101 research outputs found
A Techno-Economic Analysis of a Cargo Ship Using Flettner Rotors
No full textIn the last twenty years, the global shipping transport demand has strongly increased (around 4% per year since the 1990s), together with the request for new green propulsion technologies to break down carbon emissions and face the costs deriving from the usage of conventional diesel fuels. Flettner rotors (hereafter: FRs) have been identified by several researchers as a promising solution to exploit wind energy on commercial ships, reducing fuel consumption. The present work presents a six-degree-of-freedom (6DOF) ship performance model set up to evaluate the best way of using a pair of Flettner rotors. The study analyses the performance of this propulsion system in consideration of weather and sea conditions, evaluating the related reduction in fuel consumption. A discussion about the economic and environmental advantages of the usage of FRs is provided, considering the costs linked to their installation and the new emission restrictions. Relevant results have been obtained for different routes, speed ranges and rotor dimensions while investigating the best Flettner rotor arrangement to minimise both the emissions and the installation cost payback period
Experiments on a Flettner rotor at critical and supercritical Reynolds numbers
No full textThe Flettner rotor is attracting increasing attention as a viable technology for wind-assisted ship propulsion. Nonetheless, the influence of the Reynolds number on the aerodynamic performance of rotating cylinders is still unclear and under debate. The present study deals with a series of wind-tunnel experiments on a large-scale Flettner rotor in which the forces and pressures acting on the cylinder were measured for Reynolds numbers as large as Re=1.0⋅10 6 . The rotating cylinder used in the experimental campaign had a diameter of 1.0 m and span of 3.73 m. The results indicate that the lift coefficient is only affected by the Reynolds number in the critical flow region and below velocity ratio k=2.5. Conversely, in the velocity ratio range
A device for pressure measurements on yacht sails
No full textThe present invention relates to the field of ship building, in particular ships propelled by sails, more in particular to sail design.
The present invention discloses a sail pressure measurement system based on MEMS sensors and pressure strips and pads technology. The system is capable to give differential measurement between the leeward and windward side of the sails
Low molecular weight heparin : does it represent a clinical opportunity for preventing preeclampisa associated with fetal growth restriction?
No full textExperimental validation of the aero-servo design of a large-scale floating offshore wind turbine model
No full textOffshore floating wind turbines are such complex systems from the point of view of global dynamics that numerical models are often insufficient in describing completely and correctly their behavior. In this framework large scale models deployed in a natural outdoor environment are a valid complement in understanding the real features of the system and in updating or validating codes. In the case of wind turbines adopting a large scale allows to better reproduce the aerodynamic behavior of the rotor. Objective of the present work is the validation of the aerodynamic design of a large-scale 1:15 model of the DTU 10 MW wind turbine deployed on a multipurpose floating platform, built in the framework of the Horizon 2020 project termed as "The Blue Growth Farm Project". It is requested to assess the effective aerodynamic characteristics of the rotor so to understand if the physical design is well respecting the aerodynamic properties requested in the design phase. Particular care is put in the correct reproduction of the operating parameters as part of the assessment of the control system. For initial analysis a good compliance between design and physical model is found. Regarding the aerodynamic characteristics, a good agreement between the experimental Cp values and the numerical curves is observed. Overall, the physical rotor aerodynamic design is validated and the power controller steady-state performances are assessed
A large-scale wind turbine model installed on a floating structure:experimental validation of the numerical design
No full textIn the field of floating wind energy, large-scale wind turbine models deployed in natural environments represent a key link between small-scale laboratory tests and full-scale prototypes. While implying smaller cost, design and installation effort than a full-scale prototype, large-scale models are technologically very similar to prototypes, can be tested in natural sea and wind conditions, and reduce by a consistent amount the dimensional scaling issues arising in small-scale experiments. In this framework the presented work report the aerodynamic and control system assessment of a 1:15 model of the DTU 10 MW wind turbine installed on a multipurpose-platform model for fish farming and energy production. The model has operated for 6 months in a natural laboratory and has been exposed to fully natural and uncontrolled environmental conditions. Assessment is performed in terms of rotor thrust force and power controller parameters such as rotor speed, blade pitch and rotor power as a function of incoming wind speed
Numerical Simulation of an Oscillating Cylinder at High Reynolds Number
No full textIn this work, we propose a numerical investigation of the main flow field characteristics around a free oscillating rigid circular cylinder that is immersed in a turbulent flow (Re≈5∙〖10〗^4). The cylinder is characterized by high value of mass ratio and mass damping (m^*=145; ξ=0.6÷1.14∙〖10〗^(-3);m^* ξ=0.1÷0.25). Then the numerical results are compared with previous experimental data obtained in the wind tunnel under very similar fluid dynamic conditions. There are few works in literature that consider both numerical and experimental results under these conditions. This is probably due to the experimental facilities limitations and the computational difficulties correlated to modeling the flow with high Reynolds number. With the aim of matching the experimental analysis, developed in the last years in the Politecnico di Milano Wind Tunnel on a suspended oscillating cylinder, with numerical results, we set-up a numerical URANS model through a CFD commercial code using a k-ω SST turbulence model in a 3D domain.
The numerical setup is characterized by the use of the DFBI-Morphing (Dynamic Fluid Body Interaction) model that allows the modeling of the body motion in response to fluid forces treating the cylinder as a mass-damping-spring system by introducing spring and damping forces acting on it.
A preliminary check of this numerical setup was provided by a benchmark involving a simple case of fixed cylinder at the same Reynolds number, where the movements of the cylinder were disabled. The numerical results of this case have been compared with experimental and numerical results reported in literature by means of Drag and Lift coefficients and Strouhal number at high Reynolds (Re≈5∙〖10〗^4). After that benchmark, the full setup has been checked by considering specific fluid dynamic conditions where the cylinder was out of the lock in region in which the oscillations of the cylinder are negligible.
Finally we have investigated two points of the steady state oscillating response curve of the cylinder in the lock in region. The numerical model gave good results in terms of amplitude response of the cylinder and aerodynamic forces if compared with experimental results.
The analysis of the numerical reconstruction of the flow field evolution are therefore considered to have more information on the vortex shedding mode especially in the transition region between 2S and 2P mode
Travaglio di prova dopo taglio cesareo:quali fattori intervengono nella scelta delle modalità del parto? Due esperienze cliniche milanesi a confronto
No full textThe frequency of caesarean section is gradually increased over the years. Women that after a caesarean section decide to endure a pregnancy need to discuss with their gynecologist about the way of delivering. In the first part of the thesis are described the factors that may influence the success or failure of trial of labor, contraindications, advantages, disadvantages, both vaginal birth after caesarean section and elective repeat caesarean section. In the second chapter, I dealt with the principal and most feared risk of trial of labor after a prior caesarean delivery: the uterine rupture.
The aim of the thesis have been to evaluate the type of information about mode of delivery that the pregnant women after a previous caesarean section received during a following pregnancy; to highlight the factors that influence this choice; to analyze the opinion of the operators that, every day, have to deal with this topic, and to observe any potential differences between two Hospitals in Milan.
To reach the goal it has made:
- 48 interviews to women during puerperium at the Clinic “Luigi Mangiagalli” and 11 at the Hospital “Vittore Buzzi”;
- 11 questionnaires compiled by midwives in the Clinic “Luigi Mangiagalli” and 14 at the Hospital “Vittore Buzzi”;
- 10 questionnaires compiled by doctors of the Clinic “Luigi Mangiagalli” and 10 at the Hospital “Vittore Buzzi”.
Finally, it can be stated that the major referrers for women that look for this kind of information are gynecologists, even if sometimes it is not scientific evidence based. Professionals words are able to influence the choice of mode of delivery, influencing satisfaction or dissatisfaction of the women. Another important factor in women choices are the previous experiences of labor and the desire to live the experience of vaginal birth
High Speed Small Craft Aerodynamic Resistance
No full textHigh cruising speed, at present commonly achieved by small size pleasure and working boats highlights the importance of aerodynamic drag and suggest to consider also aerodynamic lift.
To this aim an experimental research program has been jointly carried on at Department of Naval Architecture of Universita’ di Napoli Federico II and at Department of Mechanics of Politecnico di Milano
A 1:10 scale model of a planing pleasure boat, decked and GRP built, has been tested in towing tank to assess bare hull resistance, running trim and hull raise at Fn range 1.1-2.1.
In the wind tunnel the same model has been connected to a six DOF. dynamometric balance; a set of wedges has been used to set the scale model at trim angles and hull raises previously assessed in towing tank and a flat plane to simulate the water surface. Aerodynamic drag has been assessed at the same speed values used in the towing tank to evaluate the aerodynamic contribution to the total resistance. Then in order to check Reynolds number effect on the aerodynamic coefficients, further tests at higher wind speed values up to 16 m/s have been performed.
The obtained results allow the assessment of scale models aerodynamic resistance and represent a contribution for a sound application of the experimental procedure used for planing craft resistance evaluation
- …
