Roll of a Ship in Astern Seas—Response to GM Fluctuations

1989 ◽  
Vol 33 (04) ◽  
pp. 284-290
Author(s):  
A. Bruce Dunwoody
Keyword(s):  
Numerical Simulations ◽  
Narrow Band ◽  
Wide Band ◽  
Random Processes ◽  
Roll Motion ◽  
Roll Damping ◽  
Metacentric Height ◽  
Good Agreement

An effect of astern seas on a ship is to produce fluctuations in the metacentric height (GM) of the ship. GM fluctuations are shown to produce an effect analogous to a reduction in the roll damping. Roll damping reductions are predicted for two extreme types of random GM fluctuations: wide-band and narrow-band random processes. Numerical simulations of the roll motion of a ship with realistic random GM fluctuations are used to compare with the predictions of damping reduction. Good agreement is found. Implications of a reduced roll damping are discussed.

The penetration and ricochet of ogive-nosed rigid projectiles obliquely impacting metallic targets

2021 ◽  
pp. 204141962110377
Author(s):  
Yaniv Vayig ◽  
Zvi Rosenberg
Keyword(s):  
Experimental Data ◽  
Numerical Simulations ◽  
Dynamic Pressure ◽  
Oblique Impacts ◽  
Simulation Results ◽  
The Impact ◽  
Penetration Depths ◽  
Resistance To Penetration ◽  
Good Agreement

A large number of 3D numerical simulations were performed in order to follow the trajectory changes of rigid CRH3 ogive-nosed projectiles, impacting semi-infinite metallic targets at various obliquities. These trajectory changes are shown to be related to the threshold ricochet angles of the projectile/target pairs. These threshold angles are the impact obliquities where the projectiles end up moving in a path parallel to the target’s face. They were found to depend on a non-dimensional entity which is equal to the ratio between the target’s resistance to penetration and the dynamic pressure exerted by the projectile upon impact. Good agreement was obtained by comparing simulation results for these trajectory changes with experimental data from several published works. In addition, numerically-based relations were derived for the penetration depths of these ogive-nosed projectiles at oblique impacts, which are shown to agree with the simulation results.

Free and Forced Vibrations of the Strongly Nonlinear Cubic-Quintic Duffing Oscillators

2017 ◽  
Vol 72 (1) ◽  
pp. 59-69 ◽  
Author(s):  
M.M. Fatih Karahan ◽  
Mehmet Pakdemirli
Keyword(s):  
Numerical Simulations ◽  
Numerical Solutions ◽  
Multiple Scales ◽  
Approximate Solutions ◽  
Response Curves ◽  
Strongly Nonlinear ◽  
Free And Forced Vibrations ◽  
Approximate Analytical Solutions ◽  
Strongly Nonlinear Oscillators ◽  
Good Agreement

AbstractStrongly nonlinear cubic-quintic Duffing oscillatoris considered. Approximate solutions are derived using the multiple scales Lindstedt Poincare method (MSLP), a relatively new method developed for strongly nonlinear oscillators. The free undamped oscillator is considered first. Approximate analytical solutions of the MSLP are contrasted with the classical multiple scales (MS) method and numerical simulations. It is found that contrary to the classical MS method, the MSLP can provide acceptable solutions for the case of strong nonlinearities. Next, the forced and damped case is treated. Frequency response curves of both the MS and MSLP methods are obtained and contrasted with the numerical solutions. The MSLP method and numerical simulations are in good agreement while there are discrepancies between the MS and numerical solutions.

scholarly journals Numerical Simulations of V-Shaped Plates Subjected to Blast Loadings: A Validation Study

2016 ◽  
Vol 10 (11) ◽  
pp. 203
Author(s):  
Mohd Zaid Othman ◽  
Qasim H. Shah ◽  
Muhammad Akram Muhammad Khan ◽  
Tan Kean Sheng ◽  
M. A. Yahaya ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Numerical Simulations ◽  
Variable Mass ◽  
Blast Loading ◽  
Experimental Results ◽  
Average Difference ◽  
Simulation Results ◽  
Blast Loadings ◽  
Carrier Vehicle ◽  
Good Agreement

A series of numerical simulations utilizing LS-DYNA was performed to determine the mid-point deformations of V-shaped plates due to blast loading. The numerical simulation results were then compared with experimental results from published literature. The V-shaped plate is made of DOMEX 700 and is used underneath an armour personal carrier vehicle as an anti-tank mine to mitigate the effects of explosion from landmines in a battlefield. The performed numerical simulations of blast loading of V-shaped plates consisted of various angles i.e. 60°, 90°, 120°, 150° and 180°; variable mass of explosives located at the central mid-point of the V-shaped vertex with various stand-off distances. It could be seen that the numerical simulations produced good agreement with the experimental results where the average difference was about 26.6%.

The transient start of supersonic jets

2007 ◽  
Vol 578 ◽  
pp. 331-369 ◽  
Author(s):  
MATEI I. RADULESCU ◽  
CHUNG K. LAW
Keyword(s):  
Numerical Simulations ◽  
Ambient Air ◽  
Hydrogen Gas ◽  
Shock Interactions ◽  
Round Jets ◽  
Reactive Gases ◽  
Acoustic Instabilities ◽  
Diffusive Fluxes ◽  
Experimental Findings ◽  
Good Agreement

This study investigates the initial transient hydrodynamic evolution of highly under-expanded slit and round jets. A closed-form analytic similarity solution is derived for the temporal evolution of temperature, pressure and density at the jet head for vanishing diffusive fluxes, generalizing a previous model of Chekmarev using Chernyi's boundary-layer method for hypersonic flows. Two-dimensional numerical simulations were also performed to investigate the flow field during the initial stages over distances of ~ 1000 orifice radii. The parameters used in the simulations correspond to the release of pressurized hydrogen gas into ambient air, with pressure ratios varying between approximately 100 and 1000. The simulations confirm the similarity laws derived theoretically and indicate that the head of the jet is laminar at early stages, while complex acoustic instabilities are established at the sides of the jet, involving shock interactions within the vortex rings, in good agreement with previous experimental findings. Very good agreement is found between the present model, the numerical simulations and previous experimental results obtained for both slit and round jets during the transient establishment of the jet. Criteria for Rayleigh–Taylor instability of the decelerating density gradients at the jet head are also derived, as well as the formulation of a model addressing the ignition of unsteady expanding diffusive layers formed during the sudden release of reactive gases.

Spread-of-Masking Effects on Pure Tones and Several Speech Stimuli

1973 ◽  
Vol 16 (3) ◽  
pp. 385-396
Author(s):  
Richard H. Wilson ◽  
Richard W. Stream ◽  
Donald D. Dirks
Keyword(s):  
Pure Tone ◽  
Narrow Band ◽  
Wide Band ◽  
Intensity Level ◽  
Speech Stimuli ◽  
Intensity Range ◽  
Speech Spectrum ◽  
Series Of Experiments ◽  
Pure Tones ◽  
Upper Slope

A series of experiments was performed to study the upward-spread-of-masking phenomena as it pertains to pure-tone and speech stimuli. In the initial two experiments, three maskers were employed over a 40–60-dB intensity range. They included a wide band (50–5500 Hz), a speech spectrum (50–1000 Hz), and a narrow-band (50–950 Hz) noise. All filter slopes were 48 dB/octave, except for the upper slope of the speech-spectrum noise that was 6 dB/octave. In the first experiment, pure-tone thresholds obtained by a tracking procedure revealed no spread of masking when the wide-band and speech-spectrum maskers were used. Substantial spread-of-masking effects, characterized by nonlinear threshold increments outside the spectrum of the masker, were observed with the narrow-band masker. The second experiment included three types of speech stimuli (PBs, spondees, and synthetic sentences) under the same mask conditions used with the pure tones. Threshold shifts observed for the wide- and speech-spectrum maskers were linear with the masking intensity level. However, increased shifts, attributable to spread of masking, were observed with the narrow band and progressed nonlinearly as a function of the masking level. Finally, two additional experiments, performed with two different narrow-band maskers and spondee words, provided insightful information regarding the effects of the spread of masking on speech stimuli.

scholarly journals A Useful Manufacturing Guide for Rotary Piercing Seamless Pipe by ALE Method

2020 ◽  
Vol 8 (10) ◽  
pp. 756
Author(s):  
Ameen Topa ◽  
Burak Can Cerik ◽  
Do Kyun Kim
Keyword(s):  
Numerical Simulations ◽  
Maximum Stress ◽  
Three Dimensional ◽  
Material Model ◽  
Manufacturing Processes ◽  
Arbitrary Lagrangian Eulerian ◽  
Analysis Method ◽  
Seamless Pipe ◽  
Ale Formulation ◽  
Good Agreement

The development of numerical simulations is potentially useful in predicting the most suitable manufacturing processes and ultimately improving product quality. Seamless pipes are manufactured by a rotary piercing process in which round billets (workpiece) are fed between two rolls and pierced by a stationary plug. During this process, the material undergoes severe deformation which renders it impractical to be modelled and analysed with conventional finite element methods. In this paper, three-dimensional numerical simulations of the piercing process are performed with an arbitrary Lagrangian–Eulerian (ALE) formulation in LS-DYNA software. Details about the material model as well as the elements’ formulations are elaborated here, and mesh sensitivity analysis was performed. The results of the numerical simulations are in good agreement with experimental data found in the literature and the validity of the analysis method is confirmed. The effects of varying workpiece velocity, process temperature, and wall thickness on the maximum stress levels of the product material/pipes are investigated by performing simulations of sixty scenarios. Three-dimensional surface plots are generated which can be utilized to predict the maximum stress value at any given combination of the three parameters.

scholarly journals Temperature Robust PCA Based Stress Monitoring Approach

2016 ◽  
Vol 713 ◽  
pp. 288-292 ◽  
Author(s):  
Jabid Quiroga ◽  
John Quiroga ◽  
Luis Mujica ◽  
Rodolfo Villamizar ◽  
Magda Ruiz
Keyword(s):  
Statistical Model ◽  
Numerical Simulations ◽  
Environmental Conditions ◽  
Guided Wave ◽  
Stress Monitoring ◽  
Robust Pca ◽  
Different Temperatures ◽  
Stress States ◽  
Good Agreement

In this paper, a guided wave temperature robust PCA-based stress monitoring methodology is proposed. It is based on the analysis of the longitudinal guided wave propagating along the path under stress. Slight changes in the wave are detected by means of PCA via statistical T2 and Q indices. Experimental and numerical simulations of the guided wave propagating in material under different temperatures have shown significant variations in the amplitude and the velocity of the wave. This condition can jeopardize the discrimination of the different stress scenarios detected by the PCA indices. Thus, it is proposed a methodology based on an extended knowledge base, composed by a PCA statistical model for different discrete temperatures to produce a robust classification of stress states under variable environmental conditions. Experimental results have shown a good agreement between the predicted scenarios and the real ones

Full-Spectrum k-Distribution Model for Radiation in Gas Based on Multi-Group Methods

2014 ◽  
Vol 1008-1009 ◽  
pp. 839-845
Author(s):  
Yue Zhou ◽  
Qiang Wang ◽  
Hai Yang Hu
Keyword(s):  
Narrow Band ◽  
Wide Band ◽  
Distribution Model ◽  
Full Spectrum ◽  
Distribution Method ◽  
One Dimensional ◽  
Group Methods ◽  
Monotonically Increasing Function ◽  
Homogeneous Media ◽  
Increasing Function

The k-distribution method applied in narrow band and wide band is extended to the full spectrum based on spectroscopic datebase HITEMP, educing the full-spectrum k-distribution model. Absorption coefficents in this model are reordered into a smooth,monotonically increasing function such that the intensity calculations are performed only once for each absorption coefficent value and the resulting computations are immensely more efficent.Accuracy of this model is examined for cases ranging from homogeneous one-dimensional carbon dioxide to inhomogeneous ones with simultaneous variations in temperature. Comparision with line-by-line calculations (LBL) and narrow-band k-distribution (NBK) method as well as wide-band k-distribution (WBK) method shows that the full-spectrum k-distribution model is exact for homogeneous media, although the errors are greater than the other two models. After dividing the absorption coefficients into several groups according to their temperature dependence, the full-spectrum k-distribution model achieves line-by-line accuracy for gases inhomogeneous in temperature, accompanied by lower computational expense as compared to NBK model or WBK model. It is worth noting that a new grouping scheme is provided in this paper.

A Differential UWB Quasi-Yagi Antenna with A Reconfigurable Notched Band

Frequenz ◽  
2018 ◽  
Vol 72 (9-10) ◽  
pp. 401-406 ◽  
Author(s):  
Feng Wei ◽  
Xin Tong Zou ◽  
Xin Yi Wang ◽  
Bin Li ◽  
Xi Bei Zhao
Keyword(s):  
Microstrip Line ◽  
Design Procedure ◽  
Wide Band ◽  
Impedance Bandwidth ◽  
Differential Mode ◽  
Transition Structure ◽  
Notched Band ◽  
Quarter Wavelength ◽  
Yagi Antenna ◽  
Good Agreement

Abstract A compact differential ultra-wide band (UWB) planar quasi-Yagi antenna is presented in this paper. The proposed antenna consists of a balanced stepped-impedance microstrip-slotline transition structure, a driver dipole and one parasitic strip. A wide differential-mode (DM) impedance bandwidth covering from 3.8 to 9.5 GHz is realized. Meanwhile, a high and wideband common-mode (CM) suppression can be achieved by employing the balanced stepped-impedance microstrip-slotline transition structure. It is noted that the DM passband is independent from the CM response, which can significantly simplify the design procedure. In addition, a reconfigurable sharp DM notched band from 5.6 to 6.7 GHz is generated by adding one pair of quarter-wavelength varactor-loaded short-circuited stubs adjacent to the microstrip line symmetrically. In order to illustrate the effectiveness of the design, two prototypes of the antennas are designed, fabricated, and measured. A good agreement between the simulated and measured results is observed.

Sign in / Sign up

Export Citation Format

Share Document