A method based on potential theory for calculating air ca formation of an air cavity resistance reduction ship

This research is intended to provide academic reference and design guidance for further studies to determine the most effective means to reduce a ship’s resistance through an air-cavity. On the basis of potential theory and on the assumption of an ideal and irrotational fluid, this paper drives a method for calculating air cavity formation using slender ship theory then points out the parameters directly related to the formation of air cavities and their interrelationships. Simulations showed that the formation of an air cavity is affected by cavitation number, velocity, groove geometry and groove size. When the ship’s velocity and groove structure are given, the cavitation number must be within range to form a steady air cavity. The interface between air and water forms a wave shape and could be adjusted by an air injection system.

Insulation effect of air cavity in sand mold using 3D printing technology

The insulation effect of the air cavity surrounding the riser in a 3D printed sand mold was studied. The influence of the air cavity on heat flux was theoretically analyzed. The results demonstrated that the heat flux of the air cavity in the 3D printed sand mold was significantly less than that of resin-bonded sand. The insulation effect of the air cavity in sand molds for a cylinder casting and a stress-frame casting were simulated using software COMSOL. The results illustrated that the air cavity could be used to insulate the riser and it was more suitable for a lower melting point metal casting. An air cavity with 10-15 mm width and 5-10 mm away from the riser can significantly prolong the solidification of the riser by over 10%. Meanwhile, the sand mold for the stressframe was made by 3D printing technology and poured with aluminum alloy A356 melt. The experiment results showed that the presence of the air cavity led to a 12.5% increase of the solidification time of its riser.

Numerical study of air cavity characteristics of bow wave breaking of KCS ship under different speeds

Ship bow wave breaking contains complex flow mechanism,which is very important for ship performance.In this study,a practical numerical simulation scheme for bow wave breaking is proposed and the scheme is applied to the simulation of bow wave breaking of KCS ship model with Fr=0.26,0.30,0.35,0.40,analyzing the impact of speed on the bow wave breaking.The results indicate that an increase in speed leads to a significant rise in viscous pressure resistance and more pronounced bow wave breaking.Moreover,it is found that the traditional wave height function in OpenFOAM is not suitable for detailed studies of bow wave breaking.This study extracts different free surfaces through top and bottom views to further analyze the free surface overturning,droplet splashing,and cavity entrainment in bow wave breaking.Additionally,the spatial and temporal distribution of cavities at Fr=0.40 is analyzed,revealing that cavity distribution is closely related to vortex structures and exhibits a periodic pulsation characteristic of approximately 12 s.

Monolithic homogeneous integrated miniaturized triboelectric nanogenerator with an inner air cavity for energy harvesting

To realize the high-efficiency acquisition of environmental mechanical energy,traditional triboelectric nanogenerators(TENGs)based on contact-separation consist of two separate triboelectric layers.Their large contact-separation gap increases the overall volume of the device,making it difficult to realize miniaturization and flexibility.This work,therefore,presents a fully enclosed all-in-one-shaped flexible TENG(FEAST)with an air cavity using rubber mixing and high-temperature vulcanization.The air pressure inside the enclosed air cavity facilitates effective contact-separation of the FEAST.The homogeneous integration between the triboelectric layer and the electrode layer enhances structural firmness without using extra spacer materials.The developed FEAST presents excellent mechanical durability even after 10000 cycles.By increasing the active contact area between the triboelectric materials,a maximum peak-peak output voltage,current,and power density of 130 V,1.1μA,and277 m W/m^(2),respectively,were obtained with an effective stress area of 1 cm2.Moreover,the fully enclosed structure ensures that the output performance is not affected by the external environment.The FEAST was fixed onto the sole of a shoe to demonstrate its applicability in harvesting mechanical energy from human motions.Overall,the developed method provides a simple approach for optimizing the structure of TENGs and is compatible with large-scale manufacturing.

Future Outlook of Artificial Cavity Application for Reducing Hydrodynamic Resistance of Containerships

Absolute commitment to reduce the impact of greenhouse gas emissions while increasing fuel efficiency and power density requires further enhancement of prime mover characteristics and special coatings, but mostly requires compliance with EEDI （energy efficiency design index） measures. For the container shipping industry this represents significant increases in fuel costs that can be mitigated above all by reduction of power demand, that is, of ship frictional resistance. In this respect, this paper discusses advantages attainable by application of the ACS （air cavity system） technology on the basis of recent KSRC （Krylov State Research Centre） studies Savings in operating costs yielded by the enhanced propulsion performance for ships fitted with this system are illustrated by a case study of a containership.

Influence of Local Weather Conditions on Ventilation ofa Pitched Wooden Roof

This paper investigates the influence of temperature and wind conditions on ventilation of the air cavity beneath the roofing in a full-scale pitched wooden roof construction.The potential for condensation in the air cavity is studied.The relevant roof construction is equipped with 81 thermocouples and four air velocity measurement devices.A weather station at the site records outdoor temperature and wind conditions.Five periods between 2016 and 2018 are investigated.The findings show distinct periods of below-ambient temperature and positive condensation potential in the ventilated air cavity of the roof.A relation between low wind speed and positive condensation potential is shown.Difference in size of periods with below-ambient temperature and periods with positive condensation potential implies that the materials in the roof regulate the humidity in the air cavity.Large negative peaks in the condensation potential indicate dry-out of the construction.

The effect of the magnetic fields from three different configurations of the MRIgRT systems on the dose deposition from lateral opposing photon beams in a laryngeal geometry–A Monte Carlo study

Objective:To investigate the impact of different magnetic field strengths and orientations on the dose deposition from lateral opposing photon beams irradiating a laryngeal geometry,with particular attention focused on the dose homogeneity of the area around the air cavity inside the larynx.Methods:Geant4 simulation toolkit was used to perform Monte Carlo simulations on a phantom resembling the larynx.The energy spectrum of a 6 MV photon beam from a Varian Clinac iX machine was used to provide the source of radiation.Three configurations of the Magnetic Resonance Image-Guided Radiation Therapy(MRIgRT)system were simulated:the Fixed Cylindrical(FC)geometry,the Longitudinal Rotating Biplanar(LRBP)geometry,and the Transverse Rotating Biplanar(TRBP)geometry.Uniform magnetic fields of different field strengths were applied.The relative dose maps and the homogeneity index(HI)were obtained for evaluations.Results:The LRBP geometry together with a magnetic field strength of 0.5 T produced the most homogeneous dose distribution with a HI of 0.139 for the region of interest around the air cavity,compared with a HI of 0.180 when the magnetic field was absent.For TRBP geometry,the dose distribution shifted towards the cranial direction,leading to a region of hot spots at the superior edge and a region of cold spots at the inferior edge of the irradiated volume.The HI around the air cavity was therefore worse.In addition,strong electron streaming effect(ESE)was observed.For the FC geometry,hot and cold spots were formed around the air cavity which increased the HI.Conclusions:Out of the three configurations of the MRIgRT systems,the LRBP geometry produced the most clinically beneficial dose distribution in which it provided a higher dose to the treatment area and a boost in dose to the tissue immediately adjacent to the air cavity.