The Air-Water Sloshing Problem: Parametric Studies on Excitation Magnitude and Frequency

2008 ◽  
Author(s):  
P. von Bergheim ◽  
K. P. Thiagarajan
Keyword(s):  
Excitation Amplitude ◽  
Linear Potential ◽  
Flow Models ◽  
Closed Form Solutions ◽  
Pressure Time ◽  
Parametric Studies ◽  
Linear Potential Theory ◽  
Dynamic Meshing ◽  
The Impact ◽  
Good Agreement

The problem of liquid sloshing has gained recent attention with the proliferation of liquefied natural gas (LNG) transport in partially filled tanks of a tanker vessel. In this paper, we first present the rudiments of a linear potential theory for sloshing motions in a two-dimensional rectangular tank due to small amplitude sway motions. We obtain closed form solutions for the Response Amplitude Operator (RAO) of slosh amplitude as a function of frequency. Then we present the computational fluid dynamics (CFD) formulation of the problem using dynamic meshing features. The CFD results for RAO are compared with theory, and good agreement is noticed. The impact pressure time series is compared with published experimental data, and good agreement is seen. Contrary to common observations, we notice that turbulent flow models give better and more accurate results than laminar models. CFD simulations are then performed for a range of excitation amplitudes and frequencies. Pressure contours and water surface elevation are monitored as function of excitation amplitude and frequency, and the regions of impacting vs. non-impacting are delineated.

Numerical Analysis on the Response of Deck Plates Laterally Impacted by a Rectangular Indenter

2018 ◽  
Author(s):  
Ling Zhu ◽  
Junying Gao ◽  
Yinggang Li
Keyword(s):  
Permanent Deformation ◽  
Dynamic Loads ◽  
Parametric Studies ◽  
Ice Floes ◽  
Maximum Impact Force ◽  
Impact Energies ◽  
The Impact ◽  
Deformation Modes ◽  
Theoretical Procedure ◽  
Good Agreement

Ship deck plates are often subjected to localized dynamic loads, such as the loads of landing helicopter or impacts of ice floes. In order to investigate the dynamic response of ship plates subjected to such dynamic loads, a series of numerical simulations are performed on ship plates with different thicknesses. Parametric studies are performed on the impact response of plates, including the thickness of the plates, mass and impact velocity of the rectangular indenter. The maximum permanent deflections of the plates are obtained during the simulation. The relation between maximum force and permanent deflection is obtained and the deformation modes are analyzed. A theoretical procedure is developed to predict the deformation of plates with different initial impact energies, and a good agreement between the theoretical and numerical results is obtained. It has also been observed that the thickness of plates has little effect on the dimensionless maximum permanent deformation and dimensionless maximum impact force.

Time-variant characteristic under the piston wind on subway tunnel billboard

2019 ◽  
Vol 233 (16) ◽  
pp. 5637-5646
Author(s):  
Guixin Han ◽  
Zhong Luo ◽  
Yonghang Sun ◽  
Chaoshuai Li
Keyword(s):  
Uniform Distribution ◽  
Static Pressure ◽  
Wind Pressure ◽  
Experimental Result ◽  
Subway Tunnel ◽  
Pressure Time ◽  
Practical Engineering ◽  
Left And Right ◽  
Dynamic Meshing ◽  
Good Agreement

The study of the time-variant characteristic on billboards caused by the piston wind deals with the issue of the billboards falling out in the subway tunnel. A method of a full-scale physical model and the corresponding numerical model are established, and the dynamic meshing deformation to simulate the metro runs in the tunnel was used, where good agreement between the simulation result and the experimental result was achieved proving the model to be correct. On this basis, the flow field in the actual subway tunnel is simulated, and the wind pressure time-variant characteristic on the billboards is analyzed. The results demonstrate that the static pressure on the billboard surface goes through a series of changes: “uniform distribution – left and right gradient – up and down gradient – uniform distribution”. The billboard’s upper right corner of the driving direction is subjected to the largest pressure and hence most vulnerable to damage. This method can provide guidance to the installation and maintenance of billboards in practical engineering applications.

Bursting water balloons

2014 ◽  
Vol 756 ◽  
pp. 771-815 ◽  
Author(s):  
Hugh M. Lund ◽  
Stuart B. Dalziel
Keyword(s):  
High Speed ◽  
Shear Instability ◽  
High Speed Photography ◽  
Linear Potential ◽  
Scale Growth ◽  
Restoring Force ◽  
Interfacial Growth ◽  
Linear Potential Theory ◽  
The Impact ◽  
Asymptotic Growth Rate

AbstractThe impact and rupture of a water-filled latex balloon on a flat, rigid surface is investigated using high-speed photography. Three distinct stages of the flow are observed, for which physical explanations are given. As the balloon lands and deforms, waves are formed on the balloon’s surface for which the restoring force is tension in the latex. These waves are shown to closely obey linear potential theory for constant surface tension. Should the balloon rupture, a crack forms, from which the membrane retracts. Spray is simultaneously ejected from the water’s surface, a consequence of a shear instability in the wake behind the retracting membrane. At later times, a larger-scale growth of the interfacial amplitude is observed, for which the generation mechanism is momentum in the water due to the preburst waves. However, it is argued that this is also a manifestation of the same mechanism that drives Richtmyer–Meshkov instability (RMI). Further, it is shown experimentally that this growth of the interface may also occur when there is no density difference across the balloon, a situation that does not arise for the standard RMI. An analytical model is then derived to predict the interfacial growth for such an interface, and is shown to predict the asymptotic growth rate of the interface accurately.

Probability-based cumulative damage assessment of structures subjected to non-stationary repeated loads

2017 ◽  
Vol 20 (11) ◽  
pp. 1784-1790 ◽  
Author(s):  
Cao Wang ◽  
Hao Zhang
Keyword(s):  
Structural Damage ◽  
Structural Reliability ◽  
Limit State ◽  
Mean Value ◽  
Cumulative Damage ◽  
Occurrence Rate ◽  
Closed Form Solutions ◽  
Parametric Studies ◽  
The Impact ◽  
External Loads

In-service civil structures are often subjected to repeated external loads (shock events), which may lead to an accumulation of structural damage and further an increase in the probability of structural failure. The shock actions are by nature stochastic with randomness arising from their intensities and occurrence times. A varying trend in future intensity and/or occurrence rate of many types of shock action has been projected in the literature, such as cyclone actions due to the potential impact of climate change. This article proposes a method to assess the structural reliability in the presence of uncertainty and non-stationarity in external shock events, with a limit state that the cumulative damage exceeds the permissible level. The mean value and variance of the cumulative damage are estimated with proposed closed-form solutions, and the gamma distribution is suggested to describe the probabilistic characteristics of the cumulative damage, whose accuracy is verified through a comparison with Monte Carlo simulation. Furthermore, the cumulative density function of structural service life is derived explicitly. Parametric studies are conducted to investigate the impact of non-stationarity in shock actions on structural reliability.

Non-Linear Run-Up on a Vertical Surface-Piercing Cylinder

2004 ◽  
Author(s):  
C. H. Retzler ◽  
R. C. T. Rainey ◽  
J. R. Chaplin
Keyword(s):  
Vertical Surface ◽  
Linear Potential ◽  
Spatial Frequencies ◽  
Wide Range ◽  
Non Linear ◽  
Leading Term ◽  
Temporal And Spatial ◽  
Run Up ◽  
Linear Potential Theory ◽  
Good Agreement

This paper presents and analyses results of experiments in which a vertical surface-piercing cylinder was driven with a horizontal motion a cos ωt in water initially at rest. Using a novel system of 112 water surface elevation gauges that were monitored almost simultaneously at high frequency, measurements were made of the run-up on the cylinder over a wide range of conditions. According to linear theory, the run-up is of the form a cos ωt cos θ. Non-linear components at temporal and spatial frequencies up to the 3rd harmonic were identified in the measurements, and in some of these, the coefficient of the leading term in a polynomial expansion in the amplitude of motion could be computed with reasonable confidence. Very successful comparisons are made with conventional linear potential theory. Some features of the free surface motion that are normally associated with higher order solutions were also computed from the first-order potential, and in some respects they were in good agreement with the measurements.

Water waves in shallow channels of rapidly varying depth

1992 ◽  
Vol 241 ◽  
pp. 311-332 ◽  
Author(s):  
A. Nachbin ◽  
G. C. Papanicolaou
Keyword(s):  
Shallow Water Equations ◽  
Water Waves ◽  
Water Wave ◽  
Wave Equations ◽  
Linear Potential ◽  
Reflected Waves ◽  
Time Harmonic ◽  
Linear Potential Theory ◽  
Vertical Scales ◽  
Good Agreement

We analyse the linear water-wave equations for shallow channels with arbitrary rapidly varying bottoms. We develop a theory for reflected waves based on an asymptotic analysis for stochastic differential equations when both the horizontal and vertical scales of the bottom variations are comparable to the depth but small compared to a typical wavelength so the shallow water equations cannot be used. We use the full, linear potential theory and study the reflection–transmission problem for time-harmonic (monochromatic) and pulse-shaped disturbances. For the monochromatic waves we give a formula for the expected value of the transmission coefficient which depends on depth and on the spectral density of the O(1) random depth perturbations. For the pulse problem we give an explicit formula for the correlation function of the reflection process. We compare our theory with numerical results produced using the boundary-element method. We consider several realizations of the bottom profile, let a Gaussian-shaped disturbance propagate over each topography sampled and record the reflected signal for each realization. Our numerical experiments produced reflected waves whose statistics are in good agreement with the theory.

Modeling of Tread Block Contact Mechanics Using Linear Viscoelastic Theory3

2008 ◽  
Vol 36 (3) ◽  
pp. 211-226 ◽  
Author(s):  
F. Liu ◽  
M. P. F. Sutcliffe ◽  
W. R. Graham
Keyword(s):  
High Speed ◽  
Slip Rate ◽  
Material Model ◽  
Contact Forces ◽  
Block Modeling ◽  
Rate Dependent ◽  
Linear Viscoelastic Material ◽  
Linear Viscoelastic ◽  
The Impact ◽  
Good Agreement

Abstract In an effort to understand the dynamic hub forces on road vehicles, an advanced free-rolling tire-model is being developed in which the tread blocks and tire belt are modeled separately. This paper presents the interim results for the tread block modeling. The finite element code ABAQUS/Explicit is used to predict the contact forces on the tread blocks based on a linear viscoelastic material model. Special attention is paid to investigating the forces on the tread blocks during the impact and release motions. A pressure and slip-rate-dependent frictional law is applied in the analysis. A simplified numerical model is also proposed where the tread blocks are discretized into linear viscoelastic spring elements. The results from both models are validated via experiments in a high-speed rolling test rig and found to be in good agreement.

Dynamic model for high-speed rotors based on their experimental characterization

2017 ◽  
Vol 2 (4) ◽  
pp. 25
Author(s):  
L. A. Montoya ◽  
E. E. Rodríguez ◽  
H. J. Zúñiga ◽  
I. Mejía
Keyword(s):  
Dynamic Model ◽  
High Speed ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Experimental Characterization ◽  
Rotating Systems ◽  
Computing Performance ◽  
The Impact ◽  
Stiffness Distribution ◽  
Good Agreement

Rotating systems components such as rotors, have dynamic characteristics that are of great importance to understand because they may cause failure of turbomachinery. Therefore, it is required to study a dynamic model to predict some vibration characteristics, in this case, the natural frequencies and mode shapes (both of free vibration) of a centrifugal compressor shaft. The peculiarity of the dynamic model proposed is that using frequency and displacements values obtained experimentally, it is possible to calculate the mass and stiffness distribution of the shaft, and then use these values to estimate the theoretical modal parameters. The natural frequencies and mode shapes of the shaft were obtained with experimental modal analysis by using the impact test. The results predicted by the model are in good agreement with the experimental test. The model is also flexible with other geometries and has a great time and computing performance, which can be evaluated with respect to other commercial software in the future.

scholarly journals Measuring Hydrometeors Using a Precipitation Microphysical Characteristics Sensor: Sampling Effect of Different Bin Sizes on Drop Size Distribution Parameters

2018 ◽  
Vol 2018 ◽  
pp. 1-15 ◽  
Author(s):  
Xichuan Liu ◽  
Taichang Gao ◽  
Yuntao Hu ◽  
Xiaojian Shu
Keyword(s):  
Drop Size ◽  
Rain Rate ◽  
Monte Carlo Model ◽  
Rain Gauge ◽  
Sampling Schemes ◽  
Distribution Parameters ◽  
Optimum Sampling ◽  
Simulation Results ◽  
The Impact ◽  
Good Agreement

In order to improve the measurement of precipitation microphysical characteristics sensor (PMCS), the sampling process of raindrops by PMCS based on a particle-by-particle Monte-Carlo model was simulated to discuss the effect of different bin sizes on DSD measurement, and the optimum sampling bin sizes for PMCS were proposed based on the simulation results. The simulation results of five sampling schemes of bin sizes in four rain-rate categories show that the raw capture DSD has a significant fluctuation variation influenced by the capture probability, whereas the appropriate sampling bin size and width can reduce the impact of variation of raindrop number on DSD shape. A field measurement of a PMCS, an OTT PARSIVEL disdrometer, and a tipping bucket rain Gauge shows that the rain-rate and rainfall accumulations have good consistencies between PMCS, OTT, and Gauge; the DSD obtained by PMCS and OTT has a good agreement; the probability of N0, μ, and Λ shows that there is a good agreement between the Gamma parameters of PMCS and OTT; the fitted μ-Λ and Z-R relationship measured by PMCS is close to that measured by OTT, which validates the performance of PMCS on rain-rate, rainfall accumulation, and DSD related parameters.

scholarly journals Deep Neural Network and Polynomial Chaos Expansion-Based Surrogate Models for Sensitivity and Uncertainty Propagation: An Application to a Rockfill Dam

Water ◽  
2021 ◽  
Vol 13 (13) ◽  
pp. 1830
Author(s):  
Gullnaz Shahzadi ◽  
Azzeddine Soulaïmani
Keyword(s):  
Polynomial Chaos ◽  
Complex Structure ◽  
Uncertainty Propagation ◽  
Surrogate Models ◽  
Polynomial Chaos Expansion ◽  
Soil Parameters ◽  
Chaos Expansion ◽  
Rockfill Dam ◽  
Parametric Studies ◽  
The Impact

Computational modeling plays a significant role in the design of rockfill dams. Various constitutive soil parameters are used to design such models, which often involve high uncertainties due to the complex structure of rockfill dams comprising various zones of different soil parameters. This study performs an uncertainty analysis and a global sensitivity analysis to assess the effect of constitutive soil parameters on the behavior of a rockfill dam. A Finite Element code (Plaxis) is utilized for the structure analysis. A database of the computed displacements at inclinometers installed in the dam is generated and compared to in situ measurements. Surrogate models are significant tools for approximating the relationship between input soil parameters and displacements and thereby reducing the computational costs of parametric studies. Polynomial chaos expansion and deep neural networks are used to build surrogate models to compute the Sobol indices required to identify the impact of soil parameters on dam behavior.

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