Search Results (17)

The present paper reports the comparison of the ship motions and added resistance assessment using high fidelity RANSE simulations in virtual towing tank LincoSim, using 2D strip theory as implemented in ShipX v4.4.0 and 3D BEM potential flow software Hydrostar v8.2.1. All calculations are performed for a medium-sized RoPax ferry of Levante Ferries fleet, which operates daily routes in the Ionian Sea. Calculations by ShipX are performed in frequency domain (using strip-theory and direct pressure integration) and in time domain. The high-fidelity RANSE seakeeping modeling is based on the open-source CFD code OpenFOAM v12 using a standardized framework, tailored to take advantage of HPC facilities and based on a forcing zone formulation. The CFD simulations are performed for six wave periods in head and beam seas at the constant wave height of 3 m. Comparison of the obtained results shows that potential-flow methods are very efficient and reliable tools, suitable for the massive calculations in the first stages of the project. High-fidelity RANSE modeling seems to be more suited for selected cases such as analysis of roll and added resistance in beam waves. Full article

Axial waterjets are widely used for marine propulsion due to their efficiency and maneuverability. However, conventional design procedures heavily rely on empirical correlations and simplified models, limiting their ability to fully exploit the hydrodynamic performance potential of these devices. The study highlights how Simulation-Based Design Optimization (SBDO) approaches, coupled with the high-fidelity simulations required to hydrodynamically characterize the complex phenomena that occur in the case of waterjets, can enable the identification of non-intuitive design improvements over a wider design space that may be missed by traditional methods. In particular, the Reynolds-Averaged Navier–Stokes (RANS) equations are used to provide accurate performance predictions, capturing complex flow phenomena such as secondary flows (i.e., leakage vortices) and pressure distributions critical to waterjet design, of systematically varied configurations using a 42-dimensional parametric model. Simplified key performance indicators, in the specific cavitation inception obtained from the non-cavitating analysis, work in conjunction with the calculated hydraulic efficiency to identify geometries capable of improving (or not worsening) efficiency while postponing cavitation. The systematic and automated analysis of thousands of different configurations, iteratively modified by a genetic algorithm, is finally able to identify better waterjets, whose performances are confirmed by dedicated cavitating RANSE analyses. This demonstrates how RANS-based simulations, integrated with optimization algorithms, can lead to superior axial waterjet designs, providing a flexible, more robust, and effective methodology compared to conventional approaches. Full article

A pre-swirl fin (PSF), pre-swirl duct (PSD) and wake-equalizing duct (WED) energy-saving devices (ESD) are designed for the Duisburg Test Case (DTC). To this aim, a simulation-based design optimization method, combining RANSE analyses (ship resistance) with BEM calculations (unsteady propeller performances) in a simplified optimization process realized through a parametric description of ESD geometries, was employed. Fully resolved RANSE analyses were used to validate the outcomes of this affordable design process, which identifies devices capable of saving energy in the delivered power for this type of challenging test case by up to 2.6%. Comparisons with model-scale calculations, furthermore, permit us to discuss the influence of each appendage in different flowfields (model- and full-scale, as well as under the action of the simplified or the resolved propeller) and the reliability of the full-scale extrapolation methods recently proposed for these types of devices. Full article

Near-surface simulation methods for shallowly submerged underwater vehicles are necessary for the population of a variety of free-surface-affected, coefficient-based maneuvering and seakeeping models. Simulations vary in complexity and computational costs, often sacrificing accuracy for simplicity and speed. One particular simplifying assumption, the linearization of the free surface boundary conditions, is explored in this study by comparing the steady-state wave-making characteristics of a shallowly submerged prolate spheroid using two different simulation methods at several submergence depths and forward speeds. Hydrodynamic responses are compared between a time-domain boundary element method that makes use of a linearized free surface boundary condition and an inviscid, volume of fluid Reynolds-Averaged Navier–Stokes computational fluid dynamics code that imposes no explicit free surface boundary condition. Differences of up to 22.6%, 32.5%, and 33.3% are found in the prediction of steady state surge force, heave force, and pitch moment, respectively. The largest differences between the two simulation methods arise for motions occurring at small submergences and large wave-making velocities where linear free-surface assumptions become less valid. Nonlinearities that occur in such cases are revealed through physical artifacts such as wave steepening, wave breaking, and high-energy waves. A further examination of near-surface viscous forces reveals that the viscous drag on the vessel is depth dependent due to the changing velocity profile around the body. Full article

The hydrodynamic interaction effects between ships are significantly pronounced in restricted waters, and this may potentially threaten the safety of ships, especially given that ship dimensions and waterway traffic have kept increasing. Although there has been a good amount of research on ship hydrodynamic interactions, the study of the effect of the propeller on the ship’s hydrodynamic interaction is very limited. In this paper, a series of RANSE-based numerical simulations are carried out to study the characteristics of the propeller in near-field interaction between ships without speed. The hydrodynamic forces and moment acting on the ship are calculated and analyzed. Through the analysis of the characteristics of the flow field and the behavioral pattern of the hydrodynamic forces, it is found that the propeller has a significant influence on the pressure distribution on the hull as well as on the hydrodynamic interaction forces. The maximum lateral force acting on the interacting ship could reach 0.58 times the standard thrust of a KP458 propeller (the revolution is 594 rpm and the velocity coefficient is 0.25 in open water). Full article

Hospitals’ operational performance during disasters varies from failing, to being responsive and resilient, to dealing with disruption and surprise. Transformational leaders enable continuously learning hospitals that are resilient in the face of disasters by adapting regeneratively and evolving beyond undertaking conventional lesson-learning after each disaster. However, learning from successful transformational leaders in healthcare is still ad hoc with a lack of guidance on how to develop such leaders. Hence, this study sought to identify key competencies of transformational leaders by exploring hospital leaders’ actions in dealing with disasters, considering the disaster cycle of prevention, preparedness, response, and recovery (PPRR). A qualitative case-study design was adopted comprising in-depth semi-structured interviews with twelve senior hospital staff with operational leadership experience with disasters. Three significant categories (themes) and seven key component competencies (sub-themes, in brackets) of transformational leaders were revealed through the analysis of transcripts: (1) ‘Governance and leadership’ (‘transformative agency’ and ‘decisive accountability’); (2) ‘Planning and risk assessment’ (‘risk navigation’, ‘disaster attunement’, and ‘planning agility’); and (3) ‘Communication and network engagement’ (‘communication accelerator’ and ‘collaboration innovator’). The authors propose a transformational leadership model for hospital disaster resilience and an assessment checklist for leaders’ self-reflection to support hospitals in their transition to resilient operations. Full article

Climate change has been recognised as a multiplier of risk factors affecting public health. Disruptions caused by natural disasters and other climate-driven impacts are placing increasing demands on healthcare systems. These, in turn, impact the wellness and performance of healthcare workers (HCWs) and hinder the accessibility, functionality and safety of healthcare systems. This study explored factors influencing HCWs’ disaster management capabilities with the aim of improving their resilience and adaptive capacity in the face of climate change. In-depth, semi-structured interviews were conducted with thirteen HCWs who dealt with disasters within two hospitals in Queensland, Australia. Analysis of the results identified two significant themes, HCWs’ disaster education and HCWs’ wellness and needs. The latter comprised five subthemes: HCWs’ fear and vulnerability, doubts and uncertainty, competing priorities, resilience and adaptation, and needs assessment. This study developed an ‘HCWs Resilience Toolkit’, which encourages mindfulness amongst leaders, managers and policymakers about supporting four priority HCWs’ needs: ‘Wellness’, ‘Education’, ‘Resources’ and ‘Communication’. The authors focused on the ‘Education’ component to detail recommended training for each of the pre-disaster, mid-disaster and post-disaster phases. The authors conclude the significance of the toolkit, which provides a timely contribution to the healthcare sector amidst ongoing adversity. Full article

This paper proposes a fast multigrid algorithm to simulate the non-linear motion of ships in both intact and damaged conditions. The simulations of ship motions in waves are known to require much time to calculate due to the strong non-linear interactions between ship and waves. To improve the calculation efficiency while retaining the accuracy, a prediction-correction strategy was designed to accelerate the simulation through three sets of locally refined meshes. The flow field was first estimated in a coarse mesh and then mapped to a locally refine mesh for further higher-fidelity corrections. A partitioned radial basis function (PRBF) method is proposed to interpolate and reconstruct the flow field for the refined mesh. A new two-phase flow solver was developed with a fast multigrid algorithm based on the Reynolds-averaged Navier–Stokes equations (RANSE). The new solver was applied to study the non-linear behavior of a damaged ship in beam waves and the effect of damaged compartments on ship rolling motion. Validation against the solution with the original method of single set meshes and experimental data indicates that the proposed algorithm yields satisfactory results while saving 30–40% of the computational time. Full article

Flapping-foil thrusters arranged at the bow of the ship are examined for the exploitation of energy from wave motions by direct conversion to useful propulsive power, offering at the same time dynamic stability and reduction of added wave resistance. In the present work, the system consisting of the ship and an actively controlled wing located in front of its bow is examined in irregular waves. Frequency-domain seakeeping analysis is used for the estimation of ship-foil responses and compared against experimental measurements of a ferry model in head waves tested at the National Technical University of Athens (NTUA) towing tank. Next, to exploit the information concerning the responses from the verified seakeeping model, a detailed time-domain analysis of the loads acting on the foil, both in head and quartering seas, is presented, as obtained by means of a cost-effective time-domain boundary element method (BEM) solver validated by a higher fidelity RANSE finite volume solver. The results demonstrate the good performance of the examined system and will further support the development of the system at a larger model scale and the optimal design at full scale for specific ship types. Full article

Potential risks for public health incidents, outbreaks, and casualties are inferred at association football events, especially if event organizers have not taken appropriate preventative measures. This review explores the potential risks imposed by mass gathering (MG) football events, with particular emphasis on tools and methodologies to manage the risks of football MG events. Effective planning and implementation of MGs along with the mitigation of risks related to people’s health require special attention to all potential threats, especially in frequent and recurring MG events such as football leagues. The well-being of all participants can be compromised by ignoring a single risk. Healthcare systems should cooperate with all stakeholders and organizations who are involved in MG management and response. Provision of services during MG or a disaster must be performed by trained personnel or entities that have full access to available resources in accessible publicly known locations at the MG event site. Several MG assessment tools were developed worldwide; however, to adapt to the Saudi context, SALEM tool was developed to provide a guide for MG planning and assessment. SALEM assesses the risks of MG events with scores that help to categorize the risk of MG events by offering recommendations for required resources. Full article

During maneuvers, propellers’ operation differs from their design due to strong modification of the wake field with respect to the straight-ahead motion. The consequent modification of the loads overstresses the mechanical components of the shaftline, exacerbates propeller side effects and worsens overall efficiency. Therefore, the analysis of these situations in the early design phase is pivotal to increase the operation capabilities and safety at sea. This task relies on novel tools capable to accurately predict the complex flow field that develops past the hull and the propeller loads. Since the solution of the fully coupled problem with the rotating propeller by viscous flow solver is impractical for routine applications, hybrid approaches are a viable alternative. In this paper, an interactive RANSE/BEM methodology is presented, where the propeller is replaced by rotating body forces that map the actual loading state of the blades, allowing a fully unsteady analysis of hull–propeller interaction. The methodology is applied to the straight ahead and $8.4°$ pure drift motions of a twin screw propulsive configuration. Last, but not least, the study presents a validation study with accurate experimental data of the nominal wake field and single blade loads. Full article

Sudden cardiac arrest is one of the leading causes of death globally. The recommended clinical management in out-of-hospital cardiac arrest cases is the immediate initiation of high-quality cardiopulmonary resuscitation (CPR). Training mannequins should be combined with technology that provides students with detailed immediate feedback on the quality of CPR performance. This study aimed to verify the impacts of the type of feedback (basic or detailed) the responders receive from the device while learning CPR and how it influences the quality of their performance and the motivation to improve their skills. The study was conducted at the Medical University of Lublin among 694 multi-professional health students during first aid classes on basic life support (BLS). The students first practiced on an adult mannequin with a basic control panel; afterward, the same mannequin was connected to a laptop, ensuring a detailed record of the performed activities through a projector. Next, the participants expressed their subjective opinion on how the feedback provided during the classes, basic vs. detailed, motivated them to improve the quality of their CPR performance. Additionally, during the classes, the instructor conducted an extended observation of students’ work and behavior. In the students’ opinion, the CPR training with detailed feedback devices provided motivation for learning and improving CPR proficiency than that with a basic control panel. Furthermore, the comments given from devices seemed to be more acceptable to the students, who did not see any bias in the device’s evaluation compared to that of the instructor. Detailed device feedback motivates student health practitioners to learn and improve the overall quality of CPR. The use of mannequins that provide detailed feedback during BLS courses can improve survival in out-of-hospital cardiac arrest. Full article

The main transport channel of the global economy is represented by shipping. Engineers and hull designers are more preoccupied in ensuring fleet safety, the proper operation of the ships, and, more recently, compliance with International Maritime Organization (IMO) regulatory incentives. Considerable efforts have been devoted to in-depth understanding of the hydrodynamics mechanism and prediction of ship behavior in waves. Prediction of seakeeping performances with a certain degree of accuracy is a demanding task for naval architects and researchers. In this paper, a fully numerical approach of the seakeeping performance of a KRISO (Korea Research Institute of Ships and Ocean Engineering, Daejeon, South Korea) container ship (KCS) container vessel is presented. Several hydrodynamic methods have been employed in order to obtain accurate results of ship hydrodynamic response in regular waves. First, an in-house code DYN (Dynamic Ship Analysis, “Dunarea de Jos” University of Galati, Romania), based on linear strip theory (ST) was used. Then, a 3D fully nonlinear time-domain Boundary Element Method (BEM) was implemented, using the commercial code SHIPFLOW (FLOWTECH International AB, Gothenburg, Sweden). Finally, the commercial software NUMECA (NUMECA International, Brussels, Belgium) was used in order to solve the incompressible unsteady Reynolds-averaged Navier–Stokes equation (RANSE) flow at ship motions in head waves. The results obtained using these methods are represented and discussed, in order to establish a methodology for estimating the ship response in regular waves with accurate results and the sensitivity of hydrodynamical models. Full article

The hydrodynamic interaction induced by the complex flow around a ship maneuvering in restricted waters has a significant influence on navigation safety. In particular, when a ship moves in the vicinity of a bank, the hydrodynamic interaction forces caused by the bank effect can significantly affect the ship’s maneuverability. An efficient algorithm integrated in onboard systems or simulators for capturing the bank effect with fair accuracy would benefit navigation safety. In this study, an algorithm based on the potential-flow theory is presented for efficient calculation of ship-bank hydrodynamic interaction forces. Under the low Froude number assumption, the free surface boundary condition is approximated using the double-body model. A layer of sources is dynamically distributed on part of the seabed and bank in the vicinity of the ship to model the boundary conditions. The sinkage and trim are iteratively solved via hydrostatic balance, and the importance of including sinkage and trim is investigated. To validate the numerical method, a series of simulations with various configurations are carried out, and the results are compared with experiment and numerical results obtained with RANSE-based and Rankine source methods. The comparison and analysis show the accuracy of the method proposed in this paper satisfactory except for extreme shallow water cases. Full article

Flapping foils located beneath or to the side of the hull of the ship can be used as unsteady thrusters, augmenting ship propulsion in waves. The basic setup is composed of a horizontal wing, which undergoes an induced vertical motion due to the ship’s responses in waves, while the self-pitching motion of the wing is controlled. Flapping foil thrusters can achieve high level of thrust as indicated by measurements and numerical simulations. Due to the relatively small submergence of the above biomimetic ship thrusters, the free-surface effects become significant. In the present work, the effect of the free surface on the performance of flapping foil thruster is assessed by means of two in-house developed computational models. On one hand, a cost-effective time-domain boundary element method (BEM) solver exploiting parallel programming techniques and general purpose programming on graphics processing units (GPGPU) is employed, while on the other hand a higher fidelity RANSE finite volume solver implemented for high performance computing (HPC) is used, and comparative results are presented. BEM and RANSE calculations present quite similar trends with respect to mean submergence depth, presenting 12%, 28%, and 18% of differences concerning the mean values of lift, thrust, and moment coefficients, respectively. The latter differences become very small after enhancement of the BEM model to include viscous corrections. Useful information and data are derived supporting the design of the considered biomimetic thrusters, for moderate submergence depths and conditions characterized by minor flow separation effects. Full article