lagrange and Smooth Particle Hydrodynamics (SPH) processors. The numerical results are compared and discussed with the corresponding experimental results from the standpoint of assessing the protection of satellites against M/OD hypervelocity impacts. The material models used in the numerical simulation are also discussed, as well as a wide range of impact velocities, including shock-induced vaporization. The projectiles used to simulate M/OD consist of 100 μm to 1 mm diameter alumina with impact velocities of 2–15 km/s. In order to assess the structural integrity of unmanned spacecraft subjected to the threat of hypervelocity impact by space debris, the numerical method was proposed mainly from the standpoint of material modeling suitable for extremely severe physical conditions such as high pressure, high temperature, high strain, and high strain rate, sometimes accompanied by shock-induced vaporization. The numerical results adopting these material models were compared with the corresponding hypervelocity impact tests by using the two-stage light-gas gun at ISAS/JAXA. Although examples of the impacts on the aluminum honeycomb can be shown, it has been demonstrated that the numerical analysis can effectively simulate the overall corresponding experimental results. We show the response of an aluminum honeycomb as derived from analysis of hypervelocity impact at 2 km/s to 15 km/s using the Lagrange and SPH processors. We also verified that the ballistic limit curve of an aluminum honeycomb panel is shown as a downward line using both processors, which is unlike the up and down ballistic limit curve of a Whipple shield.

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