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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.

The impressive high thermal conductivity and low weight allow the carbon nanotubes (CNTs) to improve heat dissipation and cooling. In the present problem, we aim to analyze the CNTs embedded micropolar nanofluid flow between two parallel stretching sheets with the base fluid ethylene glycol (EG) which is effectively used as antifreeze and coolant. Both single‐walled carbon nanotubes and multiwalled carbon nanotubes (MWCNTs) are considered. The fluid is influenced by the external magnetic field parallel to the microrotation along with viscous and Joule dissipations. The flow and heat equations are converted to a set of coupled ordinary differential equations with the aid of similarity transformations. Due to the nonexistence of the closed‐form solution, we have developed the analytical approximate solution by homotopy analysis method using the polynomial base function. Furthermore, we have used the most efficient Runge–Kutta integration scheme of the fourth order associated with shooting technique to solve the system of equations. Results are exhibited graphically for various physical parameters and also found a good agreement with earlier work. From the results, we noticed that squeezing increases the angular velocity of the fluid particles. Also, in the case of squeezing, the volume fraction has enhanced the viscous drag and was found high for MWCNT–EG nanofluid. [ABSTRACT FROM AUTHOR]

Pressure and viscous drags acting on a bubble rising in a viscous fluid are numerically estimated to obtain the corresponding drag coefficients that are rarely reported in the existing papers. The numerical method has been successfully validated by solving the existing benchmark problems of a bubble rising in a quiescent liquid at various flow regimes. For spherical cap bubbles, the formula of total drag coefficient is proposed in a similar form to that by viscous potential flow theory expressed by the Reynolds number, and the corresponding formulas for pressure and viscous drag coefficients are derived. Furthermore, the effect of the density ratio of a bubble and the surrounding liquid on terminal velocity is also investigated for fixed Morton and Eotvos numbers: the lighter bubble has a higher terminal velocity having an asymptotic value as the density ratio increases although the Reynolds numbers based on the terminal velocity are nearly constant. [ABSTRACT FROM AUTHOR]

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]

Two-body point absorbers are useful for wave energy conversion in high energetic and high wave period sea locations. Analysis and simulation show that the two-body point absorbers have high efficiencies which makes them a potential candidate to promote wave energy harvesting technology towards commercialization and implementation. The submerged body of the two-body point absorbers has a large effect on their performance, hence the question arises: which geometric shape of the submerged body will lead to the best performance of the two-body wave energy harvesters? This paper presents a comprehensive study that analyses the different shapes of the submerged bodies based on the numerical wave tank simulated viscous drag coefficient and hydrodynamic property parameters of the oscillating device. A set of transient and three-dimensional computational fluid dynamic simulations of a numerical wave tank were carried out in Ansys Fluent to determine the viscous drag coefficients of the different submerged body shapes. And then the boundary element hydrodynamic simulation and linear dynamic frequency-domain modeling have been applied to identify the optimized PTO damping. Finally, non-linear time-domain modeling has been applied with the identified viscous damping drag coefficient and PTO damping coefficients to predict and compare the power output performance of different large-scale devices with different shapes of submerged bodies. It is found that each submerged body shape is suitable for a different range of wave frequencies, as one must establish a balance between the hydrodynamic properties and the viscous drag of the submerged body based on the sea location. It is also found that the typical viscous drag coefficient values used in the past studies underestimate the drag coefficient, and the linearized model widely adopted in frequency domain models is non-accurate for the devices with large viscous drag forces. [Display omitted] • Viscous drag coefficient simulated by numerical wave tank CFD. • PTO damping coefficient estimated by linearized frequency domain modelling. • Non-linearized time domain modelling for the power output of different submerged body shapes. • The best submerged body shape determined for a specific sea location. [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]

The performance assessment of industrial marine energy converters involves the integrated treatment of their hydrodynamic design and the optimization of their device hulls. Nowadays, such tasks require extensive experimental work and simulation plans, consuming considerable resources and time. In this comprehensive review of integrated approaches to numerical and experimental testing, the advantages and disadvantages of existing tools, from full-scale prototype and wave tank models to Computational Fluid Dynamics (CFD) and potential flow simulations, are all analysed. Likewise, current challenges such as experimental scale effects, numerical viscosity, and turbulence treatment are all studied. The novelty of this research is an integrated approach that employs experimental wave tank tests to validate a numerical wave tank model based on CFD that serves to calibrate a fast potential flow solver with Morison's correction terms. The model allows running, on tight resources, the necessary simulation for the design and optimisation of marine energy converters under multiple sea state conditions. Given the operating regimes of conventional marine energy converters, the results show that the influence of turbulence may be small, due to the unsteady nature of the oscillatory boundary layer flows. • Morison equation is used to correct potential flow results. • Morison equation terms are calibrated with numerical wave tank modelling. • Numerical wave tank model is calibrated with experimental data from decay tests. • The methodology aims to reduce the dependence on scale and tank effects. • Turbulence effects may be small in wave-induced flows. [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]

Understanding the influence of low temperature and high hydrostatic pressure in the starting performance of deep-sea pressure-compensated (PC) induction motors is essential for sizing of the motor and upstream power systems. This paper presents the observations from experiments carried out on industry-standard 3000-V rated deep-sea PC induction motors of 30- and 60-kW capacities in a hyperbaric chamber. It is identified that the motors consume about 30% of their rated power when started at a pressure of 600 bar and a temperature of 2°C. The results could be used for sizing of deep sea electric motors taking into consideration the increased starting power requirements due to the viscous drag of the PC fluid and to design PC oil viscosity management systems. [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 The grain size dependence of the strain rate sensitivity (SRS) of copper were systematically investigated via tensile deformation at strain rates of ~10−4 s−1 and ~103 s−1. In contrast to the general perception that SRS increases with decreasing grain size at low strain rates in FCC metals, the SRS increases monotonously with grain size under deformation at high strain-rates of ~103 s−1. Analytical formulation based on the Nemat-Nasser-Li (NNL) and Modified-Rusinek-Klepaczko (MRK) models was established to reveal the essential dependence of SRS on grain size, at the change of strain rate: that the opposite dependence of SRS on grain size at low vs high strain rates can be attributed to the transformation of the dominant rate-controlling deformation mechanism from thermal activation at low strain rates to viscous drag at high strain rates. It is demonstrated that the thermal activation component of SRS, m * , which is nearly strain rate independent, increases with reducing grain size; while the viscous drag component of SRS, m v s , which is enhanced significantly at high strain rates, decreases with reducing grain size. Microstructural observation based on local misorientation characterization and statistics confirms that the viscous-drag dominates at high strain-rate deformation, and becomes progressively influential as grain size increases. This unveils the essence of viscous drag in the opposite grain size dependence of SRS at low vs high strain rates. [ABSTRACT FROM AUTHOR]

A numerical model based on a boundary element method (BEM) is developed to predict the performance of two-body self-reacting floating-point absorber (SRFPA) wave energy systems that operate predominantly in heave. The key numerical issues in applying the BEM are systematically discussed. In particular, some improvements and simplifications in the numerical scheme are developed to evaluate the free surface Green’s function, which is a main element of difficulty in the BEM. For a locked SRFPA system, the present method is compared with the existing experiment and the Reynolds-averaged Navier-Stokes (RANS)-based method, where it is shown that the inviscid assumption leads to substantial over-prediction of the heave response. For the unlocked SRFPA model we study in this paper, the additional viscous damping primarily induced by flow separation and vortex shedding, is modelled as a quadratic drag force, which is proportional to the square of body velocity. The inclusion of viscous drag in present method significantly improves the prediction of the heave responses and the power absorption performance of the SRFPA system, obtaining results excellent agreement with experimental data and the RANS simulation results over a broad range of incident wave periods, except near resonance in larger wave height scenarios. It is found that the wave overtopping and the re-entering impact of out-of-water floating body are observed more frequently in larger waves, where these non-linear effects are the dominant damping sources and could significantly reduce the power output and the motion responses of the SRFPA system. [ABSTRACT FROM AUTHOR]

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.

Designing, optimizing and controlling a wave energy converter requires the construction of a mathematical model in order to simulate the behaviour of the device. Given the nonlinear nature of fluid-structure interactions, the definition of the model is not straightforward and should take into account the specific application it is intended for. Two of the most important characteristics of a model are the computational time and the expected accuracy, which usually are mutually conflicting. The inclusion of nonlinearities potentially increases the model accuracy, but at a higher computational price. Considering a heaving wave energy converter with and without the application of latching control, this paper studies and compares nine different modelling options, eight of which are based on potential theory and consider nonlinear Froude-Krylov and viscous drag forces, while one is based on fully-nonlinear computational fluid dynamics. The value of including nonlinearities in the hydrodynamic model is discussed in relation to the computational cost of the eventual accuracy benefits, under a range of scenarios. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of initial volume fraction on the runout characteristics of collapse of granular columns on slopes in fluid. 2-D sub-grain scale numerical simulations are performed to understand the flow dynamics of granular collapse in fluid. The discrete element method (DEM) technique is coupled with the lattice Boltzmann method (LBM), for fluid-grain interactions, to understand the evolution of submerged granular flows. The fluid phase is simulated using multiple-relaxation-time LBM (LBM-MRT) for numerical stability. In order to simulate interconnected pore space in 2-D, a reduction in the radius of the grains (hydrodynamic radius) is assumed during LBM computations. The collapse of granular column in fluid is compared with the dry cases to understand the effect of fluid on the runout behaviour. A parametric analysis is performed to assess the influence of the granular characteristics (initial packing) on the evolution of flow and run-out distances for slope angles of 0°, 2.5°, 5° and 7.5°. The granular flow dynamics is investigated by analysing the effect of hydroplaning, water entrainment and viscous drag on the granular mass. The mechanism of energy dissipation, shape of the flow front, water entrainment and evolution of packing density is used to explain the difference in the flow characteristics of loose and dense granular column collapse in fluid. [ABSTRACT FROM AUTHOR]