Field verification of ADCP surface gravity wave elevation spectra

Acoustic Doppler current profilers (ADCPs) can measure orbital velocities induced by surface gravity waves, yet the ADCP estimates of these velocities are subject to a relatively high noise level. The present paper introduces a linear filtration technique to significantly reduce the influence of noise and turbulence from energy spectra of combined orbital velocity measurements. Data were collected in 13-m-deep water with a 1.2-MHz ADCP sampling in mode 12, where a collocated wave buoy was used for verification. The surface elevation spectra derived from the filtrated and nonfiltrated measurements were compared with corresponding wave buoy spectra. In the frequency range between 0.12 and 0.5 Hz, ADCP- and wave-buoy-derived spectral estimates matched very well, even without applying the filtration technique. At frequencies below 0.12 Hz, the ADCP-derived surface elevation spectra are biased, caused by a depth-varying excess of spectral energy density in the measured orbital velocities, peaking at middepth. Internal waves may provide an explanation for the energy excess, as the experiment was conducted in the region of influence of the Rhine freshwater plume. Alternatively, infragravity waves may be the cause of the depth variation of low-frequency spectral energy density

Direct numerical simulation of a non-isothermal non-adiabatic packed bed reactor

A fundamental continuum-based numerical model was developed to simulate a non-isothermal non-adiabatic reactor which does not employ any empirical closures. The model was able to capture unique features of an exothermic catalytic reactor such as parametric sensitivity, hot-spot formations and multiplicity of steady states. Furthermore, the model inherently accounts for the various aspects of classical phenomenological models such as axial and radial dispersion of heat and mass and the intrinsic coupling of heat and mass transport between the fluid phase and the solid phase. The numerical procedure was validated with existing literature data before moving on to the simulation of a bed consisting of 340 spherical particles packed using the Discrete Element Method. Five simulations were performed by varying the rate of reaction and keeping all other parameters constant to capture the ignition/extinction phenomena exhibited by exothermic packed bed reactors

Solicitous and invalidating responses are associated with health care visits in fibromyalgia

Objectives: Health care use in fibromyalgia is substantial. Besides the severity of the disease and psychological factors, previous research suggests that the social environment can influence patients’ health care use. This study describes health care use in patients with fibromyalgia and investigates the relation of social responses of the partner and family with health care use. Methods: Cross-sectional data of 280 patients with fibromyalgia were analysed. Socio-demographic variables, health status variables, health care use, partner’s solicitous and punishing responses, and invalidation (i.e., discounting and lack of understanding) by family were assessed. Heath care use was defined as number of visits to physicians and health professionals. Associations of independent variables with health care use were examined using univariate and hierarchical regression analyses. Results: In the preceding 6 months, 99% of the patients visited at least one physician and 66% visited at least one health professional. Mean (SD) total health care visits and the number of different disciplines consulted were 18.5 (17.7) and 3.6 (1.7), respectively. Being female, paid employment, having a co-morbid condition, a higher severity of fibromyalgia, more partner’s solicitous responses, and more invalidating responses by family were univariately associated with visits to a physician. Having a comorbid condition, severity of fibromyalgia, and invalidation by family were uniquely associated with visits to a physician. No other associations were found. Conclusions: Therapeutic attention to patients’ close social environment might be a useful approach to improve health-related outcomes, including health care use in patients with fibromyalgia

Solicitous and invalidating responses are associated with health-care visits in fibromyalgia

Contains fulltext : 208568.pdf (publisher's version ) (Open Access)Objectives: Health-care use in FM is substantial. Besides the severity of the disease and psychological factors, previous research suggests that the social environment can influence patients' health-care use. In this study, we describe health-care use in patients with FM and investigate the relationship of social responses of the partner and family with health-care use. Methods: Cross-sectional data of 280 patients with FM were analysed. Sociodemographic variables, health-status variables, health-care use, partner's solicitous and punishing responses, and invalidation (i.e. discounting and lack of understanding) by family were assessed. Heath-care use was defined as the number of visits to physicians and health professionals. Associations of independent variables with health-care use were examined using univariate and hierarchical regression analyses. Results: In the preceding 6 months, 99% of the patients visited at least one physician and 66% visited at least one health professional. The mean (s.d.) total health-care visits and the number of different disciplines consulted were 18.5 (17.7) and 3.6 (1.7), respectively. Being female, paid employment, having a co-morbid condition, a higher severity of FM, more partner's solicitous responses and more invalidating responses by family were univariately associated with visits to a physician. Having a co-morbid condition, severity of FM and invalidation by family were uniquely associated with visits to a physician. No other associations were found. Conclusion: Therapeutic attention to patients' close social environment might be a useful approach to improve health-related outcomes, including health-care use, in patients with FM

Solicitous and invalidating responses are associated with health care visits in fibromyalgia

Objectives: Health care use in fibromyalgia is substantial. Besides the severity of the disease and psychological factors, previous research suggests that the social environment can influence patients’ health care use. This study describes health care use in patients with fibromyalgia and investigates the relation of social responses of the partner and family with health care use. Methods: Cross-sectional data of 280 patients with fibromyalgia were analysed. Socio-demographic variables, health status variables, health care use, partner’s solicitous and punishing responses, and invalidation (i.e., discounting and lack of understanding) by family were assessed. Heath care use was defined as number of visits to physicians and health professionals. Associations of independent variables with health care use were examined using univariate and hierarchical regression analyses. Results: In the preceding 6 months, 99% of the patients visited at least one physician and 66% visited at least one health professional. Mean (SD) total health care visits and the number of different disciplines consulted were 18.5 (17.7) and 3.6 (1.7), respectively. Being female, paid employment, having a co-morbid condition, a higher severity of fibromyalgia, more partner’s solicitous responses, and more invalidating responses by family were univariately associated with visits to a physician. Having a comorbid condition, severity of fibromyalgia, and invalidation by family were uniquely associated with visits to a physician. No other associations were found. Conclusions: Therapeutic attention to patients’ close social environment might be a useful approach to improve health-related outcomes, including health care use in patients with fibromyalgia

Immersed boundary method

In this paper, we report the extension of an earlier developed Direct Numerical Simulation (DNS) model to study coupled heat and mass transfer problems in particulate flows. The DNS model builds on an efficient ghost-cell based Immersed Boundary Method (IBM) which implicitly incorporates the boundary conditions into the discretized momentum, thermal and species conservation equations of the fluid phase. On the particles an exothermic surface reaction takes place. The heat and mass transport is coupled through the particle temperature, which offers a dynamic boundary condition for the fluid phase thermal energy equation. The present simulations are performed for four fluid-solid systems. Following the case of the unsteady mass and heat diffusion in a large pool of quiescent fluid, we consider a stationary sphere under forced convection. In both cases variable reaction rates are imposed at the particle surface, and the particle temperatures obtained from DNS show a good agreement with analytical/empirical solutions. After that, we apply our DNS model to the three-bead reactor and finally, a dense particle array consisting of hundreds of particles distributed in a random fashion is studied. The concentration and temperature profiles are compared with a ID heterogeneous reactor model and the heterogeneity inside the array is discussed.

A multiple resolution approach using adaptive grids for fully resolved boundary layers on deformable gas-liquid interfaces at high Schmidt numbers

Gas–liquid systems involving dispersed bubbly flows are often encountered in industry due to their favourable heat and mass transport characteristics. A key element of such systems involving interfacial mass transfer are the thin mass boundary layers prevailing at the phase boundaries. Resolving these thin boundary layers in numerical simulations is very challenging because of the need for very fine grids. Such grids often over-resolve the hydrodynamics which accounts for most of the CPU time. In this paper, we propose a multiple resolution approach that resolves the momentum boundary layers on a coarse (fixed) Cartesian grid and the mass boundary layers on a finer (adaptive) grid. The methodology proposed in Panda et al. (2019) for static rigid particles is extended to deformable moving interfaces and applied to single rising bubbles where the computed Sherwood number is compared with empirical correlations and numerical simulations available in literature

Lift-off of multiple particles in a narrow channel

In this work, we perform simulations of particle laden flow in a wide and long narrow channel in a Newtonian fluid. Simulations are performed for mono-sized and equal density spheres with varying Archimedes and Reynolds number. In the simulations, different phases of particle transport - rolling, saltation and suspension are observed. During simulations the average bed height is monitored and its steady state value is used for proposing a correlation between solids volume fraction (ϕ), shear Reynolds number (Res) and Archimedes number (Ar). This correlation is used to predict the critical shear Reynolds number for particle lift-off and a condition at which particles would occupy the whole channel at a given Archimedes number. The value of this critical Reynolds number is compared with the critical Reynolds number for single particle lift-off.Complex Fluid Processin

A new drag correlation for monodisperse suspensions using immersed boundary method simulations

Quantitative description of gas-solid momentum transfer is of fundamental importance to predict the behavior of suspensions of sedimenting or fluidized particles. It is usually characterized by the dependence of normalized average drag force Fd on mean Reynolds number (Re) and solids volume fraction (φ). In this work we report detailed direct numerical simulation (DNS) results of interphase momentum transfer in flows past fixed assemblies of monodisperse spheres using an iterative immersed boundary method (IBM). A methodology has been applied for all the IBM simulations, which was validated to obtain highly accurate results of drag force and flow velocity field at relatively low computational cost. Simulations were performed for Re ranging from 50 to 1000 and φ varying from 0.1 to 0.6. A new drag correlation is finally obtained with an average standard deviation of only 4.0% from the underlying IBM simulation data. In comparison to some correlations reported in literature, this new correlation gives more reliable predictions of the drag force for high Re and dense packings. It is considered to be so far the best possible expression of the drag law for gas-solid flows. In addition, this new drag correlation can be used in large-scale models, in which the interphase momentum exchange is not directly resolved, thus finally enhancing the predictive capability of computational fluid dynamics (CFD) simulations for gas-solid flows

Bubble formation from an orifice in liquid cross-flow

The formation of gas bubbles by submerged orifices in a cross-flowing liquid is encountered in many industrial applications. It is therefore important to understand the dynamics of bubble formation and to accurately predict the bubble detachment characteristics under such situations. In the present work, the process is numerically studied using the Local Front Reconstruction Method (LFRM), a Front Tracking Direct Numerical Simulation method that enables the simulation of interface merging and breakup. Experiments of bubble formation subjected to cross-flow induced shear are also performed to provide data for the validation of the numerical simulations. The predictions of the bubble shape and the detached bubble volume obtained by the numerical model show good agreement with the experimental results. The validated numerical model is then used to study the effects of volumetric gas flow rate and fluid physical properties on the bubble detachment characteristics under various shear rates in the quasi-static bubble growth regime. The simulation results show that the shear flow advances the bubble detachment and decreases the bubble size. Consequently, the bubble formation frequency and the detached bubble size can be controlled by exerting different shear rates. At higher shear rates, the simulated bubbles are highly deformed due to the drag force created by the tangential liquid flow and the influence of liquid properties on the bubble detachment characteristics becomes less significant