Showing papers by "Istanbul Technical University published in 1978"

Optimal control of multilevel large-scale systems†

Abstract: Optimum control of multilevel composite systems is considered. Regulators for linear multilevel composite systems with local quadratic cost functions are designed. Extensions to non-linear non-quadratic problems are developed. Connections with differential game solution strategies are established. A string-of-vehicles transportation system illustrates the procedures.

The influence of intercritical heat treatment on the temper embrittlement susceptibility of aP-Doped Ni-Cr steel

Abstract: Temper embrittlement of a Ni-Cr steel doped with 0.06 wt pct P aged at 480°C after an intercritical heat treatment (IHT) has been compared with that of the conventionally heat treated steel with a range of prior austenite grain sizes. The IHT virtually eliminated the embrittlement susceptibility, but low temperature brittle fracture was still intergranular. It appears that most of the benefit of IHT in this steel comes from microstructural refinement; however, IHT also reduced the amount of segregation of Ni and P to grain boundaries. This is believed to be connected with partitioning of Cr during IHT.

On the axially symmetric vibration of thick circular plates

Abstract: The method of initial functions is developed in cylindrical coordinates for axially symmetric elastodynamic deformation of the circular plate The governing equations are derived from the three dimensional elastodynamic equations Using a suitable transformation the difficulty in the application of the method of initial functions is removed The method is used to obtain the free vibration frequencies of thick circular plates Numerical results are given for the circular plate with clamped edges and compared with those of the known solutions

Past and present use of underground openings excavated in volcanic tuffs at cappodocia area

Abstract: Cappodocia area extends over 5000 km2. within the triangle of Kayseri-Aksaray-Nigde in central Anatolia. This area form a high plateau and is covered with horizontally layered acidic volcanic tuffs and lavas erupted by Erciyes and Hasandag volcanoes in several hundred meters thicknesses. Easy carving and thermal isolation properties of these soft tuffs have been the main reasons for the extensive multi-purpose underground settlement in this area, from past to the present. There are several underground cities in which thousands of people lived in Cappodocia area, in historical times. This self supporting structures in soft rock consisted of 8–10 floors with ceremony halls, storage areas, with an amazing ventilation system. The underground openings with different sizes and shapes excavated in this area, are being used today for housing, storage of foods and fruits, in a limited extend compared to the past use. Cappadoce couvre une etendu de plus de 5000 km2 dans le triangle Kayseri-Aksaray-Nigde en Anatolia centrale. Cette region forme un haut-plateau couvert, en couches horizontales de plusieurs centaines de metres d'epaisseur, par les laves et les tuffs volcaniques acides emis par les volcans Erciyes et Hasandag. La facilite de taille et l'excellente propriete d'isolation thermique de ces tuffs volcaniques tendres ont ete les causes principales de l'etablissement, dans cette region d'un centre de residence souterrain depuis les temps anciens jusqu'a nos jours. Il y a de multiples villes souterraines en Cappadoce oo vecurent des milliers de personnes dans les temps historiques. Ces villes consistaient de bloques de roche tendre de 8 a 10 etages comprenant des salles de ceremonie, des depots, des caves et ayant un systeme de ventilation etonnant. Ces ouvertures souterraines de dimensions et formes variees sont a present utilisees, d'une facon moins rependue qu'autrefois, comme demeure et comme depot de ravitaillement. Das Gebiet Cappodocia ist auf der Hochebene von Mittelanotolien im Kayseri-Nigde-Aksaray Dreieck auf einer Flache von mehr als 5.000 km2.verbreitet.Das Gelande ist mit den horizontal geschichteten surehaltigen vulkanischen Tuffen und Laven bedeckt. Diese aus Erciyes und Hasandag Vulkanen ausgespeite uberlagerung hat eine Machtigkeit von einigen Hunderten Metern. Die leichten Aushub-und die guten Warmeisolationeigenschaften dieses ziemlich weichten Tuffs haben in der Vergangenheit sowie heute die Menschen veranlasst, fur verschiedene Zwecke sich unterirdisch niederzulassen. Im Gebiet von Cappodocia gibt es aus der historischen Zeit mehrere unterirdische Stadte, wo Tausende von Leuten lebten. Dieser standfeste und leiche Fels enthalt 8–10 geschossige Bauwerke mit Zeremoniehallen, Lagerhallen, die mit einem wunderbaren Luftungssystem ausgestattet sind. Die in verschieden Abmessungen und Formen hergestellten Hohlraume werden heute als Wohnung und Largerhalle fur Fruchte und andere Nahrungsmittet, wenn auch zum Vergleich der Vergangenheit sehr beschrnkt, verwendet.

On a non-Newtonian fluid

Abstract: A non-Newtonian fluid for which the stress is supposed to be symmetrical tensor and a function of gradients of the velocity field of the first order, the second order and the third order is considered. The constitutive equation shows that an incompressible fluid of this type is characterized by two material constants. The equation of motion is a fourth order differential equation in terms of velocity and there is similarity between the present equation of motion and those of the dipolar fluid theory and the couple stress theory, although the stress is a symmetrical tensor in the present case and antisymmetric one in the dipolar fluid theory and the couple stress theory. As an illustrative example, the flow in a circular pipe is discussed. The usual no-slip boundary condition and an extra boundary condition, are used. An expression for the apparent viscosity, which may show a decreasing effect in tube diameter is obtained.