Cut and Shoot, TX, United States
Cut and Shoot, TX, United States

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Cao Y.,MARINTEK United States Inc. | Zhang F.,MARINTEK United States Inc. | Liapis S.,Global Solutions U.S. Inc.
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2013

Sloshing in liquid tanks is a serious safety and operational concern. A computer tool that can be employed to predict the onset of sloshing in tanks and estimate the severity of the hydrodynamic pressures applied on the tank walls was developed in 2010 and reported in ISOPE 2011. The work reported here is a continuation of this effort with particular emphasis on speeding up the code so it is faster than real time. The code uses a potential flow model with linear boundary conditions. The liquid in the tank is assumed incompressible and inviscid, and the flow is assumed irrotational. The flow can then be described by a velocity potential Φ(t, x, y, z) which is governed by the Laplace equation. The flow problem can be formulated as an initial-boundary value problem. At each time instant, a boundary value problem for the velocity potential is solved using the Desingularized Rankine Singularity method. A time-stepping approach is used, in which the kinematic and dynamic boundary conditions on the liquid free surface are integrated in time to update the surface elevation and the velocity potential for the next time instant. A significant speedup is achieved through parallel computation and better memory management for faster accessing stored data. Two test cases were chosen to assess the performance of the code: A square-base tank and a prismatic tank. Using a standard desktop, the code runs faster than real time, which is a prerequisite for any predictive on-line sloshing tool. Copyright © 2013 by the International Society of Offshore and Polar Engineers (ISOPE).


Cao Y.,MARINTEK United States Inc. | Graczyk M.,Norwegian Marine Technology Research Institute | Pakozdi C.,Norwegian Marine Technology Research Institute | Lu H.,George Mason University | And 2 more authors.
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2010

Motion of fluid in a moving liquid tank can be very complicated and violent. It remains a great challenge to accurately predict the flow and the hydrodynamic load on the tank which affects the motion of the vessel carrying the tank. Although significant progress has been made in the experimental techniques and advanced nonlinear computational methods (CFD), they are still very costly and time consuming to perform and it is not feasible to use these methods to study the liquid sloshing effects at the early stage of the vessel design. At the moment, a more practical way to include the liquid sloshing effects on the vessel motion is use of the potential flow model. Although the potential flow model cannot handle the violet free surface motion with wave breaking, it still can be used effectively in many applications. For instance, an effective way to achieve a good vessel motion performance is to avoid the vessel natural frequencies being close to the dominant frequencies of the environment conditions. This may be achieved with a linear wave model for the wave motion in the tanks. Some numerical methods based on the potential flow model and associated computer programs have been developed. These programs compute the sloshing load coefficients (in terms of added mass and hydrostatic stiffness) and the vessel wave frequency motion responses in the frequency domain. They give reasonably good predictions of the natural frequencies. In many situations, however, the computations of the motions of a floating system (with a vessel, mooring, risers, dynamic positioning system, and other devices⋯) need to be carried out in the time domain. The frequency-dependent added mass and hydrostatic stiffness due to the liquid sloshing must be transferred to the sloshing loads in the timedomain. Or it may be more efficient to solve for the flow and calculate the sloshing load directly in the time domain. It is important to know the limits within which the potential flow models (linear and nonlinear) are valid. This paper presents an attempt to gain a better feeling about the range of the validity of the potential flow models by comparing the predictions from the potential flow models with those by other CFD simulations and experiment measurements of the liquid motion in an oscillating tank. © 2010 by The International Society of Offshore and Polar Engineers (ISOPE).


Cao Y.,MARINTEK United States Inc. | Tahchiev G.,MARINTEK United States Inc. | Zhang F.,MARINTEK United States Inc. | Jin J.,ExxonMobil | Reid D.,ExxonMobil
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2015

A coupled 3-D finite element model of a buoy system including a surface buoy, an umbilical and a riser was developed to study the system's global dynamic responses in sea states (irregular waves and currents) using commercially available software (such as WAMIT, RIMO, RIFLEX). The model is used for verification of the design of the system and determination/assessment of the limiting sea states based on the system's performance and the design criteria. The limiting sea states are the sea states on a boundary curve of a sea state range (domain) within which all the system design criteria are met. The design criteria include the maximum tension, maximum compression and minimum bend radius for the umbilical, and the maximum tension, minimum bend radius and maximum angle relative to the axis of the bellmouth for the riser. The method has been used successfully for the verification of the design of a buoy system and the assessment of its global performance. It is confirmed that the design meets the project's expectations and the system is fit-for-service. Copyright © 2015 by the International Society of Offshore and Polar Engineers (ISOPE).


Cao Y.,MARINTEK United States Inc. | Beck R.F.,University of Michigan
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2015

Desingularized boundary integral equation methods (DBIEM) and their applications in water wave dynamics and body motion dynamics over the past 30 years are reviewed. In solving the potential flow problem for wave dynamics, unlike conventional boundary integral methods, a DBIEM separates the integration surface and the control (collocation) surface, resulting in a BIE with non-singular kernels. The desingularization allows simpler and faster numerical evaluation of the boundary integrals, and thus a fast numerical solution. The paper reviews the fundamental aspects and advantages of DBIEMs. Examples of applications of DBIEMs in wave dynamics and body motion dynamics are given and the outlook of future DBIEMs development is discussed. © 2015 by ASME.


Cao Y.,MARINTEK United States Inc. | Cao Y.,C Z Marine Technology LLC | Zhang F.,MARINTEK United States Inc. | Zhang F.,C Z Marine Technology LLC
Journal of Offshore Mechanics and Arctic Engineering | Year: 2016

This paper presents a simple and fast method to include the effect of liquid tanks of a vessel in the prediction of the vessel motions. The effects are expressed in terms of modifications to the added mass and stiffness matrices of the vessels calculated with the liquids in the tanks assumed being rigid. The flows in the liquid tanks are solved using a panel method based on the desingularized boundary integral equations (DBIEs). The numerical results were validated by the experiments of a square tank partially filled. An application example for a vessel with two internal liquid tanks is demonstrated. © 2016 by ASME.


Cao Y.,MARINTEK United States Inc. | Lu H.,MARINTEK United States Inc. | Zhang F.,MARINTEK United States Inc.
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2013

In this paper, based on the results of CFD simulations, we demonstrate the importance of considering the effect of the liquid movement inside a fully-filled liquid tank on the moment on the vessel. The equivalent moment of inertia ratio is introduced for assessment of the effect of the liquid movement. It is found that the effect depends on the distance between the rotation axis and the tank axis. The closer the tank is to the rotation axis, the stronger the effect of the liquid movement is on the moment on the tank. It is also found that the dependency of the equivalent moment of inertia ratio on the tank rotation frequency and amplitude is very weak, which lays a base for a simple approach to include the effect of liquid movement in the fully-filled tank on the motions of the vessel carrying the tank. Copyright © 2013 by the International Society of Offshore and Polar Engineers (ISOPE).


Cao Y.,MARINTEK United States Inc. | Tahchiev G.,MARINTEK United States Inc.
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2013

The paper presents a theoretical study on an active hybrid decomposed mooring system for model testing of offshore platform in wave basin. The basic concept and the working principles are described. Important issues for achieving a correct simulation will be discussed. The feasibility of the approach is demonstrated based on numerical investigations. Plans for potential implementation in an ocean basin are also discussed. Copyright © 2013 by ASME.


Graczyk M.,MARINTEK United States Inc. | Berget K.,MARINTEK United States Inc. | Allers J.,MARINTEK United States Inc.
Journal of Offshore Mechanics and Arctic Engineering | Year: 2012

Sloshing, a violent fluid motion in tanks is of current interest for many branches of the industry, among them gas shipping. Although different methods are commonly combined for analyzing sloshing in LNG carriers, time histories of the pressure in the tanks are most reliably obtained by experiments. Very localized pressures may be important for the structural response of the tank containment system. Moreover, the typical pressure time history duration is similar to the structural natural frequency. Therefore, pressure measurements need to be performed with due account for temporal and spatial distribution. This requires a high sampling resolution both in time and space. Fine spatial resolution becomes especially important when local pressure effects are of interest, such as pressure profile passing a membrane corrugation of Mark III containment or the Invar edge No.96 containment. In this paper an experimental approach applied by MARINTEK for analyzing sloshing phenomenon is presented. The focus is put on investigating the effects of Invar edges. A transverse 2D model of a typical LNG carrier is used. Local pressure effects are investigated based on low filling level tests with different wall surfaces: smooth and with horizontal protrusions representing the surface similar to the No.96 containment system.


Allers J.,MARINTEK United States Inc.
Journal of Offshore Mechanics and Arctic Engineering | Year: 2012

Sloshing, a violent fluid motion in tanks is of current interest for many branches of the industry, among them gas shipping. Although different methods are commonly combined for analyzing sloshing in liquid natural gas (LNG) carriers, time histories of the pressure in the tanks are most reliably obtained by experiments. Very localized pressures may be important for the structural response of the tank containment system. Moreover, the typical pressure time history duration is similar to the structural natural frequency. Therefore, pressure measurements need to be performed with due account for temporal and spatial distribution. This requires a high sampling resolution both in time and space. Fine spatial resolution becomes especially important when local pressure effects are of interest, such as pressure profile passing a membrane corrugation of Mark III containment or Invar edge of No. 96 containment. In this paper experimental approach applied by MARINTEK for analyzing sloshing phenomenon is presented. The focus is put on investigating effects of Invar edges. A transverse 2D model of a typical LNG carrier is used. Local pressure effects are investigated based on low filling level tests with different wall surfaces: smooth and with horizontal protrusions representing the surface similar to the No. 96 containment system. © 2012 American Society of Mechanical Engineers.


Cao Y.,MARINTEK United States Inc. | Zhang F.,MARINTEK United States Inc.
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2014

It was demonstrated, in a study presented at ISOPE 2013 (Cao, et al 2013), that treating the liquid in a fully-filled tank as a rigid body when calculating the moment on the tank by the liquid can result in significant error. CFD simulations were performed to study the effects of the liquid movement for 2-D tanks with square and circular cross sections. Based on the results of the study, a simple method was proposed for including the effect of the liquid movement in a fullyfilled tank in the calculation of the motions of the ship (or vessel) in regular wave. This paper extends the previous study to tanks with rectangular cross sections. The present study confirms the findings in the previous study for the tanks with square or circular cross sections. In addition, the effect of the length-height ratio of the rectangular cross section is investigated. A preliminary investigation indicates that it is possible to extend the simple method to the prediction of the ship motions in random seas using the frequency-domain approach. Copyright © 2014 by the International Society of Offshore and Polar Engineers (ISOPE).

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