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Technical Note: PreSquat – Workshop on Numerical Prediction of Ship Squat in Restricted Waters
Abstract
: In September 2013, the PreSquat workshop on numerical prediction of dynamic squat of ships in shallow and restricted waters was held by the University of Duisburg-Essen, the Federal Waterways Engineering and Research Institute (BAW) and Germanischer Lloyd (now DNV GL) in Mülheim a.d.R., Germany. The purpose of the workshop was to benchmark the capabilities of available numerical methods for squat prediction through comparison with experimental data for a large container carrier of Post-Panamax type. With the exception of one test case the comparison with model test results was blind, i.e. the results were not provided prior to the workshop. This technical note describes the model tests and the numerical results submitted to the workshop.
... Moreover, in September 2013, a workshop on the numerical prediction of the squat of ships in shallow and restricted water regions (named PreSquat) was jointly organized by the University of Duisburg-Essen, the Federal Waterways Engineering and Research Institute (BAW) and Germanischer Lloyd (GL) in Mulheim, Germany. The workshop aimed to gauge the efficiency of numerical methods for squat prediction via comparison with the available experimental data [25]. The DTC container ship model was therefore used in this work as a case study, owing to its readily available geometric data, and numerical and experimental results. ...
... The propeller appended to the hull is four bladed with right rotation and fixed pitch of the Wageningen B series type. For information about the geometry of the propeller and rudder, reference may be made to [24,25]. Since self-propelled simulations in CFD would dramatically increase the run time, the ship model was instead towed through the canal in this study. ...
As a ship approaches shallow water, a number of changes arise owing to the hydrodynamic interaction between the bottom of the ship’s hull and the seafloor. The flow velocity between the bottom of the hull and the seafloor increases, which leads to an increase in sinkage, trim and resistance. As the ship travels forward, squat of the ship may occur, stemming from this increase in sinkage and trim. Knowledge of a ship’s squat is necessary when navigating vessels through shallow water regions, such as rivers, channels and harbours. Accurate prediction of a ship’s squat is therefore essential, to minimize the risk of grounding for ships. Similarly, predicting a ship’s resistance in shallow water is equally important, to be able to calculate its power requirements. The key objective of this study was to perform fully nonlinear unsteady RANS simulations to predict the squat and resistance of a model-scale Duisburg Test Case container ship advancing in a canal. The analyses were carried out in different ship drafts at various speeds, utilizing a commercial CFD software package. The squat results obtained by CFD were then compared with available experimental data.
... More recently, the high quality experimental data has been used for the validation of numerical models for ship hydrodynamics (e.g. Böttnerm et al., 2011;Mucha et al., 2014;Böttner and Shevchuk, 2019;Shevchuk et al., 2016;Gourlay, 2017, 2018;Shevchuk et al., 2019;Bechthold and Kastens, 2020). ...
Long-period ship-generated loads have become design-relevant in many shallow and confined waterways. Numerical methods based on depth-averaged equations have conceptually proven successful to provide the ship wave parameters required for waterway management and design. Yet, the validation of these models remains challenging, due to variations in hull shapes, transient ship-motion during field data collection, and the dearth of published experimental benchmark data. The present study makes use of a new experimental data set to validate novel ship-modelling options in the shallow water equations solver REEF3D::SFLOW, using its free surface pressure extension for predicting long-period ship-generated load. The model predicts the primary wave field and the maximum return current with sufficiently low errors (MAPE) of 9.09% and 23.48%, respectively. A sensitivity study reveals that a simple slender body pressure assumption yields comparable simulation performance compared to a more complex hull-derived pressure distribution. The cross-sectional area of the respective pressure function, rather than the exact pressure function shape, is found to be decisive for the correct prediction of the design parameters primary wave height and maximum return current. Based on a systematic investigation of the ship draft to water depth relation, concise guidance on the choice of appropriate pressure functions is presented.
... More recently, the high quality experimental data has been used for the validation of numerical models for ship hydrodynamics (e.g. Böttner et al., 2011;Mucha et al., and Gourlay, 2017Shevchuk et al., 2019;Bechthold and Kastens, 2020). The experimental benchmark test data for the validation of the numerical model originate from a subset of a comprehensive test campaign that was conducted in the ship wave basin of BAW. ...
Long-period ship-generated loads have become design-relevant in many shallow and confined waterways. Numerical methods based on depth-averaged equations have conceptually proven successful to
provide the ship wave parameters required for waterway management and design. Yet, the validation of these models remains challenging, due to variations in hull shapes, transient ship-motion during field data collection, and the dearth of published experimental benchmark data. The present study
makes use of a new experimental data set to validate novel ship-modelling options in the shallow water equations solver REEF3D::SFLOW, using its free surface pressure extension for predicting long-period ship-generated load. The model predicts the primary wave field and the maximum return current with sufficiently low errors (MAPE) of 9.09% and 23.48%, respectively. A sensitivity study reveals that a simple slender body pressure assumption yields comparable simulation performance compared to a more complex hull-derived pressure distribution. The cross-sectional area of the respective pressure function, rather than the exact pressure function shape, is found to be decisive
for the correct prediction of the design parameters primary wave height and maximum return current. Based on a systematic investigation of the ship draft to water depth relation, concise guidance on the choice of appropriate pressure functions is presented.
... Simulations were set up to match one of the PreSquat workshop benchmark cases conducted in the Federal Waterways Engineering and Research Institute (BAW) where the Duisburg Test Case (DTC) hull appended with a propeller operating in an asymmetrical canal were investigated at a 1:40 scale (Mucha et al. 2014). The DTC is a generic 14,000 TEU container ship for benchmarking purposes developed by the Institute of Ship Technology, Ocean Engineering and Transport Systems (ISMT) of the University of Duisburg-Essen. ...
Various unsteady Reynolds-averaged Navier–Stokes (URANS) modeling techniques to predict container ship squat in confined water are investigated and compared in this study to assess the suitability of each modeling technique. Five methods are compared, among which three are quasi-statical estimations of squat from computational fluid dynamics (CFD)-computed hydrodynamic forces and moment (QS), and two are based on directly computed squat utilizing dynamic overset meshing (OV) technique. In addition, the effect of self-propulsion on the squat is investigated by comparing different methods of propulsion, i.e., the hull is either towed (T) or self-propelled by means of body-force propulsion virtual disc (VD) model or a fully discretized propeller (DP). The investigation shows that the QS methods tend to be superior in terms of computation efficiency, range of applicability, and trim prediction accuracy. It is also shown that the effect of self-propulsion is significant and should be accounted for to provide accurate results, especially at relatively high speeds. Moreover, virtual disc modeling is more computationally economical while also providing a degree of accuracy similar to that of a discretized propeller. Thus, the most suitable method is the quasi-static method with virtual disc self-propulsion (QS-VD). However, for very shallow cases where h/T < 1.14, the towed quasi-static squat model (QS-T) is recommended due to better accuracy.
... Simulations were set up to match one of the PreSquat workshop benchmark cases conducted in the Federal Waterways Engineering and Research Institute (BAW) where the Duisburg Test Case (DTC) hull appended with a propeller operating in an asymmetrical canal were investigated at a 1:40 scale (Mucha et al. 2014). The DTC is a generic 14,000 TEU container ship for benchmarking purposes developed by the Institute of Ship Technology, Ocean Engineering and Transport Systems (ISMT) of the University of Duisburg-Essen. ...
Various URANS modelling techniques to predict container ship squat in confined water are investigated and compared in this study to assess the suitability of each modelling technique. Five methods are compared, among which three are quasi-statical estimations of squat from CFD computed hydrodynamic forces and moment (QS), and two are based on directly computed squat utilising dynamic overset meshing (OV) technique. In addition, the effect of self-propulsion on squat is investigated by comparing different methods of propulsion i.e. the hull is either towed (T) or self-propelled by means of body-force propulsion virtual disc model (VD) or a fully discretised propeller (DP).
... In that study, the effect of ship squat on resistance results were not taken into account. Tezdogan et al. (2015) performed squat and resistance calculations in restricted waters with commercial CFD software STAR-CCM+ and compared their results with the squat empirical data from the PreSquat workshop (Mucha et al., 2014). That workshop used the Duisburg Test Case (Moctar et al., 2012), a 14 000 TEU (twenty-foot equivalent unit) container carrier whose geometry is typical of a post-panamax container ship (sea vessel), for their model ship. ...
An eco-driving prototype, named EcoNav, is developed with the aim of optimizing a vessel speed in order to reduce fuel consumption for a given itinerary. EcoNav is organized in several modules : - a 2D hydraulic model simulating the flow conditions (current speed and water depth) along the itinerary; - a ship resistance model calculating the thrust necessary to counteract the hydrodynamic forces ; - a fuel consumption model calculating the fuel consumption corresponding to the thrust input; - a non linear optimization algorithm calculating the optimal speed profile. In order to evaluate the fuel consumption of an inland vessel, a ship resistance numerical model is developed in the first part of this PhD. This 3D numerical model simulates the flow around an inland self-propelled vessel and evaluates the hydrodynamic forces acting on the hull. A RANS solver is coupled with a quasi-Newton approach to find the equilibrium position and calculate ship sinkage. This method is validated by comparing the results of numerical simulations to towing tank tests. The numerical results with and without sinkage are also compared to study the influence of sinkage on ship resistance and on the accuracy of the method. Additionally, some empirical models are investigated and compared with the accuracy of the numerical method. Finally, the numerical model is used to determine if channel with and water depth restriction contribute to the same amount of ship resistance increase for the same level of restriction. The results of that investigation give insight to whether channel restriction can be characterized by a unique parameter (for instance the blockage ratio) or two parameters to distinguish water depth and channel with effects. In the second part of this PhD, the numerical methods used in the speed optimization model are described and validated. The speed optimization model is then used to simulate a real case: the itinerary of the self-propelled ship Oural on river Seine, between Chatou and Poses (153 km). The optimized fuel consumption is compared with the non-optimized fuel consumption, based on AIS speed profile retrieved on this itinerary. The effects of the ship trajectory and travel duration on fuel consumption are also investigated. The results of those investigations showed that optimizing the ship speed lead to an average fuel saving of 8 % and that using an optimal track and including real time information such as lock availability and river traffic can lead to additional fuel savings.
... Particularly, dynamic vertical ship motions (i.e., ship squat, heel, and wave-induced motions) are significant factors affecting UKC requirements. Various approaches have been taken in an effort to better predict the squat effect, such as model-scale tests (Lataire et al. 2012) and full-scale tests for bulk carriers and model-scale tests (Mucha et al. 2014) and full-scale tests (Uliczka and Kondziella 2006;Gourlay 2008) for container ships. For calculating heeling moments due to turning and wind, standard methods exist (PIANC 2014). ...
In this article, validation of numerical models of ship wave-induced motions in port-approach channels is carried out. A selected set of high-quality data from recent full-scale trials measuring vertical motions of container ship transits entering and leaving the Port of Fremantle, Western Australia, is used. The measured wave-induced heave, roll, and pitch motions of six example container ship transits are discussed in detail, together with descriptions of in situ wave measurements and wave spectral analysis. A linear strip method, as implemented in the computer code OCTOPUS, is applied to predict the ship wave-induced motions. A comparison is made between measured and predicted ship motion responses to validate the ship motion software, and the measured roll response can be particularly used to assess the suitability of existing roll damping methods at full scale. The method is shown to give predictions of heave, roll, and pitch responses with reasonable accuracy for container ships at full scale in open dredged channels. Large-amplitude long-period roll motions were observed in some cases of the present trials, and unexpected harmonic pitch motions were also observed in other cases. Further research is recommended to study these seemingly nonlinear effects.
... Gronarz (1997) and Mucha (2017) focused on the mathematical modelling of manoeuvring in shallow water. Validation studies on computational methods for the prediction of resistance and squat are found in Deng et al. (2014) and Mucha et al. (2015Mucha et al. ( , 2016. Terziev et al., 2018 present another effort to assess the capabilities of numerical methods to model ship hydrodynamics in shallow water. ...
We present an experimental study on resistance and propulsion characteristics of an inland waterway ship in confined water. Physical experiments of resistance and propulsion with an inland waterway ship were performed. The effects of water depth, separation distance to a vertical wall (bank effects) and forward speed are discussed. The objective of the investigation was to generate benchmark data for validation of Computational Fluid Dynamics (CFD) solvers.
... These trials have played important roles in furnishing accurate and reliable full-scale data that may be utilized by ports, pilots and deck officers. Model-scale tests, being in a controlled environment, remain the method of choice for benchmarking studies (Mucha et al. 2014;Gourlay et al. 2015b), with appropriate allowance for scale effects (Graff et al. 1964;Deng et al. 2014). ...
In this paper, selected results are presented from a set of recent full-scale trials measuring the dynamic sinkage, trim, and heel of 16 container ship transits entering and leaving the Port of Fremantle, Western Australia. Measurements were made using high-accuracy Global Navigation Satellite System (GNSS) receivers and a fixed reference station. The measured dynamic sinkage, trim, and heel of three example container ship transits are discussed in detail. Maximum dynamic sinkage and dynamic draught, as well as elevations of the ship's keel relative to chart datum, are calculated. A theoretical method using slender-body shallow-water theory is applied to calculate sinkage and trim for the transits. It is shown that the theory is able to predict ship squat (steady sinkage and trim) with reasonable accuracy for container ships at full scale in open dredged channels. In future work, the measured ship motions, along with full measured wave time series data, will be used for validating wave-induced motion software.
... RANS methods are also becoming increasingly common for modelling ship sinkage and trim, especially in confined waterways (Mucha et al., 2014). ...
n this paper, we develop sinkage coefficients for ships in shallow open water, or harbour approach channels with minimal transverse restriction. These sinkage coefficients may be used for under-keel clearance management by ports, pilots, and deck officers. The coefficients are calculated using slender-body shallow-water theory applied to 12 published hull forms. Results are condensed into sinkage coefficient ranges for container ships, oil tankers, bulk carriers, and membrane LNG carriers. Limitations on use of the coefficients are suggested, based on ship and navigation channel dimensions. Examples are given for container ships, bulk carriers, and LNG carriers in Australian ports.
... Tezdogan et al. (2015Tezdogan et al. ( ,2016) fully adopted the nonlinear-unsteady RANS simulation to predict the squat and resistance of a model-scale Duisburg Test Case container ship. It showed that the simulation results had the higher precision compared with experimental data by Mucha et al. (2014). By this taken, the precision of numerical simulation of the realistic ship behavior in water area has made great progress, and it also makes a useful exploration on the prediction of ship advancing in shallow water, which are suitable for the situation with simple boundary conditions at the present stage. ...
Aiming at determining the controlling standard of extra-large ship entering or exiting the Three Gorges ship lock of China, the maximum squat of typical ships with physical model test was examined in this study. Physical model tests include hydraulic and 5000 t ship model tests at the scale of 1:36.3, with the purpose of obtaining the squat of ships entering or exiting ship lock at different depths, draft and speeds. Based on the theoretical analysis and previous achievements, this study advanced the mathematical models to estimate the maximum squat of ship driving in special restricted channel. For the typical ships, it is reliable to take the ratio of water depth to draft (i.e., H/T≥1.6) as controlling standard of ship entering or exiting ship lock. The results showed that the squat obviously increased with the ship passing by moored ships in the lock. The speed of typical ship with different lanes should be slower than 0.5 m/s to ensure the safety when other ship berthing in ship lock, which matched well with the observations. The proposed formula is feasible in scientific method, reasonable conclusion with accurate calculation, and therefore can be applied to the squat studies.
... This conflict is aggravated by the predominate investigation of model ship flows to establish a common basis for validation through comparison with experiments, because viscous effects are overbooked in lower Reynolds number regimes. For the particular problem of squat prediction the significance of these aspects was confirmed in the PreSquat workshop [1]. PreSquat aimed at benchmarking capabilities of available numerical methods for squat prediction through comparison with model experiments with the DTC container ship. ...
A validation study on numerical prediction of ship squat and resistance in shallow water is presented. Two methods based on the solution of the Reynolds-averaged Navier-Stokes (RANS) equations, a Rankine Panel Method and a method based on slender-body shallow water theory were applied and explored in terms of reliability and performance. Validation studies relied on comparison with model experiments for Post-Panmax container ship Duisburg Test Case (DTC), Panmax Kriso Container Ship (KCS) and Kriso Very Large Crude Carrier (KVLCC) 2. It was found that all methods are generally capable of predicting midship sinkage with good accuracy, while the boundary element methods (BEM) yield larger deviations in higher Froude depth number regimes, especially in predicting trim. For very shallow water ship flows, resistance predictions with viscous flow solvers were shown to be sensitive to turbulence modelling, near-wall treatment and the boundary condition on the tank bottom. In shallow water lifting ship flows, consideration of squat was found to be crucial for accurate computation of transverse forces and yaw moments.
... Tests on a 1:40 scale self-propelled model of the DTC were carried out in Duisburg in the standard rectangular tank cross-section [8,9]. Tests on the same model were undertaken at Federal Waterways Engineering and Research Institute (BAW) in Hamburg, in an asymmetric trapezoidal canal of similar cross-section area to the Duisburg tank. ...
This paper concerns dynamic sinkage and trim of modern container ships. A review is made of changing container ship hull designs up to the present time, together with available model test data for sinkage and trim. Two potential flow methods (slender-body method and Rankine-source method) are discussed with reference to the model test results. It is shown that slender-body theory is able to give good predictions of dynamic sinkage and trim in wide canals or open water, while Rankine-source methods offer an accurate solution particularly for ships at high speed in narrow canals.
Ship-seabed interaction is highly critical to ship safety and ship performance when ship operates over shallow water with uneven seabed. However, the prediction method for ship reaction is still yet to be fully developed. In this paper, a high-fidelity transient numerical simulation method with sliding mesh is developed based on computational fluid dynamics to model a vessel passing a step bank, demonstrating to be a computational cost economical solution. The comprehensive numerical model is validated and verified against benchmarked experimental and numerical studies, which is proved to be highly accurate in predicting force characteristics and wave development. Meanwhile, during the research the impulse effect generated by the step bank was found to have striking effects on the wave elevation, wake development and vessel sinkage. Five regions on the behaviour of vessel sinkage are defined in the present work. According to the result, the vessel will encounter the extreme sinkage after a relatively long distance (12 L pp at F h2 = 0.519) passing the step bank instead of immediately.
The resistance and ship-generated waves of two inland vessels in the fully-confined waterway are investigated based on numerical simulations. The simulation results are validated using towing tank experiments. The influences of the channel dimension, water depth, ship draught and velocity are studied. Specially, the ship resistance is characterized as a function of the blockage ratio and the theory of the linear ship wakes is corrected using the ship draught. These results are expected to predict the ship hydrodynamics in the restricted waterway and reveal the acting mechanism of the confinement effect on a certain level.
A URANS CFD-based study has been undertaken to investigate scale effect in container ship squat. Initially, CFD studies were carried out for the model scale benchmarking squat cases of a self-propelled DTC container ship. Propulsion of the vessel was modelled by the body-force actuator disc method. Full scale investigations were then undertaken. Validation of the full scale set-up was demonstrated by computing the full scale bare hull resistance in deep, laterally unrestricted water and comparing against the extrapolated resistance of model scale benchmark resistance data. Upon validating the setup, it was used to predict full scale ship squat in confined waters. The credibility of the full scale confined water model was checked by comparing vessel resistance in confined water against the Landweber (1933) empirical prediction. To quantify scale effect in ship squat predicitons, the benchmarking squat cases were computed by adopting the validated full scale CFD model with body-force propulsion. Comparison between the full scale CFD, model scale CFD and model scale benchmark EFD squat results demonstrates that scale effect is negligible. In addition, model scale predicted ship squat results were compared with physical full scale squat measurements of similar hulls. The two series of results are in good agreement which also demonstrate that the scale effect is insignificant.
The increasing use of maritime transport has led to an increase in ship size. However, the dimensions of channels and harbours cannot follow the expansion rate of ships. Large ships will experience shallow water effects such as the bottom effect more severely, which plays an important role in the manoeuvrability and the stability of ships. To reduce navigational restriction in estuary environment and close to ports, the World Association for Waterborne Transport Infrastructure (PIANC) established the concept of the nautical bottom. Using this concept, ships can navigate with both small and negative under keel clearance (UKC) relative to the water-mud interface. Hence, the aim of this work, is to conduct a numerical investigation in order to study the influence of the muddy seabed on the ship's manoeuvrability especially on the ship's resistance and squat. Accordingly, a 3D Computational Fluid Dynamics (CFD) model based on the Volume of Fluid (VoF) method was used to simulate the multiphase flow for various setups. Four parameters were tested: the mud properties, the ship's speed, the mud thickness and the UKC value relative to the water-mud interface. The numerical results of this investigation were in reasonable agreement with experimental data. Through this investigation it was also shown the performances of the CFD method to simulate setups difficult to achieve in towing tank.
Estimating ship squat is necessary to maintain safe navigation in the approach channel of harbors. The trim pattern of ships in shallow and restricted water can vary from trim bow down to stern down or variable trim orientation in dependence of the speed. The sinkage and trim pattern of three Postpanmax container ships in extreme shallow and confined water, with a water depth to draft ratio of less than 1.2, are predicted by using a RANSE based CFD method. The developed CFD setup is also applied for simulations of the DTC (Duisburg Test Case) container ship benchmark of the 5th International Conference on Ship Manoeuvring in Shallow and Confined Water (MASHCON). The predicted results are compared with model test data to analyze the robustness of the CFD method and to evaluate the quality of the squat predictions. The presented RANS method is robust and the quality of the predicted squat values is better than 20% deviation. When both CFD and EFD share the same model setup, the prediction deviation is less than 10%.
A simulation-based framework for the prediction of ship maneuvering in deep and shallow
water is presented. A mathematical model for maneuvering represented by coupled
nonlinear differential equations stemming from Newtonian mechanics is derived. Hydrodynamic forces are modeled by multivariat polynomials, and therein included are coefficients representing ship-specific hydrodynamic properties which are determined by way of captive maneuvering tests using Computational Fluid Dynamics (CFD). The development and evaluation of efficacy of the proposed framework encompasses verification and validation studies on numerical methods for maneuvering and flows around ships in shallow water. The flow field information available from numerical simulations are used to discuss hydrodynamic phenomena related to viscous and free surface effects, as well as squat.
Upon entering shallow waters, ships experience a number of changes due to the hydrodynamic interaction between the hull and the seabed. Some of these changes are expressed in a pronounced increase in sinkage, trim and resistance. In this paper, a numerical study is performed on the Duisburg Test Case (DTC) container ship using Computational Fluid Dynamics (CFD), the Slender-Body theory and various empirical methods. A parametric comparison of the behaviour and performance estimation techniques in shallow waters for varying channel cross-sections and ship speeds is performed. The main objective of this research is to quantify the effect a step in the channel topography on ship sinkage, trim and resistance. Significant differences are shown in the computed parameters for the DTC advancing through dredged channels and conventional shallow water topographies. The different techniques employed show good agreement, especially in the low speed range.
A novel test case representative of modern inland waterway ships is established for provision of reference data for benchmarking of numerical methods. Hull geometry, main particulars and appendages for propulsion and manoeuvring are introduced. Results of resistance and propulsion model tests in shallow water condition are described and discussed. Design peculiarities, challenges for model experiments and computations are addressed. © 2017 University of Duisburg-Essen and Federal Waterways Engineering and Research Institute
A three-dimensional (3D) hydrodynamic numerical model is proposed to predict ship resistance and sinkage of an inland vessel sailing in restricted waterways. The flow around the ship is simulated, and the hydrodynamic forces acting on the hull are calculated. A quasi-Newton method is applied to find the vertical equilibrium position and to update the ship position. The numerical results are validated against experimental data and compared with empirical models. The effects of ship sinkage and channel restriction on ship resistance are also investigated. Including ship sinkage into the calculations significantly increases the model accuracy. Additionally, the empirical models tested in this study are not able to accurately predict ship resistance for the most restricted configurations. Finally, it is shown that ship resistance is more sensitive to water depth than channel width restriction.
Duisburg Test Case (DTC) is a hull design of a typical 14000 TEU container ship, developed at the Institute
of Ship Technology, Ocean Engineering and Transport Systems (ISMT) for benchmarking and validation of
numerical methods. Hull geometry and model test results of resistance, propulsion and roll damping are publicly available. The paper presents existing data from model tests and computations.
An interface capturing method based on a numerically revisited procedure for velocity and pressure coupling is worked out. The new treatment of density discontinuity is formulated in the framework of the finite volume methodology for arbitrary unstructured grids. A simple analytical pressure-like model case is presented to illustrate the accuracy of the numerical implementation of the treatment of discontinuous variables. Then, the method is implemented in a viscous flow solver and applied to free-surface flows, including the two-dimensional Rayleigh–Taylor instability problem and three-dimensional hydrodynamic flows for the prediction of ship waves around the Series 60 model ship with and without drift angles. These latter simulations show excellent agreement with the experimental results illustrated by comparisons of free-surface elevations and also velocity field.
A review is made of linear slender-body methods for predicting the squat of a ship in shallow open water, dredged channels or canals. The results are summarized into a general formula based on Fourier transforms, and the method is extended to cater to stepped canals. An approximate solution for canals of arbitrary cross-section is proposed.
The paper presents results of dynamic squat computations in restricted waterways with two potential flow solution methods and a solver of Reynolds-averaged Navier-Stokes equations (RANSE). Computational results are compared with model tests and full-scale measurements for two large post-panamax class container carriers. Ways of computational time reduction are discussed.
The SIMMAN 2008 workshop was held in Copenhagen, Denmark in April 2008. The purpose of the workshop was to benchmark the prediction capabilities of different ship maneuvering simulation methods including systems- and CFD-based methods through systematic quantitative comparisons and validation against EFD data for tanker (KVLCC), container ship (KCS), and surface combatant (5415) hull form test cases. For the KVLCC test case, two stern shape variants named KVLCC1 and KVLCC2 giving different instability loops were included. Free model test data was compared with systems-based methods and CFD for specified free maneuvers. Some of the systems-based methods used provided PMM and CMT data, and two used CFD instead. CFD-based methods were used to simulate forced motions and were compared with PMM/CMT model test data. The submissions were blind in the sense that the benchmark model test data was not provided prior to the workshop, unless data was required as input to the simulation method. A total of 64 submissions were received for the free maneuver simulations, which included a wide range of the state-of-the-art methods in use today, such as PMM- and CMT-based methods, CFDbased methods, system identification, neural network tools and various empirical methods. For the forced motion simulations a total of 16 submissions were received, comprising different CFD-based methods such as RANS, URANS, and DES. This paper gives an overview of hulls, model tests, test cases, submissions, comparison results as well as the most important observations and conclusions.
The Gothenburg 2000 was an international benchmark workshop for computational fluid dynamics applied to ship flows. Test cases were three modern hull forms. One case without a free surface focused on turbulence modeling, whereas wave prediction was of interest for the other two. Of the free-surface cases, one had an operating propeller. For the first time, verification and validation procedures were an integral part of such benchmark efforts in ship flows. The workshop showed that free-surface waves may now be well predicted also away from the hull. There is a general improvement in the computation of the stern flow thanks to better turbulence modeling, but there is still room for improvement. Full-scale viscous flows may be computed without numerical difficulties. Verification and validation procedures should be applied for uncertainty analysis, and there is a discussion of the uncertainty in the predicted integral quantities in the paper. Further detailed conclusions and recommendations are also given based on the comparison of extensive standardized plots of the comparative computations and evaluation of the integral quantities.
The present study is devoted to the computation of the KVLCC2 tanker in head wave with free heave and pitch motion. A RANS solver using finite-volume discretization and free-surface capturing approach is employed for the computation. Free ship motion is captured with a mesh deformation approach. Three different wave lengths (0.6Lpp, 1.1Lpp and 1.6Lpp) are computed. We focus on numerical uncertainty estimation in this paper. For each test case, three different meshes and at least three different time steps have been used to access both time and spatial discretization error. Additional computations with different setups aimed at identifying different numerical discretization errors will also be performed. It is demonstrated that special attention needs to be paid to time discretization. To keep the same time accuracy, time step needs to be reduced on fine mesh for such kind of unsteady free-surface computation involving important pitch or roll motion.