Day 2 :
National Institute of Standards and Technology, USA
Time : 09:00-09:35
Emil Simiu is a NIST Fellow, National Institute of Standards and Technology, and a Professor of Practice in Wind Engineering, Florida International University. He is the author or co-author of Wind Effects of Structures (Russian translation, 1981; Chinese translation 1984), to be published in a 4th ed. by Wiley (2018), Chaotic Transitions in Deterministic and Stochastic Dynamical Systems (Princeton Univ. Press, 2001), Design of Buildings for Wind, 2nd ed., (Wiley 2011), and A Modern Course in Aeroelasticity (4th ed., Kluwer, 2004; Chinese translation, 2013).
Statement of the Problem: The effectiveness of structural design for wind depends upon the quality of the aerodynamic input to the design process. The estimation of wind-induced loading on structures was originally based on measurements at small numbers of taps, yielding pressure time histories but no information on spatial coherences. The loading estimates were therefore largely subjective. The subjective component of the estimates was reduced somewhat by the later development of devices allowing the measurement of moments and shears at the base of the building but providing no information on the load distribution on the building. Only following the development in the 1990s of the pressure scanner, which allows the simultaneous measurement in the wind tunnel of pressure time series at hundreds of pressure taps, could the data needed to fully define the aerodynamic and dynamic loading be obtained. This development, and the new availability of the requisite computational power, allowed the recent development of a novel conceptual basis for the accurate, differentiated, and risk-consistent design of thousands of structural members.
Methodology & Theoretical Approach: Unlike in past practices, the modern approach to structural design for wind makes it possible to clearly separate the tasks of the wind engineer, including the requisite aerodynamic measurements, from the tasks of the designer, which include the determination of the structure’s dynamic behavior. The paper describes the methodology by which time histories of pressures (Figure 1) at large numbers of taps can be used to obtain peak wind effects that can be used directly for the sizing of structural members.
Conclusion & Significance: In addition to achieving safer and more economical designs, the procedure described herein creates a demand for an enhanced role of the aerodynamicist, wherein simultaneous pressure time histories for bluff bodies in shear, turbulent flow would be obtained by numerical simulation, instead of in the wind tunnel. The paper discusses preliminary results of efforts aimed to achieve this goal.
Figure 1: Record of pressure coefficients measured on a wind tunnel model.
1. Spence S M J (2009) High-rise database-assisted design 1.1 (HR_DAD_1.1): Concepts, software, and examples, NIST Building Science Series 181, National Institute of Standards and Technology, Gaithersburg, MD.
2.Yeo D and Simiu E (2011) High-rise reinforced concrete structures: Database-assisted design for wind. Journal of Structural Engineering 137:1340-1349.
3.Simiu E and Yeo D (2015) Advances in the design of high-rise structures by the wind tunnel procedure: conceptual framework. Wind and Structures 21:489-503.
4.Shi L and Yeo D (2017) Large-eddy simulations of model-scale turbulent atmospheric boundary layers for structural engineering applications. Journal of Engineering Mechanics doi:10.1061/(ASCE)EM.1943-7889.0001281
Research Institute for Mechanics of MSU, Russia
Keynote: Stable detonative combustion of hydrogen in a supersonic flow coming in a convergent - divergent nozzle
Time : 09:35-10:10
Yuri V Tunik graduated from a usual school in the small town of Moscow region and entered the Mechanical Mathematics Department of Moscow State University by name M V Lomonosov (MSU). In 1970, he received higher education and continued to study at the graduate school of the same faculty. In 1976, he defended his thesis on gas-dynamic lasers and in 2002, the thesis "Dynamics of combustion in two-phase media containing methane" to acquire scientific degree of the Doctor of Physical and Mathematical Sciences. Since 1974, he has been working as a Researcher in the Research Institute of Mechanics of MSU. Currently he is a leading Researcher.
The possibility of stationary detonation combustion of hydrogen-air mixture coming into an axisymmetric convergent-divergent nozzle with a high supersonic velocity is investigated. A necessary condition for the stabilization is the formation of supersonic flow in the convergent section of the nozzle Therefore first, this work experimentally and numerically solves the problem of the starting of a convergent - divergent nozzle in a supersonic flow. It is shown that the supersonic start-up can be realized both by throwing a nozzle into the formed supersonic stream, and when the nozzle is accelerated to a given velocity. A peculiarity of the flow formed is the emergence of an oblique shock wave in the convergent section of the nozzle and the Mach disk because of this wave interaction with the axis of symmetry. In calculations with combustion, air at the inlet to the nozzle is replaced by a hydrogen-air mixture of a given concentration. The main difficulty in the problem of stabilization of detonative combustion is associated with the spontaneous ignition of hydrogen behind the Mach disk and the propagation of detonation upstream. Additional problems arise when initiating detonative combustion of hydrogen under conditions of a rarefied atmosphere: the ignition does not guarantee the formation of a stationary detonation in the nozzle. Investigations are fulfilled on the base of Euler gas dynamics equations with detailed kinetics of combustion. Calculations are made use modified Godunov’method. It is shown the possibility of stabilizing the detonative combustion of hydrogen-air mixtures coming into the axisymmetric nozzle at the Mach number from 7 to 9 at heights up to 16 km.
Figure1: Nozzle startup experiment: a - unsuccessful startup if the nozzle is installed before the start of blow down, b - a successful starting if the nozzle is thrown into the airflow at Mach number of 6.
Figure 2: Lines of a constant Mach number against the background of the OH concentration at stable detonative combustion of the hydrogen-air mixture 0.19H2 + 0.21O2 + 0.79N2 at the altitude of 14 km.
1.Tunik YuV (2010) Numerical modeling of detonation combustion of hydrogen – air mixtures in a convergent – divergent nozzle. Fluid Dynamics. 45(2):264-270.
2.Isakova NP, Kraiko AN, P’yankov KS, Tillyaeva NI (2012) The amplification of weak shock waves in axisymmetric supersonic flow and their reflection from an axis of symmetry. Journal of Applied