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PL
W artykule omówiono badania nad zastosowaniem zaawansowanych obliczeń numerycznej mechaniki płynów do wyznaczania trajektorii ruchu (w sześciu stopniach swobody) statku morskiego żeglującego na akwenie ograniczonym podczas manewru wymijania z innym statkiem. Uwzględniono jednocześnie zarówno oddziaływanie dna i brzegów kanału o zadanej geometrii jak również oddziaływanie wymijanego statku, co jest podejściem nowatorskim na skalę światową. Wyniki symulacji przeanalizowano pod wzglądem hydrodynamicznego zjawiska osiadania, powstającego podczas przejścia statku przez akwen ograniczony głębokością i brzegami kanału przy jednoczesnej interakcji z wymijanym statkiem. W obliczeniach wykorzystano geometrię typowego statku kontenerowego.
EN
Paper describes a research into ship’s squat phenomenon which is related to the safe entering of large ships into contemporary existing sea harbors. As the significant research effort in ship hydromechanics is devoted in recent years to the practical navigation problems, the Authors follow this trend and addressed the squat by means of CFD numerical simulations. The analysis of 6 DOF ship motion was performed, including the effects of shallow water, horizontal restrictions, extend of a channel and especially ship squat during passing by maneuver at a waterway. An exemplary case-study is carried out for a large container vessel. The obtained results were experimentally verified by comparison to one German experiment and own models tests. Such complex approach is a novelty worldwide.
PL
W pracy zostaną przedstawione wyniki pomiarów odkształceń rur rozpęczanych hydromechanicznie na stanowisku badawczym TH. Stanowisko TH zostanie przedstawione na tle podobnych urządzeń badawczych, co pozwoli podkreślić jego uniwersalność. Wyjaśniona zostanie przybliżona zasada pomiarów realizowanych na stanowisku oraz zostaną przedstawione przykładowe wyniki prób badawczych. Odkształcenia rur uzyskane podczas prób zostaną zestawione z parametrami procesu oraz charakterystycznymi fazami procesu kształtowania.
EN
The problem of two dimensional internal wave scattering by a vertical barrier in the form of a submerged plate, or a thin wall with a gap in an exponentially stratified fluid of uniform finite depth bounded by a rigid plane at the top, is considered in this paper. Assuming linear theory and the Boussinesq approximation, the problem is formulated in terms of the stream function. In the regions of the two sides of the vertical barrier, the scattered stream function is represented by appropriate eigen function expansions. By the use of appropriate conditions on the barrier and the gap, a dual series relation involving the unknown elements of the scattering matrix is produced. By defining a function with these unknown elements as its Fourier sine expansion series, it is found that this function satisfies a Carleman type integral equation on the barrier whose solution is immediate. The elements of the scattering matrix are then obtained analytically as well as numerically corresponding to any mode of the incident internal wave train for each barrier configuration. A comparison with earlier results available in the literature shows good agreement. To visualize the effect of the barrier on the fluid motion, the stream lines for an incident internal wave train at the lowest mode are plotted.
EN
The analysis of spatial functions of pressure considering the geometrical deviations and the elastic deformation of conjugate surace have been considered. The analysis of spatial functions of pressure is performed by the finite element method. The difference of the size of pressure in a tangential direction of a pocket of a support under various service conditions has been investigated. A recommendation for improving of operational characteristics in regulated hydrostatic radial bearing has been developed.
EN
The aim of this study was to improve properties of blood contacting materials such as polyurethane, in a form of intelligent, self-organizing and self-controlling coatings, which allow the selective mobilization and colonization of the endothelial cells on their surface. The prepared multilayer polyelectrolyte scaffolds were cross-linked chemically by EDC/NHS reagents in order to control their physicochemical properties and thus improving potential to endothelialization. Four types of coatings, i.e. non-cross-linked, cross-linked by 260 mM, 400 mM and 800 mM EDC reagent, were investigated. Their comparison was performed based on the results of the surface topography measurements using Atomic Force Microscopy (AFM), cellular morphology and proliferation analysis using Confocal Laser Scanning Microscopy (CLSM) and the mechanical properties examinations. The optimal multilayer rigidity and surface roughness parameters were found for an effective control of the endothelial cells growth. Surface topography analysis indicated an increase in the coating’s roughness due to application of higher EDC cross-linker concentrations. Mechanical studies revealed that cross-linking caused a significant increase in the hardness and elastic modulus. The results from the cellular experiments allowed the conformation that 400 mM cross-linked PLL/HA films possess desired properties.
PL
W artykule przeanalizowano możliwość efektywnego stosowania metody hydromechanicznego urabiania węgla z wykorzystaniem wyprzedzającego podcinania strumieniem wody w pokładzie urabianym strugiem. Istotą metody jest wstępne podcinanie ociosu na poziomie stropu i spągu, strumieniem wody pod dużym ciśnieniem, w celu zmniejszenia sił spójności i przylegania warstwy węgla do skał. W efekcie uzyskuje się znaczące zmniejszenie siły niezbędnej do urabiania górotworu i w rezultacie mniejszy wydatek energetyczny na jednostkę urobku. Podcinania dokonuje się cienkim strumieniem wody tłoczonej przez specjalnie uformowane dysze pod bardzo wysokim ciśnieniem tłocznym, powyżej 100 MPa. Przy oddziaływaniu tego strumienia wody na górotwór, jego energia przekształca się w pracę mechaniczną cięcia, a sam strumień staje się narzędziem tnącym. W rozpatrywanym procesie urabiania górotworu są stosowane dwa sposoby niszczenia materiału – jest to cięcie nożami struga z wykształceniem elementarnego wióra i uderzeniowe niszczenie strumieniem wody. Samo nacięcie strumieniem wody nie powoduje tworzenia się szczelin lub stref deformacji plastycznej w górotworze, a skała jest niszczona natychmiast na całym obszarze przyłożenia obciążenia, bez powodowania efektu krawędziowego. Dlatego też ciśnienie wody niezbędne do wykonania nacięcia jest wprost proporcjonalne do granicznej wytrzymałości materiału na jednoosiowe ściskanie. W artykule określono uogólnione zależności między regulowanymi parametrami podcinania i stratami energii zużytej na urabianie węgla zalegającego w skałach o wysokich charakterystykach wytrzymałościowych. Z przywołanych w artykule pozycji literatury wynika, że z technologicznego punktu widzenia najbardziej racjonalne głębokości nacinania strumieniem wody powinny mieścić się w granicach 30–40 mm.
XX
The article contains an assessment of the effectiveness of the application of hydromechanical destruction of coal deposits using the pre-emptive undercutting with waterjet in the deposite treated with plane. The aim of the work is to make a preliminary cutting of side wall at the roof and floor level, in order to reduce the cohesion and adhesion force between carbon layer and rocks. As a result of this cutting there is a significant reduction in force necessary to mine the rock mass and consequently less energy expenditure per mining unit. The undercutting is carried out by a thin water stream pressed by the specially formed nozzles under very high pressure discharged at above 100 MPa. When this water stream has the influence on the material, its energy is converted into cutting mechanical work, and the stream itself becomes the cutting tool. In the process of mining the rock mass, the two technologies of material destruction are present - cutting with plane blades with elementary chip as well as impact destruction by the water stream. The cut with water stream does not cause the formation of cracks or zones of plastic deformation in rock masses and the rock is destroyed immediately at the whole surface of application of the load, without causing the edge effect. Therefore, the water pressure necessary for the implementation of the incision is directly proportional to the border strength of the material to the uniaxial compressive strength. The article specifies the generalized relationship between adjustable undercutting parameters and levels of lost energy used for mining the coal occuring in the rocks of high strength characteristics. On the basis of the bibliography referred to in the article it can be stated that from the technological point of view the most rational depth of cutting with waterjet should be within the limits of 30-40 mm.
PL
Ośrodek Hydromechaniki Okrętu jest specjalistyczną placówką badawczo-rozwojową Centrum Techniki Okrętowej S.A. w Gdańsku. Ośrodek wykonuje prace badawcze i usługowe w zakresie hydromechaniki, związane z projektowaniem i eksploatacją statków, okrętów oraz innych konstrukcji pływających. Zakres wykonywanych prac obejmuje: prognozy, analizy numeryczne, projekty - kształtu kadłuba zoptymalizowanego pod kątem funkcji statku w oparciu o nowoczesne narzędzia projektowe, pędników śrubowych z uwzględnieniem kawitacji i wymuszeń. Spółka osiąga sukcesy nie tylko w branży okrętowej. CTO S.A. realizuje także szereg innych programów: jachtowy, inżynierii środowiska, urządzeń badawczych, energii odnawialnej i offshore, a nawet inżynierii medycznej.
EN
Ship Hydromechanics Division is a specialized research and development department of Ship Design and Research Centre conducting tests and research in the field of hydromechanics, connected with design and operation of ships and other floating structures, in scope of: predictions, numerical analyses, designs of - hull shape optimized with respect to the ship's functions with the application of modern design tools, screw propellers considering cavitation and excitations. Company achieves success not only in marine sector. CTO S.A. also implements several other programmers: sailing, environmental engineering, research facilities, renewable energy and offshore, and even medical engineering.
EN
We consider the steady, laminar natural convection heat transfer of a particulate suspension in an electrically-conducting fluid through a two-dimensional channel containing a non-Darcian porous material in the presence of a transverse magnetic field. The transport equations for both fluid and particle phases are formulated using a two-phase continuum model and a heat source term is included which simulates either absorption or generation. A set of transformations are implemented to reduce the partial differential equations for momentum and energy conservation (for both phases) from a two-dimensional coordinate system to a one-dimensional system. Finite element solutions are obtained for the transformed model. A comprehensive parametric study of the effects of the heat source parameter (E), Prandtl number (Pr), Grashof number (Gr), momentum inverse Stokes number (Skm), Darcy number (Da), Forchheimer number (Fs), particle loading parameter (PL), buoyancy parameter (B), Hartmann number (Ha), temperature inverse Stokes number (SkT), viscosity ratio [...], specific heat ratio [...], dimensionless particle-phase wall slip parameter [...] on the dimensionless fluid phase velocity (U), dimensionless particle phase velocity ( ), dimensionless fluid phase temperature [...] and the dimensionless temperature of particle phase [...] are presented graphically. In addition, we also describe numerical solutions for several special cases of the model, for example, the inviscid hydromagnetic two phase non-Darcian free convection, heat transfer [...], forced convection case (GrŽ0) etc. Fluid phase velocities are found to be strongly reduced by the magnetic field, Darcian drag and also Forchheimer drag; a lesser reduction is observed for the particle phase velocity field. The Prandtl number is shown to depress both the fluid temperature and particle phase temperature in the left hand side of the channel but to boost both temperatures at the right hand side of the channel [...]. The inverse momentum Stokes number is seen to reduce fluid phase velocities and increase particle phase velocities. The influence of other thermophysical parameters is discussed in detail and computations compared with previous studies. The model finds applications in MHD plasma accelerators, astrophysical flows, geophysics, geothermics and industrial materials processing.
PL
W artykule są analizowane nieustalone przepływy cieczy w przewodach pracujących pod ciśnieniem. Ocenie poddano zjawisko uderzenia hydraulicznego oraz wahań masy cieczy w przewodzie, na przykładzie oscylacyjnego przepływu wody w sztolni, w przewodzie elastycznym oraz w U-rurce. Przeanalizowano równania ruchu i ciągłości opisujące rozważane zjawiska. Zwrócono uwagę na wpływ oporów tarcia na rozważany przepływ. Stwierdzono, że w wielu sytuacjach, np. dla typowych warunków pracy sieci wodociągowych, równanie ruchu może być uproszczone i zapisane w postaci równania Bernoulliego. Przeprowadzono badania doświadczalne oscylacyjnego przepływu wody w przewodzie stalowym oraz polietylenowym. Przedmiotem dalszych rozważań jest analiza wpływu rozważanych warunków na opory liniowe. Porównane będą wartości współczynnika oporów liniowych dla ruchu ustalonego i quasi-ustalonego.
EN
Unsteady liquid flow in pressurized pipes is considered in a paper. The phenomenon of water hammer and oscillation of liquid mass in a power tunnel, an elastic tube as well as in U-tube are described. Differential equations of continuity and motion are analyzed. Influence of hydraulic losses on the flow is taken into account. It has been found out that for a lot of cases, like for a typical work of water pipe networks, the equation of motion may be simplified and written out in the form of Bernoulli equation. Experimental tests of oscillation liquid flow in steel and polyethylene pipes have been carried out. The flow was considered as quasi-steady flow. The coefficient of friction will be estimated at the conditions used in the experiments.
EN
An analysis has been carried out to obtain the nonlinear MHD flow with heat transfer characteristics of an incompressible, viscous and Boussinesq fluid on a vertical stretching surface with power-Iaw velocity. An approximate numerical solution for the flow problem has been obtained by solving the goveming equations using a numerical technique. A magnetic field is applied transversely to the direction of the flow. Adopting the similarity transformation, goveming nonlinear partial differential equations of the problem are transformed to nonlinear ordinary differential equations. Then the numerical solution of the problem is drawn using the Runge Kutta Gili method. NumericaI caIculations are carried out for different values of the dimensionless parameters in !he problem and an analysis of the results obtained show that the flow field is influenced appreciably by the presence of the magnetic field and thermal stratification effect.
EN
The present paper deals with the free convection laminar boundary layer flow and heat transfer of an incompressible, electrically conducting, viscous fluid through a porous medium caused by stretching a porous wall in the presence of a heat source and under the influence of uniform magnetic field. Exact solutions of the basic equations of momentu m and energy ar e obtained after reducing them i n to non-linear ordinary differential equations and using confluent hypergeometric functions. The variations in the velocity field and temperature distribution with the Prandtl number (Pr), hydromagnetic parameter (M), permeability param eter (K), suction parameter (N), wall temperature parameler (S), and the heat sink parameter (Q) are obtained and depicted graphically. The skin-friction at the wall is also derived, and the numerical values for various physical parameters are also tabulaled. Magnetic field (M) is seen to reduce both longitudinal and translational velocities and also lower temperalures, aiding in controlling momentum and heat transfer during materiaIs processing. Suction (N) posivitely influences the transverse velocity but depresses the longitudinal velocity magnitudes as we II as decreasing tempcratures. Suction therefore also assists in controlling heat transfer in Ihe boundary layer. Increasing permeability parameter (K) depresses the longitudinal velocity but elevates transverse velocities and increases the skin friction at the wall. Both rising temperature (non-isothermal wall) parameter (S) and heat sink parameter (Q) decrease temperature values. The model finds applications in nucIear engineering control systems and MHD energy systems.
14
Content available remote The effect of variable viscosity on MHD natural convection in micropolar fluids
EN
The influence of variable viscosity and a transverse magnetic field on natural convection in micropolar fluids is examined. The fluid viscosity is assumed to vary as an inverse linear function of temperature. Four different vertical flows have been analyzed, those adjacent to an isothermal surface and uniform heat flux surface, a plane plume and flow generated from a horizontal line energy source on a vertical adiabatic surface, or wall plume. By means of similarity solutions and deviation of the velocity, temperature and micro-rotation fields as well as the skin friction, heat transfer and wall couple stress results from their constant values are determined.
EN
A regular perturbation is presented to study the effect of heat and mass transfer on free convection flow with a uniform suction and injection over a cone in a micropolar fluid. The velocity, temperature, concentration and microrotation profiles were computed for various values of suction/injection, Schmidt number and micropolar parameters. The governing equations are first cast into a dimensionless form by a nonsimilar transformation and the resulting equations are then solved numerically by using the Runge-Kutta numerical integration, the procedure in conjunction with the shooting technique. The results indicate that as the micropolar parameter increases the wall couple stress, the shear stress, the Nusselt number and Sherwood number decrease with it. While the Shmidt number increases the shear stress, the wall couple stress and Nusselt number decrease, the opposite is true for the Sherwood number. The results are shown in figures and tables followed by a quantitative discussion.
EN
A boundary layer analysis is presented to study the effects of thermal dispersion of a non-Newtonian fluid on non-Darcy axisymmetric free convection over a horizontal surface embedded in a porous medium. The Ostwald-de-Waele power-law model is used to characterize the non-Newtonian fluid behavior. The thermal diffusivity coefficient has been assumed to be the sum of the molecular diffusivity and the dynamic diffusivity due to mechanical dispersion. Similarity solutions are obtained when the surface temperature varies as the square root of the radial distance (i.e., the prescribed temperature PT) or when heat flux is constant (i.e., the prescribed heat flux PHF). The effects of the dispersion and non-Darcy parameters as well as the power-law index n on the velocity, temperature, the Nusselt number and the boundary layer thickness are shown on graphs. The numerical values of the rate of heat transfer through the boundary layer in terms of the Nusselt number are entered in a table.
17
Content available remote Stokes flow past a porous approximate sphere
EN
In this paper, the flow of an incompressible viscous fluid past and within a porous approximate sphere directed along its axis of symmetry is considered. By assuming that Stokes equations for a creeping flow govern the flow outside the body and Darcy's law governs the tluid motion within the porous region of the body, an analytical soIution for the stream function is obtained. The drag experienced by the body is calculated and its variation with respect to the permeability parameter is studied numericaIly. Prom the present analysis, the flow past a porous sphere and spheroid are obtained as special cases.
EN
On the basis of Christensen’s stochastic model of rough surfaces, different forms of Reynolds equation with rotational inertia effect are obtained for various types of surface roughness pattern and for couple stress lubricant. As results one obtained the formulae expressing the mean film pressure distribution for externally pressurized bearings and for bearings with a squeeze film. Examples of spherical and step bearings are considered.
EN
The present paper is a synthesis of the work performed by the authors on the problems characterising the high Reynolds number lubrication namely the turbulent flow regime and the presence of inertia effects. The paper introduces the first approach of the turbulent regime based on the mixing length concept and shows how the Reynolds equation was modified. The problem of distributed inertia forces is then addressed by showing the adaptation of an approach borrowed from the boundary layer theory. The inertia dominated thin film model is reliable as long as the main hypotheses of lubrication theory are verified. A different approach should be used if concentrated inertia effects have an important influence as for hydrostatic and hybrid bearings and for labyrinth seals. This approach is based on a combination between the inertia dominated thin film model and the numerical solution of the complete Navier-Stokes equations. The thin film model predicts the characteristics of the seal or of the bearing and the numerical solution of the Navier-Stokes equations enables the estimation of concentrated inertia effects. On the authors experience this is a successful compromise between the accuracy and the computational effort. The paper briefly presents how this combined approach is used for stator-grooved labyrinth seals and for hybrid bearings.
20
Content available remote On some issues concerning the modeling of the motion of fluids
EN
We address some issues regarding the use of the Lagrangian description and convected frames in describing fluid motions. We also discuss the implications of Brownian motion on modeling the macroscopic motion of fluids and the schemes of filtered simulations. The relevance of these issues to the modeling of turbulence is discussed in detail.
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