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Code_Aster, free CAE software based on finite elements
 

Code_Aster is a software for finite element analysis and numerical simulation in structural mechanics and multiphysics.

Code_Aster feature:

- Type FEM : Linear & non-linear static / dynamic, thermal & fluid analysis
- Type of License : GPL
- Developer : Electricite de France (EDF)
-
Download
: Code_Aster
 

It was developed by the French company Electricite de France (EDF), for the study and maintenance of plants and power grids. He was released under the GNU General Public License in October 2001. Most documentation is available in French.

Code_Aster is a solver or processing engine, i.e. it does not include preprocessing and post - processing tools. This means that meshing and presentation of the solutions must be realized using other softwares for instance SALOME and ParaView respectively. In this regard, the version SALOME-MECA allows full functionality.

Their  applications span multiple disciplines: mechanical, thermal analysis, hydrodynamics, metallurgy, hydration, drying ...  Stationary or transient conditions, and both linear and nonlinear processes can be modelled. It also includes specific tools for fatigue, deformation, fracture, contact, geotechnics, porous materials, etc.


Code_Aster contains 1500000 lines of source code, mostly in Fortran and Python, and is constantly being developed, updated and improved with new models. The qualitative standards required by the nuclear industry have provided improvements to reach the highest levels of functionality and accuracy, which have been validated by independent comparisons with analytical and experimental results.

The software is provided with about 2000 test, dedicated to elementary grade, and are useful as examples. Code_Aster documentation includes over 14000 pages. Most of this documentation is only in French language.



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- Code Aster online course


 
Published 2016-04-14 12:56:15 by | Open
 
Hull modeling using Rhinoceros 3D
 
The most common way to model a 3D hull is using its plane forms. A plane form represents the water lines, as well as the longitudinal and transverse vertical sections. 



Plane forms of a small fishing ship.

By symmetry, only half ot the shift is drawn in the plane forms.

The most appropiate softwares for 3D modeling of the hull are Maxsurf and Rhinoceros, both work from NURBS surfaces. NURBS (acronym for non-uniform rational B-spline) is a mathematical model widely used to generate and represent curves and surfaces

The advantages of the 3D modeler Rhinoceros, are its facility to handle and its versality to adjust the geometry of the hull.
It also has tools for smoothing the hull (fairing), which is essential for a good 3D modeling and can be used later in the phase of numerical analysis.


Rhinoceros 3D was created by Robert McNeel & Associates. Recently, it has become popular in different industries, due to its multiple functions and relative low cost. It includes extensive import and export options since it is compatible with many softwares. Several additions (add-ons) are available, also developed by Robert McNeel & Associates, photorealistic rendering for raytracing (Flamingo) and KeyShot, photorealistic rendering non (Penguin) and animation (Bongo).

The version
RhinoMarine is adapted to the special characteristics required by naval designers including windbreaks, developable surfaces, curvature analysis, etc. In addition, RhinoMarine has the Orca3D supplement, an external plug-in that provides a full suite of specialized tools for shipbuilding design and analysis in Rhino.

An easy procedure to model a hull using Rhinoceros 3D is indicated below:
  • In Rhinoceros, it is possible to use a bipmap image as background. Using this image, it is possible to realize the plane forms. 
  • These curves can be used to generate NURBS surfaces corresponding to the true forms of the hull. 
  • Rhinoceros has a very useful tool "surface from network of curves". We can not use the curves that do not meet all conditions of validity. It is neccesary to selected curves intelligently to represent hull shapes.
  • It is neccesary to reconstruct and smooth NURBS surfaces.
 
Published 2016-04-11 11:42:11 by Carlos Rodríguez & Joshua | Open
 
CFD analysis of a biologically-inspired undulating marine propeller
 
Introduction:

Throughout history, practical implementation of rotating propulsion mechanisms was highly used because they are very easy to deal with; however, undulating mechanisms, which are very common in the nature, have been poorly considered.

Nowadays, engineering of marine vehicles and machines is maturing and new propulsion methods are being considered. The designs based on biologically-inspired propulsors are being increasingly studied. The problem is that many mechanisms of propulsion are not well understood yet. An important advance which helps to understand the hydrodynamics of biological swimming is the computational fluid dynamics (CFD). There are a lot of researchers who applied the CFD to study biological  swimming, for example, Borazjani, Sotiropoulos, Carling, Fauci, Liu, Lamas, Lewin, Sfakiotakis, Triantafyllou, Shen, etc.

In this work, a CFD model was developed to analyze the fluid flow over an undulating propeller. It is organized as follows.

CFD analysis:

The design of the experimental prototype was done from the CFD analysis to assess the most suitable configuration. The experimental prototype, shown in the figure, consists of an undulating foil propeller of 0.52 m wavelength, 0.02 m amplitude and 0.2 m width.

Innovacións Mariñas” Research Group (Coruña University - Spain) developed an undulanting propeller based on the patent No. 200002012. This patent refers to undulating systems and bodies in fluid mediums




The pressure field is indicated in the figure:




This is a video about the CFD simulation:




The main advantage of this system is that it is reversible, i.e., it has the same efficiency either operating forward or backward. This makes it ideal for vehicles that require high maneuverability.

COURSES RECOMMENDED:


imagencursoCFD with OpenFOAM online course

 
Published 2014-04-04 17:31:42 by Isabel Lamas & J.D. Rodríguez | Open
 
CFD analysis of the marine engine MAN 7S50MC
 

The MC series of the two-stroke MAN B&W Diesel were introduced in the early 80s of last century. Its main application is the propulsion of all types of vessels, medium and large sizes. These engines have also been used in terrestrial applications, mainly for production of electrical power.

 


An advantage of the MAN B&W MC series is that they incorporate the uniflow scavenging, much more efficient than the former competitors, such as Sulzer RND, MAN KSZ, among others, who employ loop or cross scavenging. 

Two-stroke engines generally have a drawback which has a great influence on the development of its operating cycle. This problem is motivated by the neccesity of the four phases of the operating cycle (expansion, exhaust, intake and compression ) in a single turn of the crankshaft, therefore the periods required for each of the phases are necessarily shorter than a four-stroke engine. Between them, the most critical stages are exhaust-intake, when the charge in the cylinder is renewed. For this reason, the design of the engine is extremely important.




The process of displacement the flue gases out of the cylinder, and filling with fresh air charge, called "scavenging", has a decisive influence on fuel consumption, power and pollution. 

 The following figure shows the airflow (red) and exhaust gas (blue) inside one of the cylinders.




As can be seen in the previous figure, incoming air is used to blow out or exhaust gas sweep and meanwhile filling the space with fresh air. 

The following figure was obtained through a CFD analysis. It shows the velocity distribution of the flow in the cylinder during the renovation of the load.



The following figure shows the mass fractions exhaust (blue) and air (red) for a tour from 90° to 270° crank angle.





In this CFD analysis, the free software OpenFOAM was employed. The reason is that this is an open source and thus it allows a complete manipulation of the governing equations. This is essential to carry out this type of analysis. It is necessary to adjust several parameters and some of them cannot be modified with other commercial softwares.

To read more about the realization of a CFD study of the scanning system of a type of two slow times we encourage you to read the article " Computational Fluid Dynamics Analysis of theScavenging Process in the MAN B & W 7S50MC Two-Stroke Marine Diesel Engine " published in journal of Ship Research, one of the publications with the highest impact factor in the world in its sector, with a type a classification according to the basis of JCR (journal Citation Reports) data.


COURSES RECOMMENDED:


imagencursoCFD with OpenFOAM online course



LINKS:

[5Grupo de Innovaciones Mariñas de la Universidad de La Coruña
 
Published 2016-02-12 15:30:35 by Carlos Rodriguez & Isabel Lamas | Open
 
CFD analysis about valve overlap period in the Wartsila 6L 46 four-stroke marine engine
 

Wartsila 6L 46 has six cylinders in line, and every cylinder has two inlet and two exhaust valves. The valve follower is of the roller tappet type, where the roller profile is slightly convex for good load distribution. The valve mechanism includes rocker arms working on yokes guided by pins. The Wartsila 46 is provided with Spex (Single pipe exhaust) system and with high efficiency turbocharger.

In the field of four-stroke marine engines, the Wartsila 6L 46 has become very popular on new cruise vessels, bulk carriers, cargo vessels, ferries, fishing boats, tankers, etc since it was launched onto the market in 1988. As the Wartsila 6L 46 is a non-reversing engine, in marine applications it is used as auxiliary engine (electric generator) or as main engine connected to a controllable pitch propeller. 

Figure 1: Trasversal cut marine diesel engine Wärtsilä 46.


Some examples of recent applications are the large Spain tuna fish vessels “Albatún 2” and “Panama Tuna”. Other example is the chemical tanker and the cruise vessel "Oasis of the Seas”.


Figure 2: Engine room in Oasis of the Seas, with Wartsilla 46 as electric generator.

Particularly, the valve timing events for the Wartsila 6L 46 are shown in the next Fig. As can be seen, the exhaust valves open 53º before BDC and close 44º after TDC. On the other hand, the intake valves open 50º before TDC and close 26º after BDC. As can be seen, there is a period of 94º between the exhaust and intake strokes when the intake valves are opening and the exhaust valves are closing, i.e., all valves are opened simultaneously. This is called the valve overlap period.


Figure 4: Valves period in Wärtsilä 46.

Valve overlap period, and is very important in large four-stroke diesel engines with high turbocharging because the expelling of the burnt gases by the fresh air is more efficient. The overlap period is also useful to refrigerate (the entering air at low temperature refrigerates the walls of the combustion chamber, piston head and exhaust valves. Besides, this air mixes with the burnt gases, which are directed to the turbocharger turbine. If these gases were too hot, the turbine blades would be damaged).

For these reasons, the overlap period is very necessary. Unfortunately, the potential for mechanical or gas flow mayhem during the overlap period is obvious. If the cylinder and exhaust pressures are too high, large quantities of exhaust gas can be shuttled into the intake tract. This gas is hot, maybe 1000ºC, and can cause fuel residues on the back of the intake valves. Besides, if exhaust gas occupies the inlet conduct, only a fraction mass of air can be induced into the cylinder. If the air is not enough, the combustion is incomplete and the consequence is that an excess of unburned hydrocarbon emissions are expelled to the atmosphere. Hence, the design process of the engine during the valve overlap period is a very critical issue. In this regard, CFD is a very useful tool.

The principle of operation of CFD codes is subdividing the domain into a number of smaller, non-overlapping subdomains. The result is a grid (or mesh) of cells (or elements). In this work, a grid generation program, Gambit 2.4.6, was used to generate the mesh. Due to the movement of the piston and valves, the domain changes into a new position of the calculation and the grid must be automatically reconstruct at each time step. The number of elements varies from 40000 at top dead center, to 500000 at bottom dead center. In order to minimize the number of cells and obtain good convergence, hexahedral elements were used to mesh the cylinder. Unfortunately, hexahedral elements do not adapt properly to the complex geometry of the valves and ducts, for this reason, tetrahedral elements were employed to the cylinder head and ducts. The cylinder head, especially around valves, was refined in order to capture the complex characteristics of the flow.



Figure 5: Mesh cylinder Wartsilla 46.

At the beginning of the simulation, the pressure descends drastically due to the expansion of the piston. When the exhaust valves are opened, the in-cylinder pressure is slightly superior to the exhaust pressure, therefore burnt gasses are expelled through the exhaust ducts. When the intake valves are also opened, the in-cylinder pressure has an appropriate value, between the exhaust and intake pressures. Consequently, air enters through the intake ducts and burnt gases continue being expelled through the exhaust ducts.

The velocity field overlaid with the pressure field. As initial conditions, the velocity inside the cylinder was imposed as the lineal velocity of the piston and it was assumed that the cylinder and exhaust ducts are full of burnt gases (red color), while the intake duct is full of air (blue color). When the exhaust valves are opened, high velocity burnt gases are expelled trough the exhaust ducts. A short time later, the inlet valves are opened and air enters through the intake ducts and burnt gases are expelled through the exhaust ducts. This process of entering fresh air and expelling burnt gases was verified during all the overlap period, i.e., between 310º and 404º. No retrocesión of burnt gases to the intake ducts was produced. This jeans that these operating conditions are adequate. Finally, at the end of the simulation, all valves are closed and residual velocities remain into the cylinder.



Figure 6: Results velocity field with CFD analysis

In this work, numerical and experimental tests were performed over a commercial four-stroke marine engine, the Wartsila 6L 46. A CFD model has been used to simulate the exhaust, intake and compression strokes. Special attention was focused on the overlap valve period, which has a crucial influence on the performance of the engine. It was verified that the fluid flow during the overlap period is correct (no reverse flow was obtained). This work was validated, verifying measurements of the in-cylinder pressure.

This model is an unprecedented opportunity for engineers to understand the highly complex flow interactions that occur in an engine, providing extra information which can not be analyzed with experimental techniques. Besides, this is a very useful tool do improve the performance of the new designs of engines because it is very easy and reasonably cheap to study the influence of parameters such as the exhaust and intake pressures, engine speed, cam profile design, etc. In order to obtain good results, it is necessary to make several meshes and ensure that the results are independent of the mesh.

 

COURSES RECOMMENDED:


imagencursoCFD with OpenFOAM online course


LINKS
: Wärtsilä, OpenFOAM, Polish Maritime Research
 
Published 2014-04-09 11:58:46 by Carlos Rodriguez & Isabel Lamas | Open
 
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