Acousto-elastic interaction in combustion chambers

This thesis deals with the interaction between combustion, acoustics and vibrations with emphasis on frequencies below 500 Hz. Extensive literature is available on the interaction between combustion and acoustics and much work is also available on the interaction between acoustics and vibration. The work presented in this thesis attempts to combine these fields in order to calculate the vibrations of the liner

A Transfer Function Approach to Structural Vibrations Induced by Thermoacoustic Sources

To decrease NOx emissions from a combustion system, lean premixed combustion in combination with an annular combustor is used. One of the disadvantages is an increase in sound pressure levels in the combustion system, resulting in an increased excitation of the surrounding structure, the liner. This causes fatigue, which limits the life time of the combustor. To model the interaction between flame, acoustics and structure, a transfer function approach is used. In this approach, the components are represented by the frequency dependent linear transfer between their inputs and outputs. For the flame a low pass filter with convective time delay is used as transfer function between velocity perturbations at the burner outlet and the flame as acoustic volume source. The acoustic transfer from volume source to velocity perturbation at the burner outlet is obtained from a harmonic finite element analysis, in which a temperature field from CFD calculations is used. The calculated response is subsequently curve-fitted using a pole-zero model to allow for fast calculations. The finite element model includes the two way coupling between structural vibrations and acoustics, which allows extraction of the vibration levels. The different transfers are finally coupled in one model. Results show frequencies of high acoustic response which are susceptible to thermoacoustic instability. Damping mechanisms and the phase relation between the different components determine stable or unstable behavior and the amplitude of the resulting perturbations. Furthermore there are also frequencies of high structural response. Especially when the two coincide, the risk of structural damage is high, whereas when they move away from each other, the risk decreases

From theology to mystagogy. The interiorisation of the Protestant tradition by a world citizen: Dag Hammarskjöld

This essay presents as paradigm the reflection of Dag Hammarskjöld on the history of his belief. It investigates how his initial expression of theological concepts gradually became a mystagogical process, interiorising the religious traditions in which he has grown up

Vibration of the liner in an industrial combustion system due to an acoustic field

The subject of this paper is a numerical study of the properties of the liner of a test rig to be built in the future. The test-rig consists of a flexible tube of square crosssection surrounded by a pressure vessel, also with a square cross-section. At first instance, a two dimensional structural analytical model of the cross-section is made. The influence of the air between liner and pressure vessel and that within the liner on the vibration of the liner is studied using a coupled 2D finite element model. Furthermore the influence of the vibration of the liner on the acoustics of the setup is studied. After this the problem is extended to three dimensions and again the influence of the cavity surrounding the liner is analyzed. Both 2D and 3D results are compared. The cavities are found to substantially influence the structural behavior and therefore they cannot be neglected in predicting the behavior of the liner

Thermoreversible gelation of cellulose acetate solutions studied by differential scanning calorimetry

Thermoreversible gels of cellulose acetate can be obtained by cooling concentrated cellulose acetate solutions in solvent-nonsolvent mixtures of dioxane and water. Upon heating the gels, endothermic effects were observed with differential scanning calorimetry. The heat effects are ascribed to the melting of a crystalline phase consisting of cellulose triacetate units. The endothermic peaks appear only after long aging periods of up to several days. Melting points generally decrease and heats of melting increase with increasing polymer concentration and with increasing nonsolvent content. The maximum degree of crystallinity is estimated as 8%. The kinetic effects of varying the water content in the solvent mixture are discussed

Access to Health

Access to health is an often-overlooked aspect of the right to health. Without practical access, the right to health becomes an empty promise. International human rights conventions and declarations do not directly mention access to health, but the above comment on the International Covenant on Economic, Social, and Cultural Rights does address the issue

The use of scripture in the "imitation of Christ" by Thomas A Kempis

This essay investigates the use of Scripture in The Imitation of Christ by Thomas a Kempis. It discusses some of the conditions during the time of its appearance, focussing on the Devotio Moderna as reform movement, the life of Thomas. It then discusses the Imitation and its use of Scripture in detail

Conrad’s allegorical reading of 1 Sam. 14: An analysis of a sermon by Conrad of Saint George on the worthy reception of the blessed sacrament

The sermon on 1 Samuel 14 is a paradigm for the allegorical mode of reading in the Middle Ages. This mode of reading first of all relates the Bible text to our life and in doing so places the relationship with God in a central position. The text is an expression of a divine address. Subsequently the whole of the text is read from the perspective of the mystagogic moment as the reader’s personal transformation process. In this way the historical context falls away and the development of the spiritual path becomes central. This shows that the allegorical mode of reading has its own logic and cannot be dismissed as human fantasy. This mode of reading is characterized by a great precision and a pure orientation on God’s action. Modern readers will have to discover anew the divine address in the text, again and again