Transient Hydrodynamic Forces Research Articles

Dynamic Analysis of a Rotating Cardan Shaft under the Influence of a Breathing Crack and Dense Fluid Force

To extract any information from a complex data vibration, the time-frequency technique represents a suitable tool and a better indicator of the overall asset health of a rotating machine. Fluid influences on a cracked driveshaft and dynamic analysis of a rotating Cardan shaft are discussed in this paper. The study of the forced vibration signals of the rotating Cardan shaft focused uniquely on the impact of the hydrodynamic forces near the cracked driveshaft and its transmission of power to a driven shaft. By merging each subsystem consisting of the breathing crack mechanism in a rotating shaft, the perturbation function between misaligned shafts and transient hydrodynamic forces results in a strongly nonlinear system of partial differential equations, which becomes complicated when analyzing the dynamic response of the Cardan system. In view of the complexity of the Cardan system, the instantaneous frequency identification based on synchrosqueezing wavelet transform filters is numerically used to provide a reliable indication of the rotating system equipment’s health. A conclusive dynamic analysis through the wavelet synchrosqueezing demonstrated that the Cardan joint and the hydrodynamic resistance forces have a high impact on the system’s vibration characteristics and significantly influence the transmission motion with a continuous increase of the driven shaft vibration amplitudes.

Применение модернизированного метода маркеров для определения нестационарного силового воздействия при многофазном обтекании

Numerical simulation of transient hydrodynamic forces from shaped gas cavities formed in liquid under active interaction of liquid and a jet source of high-temperature gas and intensive heat and mass transfer is performed. To solve the task, a method of coarse particle markers with, as opposed to the classical one, an additional stage, when moving boundaries of different media in cells with interfaces of these media are as if stitched, is updated. In addition, problems of inter-media heat and mass transfer by condensation and evaporation are simultaneously solved. The predicted results are compared with the experimental data. Validation and verification are performed by comparing the analysis results with the experimental data. The applicability of the updated method of coarse particle markers to defining transient force impact under multiphase flowing is demonstrated.

Formation of stable aggregates by fluid-assembled solid bridges

When a colloidal suspension is dried, capillary pressure may overwhelm repulsive electrostatic forces, assembling aggregates that are out of thermal equilibrium. This poorly understood process confers cohesive strength to many geological and industrial materials. Here we observe evaporation-driven aggregation of natural and synthesized particulates, probe their stability under rewetting, and measure bonding strength using an atomic force microscope. Cohesion arises at a common length scale (∼5 μm), where interparticle attractive forces exceed particle weight. In polydisperse mixtures, smaller particles condense within shrinking capillary bridges to build stabilizing "solid bridges" among larger grains. This dynamic repeats across scales, forming remarkably strong, hierarchical clusters, whose cohesion derives from grain size rather than mineralogy. These results may help toward understanding the strength and erodibility of natural soils, and other polydisperse particulates that experience transient hydrodynamic forces.

Rotor dynamic analysis of a tidal turbine considering fluid–structure interaction under shear flow and waves

A rotor dynamic analysis is mandatory for stability and design optimization of submerged propellers and turbines. An accurate simulation requires a proper consideration of fluid-induced reaction forces. This paper presents a bi-directional coupling of a bond graph method solver and an unsteady vortex lattice method solver where the former is used to model the rotor dynamics of the power train and the latter is used to predict transient hydrodynamic forces. Due to solver coupling, determination of hydrodynamic coefficients is obsolete and added mass effects are considered automatically. Additionally, power grid and structural faults like grid fluctuations, eccentricity or failure could be investigated using the same model. In this research work a fast, time resolved dynamic simulation of the complete power train is conducted. As an example, the rotor dynamics of a tidal stream turbine is investigated under two inflow conditions: I - shear flow, II - shear flow + water waves.

An efficient methodology for simulating roll dynamics of a tank vehicle coupled with transient fluid slosh

An efficient methodology is proposed for simulation of roll dynamics of a tank vehicle system coupled with transient hydrodynamic forces due to fluid slosh. The transient fluid slosh in a horizontal cylindrical tank is analytically modeled considering simultaneous lateral, vertical and roll excitations assuming potential flows and a linearized free-surface boundary condition. For this purpose, the fluid domain in the Cartesian coordinate system is transformed to the bipolar coordinates, where the Laplace equation could be solved using separation of variables. The resulting hydrodynamic pressure, free-surface elevation and slosh force and roll moment are formulated in the tank-fixed coordinate system. The transient fluid slosh model is subsequently integrated to a dynamic roll plane model of a tank vehicle combination to investigate the effect of transient liquid slosh on the roll stability of the vehicle during steady-turning as well as path-change maneuvers. The analyses are performed for different fluid fill heights considering both variable and constant cargo load conditions. The results suggest that the roll stability of tank vehicles can be efficiently analyzed using the coupled linear slosh and multi-body vehicle models with significantly lower computational effort than the methods employing computational fluid dynamic fluid slosh models.

The Sensitivity of the Dinoflagellate Crypthecodinium cohnii to Transient Hydrodynamic Forces and Cell‐Bubble Interactions

The increased interest in the benefits of omega-3 fatty acids for human health has resulted in the commercial development of the dinoflagellate Crypthecodinium cohnii for production of docosahexaenoic acid (DHA). The growing market demand for DHA requires highly efficient, very large scale cultures of DHA. While the effects of hydrodynamic forces on dinoflagellates have been investigated for several decades, the majority of the work focused on the negative effects of oceanic turbulence on the population growth of environmentally important dinoflagellates. In contrast, significantly less is known on the effect of hydrodynamic forces encountered by algae in bioprocesses. Unlike other studies conducted on algae, this study employed a microfluidic, flow contraction device to evaluate the effect of transient hydrodynamic forces on C. cohnii cells. It was found that C. cohnii cells can sustain the energy dissipation rate of 5.8 x 10(7) W/m3 without lysis. However, an obvious sublethal effect, the loss of flagella, was observed at a lower level of 1.6 x 10(7) W/m3. Finally the cell-bubble interaction and the effect of bubble rupture were also explored to simulate the conditions of sparged bioreactors.

Hydrodynamic properties important for control of trawl doors

The paper presents a method for mathematical modelling of threedimensional foils applied totrawl doors. Experimental data are parametrized to give the steady-state hydrodynamic coefficients. Transient effects are investigated by the use of a numerical vortex lattice method. A method for approximating these effects is suggested, along with the appropriate coefficients. The proposed model accounts for steady-state and transient hydrodynamic forces and moments in 6 degrees of freedom. It will be used for the purpose of trawl control system design and analysis.

Unit force hydrograph method for transient hydrodynamics forces on dams subjected to arbitrary earthquakes

The calculations of transient hydrodynamic forces acting on dams subjected to arbitrary earthquakes are considered. A simple computational method based on the unit force hydrograph and the principle of linear superposition is proposed. The unit force hydrograph is calculated from analytic solution of a unit earthquake with a unit duration. Two test examples of earthquakes, one a linear earthquake with a finite duration and the other the EL Centro earthquake, are considered. The present results are compared with other analytic hydrodynamic solutions, and the comparisons show that the present computational method can predict very well the hydrodynamic forces acting on dams.

Coupled Pitch and Heave Porpoising Instability in Hydrodynamic Planing

Porpoising is a form of longitudinal instability characterized by an unstable coupling between heave and pitch degrees of freedom. In connection with flying boat stability, it was first analyzed by Perring and Glauert.2 In this paper, a simple theoretical description is first presented, based on quasistatic forces and moments, to show that stability is a function of center of gravity (c.g) location with respect to the center of pressure; and to a lesser extent, on the longitudinal radius of gyration. It is found that there are two stable zones; one where the c.g. is well forward of the center of pressure (analogous to a longitudinally stable aeroplane), and a second with the c.g. close to the trailing edge, which has no parallel in aircraft stability theory. Buoyancy terms are found to have a favorable effect for all c.g. positions, so that porpoising is essentially a high speed phenomenon, when most of the weight is supported by dynamic forces. Expressions are then developed for the transient hydrodynamic forces due to heave and pitch rates and accelerations, and the complete pitch and heave equations of motion are studied in some detail. It is concluded that there are several different ways of achieving stability, only one of which (moving the c.g. forward) is intuitively obvious. Other solutions include moving the c.g. right aft, the use of a very large radius of gyration in relation to the length of the planing surface, and the use of a high aspect ratio planing surface. All of these solutions can be identified in successful high-speed boats and hydroplanes. The calculations in the main body of the report assume that the fluid is inviscid. It can be shown (the calculations are omitted for brevity) that skin friction on the planing bottom results in additional terms in the stability equations, but that these are an order of magnitude less than the inviscid terms for a typical planing hull. But at very high speeds, coupled with a high c.g. position, the skin friction term in the pitching moment equation can become important, and may then have a dominant effect on stability. Generally, skin friction terms increase static stability and degrade dynamic stability. Despite the many porpoising tests made in the past with specific flying boat designs, there is very little experimental data available for simple planing surfaces alone; in fact, only the work of Day and Haag12 is known to the writer. A comparison between the theory and their experimental data gives reasonable agreement under the circumstances, but also points to the need for more experimental work.