scholarly journals Minimising Numerical Ventilation in CFD Simulations of High-speed Planing Hulls

2021 ◽  
pp. 1-33
Author(s):  
Angus Gray-Stephens ◽  
Tahsin Tezdogan ◽  
Sandy Day
Keyword(s):  
Free Surface ◽  
High Speed ◽  
Volume Of Fluid Method ◽  
Cfd Simulations ◽  
Entrance Angle ◽  
Depth Analysis ◽  
Prism Layer ◽  
The Impact ◽  
Mesh Refinements ◽  
Volume Mesh

Abstract Numerical Ventilation (NV) is a well-known problem that occurs when the Volume of Fluid method is used to model vessels with a bow that creates an acute entrance angle with the free surface, as is typical for both planing hulls and yachts. Numerical Ventilation may be considered one of the main sources of error in numerical simulations of planing hulls and as such warrants an in-depth analysis. This paper sets out to bring together the available work, as well as performing its own investigation into the problem to develop a better understanding of Numerical Ventilation and present alternate solutions. Additionally, the success and impact of different approaches is presented in an attempt to help other researchers avoid and correct for Numerical Ventilation. Interface smearing caused by the simulation being unable to track the free surface is identified as the main source of Numerical Ventilation. This originates from the interface between the volume mesh and the prism layer mesh. This study investigates this interface, presenting a novel solution to prism layer meshing that was found to minimize Numerical Ventilation. Through the implementation of a modified High Resolution Interface Capture (HRIC) scheme and the correct mesh refinements, it is possible to minimize the impact of Numerical Ventilation to a level that will not affect the results of a simulation and is acceptable for engineering applications.

scholarly journals Strategies to Minimise Numerical Ventilation in CFD Simulations of High-Speed Planing Hulls

2019 ◽  
Author(s):  
Angus Gray-Stephens ◽  
Tahsin Tezdogan ◽  
Sandy Day
Keyword(s):  
Free Surface ◽  
High Speed ◽  
Positive Impact ◽  
Entrance Angle ◽  
The Public ◽  
Depth Analysis ◽  
Niche Area ◽  
Prism Layer ◽  
The Impact ◽  
Mesh Refinements

Abstract Numerical Ventilation (NV) is a well-known problem that occurs when the Volume of Fluid method is used to model vessels with a bow that creates a small, acute entrance angle with the free surface. These are typical of both planing hulls and yachts. There is a general lack of discussion focusing upon Numerical Ventilation available within the public domain, which is attributable to the fact that it only affects such a niche area of naval architecture. The information available is difficult to find, often fleetingly mentioned in papers with a different focus. Numerical Ventilation may be considered one of the main sources of error in numerical simulations of planing hulls and as such warrants an in-depth analysis. This paper sets out to bring together the available work, as well as performing its own investigation into the problem to develop a better understanding of Numerical Ventilation and present alternate solutions. Additionally, the success and impact of different approaches is presented in an attempt to help other researchers avoid and correct for Numerical Ventilation. Interface smearing caused by the simulations inability to track the free surface is identified as the main source of Numerical Ventilation. This originates from the interface between the volume mesh and the prism layer mesh. This study looks into the interface to identify strategies that minimise Numerical Ventilation, presenting a novel solution to prism layer meshing that was found to have a positive impact. Through the implementation of a modified High Resolution Interface Capture (HRIC) scheme and the correct mesh refinements, it is possible to minimise the impact of Numerical Ventilation to a level that will not affect the results of a simulation and is acceptable for engineering applications.

A Methodology for a Detailed Loss Prediction in Low Pressure Steam Turbines

2017 ◽  
Author(s):  
Marius Grübel ◽  
Robin M. Dovik ◽  
Markus Schatz ◽  
Damian M. Vogt
Keyword(s):  
Boundary Layer ◽  
Evaluation Method ◽  
Three Dimensional ◽  
Low Pressure ◽  
Steam Turbines ◽  
Cfd Simulations ◽  
Depth Analysis ◽  
Pressure Steam ◽  
The Impact ◽  
Loss Mechanisms

An evaluation method for CFD simulations is presented, which allows an in-depth analysis of different loss mechanisms applying the approach of entropy creation proposed by Denton. The entropy creation within each single mesh element is determined based on the entropy flux through the cell faces and therefore the locations, where losses occur, can be identified clearly. By using unique features of the different loss mechanisms present in low pressure steam turbines, the losses are categorized into boundary layer, wake mixing and shock losses as well as thermodynamic wetness losses. The suitability of the evaluation method is demonstrated by means of steady state CFD simulations of the flow through a generic last stage of a low pressure steam turbine. The simulations have been performed on streamtubes extracted from three-dimensional simulations representing the flow at 10 % span. The impact of non-equilibrium steam effects on the overall loss composition of the stator passage is investigated by comparing the results to an equilibrium steam simulation. It is shown, that the boundary layer losses for the investigated case are of similar magnitude, but the shock and wake losses exhibit significant differences.

The Impacts of Model Uncertainty on RANS CFD Simulations of a High-Speed Craft

2021 ◽  
Author(s):  
Joseph Messler ◽  
Nicholas Husser ◽  
Stefano Brizzolara
Keyword(s):  
Numerical Methods ◽  
Model Uncertainty ◽  
High Speed ◽  
Critical Element ◽  
Cfd Model ◽  
Three Dimensional Model ◽  
Cfd Simulations ◽  
High Quality ◽  
Sources Of Uncertainty ◽  
The Impact

Computational scientists frequently publish papers discussing various sources of uncertainty in numerical methods for computational fluid dynamics. The frequently discussed sources of uncertainty are round off error, discretization error, iterative error, and mathematical model uncertainty (i.e. uncertainty in turbulence modeling). While all of these sources of uncertainty are real and impact the results of a simulation, the authors have found through experience that the most critical element to achieving accurate simulation results for high-speed craft is the generation of a high quality mesh on which the numerical methods are solved. There are, in general, two requirements for a high quality mesh; refinement regions must be applied in regions where the physics of the flow are most significant, and the three dimensional model of the hull form must be appropriately defined and fair. The latter appears to be a major contributing factor to uncertainty in CFD simulations that is not often discussed in the literature. Further, in practice there are numerous sources of geometric uncertainty between a prescribed CAD geometry and physically constructed model. In this paper, simulations are performed on two models of GPPH, with and without an edge radius on the transom to evaluate the impact of including fine geometric details (like tooling radii) in a RANS CFD model. The results of the simulations show that the inclusion of the rounded edge leads to large simulation errors in resistance and running attitude. This work has concluded that inclusion of fine geometric details in a planing hull CFD model is not beneficial to the overall accuracy of the simulations relative to necessary design accuracy.

Study on Deformation and Energy Absorption of Liquid Cabin Under Ballistic Impact

2018 ◽  
Author(s):  
Zhang Lei ◽  
Zhao Pengduo
Keyword(s):  
Free Surface ◽  
Energy Conversion ◽  
Liquid Medium ◽  
Energy Absorption ◽  
High Speed ◽  
Water Layer ◽  
Simulation Method ◽  
Absorption Model ◽  
Impact Wave ◽  
The Impact

Liquid cabin is the most significance part protecting the ship from damage due to high-speed fragments. In order to guide the design of liquid cabin, response regularity of the impact wave in water and the speed of projectile were studied by simulation method. The deformation and energy conversion of liquid cabin in different design were also investigated. The results show that, the existence of a liquid medium can change the energy absorption model of a cabin. The thickness of water layer put significance influence on the deformation and energy absorption model of liquid cabin. Lower the level of the water lead to the free surface truncation effect of impact wave. The asymmetry and locality of the deformation of bulkhead occur to the free surface truncation effect, but it put little effect on energy absorption of liquid cabin.

The Impact of Australia’s Government Policy on Broadband Internet Access

2013 ◽  
Vol 6 (4) ◽  
pp. 18-35 ◽  
Author(s):  
Qiuyan Fan
Keyword(s):  
High Speed ◽  
Internet Access ◽  
Regulatory Competition ◽  
Australian Government ◽  
Broadband Internet ◽  
Telecommunications Sector ◽  
Depth Analysis ◽  
Broadband Network ◽  
The Government ◽  
The Impact

The Australian government has recognised the importance of broadband for their social and economic development. This paper provides an in-depth analysis of the impact of policy issues on broadband Internet access in Australia. This research has clearly indicated that the state of broadband Internet access is closely related to the Government’s policy and regulatory framework. The Government based its actions on market forces as a principal driver for broadband Internet connectivity. The research has indicated that the previous regulatory competition regime, by and large, has failed to address concerns of market dominance and market power in the Telecommunications sector as is evidenced by a relatively lower speed and value of broadband services in Australia. To rectify the situation, the Australian government has recently adopted a unique National Broadband Network (NBN) plan, which is linked to the national digital economy strategy. Australia is the first country in the world where a national broadband network infrastructure company, NBN Co, is regarded as a regulated national infrastructure provider rather than as a telecommunication company. The NBN Co builds and operates an open access, wholesale only and non-discrimination high-speed broadband network, the National Broadband Network (NBN). The Australian Government's goal for the NBN is to reform the telecommunications sector and ensure every home and business across the country has access to the NBN by 2020. This paper examines the policies underlying the NBN and discusses current practices and potential benefits of the NBN.

scholarly journals Energy-Efficient Multiple-Relay Cooperative Networks Using Hamming Coding

2021 ◽  
pp. 22-28
Author(s):  
Nasaruddin Nasaruddin ◽  
◽  
Ramzi Adriman ◽  
Afdhal Afdhal
Keyword(s):  
Communication Network ◽  
Energy Consumption ◽  
Cooperative Communication ◽  
Energy Efficient ◽  
High Speed ◽  
Cooperative Networks ◽  
Base Station ◽  
Depth Analysis ◽  
Multiple Relay ◽  
The Impact

Using a multiple-relay cooperative communication network is one of the most effective methods for reducing the impact of fading on wireless channels. In such a network, a source sends information to a destination via several nearby nodes, which form virtual antennas regardless of the size and cost of the mobile equipment. The network is also required to transmit multimedia and allow access to high-speed data, thus requiring significant energy consumption. Until now, mobile devices have only been able to store a limited amount of energy, leading to rapid battery depletion in relay and mobile user devices. Moreover, the Base Station (BS) itself consumes considerable energy and the number of BSs continues to grow. Therefore, the development of an energy-efficient cooperative communication network that reduces energy consumption while maintaining the highest possible level of performance is urgently required. To this end, this paper proposes the application of Hamming coding to a multiple-relay cooperative communication network for Energy Efficiency (EE) analysis. Then, the relay protocol aspect is also determined to increase the level of EE. This study considers two practical protocol relays, Amplify-and-Forward (AF) and Quantize-and-Forward (QF), for a more in-depth analysis of EE. The results show that the multiple-relay QF network demonstrates EE when compared to a multiple-relay AF network.

Modeling of Tread Block Contact Mechanics Using Linear Viscoelastic Theory3

2008 ◽  
Vol 36 (3) ◽  
pp. 211-226 ◽  
Author(s):  
F. Liu ◽  
M. P. F. Sutcliffe ◽  
W. R. Graham
Keyword(s):  
High Speed ◽  
Slip Rate ◽  
Material Model ◽  
Contact Forces ◽  
Block Modeling ◽  
Rate Dependent ◽  
Linear Viscoelastic Material ◽  
Linear Viscoelastic ◽  
The Impact ◽  
Good Agreement

Abstract In an effort to understand the dynamic hub forces on road vehicles, an advanced free-rolling tire-model is being developed in which the tread blocks and tire belt are modeled separately. This paper presents the interim results for the tread block modeling. The finite element code ABAQUS/Explicit is used to predict the contact forces on the tread blocks based on a linear viscoelastic material model. Special attention is paid to investigating the forces on the tread blocks during the impact and release motions. A pressure and slip-rate-dependent frictional law is applied in the analysis. A simplified numerical model is also proposed where the tread blocks are discretized into linear viscoelastic spring elements. The results from both models are validated via experiments in a high-speed rolling test rig and found to be in good agreement.

Case study: Prediction and field tests of railway noise and effects of a low-height noise barrier

2020 ◽  
Vol 68 (4) ◽  
pp. 303-314
Author(s):  
Yuna Park ◽  
Hyo-In Koh ◽  
University of Science and Technology, Transpo ◽  
University of Science and Technology, Transpo ◽  
University of Science and Technology, Transpo ◽  
...  
Keyword(s):  
High Speed ◽  
Field Tests ◽  
Residential Areas ◽  
Railway Systems ◽  
Railway Noise ◽  
Sound Levels ◽  
Noise Barrier ◽  
The Difference ◽  
Reduction Effect ◽  
The Impact

Railway noise is calculated to predict the impact of new or reconstructed railway tracks on nearby residential areas. The results are used to prepare adequate counter- measures, and the calculation results are directly related to the cost of the action plans. The calculated values were used to produce noise maps for each area of inter- est. The Schall 03 2012 is one of the most frequently used methods for the production of noise maps. The latest version was released in 2012 and uses various input para- meters associated with the latest rail vehicles and track systems in Germany. This version has not been sufficiently used in South Korea, and there is a lack of standard guidelines and a precise manual for Korean railway systems. Thus, it is not clear what input parameters will match specific local cases. This study investigates the modeling procedure for Korean railway systems and the differences between calcu- lated railway sound levels and measured values obtained using the Schall 03 2012 model. Depending on the location of sound receivers, the difference between the cal- culated and measured values was within approximately 4 dB for various train types. In the case of high-speed trains, the value was approximately 7 dB. A noise-reducing measure was also modeled. The noise reduction effect of a low-height noise barrier system was predicted and evaluated for operating railway sites within the frame- work of a national research project in Korea. The comparison of calculated and measured values showed differences within 2.5 dB.

Sign in / Sign up

Export Citation Format

Share Document