A Comparison of Alternative Bow Configurations

1995 ◽  
Vol 32 (03) ◽  
pp. 224-230
Author(s):  
Chel Stromgren
Keyword(s):  
State Of The Art ◽  
Computer Software ◽  
Hydrodynamic Performance ◽  
Construction Costs ◽  
Hull Form ◽  
Newport News ◽  
Standard Product ◽  
Computational Fluid Dynamics Cfd ◽  
Hydrodynamic Effects ◽  
Ship Speed

Newport News Shipbuilding (NNS) has been preparing for a reentry into the commercial shipbuilding market for several years. Those preparations resulted in the signing of a contract in October of 1994 with Eletson Corporation for the construction of two (with an option for an additional two)46500 dwt product carriers. This is the first contract for a U.S. shipyard to build commercial ships for a foreign owner in 37 years. In developing the hull form for the standard product carrier Double Eagle, NNS performed studies to determine the economic and hydrodynamic effects of alternative bow configurations on a representative modern, high-block tanker. The objectives of the study were to update the NNS commercial ship speed-power database, investigate the application of state of the art computer software, and create a bow design which strikes a balance between hydrodynamic performance and producibility. To achieve these goals, NNS worked with SAIC to use the computational fluid dynamics (CFD) SLAW software to mathematically analyze several candidate bows. These designs were then model tested at the Swedish State Model Basin in Gothenburg to validate the results of the CFD codes. Construction costs were then estimated for each design and finally, the bow forms were compared on an overall economic basis.

scholarly journals Validation of a CFD Methodology for Positive Displacement LVAD Analysis Using PIV Data

2009 ◽  
Vol 131 (11) ◽  
Author(s):  
Richard B. Medvitz ◽  
Varun Reddy ◽  
Steve Deutsch ◽  
Keefe B. Manning ◽  
Eric G. Paterson
Keyword(s):  
Left Ventricular ◽  
Hydrodynamic Performance ◽  
Ventricular Assist ◽  
Shear Rates ◽  
Eddy Simulation ◽  
Positive Displacement ◽  
Image Velocimetry ◽  
Computational Fluid Dynamics Cfd ◽  
High Level

Computational fluid dynamics (CFD) is used to asses the hydrodynamic performance of a positive displacement left ventricular assist device. The computational model uses implicit large eddy simulation direct resolution of the chamber compression and modeled valve closure to reproduce the in vitro results. The computations are validated through comparisons with experimental particle image velocimetry (PIV) data. Qualitative comparisons of flow patterns, velocity fields, and wall-shear rates demonstrate a high level of agreement between the computations and experiments. Quantitatively, the PIV and CFD show similar probed velocity histories, closely matching jet velocities and comparable wall-strain rates. Overall, it has been shown that CFD can provide detailed flow field and wall-strain rate data, which is important in evaluating blood pump performance.

An Integrated Ship Re-Design/Modification Strategy

2019 ◽  
Vol 161 (A1) ◽  
Keyword(s):  
Computer Aided Design ◽  
Modular Design ◽  
Ship Hull ◽  
Cfd Model ◽  
Hull Form ◽  
Design Modification ◽  
Technical Parameters ◽  
Computational Fluid Dynamics Cfd ◽  
Bulbous Bow ◽  
Aided Design

Herein, we present an integrated ship re-design/modification strategy that integrates the ‘Computer-Aided Design (CAD)’ and ‘Computational Fluid Dynamics (CFD)’ to modify the ship hull form for better performance in resistance. We assume a modular design and the ship hull form modification focuses on the forward module (e.g. bulbous bow) and aft module (e.g. stern bulb) only. The ship hull form CAD model is implemented with NAPA*TM and CFD model is implemented with Shipflow**TM. The basic ship hull form parameters are not changed and the modifications in some of the technical parameters because of re-designed bulbous bow and stern bulb are kept at very minimum. The bulbous bow is re-designed by extending an earlier method (Sharma and Sha (2005b)) and stern bulb parameters for re-design are computed from the experience gained from literature survey. The re-designed hull form is modeled in CAD and is integrated and analyzed with Shipflow**TM. The CAD and CFD integrated model is validated and verified with the ITTC approved recommendations and guidelines. The proposed numerical methodology is implemented on the ship hull form modification of a benchmark ship, i.e. KRISO container ship (KCS). The presented results show that the modified ship hull form of KCS - with only bow and stern modifications - using the present strategy, results into resistance and propulsive improvement.

New Promising Generation of Twin-Gondola LNG Carriers Optimized with the Aid of CFD Calculations

2005 ◽  
Author(s):  
Henk V. Valkhof ◽  
Eduardo Minguito ◽  
Klaas Kooiker
Keyword(s):  
Viscous Flow ◽  
Far East ◽  
Point Of View ◽  
Maximum Efficiency ◽  
Hull Form ◽  
Overall Design ◽  
Computational Fluid Dynamics Cfd ◽  
New Generation ◽  
Hydrodynamic Optimization ◽  
Adequate Design

As natural gas is becoming an important energy source, a large fleet is needed to transport it in liquefied form across the oceans in specially designed LNG carriers from mainly the Middle East towards the Far East. During the overall design process of such a vessel the shape of the hull form and its propulsors play an important role from a hydrodynamic point of view. This paper describes the design of a twin-gondola LNG carrier for Navantia. The twingondola aft body has proven to be an adequate design concept, but due to the complexity of the flow around the aft body the design should be carried out with great care. Computational Fluid Dynamics (CFD) tools are extremely valuable in the hydrodynamic optimization process of the hull. In this design both potential flow codes and viscous flow codes have been used to obtain the optimum hull form. With the results of the PARNASSOS viscous flow calculations it was possible to make decisions with regard to the horizontal angle and the inclination of the gondolas, and the slope of the buttocks in the area between the gondolas. Special attention has been paid to avoid flow separation around the aft body. The gondolas have been oriented in such a way that maximum efficiency is achieved. The performance of the resulting design has been verified by model tests in MARIN’s Deep Water Towing Tank. Given the very promising results of this new generation of LNG carriers, achieving besides the excellent propulsive properties also a higher payload target, the yard became more competitive and is expecting quite some orders for this particular ship type.

CFD-BASED SIMULATION OF THE FLOW AROUND A SHIP IN OBLIQUE MOTION AT LOW SPEED

2021 ◽  
Vol 158 (A4) ◽  
Author(s):  
J Chen ◽  
Z J Zou ◽  
M Chen ◽  
H M Wang
Keyword(s):  
Verification And Validation ◽  
Hydrodynamic Performance ◽  
Dynamic Positioning ◽  
Drift Angle ◽  
Low Speed ◽  
Safety Issues ◽  
High Speeds ◽  
Ship Maneuverability ◽  
Ship Speed ◽  
Ship Flows

Ships tend to maneuver in oblique motion at low speed in situations such as turning in a harbor, or during offloading, dynamic positioning and mooring processes. The maneuverability criteria proposed by IMO are valid for ships sailing with relatively high speeds and small drift angles, which are inadequate to predict ship maneuverability in low speed condition. Hydrodynamic performance of ships maneuvering at low speed is needed to know for safety issues. A CFD-based method is employed to predict the flow around an Esso Osaka bare hull model in oblique motion at low speed, where the drift angle varies from 0° to 180°. The URANS method with the SST k-ω model is used for simulating ship flows with drift angles 0°~30° and 150°~180°, and DES method for simulating ship flows with drift angles 40°~150°. Verification and validation studies are conducted for drift angles of 0° and 70°. The vortex structures at typical drift angles of 0°, 30°, 50°, 70°, 90° and 180° are analyzed. The effects of drift angle and ship speed are demonstrated.

Hydrodynamic Optimization of a Wedge Hull

2015 ◽  
Author(s):  
Lijue Wang ◽  
Fuxin Huang ◽  
Chi Yang ◽  
Raju Datla
Keyword(s):  
Hydrodynamic Performance ◽  
Surface Mesh ◽  
Nurbs Surface ◽  
Bottom Edge ◽  
Hull Form ◽  
Entrance Angle ◽  
Total Drag ◽  
Rounded Corner ◽  
Bulbous Bow ◽  
Hydrodynamic Optimization

A novel wedge-shaped hull form is optimized for reduced drag using a further developed practical hydrodynamic optimization tool. The hull features a sharp entrance angle, rectilinear sides, sharp bottom edges, a triangular waterplane and a linear aftward taper from a deep bow to a shallow transom. The optimization involves two modifications of the hull form, one is to smooth out the sharp bottom edge with a rounded corner and the other is to generate a bulbous bow. In order to perform the hydrodynamic optimization of the hull, a Non-Uniform Rational BSpline (NURBS)-based hull surface modification tool, a NURBS surface mesh generator, a surrogate model and an evolutionary optimization solver are developed and integrated into the practical hydrodynamic optimization tool. The hydrodynamic performances, i.e., the total drag and the flow field near the obtained hull bodies are assessed and compared with the original wedge hull using numerical simulations. Results showed that rounding the sharp edge of the wedge hull can reduce the total drag by alleviating the flow separations around the hull body. The wedge hull with rounded bottom edge and optimized bulbous bow can achieve larger drag reduction and the flow separations are almost eliminated. The total drag of the optimal hull is compared with an earlier-optimized wedge hull that has a different type of bulbous bow, whose hydrodynamic performance has been validated by model tests.

On the Influence of a Hubside Exducer Cavity and Bleed Air in a Close-Coupled Centrifugal Compressor Stage

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Peter Kaluza ◽  
Christian Landgraf ◽  
Philipp Schwarz ◽  
Peter Jeschke ◽  
Caitlin Smythe
Keyword(s):  
Centrifugal Compressor ◽  
Pressure Field ◽  
State Of The Art ◽  
Test Rig ◽  
Cfd Simulations ◽  
Trailing Edge ◽  
Loss Mechanism ◽  
Aero Engine ◽  
Computational Fluid Dynamics Cfd ◽  
Stage Efficiency

In aero-engine applications, centrifugal compressors are often close-coupled with their respective diffusers to increase efficiency at the expense of a reduced operating range. The aim of this paper is to show that state-of-the art steady-state computational fluid dynamics (CFD) simulations can model a hubside cavity between an impeller and a close-coupled diffuser and to enhance the understanding of how the cavity affects performance. The investigated cavity is located at the impeller trailing edge, and bleed air is extracted through it. Due to geometrical limitations, the mixing plane is located in the cavity region. Therefore, the previous analyses used only a cut (“simple”) model of the cavity. With the new, “full” cavity model, the region inside the cavity right after the impeller trailing edge is not neglected anymore. The numerical setup is validated using the experimental data gathered on a state-of-the art centrifugal compressor test-rig. For the total pressure field in front of the diffuser throat, a clear improvement is achieved. The results presented reveal a drop in stage efficiency by 0.5%-points caused by a new loss mechanism at the impeller trailing edge. On the hubside, the fundamentally different interaction of the cavity with the coreflow increases the losses in the downstream components resulting in the mentioned stage efficiency drop. Finally, varying bleed air extraction is investigated with both cavity models. Only the full cavity (FC) model captures the changes measured in the experiment.

Hydrodynamic Performance Characteristics of a Fluid Film Journal Bearing With a Rectangular Jacking Pocket

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Michael Branagan ◽  
Neal Morgan ◽  
Christopher Goyne ◽  
Roger Fittro ◽  
Robert Rockwell ◽  
...  
Keyword(s):  
Journal Bearing ◽  
Pressure Profile ◽  
Fluid Film ◽  
Hydrodynamic Performance ◽  
Pocket Depth ◽  
Response Surface Models ◽  
Fluid Film Bearings ◽  
Surface Models ◽  
Computational Fluid Dynamics Cfd ◽  
Stiffness Characteristics

Abstract To compensate for an extremely heavy journal, jacking pockets can be added to the surface of pads in fluid film bearings. Jacking pockets can range in size and shape and will have an influence on the hydrodynamic performance of the bearing. Computational fluid dynamics (CFD) was used to better understand the influence of the geometry of a rectangular/stadium-shaped, jacking pocket on the performance of bearings. First, the influence of the pocket depth on the pressure profile of the bearing was investigated. A varying profile occurred with jacking pocket depths less than 6.6 × Cb. After this threshold, the pocket depth ceased to have an influence on the pressure profile. A second study examined the circumferential length of the pocket, and the pressure profile was found to approach the smooth case as the pocket circumferential length decreased. Response surface models were created to map the influence of the jacking pocket geometry on the journal location in the bearing, power loss, and stiffness characteristics of the bearing. This is the first study on influence of the geometry of a jacking pocket on the operation and linear stiffnesses of the bearing in fluid film journal bearings.

Development of a Ship Performance Simulator in Actual Seas

2015 ◽  
Author(s):  
Masaru Tsujimoto ◽  
Naoto Sogihara ◽  
Mariko Kuroda ◽  
Akiko Sakurada
Keyword(s):  
Energy Efficiency ◽  
Fuel Consumption ◽  
Hydrodynamic Performance ◽  
Wave Forces ◽  
Ship Hydrodynamic ◽  
Main Engine ◽  
Ship Performance ◽  
Actual Seas ◽  
Ship Speed ◽  
Drift Forces

Greenhouse gas shall be reduced from shipping sector. For that purpose the regulation of EEDI (energy efficiency design index for new ships) and SEEMP (ship energy efficiency management plan) were entry into force from 2013. In order to improve energy efficiency of ships in service it is necessary to predict the fuel consumption in actual seas. In order to reduce GHG emission from ships, a Vessel Performance Simulator in Actual Seas has been developed. It simulates ship speed and fuel consumption at steady condition by using weather data and designated engine revolution. Physical models for hull, propeller, rudder and engine are used in the simulator. Especially steady wave forces, wind forces, drift forces, steering forces and engine/governor model are important factor for the estimation. The fuel consumption should be evaluated combined the ship hydrodynamic performance with the engine/governor characteristics. Considering the external forces by winds and waves, the operation point of the main engine is important for the estimation, since the torque limit and the other limit of the engine/governor are affected to the ship hydrodynamic performance. To prevent the increase of fuel consumption in service, the engine control system by the Fuel Index has been applied to present ships. In rough weather condition the revolution of the main engine is reduced to lower revolution by the Fuel Index limit. It causes the large decrease of ship speed but reduces the fuel consumption due to reduction of engine revolution. Using the simulator the navigation performance of a container ship, a RoRo vehicle carrier and a bulk carrier is simulated along the route. In this paper following contents are discussed; 1) evaluation of the physical model; steady wave forces, wind forces, drift forces, steering forces and engine/governor model, 2) simulation and validation of the physical model by tank tests and on-board measurements and 3) effectiveness of the ship performance simulator for GHG reduction.

scholarly journals Numerical Analysis on the Hydrodynamic Performance of an Artificially Ventilated Surface-Piercing Propeller

Water ◽  
2018 ◽  
Vol 10 (11) ◽  
pp. 1499 ◽  
Author(s):  
Dongmei Yang ◽  
Zhen Ren ◽  
Zhiqun Guo ◽  
Zeyang Gao
Keyword(s):  
High Speed ◽  
Artificial Ventilation ◽  
Water Immersion ◽  
Numerical Results ◽  
Hydrodynamic Performance ◽  
Heavy Load ◽  
Computational Fluid Dynamics Cfd ◽  
Large Water ◽  
Cfd Method ◽  
Surface Piercing Propeller

When operated under large water immersion, surface piercing propellers are prone to be in heavy load conditions. To improve the hydrodynamic performance of the surface piercing propellers, engineers usually artificially ventilate the blades by equipping a vent pipe in front of the propeller disc. In this paper, the influence of artificial ventilation on the hydrodynamic performance of surface piercing propellers under full immersion conditions was investigated using the Computational Fluid Dynamics (CFD) method. The numerical results suggest that the effect of artificial ventilation on the pressure distribution on the blades decreases along the radial direction. And at low advancing speed, the thrust, torque as well as the efficiency of the propeller are smaller than those without ventilation. However, with the increase of the advancing speed, the efficiency of the propeller rapidly increases and can be greater than the without-ventilation case. The numerical results demonstrates the effectiveness of the artificial ventilation approach for improving the hydrodynamic performance of the surface piercing propellers for high speed planning crafts.

Two-Phase Flow Model Applied in the Oxidation Ditch

2013 ◽  
Vol 838-841 ◽  
pp. 1659-1662
Author(s):  
Lin Chen ◽  
Qian Feng
Keyword(s):  
Close Relation ◽  
Phase Model ◽  
Hydrodynamic Performance ◽  
Oxidation Ditch ◽  
Two Phase ◽  
Good Correspondence ◽  
Design And Optimization ◽  
Numerical Tools ◽  
Computational Fluid Dynamics Cfd

The unique hydraulic characteristics in oxidation ditch have a close relation with the quality of treated water, the design and optimization of the oxidation ditch. The experimentally validated numerical tools, based on computational fluid dynamics(CFD), were proposed. Sewage- sludge two-phase model and liquid-gas two-phase model of an oxidation ditch were built through CFD numerical method. Meanwhile, a velocity field measurement was enforced on the ditch by Acoustic Doppler Velocimeter(ADV). The simulated results and experimental data were in good correspondence, which verify the simulation methods are reasonable and the simulation results are acceptable. The combination of simulation and experimrntal measurement has profound influence on the hydraulic optimization of oxidation ditch. 3D simulation could be a good supplement for improving the hydrodynamic performance in oxidation ditch designs.

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