63,807 research outputs found
Stability of rigid and deformable roll coating flows
No full textThis thesis is concerned with developing suitable models for the investigation of instabilities in rigid and deformable roll coating flows. Consideration is restricted to Newtonian, incompressible fluids in the absence of inertia. In each coating flow analysed the steady two dimensional base state solutions of the system axe explored before the stability of the system is considered.
The particular rigid roll coating flow that is studied in this thesis is the flow formed between an intermediate pair of contra-rotating rolls within a multiple roll coater. The
base state is modelled using lubrication theory and the flow domain is terminated with simple boundary conditions. It is found that the form of the meniscus location
solutions differ from those found in similax flows by previous workers and this motivates a detailed re-examination of the boundaxy conditions. A matched asymptotic analysis applicable for small capillaxy numbers Ca and small inter-roll gaps gives the leading order correction to the boundary conditions and it is found that the inclusion of the correction terms alter the results significantly. It is found that a critical roll speed ratio,
Sc exists beyond which no steady two dimensional solutions exist. A simple stability hypothesis predicts the upstream meniscus to be neutrally stable at Sc and this point is
associated with bead break. Under certain operating conditions the stability hypothesis predicts multiple steady states.
The lineax stability of this multiple roll coating flow is investigated. Special attention is given to the relationship between the wavelength of the disturbance and
the form of the boundary conditions. The main predictions of the stability hypothesis axe confirmed and an additional ribbing instability on the downstream meniscus is predicted.
The base flow of a deformable roll coater is investigated using lubrication theory for the fluid and a linear elastic plain strain model for the compliant layer. The boundary
conditions developed for the multiple roll problem are extended to higher values of Ca. A finite element method is developed to numerically solve the governing equations.
The effects of Youngs modulus E and layer thickness L on the steady state operation of the coater are investigated. Previous workers have used spring models to describe
the compliant layer with the implicit assumption that E and L-1 have the same affect. Here it is shown that E and L-1 have a different effect upon the meniscus location in the negative gap regime and hence the underlying assumption of all spring models is shown to be incorrect. The plain strain model is extended to include viscoelastic terms
and it is shown that these terms can account for the discrepancy between experimental results and previous steady state elastic theories.
The lineax stability of the deformable roll coater is investigated with the plain strain model being extended to account for lateral disturbances. The effect of E and L-1 on
the stability of the system is investigated and it is found that in keeping with the steady state results, they have a different effect on the stability of the system in the
negative gap regime. It is demonstrated that perturbations to the compliant layer play a negligible role in the stability analysis and it is shown how the viscoelastic extension to the base state can be incorporated
Flow phenomena in fixed-gap and gravure roll coating systems
No full textThis thesis describes investigations into a number of coating processes using experimental, analytical and computational techniques.
The first problem, considered experimentally, is that of reverse roll coating with a liquid reservoir positioned directly above horizontally aligned rollers. Measurements
of the film thickness as a function of the height of fluid in the reservoir and speed ratio are presented. When the wetting line is located downstream of the nip, either
a decrease in the height of the associated hydrostatic head or an increase in the speed ratio causes a reduction in the thickness of the outgoing film. However, when the wetting line is located upstream of the nip the opposite is found to be true.
The bead-break instability in forward meniscus coating is considered both experimentally and analytically. Agreement between predictions from a simple mathematical model of the stable bead and experimentally determined meniscus positions
is seen to be excellent. A perturbation hypothesis is used to predict the onset of the bead-break instability, at which the upstream meniscus accelerates rapidly towards
the downstream one, so the two collide and the bead collapses. The results from the model compare well with experiments. An outline of a method for using the
bead-break instability as a design criterion is also presented.
Typically in a slot, blade or knife coater the downstream meniscus is assumed to pin at a corner of the coating device. In chapter 5, a series of experiments and a
corresponding computational study, are presented which illustrate that the meniscus can advance up the face of such coating devices (in this case a roll-flat plate system). Reducing the corner angle is seen to reduce the size of the climb region and the associated recirculation at this point at the downstream meniscus. It is also shown
that the meniscus can detach from the corner and retreat into the gap, which can in turn give rise to the ribbing instability.
An offset gravure coating arrangement is considered in chapter 6. The coating arrangement is split into two areas of study - the offset gravure nip and the kiss coating bead. An experimental investigation of the offset nip with the two rolls vertically aligned and running at the same speed in forward mode reveals two ways in which the metered film thickness can be influenced. Either increasing the nip force by pressing the two rolls together or decreasing the roll speeds causes a reduction in the metered film thickness. At higher speeds the metered film thickness is observed to asymptote to a limiting value, the value of which depends on the gravure pattern.
The reverse mode kiss coating bead operating at speed ratios greater than one is also investigated. Experiments reveal that under these conditions, all the fluid is
transferred from the roll surface to the web and the two make contact due to the generation of a sub-ambient pressure field within the bead. Two models based on lubrication theory are derived, one assuming an infinitely tensioned web and a second that incorporates the effect of web flexibility. The latter is found to give much better agreement with the experimental data. Finally a perturbation hypothesis is applied to these to models in order to predict the onset of the ribbing instability,
both of which are found to give reasonable agreement with the experimental data.
Finally, the results of a systematic experimental investigation of reverse mode direct gravure coating is reported, where the web runs directly over a gravure roll surface. This wide ranging parametric study illustrates the effect of the operating parameters on the final film thickness. Key findings are that speed ratio, fluid properties and cell shape and size can significantly influence the final film thickness. For a fixed roll
speed it is observed that as the web speed is increased the gravure bead becomes unstable. This results in streaking on the web, and gives an upper limit to the speed ratio
Work roll system optimisation using thermal analysis and genetic algroithm
No full textIn today‟s highly competitive business environment it is vital to have smart and robust decision making framework for companies to be competitive or even to stay in the business. Profit margin increases is no longer a result of producing and bring more products to the market. Instead it is also a result of reducing cost, in particular tooling cost. In order to succeed with this, industry need to look in to innovative intelligent systems to enhance their process development so that maximum utilisation of tools can be achieved. Tooling is part of a process hence having an optimal process design is one ideal strategy for best utilising of tools. In design optimisation however presence of uncertainty in design variables and in the mathematical model (used for representing the real life process) is inevitable. For reliable design solution to be found this process complexity need to be addressed. The aim of this research is to understand work roll system optimisation and thermal issues within rolling system design, understand uncertainties and sources of uncertainties and develop Genetic Algorithm (GA) based solution frameworks so that a conscious decision, that prolong tool life can be made.
The thesis has proposed a framework for generating approximate models from numeric finite element (FE) data. Using the proposed framework a number of quantitative work roll system thermal analysis and optimisation models were generated and used in subsequent optimisation process. In the absence of a suitable multi-pass model that exhibits the features of a multi-stage process; confident decision making will not be possible. Hence the research has developed a quantitative multi-pass model to simulate the work roll system thermal analysis and optimisation problem that represents the relationships as well as inherited features between passes.
The research has developed a Genetic Algorithm based optimisation framework that deals with the constraint quantitative problem as well as the uncertainty, in the design space and fitness function. The research also proposed a post GA result analysis methodology for identifying the final best optimal design solution for the research many objective high dimensional work roll system problems in presence of uncertainty
The performance of the proposed frameworks was studied and analysed through case studies. The research also identifies future research directions in the subject area
Stabilization of Parametric Roll Resonance with Active U-Tanks via Lyapunov Control Design
No full textParametric ship roll resonance is a phenomenon where a ship can rapidly develop high roll motion while sailing in longitudinal waves. This effect can be described mathematically by periodic changes of the parameters of the equations of motion, which lead to a bifurcation. In this paper, the control design of an active u-tank stabilizer is carried out using Lyapunov theory. A nonlinear backstepping controller is developed to provide global exponential stability of roll. An extension of commonly used u-tank models is presented to account for large roll angles, and the control design is tested via simulation on a high-fidelity model of a vessel under parametric roll resonance
Measurements of small radius ratio turbulent Taylor-Couette flow
No full textIn Taylor-Couette flow, the radius ratio () is one of the key parameters of the system. For small , the asymmetry of the inner and outer boundary layer becomes more important, affecting the general flow structure and boundary layer characteristics. Using high-resolution particle image velocimetry we measure flow profiles for a radius ratio of 0.5 and Taylor number of up to . By measuring at varying heights, roll structures are characterized for two different rotation ratios of the inner and outer cylinder. In addition, we investigate how the turbulent bursts coming from the inner and outer cylinder affect the flow profiles. These results exemplify how curvature affects flow in strongly turbulent Taylor-Couette Flow
Discomfort of seated persons exposed to low frequency lateral and roll motion
No full textPassengers of land transport are exposed to horizontal and rotational oscillations at frequencies less than 1 Hz which may cause vibration discomfort and motion sickness. Previous knowledge of human responses to motion is insufficient for predicting the discomfort caused by low frequencies. The objective of this thesis is to improve understanding of subjective responses to lateral and roll oscillation (presented in isolation and in combination) at frequencies less than 1 Hz in order to establish a predictive model of comfort.The first of five experiments tested the predictions of a conceptual model of motion sickness. Illness ratings were obtained over a 30-minute exposure to 0.2 Hz fully roll-compensated lateral oscillation where the point of full roll-compensation was either at the seat surface (i.e. ‘seat compensation’) or at head height (i.e. ‘head compensation’). Median illness ratings were greater during ‘head compensation’, showing some support for the motion sickness model, but differences were not statistically significant. Age, stature and body weight had no effect on illness ratings, but Asians were more than three-times as likely to experience ‘mild nausea’ than Europeans. It is concluded that differences in the position of full roll-compensation in transport vehicles are less important for motion sickness than inherent differences in passenger populations.The next four experiments used the method of magnitude estimation to determine the vibration discomfort caused by lateral oscillation, roll oscillation, and fully roll-compensated lateral oscillation with a variety of seating configurations. In the second experiment, lateral acceleration between 0.2 and 1.0 Hz caused less discomfort when sitting with a backrest than when sitting without a backrest on both a rigid seat and on a cushioned train seat; contrary to the predictions of current standards. In the third experiment, 0.25 to 0.4 Hz lateral acceleration in the plane of the seat caused similar discomfort regardless of whether the acceleration was due to lateral oscillation or roll oscillation through the gravitational vector, but above 0.4 Hz, discomfort from the roll was far greater. At frequencies less than 0.5 Hz, fully compensating the lateral acceleration with roll improved comfort compared to uncompensated lateral acceleration, but at greater frequencies, roll-compensation worsened comfort and caused discomfort similar to pure roll oscillation at 1 Hz.The fourth and fifth experiments examined differences in discomfort caused by the rigidity of the seat pan and the height of the backrest. In the fourth experiment, discomfort was greater on a soft foam seat than on a rigid seat during lateral oscillation below 0.63 Hz, during roll oscillation below 0.5 Hz and during fully roll-compensated lateral oscillation between 0.315 and 0.5 Hz. In the fifth experiment, discomfort was greater without a backrest than with a short backrest for lateral oscillation between 0.315 and 0.5 Hz. Contrary to current standards, discomfort was also greater without a backrest than with a high backrest for lateral oscillation below 1 Hz and for roll oscillation below 0.5 Hz. In addition, sitting with a backrest was beneficial for comfort with fully roll-compensated lateral oscillation between 0.4 and 0.63 Hz.The results of the five experiments were collated to provide recommendations for the improvement of current vibration standards. On the basis of experiment 1, a new multiplying factor for the prediction of vomiting incidence in an unadapted group of male Asian adults is offered. On the basis of the four discomfort experiments, modifications to current frequency weightings for lateral acceleration and roll acceleration are offered so as to extend the prediction to frequencies less than 0.5 Hz. Guidance for the prediction of discomfort with fully roll-compensated lateral oscillation is also provided. The thesis is concluded with recommendations for future research
Predicting Plastic Deformation and Work Hardening during V-Band Formation
No full textV-Band Clamps are manufactured using a cold roll forming process consisting of six passes which plastically deform an initially flat strip by bending to produce the band’s V-section. In this paper a new method of validating numerically predicted plastic deformation in a cold formed metal strip is presented. Tensile testing of samples of the band’s material was used to obtain a direct link between plastic strain and work hardness of this particular material. Using this correlation, the equivalent plastic strain (PEEQ) values predicted by finite element simulations were converted into hardness values. These values were compared to experimental work, in which samples of each pass of the roll forming process were taken to determine the work hardness in the cross section of the V-band using a micro-hardness machine. The error in strain predicted by the numerical method and hardness obtained by testing was found to be between 0.4% and 16.9%. This error was mainly due to uncertainty in material properties and the accuracy of the measurement technique. Compared to the more classical approach of measuring strain distribution with strain gauges, this method is more precise and accurate, as it is able to pick up even small changes in strain distribution
Optimization of the training process with skilled athletes acrobatic rock and roll in the annual preparation of macrocycles based on model characteristics
No full textPurpose : to develop and prove experimentally the content of the special physical and technical training athletes. Material : the study involved 36 athletes (18 pairs). Results : to determine anthropometric indices athletes to perform matchmaking sports couple. Had the most significant biomechanical parameters of the exercise equipment. Developed a biomechanical model of the target technology implementation competitive exercise. Assessment methodology presented special physical and technical training. The technique of selection of partners based on a pair of sports: anthropometric and growth indicators weighty partner and partner. Conclusions : it was determined that the determining factor in successful sports couple acrobatic rock-roll the same rate of development of physical effort in joint actions. Characterized by quickness growth efforts, which develops on the joint angle straightening bio kinematic chain
Primary auditory cortex’s vowel representation
No full textSound frequencies are represented in the primary auditory cortex (PAC) in a tonotopic structure which can be measured using functional magnetic resonance imaging (fMRI). A previous study has investigated vowels[ъ]and [i]and seen a correlation between the vowels¶ activation and the activation of simple tones corresponding to the vowels¶ formant frequencies. Other vowels have not \et been studied. In this study, we are investigating [ъ],[ѓ], [i], and [u]and compared those with activation of simple tones corresponding to their formant frequencies. This is ongoing work, and only five volunteers have participated. The preliminary results vary from high correlation between areas activated to low or no correlation. More data has to be collected to draw any further conclusions
Lehrpersonen im Austausch – Grenzüberschreitende Schulaustauschbegegnungen aus Lehrerperspektive. Eine Studie zur Lehrerperspektive im Rahmen des niederländisch-deutschen Schulaustauschprojektes
No full textContains fulltext :
239429.pdf (Publisher’s version ) (Open Access)Radboud University, 28 oktober 2021Promotores : Sars, P.L.M., Roll, H., Boonen, U. K. Co-promotor : Jentges, S.325 p
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