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Unlike uniform motion, when an object moves underwater with variable speed, it experiences additional resistance from the water, commonly referred to as added mass force. At present, several methods exist to solve this force, including theoretical, experimental, and simulation approaches. This paper addresses the challenge of determining the added mass force for irregularly shaped small objects undergoing variable speed motion underwater, proposing a method to obtain the added mass force through numerical simulation. It employs regression analysis and parameter separation analysis to solve the added mass force, added mass, viscous drag coefficient, and pressure drag coefficient. The results indicate that an added mass force exists during both the acceleration and deceleration of the object, with little difference between them. Under the same velocity conditions, significant differences exist in pressure drag forces, while differences in viscous drag forces are not significant. This suggests that the primary source of added mass force is pressure drag, with viscous drag having little effect on it. During acceleration, the surrounding fluid accelerates with the object, increasing the pressure drag with a high-pressure area concentrating at the object's front, forming an added mass force that is directed backward. By contrast, during deceleration, the fluid at the object's front tends to detach, and the fluid at the rear rushes forward, leading to a smaller high-pressure area at the front and a larger one at the rear, reducing the pressure drag and forming an added mass force that is directed forward. By comparing the added mass of a standard ellipsoid obtained from numerical simulation with theoretical values, the regression analysis method is proven to be highly accurate and entirely applicable for solving the added mass of underwater vehicles. [ABSTRACT FROM AUTHOR]

This paper focuses on the dynamics of a submerged compound pendulum (SCP). The considered pendulum consists of a horizontal cylindrical element at its lowermost portion and a plate between the cylindrical element and the pivot. An approximate analytical expression for the natural frequency of the submerged compound pendulum is proposed. Further, a two-dimensional (2D) numerical model of the pendulum is developed using ANSYS (FLUENT). The natural periods of the SCP are determined for different geometric configurations. The analytically estimated natural periods of the pendulum match well with those obtained from numerical simulation. [ABSTRACT FROM AUTHOR]

The development of partial-pressure field (PPF) theory (Schmitz, S "Drag Decomposition Using Partial-Pressure Fields in the Compressible Navier-Stokes Equations," AIAA Journal, Vol. 57, No. 5, 2019, pp. 2030-2038) and the application of the concept to conditions relevant to commercial transport aircraft, operating in both the subsonic and transonic regimes (Hart, P. L., and Schmitz, S., "Drag Decomposition using Partial-Pressure Fields: ONERA M6 Wing," AIAA Journal, Vol. 60, No. 5, 2022 pp. 2941-2951), have shown promise as complements to classical far-field methods. In the present work, a further comprehensive analysis of drag decomposition methods is applied to wing and aircraft configurations. First, the Ventus-3 sailplane wing case demonstrates the ability of PPFs to successfully deconstruct drag on industry-relevant cases including transition modeling and winglets. A quantitative comparison to classical aerodynamic theory and far-field methods supports PPF theory and provides additional insight to viscous-inviscid interaction by means of a viscous interactional aerodynamics term in PPF theory. Second, the NASA Common Research Model is simulated in transonic flow to showcase drag decomposition of full aircraft configurations where PPF applications are used to provide further insight into wave drag sources acting on the aircraft in comparison to classical far-field decomposition methods. [ABSTRACT FROM AUTHOR]

Unlike uniform motion, when an object moves underwater with variable speed, it experiences additional resistance from the water, commonly referred to as added mass force. At present, several methods exist to solve this force, including theoretical, experimental, and simulation approaches. This paper addresses the challenge of determining the added mass force for irregularly shaped small objects undergoing variable speed motion underwater, proposing a method to obtain the added mass force through numerical simulation. It employs regression analysis and parameter separation analysis to solve the added mass force, added mass, viscous drag coefficient, and pressure drag coefficient. The results indicate that an added mass force exists during both the acceleration and deceleration of the object, with little difference between them. Under the same velocity conditions, significant differences exist in pressure drag forces, while differences in viscous drag forces are not significant. This suggests that the primary source of added mass force is pressure drag, with viscous drag having little effect on it. During acceleration, the surrounding fluid accelerates with the object, increasing the pressure drag with a high-pressure area concentrating at the object’s front, forming an added mass force that is directed backward. By contrast, during deceleration, the fluid at the object’s front tends to detach, and the fluid at the rear rushes forward, leading to a smaller high-pressure area at the front and a larger one at the rear, reducing the pressure drag and forming an added mass force that is directed forward. By comparing the added mass of a standard ellipsoid obtained from numerical simulation with theoretical values, the regression analysis method is proven to be highly accurate and entirely applicable for solving the added mass of underwater vehicles.

Abstract This paper investigates the accuracy of three aerodynamic models to compute loads on wind turbine rotors under turbulent inflow: Blade Element Momentum (BEM), Unsteady Vortex Lattice Method (UVLM), and Large Eddy Simulation with Actuator Line (LES‐AL). Turbulent inflow conditions are numerically generated with a new approach that combines control of turbulence and realistic velocity spectrum by using Mann boxes and LES simulations, respectively. Several deficiencies of the tested models are found and overcome through proposed improvements. First, the BEM assumption of independent radial sections does not hold in turbulent cases with long blades. Thus, a spatial filter to account for the interaction of radial sections in BEM is designed through the analysis of these interactions with UVLM. Second, the absence of viscous drag in UVLM is observed to lead to a very high rotor power coefficient, and it is shown that this can be mitigated by including drag in UVLM with a BEM‐like‐approach through look‐up tables. Third, the free wake model in UVLM, required to accurately capture rotor thrust, significantly increases computational cost. For this reason, a new wake discretisation scheme for the wake convection equation in UVLM is proposed, in which a coarse discretisation is employed far from the solid surfaces, which significantly reduces the computational time. Finally, these improvements and the performance of the three fidelities are analysed in a reference 10 MW wind turbine rotor demonstrating, in general, good agreement.

This paper investigates the accuracy of three aerodynamic models to compute loads on wind turbine rotors under turbulent inflow: Blade Element Momentum (BEM), Unsteady Vortex Lattice Method (UVLM), and Large Eddy Simulation with Actuator Line (LES‐AL). Turbulent inflow conditions are numerically generated with a new approach that combines control of turbulence and realistic velocity spectrum by using Mann boxes and LES simulations, respectively. Several deficiencies of the tested models are found and overcome through proposed improvements. First, the BEM assumption of independent radial sections does not hold in turbulent cases with long blades. Thus, a spatial filter to account for the interaction of radial sections in BEM is designed through the analysis of these interactions with UVLM. Second, the absence of viscous drag in UVLM is observed to lead to a very high rotor power coefficient, and it is shown that this can be mitigated by including drag in UVLM with a BEM‐like‐approach through look‐up tables. Third, the free wake model in UVLM, required to accurately capture rotor thrust, significantly increases computational cost. For this reason, a new wake discretisation scheme for the wake convection equation in UVLM is proposed, in which a coarse discretisation is employed far from the solid surfaces, which significantly reduces the computational time. Finally, these improvements and the performance of the three fidelities are analysed in a reference 10 MW wind turbine rotor demonstrating, in general, good agreement. [ABSTRACT FROM AUTHOR]

The present study aims to implement the software ANSYS AQWA to discuss the hydrodynamic analysis of the DeepCwind semi-submersible floating platform in waves based on the potential flow theory by considering the second-order wave exciting force. In this study, the linearized potential-flow hydrodynamic radiation and diffraction problems in the frequency domain were firstly solved by adopting the three-dimensional panel method. Subsequently, the hydrodynamic coefficients and wave loading data were transformed to time domain forms by the Cummins time domain equation as a system loading input. Furthermore, the quadratic transfer function (QTF) matrices with different frequencies and directions deduced based on the near field integration over the mean wetted hull surface were adopted for the calculation of slow-drift forces. In order to represent the damping in a real system for modeling potential flow without Morison's elements, an additional quadratic damping matrix was added to capture the viscous drag. Eventually, both of the dynamic mooring model based on the lump-mass (LM) approach and the quasi-static mooring model based on the multi-segmented, quasi-static (MSQS) approach are introduced to discuss the mooring effect on the platform hydrodynamics. The effect of wave heading angles on the platform motion is considered as an influential parameter as well. [ABSTRACT FROM AUTHOR]

It was shown recently that small particles and powders spontaneously disperse on liquid surfaces when they come in contact with the interface for the first time (Figure 2). This happens due to the combined effect of the capillary force, buoyant weight of the particle and the viscous drag that the particles experience when they encounter the liquid surface. The particles undergo oscillations normal to the interface before they come to the equilibrium position on the interface. These oscillations, in turn, induce a flow on the interface which disperses the particles radially outward. This phenomenon has a significant role in the pollination of sea plants such as "Ruppia" in which the formation of "pollen rafts" is the first step which results from the spontaneous dispersion of their pollens on the water surface. This work investigates, experimentally, the influence of temperature of the liquid on which this dispersion occurs. It was observed that the frequency of oscillations of the particles decreased with the increase in the temperature of the liquid. It is because the magnitude of capillary force that the particle experiences also decreased when the temperature of the liquid increased. [ABSTRACT FROM AUTHOR]

Disc pumps are used for difficult pumping applications, such as, pumping of high suspension solids and abrasives, viscous fluids, air entrained and shear sensitive fluids. The pumping mechanism, based on the boundary layer effect and the viscous drag minimizes the contact between the pump and the fluid reducing the wear level; but the pumping mechanism itself makes its efficiency low in comparison with other pumps for similar applications. This research aims to increase the performance of this pump developing a new experimental study based on the turbulization of flow by the placement of turbulizers in the interdisc channel output. The variables involved are the angular velocity (ω) and the cross section shape of the turbulizers. Eight impellers were constructed and evaluated using as cross section shape of turbulizers: the triangular, circular, and square. The experimental results show that the creation of circulatory currents, according to the Kutta-Johkovsky theorem, contributes to the increase the efficiency and the head of the disc pump and the square cross section shape of the turbulizers offers the best results. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Hypothesis Rotational Brownian diffusions of colloidal particles at a fluid interface play important roles in particle self-assembly and in surface microrheology. Recent experiments on translational Brownian motion of spherical particles at the air-water interface show a significant slowing down of the translational diffusion with respect to the hydrodynamic predictions (Boniello et al., 2015). For the rotational diffusions of partially wetted colloids, slowing down of the particle dynamics can be also expected. Experiments Here, the rotational dynamics of Janus colloids at the air-water interface have been experimentally investigated using optical microscopy. Bright field and fluorescent microscopies have been used to measure the in-plane and out-of-plane particle rotational diffusions exploiting the Janus geometry of the colloids we fabricated. Findings Our results show a severe slowing down of the rotational diffusion D r, ⊥ connected to the contact line motion and wetting-dewetting dynamics occurring on particle regions located at opposite liquid wedges. A slowing down of the particle rotational diffusion about an axis parallel to the interfacial normal D r, || was also observed. Contact line fluctuations due to partial wetting dynamics lead to a rotational line friction that we have modelled in order to describe our results. [ABSTRACT FROM AUTHOR]

The present study aims to implement the software ANSYS AQWA to discuss the hydrodynamic analysis of the DeepCwind semi-submersible floating platform in waves based on the potential flow theory by considering the second-order wave exciting force. In this study, the linearized potential-flow hydrodynamic radiation and diffraction problems in the frequency domain were firstly solved by adopting the three-dimensional panel method. Subsequently, the hydrodynamic coefficients and wave loading data were transformed to time domain forms by the Cummins time domain equation as a system loading input. Furthermore, the quadratic transfer function (QTF) matrices with different frequencies and directions deduced based on the near field integration over the mean wetted hull surface were adopted for the calculation of slow-drift forces. In order to represent the damping in a real system for modeling potential flow without Morison’s elements, an additional quadratic damping matrix was added to capture the viscous drag. Eventually, both of the dynamic mooring model based on the lump-mass (LM) approach and the quasi-static mooring model based on the multi-segmented, quasi-static (MSQS) approach are introduced to discuss the mooring effect on the platform hydrodynamics. The effect of wave heading angles on the platform motion is considered as an influential parameter as well.

Boundary layer akan terbentuk apabila aliran viscous melewati suatu kontur permukaan. Hal ini menyebabkan terjadinya gaya drag di kontur permukaan, oleh karena itu boundary layer yang terbentuk perlu dikontrol. Salah satu cara untuk mengkontrol boundary layer yang terbentuk adalah dengan memberi alur permukaan yang dilalui aliran. Pada penelitian ini, aliran yang dikaji adalah aliran boundary layer turbulen yang melintasi suatu pelat datar dengan alur melintang tipe-D. Alur tipe-D adalah tipe alur berbentuk persegi dengan kedalaman dan jarak antar alur yang sama, diletakan normal terhadap arah aliran. Penelitian ini dilakukan secara simulasi numerik. Terdapat 4 model yang disimulasikan yaitu pelat datar (smooth-wall), pelat beralur tipe-D ukuran 4mm, 10mm, dan 30mm . Bilangan Reynolds berdasarkan panjang pelat yaitu Rel = 2.16 x 106 dan kecepatan freestream pada inlet sebesar 10 m/s. Pemodelan numerik dilakukan menggunakan software Gambit 2.4.6 dan Fluent 6.3.26 dengan model 2ddp unsteady, viscous model standart k-epsilon. Berdasarkan hasil penelitian, penambahan alur tipe-D berbagai ukuran meningkatkan koefisien drag total dibanding pelat datar (smooth-wall). Pressure-gradient yang terbentuk didalam alur berkontribusi pada peningkatan ini walaupun nilai koefisien skin-friction mengalami penurunan. Tidak hanya koefisien drag total, tapi nilai intensitas turbulensi juga mengalami peningkatan dibanding pelat datar (smooth-wall). Didalam alur juga terbentuk vortex yang berkontribusi dalam penurunan koefisien skin-friction. Dari ketiga ukuran alur yang berbeda, ditemukan ukuran alur tipe-D ukuran 4mm memiliki nilai koefisien drag total yang lebih rendah daripada lainya.

Viscous drag, nonlinear in nature, is an important aspect of the fluid−structure interaction modelling and is usually not taken into account when the fluid is assumed to be inviscid. Potential flow solvers can competently compute radiation damping, which is related to the radiated wave field. However, the drag damping primarily related to the viscous effects is usually neglected in the radiation/diffraction problems solved by the boundary element method (BEM), also known as the boundary integral element method (BIEM). This drag force can have a significant impact in the case of structures extending much deeper below the free surface, or for those that are completely submerged. In this paper, the drag coefficient C d was quantified for the heave and surge response of a structure which consists of a moored horizontally oriented domed cylinder with two surface piercing square columns located at the top surface. The domed cylinder is the primary part and is submerged. The drag coefficient is estimated using the experimental measurements related to harmonic monochromatic wave−structure interaction. Finally, this estimated drag coefficient was used in the modified time domain model, which includes the nonlinear viscous correction term, and the resulting device response in heave and surge directions is presented for an irregular incoming wave field. The comparison of the numerical model and the experiments validates the estimated C d values obtained earlier. Prior to the time domain model, frequency-dependent parameters such as added mass, radiation damping, and excitation force were computed using three mainstream potential flow packages (that is, ANSYS AQWA, WAMIT, and NEMOH), and a comparison is presented. The effect of free surface on the drag coefficient is investigated through differences in C d values between heave and surge modes.

The dynamic response of floating horizontal axis wind turbines (FHWATs) are affected by the viscous and inertia effects. In free decay motion, viscous drag reduces the amplitude of pitch and roll fluctuation, the quasi-static mooring system overestimates the resonant amplitude values of pitch and roll. In this paper, the quasi-static mooring system is modified by introducing linear damping and quadratic damping. The dynamic response characteristics of the FHAWT modified model of the DTU 10 MW tension leg platform (TLP) were studied. Dynamic response of the blade was mainly caused by wind load, while the wave increased the blade short-term damage equivalent load. The tower base bending moment was affected by inclination of the tower and the misaligned angle βwave between wind and wave. Except the yaw motion, other degrees of freedom motions of the TLP were substantially affected by βwave. Ultimate tension of the mooring system was related to the displacement caused by pitch and roll motions, and standard deviation of the tension was significantly affected by the wave frequency response. Under the action of wave load, the viscous drag would stimulate the mooring system and increase the resonance of the platform motion.

This paper analyses the nonlinear forces on a moored point-absorbing wave energy converter (WEC) in resonance at prototype scale (1:1) and at model scale (1:16). Three simulation types were used: Reynolds Averaged Navier–Stokes (RANS), Euler and the linear radiation-diffraction method (linear). Results show that when the wave steepness is doubled, the response reduction is: (i) 3% due to the nonlinear mooring response and the Froude–Krylov force; (ii) 1–4% due to viscous forces; and (iii) 18–19% due to induced drag and non-linear added mass and radiation forces. The effect of the induced drag is shown to be largely scale-independent. It is caused by local pressure variations due to vortex generation below the body, which reduce the total pressure force on the hull. Euler simulations are shown to be scale-independent and the scale effects of the WEC are limited by the purely viscous contribution (1–4%) for the two waves studied. We recommend that experimental model scale test campaigns of WECs should be accompanied by RANS simulations, and the analysis complemented by scale-independent Euler simulations to quantify the scale-dependent part of the nonlinear effects.

Optical tweezers have become an important instrument in force measurements associated with various physical, biological, and biophysical phenomena. Quantitative use of optical tweezers relies on accurate calibration of the stiffness of the optical trap. Using the same optical tweezers platform operating at 1064 nm and beads with two different diameters, we present a comparative study of viscous drag force, equipartition theorem, Boltzmann statistics, and power spectral density (PSD) as methods in calibrating the stiffness of a single beam gradient force optical trap at trapping laser powers in the range of 0.05 to 1.38 W at the focal plane. The equipartition theorem and Boltzmann statistic methods demonstrate a linear stiffness with trapping laser powers up to 355 mW, when used in conjunction with video position sensing means. The PSD of a trapped particle's Brownian motion or measurements of the particle displacement against known viscous drag forces can be reliably used for stiffness calibration of an optical trap over a greater range of trapping laser powers. Viscous drag stiffness calibration method produces results relevant to applications where trapped particle undergoes large displacements, and at a given position sensing resolution, can be used for stiffness calibration at higher trapping laser powers than the PSD method. [ABSTRACT FROM AUTHOR]

Abstract: A surrogate model is presented to predict viscous drag in the context of conceptual design activities in aeronautics, where the norm is the use of low fidelity methods. The surrogate is developed with the requirement that its computational cost has to be comparable to that of its lower fidelity counterparts. The specific problem that has been chosen to test the method capabilities is the optimization of an unconventional aircraft empennage. The surrogate model is based on the high order singular value decomposition of a multidimensional tensor that contains a limited amount of information on viscous drag as a function of various design parameters defining the configuration of the empennage. This limited amount of information is generated using a medium level fidelity method, namely a panel method plus a boundary layer formulation, but the surrogate only uses the drag information and is independent of both the method used to generate this information and the specific problem that is considered for illustration. Thus, the proposed surrogate model is generic and can be seen as a means to bring information from higher fidelity models into the lower fidelity methods that are commonly used in the conceptual design phases of aeronautic design. [Copyright &y& Elsevier]

Abstract: Monte Carlo simulation of the rupture of multiple receptor–ligand bonds between two PMN cells suspended in a Newtonian fluid is performed. We demonstrate via micro-mechanical model of two cells adhered by multiple receptor–ligand bonds that viscous drag caused by relative motion of cell suspended in a Newtonian fluid modulates transmission of an applied external load to bonds. Specifically, it is demonstrated that at any time the intermolecular bond force is not equivalent to the instantaneous applied force. The difference in the instantaneous applied force and the intermolecular bond force depends on the viscosity of fluid, the size of cell, the applied loading rate, and the number of bonds at any instant of time. Viscous drag acting on cell reduces average bond rupture forces. [Copyright &y& Elsevier]

The deep sea oil-filled brushless DC (BLDC) motor operates in an underwater environment. The pressure varies with the working depth. The viscosity of the oil in the motor is sensitive to the pressure and hence the viscous drag loss varies with the pressure. The high pressure has influence on the loss characteristics of silicon steel and results in the increase of the core loss in the motor. Computational fluid dynamics (CFD) method is adopted to calculate the flow field in the air gap and the viscous drag loss at different pressures is obtained. Finite element method (FEM) is adopted to obtain the core loss at high pressure. The motor design considering the high pressure effect is compared with the motor design neglecting the pressure effect. The comparison results show that high pressure has large influence on viscous drag loss and core loss, resulting in the decrease in the efficiency and increase in the temperature rise. The experiment is done and the results verify the effectiveness of the calculated results. [ABSTRACT FROM PUBLISHER]

The aim of this work is to develop a simple nonlinear model of a wave energy converter (WEC) for capturing power from ocean waves and converting it into electrical power. A generic axisymmetric device is considered, which consists of a vertical circular cylinder surrounded by a circular annulus. The nonlinear system of equations of motion of this generic WEC are derived; these include the nonlinear term arising from viscous drag due to boundary layer separation. The expressions for radiation damping and added mass are determined by dimensional analysis. These equations are then solved numerically and the results are displayed graphically in a number of figures. Consideration of these graphs leads to conclusions that should be taken into account by the design engineer. [ABSTRACT FROM AUTHOR]

Abstract: In this paper a physical-based constitutive relation for defining the thermo-viscoplastic behaviour of FCC metals with dependence on strain on thermal activation processes is presented. The model, based on previous considerations reported by Rusinek and Klepaczko [Rusinek A, Klepaczko JR. Shear testing of sheet steel at wide range of strain rates and a constitutive relation with strain-rate and temperature dependence of the flow stress. Int J Plasticity 2001;17:87–115], is founded on physical aspects of the material behaviour. The proposed constitutive relation is applied to define the behaviour of oxygen-free high conductivity (OFHC) copper using the experimental data reported in Nemat-Nasser and Li [Nemat-Nasser S, Li Y. Flow stress of FCC polycrystals with application to OFHC copper. Acta Mater 1998;46:565–77]. The description of the material behaviour provided by the model gets satisfactory agreement with the experiments. The analytical predictions of this constitutive description are compared with those obtained from the models due to Voyiadjis and Almasri [Voyiadjis GZ, Almasri AH. A physically based constitutive model for fcc metals with applications to dynamic hardness. Mech Mater 2008;40:549–63], and Nemat-Nasser and Li. This comparison reveals that the original formulation proposed in this paper is a suitable alternative to other physically based relations for modeling OFHC copper. [Copyright &y& Elsevier]

Abstract: Spacers are designed to generate significant secondary flow structures and create directional changes in the flow through membrane modules. Shape of the spacers used in membrane modules strongly influences the resulting flow and therefore performance of the module. In this work fluid dynamics of rectangular channels similar to membrane modules and containing different spacers was simulated using a three-dimensional computational fluid dynamics (CFD) model. A ‘unit cell’ approach was evaluated and used for this purpose. In addition to predicting the pressure drop, the simulated results provided significant insight into fluid dynamics of spacer filled channels. The validated CFD model was used to evaluate performance of different spacer shapes and understand the role of spacer shape and resulting fluid dynamics. The models were extended for the first time to simulate flow in spacer filled curvilinear channels, which could be useful in understanding the fluid behavior in spiral modules. The results were compared with those obtained with the flat channel. The approach and results presented in this work will have significant implications for identifying improved spacers with higher propensities to reduce fouling in membrane modules. [Copyright &y& Elsevier]

Drag/thrust analysis of jet-propelled transonic transport aircraft on the basis of calculated viscous flow is discussed. Unique definitions for viscous drag plus wave drag and for induced drag are established. The concept of additive throughflow drag is introduced. Drag/thrust bookkeeping is given attention. All drag components can be calculated in the flow region adjacent to the aircraft, where numerical accuracy is expectedly highest. Uniform handling of complex aircraft configurations is brought within reach. Near-field/far-field drag balances are exact. Computational aspects are discussed, in particular the elimination of spurious drag sources. Numerical examples are given for a wing-body and for a wing-body-pylon-nacelle configuration. In either case, the spurious drag sources are eliminated. Acceptable agreement is obtained for the total drag in the first case, and for the installation drag in the second case. Extension of the analysis presented to propeller-driven transport aircraft is straightforward. [Copyright &y& Elsevier]

The present study involves the thermodynamic performance and entropy production analysis of an infrared suppression (IRS) system. The IRS device is usually used in ocean liners, warships, and cargo ships to reduce the turbine exhaust temperature. First, the governing differential equations (Navier-Stokes, energy, turbulence, radiation equations) are solved using ANSYS Fluent 19.0 to elucidate the thermodynamic performance of the IRS device. Then entropy production and irreversibilities are calculated in post-processing. The pertinent parameters, viz. Reynolds number at nozzle inlet (6.12 × 105 to 3.11 × 106), the nozzle outlet fluid temperature (400 to 600 K), nozzle overlap, funnel overlap, and the types of guide vanes are varied to analyze the impact of these parameters on entropy generation. The effect of different boundary conditions for funnel walls (i.e., adiabatic, diathermic with or without radiation) on entropy generation is discussed. A comparison of various types of guide vanes is also performed. It is found that entropy production (or irreversibility) is less when mass entrainment is more, i.e., device outlet temperature is less. Moreover, entropy production caused by heat transfer has the main contribution in total entropy production than that caused due to fluid friction. The entropy generation is found to be minimum for zero nozzle overlapping, zero funnel overlapping, diathermic funnel wall with radiation, and QCGV (quarter circular guide vane) type. The mass entertainment is maximum, and device outlet temperature is minimum with the mentioned conditions. [ABSTRACT FROM AUTHOR]

The forces generated by microtubules (MTs) and their associated motors orchestrate essential cellular processes ranging from vesicular trafficking to centrosome positioning 1 , 2. To date, most studies have focused on MT force exertion by motors anchored to a static surface, such as the cell cortex in vivo or glass surfaces in vitro 2–4. However, motors also transport large cargos and endomembrane networks, whose hydrodynamic interactions with the viscous cytoplasm should generate sizable forces in bulk. Such forces may contribute to MT aster centration, organization, and orientation 5–14 but have yet to be evidenced and studied in a minimal reconstituted system. By developing a bulk motility assay, based on stabilized MTs and dynein-coated beads freely floating in a viscous medium away from any surface, we demonstrate that the motion of a cargo exerts a pulling force on the MT and propels it in opposite direction. Quantification of resulting MT movements for different motors, motor velocities, over a range of cargo sizes and medium viscosities shows that the efficiency of this mechanism is primarily determined by cargo size and MT length. Forces exerted by cargos are additive, allowing us to recapitulate tug-of-war situations or bi-dimensional motions of minimal asters. These data also reveal unappreciated effects of the nature of viscous crowders and hydrodynamic interactions between cargos and MTs, likely relevant to understand this mode of force exertion in living cells. This study reinforces the notion that endomembrane transport can exert significant forces on MTs. • A bulk motility assay reconstitutes dynein pulling microtubules in the cytoplasm • A single motile cargo in a viscous solution generates near pN forces on a microtubule • Forces are additive, recapitulating a length-dependent model • Tug-of-war situations yield centration of minimal asters in bulk By developing a bulk motility assay, Palenzuela et al. demonstrate that the sole motion of dynein-driven cargos in a viscous solution can generate pulling forces that move microtubules in the direction opposite to the cargo's. These data provide key support for dynein pulling in bulk cytoplasm as an important mode of cytoskeleton force exertion. [ABSTRACT FROM AUTHOR]

Numerical investigation of fluid flow and heat transfer characteristics of a full-scale Infrared suppression (IRS) device for ocean liners is carried out in the present study. The main objective of the work is to reduce the temperature of the turbine exhaust by incorporating the IRS device, which can be effectively used in stealth technology for naval ships. In this study, the IRS device having multiple cylindrical funnels are used for conducting the computational experiment. The numerical solution of the Navier-Stokes equation along with the turbulence as well as the energy equation is solved using the algebraic multigrid solver of ANSYS Fluent 15.0. Many pertinent input parameters, like the inlet Reynolds number, fluid temperature, the number of funnels, and their sizes with overlapping or without it, have been varied in a practical range to study the mass suction into the IRS device. It is observed that the mass entrainment increases with an increase in the nozzle fluid temperature as well as its velocity. Visualization of temperature plume and flow field over the IRS device with multiple funnels has been picturized in this analysis. Furthermore, correlations for the prediction of mass entrainment rate as a function of pertinent input parameters have been developed, which can be used for academic and industrial purposes. • The present study captures a complete picture of flow and heat transfer characteristics over a full-scale IRS device. • The nozzle Reynolds number is varied between to , and the temperature is varied within 423 K to 723 K. • The parameters such as nozzle velocity, number of funnels, size of the funnel and overlapping has also been varied. • Visualization of temperature plume and flow field over the IRS device is reported pictorially. • A generalized correlation for mass entrainment is developed that can be used for academic and industrial applications. [ABSTRACT FROM AUTHOR]

Viscous drag, nonlinear in nature, is an important aspect of the fluid–structure interaction modelling and is usually not taken into account when the fluid is assumed to be inviscid. Potential flow solvers can competently compute radiation damping, which is related to the radiated wave field. However, the drag damping primarily related to the viscous effects is usually neglected in the radiation/diffraction problems solved by the boundary element method (BEM), also known as the boundary integral element method (BIEM). This drag force can have a significant impact in the case of structures extending much deeper below the free surface, or for those that are completely submerged. In this paper, the drag coefficient C d was quantified for the heave and surge response of a structure which consists of a moored horizontally oriented domed cylinder with two surface piercing square columns located at the top surface. The domed cylinder is the primary part and is submerged. The drag coefficient is estimated using the experimental measurements related to harmonic monochromatic wave–structure interaction. Finally, this estimated drag coefficient was used in the modified time domain model, which includes the nonlinear viscous correction term, and the resulting device response in heave and surge directions is presented for an irregular incoming wave field. The comparison of the numerical model and the experiments validates the estimated C d values obtained earlier. Prior to the time domain model, frequency-dependent parameters such as added mass, radiation damping, and excitation force were computed using three mainstream potential flow packages (that is, ANSYS AQWA, WAMIT, and NEMOH), and a comparison is presented. The effect of free surface on the drag coefficient is investigated through differences in C d values between heave and surge modes. [ABSTRACT FROM AUTHOR]