Simulation of Sloshing in LNG-Tanks

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Milovan Peric ◽  
Tobias Zorn ◽  
Ould el Moctar ◽  
Thomas E. Schellin ◽  
Yong-Soo Kim
Keyword(s):  
Three Dimensional ◽  
Mesh Size ◽  
Breaking Waves ◽  
Ship Motions ◽  
Sea Waves ◽  
Interface Capturing ◽  
Grid Approach ◽  
Numerical Mixing ◽  
Lng Tank

The purpose of this paper was to demonstrate the application of a procedure to predict internal sloshing loads on partially filled tank walls of liquefied natural gas (LNG) tankers that are subject to the action of sea waves. The method is numerical. We used a moving grid approach and a finite-volume solution method designed to allow for arbitrary ship motions. An interface-capturing scheme that accounts for overturning and breaking waves computed the motion of liquid inside the tanks. The method suppressed numerical mixing. Mixing effects close to the interface were buried in the numerical treatment of the interface. This interface, which was at least one cell wide, amounted to about 20–50 cm at full scale. Droplets and bubbles smaller than mesh size were not resolved. Tank walls were considered rigid. The results are first presented for an LNG tank whose motion was prescribed in accordance with planned laboratory experiments. Both two-dimensional and three-dimensional simulations were performed. The aim was to demonstrate that (1) realistic loads can be predicted using grids of moderate fineness, (2) the numerical method accurately resolves the free surface even when severe fragmentation occurs, and (3) long-term simulations over many oscillation periods are possible without numerical mixing of liquid and gas. The coupled simulation of a sea-going full-sized LNG tanker with partially filled tanks demonstrated the plausibility of this approach. Comparative experimental data were unavailable for validation; however, results were plausible and encouraged further validation.

Simulation of Sloshing in LNG Tanks

2007 ◽  
Author(s):  
Milovan Peric ◽  
Tobias Zorn ◽  
Ould el Moctar ◽  
Thomas E. Schellin ◽  
Yong-Soo Kim
Keyword(s):  
Three Dimensional ◽  
Breaking Waves ◽  
Offshore Platforms ◽  
Sea Waves ◽  
Coupled Simulation ◽  
Grid Approach ◽  
Head Waves ◽  
Numerical Mixing ◽  
Vessel Motion ◽  
Resultant Forces

The aim of this paper is to demonstrate the prediction of internal loads on liquified natural gas (LNG) tanker ships and on offshore platforms. We use the moving grid approach and a finite volume solution method designed to allow for arbitrary ship motion. The motion of liquid is computed using an interface-capturing scheme which allows overturning and breaking waves. By performing a coupled simulation of the flow and vessel motion, it is possible to obtain a realistic response of the liquid in a tank to external excitation, e.g. by sea waves. Results are first presented for an LNG tanks whose motion is prescribed in accordance with planned laboratory experiments. Both two-dimensional (2D) and three-dimensional (3D) simulations are performed. The aim is to demonstrate that 1) realistic loads can be predicted using grids of moderate fineness, 2) the numerical method is able to accurately resolve the free surface even when severe fragmentation occurs, and 3) long-term simulations over many oscillation periods are possible without numerical mixing of liquid and gas. The plausibility of a coupled simulation of both vessel motion and the flow inside tanks and outside the vessel is then demonstrated for a full-size ship with partially-filled tanks exposed to head waves. In this simulation the forces and moments exerted by the sea cause the vessel to move, exciting the sloshing of liquid in tanks. For the computation of vessel motion, both sea-induced forces and forces due to sloshing in tanks are taken into account when determining the resultant forces and moments. While there are no experimental data for comparison at this time, the results look plausible and encourage further validation and application studies.

Free Surface Effects on Hydrodynamic Analysis of Flapping Foil Thruster in Waves

2013 ◽  
Author(s):  
E. S. Filippas ◽  
K. A. Belibassakis
Keyword(s):  
Free Surface ◽  
Breaking Waves ◽  
Numerical Results ◽  
Operating Conditions ◽  
Oscillatory Motion ◽  
Ship Motions ◽  
Sea Waves ◽  
Thrust Coefficient ◽  
Hydrodynamic Analysis ◽  
Stage Of Development

The analysis of an oscillating wing located beneath the ship’s hull is investigated as an unsteady thruster, augmenting the overall propulsion of the ship and offering dynamic stabilization. The unsteady thruster undergoes a combined oscillatory motion in the presence of waves. For the system in horizontal arrangement the vertical heaving motion is induced by the motion of the ship in waves, essentially ship heave and pitch, while the rotational pitching motion of the flapping propulsor about its pivot axis is set by an active control mechanism. Our method is based on coupling the seakeeping operators associated with the longitudinal and transverse ship motions with the hydrodynamic forces and moments produced by the flapping lifting surfaces, using simplified unsteady lifting line theory. First numerical results presented in Belibassakis & Politis [1],[2] indicate that high levels of efficiency are obtained in sea conditions of moderate and higher severity, under optimal control settings. For the detailed investigation of the effects of the free surface in the present paper a potential-based panel method has been developed for the hydrodynamic analysis of 2D hydrofoil operating beneath the free surface, undergoing heaving and pitching oscillations while moving with constant forward speed. The instantaneous angle of attack is influenced by the foil oscillatory motion and by the incident waves. At a first stage of development we consider moderate submergence and relatively low speeds permitting us to approximately neglect effects due to breaking waves and cavitation. Numerical results are presented concerning the numerical performance of the developed BEM. Also results concerning the thrust coefficient and the efficiency of the system over a range of motion parameters, including reduced frequency, Strouhal number, feathering parameter and compared against other methods. Our analysis indicates that significant efficiency can be obtained under optimal operating conditions. Thus, the present method can serve as a useful tool for assessment and the preliminary design and control of such systems extracting energy from sea waves for marine propulsion.

Simulation of Sloshing Loads on Moving Tanks

2005 ◽  
Author(s):  
Milovan Peric´ ◽  
Tobias Zorn
Keyword(s):  
Experimental Data ◽  
Solution Method ◽  
Offshore Platforms ◽  
Sea Waves ◽  
Interface Capturing ◽  
Grid Approach ◽  
Vessel Motion ◽  
Control Volumes ◽  
Peak Pressures ◽  
Good Agreement

The aim of the presentation is to demonstrate the possibilities of predicting loads on partially submerged, moving structures, in particular on tanks in ships and on offshore platforms. Since tanks can in reality move arbitrarily, we are using the moving grid approach and a Finite Volume solution method designed to cater for arbitrary motions of polyhedral control volumes. The motion of liquid is computed using an interface-capturing scheme which allows overturning and breaking of waves. By performing a coupled simulation of the flow and vessel motion, it is possible to obtain a realistic response of the liquid in a tank to external excitation, e.g. by sea waves. Results are first presented for tanks whose motion is prescribed in accordance with experimental setups, with which the solutions are compared. A very good agreement between pressures computed in simulations and experimental data at representative locations is obtained. It was possible by means of simulation to clearly distinguish between off-resonance and resonance cases, in which peak pressures reached the highest values, in accordance with experimental observations. Following validation by experimental data in laboratory setups, we demonstrate the plausibility of simulation of both vessel motion and the flow inside and outside vessel. The forces and moments exerted by the sea cause the vessel to move, which excites the sloshing of liquid in tanks. For the computation of vessel motion, both sea-induced forces and forces due to sloshing in tanks are taken into account. While there are no experimental data to compare with, the results look plausible and encourage further validation and application studies.

Analysis of Motions of a Semisubmersible in Sea Waves

1982 ◽  
Vol 104 (1) ◽  
pp. 29-38
Author(s):  
F. Z. Sun
Keyword(s):  
Transfer Functions ◽  
Three Dimensional ◽  
Theoretical Data ◽  
Statistical Characteristics ◽  
Sea Waves ◽  
Regular Waves ◽  
Short Term ◽  
Equivalent Wave ◽  
Processing Techniques

The forces acting on a three-dimensional cylinder with arbitrary symmetrical cross section are derived taking into account viscous effect and applying linear-processing techniques. Then general expressions for the hydrodynamic forces, motion equation and its solution for a semisubmersible platform in regular waves are obtained. Based on linear theory of statistical analysis, it is proposed to employ the concept of “equivalent wave height” for the calculation of transfer functions with which both the short-term and long-term distribution and statistical characteristics of the motion of a semisubmersible may be estimated. A computer program has been developed. Comparison between model experimental and theoretical data has shown satisfactory agreement.

scholarly journals REEF3D:NSEWAVE, A THREE-DIMENSIONAL NON-HYDROSTATIC WAVE MODEL ON A FIXED GRID

2018 ◽  
pp. 8
Author(s):  
Hans Bihs ◽  
Kristina Heveling ◽  
Arun Kamath
Keyword(s):  
Large Scale ◽  
Stokes Equations ◽  
Spatial Scales ◽  
Phase Interface ◽  
Computational Cost ◽  
Three Dimensional ◽  
Free Water ◽  
Wave Model ◽  
Breaking Waves ◽  
Interface Capturing

For coastal engineering problems, wave modeling is required for various spatial scales. In recent years, the development of high-resolution Computational Fluid Dynamics (CFD) based numerical wave tanks (NWT) has gained a lot of attention. Here, the Navier-Stokes equations are solved together with a two-phase interface capturing algorithm for the calculation of the free surface location. The interface capturing treatment of the free water surface is performed on fixed grids, allowing for the simulation of complex wave phenomena such as breaking waves. The CFD-based NWT are preferably used for nearfield problems, such as wave-structure interaction. For larger spatial scales, the computational cost becomes rather expensive. In the current paper, the three-dimensional open-source hydrodynamics model REEF3D is extended from a CFD-based NWT to a non-hydrostatic wave model, suitable for economic large scale computation of waves.

Practical electron tomography

1995 ◽  
Vol 53 ◽  
pp. 742-743
Author(s):  
C.L. Woodcock
Keyword(s):  
Electron Tomography ◽  
Tomographic Reconstruction ◽  
Three Dimensional ◽  
3D Shape ◽  
Computational Resources ◽  
Shape Of Particles

Despite the potential of the technique, electron tomography has yet to be widely used by biologists. This is in part related to the rather daunting list of equipment and expertise that are required. Thanks to continuing advances in theory and instrumentation, tomography is now more feasible for the non-specialist. One barrier that has essentially disappeared is the expense of computational resources. In view of this progress, it is time to give more attention to practical issues that need to be considered when embarking on a tomographic project. The following recommendations and comments are derived from experience gained during two long-term collaborative projects.Tomographic reconstruction results in a three dimensional description of an individual EM specimen, most commonly a section, and is therefore applicable to problems in which ultrastructural details within the thickness of the specimen are obscured in single micrographs. Information that can be recovered using tomography includes the 3D shape of particles, and the arrangement and dispostion of overlapping fibrous and membranous structures.

Custom Presurgical Planning for Midfacial Reconstruction

2020 ◽  
Vol 36 (06) ◽  
pp. 696-702
Author(s):  
Nolan B. Seim ◽  
Enver Ozer ◽  
Sasha Valentin ◽  
Amit Agrawal ◽  
Mead VanPutten ◽  
...  
Keyword(s):  
Multidisciplinary Approach ◽  
Functional Performance ◽  
Three Dimensional ◽  
Free Tissue Transfer ◽  
Long Term Effects ◽  
Presurgical Planning ◽  
Dental Rehabilitation ◽  
Midface Reconstruction ◽  
Reconstructive Algorithm

AbstractResection and reconstruction of midface involve complex ablative and reconstructive tools in head and oncology and maxillofacial prosthodontics. This region is extraordinarily important for long-term aesthetic and functional performance. From a reconstructive standpoint, this region has always been known to present challenges to a reconstructive surgeon due to the complex three-dimensional anatomy, the variable defects created, combination of the medical and dental functionalities, and the distance from reliable donor vessels for free tissue transfer. Another challenge one faces is the unique features of each individual resection defect as well as individual patient factors making each preoperative planning session and reconstruction unique. Understanding the long-term effects on speech, swallowing, and vision, one should routinely utilize a multidisciplinary approach to resection and reconstruction, including head and neck reconstructive surgeons, prosthodontists, speech language pathologists, oculoplastic surgeons, dentists, and/or craniofacial teams as indicated and with each practice pattern. With this in mind, we present our planning and reconstructive algorithm in midface reconstruction, including a dedicated focus on dental rehabilitation via custom presurgical planning.

Prediction of Ship Motions Via a Three-Dimensional Time-Domain Method Following a Quad-Tree Adaptive Mesh Technique

2020 ◽  
Vol 27 (1) ◽  
pp. 29-38
Author(s):  
Teng Zhang ◽  
Junsheng Ren ◽  
Lu Liu
Keyword(s):  
Free Surface ◽  
Incident Wave ◽  
Time Domain ◽  
Three Dimensional ◽  
Adaptive Mesh ◽  
Wave Profile ◽  
Time Domain Method ◽  
Ship Motions ◽  
Quad Tree ◽  
Mesh Technique

AbstractA three-dimensional (3D) time-domain method is developed to predict ship motions in waves. To evaluate the Froude-Krylov (F-K) forces and hydrostatic forces under the instantaneous incident wave profile, an adaptive mesh technique based on a quad-tree subdivision is adopted to generate instantaneous wet meshes for ship. For quadrilateral panels under both mean free surface and instantaneous incident wave profiles, Froude-Krylov forces and hydrostatic forces are computed by analytical exact pressure integration expressions, allowing for considerably coarse meshes without loss of accuracy. And for quadrilateral panels interacting with the wave profile, F-K and hydrostatic forces are evaluated following a quad-tree subdivision. The transient free surface Green function (TFSGF) is essential to evaluate radiation and diffraction forces based on linear theory. To reduce the numerical error due to unclear partition, a precise integration method is applied to solve the TFSGF in the partition computation time domain. Computations are carried out for a Wigley hull form and S175 container ship, and the results show good agreement with both experimental results and published results.

Sign in / Sign up

Export Citation Format

Share Document