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A comparison study of water impact and water exit models
Korobkin, Alexander,Khabakhpasheva, Tatyana,Malenica, Sime,Kim, Yonghwan The Society of Naval Architects of Korea 2014 International Journal of Naval Architecture and Oc Vol.6 No.4
In problems of global hydroelastic ship response in severe seas including the whipping problem, we need to know the hydrodynamic forces acting on the ship hull during almost arbitrary ship motions. In terms of ship sections, some of them can enter water but others exit from water. Computations of nonlinear free surface flows, pressure distributions and hydrodynamic forces in parallel with the computations of the ship motions including elastic vibrations of the ship hull are time consuming and are suitable only for research purposes but not for practical calculations. In this paper, it is shown that the slamming forces can be decomposed in two components within three semi-analytical models of water entry. Only heave motion is considered. The first component is proportional to the entry speed squared and the second one to the body acceleration. The coefficients in these two components are functions of the penetration depth only and can be precomputed for given shape of the body. During the exit stage the hydrodynamic force is proportional to the acceleration of the body and independent of the body shape for bodies with small deadrise angles.
A comparison study of water impact and water exit models
Alexander Korobkin,Tatyana Khabakhpasheva,Sime Malenica,김용환 대한조선학회 2014 International Journal of Naval Architecture and Oc Vol.6 No.4
In problems of global hydroelastic ship response in severe seas including the whipping problem, we needto know the hydrodynamic forces acting on the ship hull during almost arbitrary ship motions. In terms of ship sections,some of them can enter water but others exit from water. Computations of nonlinear free surface flows, pressure distributionsand hydrodynamic forces in parallel with the computations of the ship motions including elastic vibrations ofthe ship hull are time consuming and are suitable only for research purposes but not for practical calculations. In thispaper, it is shown that the slamming forces can be decomposed in two components within three semi-analytical modelsof water entry. Only heave motion is considered. The first component is proportional to the entry speed squared and thesecond one to the body acceleration. The coefficients in these two components are functions of the penetration depthonly and can be precomputed for given shape of the body. During the exit stage the hydrodynamic force is proportionalto the acceleration of the body and independent of the body shape for bodies with small deadrise angles.
Khabakhpasheva, Tatyana,Chen, Yang,Korobkin, Alexander,Maki, Kevin Korean Society of Ocean Engineers 2018 Journal of advanced research in ocean engineering Vol.4 No.4
The unsteady problem of a rigid body impact onto a floating plate is studied. Both the plate and the water are at rest before impact. The plate motion is caused by the impact force transmitted to the plate through an elastic layer with viscous damping on the top of the plate. The hydrodynamic force is calculated by using the second-order model of plate impact by Iafrati and Korobkin (2011). The present study is concerned with the deceleration experienced by a rigid body during its collision with a floating object. The problem is studied also by a fully-nonlinear computational-fluid-dynamics method. The elastic layer is treated with a moving body-fitted grid, the impacting body with an immersed boundary method, and a discrete-element method is used for the contact-force model. The presence of the elastic layer between the impacting bod- ies may lead to multiple bouncing of them, if the bodies are relatively light, before their interaction is settled and they continue to penetrate together into the water. The present study is motivated by ship slamming in icy waters, and by the effect of ice conditions on conventional free-fall lifeboats.
김정현,김용환,Alexander Korobkin 대한조선학회 2014 International Journal of Naval Architecture and Oc Vol.6 No.4
This paper presents a numerical analysis of slamming and whipping using a fully coupled hydroelasticmodel. The coupled model uses a 3-D Rankine panel method, a 1-D or 3-D finite element method, and a 2-D GeneralizedWagner Model (GWM), which are strongly coupled in time domain. First, the GWM is validated against resultsof a free drop test of wedges. Second, the fully coupled method is validated against model test results for a 10,000twenty-foot equivalent unit (TEU) containership. Slamming pressures and whipping responses to regular waves arecompared. A spatial distribution of local slamming forces is measured using 14 force sensors in the model test, and it iscompared with the integration of the pressure distribution by the computation. Furthermore, the pressure is decomposedinto the added mass, impact, and hydrostatic components, in the computational results. The validity and characteristicsof the numerical model are discussed.
Kim, Jung-Hyun,Kim, Yonghwan,Korobkin, Alexander The Society of Naval Architects of Korea 2014 International Journal of Naval Architecture and Oc Vol.6 No.4
This paper presents a numerical analysis of slamming and whipping using a fully coupled hydroelastic model. The coupled model uses a 3-D Rankine panel method, a 1-D or 3-D finite element method, and a 2-D Generalized Wagner Model (GWM), which are strongly coupled in time domain. First, the GWM is validated against results of a free drop test of wedges. Second, the fully coupled method is validated against model test results for a 10,000 twenty-foot equivalent unit (TEU) containership. Slamming pressures and whipping responses to regular waves are compared. A spatial distribution of local slamming forces is measured using 14 force sensors in the model test, and it is compared with the integration of the pressure distribution by the computation. Furthermore, the pressure is decomposed into the added mass, impact, and hydrostatic components, in the computational results. The validity and characteristics of the numerical model are discussed.
The X-ray counterpart to the gravitational-wave event GW170817
Troja, E.,Piro, L.,van Eerten, H.,Wollaeger, R. T.,Im, M.,Fox, O. D.,Butler, N. R.,Cenko, S. B.,Sakamoto, T.,Fryer, C. L.,Ricci, R.,Lien, A.,Ryan Jr, R. E.,Korobkin, O.,Lee, S.-K.,Burgess, J. M.,Lee, Nature Publishing Group 2017 Nature Vol. No.
A long-standing paradigm in astrophysics is that collisions—or mergers—of two neutron stars form highly relativistic and collimated outflows (jets) that power γ-ray bursts of short (less than two seconds) duration. The observational support for this model, however, is only indirect. A hitherto outstanding prediction is that gravitational-wave events from such mergers should be associated with γ-ray bursts, and that a majority of these bursts should be seen off-axis, that is, they should point away from Earth. Here we report the discovery observations of the X-ray counterpart associated with the gravitational-wave event GW170817. Although the electromagnetic counterpart at optical and infrared frequencies is dominated by the radioactive glow (known as a ‘kilonova’) from freshly synthesized rapid neutron capture (r-process) material in the merger ejecta, observations at X-ray and, later, radio frequencies are consistent with a short γ-ray burst viewed off-axis. Our detection of X-ray emission at a location coincident with the kilonova transient provides the missing observational link between short γ-ray bursts and gravitational waves from neutron-star mergers, and gives independent confirmation of the collimated nature of the γ-ray-burst emission.