Fluid-Structure Interaction of Stirrers in Mixing Vessels: Part II — Fully Coupled Simulation

2002 ◽  
Author(s):  
Thomas Berger ◽  
Bernhard Eckl ◽  
Klaus Strohmeier
Keyword(s):  
Rotational Speed ◽  
Analytical Data ◽  
Coupled Analysis ◽  
Structural Dynamic ◽  
Fluid Medium ◽  
Sliding Mesh ◽  
User Subroutine ◽  
Accurate Design ◽  
Critical Rotational Speed ◽  
Fully Coupled

Mixing Stirrers are subjected to severe damages [Strohmeier (1996), Strohmeier and Ho¨lzl (1998)] when the rotational speed approaches the critical rotational speed nkrit (eigenfrequency). Because of resonant vibrations, the stirrer deflection approaches infinity (no damping case). The possibilities of an accurate design of mixing stirrers with analytical calculations [Fischer and Strohmeier (2000)] are often very unsatisfactional, due to the complex effects of the fluid medium on the structure (impeller), and consequently its critical speed and its vibrational amplitudes cannot be readily defined. To consider transient fluid effects and out-of-balance forces, it is necessary to implement a coupled analysis of flow field and structural dynamic response of the stirrer in the CFD code as a user subroutine. As a new aspect, a rotating grid (sliding mesh) was combined with a deformable grid to simulate the impeller movement. The results are compared to experimental and analytical data and show good agreement.

Numerical Simulation of Stirrer Oscillations in Consideration of Fluid-Structure-Interaction and Flexible Restraint Systems

2003 ◽  
Author(s):  
Thomas Berger ◽  
Klaus Strohmeier
Keyword(s):  
Rotational Speed ◽  
Fluid Dynamic ◽  
Dynamic Effects ◽  
Resonant Vibrations ◽  
Structural Dynamic ◽  
Structure Interaction ◽  
Critical Rotational Speed ◽  
Method Of Solution ◽  
Fully Coupled ◽  
Good Agreement

Stirrers are subjected to severe damages when the rotational speed n approaches the critical rotational speed nkrit (eigenfrequency). Appearing resonant vibrations result in huge stirrer shaft bending deformations and possible stirrer damages (see Figure 1). The possibilities of an accurate stirrer design (regarding the shaft vibrations) with analytical calculations [Fischer and Strohmeier (2000)] are often very unsatisfactional: The fluid dynamic effects on the structure and the real, often flexible, restraint systems cannot be considered. Both aspects, however, have an important influence, both on the critical rotational speed nkrit, and the oscillation amplitudes of the stirrer. As a method of solution, a fully coupled interaction of flow field and structural dynamic response of the stirrer is implemented in a commercial CFD-Code. The simulated results are compared to experimental data and show good agreement.

Fluid-Structure Interaction of Stirrers in Mixing Vessels

2003 ◽  
Vol 125 (4) ◽  
pp. 440-445 ◽  
Author(s):  
Thomas Berger ◽  
Michael Fischer ◽  
Klaus Strohmeier
Keyword(s):  
Analytical Data ◽  
Fluid Structure Interaction ◽  
Life Time ◽  
Coupled Analysis ◽  
Major Influence ◽  
Integration Scheme ◽  
Structural Dynamic ◽  
Fluid Structure ◽  
Structure Interaction ◽  
Analytical Formulas

Mixing stirrers are subject to severe damages when the rotational speed approaches the Eigenfrequency. Because of resonant vibrations, the stirrer deflection approaches infinity in the no damping case. Damping due to fluid-structure interaction between the mixing stirrer and the fluid in the vessel has major influence on the Eigenfrequency. Coupled analysis of the flow field within a mixing vessel and the structural dynamic response of the stirrer is necessary in order to evaluate vibrational amplitudes to guarantee life time safety for the stirrer. A simplified numerical model based on Newmark’s integration scheme is developed for the stirrer dynamics that is suitable to be implemented in a CFD code as a user subroutine. Results in terms of Eigenfrequencies are compared to results of analytical formulas and FEM results and show excellent agreement. The fully fluid-structure coupled analysis is also presented. As a new aspect, a rotating grid (sliding mesh) was combined with a deformable grid to simulate the impeller movement. The results are compared to experimental and analytical data and show good agreement.

Reliability Analysis of Short Term Mooring Tension of a Semi-Submersible System

2018 ◽  
Author(s):  
Sheng Xu ◽  
C. Guedes Soares ◽  
Ângelo P. Teixeira
Keyword(s):  
Reliability Analysis ◽  
Line Strength ◽  
Coupled Analysis ◽  
Mooring Line ◽  
Global Maximum ◽  
Hydrodynamic Drag ◽  
Sampling Point ◽  
Wave Condition ◽  
Drag Coefficients ◽  
Fully Coupled

A detail procedure to study mooring line strength reliability is presented. A fully coupled analysis is carried out to get the mooring tensions of a deep water semi-submersible floating systems operated in 100 year wave condition in South China Sea. The ACER method is applied to predict the 3h extreme mooring tension, and the results are validated by global maximum method. The hydrodynamic sampling points are generated by Latin Hypercube Sampling technique. The 3h extreme mooring tension is calculated by the ACER method with 10 minutes fully coupled dynamic simulation for each sampling point. The Kriging meta model method is trained to predict 3h mooring extreme tension under the effects of random hydrodynamic drag coefficients. A reliability analysis is carried out by implementing Monte Carlo simulation with the random hydrodynamic drag coefficients and mooring breaking strength considered.

Numerical and Experimental Tools for Offshore DP Operations

2011 ◽  
Author(s):  
Fabiano P. Rampazzo ◽  
Joa˜o Luis B. Silva ◽  
Daniel P. Vieira ◽  
Antonio L. Pacifico ◽  
Lazaro Moratelli Junior ◽  
...  
Keyword(s):  
Environmental Conditions ◽  
Experimental Tests ◽  
Coupled System ◽  
Coupled Analysis ◽  
Cfd Analysis ◽  
Maximum Condition ◽  
Commercial Code ◽  
Close Proximity ◽  
Fully Coupled ◽  
Two Bodies

DP crane vessel operation can be analyzed based on the uncoupled system or considering the fully coupled system. Parameters such as top-crane acceleration, thruster capability and vessel motions are evaluated for several environmental conditions. Numerical and experimental tools are used and the important result of this analysis is the maximum condition in such that the operation can be safely executed. Those operations are critical, since the vessel is kept in close proximity with other unit and large loads are transported in a pendulum configuration. A precise positioning of the crane-vessel is required, in order to avoid unsafe relative motions, as well as keep the load being transported on a stable position. The uncoupled analysis approach does not consider the influence of the other unit in the crane vessel. This paper presents a methodology for evaluating a DP crane vessel in the offshore operations (DP crane vessel, load being transported, mooring and assistance lines, platform) considering the fully coupled method based on integration of the in house codes with the commercial code WAMIT® system. The methodology is based on the integration of numerical and experimental tools. The dimensions of the transported modules and the proximity of the vessels change the behavior of the vessel motions and line tensions. So, a full nonlinear time domain simulator (TPN – Numerical Offshore Tank) is used to perform the coupled analysis of the system subjected to several environmental conditions, considering also the dynamics of the suspended load and the hydrodynamic interference between the bodies. In order to calibrate the numerical model, several experimental tests are performed such as wind tests with some positions of the crane, tests in towing tanks to evaluated the current effects, thrusters tests to calibrate DP algorithm and wave test with the two bodies. In some cases a complementary CFD analysis is requested in order to evaluate the current and wind shadow effect. Several alternative relative positions between the vessels can be evaluated. This methodology results a more accurate estimative of the system performance.

Numerical Design of Extrusion Process Using Finite Thermo-Elastoviscoplasticity with Damage. Prediction of Chevron Shaped Cracks

2009 ◽  
Vol 424 ◽  
pp. 265-272 ◽  
Author(s):  
Carl Labergère ◽  
Khemais Saanouni ◽  
Philippe Lestriez
Keyword(s):  
Constitutive Equations ◽  
Thermal Effects ◽  
Initial Temperature ◽  
Kinematic Hardening ◽  
Extrusion Process ◽  
Main Process ◽  
Damage Prediction ◽  
User Subroutine ◽  
Micro Cracks ◽  
Fully Coupled

The influence of the initial temperature and its evolution with large plastic deformation on the formation of the fully coupled chevron shaped cracks in extrusion is numerically investigated. Fully coupled thermo-elasto-viscoplastic constitutive equations accounting for thermal effects, mixed and nonlinear isotropic and kinematic hardening, isotropic ductile damage with micro-cracks closure effects are used. These constitutive equations have been implemented in Abaqus/Explicit code thanks to the user subroutine vumat and used to perform various numerical simulations needed to investigate the problem. It has been shown that the proposed methodology is efficient to predict the chevron shaped cracks in extrusion function of the main process parameters including the temperature effect.

Towards the Integration of Analysis and Design of Mooring Systems and Risers: Part I — Studies on a Semisubmersible Platform

2002 ◽  
Author(s):  
Stael Ferreira Senra ◽  
Fabricio Nogueira Correa ◽  
Breno Pinheiro Jacob ◽  
Ma´rcio Martins Mourelle ◽  
Isai´as Quaresma Masetti
Keyword(s):  
Motion Analysis ◽  
Production Systems ◽  
Companion Paper ◽  
Coupled Analysis ◽  
Mooring Line ◽  
Mooring System ◽  
Analysis And Design ◽  
Design Methodologies ◽  
Campos Basin ◽  
Fully Coupled

The objective of this paper is to study different analysis methodologies for the design of floating production systems. The main issues are the use of uncoupled and coupled analysis methods, and the integration in the analysis and design of the mooring system and the risers. This paper is a companion to another paper also presented in the OMAE2002 Conference [1] The present paper begins describing a “basic” classic, uncoupled methodology, and proceeds with comments on some refinements in the representation of the behavior of the lines in the motion analysis of the vessel. Comments regarding the introduction of some level of integration between mooring line and riser behavior are also presented. These issues are illustrated with studies applying some of the considered design methodologies to the P-18 semi-submersible platform in Campos basin. The companion paper [1] proceeds describing a fully coupled methodology, and some hybrid methodologies that combine coupled and uncoupled analysis tools, and illustrates their application to a DICAS system for deepwater applications in Campos basin.

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