Tallinn University of Technology

About: Tallinn University of Technology is a education organization based out in Tallinn, Estonia. It is known for research contribution in the topics: European union & Computer science. The organization has 3688 authors who have published 10313 publications receiving 145058 citations. The organization is also known as: Tallinn Technical University & Tallinna Tehnikaülikool.

Field survey of overheating problems in Estonian apartment buildings

Abstract: In Nordic countries overheating problems have not constituted a recognized problem to date. However, modern buildings, typically with larger windows, have changed this situation. New regulations based on Energy Performance of Buildings Directive (EPBD) directive require that overheating problems are controlled and recommend the use of passive cooling measures. EPBD sets that temperature simulations or other verifications are to be used at the design stage. If necessary, passive measures may be supported with active cooling systems to meet the requirements for summer thermal comfort. During this study field measurements were conducted in more than 100 Estonian apartments by recording indoor temperatures from a 3-month period; an overheating assessment and the impact of ventilation, orientation and window size on recorded overheating were studied. Our results show that overheating occurs in the modern buildings where the average room temperature was continuously about 1K higher than in the old buildings. Ac...

Against the flow: A Braitenberg controller for a fish robot

Abstract: Underwater vehicles do not localise or navigate with respect to the flow, an ability needed for many underwater tasks. In this paper we implement rheotaxis behaviour in a fish robot, a behaviour common to many aquatic species. We use two pressure sensors on the head of the robot to identify the pressure differences on the left and right side and control the heading of the fish robot by turning a servo-motor actuated tail. The controller is inspired by the Braitenberg vehicle 2b, a simple biological model of tropotaxis, that has been used in many robotic applications. The experiments, conducted in a flow pipe with a uniform flow, show that the robot is able to orient itself, and keep the orientation, to the incoming current. Our results demonstrate that guidance of a fish robot relative to a flow can be implemented as a simple rheotaxis behaviour using two sensors and a Braitenberg 2b controller.

Grain refinement in laser manufactured Al-based composites with TiB2 ceramic

Abstract: Al-based composites reinforced with TiB2 ceramics (1 wt.%, 2 wt.% and 5 wt.%) have been manufactured through selective laser melting (SLM). The results show that the densification, microstructure and mechanical properties of the SLM-processed composites are sensitive to the ceramic particle fraction. The average grain size of the composites decreased from ∼6.32 to ∼1.55 μm with increasing TiB2 fraction from 1 to 5 wt.% respectively. Fine equiaxed grains with narrow size distribution were obtained for composites with relatively high amount of TiB2 particles. The effects of TiB2 ceramic fraction on grain refinement and strengthening mechanisms of SLM-processed composites were discussed. Al-based composite with 2 wt.% TiB2 ceramic was determined to be optimum, especially in the view of manufacturing quality, grain refinement and mechanical properties. The composites at an optimum fraction of 2 wt.% TiB2 exhibited high microhardness of ∼127 HV0.2, tensile strength of ∼444 MPa, yield strength of ∼283 MPa and elongation of ∼4.2% owing to collective effects of dispersion and grain refinement strengthening as well as high degree of densification. This study can readily offer reference values for laser additive manufacturing of other metal matrix composites to obtain a good compromise of strength and ductility by tuning reinforcement fraction.