scholarly journals MODELLING WAVE-INDUCED RESIDUAL PORE PRESSURE AND DEFORMATION OF SAND FOUNDATIONS UNDERNEATH CAISSON BREAKWATERS

2012 ◽  
Vol 1 (33) ◽  
pp. 56
Author(s):  
Hisham El Safti ◽  
Matthias Kudella ◽  
Hocine Oumeraci
Keyword(s):  
Large Scale ◽  
Pore Fluid ◽  
Model Verification ◽  
Computational Time ◽  
Governing Equations ◽  
Surface Plasticity ◽  
Preliminary Validation ◽  
Fluid Convection ◽  
Wave Induced ◽  
Fully Coupled

A finite volume model is developed for modelling the behaviour of the seabed underneath monolithic breakwaters. The fully coupled and fully dynamic Biot’s governing equations are solved in a segregated approach. Two simplifications to the governing equations are presented and tested: (i) the pore fluid acceleration is completely neglected (the u-p approximation) and (ii) only the convective part is neglected. It is found that neglecting the pore fluid convection does not reduce the computational time for the presented model. Verification of the model results with the analytical solution of the quasi-static equations is presented. A multi-yield surface plasticity model is implemented in the model to simulate the foundation behaviour under cyclic loads. Preliminary validation of the model with large-scale physical model data is presented.

Modelling Sand Foundation Behaviour Underneath Caisson Breakwaters Subject to Breaking Wave Impact

2013 ◽  
Author(s):  
Hisham El Safti ◽  
Hocine Oumeraci
Keyword(s):  
Porous Media ◽  
Fluid Pressure ◽  
Model System ◽  
Pore Fluid ◽  
Constant Density ◽  
Pore Fluid Pressure ◽  
Wave Impact ◽  
Surface Plasticity ◽  
Caisson Breakwater ◽  
Fully Coupled

A one-way CFD-CSD coupled model system is presented to reproduce large scale experiments of a caisson breakwater, subject to wave attack. The Computational Structural Dynamics (CSD) model is developed using the finite volume method for the fully dynamic, fully coupled Biot equations. The fully coupled poro-mechanical analysis is handled in a segregated approach in which the skeleton displacement, the pore fluid pressure and the pore fluid velocity (relative to the skeleton) are decoupled at the iteration level. The pore fluid pressure-velocity coupling is resolved using the PISO (Pressure Implicit with Splitting of Operators) algorithm. Two simplifications to the porous media formulations were introduced: (1) neglecting convective acceleration of pore fluid and (2) fully neglecting acceleration of the pore fluid (the u-p approximation). A frictional contact model is implemented to model soil-structure interaction. A multi-surface plasticity model with the Drucker-Prager failure criterion is introduced to model the behavior of sand foundations under cyclic load posed by wave action on the caisson breakwater. An incompressible (constant density) multiphase Computational Fluid Dynamics (CFD) solver is developed for solving flow inside and outside porous media simultaneously using the principle of volume averaged velocity. A seepage model is implemented to model flow resistance of porous media that includes viscous, transitional, inertial and transient terms. An additional term is introduced to the fluid continuity equation to account for fluid mixture (water and air) compressibility (inverse of bulk modulus). The CFD-CSD model system is developed using the OpenFOAM® framework.

Parallel Computation of a Mixed Convection Problem Using Fully-Coupled and Segregated Algorithms

2004 ◽  
Author(s):  
Masoud Darbandi ◽  
Araz Banaeizadeh ◽  
Gerry E. Schneider
Keyword(s):  
Mixed Convection ◽  
Parallel Computation ◽  
Large Scale ◽  
Stokes Equations ◽  
Computational Time ◽  
Linear Algebraic Equations ◽  
The Matrix ◽  
Convection Problem ◽  
Run Time ◽  
Fully Coupled

In this work, parallel solution of the Navier-Stokes equations for a mixed convection heat problem is achieved using a finite-element-based finite-volume method in fully coupled and semi coupled algorithms. A major drawback with the implicit methods is the need for solving the huge set of linear algebraic equations in large scale problems. The current parallel computation is developed on distributed memory machines. The matrix decomposition and solution are carried out using PETSc library. In the fully coupled algorithm, there is a 36-diagonal global matrix for the two-dimensional governing equations. In order to reduce the computational time, the matrix is suitably broken in several sub-matrices and they are subsequently solved in a segregated manner. This approach results in four 9-diagonal matrices. Different sparse solver algorithms are utilized to solve a mixed natural-forced convection problem using either fully-coupled or semi-coupled algorithms. The performance of the solvers are then investigated in solving on a distributed computing environment. The study shows that the iteration run time considerably decreases although the overall run time of the fully coupled algorithm still looks better.

A Simplified Numerical Method to Determine the Loads Acting on the Cutterhead of a Compound Shield

2011 ◽  
Vol 199-200 ◽  
pp. 25-31
Author(s):  
Fei Jiang He ◽  
Qiang Zhang ◽  
Zong Xi Cai
Keyword(s):  
Large Scale ◽  
Earth Pressure ◽  
Coupled System ◽  
Governing Equations ◽  
The Earth ◽  
Nonlinear Contact ◽  
Total Thrust ◽  
Set Up ◽  
The Relationship ◽  
Fully Coupled

In order to determine the loads acting on the cutterhead of a compound shield, this paper aims at the large-scale and fully coupled system of the excavation face. Firstly, a new model is proposed to calculate the loads acting on a single cutter, in which the earth pressure of the chamber is taken into consideration. Then, by transforming the large-scale nonlinear contact problem into a smaller one, we set up the governing equations only including the penetration depth of cutters in the approach of the sub-structure condensation, to calculate the loads acting on the cutterhead. Finally, the relationship between the penetration per revolution and the total thrust and total torque acting on the cutters of the cutterhead of a compound shield is investigated.

Combustion Driven by Fragment-based Ab Initio Molecular Dynamics Simulation

2019 ◽  
Author(s):  
Liqun Cao ◽  
Jinzhe Zeng ◽  
Mingyuan Xu ◽  
Chih-Hao Chin ◽  
Tong Zhu ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Ab Initio ◽  
Large Scale ◽  
Methane Combustion ◽  
Combustion Method ◽  
Dynamics Simulation ◽  
Ab Initio Molecular Dynamics ◽  
Computational Time ◽  
Combustion Mechanism ◽  
Daily Lives

Combustion is a kind of important reaction that affects people's daily lives and the development of aerospace. Exploring the reaction mechanism contributes to the understanding of combustion and the more efficient use of fuels. Ab initio quantum mechanical (QM) calculation is precise but limited by its computational time for large-scale systems. In order to carry out reactive molecular dynamics (MD) simulation for combustion accurately and quickly, we develop the MFCC-combustion method in this study, which calculates the interaction between atoms using QM method at the level of MN15/6-31G(d). Each molecule in systems is treated as a fragment, and when the distance between any two atoms in different molecules is greater than 3.5 Å, a new fragment involved two molecules is produced in order to consider the two-body interaction. The deviations of MFCC-combustion from full system calculations are within a few kcal/mol, and the result clearly shows that the calculated energies of the different systems using MFCC-combustion are close to converging after the distance thresholds are larger than 3.5 Å for the two-body QM interactions. The methane combustion was studied with the MFCC-combustion method to explore the combustion mechanism of the methane-oxygen system.

scholarly journals Modeling of Thermal Effects in Semiconductor Structures

VLSI Design ◽  
1998 ◽  
Vol 8 (1-4) ◽  
pp. 53-58
Author(s):  
Christopher M. Snowden
Keyword(s):  
Thermal Effects ◽  
Large Scale ◽  
High Electron Mobility Transistors ◽  
Thermal Modelling ◽  
High Electron ◽  
Temperature Model ◽  
Active Devices ◽  
Electron Mobility Transistors ◽  
Fully Coupled ◽  
Scale Surface

A fully coupled electro-thermal hydrodynamic model is described which is suitable for modelling active devices. The model is applied to the non-isothermal simulation of pseudomorphic high electron mobility transistors (pHEMTs). A large-scale surface temperature model is described which allows thermal modelling of semiconductor devices and monolithic circuits. An example of the application of thermal modelling to monolithic circuit characterization is given.

Reduction of Noise Inside a Cavity by Piezoelectric Actuators

2003 ◽  
Vol 125 (1) ◽  
pp. 12-17 ◽  
Author(s):  
I. Hagiwara ◽  
D. W. Wang ◽  
Q. Z. Shi ◽  
R. S. Rao
Keyword(s):  
Sound Pressure ◽  
Control Mechanism ◽  
Equations Of Motion ◽  
Piezoelectric Actuators ◽  
Governing Equations ◽  
Control Laws ◽  
Modal Coupling ◽  
Modal Amplitude ◽  
Global And Local ◽  
Fully Coupled

A new analytical model is developed for the reduction of noise inside a cavity using distributed piezoelectric actuators. A modal coupling method is used to establish the governing equations of motion of the fully coupled acoustics-structure-piezoelectric patch system. Two performance functions relating “global” and “local” optimal control of sound pressure levels (SPL) respectively are applied to obtain the control laws. The discussions on associated control mechanism show that both the mechanisms of modal amplitude suppression and modal rearrangement may sometimes coexist in the implementation of optimal noise control.

A New Memetic Approach to Solve the Strategic Berth Template Problem

2021 ◽  
Vol 12 (3) ◽  
pp. 212-231
Author(s):  
Issam El Hammouti ◽  
Azza Lajjam ◽  
Mohamed El Merouani
Keyword(s):  
Large Scale ◽  
Container Terminal ◽  
Mathematical Formulation ◽  
Population Based ◽  
Allocation Problem ◽  
Computational Time ◽  
Berth Allocation ◽  
Berth Allocation Problem ◽  
Simulating Annealing ◽  
Annealing Algorithm

The berth allocation problem is one of the main concerns of port operators at a container terminal. In this paper, the authors study the berth allocation problem at the strategic level commonly known as the strategic berth template problem (SBTP). This problem aims to find the best berth template for a set of calling ships accepted to be served at the port. At strategic level, port operator can reject some ships to be served for avoid congestion. Since the computational complexity of the mathematical formulation proposed for SBTP, solution approaches presented so far for the problem are limited especially at level of large-scale instances. In order to find high quality solutions with a short computational time, this work proposes a population based memetic algorithm which combine a first-come-first-served (FCFS) technique, two genetics operators, and a simulating annealing algorithm. Different computational experiences and comparisons against the best known solutions so far have been presented to show the performance and effectiveness of the proposed method.

Advanced CFD Simulations of free-surface flows around modern sailing yachts using a newly developed openFOAM solver

2016 ◽  
Author(s):  
Janek Meyer ◽  
Hannes Renzsch ◽  
Kai Graf ◽  
Thomas Slawig
Keyword(s):  
Free Surface ◽  
Large Scale ◽  
Breaking Waves ◽  
Free Surface Flows ◽  
Body Motion ◽  
Computational Time ◽  
Efficient Computation ◽  
Surface Flows ◽  
Scale Free ◽  
Wide Range

While plain vanilla OpenFOAM has strong capabilities with regards to quite a few typical CFD-tasks, some problems actually require additional bespoke solvers and numerics for efficient computation of high-quality results. One of the fields requiring these additions is the computation of large-scale free-surface flows as found e.g. in naval architecture. This holds especially for the flow around typical modern yacht hulls, often planing, sometimes with surface-piercing appendages. Particular challenges include, but are not limited to, breaking waves, sharpness of interface, numerical ventilation (aka streaking) and a wide range of flow phenomenon scales. A new OF-based application including newly implemented discretization schemes, gradient computation and rigid body motion computation is described. In the following the new code will be validated against published experimental data; the effect on accuracy, computational time and solver stability will be shown by comparison to standard OF-solvers (interFoam / interDyMFoam) and Star CCM+. The code’s capabilities to simulate complex “real-world” flows are shown on a well-known racing yacht design.

Two-point similarity in temporally evolving plane wakes

2007 ◽  
Vol 577 ◽  
pp. 287-307 ◽  
Author(s):  
D. EWING ◽  
W. K. GEORGE ◽  
M. M. ROGERS ◽  
R. D. MOSER
Keyword(s):  
Large Scale ◽  
Single Point ◽  
Similarity Solutions ◽  
Similarity Analysis ◽  
Governing Equations ◽  
Large Scale Structures ◽  
Rate Dependent ◽  
Dependent Parameter ◽  
Scale Structures ◽  
Point Velocity

The governing equations for the two-point correlations of the turbulent fluctuating velocity in the temporally evolving wake were analysed to determine whether they could have equilibrium similarity solutions. It was found that these equations could have such solutions for a finite-Reynolds-number wake, where the two-point velocity correlations could be written as a product of a time-dependent scale and a function dependent only on similarity variables. It is therefore possible to collapse the two-point measures of all the scales of motions in the temporally evolving wake using a single set of similarity variables. As in an earlier single-point analysis, it was found that the governing equations for the equilibrium similarity solutions could not be reduced to a form that was independent of a growth-rate dependent parameter. Thus, there is not a single ‘universal’ solution that describes the state of the large-scale structures, so that the large-scale structures in the far field may depend on how the flow is generated.The predictions of the similarity analysis were compared to the data from two direct numerical simulations of the temporally evolving wakes examined previously. It was found that the two-point velocity spectra of these temporally evolving wakes collapsed reasonably well over the entire range of scales when they were scaled in the manner deduced from the equilibrium similarity analysis. Thus, actual flows do seem to evolve in a manner consistent with the equilibrium similarity solutions.

Integrated Redesign of Large-Scale Structures by Large Admissible Perturbations

2003 ◽  
Vol 125 (4) ◽  
pp. 234-241 ◽  
Author(s):  
Vincent Y. Blouin ◽  
Michael M. Bernitsas ◽  
Denby Morrison
Keyword(s):  
Degrees Of Freedom ◽  
Large Scale ◽  
Direct Method ◽  
Computational Effort ◽  
Forced Response ◽  
Response Amplitude ◽  
Computational Time ◽  
Performance Constraints ◽  
Large Admissible Perturbations ◽  
Design Selection

In structural redesign (inverse design), selection of the number and type of performance constraints is a major challenge. This issue is directly related to the computational effort and, most importantly, to the success of the optimization solver in finding a solution. These issues are the focus of this paper, which provides and discusses techniques that can help designers formulate a well-posed integrated complex redesign problem. LargE Admissible Perturbations (LEAP) is a general methodology, which solves redesign problems of complex structures with, among others, free vibration, static deformation, and forced response amplitude constraints. The existing algorithm, referred to as the Incremental Method is improved in this paper for problems with static and forced response amplitude constraints. This new algorithm, referred to as the Direct Method, offers comparable level of accuracy for less computational time and provides robustness in solving large-scale redesign problems in the presence of damping, nonstructural mass, and fluid-structure interaction effects. Common redesign problems include several natural frequency constraints and forced response amplitude constraints at various frequencies of excitation. Several locations on the structure and degrees of freedom can be constrained simultaneously. The designer must exercise judgment and physical intuition to limit the number of constraints and consequently the computational time. Strategies and guidelines are discussed. Such techniques are presented and applied to a 2,694 degree of freedom offshore tower.

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