1,721,054 research outputs found
Modellprädiktive Regelung eines semi-aktiven Flüssigkeitsdämpfers zur Reduktion von Schwingungen turmartiger Bauwerke
No full textThe steady increase in urbanization, the subsequent growing scarcity of construction space,and the intensified focus on sustainable and economical design in building construction, is driving the need for lightweight, slender structures. Such structures generally have a low inherent damping and are therefore very responsive to structural vibrations. In order to reduce the influence of wind or earthquakes on the stability and service life of the structure, it is neccesary to integrate suitable vibration control stategies. For slender structures, the use of vibration control devices has proven effective in practice. The semi-active tuned liquid column damper (S-TLCD) poses one particular design of such devices, whose excitation-dependent tuning through closed loop control approaches presents the main contribution of this work. Within the scope of this dissertation, a general model-based control concept for structural vibration control using the S-TLCD is developed. For this purpose, the potential of acontrolled S-TLCD compared over a passive tuned liquid column damper (TLCD) is shown within simulative investigations. Moreover, the automation of two test benches is presented, which were developed within the scope of the research activities and serve to validate the control concept. The simulative study is futher used to answer the research question regarding a suitable modeling of the S-TLCD in context of the derived control concept. For this, two models of different complexity are presented and discussed with regards to the model-based controlconcept. Based on these findings, the control concept is experimentally validated on a laboratory test bench. The results show a significant improvement in the effective restoring force of the S-OTLCD over a wide frequency range, whereas the passive tuned liquid column damper can only be tuned for a single excitation frequency. Furthermore, the experiments demonstrate the practical applicability of the developed control concept. In addition to the development and validation of the model-based control concept, the damping characteristics of the S-OTLCD are investigated in the context of a 28 m high steel tower. For this purpose, an experimental platform was installed on the steel tower,which in addition to the attachment of the liquid damper also allows to apply user-defined excitation on the steel tower. Hereby, three approaches for estimation of the dominant vibration frequency of the steel tower are investigated, which is an essential prerequisite for the proposed control concept
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Wirkung von semi-aktiven Schwingungsdämpfern bei böenerregten Zufallsschwingungen von Hochbauten
No full text
Flüssigkeitsdämpfer zur Reduktion periodischer und stochastischer Schwingungen turmartiger Bauwerke
No full textThe tuned liquid column damper (TLCD), patented by Frahm already in 1910, consists of a U-shaped tube system filled with a Newtonian liquid. The tuned parameters of the liquid damper enable the liquid mass to oscillate with a 90° phase shift with respect to the motion of the structure, leading to interaction forces on the primary structure such as viscous damping loads. The oscillation energy of the liquid dissipates in the tube system because of turbulence effects and local pressure loss caused by friction. The mathematical expression of the liquid motion is carried out using the instationary Bernoulli equation. The natural frequency of the liquid damper depends on the geometry of the tube system. The dissipation forces of the absorber result from the impulse, which is caused by the liquid column motion. In order to determine the parameters of the liquid damper the tuning criteria of Den Hartog, Warburton and Lyapunov, which are valid for mechanical dampers, can be applied through the already known analogy approaches. The results of these criteria are the optimal natural frequency and the optimal damping ratio of the liquid damper. The geometry factors of the liquid damper affect the effective liquid mass ratio, which is critical for the reduction of the oscillation. The geometry factors are defined by the angle of inclination of the vertical stream line of fluid flow, the sectional area and the length of the liquid column. In order to solve the optimization problem in the research works so far developed, the geometry factors have always been assumed as known values. As the absorber efficiency depends not only on the tuning of the natural frequency and the damping ratio but also on the effective liquid mass ratio, the geometry factors must be included in the optimization procedure of the liquid damper. To achieve this purpose in this research work the tuning criteria of Den Hartog, Warburton and as well as Lyapunov are set up with a new expanded optimization approach. The practical application of the new optimization approach is demonstrated with the aid of two examples. The first example deals with a wind turbine, which is periodically excited by a non-uniform wind flow. The second example shows the application on a seismically excited benchmark building. The efficiency of the liquid damper and the influence of the absorber parameter are calculated through sensitivity analysis and compared with the conventional mechanical tuned mass dampers. This research work includes the conceptual design of a new semi-active liquid damper. The nonlinear equations of motion as well as the interaction forces are mathematically derived and the damper efficiency is numerically validated
- …
