Design of a stationary disc chipper project for dendromass chipping with stress analysis FEM methods

The design of a stationary disc wood chipping machine was considered, as well as the stress-strain analysis of a cutting knife with a flat and shaped cutting edge, which will produce a dimensional chip. The design consisted of the conceptual design of a cutting knife, a cutting mechanism, and an entire disc chipping machine, which includes cutting tools. The design solution is based on mathematical calculations of the individual parts of the cutting device. Calculations of the cutting mechanism and the cutting tool were performed using the finite element method. The results of the stress analysis found that the maximum stress acting on the edge of the knife during cutting corresponded to the permissible stresses of the knife material and subsequent use in practice. Based on the design and physical parameters of the wood cutting process, the design of the entire chipping machine was simulated and then was modeled using the PTC Creo parametric 5.0 program. Additional finite element analysis was performed using the Creo Simulate 5.0 software.

Smoldering and Flaming of Disc Wood Particles Under External Radiation: Autoignition and Size Effect

Wildfires are global issues that cause severe damages to the society and environment. Wood particles and firebrands are the most common fuels in wildfires, but the size effect on the flaming and smoldering ignitions as well as the subsequent burning behavior is still poorly understood. In this work, a well-controlled experiment was performed to investigate smoldering and flaming ignitions of stationary disc-shaped wood particles with different diameters (25–60 mm) and thicknesses (15–25 mm) under varying radiant heat flux. The ignition difficulty, in terms of the minimum heat flux, increases from smoldering ignition to piloted flaming ignition and then to flaming autoignition. As the sample thickness increases, the minimum heat flux, ignition temperature, and burning duration for flaming autoignition all increase, while the peak burning flux decreases, but they are insensitive to the sample diameter. During ignition and burning processes, the disc particle is deformed due to the interaction between chemical reactions and thermomechanical stresses, especially for smoldering. The characteristic thickness of the smoldering front on wood is also found to be 10–15 mm. This study sheds light on the size effect on the ignition of wood particles by wildfire radiation and helps understand the interaction between flaming and smoldering wildfires.

Mixing in a vortex breakdown flow

In this paper we present experimental and theoretical results on the mixing inside a cylinder with a rotating lid. The helical flow that is created by the rotation of the disc is well known to exhibit a vortex breakdown bubble over a finite range of Reynolds numbers. The mixing properties of the flow are analysed quantitatively by measuring the exponential decay of the variance as a function of time. This homogenization time is extremely sensitive to the asymmetries of the flow, which are introduced by tilting the rotating or the stationary disc and accurately measured using particle image velocimetry (PIV). In the absence of vortex breakdown, the homogenization time is strongly decreased (by a factor of 10) with only a moderate tilt angle of the rotating lid (of the order of $1{5}^{\circ } $). This phenomenon can be explained by the presence of small radial jets at the periphery which create a strong convective mixing. A simple model of exchange flow between the periphery and the bulk correctly predicts the scaling laws for the homogenization time. In the presence of vortex breakdown, the scalar is trapped inside the vortex breakdown bubble, and thus increases substantially the time needed for homogenization. Curiously, the tilt of the rotating lid has a weak effect on the mixing, but a small tilt of the stationary disc (of the order of ${2}^{\circ } $) strongly decreases (by a factor of 10) the homogenization time. Even more surprising is that the homogenization time diverges when the size of the bubble vanishes. All of these features are recovered by applying the Melnikov theory to calculate the volume of the lobes that exit the bubble. It is the first time that this technique has been applied to a three-dimensional stationary flow with a non-axisymmetric perturbation and compared with experimental results, although it has been applied often to two-dimensional flows with a periodic perturbation.

On the Flow Behavior in Rotor-Stator System with Superposed Flow

The flow between a rotor and a stator at high Reynolds number and small Ekman number is divided into three domains, two boundary layers adjacent to the discs separated by a central core. In the present work, a simple theoretical approach provides analytical solutions for the radial distribution of the core swirl ratio valid for a rotor-stator system with a superposed radial inflow rate. At first, the flow in the rotor boundary layer is assumed to behave as expressed by Owen and Rogers (1989) in the case of a turbulent flow on a rotating single disc. On the stator side, a necessary compensation flow rate must take place according to the conservation of mass. It is found that this compensation flow rate cannot be estimated with a good accuracy using the hypotheses of a stationary disc in a rotating fluid by Owen and Rogers (1989). Thus, two innovative weighting functions are tested, leading to new analytical laws relating the core swirl ratioKto the coefficient of flow rateCqrintroduced by Poncet et al. (2005). The adequacy between the theoretical solutions and numerous results of the literature is clearly improved and the discussion allows a better understanding of the flow behavior.

Optimal suppression of parametric vibration in discs under rotating frictional loads

This paper investigates the parametric resonances of a stationary disc excited by a rotating frictional load and influenced by a series of mass-spring-damper systems with or without friction. The genetic algorithm is used to find out the right number of mass-spring-damper systems and their optimal positions in order to reduce and even eliminate the dynamic instability caused by the rotating friction as a follower force on the disc surface. It is found that, if these mass-spring-damper systems involve no or low friction, they can reduce or suppress the dynamic instability of friction-induced parametric resonances when correctly located, but they have, at best, no effect when the level of friction is high.

STATIONARY DISCS OF FIBRATIONS OVER THE CIRCLE

Stationary discs of fibrations over the unit circle ∂D are considered. It is shown that if all fibers of a fibration Σ⊆∂D×Cn over the unit circle ∂D are strongly pseudoconvex hypersurfaces in Cn, then for every stationary disc f of the fibration Σ one can define the partial indices of f. In the case all fibers of Σ are strictly convex, it is proved that all partial indices of a stationary disc f are 0. It is also proved that in the case a stationary disc f of the fibration Σ is non-degenerate, the only possible partial indices of f are 0, 1 and –1. In particular, these results give information on the polynomial hull of Σ and new proofs of results related to the smoothness of the Kobayashi metric on some strongly pseudoconvex domains in Cn.