Technology development allows the design and standardization of manual work in human activities which are yet to be observed, especially those of low-volume discrete production, such as in ear, nose ...and throat (ENT) surgery, particularly endoscopic sinus surgery (ESS). The paper considers the possibilities of developing an approach that would be useful for specific ESS manual work analysis and design and its automation in a future. The consideration includes, beside other aspects, initial steps, such as the traditional work motion capture by camera and experiments by Leap Motion Controller, Perception Neuron 2.0 and Emotiv Epoc+.
One of the main goals of the ship design process is the reduction of the total resistance, which is nowadays even more highlighted due to increasingly stringent rules related to ship energy ...efficiency. In this paper, the investigation of the impact of the bow on the total resistance of a yacht is carried out for three models by towing tank tests and numerical simulations. The verification and validation studies are performed, and satisfactory agreement is achieved. Also, a comparison of three turbulence models for the prediction of the total resistance of a yacht is made. The flow around the models of the yacht is analysed and it is demonstrated that bulbous bow causes the reduction of wave elevations. Experimental and numerical results indicate that the decrease in the total resistance due to bulbous bow can be up to 7%. Finally, the applicability of CFD within the ship design process is presented.
Recently, an increasing attention is given to preservation and popularization of Croatian traditional boat building, which plays an important role in Croatian cultural and national heritage. ...Reconstruction and revitalization projects of individual historical vessels are key factors within preservation process, where the lack of technical documentation is one of the main issues. In this paper, a simple and efficient procedure for taking offsets of a traditional fishing vessel guc is presented to document and preserve the traditional Croatian vessel form. A 3D model of a guc is generated using the points on the hull surface obtained by the manual measurement and a fairing process. Numerical simulations of the resistance test for a fishing vessel are carried out for a wide range of speeds, and the curve of effective power as a function of vessel speed is provided.
Suppose G is a graph with the vertex set V (G). A set D ⊆ V (G) is a total k-dominating set if every vertex v ∈ V (G) has at least k neighbours in D. The total k-domination number γkt(G) is the size ...of the smallest total k-dominating set. When k = 2 the total 2-dominating set is referred to as a double total dominating set. In this work we compute the exact values for double total domination number on H-phenylenic nanotubes HPH(m,n), m,n ≥ 2 and H-naphtalenic nanotubes HN(m,n), n = 2k, m,n ≥ 2. As all vertices have a degree 2 or 3, there is no total k-domination for k ≥ 3 for H-phenylenic and H-naphtalenic nanotubes, and the double total domination is the maximum possible.
The ship production process is a complex manufacturing system involving numerous working stations mutually interconnected by transport devices and buffers. Such a production system can be efficiently ...modeled using the stochastic system approach and Markov chains. Once formulated, the mathematical model enables analysis of the governing production system properties like the production rate, work-in-process, and probabilities of machine blockage and starvation that govern the production system bottleneck identification and its continuous improvement. Although the continuous improvement of the production system is a well-known issue, it is usually based on managerial intuition or more complex discrete event simulation yielding sub-optimal results. Therefore, a semi-analytical procedure for the improvability analysis using the Markov chain framework is presented in this paper in the case of the shipyard’s fabrication lines. Potential benefits for the shipyards are pointed out as the main gain of the improvability analysis.
UNMANNED SURFACE VEHICLE – TRITOR Ljulj, Andrija; Slapničar, Vedran; Brigić, Juraj
Brodogradnja,
2022, Letnik:
73, Številka:
3
Journal Article, Paper
Recenzirano
Odprti dostop
This paper presents an unmanned surface vehicle Tritor that was developed, constructed, and tested within an innovative, multi-purpose, multidisciplinary, low-budget and environmentally friendly ...solution. The idea behind this work was trying to invent a new concept of a miniature surface vehicle that will be unmanned, remotely controlled and autonomous, with electric propulsion, and with an innovative Three Slender Cylinders Hull (3SCH) form gaining advantages in comparison to existing surface vehicles. This initial work is focused on vehicle prototype design, propulsion system development and optimization, control design, and trials, while research related to advantages of the vehicle in terms of naval architecture criteria such as drag and power, stability, seakeeping, and maneuverability will be investigated in further work. In addition, the paper intends to contribute to a new trend in developing vehicles with electrical propulsion that could use renewable sources of energy such as wind and solar energy. The potential usage of the vehicle can be civilian or military, and further work will be focused on larger models, improved based on the experience got during the development of the vehicle. Tritor vehicle was successfully designed, constructed, and tested in real environmental conditions. The preliminary results show that the vehicle has required performances and potential for improvements in the future. The main scientific contribution of this work is advanced surface vehicle development with a focus on a new hull form and the integration of electric propulsion in it.
A novel approach for the solution of Stefan problem within the framework of the multi fluid model supplemented with Volume of Fluid (VOF) method, i.e. two-fluid VOF, is presented in this paper. The ...governing equation set is comprised of mass, momentum and energy conservation equations, written on a per phase basis and supplemented with closure models via the source terms. In our method, the heat and mass transfer is calculated from the heat transfer coefficient, which has a fictitious function and depends on the local cell size and the thermal conductivity, and the implementation is straightforward because of the usage of the local value instead of a global parameter. The interface sharpness is ensured by the application of the geometrical reconstruction scheme implemented in VOF. The model is verified for three types of computational meshes including triangular cells, and good agreement was obtained for the interface position and the temperature field. Although the developed method was validated only for Stefan problem, the application of the method to engineering problems is considered to be straightforward since it is implemented to a commercial CFD code only using a local value; especially in the field of naval hydrodynamics wherein the reduction of ship resistance using boiling flow can be computed efficiently since the method handles phase change processes using low resolution meshes.
Power reduction is the central goal to maximize cruising duration of tourist underwater vehicles (UV) that can be achieved by shaping the hull. So, in this paper, hydrodynamic force of resistance of ...the tourist UV’s bare hull is analysed. A numerical model based on Computational Fluid Dynamics in OpenFOAM is developed to simulate the longitudinal movement of an UV in a viscous and incompressible fluid for the infinite water depth. Three head geometries, including both spherical heads (S-S), spherical bow and elliptical stern head (S-E), and UV with both elliptical heads (E-E) are compared. At the first step, the effects of the length-to-diameter ratio and forward speed is studied for the S-S UV. The mesh size is calibrated using Grid Convergence Index, provided by ASME, while the model validation is based on the results for cube and sphere as well as by comparison with resistance coefficient of a SUBOFF bare hull. S-E and E-E UVs are then analysed for typical length-to-diameter ratio, comparing their force of resistance to the S-S type. The elongated elliptical heads are in many cases found favourable compared to the spherical heads. The results of this study may be useful for the conceptual design of tourist UV and for verification of the complex numerical models that are necessary to account for the influence of appendages on the force of resistance of such innovative UV.
Hilly terrain may considerably influence energy yield and structural loading of wind turbines. Wind energy developers are therefore required to accurately predict wind characteristics at the wind ...farm site already in the designing phase. It is necessary to determine how particular hill shape and size affect wind characteristics at the location of wind turbines operating in the wake of a hill. In order to address this complex issue, small-scale laboratory experiments were carried out in a boundary layer wind tunnel (BLWT). The focus was on characteristics of the flow at the same position downstream of the hill and the wind turbine models studied on various sizes and shapes of the hill model. Three hill models (a small and a large hill with laterally uniform heights and a hill with a bay) were exposed to the thermally neutrally stratified atmospheric boundary layer (ABL) simulation. In each experiment, there was only one hill model in the BLWT test section. The configuration without the hill, i.e. the flat terrain model, was tested as a reference case. Downstream of the hill model, there was a single (alone-standing) wind turbine model. Flow characteristics were studied downstream (behind) the wind turbine model. The wind turbine model was in the parking position in order to study wind characteristics in the situation with a strong wind when there is no rotation of rotor blades. The experimental results indicate a velocity decrease and stronger turbulence in the wind turbine wake in the presence of a hill, which trend is more pronounced in the case of larger hills. Strong velocity gradients are observed around the hub height in the large hill configuration, while this velocity deficit is the smallest in the hill with a bay configuration due to flow channeling. The velocity power spectra reveal the characteristic peak due to the vortex shedding from the hill ridge. The obtained results provide a new insight into the turbulent wake characteristics of a single wind turbine placed downstream of a hill with a potential to serve as a validation tool for computational studies.
The presented research shows the time dependent temperature distribution and thermal time constant within a typical industrial X-ray computed tomography (XCT) system used for dimensional metrology. ...Temperature effects can significantly affect measurement results of XCT scans either by directly changing the dimensions of the measurement object, or by indirectly changing the geometry of XCT scanner. In either case, the effect is not known well enough to be used for correction of measurement results or estimation of measurement uncertainty. In order to determine these effects, traceable temperature measurements were performed with a custom measurement system designed for this application. The influence of temperature fluctuations on length errors was determined by correlation of the measured temperature fluctuations with measurement deviations of a reference standard in repeated CT scans at different X-ray power levels. After experimental determination of X-ray focal spot displacement due to thermal expansion, a simple mathematical model of X-ray source displacement as a function of its temperature was developed and validated for a selected X-ray power level.
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