Stability Analysis of an Initially Inclined Ship in Following Sea

2000 ◽  
Vol 67 (4) ◽  
pp. 717-719 ◽  
Author(s):  
S. K. Lee
Keyword(s):  
Computer Simulation ◽  
Stability Analysis ◽  
Longitudinal Wave ◽  
Roll Motion ◽  
Parametric Oscillation ◽  
Loss Of Stability ◽  
Longitudinal Waves ◽  
Analytic Expression ◽  
Ship Capsizing

Generally speaking, the causes of ship capsizing in waves are due to the pure loss of stability, parametric oscillation, and broaching-to phenomenon. In this paper, an analytic expression for the GZ value of a ship, inclined initially by some reasons like damage in longitudinal waves, is derived. And, the roll motion is calculated through the computer simulation to give the necessary information for the safe regions of various parameters of a ship moving in a longitudinal wave. [S0021-8936(00)00704-2]

ON THE INFLUENCE OF THE SIZE OF FLAKE GRAPHITE INCLUSIONS AND ITS VOLUME CONTENT ON THE ACOUSTIC PARAMETERS OF CAST IRON AND THE CHARACTERISTICS OF ULTRASONIC LONGITUDINAL WAVE SIGNALS

2021 ◽  
pp. 4-15
Author(s):  
V. N. Danilov ◽  
L. V. Voronkova
Keyword(s):  
Computer Simulation ◽  
Cast Iron ◽  
Longitudinal Wave ◽  
Attenuation Coefficient ◽  
Volume Content ◽  
Phased Array ◽  
Flake Graphite ◽  
Layered Model ◽  
Linear Probe ◽  
Graphite Inclusions

Algorithms have been presented for calculating the velocity (in the approximation of a fine-layered model) and the attenuation coefficient of a longitudinal ultrasonic wave in cast iron, depending on the average size of graphite elements and its volume content, the calculation results for which are qualitatively confirmed experimentally. The calculation was performed using a fine-layered model of the structure, the graphite inclusions were described in the form of plane-parallel layers placed in an isotropic elastic medium (metal base). Computer simulation of acoustic paths for a mediumcast iron with flake graphite for standard direct converters is carried out in order to study the influence of such a medium on the characteristics of transmitted and received signals during ultrasonic testing. In the course of the research, a previously developed model was used to calculate the attenuation coefficient of longitudinal waves in cast iron with flake graphite due to their Rayleigh and phase scattering on graphite inclusions. Computer simulation of the acoustic characteristics of the signals of a direct linear probe with a phased array in cast iron with flake graphite was carried out, during which the shape of the acoustic pulses of the longitudinal wave was calculated, depending on the distance traveled by the wave and the value of the attenuation coefficient for various models of cast iron. The main modeled characteristics of the transducer include the directivity characteristic and the change in the signal amplitude along the acoustic axis. It is shown that for cast iron with flake graphite, there are cases when the directivity of the probe with a phased array transmitted into the cast iron is practically absent.

Numerical simulation of internal defect imaging with the longitudinal wave generated by laser induced ultrasonic array

2020 ◽  
pp. 2150103
Author(s):  
Hao Sui ◽  
Kesi Li ◽  
Zhenyu Zhu ◽  
Le Cheng ◽  
Xiaorong Gao ◽  
...  
Keyword(s):  
Longitudinal Wave ◽  
Phased Arrays ◽  
Synthetic Aperture ◽  
Wave Component ◽  
The Finite Element Method ◽  
Internal Defect ◽  
Longitudinal Waves ◽  
Synthetic Aperture Focusing ◽  
Synthetic Aperture Focusing Technique ◽  
Defect Imaging

To verify the performance of longitudinal waves induced by laser phased arrays (LPA) for detection and quantitative evaluation in internal defects, the finite element method (FEM) is utilized to establish the models of LPA scanning processing. The interaction of longitudinal wave and internal defect is analyzed. Besides, the two components of the reflected longitudinal waves (the longitudinal wave component [Formula: see text] and the shear wave component [Formula: see text] are focused on the imaging of defects with the synthetic aperture focusing technique (SAFT) and total focusing method (TFM) algorithms. It shows that the imaging of internal sub-millimeter defect is obtained using the LPA. The defect size and location are simultaneously calculated, with the relative error being 6.7% and 2.9%, respectively. The proposed longitudinal wave-based LPA is a promising method for the imaging and evaluation of internal micro defects.

scholarly journals A Study on Fatigue State Evaluation of Rail by the Use of Ultrasonic Nonlinearity

Materials ◽  
2019 ◽  
Vol 12 (17) ◽  
pp. 2698
Author(s):  
Bo Zhu ◽  
Jaesun Lee
Keyword(s):  
Longitudinal Wave ◽  
Second Harmonic ◽  
Early Stage ◽  
Wave Mixing ◽  
Third Harmonic ◽  
Longitudinal Waves ◽  
Testing Method ◽  
State Evaluation ◽  
Stress Fatigue ◽  
Train Safety

Nonlinear ultrasonic testing has been accepted as a promising manner for evaluating material integrity in an early stage. Stress fatigue is the main threats to train safety, railways examinations for stress fatigue are more significant and necessary. A series of ultrasonic nonlinear wave experiments are conducted for rail specimens extracted from railhead with different degree of fatigue produced by three-point bent loading condition. The nonlinear parameter is the indicator of nonlinear waves for expressing the degree the fatigue. The experimental results show that the sensitivity of a third harmonic longitudinal wave is higher than second harmonic longitudinal wave testing. As the same time, collinear wave mixing shows strong relative with fatigue damages than a second longitudinal wave nondestructive testing (NDT) method and provides more reliable results than third harmonic longitudinal waves nonlinear testing method.

Stability of reaction-diffusion fronts

1994 ◽  
Vol 446 (1928) ◽  
pp. 517-528 ◽  
Keyword(s):  
Growth Rate ◽  
Diffusion Coefficient ◽  
Stability Analysis ◽  
Linear Stability Analysis ◽  
Reaction Rate ◽  
Reaction Diffusion ◽  
Two Dimensional ◽  
Isothermal Reaction ◽  
Analytic Expression ◽  
Cubic Autocatalysis

Horvath, Petrov, Scott and Showalter (1993) have shown that isothermal reaction-diffusion fronts with cubic autocalysis are linearly unstable to two-dimensional disturbances if the ratio, δ , of the diffusion coefficient of the reactant to that of the autocatalyst, is sufficiently large. However, they were only able to obtain an analytic expression for the growth rate by assuming an infinitely thin reaction zone, which is a poor approximation for cubic autocatalysis. We have carried out a linear stability analysis of such fronts with a finite reaction rate, and find that the critical δ for instability is unchanged, but the range of unstable wavenumbers is larger and increases rather than decreases with δ .

The Evaluation of Agreement Between Dynamics of Electric Wheelchair and Human Behavior

2004 ◽  
Vol 16 (4) ◽  
pp. 434-442 ◽  
Author(s):  
Shigenobu Shimada ◽  
◽  
Kosei Ishimura ◽  
Mitsuo Wada ◽  
Keyword(s):  
Mathematical Model ◽  
Computer Simulation ◽  
Stability Analysis ◽  
Human Behavior ◽  
User Behavior ◽  
Electric Wheelchair ◽  
Straight Line ◽  
Almost All

We studied the problem of interaction of movement between the electric wheelchair and the user. Almost all current products have indexes such as roll stability and operability, but such indexes do not always agree with user behavior because such indexes are static. Another problem arises from the fact that the disagreement of movement causes uncontrollable situations and turnover of the wheelchairs. We evaluated wheelchairs that consider user behavior, first in an experiment to understand the cause of disagreement among users during movement by measuring straight line ands turning, then, based on this result, derived a mathematical model for disagreement in wheelchair motion. Computer simulation, showed that vibration occurred within certain parameters. We present simple roll stability analysis of wheelchairs turning. Simulation confirmed the viability of our proposals.

Coupled Nonlinear Barge Motions, Part II: Stochastic Models and Stability Analysis

2005 ◽  
Vol 127 (2) ◽  
pp. 83-95 ◽  
Author(s):  
Solomon C. S. Yim ◽  
Tongchate Nakhata ◽  
Erick T. Huang
Keyword(s):  
Stability Analysis ◽  
Stochastic Stability ◽  
First Passage Time ◽  
Passage Time ◽  
Computational Effort ◽  
Degree Of Freedom ◽  
Solution Technique ◽  
Roll Motion ◽  
Wave Elevation ◽  
Stochastic Stability Analysis

A computationally efficient quasi-two-degree-of-freedom (Q2DOF) stochastic model and a stability analysis of barges in random seas are presented in this paper. Based on the deterministic 2DOF coupled roll-heave model with high-degree polynomial approximation of restoring forces and moments developed in Part I, an attempt is made to further reduce the DOF of the model for efficient stochastic stability analysis by decoupling the heave effects on roll motion, resulting in a one-degree-of-freedom (1DOF) roll-only model. Using the Markov assumption, stochastic differential equations governing the evolution of probability densities of roll-heave and roll responses for the two low-DOF models are derived via the Fokker-Planck formulation. Numerical results of roll responses for the 2DOF and 1DOF models, using direct simulation in the time domain and the path integral solution technique in the probability domain, are compared to determine the effects of neglecting the influence of heave on roll motion and assess the relative computational efforts required. It is observed that the 1DOF model is computationally very efficient and the 2DOF model response predictions are quite accurate. However, the nonlinear roll-heave coupling is found to be significant and needs to be directly taken into account, rendering the 1DOF roll-only model inadequate for practical use. The 2DOF model is impractical for long-duration real-time response computation due to the insurmountable computational effort required. By taking advantage of the observed strong correlation between measured heave and wave elevation in the experimental results, an accurate and efficient Q2DOF model is developed by expressing the heave response in the 2DOF model as a function of wave elevation, thus reducing the effective DOF to unity. This Q2DOF model is essential as it reduces the computational effort by a factor of 10−5 compared to that of the 2DOF model, thus making practical stochastic analysis possible. A stochastic stability analysis of the barge under operational and survival sea states specified by the U.S. Navy is presented using the Q2DOF model based on first passage time formulation.

scholarly journals Propagation of Plane Waves in a Thermally Conducting Mixture

2011 ◽  
Vol 2011 ◽  
pp. 1-12
Author(s):  
Baljeet Singh
Keyword(s):  
Free Surface ◽  
Longitudinal Wave ◽  
Plane Waves ◽  
Generalized Thermoelasticity ◽  
Elastic Solid ◽  
Reflection Coefficients ◽  
Governing Equations ◽  
Transverse Waves ◽  
Longitudinal Waves ◽  
Thermally Conducting

The governing equations for generalized thermoelasticity of a mixture of an elastic solid and a Newtonian fluid are formulated in the context of Lord-Shulman and Green-Lindsay theories of generalized thermoelasticity. These equations are solved to show the existence of three coupled longitudinal waves and two coupled transverse waves, which are dispersive in nature. Reflection from a thermally insulated stress-free surface is considered for incidence of coupled longitudinal wave. The speeds and reflection coefficients of plane waves are computed numerically for a particular model.

Probabilistic Approach to Stability Analysis of a Reinforced Concrete Retaining Wall

2014 ◽  
Vol 1079-1080 ◽  
pp. 248-251
Author(s):  
David Pustka
Keyword(s):  
Computer Simulation ◽  
Monte Carlo ◽  
Reinforced Concrete ◽  
Stability Analysis ◽  
Structural Optimization ◽  
Reliability Analysis ◽  
Retaining Wall ◽  
Rapid Development ◽  
Probabilistic Approach ◽  
Simulation Monte Carlo

Rapid development of computer technologies brings possibility to exploitpowerful computers for reliability analysis of (civil) engineering structuresunder consideration of random properties of various quantities influencingtheir resulting reliabilities. Aim of this paper is to outline possibility ofutilization of computer simulation Monte Carlo to predict reliability of areinforced concrete retaining wall from the viewpoint of possible loss ofstability. One of advantages of this approach is possibility to quantifyprobability of failure allowing structural optimization leading to design ofmore effective structures.

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