Browsing by Author "Wang, Youjiang"
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- CFD modelling and analysis of ship handling operations
Insinööritieteiden korkeakoulu | Master's thesis(2021-12-13) Abdelghafor, ZeiadThe operational capability of ships to manoeuvre in restricted waters, e.g., in ports or channels, is challenging despite the development of control systems onboard ships. These risks reaffirm the role of the tugboat assistive operations in ports and channels under varying hydrometeorological conditions. This thesis presents a Reynolds Averaged Navier Stokes Computational Fluid Dynamics (RANS CFD) method that may be used for the evaluation of the contact forces acting on the tugboat and an assisted ship during pushing operations. The thesis suggests decision making charts that may aid tug masters during pushing operations. Two models are used to idealise ship dynamics during tug operations. The first model utilises the STARCCM+ solver, including an unsteady RANS method, the dynamic fluid body interaction module (DFBI), and the contact mechanics coupling module to model the contact between a tugboat and an assisted ship. The second model (tug-force equilibrium) applies the same solver with steady and unsteady RANS methods without the DFBI and the contact mechanics coupling modules. The contact force in the second model is calculated as a sum of the hydrodynamic forces on the hull and the propeller. It is demonstrated that the mean values of contact forces predicted by the two models are nearly similar, whereas the DFBI model can idealise the time variation of the contact force. The tug-force equilibrium model is shown to be more time-efficient in predicting the mean values of contact forces and for developing decision-making charts. It is concluded that the tugboat speed and orientation are vital and may amplify the pushing forces. Moreover, the pushing force at low speed might reach the bollard pull value and more when the hull forces supplement the force provided by thrusters i.e., when the sway force act on the negative direction relative to the tug-fixed coordinates, it amplifies the pushing force. - Digitalization of High Speed Craft Design and Operation Challenges and Opportunities
A4 Artikkeli konferenssijulkaisussa(2022) Dashtimanesh, Abbas; Ghaemi, Mohammad Hossein; Wang, Youjiang; Karczewski, Artur; Bilandi, Rasul Niazmand; Hirdaris, SpyrosIn recent years, global demands for safe and sustainable ships led to dramatic changes in maritime industry. Digitalization is expected to play important part in the future . This is supported by analysis of the autonomous ships market which shows that digitalization of large ship types such as tankers and container ships is well on track. Although to date designs of autonomous High Speed Craft (HSC) have been developed, there are only a few studies on the impact of digitalization on design and operations. This is because of the challenging operational profile of these assets across a spread of waterborne activities namely fishing, leisure, patrolling and rescuing. This paper reviews literature of relevance on the potential of digitalization of the HSC sector in the Baltic. An overview of the systems that could be partly digitalized and how technology developments may influence operations are also outlined. - A fast and storage-saving method for direct volumetric integration of FWH acoustic analogy
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-10-01) Wang, Youjiang; Mikkola, Tommi; Hirdaris, SpyrosThis paper proposes a new method that makes the direct volume integration of the Lighthill stress term in FWH acoustic analogy affordable in terms of both computational time and disk storage requirement. The method is based on a dual mesh concept, i.e. while a fine mesh is used in CFD, a relatively coarse mesh is used for the acoustic calculation. The terms being independent of the observer positions in the integral formula of FWH acoustic analogy are calculated on the CFD mesh and mapped onto the acoustic mesh during the simulation. These sound source terms are used for the on-the-fly acoustic computation or saved for later use in the post-processing. A formulation of the Lighthill stress tensor in cavitating flow is also derived. The method is verified with the acoustic assessment of an inclined marine propeller case. A reduction of the calculation time by 98% and disk storage by 99% is achieved while maintaining small acoustic error. - Numerical studies on tugboat performance during pushing operations
A4 Artikkeli konferenssijulkaisussa(2023-08-09) Abdelghafor, Zeiad; Taimuri, Ghalib; Kujala, Pentti; Wang, Youjiang; Hirdaris, SpyrosThis paper introduces a RANS CFD methodology for the evaluation of tugboat dynamics during pushing operations. Two- and three- dimensional methods that respectively utilize “Dynamic Fluid Body Interactions - (DFBI)” and “Tug Force Equilibrium kinematics- (TFE)” are assessed and compared with the aim to better understand the influence of fluid modelling on ship dynamics. For the DFBI method, an unsteady RANS solver comprising of a dynamic fluid body interaction module and a contact mechanics coupling algorithm are used to predict the forces between a tugboat and an assisted ship. For the TFE method, a steady RANS method is applied and contact actions are calculated as a sum of the hydrodynamic forces on the hull and the propeller. Whereas DFBI accounts for the time variation of the contact forces, the TFE is more rapid and could be used to derive operational decision support criteria. To demonstrate the latter the TFE method is used to derive the pushing forces based on a set of 16 numerical simulations. It is concluded that irrespective of the model used the tugboat speed and orientation may amplify the pushing forces. This effect could be prominent, especially at slow speeds for which the sway force acts in opposite direction to the tug.