Hans-jürgen Niemann | Ruhr-Universität Bochum (original) (raw)

Papers by Hans-jürgen Niemann

Research paper thumbnail of Mitigation of Interference-Induced Vibrations for Towers in Group Arrangements

Lecture notes in civil engineering, 2024

Research paper thumbnail of Stahlfaserbeton Und Stahlfaserverstaerkter Stahlbeton

DIE EIGENSCHAFTEN VON BETON LASSEN SICH DURCH DIE EINLAGERUNG VON STAHLFASERN GUENSTIG BEEINFLUSS... more DIE EIGENSCHAFTEN VON BETON LASSEN SICH DURCH DIE EINLAGERUNG VON STAHLFASERN GUENSTIG BEEINFLUSSEN. DIE DABEI ENTSTEHENDE RISSHEMMUNG BEWIRKT EINE ERHOEHUNG DER ZUGFESTIGKEIT, DER SCHLAGBIEGEZAEHIGKEIT UND DER BRUCHENERGIE SOWIE EINE VERBESSERUNG DER VERSCHLEISSFESTIGKEIT. DIE IM VORLIEGENDEN HEFT ZUSAMMENGESTELLTEN BEITRAEGE BEHANDELN U.A. TECHNOLOGIE, BEMESSUNGSVERFAHREN UND ANWENDUNGSMOEGLICHKEITEN VON STAHLFASERBETON, Z.B. IM TUNNELBAU UND ALS ANPRALLSCHUTZKONSTRUKTIONEN IN KERNTECHNISCHEN ANLAGEN, SOWIE WIRTSCHAFTLICHE EINSATZMOEGLICHKEITEN UND ENTWICKLUNG VON VERBUNDPLATTEN UND EXTREM DUENNEN BAUTEILEN. GLEICHZEITIG WIRD EIN UEBERBLICK UEBER DEN STAND DER FORSCHUNG UND UEBER DIE BISHER ERSCHLOSSENEN ANWENDUNGSGEBIETE GEGEBEN. (A*)

Research paper thumbnail of Insights into the Transcritical Reynolds Number Range Based on Field Measurements of a Wind Turbine Tower

Lecture notes in civil engineering, 2024

Research paper thumbnail of Windkanaluntersuchungen Zur Ausbreitung Von Abgasen an Autobahnen

DIE KENNTNISSE UEBER DIE AUSBREITUNG VON ABGASEN AN STRASSEN SIND ZUR ZEIT NOCH SEHR LUECKENHAFT,... more DIE KENNTNISSE UEBER DIE AUSBREITUNG VON ABGASEN AN STRASSEN SIND ZUR ZEIT NOCH SEHR LUECKENHAFT, DA DIE VIELZAHL DER EINFLUSSPARAMETER SELBST IN SEHR AUFWENDIGEN FELDVERSUCHEN KAUM SYSTEMATISCH ERFASST WERDEN KOENNEN UND EINE REIN MATHEMATISCHE FORMULIERUNG VERHINDERN. AM EHESTEN ERFOLG VERSPRECHEN HALBEMPIRISCHE MODELLE, BEI DENEN DIE MATHEMATISCH NICHT ERFASSBAREN PARAMETER EMPIRISCH IM WINDKANAL UNTERSUCHT WERDEN. DER BEITRAG BESCHREIBT DEN FUER DERARTIGE UNTERSUCHUNGEN AN DER UNIVERSITAET BOCHUM VERWENDETEN WINDKANAL SOWIE DIE MESSTECHNIK (TRACER-TECHNIK) UND BESCHAEFTIGT SICH AUSFUEHRLICH MIT BESONDEREN ASPEKTEN WIE AERODYNAMISCHER MASSSTAB, GRENZSCHICHTBETRACHTUNGEN ZUR BERUECKSICHTIGUNG DER VON DER HOEHE UND GELAENDEFORM ABHAENGIGEN WINDGESCHWINDIGKEITEN UND TURBULENZEN, TRANSMISSIONSPARAMETER ODER VERKEHRSBEDINGTE TURBULENZEN. AUFGRUND DER UNTERSUCHUNGSERGEBNISSE ZU AUSWIRKUNEGN VERSCHIEDENER IMISSIONSSCHUTZANLAGEN (WAELLE, WAENDE, BEPFLANZUGEN) UND VON VERGLEICHEN ZWISCHEN...

Research paper thumbnail of Wind Tunnel Investigations on the Dispersal of Exhaust Gases at Freeways

Research paper thumbnail of Wind-Induced Response of Buildings Arranged in a Group

Wind forces on buildings are usually dealt with considering the building in isolation. Controvers... more Wind forces on buildings are usually dealt with considering the building in isolation. Controversely, about 80% of buildings are situated in an urban environment and hence surrounded by other buildings: the flow fields interfere with each other altering the wind loads — both static and dynamic — in comparison to the isolated case. The effects of interference in a given situation depend very much on the position of the building group relative to the wind direction, leading either to shelter or to amplification effects. The dependence of extreme wind speeds on the wind direction becomes therefore important. The paper reviews the interference for some typical cases and discusses the directional influence in strong winds.

Research paper thumbnail of Non-Parametric Identification of a Multiple Aerodynamic Pressure Admittance

Notes on numerical fluid mechanics, 1993

Fluctuating pressures on bluff bodies in turbulent flows are caused by the upstream turbulence an... more Fluctuating pressures on bluff bodies in turbulent flows are caused by the upstream turbulence and velocity fluctuations, produced by flow separations and wake turbulence. Although the gross properties of the flow around a body and in particular the separated flow are affected by the intensity and the scale of the incident turbulence, both sources of pressure fluctuations are thought to be statistically independent. On this basis, a multiple aerodynamic pressure admittance has been developed to account for turbulence induced pressure fluctuations in the first instance. This concept has been applied for the flow around a finite circular cylinder in a simulated atmospheric boundary layer flow.

Research paper thumbnail of On the Flow Around Finite Circular Cylinders in Turbulent Shear Flows

Notes on numerical fluid mechanics, 1993

The mean flow pattern around a finite span circular cylinder reveals several stationary flow sepa... more The mean flow pattern around a finite span circular cylinder reveals several stationary flow separations. The unsteady flow is dominated by the effect of the approaching turbulent shear flow and by an alternating vortex shedding, which is significantly altered under these three-dimensional conditions.

Research paper thumbnail of Influence of adjacent buildings on wind effects on cooling towers

Engineering Structures

In a series of wind tunnel tests, the wind-induced stresses in cooling towers situated in an arra... more In a series of wind tunnel tests, the wind-induced stresses in cooling towers situated in an arrangement of typical power plant buildings, are investigated and compared to the stresses in an isolated tower. Interference factors are developed to quantify the stress increase due to the group effect. it is found that the stresses respond rather non-uniformly to interference, particularly when the distance to adjacent buildings is small and the effect of interference is strong. In order to account for the additional stresses, a global increase may be applied to the wind load, which, however, is only reasonable for moderate interference.

Research paper thumbnail of Nonlinear stochastic response of rotational shell under the action of stationary strong wind loads

Journal of Beijing Institute of Technology (English Edition)

Based on the theoretical analysis of nonlinear random response of structure, for the engineering ... more Based on the theoretical analysis of nonlinear random response of structure, for the engineering practical problem, that is, the large deformation of industry cooling tower shell structure under the action of strong wind loads, the statistic perturbation method is also used to analyze some statistic characteristics of the nonlinear random response of rotational shell with geometric nonlinearity and stationary strong wind load considered. Through computation, some average values of nornal displacements and the nonlinear effect factor of the cooling tower shell are given.

Research paper thumbnail of Wind Tunnel Experiments on Spread of Exhausts in the Vicinity of Motorways --14TH Arrb Conference, 28 August - 2 September, 1988, Canberra, Act, Australia; Proc. Parts 1 - 8

Traffic engineers are more and more interested in the emergence and spread of exhaust gas from ro... more Traffic engineers are more and more interested in the emergence and spread of exhaust gas from road traffic, especially in densely populated urban areas. The spread of exhaust gas in the vicinity of the road cannot be sufficiently predicted up to now, particularly since there are no generally acknowledged calculation methods. At the ruhr university, bochum, wind tunnel experiments have been carried out for several years, and it has been possible to observe the spread of exhaust gas in a model on a scale of 1:200. In the course of these experiments, the laws of aerodynamics have to be taken into account. The air turbulences caused by the traffic flow have a decisive influence, too. Under these circumstances, the model's results correspond to the actual spread of exhaust gas to a high degree. On the basis of these measurements, a calculation method which facilitates the estimation of the concentration of any exhaust gas component (co, ch, nox, so2) in the vicinity of the road was ...

Research paper thumbnail of Aerodynamic damping model in vortex-induced vibrations for wind engineering applications

Journal of Wind Engineering and Industrial Aerodynamics, 2018

The paper addresses the modelling of aeroelastic forces in vortex-induced vibrations (VIV) and ai... more The paper addresses the modelling of aeroelastic forces in vortex-induced vibrations (VIV) and aims to provide a suitable model to predict crosswind oscillations of circular structures. The Van der Pol and Rayleigh oscillatorsnon-linear physical systems, which attain limit cycles under self-induced vibrationsare often applied in literature to describe the aeroelastic force. Among VIV models, the paper focuses on the model developed by Vickery and Basu (1983). In the paper, the quadrature component of the force as a function of the oscillation amplitude in lock-in is investigated through forced-vibration wind tunnel experiments on a circular cylinder. In presence of aeroelastic interaction, the positive quadrature component corresponds to energy transferred to the structure, which then acts as negative aerodynamic damping. The experiments reveal an amplitude-dependent behaviour of the aerodynamic damping with positive curvature. The experimental curve can be applied as modification of the Vickery and Basu model and used to predict the oscillation of circular structures under vortex-excitation. In the paper, it is applied to the response of a cantilever beam. The prediction is validated through free-vibration wind tunnel experiments. The consistency of results is promising.

Research paper thumbnail of Dynamics of civil engineering structures

Canadian Journal of Civil Engineering, 1997

Phenomena and Evaluation of Dynamic Structural Responses p. 1 Dynamic Actions p. 73 Dynamic wind ... more Phenomena and Evaluation of Dynamic Structural Responses p. 1 Dynamic Actions p. 73 Dynamic wind actions p. 73 Machinery and traffic loads p. 105 Earthquake loading p. 110 Dynamic Behaviour of Materials and Structural Components p. 125

Research paper thumbnail of The L.R.C. (load-response-correlation) - method a general method of estimating unfavourable wind load distributions for linear and non-linear structural behaviour

Journal of Wind Engineering and Industrial Aerodynamics, 1992

Research paper thumbnail of Fatigue Life Estimation Considering the Quasi-Periodic Cross-Wind Response of Slender Structures in the Lock-In Range

XI International Conference on Structural Dynamics, 2020

Research paper thumbnail of A Model Extension for Vortex-Induced Vibrations

Lecture Notes in Civil Engineering, 2019

The paper presents free-vibration wind tunnel tests performed at WIST Boundary Layer Wind Tunnel ... more The paper presents free-vibration wind tunnel tests performed at WIST Boundary Layer Wind Tunnel at Ruhr-Universität Bochum (Germany) on a 3D aeroelastic cylindrical model with circular cross-section. The aim of the tests is to validate a model extension to the original spectral method developed by Vickery & Basu, able to calculate the maximum oscillation of a structure subjected to vortex-induced vibration in the lock-in region. The peculiarity of the extension is the implementation of an experimental curve for the negative aerodynamic damping. It was previously developed by the authors through forced vibration wind tunnel tests. The model extension is based on a linear differential equation. In fact, linearin case iterativeapproaches are usually preferred for the design of structures. However, limitations due to linearization of an intrinsically non-linear phenomenon are unavoidable. Strengths and weaknesses of the linear approach are discussed in the paper. Keywords: Circular cylinder Á Free-vibration wind tunnel tests Á Vortex-induced vibrations Á Vortex shedding Á Vortex resonance Á Aerodynamic damping

Research paper thumbnail of Structural Oscillations of High Chimneys Due to Wind Gusts and Vortex Shedding

Structural Dynamics with Applications in Earthquake and Wind Engineering, 2019

During the last 2 decades, new code generations have been introduced which incorporate the achiev... more During the last 2 decades, new code generations have been introduced which incorporate the achieved scientific and technological state of the art that has been proven its usefulness in practical application. The Eurocodes and the CICIND model codes are examples of this development. The Eurocode applies a modified gust response factor to model in-line wind loading and resonance due to turbulence through increasing the peak velocity pressure by a factor which depends on the individual size and dynamic features of the structure considered. The CICIND model codes for steel and concrete chimneys take account of the particular mechanical behaviour and the specific design requirements of these structures and utilizes the mean and the gust wind force, where the gust load defines an equivalent static load scaled to reproduce the real base bending moment of the chimney induced by wind gustiness. The cross-wind excitation of chimneys by vortex shedding is calculated in the CICIND model applyin...

Research paper thumbnail of Aerodynamic phenomena and wind-induced effects in the design of ultra-high towers

3669 ABSTRACT: The structural behaviour of thin and ultra-high shells like Solar Updraft Towers c... more 3669 ABSTRACT: The structural behaviour of thin and ultra-high shells like Solar Updraft Towers can be optimized by stiffening rings applied along the height, which guarantee a predominant beam-like behaviour. However, too dense or too big stiffening rings may become a double-edged sword, because they modify the aerodynamic of the flow past the circular cylinder and may induce an even more severe load condition. The paper reveals an experimental and numerical evidenced stochastic property of wind-induced pressures, which has been detected by analyzing slender circular cylinders with a free-end in turbulent atmospheric boundary layer flow. Cross-checked wind tunnel tests were performed at WiSt wind tunnel at Ruhr-University Bochum and at CRIACIV wind tunnel at University of Florence. Experimental results are also confirmed by numerical simulations, performed at the Industrial Energy Department, University of Florence. The investigation revealed the existence of a bi-stable and not sy...

Research paper thumbnail of Vibrations of Chimneys under the Action of the Wind

Vibrations of chimneys under the wind act ion occur in-line with the wind as forced, random v ibr... more Vibrations of chimneys under the wind act ion occur in-line with the wind as forced, random v ibrations and crosswind as vortex-induced vibrations. The former becom e i portant at extreme wind speeds, regular vortex shedding causes the latter and occurs at any wind speed. In the case of vortex resonance, when considerable vibration ampl itudes develop, the structural displacements alter the fluid force, whi ch s known as an aero-elastic coupling of force an d structural response. Regarding the random load caused by turbulent wind, Davenport's pioneering concept of the gust respons e factor was applied to develop a simplified equivalent static load. Two di fferent models are available regarding the design f or vortex resonance. One is Ruscheweyh's approach to deal with vortex resonance s a forced vibration and to incorporate the aeroelastic effects in model parameters derived from experimental data. In the s econd model, the design for vortex resonance is bas ed on Vickery & ...

Research paper thumbnail of Aerodynamic damping in vortex resonance from aeroelastic wind tunnel tests on a stack

Journal of Wind Engineering and Industrial Aerodynamics, 2021

Abstract The paper investigates the negative aerodynamic damping of circular cylinders in vortex-... more Abstract The paper investigates the negative aerodynamic damping of circular cylinders in vortex-induced vibrations and compares the results of two different types of wind tunnel experiments. Firstly, forced-vibration wind tunnel tests on a rigid sectional model allow measuring the aerodynamic damping directly from the experiments. This is because the aerodynamic damping is related to the phase shift between the force and the imposed motion. They also offer the advantage of a systematic investigation for different velocity ratios and a constant oscillation amplitude. Secondly, aeroelastic experiments on a cantilevered cylinder with distributed elasticity free to oscillate under the wind action are performed. These experiments do not impose the motion from the outside and therefore, the physical nature of the vortex-induced vibration can develop without any further constraint to the motion. However, these tests do not explicitly reveal the relationship between the load and response. Nevertheless, the aerodynamic damping can still be evaluated, if a mathematical model to describe the relationship between load and response is assumed. The cross-check of aerodynamic damping values obtained from the two experimental approaches not only gives evidence of the reliability of the proposed aerodynamic damping model, but also proves the effectiveness of the Vickery&Basu spectral model to predict vortex-induced vibrations.

Research paper thumbnail of Mitigation of Interference-Induced Vibrations for Towers in Group Arrangements

Lecture notes in civil engineering, 2024

Research paper thumbnail of Stahlfaserbeton Und Stahlfaserverstaerkter Stahlbeton

DIE EIGENSCHAFTEN VON BETON LASSEN SICH DURCH DIE EINLAGERUNG VON STAHLFASERN GUENSTIG BEEINFLUSS... more DIE EIGENSCHAFTEN VON BETON LASSEN SICH DURCH DIE EINLAGERUNG VON STAHLFASERN GUENSTIG BEEINFLUSSEN. DIE DABEI ENTSTEHENDE RISSHEMMUNG BEWIRKT EINE ERHOEHUNG DER ZUGFESTIGKEIT, DER SCHLAGBIEGEZAEHIGKEIT UND DER BRUCHENERGIE SOWIE EINE VERBESSERUNG DER VERSCHLEISSFESTIGKEIT. DIE IM VORLIEGENDEN HEFT ZUSAMMENGESTELLTEN BEITRAEGE BEHANDELN U.A. TECHNOLOGIE, BEMESSUNGSVERFAHREN UND ANWENDUNGSMOEGLICHKEITEN VON STAHLFASERBETON, Z.B. IM TUNNELBAU UND ALS ANPRALLSCHUTZKONSTRUKTIONEN IN KERNTECHNISCHEN ANLAGEN, SOWIE WIRTSCHAFTLICHE EINSATZMOEGLICHKEITEN UND ENTWICKLUNG VON VERBUNDPLATTEN UND EXTREM DUENNEN BAUTEILEN. GLEICHZEITIG WIRD EIN UEBERBLICK UEBER DEN STAND DER FORSCHUNG UND UEBER DIE BISHER ERSCHLOSSENEN ANWENDUNGSGEBIETE GEGEBEN. (A*)

Research paper thumbnail of Insights into the Transcritical Reynolds Number Range Based on Field Measurements of a Wind Turbine Tower

Lecture notes in civil engineering, 2024

Research paper thumbnail of Windkanaluntersuchungen Zur Ausbreitung Von Abgasen an Autobahnen

DIE KENNTNISSE UEBER DIE AUSBREITUNG VON ABGASEN AN STRASSEN SIND ZUR ZEIT NOCH SEHR LUECKENHAFT,... more DIE KENNTNISSE UEBER DIE AUSBREITUNG VON ABGASEN AN STRASSEN SIND ZUR ZEIT NOCH SEHR LUECKENHAFT, DA DIE VIELZAHL DER EINFLUSSPARAMETER SELBST IN SEHR AUFWENDIGEN FELDVERSUCHEN KAUM SYSTEMATISCH ERFASST WERDEN KOENNEN UND EINE REIN MATHEMATISCHE FORMULIERUNG VERHINDERN. AM EHESTEN ERFOLG VERSPRECHEN HALBEMPIRISCHE MODELLE, BEI DENEN DIE MATHEMATISCH NICHT ERFASSBAREN PARAMETER EMPIRISCH IM WINDKANAL UNTERSUCHT WERDEN. DER BEITRAG BESCHREIBT DEN FUER DERARTIGE UNTERSUCHUNGEN AN DER UNIVERSITAET BOCHUM VERWENDETEN WINDKANAL SOWIE DIE MESSTECHNIK (TRACER-TECHNIK) UND BESCHAEFTIGT SICH AUSFUEHRLICH MIT BESONDEREN ASPEKTEN WIE AERODYNAMISCHER MASSSTAB, GRENZSCHICHTBETRACHTUNGEN ZUR BERUECKSICHTIGUNG DER VON DER HOEHE UND GELAENDEFORM ABHAENGIGEN WINDGESCHWINDIGKEITEN UND TURBULENZEN, TRANSMISSIONSPARAMETER ODER VERKEHRSBEDINGTE TURBULENZEN. AUFGRUND DER UNTERSUCHUNGSERGEBNISSE ZU AUSWIRKUNEGN VERSCHIEDENER IMISSIONSSCHUTZANLAGEN (WAELLE, WAENDE, BEPFLANZUGEN) UND VON VERGLEICHEN ZWISCHEN...

Research paper thumbnail of Wind Tunnel Investigations on the Dispersal of Exhaust Gases at Freeways

Research paper thumbnail of Wind-Induced Response of Buildings Arranged in a Group

Wind forces on buildings are usually dealt with considering the building in isolation. Controvers... more Wind forces on buildings are usually dealt with considering the building in isolation. Controversely, about 80% of buildings are situated in an urban environment and hence surrounded by other buildings: the flow fields interfere with each other altering the wind loads — both static and dynamic — in comparison to the isolated case. The effects of interference in a given situation depend very much on the position of the building group relative to the wind direction, leading either to shelter or to amplification effects. The dependence of extreme wind speeds on the wind direction becomes therefore important. The paper reviews the interference for some typical cases and discusses the directional influence in strong winds.

Research paper thumbnail of Non-Parametric Identification of a Multiple Aerodynamic Pressure Admittance

Notes on numerical fluid mechanics, 1993

Fluctuating pressures on bluff bodies in turbulent flows are caused by the upstream turbulence an... more Fluctuating pressures on bluff bodies in turbulent flows are caused by the upstream turbulence and velocity fluctuations, produced by flow separations and wake turbulence. Although the gross properties of the flow around a body and in particular the separated flow are affected by the intensity and the scale of the incident turbulence, both sources of pressure fluctuations are thought to be statistically independent. On this basis, a multiple aerodynamic pressure admittance has been developed to account for turbulence induced pressure fluctuations in the first instance. This concept has been applied for the flow around a finite circular cylinder in a simulated atmospheric boundary layer flow.

Research paper thumbnail of On the Flow Around Finite Circular Cylinders in Turbulent Shear Flows

Notes on numerical fluid mechanics, 1993

The mean flow pattern around a finite span circular cylinder reveals several stationary flow sepa... more The mean flow pattern around a finite span circular cylinder reveals several stationary flow separations. The unsteady flow is dominated by the effect of the approaching turbulent shear flow and by an alternating vortex shedding, which is significantly altered under these three-dimensional conditions.

Research paper thumbnail of Influence of adjacent buildings on wind effects on cooling towers

Engineering Structures

In a series of wind tunnel tests, the wind-induced stresses in cooling towers situated in an arra... more In a series of wind tunnel tests, the wind-induced stresses in cooling towers situated in an arrangement of typical power plant buildings, are investigated and compared to the stresses in an isolated tower. Interference factors are developed to quantify the stress increase due to the group effect. it is found that the stresses respond rather non-uniformly to interference, particularly when the distance to adjacent buildings is small and the effect of interference is strong. In order to account for the additional stresses, a global increase may be applied to the wind load, which, however, is only reasonable for moderate interference.

Research paper thumbnail of Nonlinear stochastic response of rotational shell under the action of stationary strong wind loads

Journal of Beijing Institute of Technology (English Edition)

Based on the theoretical analysis of nonlinear random response of structure, for the engineering ... more Based on the theoretical analysis of nonlinear random response of structure, for the engineering practical problem, that is, the large deformation of industry cooling tower shell structure under the action of strong wind loads, the statistic perturbation method is also used to analyze some statistic characteristics of the nonlinear random response of rotational shell with geometric nonlinearity and stationary strong wind load considered. Through computation, some average values of nornal displacements and the nonlinear effect factor of the cooling tower shell are given.

Research paper thumbnail of Wind Tunnel Experiments on Spread of Exhausts in the Vicinity of Motorways --14TH Arrb Conference, 28 August - 2 September, 1988, Canberra, Act, Australia; Proc. Parts 1 - 8

Traffic engineers are more and more interested in the emergence and spread of exhaust gas from ro... more Traffic engineers are more and more interested in the emergence and spread of exhaust gas from road traffic, especially in densely populated urban areas. The spread of exhaust gas in the vicinity of the road cannot be sufficiently predicted up to now, particularly since there are no generally acknowledged calculation methods. At the ruhr university, bochum, wind tunnel experiments have been carried out for several years, and it has been possible to observe the spread of exhaust gas in a model on a scale of 1:200. In the course of these experiments, the laws of aerodynamics have to be taken into account. The air turbulences caused by the traffic flow have a decisive influence, too. Under these circumstances, the model's results correspond to the actual spread of exhaust gas to a high degree. On the basis of these measurements, a calculation method which facilitates the estimation of the concentration of any exhaust gas component (co, ch, nox, so2) in the vicinity of the road was ...

Research paper thumbnail of Aerodynamic damping model in vortex-induced vibrations for wind engineering applications

Journal of Wind Engineering and Industrial Aerodynamics, 2018

The paper addresses the modelling of aeroelastic forces in vortex-induced vibrations (VIV) and ai... more The paper addresses the modelling of aeroelastic forces in vortex-induced vibrations (VIV) and aims to provide a suitable model to predict crosswind oscillations of circular structures. The Van der Pol and Rayleigh oscillatorsnon-linear physical systems, which attain limit cycles under self-induced vibrationsare often applied in literature to describe the aeroelastic force. Among VIV models, the paper focuses on the model developed by Vickery and Basu (1983). In the paper, the quadrature component of the force as a function of the oscillation amplitude in lock-in is investigated through forced-vibration wind tunnel experiments on a circular cylinder. In presence of aeroelastic interaction, the positive quadrature component corresponds to energy transferred to the structure, which then acts as negative aerodynamic damping. The experiments reveal an amplitude-dependent behaviour of the aerodynamic damping with positive curvature. The experimental curve can be applied as modification of the Vickery and Basu model and used to predict the oscillation of circular structures under vortex-excitation. In the paper, it is applied to the response of a cantilever beam. The prediction is validated through free-vibration wind tunnel experiments. The consistency of results is promising.

Research paper thumbnail of Dynamics of civil engineering structures

Canadian Journal of Civil Engineering, 1997

Phenomena and Evaluation of Dynamic Structural Responses p. 1 Dynamic Actions p. 73 Dynamic wind ... more Phenomena and Evaluation of Dynamic Structural Responses p. 1 Dynamic Actions p. 73 Dynamic wind actions p. 73 Machinery and traffic loads p. 105 Earthquake loading p. 110 Dynamic Behaviour of Materials and Structural Components p. 125

Research paper thumbnail of The L.R.C. (load-response-correlation) - method a general method of estimating unfavourable wind load distributions for linear and non-linear structural behaviour

Journal of Wind Engineering and Industrial Aerodynamics, 1992

Research paper thumbnail of Fatigue Life Estimation Considering the Quasi-Periodic Cross-Wind Response of Slender Structures in the Lock-In Range

XI International Conference on Structural Dynamics, 2020

Research paper thumbnail of A Model Extension for Vortex-Induced Vibrations

Lecture Notes in Civil Engineering, 2019

The paper presents free-vibration wind tunnel tests performed at WIST Boundary Layer Wind Tunnel ... more The paper presents free-vibration wind tunnel tests performed at WIST Boundary Layer Wind Tunnel at Ruhr-Universität Bochum (Germany) on a 3D aeroelastic cylindrical model with circular cross-section. The aim of the tests is to validate a model extension to the original spectral method developed by Vickery & Basu, able to calculate the maximum oscillation of a structure subjected to vortex-induced vibration in the lock-in region. The peculiarity of the extension is the implementation of an experimental curve for the negative aerodynamic damping. It was previously developed by the authors through forced vibration wind tunnel tests. The model extension is based on a linear differential equation. In fact, linearin case iterativeapproaches are usually preferred for the design of structures. However, limitations due to linearization of an intrinsically non-linear phenomenon are unavoidable. Strengths and weaknesses of the linear approach are discussed in the paper. Keywords: Circular cylinder Á Free-vibration wind tunnel tests Á Vortex-induced vibrations Á Vortex shedding Á Vortex resonance Á Aerodynamic damping

Research paper thumbnail of Structural Oscillations of High Chimneys Due to Wind Gusts and Vortex Shedding

Structural Dynamics with Applications in Earthquake and Wind Engineering, 2019

During the last 2 decades, new code generations have been introduced which incorporate the achiev... more During the last 2 decades, new code generations have been introduced which incorporate the achieved scientific and technological state of the art that has been proven its usefulness in practical application. The Eurocodes and the CICIND model codes are examples of this development. The Eurocode applies a modified gust response factor to model in-line wind loading and resonance due to turbulence through increasing the peak velocity pressure by a factor which depends on the individual size and dynamic features of the structure considered. The CICIND model codes for steel and concrete chimneys take account of the particular mechanical behaviour and the specific design requirements of these structures and utilizes the mean and the gust wind force, where the gust load defines an equivalent static load scaled to reproduce the real base bending moment of the chimney induced by wind gustiness. The cross-wind excitation of chimneys by vortex shedding is calculated in the CICIND model applyin...

Research paper thumbnail of Aerodynamic phenomena and wind-induced effects in the design of ultra-high towers

3669 ABSTRACT: The structural behaviour of thin and ultra-high shells like Solar Updraft Towers c... more 3669 ABSTRACT: The structural behaviour of thin and ultra-high shells like Solar Updraft Towers can be optimized by stiffening rings applied along the height, which guarantee a predominant beam-like behaviour. However, too dense or too big stiffening rings may become a double-edged sword, because they modify the aerodynamic of the flow past the circular cylinder and may induce an even more severe load condition. The paper reveals an experimental and numerical evidenced stochastic property of wind-induced pressures, which has been detected by analyzing slender circular cylinders with a free-end in turbulent atmospheric boundary layer flow. Cross-checked wind tunnel tests were performed at WiSt wind tunnel at Ruhr-University Bochum and at CRIACIV wind tunnel at University of Florence. Experimental results are also confirmed by numerical simulations, performed at the Industrial Energy Department, University of Florence. The investigation revealed the existence of a bi-stable and not sy...

Research paper thumbnail of Vibrations of Chimneys under the Action of the Wind

Vibrations of chimneys under the wind act ion occur in-line with the wind as forced, random v ibr... more Vibrations of chimneys under the wind act ion occur in-line with the wind as forced, random v ibrations and crosswind as vortex-induced vibrations. The former becom e i portant at extreme wind speeds, regular vortex shedding causes the latter and occurs at any wind speed. In the case of vortex resonance, when considerable vibration ampl itudes develop, the structural displacements alter the fluid force, whi ch s known as an aero-elastic coupling of force an d structural response. Regarding the random load caused by turbulent wind, Davenport's pioneering concept of the gust respons e factor was applied to develop a simplified equivalent static load. Two di fferent models are available regarding the design f or vortex resonance. One is Ruscheweyh's approach to deal with vortex resonance s a forced vibration and to incorporate the aeroelastic effects in model parameters derived from experimental data. In the s econd model, the design for vortex resonance is bas ed on Vickery & ...

Research paper thumbnail of Aerodynamic damping in vortex resonance from aeroelastic wind tunnel tests on a stack

Journal of Wind Engineering and Industrial Aerodynamics, 2021

Abstract The paper investigates the negative aerodynamic damping of circular cylinders in vortex-... more Abstract The paper investigates the negative aerodynamic damping of circular cylinders in vortex-induced vibrations and compares the results of two different types of wind tunnel experiments. Firstly, forced-vibration wind tunnel tests on a rigid sectional model allow measuring the aerodynamic damping directly from the experiments. This is because the aerodynamic damping is related to the phase shift between the force and the imposed motion. They also offer the advantage of a systematic investigation for different velocity ratios and a constant oscillation amplitude. Secondly, aeroelastic experiments on a cantilevered cylinder with distributed elasticity free to oscillate under the wind action are performed. These experiments do not impose the motion from the outside and therefore, the physical nature of the vortex-induced vibration can develop without any further constraint to the motion. However, these tests do not explicitly reveal the relationship between the load and response. Nevertheless, the aerodynamic damping can still be evaluated, if a mathematical model to describe the relationship between load and response is assumed. The cross-check of aerodynamic damping values obtained from the two experimental approaches not only gives evidence of the reliability of the proposed aerodynamic damping model, but also proves the effectiveness of the Vickery&Basu spectral model to predict vortex-induced vibrations.