Numerical approach to analyze fluid flow in a type C tank for liquefied hydrogen carrier (part 1: Sloshing flow)

The demand for clean energy use has been increasing worldwide, and hydrogen has attracted attention as an alternative energy source. The efficient transport of hydrogen must be established such that hydrogen may be used as an energy source. In this study, we considered the influences of various parameters in the transportation of liquefied hydrogen using type C tanks in shipping vessels. The sloshing and thermal flows were considered in the transportation of liquefied hydrogen, which exists as a cryogenic liquid at ?253 °C. In this study, the sloshing flow was analyzed using a numerical approach. A multiphase sloshing simulation was performed using the volume of fluid method for the observation and analysis of the internal flow. First, a sloshing experiment according to the gas-liquid density ratio performed by other researchers was utilized to verify the simulation technique and investigate the characteristics of liquefied hydrogen. Based on the results of this experiment, a sloshing simulation was then performed for a type C cargo tank for liquefied hydrogen carriers under three different filling level conditions. The sloshing impact pressure inside of the tank was measured via simulation and subjected to statistical analysis. In addition, the influence of sloshing flow on the appendages installed inside of the type C tank (stiffened ring and swash bulkhead) was quantitatively evaluated. In particular, the influence of the sloshing flow inside of the type C tank on the appendages can be utilized as an important indicator at the design stage. Furthermore, if such sloshing impact forces are repeatedly experienced over an extended period of time under cryogenic conditions, the behavior of the tank and appendages must be analyzed in terms of fatigue and brittle failure to ensure the safety of the transportation operation.     

The effect of earthquake frequency content on the seismic behavior of concrete rectangular liquid tanks using the finite element method incorporating soil-structure interaction

A three-dimensional soil-structure-liquid interaction is numerically simulated using the finite element method in order to analyze the seismic behavior of partially filled concrete rectangular tanks subjected to different ground motions. In this paper, the effect of earthquake frequency content on the seismic behavior of fluid rectangular tank system is investigated using four different seismic motions. A simple model with viscous boundary is used to include deformable foundation effects as a linear elastic medium. This method is capable of considering both impulsive and convective responses of liquid-tank system. Six different soil types defined in the well-recognized seismic codes are considered. The sloshing behavior is simulated using linear free surface boundary condition. Two different finite element models corresponding with flexible shallow and tall tank configurations are studied under the effects of longitudinal, transversal and vertical ground motions. By means of changing the soil properties, comparisons are made on base shear, base moment and sloshing responses under different ground motions. It is concluded that the dynamic behavior of the fluid-tank-soil system is highly sensitive to frequency characteristics of the earthquake record.     

晃动对FLNG排管式液体分布器性能的影响

随着海洋油气开发的推进,填料塔被广泛应用于海上浮式液化天然气设备(FLNG),对天然气进行预处理。填料塔的重要元器件为液体分布器,其设计的好坏直接影响到填料性能和全塔效率的发挥。排管式液体分布器因其驱动力为液体压力,能更好地适应海上晃动。为了研究海上晃动对其液体分布性能的影响,使用可以实现横摇、纵摇、艏摇、横荡、纵荡、垂荡6种单一自由度晃动的六自由度晃动平台,对排管式液体分布器进行静止、不同晃动形式和不同晃动幅度工况下的实验研究,测量各种工况下各孔口的出口流量,分析各种晃动形式和晃动幅度对其液体分布性能的影响效果。结果表明:①6种单一晃动形式中,横摇、纵摇对排管武液体分布器的孔口流量分布影响较大,横摇5°和纵摇5°使其整体不均匀度(M_o)值分别增大了35%和15%,其余晃动形式对其性能影响较小;②随着晃动幅度的增大,排管式液体分布器的液体分布性能变差,横摇8°比横摇5°的M_o值增大30%,纵摇8°比纵摇5°的M_o值增大20%左右,艏摇运动下的M_o值变化不明显。该研究成果,为排管式液体分布器在海上的应用及优化提供了技术支持。     

Automotive fuel cell sloshing under temporally and spatially varying high acceleration using GPU-based Smoothed Particle Hydrodynamics (SPH)

Understanding how fuel sloshes in a fuel cell, as a vehicle races around a circuit, is an important but mostly unexplored factor when designing fuel containment systems. Cell designs are based on knowledge of how liquids slosh in other containers, with the design and placement of structures, such as weirs, based on engineering judgement.This work aims to provide better understanding for this difficult problem with a view to improve future designs. A Graphics Processing Unit (GPU) based Smoothed Particle Hydrodynamics (SPH) model is presented to simulate the fuel sloshing problem, with results from a simplified and real fuel cell geometry shown and compared against real data recorded in a vehicle. The vehicle motion and accelerations are included in the SPH simulations using a body force within the momentum equation. Results show good agreement between the simulation and the real fuel movement, with bulk motion captured well for accelerations up to 5 times gravity.Focus is placed on the practicality of the method for use as part of an industrial design process, therefore the amount of time needed to compute results is considered throughout. Computational performance is found to be within acceptable limits, while numerical accuracy is actively considered through the use of Kahan compensated summation. It is concluded that the model is successful in capturing the necessary fluid dynamics for it to be useful in fuel cell design. It is expected that the method will provide insight into current cell designs and highlight where improvements can be made.     

Optimization design technique for reduction of sloshing by evolutionary methods

The oscillation of a fluid caused by external force, called sloshing, occurs in moving vehicles containing liquid masses, such as trucks, railroad cars, aircraft, and liquid rockets. This sloshing effect could be a severe problem in vehicle stability and control. Therefore, development of efficient and easy method to reduce sloshing effect is positively necessary. In this study, optimization design technique for reduction of the sloshing using evolutionary method is suggested. Two evolutionary methods are employed, respectively, the artificial neural network (ANN) and genetic algorithm (GA). ANN is used for the analysis of sloshing and GA is adopted as optimization algorithm. The considered storage tank for fluid is a rectangular tank. The design variables are width and installation location of the baffle, and sloshing reduction coefficient by baffle is used as an object function in the optimization. As a result of this study, the optimal design for sloshing reduction is presented.     

Sloshing cargo in silo vehicles

The driving stability of silo vehicles is significantly affected by the type of cargo that is transported and the design of the tank. Cargo motion can have both beneficial and negative aspects in terms of driving stability and braking performance. Neglecting the influence of the dynamically moving cargo in driving simulations of silo vehicles leads to significant errors in the simulation results. We propose a new method for the dynamic simulation of silo vehicles carrying granulates. The method couples Lagrangian particle methods, such as the discrete element method, and multibody systems methods using co-simulations. We demonstrate the capability of the new approach by providing simulation results of two benchmark maneuvers. This paper was presented at the 4th Asian Conference on Multibody Dynamics(ACMD2008), Jeju, Korea, August 20–23, 2008. Florian Fleissner received his Dipl.-Ing. degree in Mechanical Engineering from the University of Erlangen, Germany, in 2003. He is currently working as research and teaching assistant, completing his Ph.D. in Mechanical Engineering at the Institute of Engineering and Computational Mechanics at the University of Stuttgart, Germany. Vincenzo D’Alessandro graduated in 2008 in Mechanical Engineering at the Politecnico di Milano, Italy. He is currently working as a Ph.D. candidate in Mechanical Engineering at the department of mechanical engineering at the Politecnico di Milano. Werner Schiehlen was educated as a mechanical engineer and received a Ph.D. on satellite dynamics in 1966. After working for 10 years with the Technical University Munich and spending one year with NASA in the US he was appointed full professor of mechanics with the University of Stuttgart until his retirement in 2002. He published more than 320 scientific papers in applied and computational dynamics including 7 books mostly translated in foreign languages, too. Werner Schiehlen served as President of IUTAM. Since 1997 he is Editor-in-Chief of the international journal MULTIBODY SYSTEM DYNAMICS. Peter Eberhard received his Dipl.-Ing. in Mechanical Engineering, his Dr.-Ing. and his Habilitation in Mechanics from the University of Stuttgart in Germany. In 2000 he was appointed as Professor of Mechanics and System Dynamics at the University of Erlangen-Nuremberg before he became 2002 Full Professor and Director of the Institute of Engineering and Computational Mechanics at the University of Stuttgart. In 2000 he received the Richard-von-Mises award and in 2007 an Honorary Professorship at the Nanjing University of Science and Technology, P.R. China. His research interests include multibody dynamics, contact mechanics, mechatronics, optimization and biomechanics.     

Analytical and numerical study of the effects of an elastically-linked body on sloshing

In order to investigate the effects of an elastically-linked moving body on liquid sloshing inside a tank, an analytical formulation and a numerical approach were proposed to assess hydrodynamic loads in a partially filled rectangular tank with a body connected to the tank by springs. The analytical approach was developed based on the potential theory to calculate fluid velocity field, and the dynamics of the liquid sloshing coupled to the moving body are described as a mechanical system with two degrees of freedom. The coupling between the fluid and the moving body is given by a damping force calculated based on the body geometry and the fluid velocity field. The proposed numerical approach is based on the Moving Particle Semi-implicit (MPS) method, which is a Lagrangian particle-based method and very effective to model nonlinear hydrodynamics due to fluid–structure interaction. In the numerical approach, the rigid body is modeled as a cluster of particles and the motions are calculated considering its mass, moment of inertia, hydrodynamic loads and springs restoring forces. The elastic link between the body and tank is modeled by applying Hooke’s law. Simple cases of floating body motion were used to validate the numerical method. Finally, analytical and numerical results were compared. Despite its simplicity, the analytical approach proposed in the present work is an efficient approach to provide qualitative understanding and a first estimate of the moving body effects on the sloshing inside the tank. On the other hand, the numerical approach can provide more detailed information about the coupling phenomena, and it is an effective mean for the assessment of the reduction of the sloshing loads due to the moving body with elastic link. Finally, the effectiveness of the concept as a sloshing suppressing device is also investigated.     

Dynamic analysis of liquid storage tank under blast using coupled Euler–Lagrange formulation

A growing number of terror attacks all over the world have become a threat to the human civilization. In the last two decades, bomb blasts in crowded business areas, underground railway stations and busy roads have taken numerous lives and destroyed properties in different parts of the world. However, blast response of many important civil infrastructures has still not been well understood due to the complexities in their material behavior, loading and higher nonlinearities. One such example of important civil infrastructure is liquid storage tanks which are undividable parts of any society for storage of water, milk, liquid petroleum, chemicals in industries etc. Blast loading on liquid storage structures may lead to disaster due to water and milk crisis, health hazard owing to the spread of chemicals and fire hazard due to the spread of liquid fuel. Hence, understanding the dynamic behavior of liquid storage structures under blast loading through numerical simulations is of utmost importance. In the present study, three dimensional (3D) finite element (FE) simulations of a steel water storage tank for different tank aspect ratios, percentages of water stored in the tank, tank wall thicknesses, boundary conditions at the bottom of the tank and magnitudes of blast loading have been performed using the FE software Abaqus. The coupled Euler–Lagrange (CEL) formulation in Abaqus has been adopted herein which has the advantage of considering the coupling of structural mechanics and fluid mechanics fundamental equations. The maximum hoop stress and shear stress in the tank wall, the water sloshing heights in tanks and the energy response of the tanks have been studied. It is observed that stresses and liquid sloshing heights in the tank increase with decreasing scaled distance of the explosive material and increasing aspect ratio, i.e. height to radius ratio.     

Numerical simulation of structure response outfitted with a tuned liquid damper

An integrated fluid–structure numerical model has been developed to simulate the response of a single degree of freedom (SDOF) structure outfitted with a Tuned Liquid Damper (TLD). The structure is exposed to random external excitations. A non-linear, two-dimensional, flow model has been developed using the finite-difference method. Unlike most existing flow models, the present model does not include any linearization assumptions; it rather solves the entire nonlinear, moving boundary, flow problem under conditions leading to large interfacial deformations. The free surface has been reconstructed using the volume of fluid method and the donor–acceptor algorithm. The Duhamel integral method has been used to determine the response of the structure. The effectiveness and accuracy of the flow model has been validated using a set of benchmark problems and experimental data. The numerical results of this model have been compared with results of an equivalent TMD model. The present fluid–structure model can be used as a valuable tool for performance evaluation and design of more effective tuned liquid dampers.     

LNG围护系统结构失效模式的有限元模拟

LNG运输船设计关键技术之一是液舱围护系统的结构安全设计。为了保证LNG液体的运输安全,需要特别关注围护系统的结构设计,其中对结构失效模式及其发生机理的研究具有很高参考价值。为了能够全面研究薄膜型液舱结构特性,采用基于有限元的数值模拟方法,针对在晃荡荷载下的结构响应,建立了一种简化的二维有限元模型。根据层式复合材料特点,分别选取对应的强度失效准则,分析结构的失效模式。数值分析结果显示,首层聚氨酯泡沫层在晃荡荷载作用下最先发生压溃破坏,在MARKⅢ型液舱设计中应该被重点关注;其他的结构失效模式依次为:次层聚氨酯泡沫层压溃失效、层合板剪切失效以及树脂绳压溃失效。采用数值模拟进行围护系统的截面失效模式分析,能够快速高效地指导LNG液舱结构设计,是在液舱设计领域新的应用尝试。