scholarly journals Experimental and numerical assessment of vertical accelerations during bow re-entry of a RIB in irregular waves

2021 ◽  
pp. 1-26
Author(s):  
Martin van der Eijk ◽  
Peter Wellens
Keyword(s):  
Numerical Method ◽  
Structural Damage ◽  
Stokes Equations ◽  
State Of The Art ◽  
Irregular Waves ◽  
Vertical Acceleration ◽  
Damage State ◽  
Severe Injuries ◽  
Strip Theory ◽  
Vertical Accelerations

This paper presents the comparison of a self-conducted towing tank experiment with the simulation results of a calibrated state-of-the-art strip-theory method and a first-principles numerical method. The experiment concerns a Rigid Inflatable Boat (RIB) in moderate-to-high irregular waves. These waves result in bow emersion events of the RIB. Bow re-entry induces vertical accelerations which, in reality, can lead to severe injuries and structural damage. State-of-the-art methods for predicting the vertical acceleration levels are based on assumptions, require calibration and are often limited in application range. We demonstrate how the vertical acceleration as a function of time is found from a 3D numerical method based on the Navier–Stokes equations, employing the Volume of Fluid (VoF) method for the free surface, without any further assumptions or limitations. 2D+t strip theory methods like Fastship are based on the mechanics of wedges falling in water. The 3D numerical method that is part of the software ComFLOW is compared to previous research on falling wedges in 2D to investigate the effect of air and to find suitable grid distances for the 3D simulation of the RIB. The 3D RIB simulations are compared to Fastship and the experiment. With respect to the experiment, the ComFLOW simulations show a slight underestimation of the levels of heave and pitch. The underestimation of Fastship is larger. The prediction of acceleration in ComFLOW is hardly different from the experiment and a significant improvement with respect to Fastship. ComFLOW is demonstrated to predict acceleration levels better than before, which creates opportunities for using it in seakeeping optimization and for the improvement of methods like Fastship. The properties of the RIB and the experiment are available as open data at Wellens (2020).

Numerical Analysis of a Surface Ship in Waves

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Shawn Aram
Keyword(s):  
Stokes Equations ◽  
Body Motion ◽  
Irregular Waves ◽  
Design Stage ◽  
Fluid Viscosity ◽  
Sea Waves ◽  
Added Resistance ◽  
Physical Mechanisms ◽  
Strip Theory ◽  
Seakeeping Analysis

Abstract Ship's resistance and engine power to sustain ship's speed in seaways are augmented due to complex non-linear interactions between the ship and the ambient sea (waves). Ship designers, in early design stage, use an ad hoc "sea margin" to account for the effects of seaways in selecting propeller and engine. A numerical tool capable of accurately predicting added resistance and power of a ship cruising in waves would greatly help select its powering (margin) requirement and determine the optimal operating point that can maximize the energy efficiency. For seakeeping analysis, strip theory-based methods have long been used. More recently, nonlinear time-domain three-dimensional (3D) panel methods have started being used widely. A more physics-based avenue to seakeeping analysis is offered by coupled solutions of two-phase unsteady Reynolds-Averaged Navier-Stokes equations and six degrees-of-freedom rigid-body motion (RBM) equations. The URANS approach also avails itself of including the effects of propulsors, either explicitly or approximately. By accounting for all the nonlinear effects in hydrodynamic forces and moments and the resulting ship motions, and the effects of fluid viscosity and turbulence, the coupled URANS-RBM method is believed not only able to predict added resistance and speed loss more accurately, but also to provide valuable insights into the physical mechanisms underlying added resistance and power. The objectives of this study are: (1) to validate a coupled URANS-RBM solver developed for high-fidelity prediction of added resistance, speed loss and added power on ships cruising in regular head sea and irregular waves, and (2) to conduct a detailed analysis of the interactions among ship hull, propeller and waves for a 1/49 scaled model of the ONR Tumblehome (ONRT) (Model 5613) in order to shed light on the physical mechanisms leading to added resistance, speed loss and added power. Figure 1 depicts the ONRT self-propellers with two 4-bladed propellers in regular waves. The main flow features such as the free surface, the hub vortices and blade-tip vortices from the propeller, as well as vortices generated by the sonar dome, shafts, shaft brackets and bilge keels are captured.

scholarly journals Smartphone monitoring of in-ambulance vibration and noise

2021 ◽  
pp. 095441192098599
Author(s):  
Tom Partridge ◽  
Lorelei Gherman ◽  
David Morris ◽  
Roger Light ◽  
Andrew Leslie ◽  
...  
Keyword(s):  
Transport Systems ◽  
Vertical Acceleration ◽  
Vehicle Speed ◽  
Noise Levels ◽  
The Road ◽  
Neonatal Transport ◽  
Mass Data ◽  
Transport Team ◽  
Vertical Accelerations ◽  
Noise Vibration

Transferring sick premature infants between hospitals increases the risk of severe brain injury, potentially linked to the excessive exposure to noise, vibration and driving-related accelerations. One method of reducing these levels may be to travel along smoother and quieter roads at an optimal speed, however this requires mass data on the effect of roads on the environment within ambulances. An app for the Android operating system has been developed for the purpose of recording vibration, noise levels, location and speed data during ambulance journeys. Smartphone accelerometers were calibrated using sinusoidal excitation and the microphones using calibrated pink noise. Four smartphones were provided to the local neonatal transport team and mounted on their neonatal transport systems to collect data. Repeatability of app recordings was assessed by comparing 37 journeys, made during the study period, along an 8.5 km single carriageway. The smartphones were found to have an accelerometer accurate to 5% up to 55 Hz and microphone accurate to 0.8 dB up to 80 dB. Use of the app was readily adopted by the neonatal transport team, recording more than 97,000 km of journeys in 1 year. To enable comparison between journeys, the 8.5 km route was split into 10 m segments. Interquartile ranges for vehicle speed, vertical acceleration and maximum noise level were consistent across all segments (within 0.99 m . s−1, 0.13 m · s−2 and 1.4 dB, respectively). Vertical accelerations registered were representative of the road surface. Noise levels correlated with vehicle speed. Android smartphones are a viable method of accurate mass data collection for this application. We now propose to utilise this approach to reduce potential harmful exposure, from vibration and noise, by routing ambulances along the most comfortable roads.

Fully Nonlinear Potential/RANSE Simulation of Wave Interaction With Ships and Marine Structures

2008 ◽  
Author(s):  
Pierre Ferrant ◽  
Lionel Gentaz ◽  
Bertrand Alessandrini ◽  
Romain Luquet ◽  
Charles Monroy ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Stokes Equations ◽  
Wave Interaction ◽  
Irregular Waves ◽  
Navier Stokes ◽  
Viscous Effects ◽  
Navier Stokes Equations ◽  
Fully Nonlinear ◽  
Nonlinear Potential ◽  
6 Degrees Of Freedom

This paper documents recent advances of the SWENSE (Spectral Wave Explicit Navier-Stokes Equations) approach, a method for simulating fully nonlinear wave-body interactions including viscous effects. The methods efficiently combines a fully nonlinear potential flow description of undisturbed wave systems with a modified set of RANS with free surface equations accounting for the interaction with a ship or marine structure. Arbitrary incident wave systems may be described, including regular, irregular waves, multidirectional waves, focused wave events, etc. The model may be fixed or moving with arbitrary speed and 6 degrees of freedom motion. The extension of the SWENSE method to 6 DOF simulations in irregular waves as well as to manoeuvring simulations in waves are discussed in this paper. Different illlustative simulations are presented and discussed. Results of the present approach compare favorably with available reference results.

scholarly journals Structural Damage Diagnosis and Prediction Using Machine Learning and Deep Learning Models: Comprehensive Review of Advances

2019 ◽  
Author(s):  
Amir Mosavi
Keyword(s):  
Machine Learning ◽  
Composite Structures ◽  
Structural Damage ◽  
Structural Integrity ◽  
State Of The Art ◽  
Future Trends ◽  
Learning Models ◽  
Damage Diagnosis ◽  
Comprehensive Review ◽  
Initiation And Propagation

The loss of integrity and adverse effect on mechanical properties can be concluded as attributing miro/macro-mechanics damage in structures, especially in composite structures. Damage as a progressive degradation of material continuity in engineering predictions for any aspects of initiation and propagation requires to be identified by a trustworthy mechanism to guarantee the safety of structures. Besides the materials design, structural integrity and health are usually prone to be monitored clearly. One of the most powerful methods for the detection of damage is machine learning (ML). This paper presents the state of the art of ML methods and their applications in structural damage and prediction. Popular ML methods are identified and the performance and future trends are discussed.

scholarly journals Numerical simulation and experimental comparison of flaw evolution on a bearing raceway: Case of thrust ball bearing

2018 ◽  
Vol 5 (4) ◽  
pp. 427-434 ◽  
Author(s):  
M.Y. Toumi ◽  
S. Murer ◽  
F. Bogard ◽  
F. Bolaers
Keyword(s):  
Structural Damage ◽  
Ball Bearing ◽  
Rolling Contact ◽  
Experimental Comparison ◽  
Ball Bearings ◽  
Damage State ◽  
Element Analysis ◽  
Rolling Surface ◽  
Experimental Apparatus ◽  
Good Agreement

Abstract Bearings are essential elements in the design of rotating machines. In an industrial context, bearing failure can have costly consequences. This paper presents a study of the rolling contact fatigue damage applied to thrust ball bearings. It consists in building a dynamic three-dimensional numerical model of the cyclic shift of a ball on an indented rolling surface, using finite element analysis (FEA). Assessment of the evolution in size of a surface spall as a function of loading cycles is also performed using FEM coupled with fatigue laws. Results are in good agreement with laboratory tests carried out under the same conditions using a fatigue test cell dedicated to ball bearings. This study may improve knowledge about estimating the lifetime of rolling components after onset of a spall using FEA and accounting for structural damage state. Highlights The experimental apparatus and damaged thrust ball bearing are described. We model a portion of the thrust ball bearing featuring a spherical indent. Numerical results in terms of stress field are compared to analytical results from the literature. A fatigue software is used to assess the evolution of spalling size. Good agreement is obtained between experimental test campaigns at different loads and FEA results.

OPERATIONAL BEHAVIOUR OF AN OFFSHORE MULTIPURPOSE SUPPORT VESSEL IN THE EASTERN MEDITERRANEAN SEA

2021 ◽  
Vol 161 (A3) ◽  
Author(s):  
Y Garbatov ◽  
N Almany ◽  
M Tekgoz
Keyword(s):  
Mediterranean Sea ◽  
Eastern Mediterranean ◽  
Probabilistic Approach ◽  
Vertical Acceleration ◽  
Operational Mode ◽  
Wave Condition ◽  
Eastern Mediterranean Sea ◽  
Seakeeping Performance ◽  
Strip Theory ◽  
Operational Behaviour

The objective of this work is to analyse the operational behaviour of an offshore multipurpose support vessel designed to operate in the Eastern Mediterranean Sea. First, the seakeeping analysis is performed in a regular wave condition for different heading angles estimating heave and pitch motions through the strip theory. After that, the effects of the vertical acceleration on the bow, occurrence of slamming or hydrodynamic impact of the hull on the surface of the water; wetted deck, occurrence or invasion of water on the deck of the vessel and propeller emersion, motion sickness and wave-induced additional resistance are analysed. The present analysis is extended in an irregular sea condition, and the estimated seakeeping criteria are compared to the acceptable levels. In defining the most suitable operational mode of the offshore support vessels, multi-criteria decision techniques and probabilistic approach are employed to perform an adequate evaluation of the seakeeping performance accounting for different hazardous events through the service life.

A Probabilistic Study of the Simultaneous Effect of Ship Motions on the Cargo Shifting Onboard

1996 ◽  
Vol 33 (01) ◽  
pp. 25-34
Author(s):  
Jianbo Hua
Keyword(s):  
Transfer Functions ◽  
Simulation Method ◽  
Point Of View ◽  
Roll Angle ◽  
Ship Motions ◽  
Vertical Acceleration ◽  
Simultaneous Effect ◽  
Strip Theory ◽  
Probabilistic Study ◽  
Mean Wave Period

Cargo movement aboard ship can occur even in waves that produce only moderate rolling motion. It is caused when the simultaneous effect of vertical acceleration, horizontal acceleration and roll motion on the cargo onboard—defined as the equivalent roll angle—becomes sufficiently large for the problem to develop. In this paper, an analytical expression is derived for the probabilistic calculation of the equivalent roll angle, which has a nonlinear characteristic. Also, a so-called indirect time-domain simulation method is described for calculating the problem. Both methods are based on motion transfer functions calculated according to strip theory. The calculations presented here show both methods to be in good agreement. A probabilistic calculation of the equivalent roll angle of a roll-on/roll-off (RO/RO) ship is carried out using the two methods and focusing on parameters such as significant wave height, mean wave period, ship speed, and relative course angle. It is proved from the point of view of probability that the nonlinearity of equivalent roll angle results in a magnifying effect on its extreme value. The calculation shows also that in severe wave conditions large peak values of equivalent roll greater than 35 deg can be experienced by the studied RO/RO ship.

Bending Moments and Shear Forces in Ships Sailing in Irregular Waves

1981 ◽  
Vol 25 (04) ◽  
pp. 243-251
Author(s):  
J. Juncher Jensen ◽  
P. Terndrup Pedersen
Keyword(s):  
Linear Part ◽  
Vertical Motion ◽  
Bending Moment ◽  
Irregular Waves ◽  
Bending Moments ◽  
Shear Forces ◽  
Strip Theory ◽  
Wave Heights ◽  
Exciting Forces ◽  
Wave Induced

This paper presents some results concerning the vertical response of two different ships sailing in regular and irregular waves. One ship is a containership with a relatively small block coefficient and with some bow flare while the other ship is a tanker with a large block coefficient. The wave-induced loads are calculated using a second-order strip theory, derived by a perturbational procedure in which the linear part is identical to the usual strip theory. The additional quadratic terms are determined by taking into account the nonlinearities of the exiting waves, the nonvertical sides of the ship, and, finally, the variations of the hydrodynamic forces during the vertical motion of the ship. The flexibility of the hull is also taken into account. The numerical results show that for the containership a substantial increase in bending moments and shear forces is caused by the quadratic terms. The results also show that for both ships the effect of the hull flexibility (springing) is a fair increase of the variance of the wave-induced midship bending moment. For the tanker the springing is due mainly to exciting forces which are linear with respect to wave heights whereas for the containership the nonlinear exciting forces are of importance.

Sign in / Sign up

Export Citation Format

Share Document