Static Drift Research Articles

Investigation of the Flow Field of a Ship in Planar Motion Mechanism Tests by the Vortex Identification Method

Planar motion mechanism (PMM) tests provide a means of obtaining the hydrodynamic derivatives needed to assess ship maneuverability properties. In this paper, the self-developed computational fluid dynamic (CFD) solver based on the open source code platform OpenFOAM, naoe-FOAM-SJTU, associated with the overset grid method is used to simulate the complex viscous flow field of PMM tests for a benchmark model Yupeng Ship. This paper discusses the effect of several parameters such as the drift angle and period on the hydrodynamic performance of the ship and compares the time histories of the predicted forces and moments with experimental data. To investigate the complex viscous flows with a large separation, four vortex identification methods are used to capture the vortex structures. The results show that the forces and moments are in good agreement in static drift and dynamic tests. By comparing the vortex structures, it is found that the third generation vortex identification methods, OmegaR and Liutex, are able to more accurately capture the vortex structures. The paper concludes that the present numerical scheme is reliable and the third generation vortex identification methods are more suitable for displaying the vortex structures in a complex viscous flow field.

Effects of a propulsor on the maneuverability of an autonomous underwater vehicle in vertical planar motion mechanism tests

The effects of a propulsor on the hydrodynamic forces acting on an autonomous underwater vehicle (AUV) were investigated by towing tank model tests. A mathematical maneuvering model using a whole vehicle model was established, and captive model tests using vertical planar motion mechanism equipment were performed to obtain maneuvering coefficients. The Reynolds number of the full scale test model in the operation condition was 4.12 × 106, and the revolution rate of the propulsor was fixed at the self-propulsion point. The forces on the body and control fins were measured in static drift, control fin deflection, pure heave and pure pitch tests with and without the propulsor. The propulsor effects on the hydrodynamic force and moment were identified as spatially irregular thrust, flow acceleration around the control fins, and added mass of the propulsor. In the simulation using the component model where the propulsor effect considered as a constant thrust, the maneuverability of the AUV was overestimated compared to that of the whole vehicle model. Thus, the mathematical maneuvering model should consider propulsor-hull interactions.

Numerical investigation on the asymmetric propeller behavior of a twin-screw ship during maneuvers by using RANS method

Aiming to improve the safety of ship navigation and main engine operation, the propulsive loads are investigated for a twin-screw ship under the maneuvering condition by using CFD method. The proposed models that describe the propeller performance during ship maneuvers are summarized. Taking the twin-screw ship model DTMB 5415M as the study object, RANS simulation is performed for a series of static drift tests and rotating arm tests. The computed propulsive loads are validated by the available experimental data. The contours of axial velocity and vortex around the hull are presented to demonstrate the influence of upstream hull on the inflow to propeller under the maneuvering conditions. The details of the velocity field around the stern provide a deeper insight into the hydrodynamic mechanism of ship wake affecting the propeller performance. It is shown that the propeller behavior is highly related to the vortices shedding from the hull and appendages, which would change remarkably with the propeller position (windward and leeward) and the maneuvering motion (drift and turning). Finally, a regression analysis is performed with the proposed propeller models, and a reasonable composite model describing the asymmetric propeller behavior of a twin-screw ship during maneuvers is obtained.

Prediction of Hydrodynamic Derivatives of KCS Based on Computational Fluid Dynamics

Aiming at predicting the maneuverability of the ship in shallow water, KCS was selected as the research object. Static drift motion, pure sway motion, and pure yaw motion were performed to calculate the dimensionless hydrodynamic derivatives of KCS. A commercial software, STAR-CCM+ was used to simulate various kinds of movement conditions, by which the force and moment on the hull can be monitored. Then, through the curve fitting, hydrodynamic derivatives of KCS were predicted, and the maneuverability of KCS can be predicted.

A numerical study on hydrodynamic maneuvering derivatives for heave-pitch coupling motion of a ray-type underwater glider

We used a numerical method to estimate the hydrodynamic maneuvering derivatives for the heave-pitch coupling motion of an underwater glider. It is very important to assess the hydrodynamic maneuvering characteristics of a specific hull form of an underwater glider in the initial design stages. Although model tests are the best way to obtain the derivatives, numerical methods such as the Reynolds-averaged Navier-Stokes (RANS) method are used to save time and cost. The RANS method is widely used to estimate the maneuvering performance of surface-piercing marine vehicles, such as tankers and container ships. However, it is rarely applied to evaluate the maneuvering performance of underwater vehicles such as gliders. This paper presents numerical studies for typical experiments such as static drift and Planar Motion Mechanism (PMM) to estimate the hydrodynamic maneuvering derivatives for a Ray-type Underwater Glider (RUG). A validation study was first performed on a manta-type Unmanned Undersea Vehicle (UUV), and the Computational Fluid Dynamics (CFD) results were compared with a model test that was conducted at the Circular Water Channel (CWC) in Korea Maritime and Ocean University. Two different RANS solvers were used (Star-CCM+ and OpenFOAM), and the results were compared. The RUG’s derivatives with both static drift and dynamic PMM (pure heave and pure pitch) are presented.

Maneuvering simulation of an X-plane submarine using computational fluid dynamics

X-plane submarines show better maneuverability as they have much longer span of control plane than that of cross plane submarines. In this study, captive model tests were conducted to evaluate the maneuverability of an X-plane submarine using Computational Fluid Dynamics (CFD) and a mathematical maneuvering model. For CFD analysis, SNUFOAM, CFD software specialized in naval hydrodynamics based on the open-source toolkit, OpenFOAM, was applied. A generic submarine Joubert BB2 was selected as a test model, which was modified by Maritime Research Institute Netherlands (MARIN). Captive model tests including propeller open water, resistance, self-propulsion, static drift, horizontal planar motion mechanism and vertical planar motion mechanism tests were carried out to obtain maneuvering coefficients of the submarine. Maneuvering simulations for turning circle tests were performed using the maneuvering coefficients obtained from the captive model tests. The simulated trajectory showed good agreement with that of free running model tests. From the results, it was proved that CFD simulations can be applicable to obtain reliable maneuvering coefficients for X-plane submarines.

Physicochemical surface-structure studies of highly active zirconocene polymerisation catalysts on solid polymethylaluminoxane activating supports

Static 91Zr ssNMR, SEM-EDX, and DRIFT spectroscopy indicate that a common zirconium species, [CpR2ZrMe]+, is present in all sMAO supported catalyst systems.

Manoeuvring Prediction of KVLCC2 with Hydrodynamic Derivatives Generated by a Virtual Captive Model Test

Abstract This paper describes the application of computational fluid dynamics rather than a towing tank test for the prediction of hydrodynamic derivatives using a RANS-based solver. Virtual captive model tests are conducted, including an oblique towing test and circular motion test for a bare model scale KVLCC2 hull, to obtain linear and nonlinear hydrodynamic derivatives in the 3rd-order MMG model. A static drift test is used in a convergence study to verify the numerical accuracy. The computed hydrodynamic forces and derivatives are compared with the available captive model test data, showing good agreement overall. Simulations of standard turning and zigzag manoeuvres are carried out with the computed hydrodynamic derivatives and are compared with available experimental data. The results show an acceptable level of prediction accuracy, indicating that the proposed method is capable of predicting manoeuvring motions.

Assessment of Computational Fluid Dynamics Capabilities for the Prediction of Three-Dimensional Separated Flows: The DELFT 372 Catamaran in Static Drift Conditions

In this paper, capabilities of state-of-the-art computational fluid dynamics (CFD) tools in the prediction of the flow-field around a multihull catamaran advancing in straight ahead motion at nonzero drift angles are investigated. CFD estimations have been provided by three research institutes by using their in-house codes: CNR-INM using Xnavis, IIHR using CFDShip-Iowa, and CNRS/ECN using ISIS. These allowed an in-depth comparison between different methodologies, such as structured overlapping grids versus unstructured grid, different turbulence models and detached eddy simulations (DES) approaches, and level-set (LS) versus volume of fluid (VoF). The activities were pursued within the NATO AVT-183 group “reliable prediction of separated flow onset and progression for air and sea vehicles,” aimed at the assessment of CFD predictions of large three-dimensional separated flows. Comparison between estimations is provided for both integral and local quantities, and for wave-induced vortices. Validation is reported by comparison against the available experimental fluid dynamics (EFD) data. Generally, all the simulations are able to capture the main features of the flow field; grid resolution effects are dominant in the onset phase of coherent structures and turbulence model affects the dynamic of the vortices. Hydrodynamic loads are in agreement between the submissions with standard deviation of about 3.5% for the resistance prediction and about 7% for lateral force and yaw moment estimation. Wave-induced vortices are correctly captured by both LS and VoF approaches, even if some differences have been highlighted, LS showing well-defined and long life vortices.

URANS investigation of the interaction between the free surface and a shallowly submerged underwater vehicle at steady drift

An axisymmetric underwater vehicle (UV) at a steady drift angle experiences the complex three-dimensional crossflow separation. This separation arises from the unfavorable circumferential pressure gradient developed from the windward side toward the leeward side. As is well known, the separated flow in the leeward side gives rise to the formation of a pair of vortices, which affects considerably the forces and moments acting on the UV. In this regard, the main purpose of the present study is to evaluate the role of the leeward vortical flow structure in the hydrodynamic behavior of a shallowly submerged UV at a moderate drift angle traveling beneath the free surface. Accordingly, the static drift tests are performed on the SUBOFF UV model using URANS equations coupled with a Reynolds stress turbulence model. The simulations are carried out in the commercial code STARCCM+ at a constant advance velocity based on Froude number equal to Fn = 0.512 over submergence depths and drift angles ranging from h = 1.1D to h = ∞ and from β = 0 to β = 18.11°, respectively. The validation of the numerical model is partially conducted by using the existing experimental data of the forces and moment acting on the totally submerged bare hull model. Significant interaction between the low-pressure region created by the leeward vortical flow structure and the free surface is observed. As a result of this interaction, the leeward vortical flow structure appears to be largely responsible for the behavior of the forces and moments exerted on a shallowly submerged UV at steady drift.

System-based prediction of maneuvering performance of twin-propeller and twin-rudder ship using a modular mathematical model

The turning circle and zigzag maneuvering performance of surface combatant, DTMB 5415 have been investigated by using system-based method. Unsteady Reynolds averaged Navier Stokes (URANS) approach is utilized to estimate hydrodynamic derivatives and hull-propeller-rudder interactions. DTMB 5415 is a twin-propeller / twin-rudder ship and there are some studies on the derivation of maneuvering coefficients in the literature but none of them took into account the propeller and rudder forces. In this study, static drift, pure yaw, combined yaw and drift, self-propulsion and rudder tests of DTMB 5415 hull have been simulated in calm and deep water condition. Bare hull PMM simulations were carried out for a fixed Froude number of Fr=0.28, while the simulations related to rudder and propeller were performed at Fr=0.25. Computational results were used by MMG (Maneuvering Modeling Group) model to estimate the maneuvering performance of the ship. Hydrodynamic derivatives from numerically generated forces and moment data were obtained by single-run and multiple-run methods. The results from both methods were tested in an in-house maneuvering simulation code (MANSIM) that solves for ship motions and they were compared with computed turning circle and zigzag maneuvering performances. Although it is known a priori that the multiple-run method would give better solution in overall, it was found that the single-run method can be a good alternative in some specific cases. For the zigzag and turning circle tests, the results from single-run method were found satisfactory when correct PMM test conditions were adopted.

URANS simulations of an axisymmetric submarine hull undergoing dynamic sway

A computational study of the flow over an axisymmetric submarine hull undergoing unsteady maneuvers is presented. The computational model is based on the Unsteady Reyonolds-Averaged Navier-Stokes equations, solved in body fixed coordinates using the Wilcox two-equation turbulence model. Static drift and dynamic sway simulations are performed on a hull geometry with a slenderness ratio of 8.5 and Reynolds number of 3.1 million, in strut-supported and unsupported configurations. Simulation results are compared with Horizontal Planar Motion Mechanism experiments at two reduced frequencies, k=0.12 and k=0.03. Simulated results for a strut supported hull are compared with experimental values to estimate simulation accuracy for static drift and dynamic sway. Simulation results for an unsupported hull demonstrate significant hysteresis of the hydrodynamic forces at k=0.12, while at k=0.03 the lateral force and yawing moment collapse towards the quasi-steady limit. Dynamic forces are decomposed in terms of the inviscid added mass and a viscous component which cannot be accounted for by the quasi-steady assumption and is attributed to flow history effects. The effect of flow history is further shown by visualisations of the wake vorticity. Finally, it is demonstrated that the presence of the support strut results in significant interference effects in all cases.

Improved virtual gyroscope technology based on "current" probability density model.

Aiming at low precision of a micro-electromechanical systems (MEMS) gyroscope, the virtual gyroscope technology is used to fuse the data of several MEMS gyroscopes. In traditional virtual gyroscope technology, the angular acceleration of maneuver is modeled as white noise, which leads to low fusion accuracy in the dynamic state. So, the "current" probability density model is introduced to model the maneuvering angular rate accurately. The one-step predictive value of angular acceleration is approximated to the mean value of the current angular acceleration. And the variance of the angular acceleration is modeled by the one-step predictive value of angular acceleration. So, the "current" probability density model is used to realize the adaptive adjustment of the mean and variance of maneuvering angular acceleration, which improves the modeling accuracy of the maneuvering angular rate and the compensation accuracy of virtual gyroscope technology. The improved virtual gyroscope fusion method is verified in a low frequency, high frequency maneuver test. The experimental results show that the 1σ standard deviation of the improved virtual gyroscope fusion error is 6.53 times lower than that of the single gyroscope static drift at low frequency and 2.04 times lower than that of the single gyroscope static drift at high frequency.

Assessment of Computational Fluid Dynamic for Surface Combatant 5415 at Straight Ahead and Static Drift β = 20 deg

Collaboration is described on assessment of computational fluid dynamics (CFD) predictions for surface combatant model 5415 at static drift β = 0 deg and 20 deg using recent tomographic particle image velocimetry (TPIV) experiments. Assessment includes N-version verification and validation to determine the confidence intervals for CFD solutions/codes, and vortex onset, progression, instability, and turbulent kinetic energy (TKE) budget analysis. The increase in β shows the following trends. Forces and moment increase quadratically/cubically, and become unsteady due to shear layer, Karman and flapping instabilities on the bow. Wave elevation becomes asymmetric; its amplitude increases, but the total wave elevation angle remains same. The vortex strength and TKE increase by about two orders of magnitude, and for large β, the primary vortices exhibit helical mode instability similar to those for delta wings. Forces and moment for both β and wave elevation for β = 0 deg are compared within 4% of the data, and are validated at 7% interval. Wave elevation for β = 20 deg, and vortex core location and velocities for both β are compared within 9% of the data, and are validated at 12% interval. The vortex strength and TKE predictions show large 70% errors and equally large scatter and are not validated. Thus, both errors and scatter need reduction. TKE budgets show transport of turbulence into the separation bubble similar to canonical cases, but pressure transport is dominant for ship flows. Improved CFD predictions require better grids and/or turbulence models. Investigations of solution-adaptive mesh refinement for better grid design and hybrid Reynolds-averaged Navier-Stokes/large eddy simulation models for improved turbulent flow predictions are highest priority.

A real-time filtering method for the drift data of a laser Doppler velocimeter

ABSTRACTTo effectively reduce the random drift of a laser Doppler velocimeter (LDV), a real-time filtering model is presented for filtering the drift data of an LDV, which is a combination of the metabolic grey model (1, 1) and the metabolic time series model AR (2). The basic principle of the metabolic grey-time series model is introduced in detail first. Then, the model is established for the static and dynamic drift data, and a Kalman filter is used to filter the drift data based on the model. The variance analysis method and the Allan variance method are employed to analyse the static drift data. The dynamic drift data are also compared before and after being modelled and filtered. The results demonstrate that the metabolic grey-time series method cannot only effectively reduce the static random drift of an LDV, but can also reduce the dynamic random drift in real time.

Estimation of hydrodynamic derivatives of a container ship using PMM simulation in OpenFOAM

Static drift, pure sway and pure yaw simulation results are determined for a container ship. For simulation, open source RANS solver, OpenFOAM was used. The simulation results were compared with two sets of experimental data. Next, hydrodynamic derivatives were predicted from simulation results and compared with experimental ones. The results show good agreement with experimental data, except for some pure yaw cases. Overall, the paper concludes that OpenFOAM is well capable of estimating hydrodynamic derivatives maintaining reasonable accuracy and computational efficiency.

The impact of free surface modelling on hydrodynamic forces for ship navigating in inland waterways: water depth, drift angle, and ship speed effect

Simulations of standard manoeuvring tests require a good estimation of the hydrodynamic derivatives. These are extracted from the hydrodynamic forces applying on the ship. The present work focuses on the investigation of the importance of free surface assessment on the estimation of the hydrodynamic forces, particularly, in the presence of the ship–bottom interaction and when certain parameters are varied, including the ship’s speed and the drift angle. This investigation aims, in particular, to mark off the confidence Interval of neglecting free surface deformation hypothesis by comparing the results of static drift test with and without considering this assumption. The study was carried on a 135 m inland containership at a scale ratio of 1:25 undergoing static drift tests. In order to recreate the ship–bottom interaction, the depth to draft ratio (h/T) is varied to obtain four channel configurations. The tests are performed by numerical code under the commercial software Ansys Fluent by solving Reynolds Averaged Navier Stokes Equations(RANSE) coupled to a $$k -\omega$$ SST turbulence model. To investigate the effect of free surface modelling, the hydrodynamic forces are compared when the free surface separating air and water is considered, using Volume Of Fluid (VOF) method, and when the free surface is neglected. The simulations are carried out for various ship speeds and various drift angles.

Investigation on hull-propeller-rudder interaction by RANS simulation of captive model tests for a twin-screw ship

The hull-propeller-rudder interaction of a twin-screw ship is investigated by using CFD method. The hydrodynamic performances of propeller and rudder during maneuvers are analyzed based on the relevant modules in MMG model, with the propeller side force and asymmetric flow-straightening effect being taken into account. Taking the ONR tumblehome ship model as the study object, self-propulsion test, rudder force test, circular motion test, and static drift test are simulated by using RANS method. The interaction coefficients among the hull, propeller, and rudder, as well as the models of propeller side force and rudder normal force are obtained from the computed hydrodynamic forces and moments. The obtained parameters in the modules show reasonable agreement with the available experimental data. The velocity field around the stern and the pressure distribution on the rudder surface are presented to provide deeper insight into the effects of ship motion and propeller load on the rudder performance. The turning circle test is simulated using the obtained hydrodynamic modules. The simulated trajectory and time histories of kinematic and dynamic quantities show good agreement with the available experimental data and other CFD results, indicating the validity of the CFD-based modelling method for hull-propeller-rudder interaction of twin-screw ships.

Development of a Small-sized and Low-cost Attitude Measurement Unit for Agricultural Robot Application

The objective of this study was to develop a small-sized and low-cost unit to provide attitude measurements for lightloaded, small-sized and cost effective agricultural robot application. The attitude measurement unit comprised an electronic control unit (ECU) and a gyroscope and an accelerometer within a small-sized and low-cost IMU. In order to avoid the measurement limitations of a single sensor, a self-adaptive complementary filter and a Kalman filter were discussed and compared for sensor fusion. By comparison, in respect of preventing angle drift and maintaining dynamic characteristics, the Kalman filter has the significant advantage, especially in dynamic motion. In the comparison with a highly precise aviation-level fiber optic gyroscope (FOG), the results showed that the static angle drift was restrained by Kalman filter which reached the performance of the FOG. And in the series of farm experiments, the dynamic characteristic of the developed attitude measurement unit is close to the FOG performance in the sub-degree level. This is an acceptable accuracy for light-loaded, small-sized and cost effective agricultural robot application such as agriculture drone, greenhouse robots, harvesting robot arm and so on.

Entanglement dynamics of two Ising-coupled qubits with nonperpendicular local driving fields

We present an approximate analytical solution to the dynamic equation of two Ising-coupled qubits with oscillating classical control fields that are nonperpendicular to the static drift fields. This is a situation that has recently arisen in some solid-state experiments. With our solution we derive the analytical expressions for the local invariants as well as the local rotations needed to isolate a purely nonlocal gate. This determines the set of parameters that are required to generate any entangling gate. Moreover, we use our results to describe a recent experimental work on capacitively coupled singlet-triplet qubits in GaAs and discuss possible differences for a similar device in silicon.