The algorithm of Ott, Grebogi and Yorke (OGY) is recognized for its efficiency in controlling chaotic dynamical systems, even if the system’s equations are not known and the input data are provided ...by measured time series in experimental settings. Recently, Santos and Graves (SG) proposed a simple method for estimating the chaos control parameters required by OGY algorithm and applied it to the logistic map. Using only two time series of 100 values, they obtained approximate results for the fixed point case within 2 % of the analytical ones. Although the outputs refer only to a particular case, their conclusion seems to be that the method works as well as in general. To check this statement, we performed a large amount of numerical simulations on different one – dimensional maps. With slight different nuances, our findings were the same so we only presented in the paper the logistic map case. We have noticed that the use of only two short time series implies high risks in a reasonable estimate of the location of the fixed points and of the two control parameters (especially of the second). For large enough number of time series (three or five sets of 400 values each, in the paper) the results provided by numerical simulation approximated the theoretical ones within the limit of a few percent at most. The role played by each method parameter, as the radius for a close encounter of the fixed point or the number of the series and their lengths, is also investigated.
Because the tsunami wavelength is much longer than the sea depth, the propagation of this powerful destructive wave can be modelled by the non-linear shallow water equations (SWEs). To solve ...accurately these hyperbolic partial differential equations, one can resort to a variety of numerical techniques, including finite difference method (FDM) or finite volume method (FVM). In this paper, we have selected FDM, as a well verified instrument on other fluid flow problems, to estimate the tsunami wave propagation in one dimension. The ability of four explicit scheme (Forward Euler, Lax Friedrichs, Mac Cormack and Richtmyer) to solve SWEs was tested on three different test problems. Starting from the idea that a tsunami may begin as a sudden rise of a column of water, the first test represents a square or a sinusoidal pulse which breaks up into two identical waves moving in opposing directions on a constant depth seabed. In the other two test problems we simulate a tsunami wave approaching the shore on a variable seabed depth having either o steady or a highly variable slope. The numerical results allow us to assert that, in general, the used explicit schemes lead to a correct description of a tsunami wave propagation, both offshore and near the coastline. The exception is represented by the Forward Euler scheme that, due to its instability, was only used in the first test.
The sloshing effect of the liquids is considered to be an important factor in area such as cargo ships (tankers) which transporting petroleum liquids or other liquids (water inside of ballast tanks). ...Sloshing can produce big problems so is essential to apply the prevention measures. For example in water ballast tanks, the sloshing motion of sea water inside of ballast tanks will bring large fluid pressures and impact loads, which might destroy the structure of tanks. It is known that ships with larger tanks, less internal structure, and more free surface area, the number of failures attributed to sloshing liquids have increased. Nowadays it is recognized that the ballast tanks which may be partly filled are the crucial group of tanks onboard. The problem of an assessment of liquid sloshing effect is more important than ever because of the obligatory ballast water management requirement. Our paper is an original fluid structure interaction analysis during sloshing phenomenon. We are using ANSYS CFX to simulate the behavior of two fluids, (seawater and air from the ballast tank), requires itself the multiphase flow model. Due to the movement of the ballast/cargo tanks is complex involving pitching and rolling of ship, it is clear that the simulation is done with the ANSYS CFX transient module. Because this complex simulation requires massive resources calculation we consider a simplified CAD models for a part of the oil chemical ballast tank structure.
Parametric roll on ships is a resonance phenomenon whose onset causes heavy roll oscillations leading to dangerous situations for the ship, the cargo and the crew. It affects both small vessels with ...marginal stability and large container ships if four conditions are met simultaneously: the wave length and ship length are approximately equal, the frequency of encounter wave is twice the roll natural frequency, the ship's roll damping is low enough and the wave height exceeds a limit value characteristic to each vessel. A good start to capture the basic features of the parametric roll is to cancel the couplings between roll and the other motions of the ship and to analyse the influence of parameters on the ship stability and the appearance of large roll amplitudes by using one-degree-of-freedom model. By doing this, one realizes that, besides increasing the damping, the roll motion can be stabilized by changing the wave encounter frequency in such a way that the resonance condition is no longer fulfilled. Two parameters mainly affect the encounter frequency: the ship forward velocity and the heading angle. In the paper, we have numerically investigated the effect of increasing or decreasing the forward speed on the roll amplitudes. We followed two strategies. In the first, we allowed the speed to change with a constant acceleration (positive or negative) so that the encounter frequency has left the dangerous region of the resonance. In the second strategy, we changed the forward speed up and down around a value that generates large roll amplitudes, by using different periodic profiles such as sinusoidal, saw tooth or trapezoidal. We noticed that both control techniques generally managed to significantly reduce the roll amplitudes (with a few exceptions). At the same time, we found that very important in how the amplitudes diminish are parameters like the moment of time when the control is activated, the speed rate of change or the period and amplitude of the speed change around the average value (in the second strategy). The data used in the paper have been obtained from experiments with a container ship model in a towing tank followed by expansion to a full scale ship.
In this article the authors realise the study regarding to the behaviour of water ballast tank during sloshing effect. The designing operation of water ballast tank (WBT) was performed using NX ...Siemens. The purposes of this article are to evaluate different stages of sloshing effect when the total pressure exerted by the fluid is changing quickly with time. We simulate using CFX Ansys different complex stages of sloshing inside of WBT without baffle design and stages when WBT has baffle design used to suppressed sloshing effect in an accelerated tank.
Parametric roll on ships is a resonance phenomenon whose onset causes heavy roll oscillations leading to dangerous situations for the ship, the cargo and the crew. It affects both small vessels with ...marginal stability and large container ships if four conditions are met simultaneously: the wave length and ship length are approximately equal, the frequency of encounter wave is twice the roll natural frequency, the ship's roll damping is low enough and the wave height exceeds a limit value characteristic to each vessel. For a container ship, the first two conditions result in a time-varying geometry of the submerged hull and thus to a periodic variation of the transverse stability. In the last two decades, several mathematical models for parametric rolling have been proposed by scientists. In the paper, we cancelled the couplings terms between heave, pitch and roll in a 3 DOF model proposed by Neves and Rodriguez to obtain an uncoupled 1 DOF model for the parametric roll. Even if it seems too simplistic, such a model based on Mathieu type equation is a good start to capture the basic features of the analysed phenomenon. There are no less than seven parameters that can influence the ship stability and the appearance of large roll amplitudes. By modifying two of these parameters one by one and keeping the others constant, a series of colour plots have been drown that capture the role played by the ship's parameters in obtaining dangerous roll amplitudes or too short times to take countermeasures. Analysing the instability regions suggested by these colour plots, one can imagine control measures to reduce the roll amplitudes, such as changing the forward velocity or the heading angle. The data used in the paper have been obtained from experiments with a container ship model in a towing tank followed by expansion to a full scale ship.
Ejectors are common devices on board liquid carrier vessels and meet on both cargo and ballast tanks. The "in-line" ejector presented in this paper is an original model that was designed with NX ...Siemens, using information and technical data from a worldwide supplier of high quality marine products. This paper presents a static analysis of fluid' influence which passing through an ejector on its metal structure using Ansys. From a previous work we took into account the data obtained with CFD (computer fluid dynamic) analysis. The pressure and fluid temperature fields were imported and applied to the meshed ejector model with finite elements, obtaining data on deformations and equivalent stresses and elastic strain.
A short number of steep breaking waves hitting a ship from the side may affect its dynamic behaviour and to determine extreme roll angles and, eventually, capsizing. This last phenomenon is a ...challenging task for naval engineers because it is responsible not only for a lot of material damages, but also for human lives. It is therefore not surprising that there have been published many relevant theoretical and experimental studies on heavy rolling and capsizing but the problem is not yet fully resolved. Generally, the ship rolling in beam regular seas could be described by a second-order non-linear differential equation with the roll angle as dependent variable. Non-linearity comes from the restoring and damping moments, which are usually represented by (odd) polynomials of roll angle or of its time derivative. Numerical integrators incorporated in modern software packages (e.g. ode45 in Matlab) encounter efficiency problems for the unbounded solutions associated with capsizing, the running time being extremely high. The alternative is to write a computer software, appropriate to the topic to be solved. In the paper, the roll equation was solved using a simple, fast and accurate iterative scheme based on Taylor expansion. Compared with Runge-Kutta 4th order numerical technique, the used scheme demonstrated not only an excellent agreement of the results, but also a significant reduction of the CPU time. The rapidity of the scheme allowed us to conduct a comprehensive investigation on fractal erosion of safe basins and to represent the normalized integrity curves and the amplitude-frequency response curves for different combinations of wave parameters. The restoring and damping coefficients corresponded to a vehicle ferry model, considered to be either intact or damaged, on the one hand, and with or without bilge keels, on the other.
Heat exchangers are common devices on board' ships, but also in the oil-chemical industry. In this paper is presented an U-tube heat-exchanger that was designed with NX Siemens. The component parts ...of this heat exchanger, the CAD models and their assembly mode in the final part are presented. It is known that the design of a heat exchanger is a real challenge, and the dimensions of the component parts are established according to some standards, engineering design guidelines and to the industrial domain where they are used. The dimensions of our device were established by the author by consulting specialized works. The details of how the component parts were designed, the CAD instructions used and the constraints applied to the component parts in the final assembly are presented in details. Subsequently, the final assembly is taken over in ANSYS where a CFX analysis of fluid flow is performed and a study of the heat transfer between the two fluids.
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A fast-timing method to determine lifetimes of nuclear states in the sub-nanosecond domain is presented. It is based on in-beam measurements of triple-gamma coincidences in heavy-ion ...fusion-evaporation reactions, performed with an array of HPGe and LaBr
3
:Ce detectors. The high-energy resolution HPGe detectors are used to define de-exciting cascades, while the fast LaBr
3
:Ce detectors are used to determine the decay time spectra of selected levels fed by these cascades. A special method to treat the time information of an array of fast detectors is employed in order to fully use the efficiency of the array. Two measurements are presented to illustrate the method: a re-determination of the known half-life
ns of the
keV,
level in
107
Cd (test experiment), and the determination of a half-life
ps for the
keV,
state of
199
Tl .
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