Free Surface Flow Simulation Using VOF Method

Viscous flow with moving free surface is an important phenomenon in nature which has broad applications in engineering. For these flows, temporal and spatial position of this moving free surface in unsteady or non‐uniform conditions is very complicated. In this chapter, free surface simulation methods based on computational grid are presented. Volume of fluid (VOF) is a powerful and the most prevailing method for modeling two immiscible incompressible fluid‐fluid interfaces. Herein, the governing equations of fluid flow including Navier‐Stokes coupled with VOF equation are discussed and the most prominent VOF schemes hierarchically presented to the readers. Meanwhile, Compressive Interface Capturing Scheme for Arbitrary Meshes (CICSAM), Higher Resolution Artificial Compressive (HiRAC), High Resolution Interface Capturing (HRIC), Switching Technique for Advection and Capturing of Surfaces (STACS), and some other newly proposed methods are introduced, and the accuracy and time calculation of each method are evaluated. Moreover, surface tension modeling and its discretization as one of the most demanding phenomena in the nature are brought to the readers. Finally, two schemes of parametric study of interfaces are discussed

Numerical Modelling of Sloshing with VOF Method

Sloshing in tanks carrying LNG, LPG and petroleum is an important phenomenon as dynamic pressure arises from sloshing can destroy the containing tanks. So it is vital to consider this phenomenon in design stages of carriers. The governing equations in fluid flow are conservation of mass and momentum. Modeling of free surface flow in tank needs a suitable tool. One of the most powerful tools to model the free surface is VOF method. Employing additional transport equation together with conservation of mass and momentum enable us to follow the free surface changes. A computer code was developed to evaluate sloshing problem. This code could calculate dynamic pressures exerted on walls of the containers. The model was validated using experimental data

Application of the Modified Weakly Compressible SPH Method to the 3D Turbulent Wave Breaking Impact

In this paper, the mesh-less weakly compressible Smoothed Particle Hydrodynamics (SPH) method was used to solve the continuity and momentum equations with laminar viscosity and the sub-particle scale (SPS) turbulence model. To correct the pressure field and improve the accuracy of free surface, modification of the kernel and its gradient is applied to weakly compressible SPH. The modified method, namely the mSPH-T-K, was also equipped with periodic smoothing of the density using the modified kernel. To validate the modified model, the pressure field and the wave front position of the 2D dam break flow were compared with those of experimental data, the standard SPH method and the mSPH-T method, which is the turbulence SPH method without modification of the kernel and its gradients. Finally, a 3D wave impact was simulated using the mSPH-T-K method. A comparison of results with experimental data showed that this model is a powerful tool for the simulation of complicated free surface flows with large deformations and impact

Analysis of Adaptive Traffic Control Systems Design of a Decision Support System for Better Choices

open3siNear half of the world population lives in cities. For many years big cities have faced the dif culties caused by junctions. Junctions and congestion are the cause of many other problems, like air pollution, time waste, delays, increased average trip time, decreased average cruise speed, increased fuel consumption and many others. These important issues cost a lot to governments in terms of both time and money. Cities suffer from the well-known problem of xed-time planning for traf c signals at intersections. In this paper the authors went through these problems and discussed about the dif culties of xed-time plan traf c lights and their solutions. Adaptive traf c control systems are one of the soltions which are exactly opposite to xed-time plans. Four different adaptive traf c control systems will be discussed. Each of them has unique characteristics that make it worthy to compare. The general architecture of these systems is based on a similar concept, but there is a great number of general and detailed differences that makes them interesting to compare. By making a deep comparison between these systems, which is one of the outputs of this research, governments and the authorities in charge can have an appropriate reference to look for their bene ts and choose an adaptive traf c control system to apply to their networks.Studer, Luca; Ketabdari, Misagh; Marchionni, GiovannaStuder, LUCA PASINO; Ketabdari, Misagh; Marchionni, Giovann

Assessing the Impact of Rutting Depth of Bituminous Airport Runway Pavements on Aircraft Landing Braking Distance during Intense Precipitation

A runway pavement during its useful life is subject to a series of deteriorations because of repeated load cycles and environmental conditions. One of the most common deteriorations is the formation of rutting (surface depression in the wheel path) on the runway surface. Rutting negatively affects aircraft performance during landings and will behave even worse during precipitation or with the existence of fluid contaminations on the surface. This paper aims to develop a model for calculating aircraft braking distance during landing on wet-pavement runways affected by rutting based on dynamic skid resistances generated by tire–fluid–pavement interactions. Intense precipitation, variable rutting depths for a 100 m length step, water film depths (e.g., 1 to 26 mm), and aircraft wheel loads (e.g., 10 to 140 kN) are considered as the boundary conditions of the developed model. The output is a model that can estimate aircraft braking distance as a function of rutting depth and can perform further assessment of the probability of the occurrence of landing overrun. After validating the model with existing methodologies and calibrating it according to the actual landing distance required for each type of aircraft, an Italian airport is simulated using a model with real data regarding the level of service of its pavement surface characteristics

SHORT-TERM PREDICTION AND ANALYSIS OF WAVE-INDUCED MOTION AND LOAD RESPONSES OF A WAVE-PIERCING TRIMARAN

In this paper, we used a statistical short-term analysis in order to determine the wave-induced motions and loads responses of a trimaran ship with three side hull configurations including symmetric, inboard and outboard types. The calculation of these wave-induced loads was carried out using MAESTRO-Wave, a seakeeping analysis code. A rule-based design for the hull was created based on the American Bureau of Shipping (ABS) rules followed by building a global FEM model of the ship with MAESTRO to predict the wave-induced motion and load responses. In order to validate the numerical prediction, we tested a rigid segmented model of trimaran with symmetric side hull configuration in the National Iranian Marine Laboratory (NIMALA) towing tank. The numerical results revealed that transverse torsion moments and shear forces are significant in head seas. But, transverse bending moments have higher response magnitudes in oblique seas. Also, in transverse wave loads, outboard side hulls offer slightly better performance in waves in comparison to the other forms. This study offers useful information on wave-induced motion and load responses for the purpose of balancing sea-keeping performance as well as other design considerations in developing the conceptual design of a wave-piercing trimaran

Influence of Embedded Charging Units Characteristics on Long-Term Structural Behavior of E-Roads

The use of Electric Vehicles (EV) seems to be a promising solution to achieve a sustainable road transport system. Among the contactless dynamic vehicle charging technologies, the use of Charging Units (CUs)—cement concrete box—embedded into the road pavement seems to be a favorable option. The available scientific papers related to the structural effects of embedding CUs in road pavements consider the CU as a solid box, even if a cavity is needed for the electrical technologies’ accommodation. This is why the current research is aimed at studying electrified roads (e-road) with different CU cavity shapes and dimensions. In detail, pavement structural responses are investigated, as a first step, adopting a Finite Element Model (FEM), and, as a second step, the long-term performances (fatigue cracking/rutting proneness) are evaluated. The study is divided into two phases: the theoretical fatigue/rutting assessment, which allows to calculate the critical load repetitions leading to pavement failure, and an urban case study with the goals of both assessing the theoretical results and computing fatigue/rutting performance with real scale traffic conditions. The outcomes demonstrate that CUs can be used with no significant impacts on the long-term road pavement structural performance, laying the foundation for a future upgrading of the existing urban road networks

Boussinesq Modelling of Waves and Currents in the Presence of Submerged Detached/Discontinuous Breakwaters

The effect of beach configurations with the main focus on the detached submerged breakwater on shoreline currents is investigated numerically. The Boussinesq equations are used to model the beach with a constant slope, continuous submerged breakwater, and discontinuous/detached submerged breakwater. Our numerical simulation results show that the transient rip currents are generated near the shoreline at the beach with constant slope while the continuous submerged breakwater structure creates a calm beach area along the shoreline. The presence of the gap in submerged breakwater changes the currents along the shoreline by generating rip currents with two pairs of vortices. One pair of vorticities, located around the gap, damage the breakwater by transmitting sediments along the breakwater foundation and eroding its surface. The second pair, created near the shoreline, erodes the shoreline due to sediment transportation and leads to a dangerous and unsafe situation for swimmers. The rip current creates five main critical areas with the maximum velocity towards the shoreline and offshore. The first set of three areas (numbered 1, 2, 3) has an approximately average velocity of 1-1.25 m/s towards the shoreline. One of these areas (numbered 2) is located close to the shoreline and the other two (numbered 1 and 3) are found to occur near the edge of the detached part of the breakwater. The second set of the two areas (numbered by 4 and 5) has the average velocity that is higher than 2.1 m/s towards the offshore and is located at the beginning part of the rip neck. An approximately linear relationship between the returning velocity and the gap length is observed. As the gap length decreases the location of the areas (numbered 4 and 5) gets closer to the center of the gap. Our simulations indicate that the return velocity towards the offshore increases at the gap center while the gap length decreases. Furthermore, the velocity profiles have a sharp jump for gap length that is approximately smaller than 80 m. Also, the return velocity at the gap center is related to the height of the breakwater. The breakwater that is higher (the breakwater height d = 4.2 m) damps wave energy more than shorter breakwater and the return velocity decreases for this structure. For smaller heights (d = 3.7 and 3.2) damping is nearly the same and the returning flow varies depending on the available space through the gap. Specifically, the return velocity for d = 3.7 is higher than that for d = 3.2. The numerical results presented herein suggest that aggressive rip currents are generated in the case of detached submerged breakwater beach configurations

Wave-induced loads on cross-deck of a wave-piercing trimaran with different hull forms of outriggers

Trimaran has unique hull form with a rapidly growth in recent years due to its application as a mode of transports and naval vessels. Designing trimaran faces many technical challenges because of its complex structural outlines and high-speeds operation. This article investigates the influence of side hulls configuration (symmetric, inboard and outboard types) for wave loads on cross-deck of a trimaran ship when advancing at sea in regular waves. The computation of these hydrodynamic forces is carried out using MAESTRO-Wave 3D panel method code. This code is based on potential flow theory that uses Green’s function with the forward speed correction in the frequency domain. The results demonstrate that the outboard side hull form has the best performance on wave-induced load among three kinds of side hull forms. Furthermore, the results of this study offer more information for selecting the side hull form of the trimaran

Effect of recycled concrete aggregate features on adhesion properties of asphalt mortar-aggregate interface

Asphalt-aggregate interface’s adhesion properties commonly affect the damage initiation and evolution within asphalt concrete materials, related to pavement durability and quality. The scope of this research was to investigate the influence of Recycled Concrete Aggregate (RCA) features on asphalt mortar-aggregate interface adhesion. Firstly, a three-dimensional reconstruction model of RCA was carried out using X-ray CT tomography and digital image processing. In this regard, five feature indicators, namely cement mortar content, sphericity, flat and elongated ratio, angularity, and surface texture, were proposed. Based on a bilinear cohesive zone model, the interface damage behavior of asphalt mortar-RCA was investigated by using a uniaxial compression simu- lation. Finally, a GA-BP artificial neural network was conducted to predict and quantify the effect of each feature indicator of RCA on interface adhesion. The results showed that when RCA had lower cement mortar content, higher sphericity value, and smoother surface, the asphalt mortar-RCA system was less prone to interface adhesion failure. The 5-14-1 GA-BP artificial neural network proposed in this study showed very good perfor- mance in predicting the interfacial dissipation damage energy with a mean-squared error value of 3.52 × 10^-4 for testing dataset. The cement mortar content parameter exhibited a remarkable influence on the interface adhesion property, and its global contribution to the interfacial dissipation damage energy (0.3486) was more than twice that of the surface texture parameter (0.1316). In future studies, the performance characteristics of cement mortar can be further investigated, thereby proposing RCA’s performance optimization technology