vibrations in buildings induced by small-scale turbines for ......moreover, vibrations in buildings...
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Bauhaus Summer School Forecast Engineering: From Past Design to Future Decision
22 August - 2 September 2016, Weimar, Germany
Vibrations in buildings induced by small-scale turbines for urban
wind harvesting: a case study
LUČIĆ Sanda
Graduate student, Josip Juraj Strossmayer University of Osijek
KRAUS Ivan
Dr.Sc., Josip Juraj Strossmayer University of Osijek
Abstract
Vibrations induced by machinery, traffic and other stochastic frequency-rich sources may cause
deformations and cracks on both structural and non-structural elements but also fatigue related
problems. Moreover, vibrations in buildings may cause discomfort for people and animals. On the
other hand, wind turbines may often be found in urban areas surrounded by buildings or placed a top
of a building. Although the turbines support green engineering and production of clean energy, they
also produce vibrations that may negatively influence the behaviour of both structures and living
beings. This paper aims to investigate effects of vibrations generated by small-scale wind turbines
placed on buildings in urban areas. A platform for this research is a soil-structure-wind turbine system,
where the structures selected for this case study are typical buildings that can be found in city of
Osijek. The aim of this research is to set the stage for a small-scale wind turbine that will harvest green
energy in Osijek in near future. Numerical analysis was performed using software Ashes 1.2 and
SAP2000, while program SeismoSignal was employed for interpretation of analysis results.
Parametric analysis provides results in the light of displacement response spectrums and acceleration
response spectrums taken from characteristic structural elements on different floors compared with
code-based thresholds. In addition, parametric study provides transfer functions calculated by dividing
output (structural vibration) and input (vibration of the top of the turbine) signals pointing out
amplified frequencies by structural members.
1. Introduction
Development of industry, traffic and modern technologies results in environmental pollution that leads
to global warming. Moreover, taking into account decrease of supplies of fossil fuels, society had to
increase interest in developing energy sources that will not be harmful to the environment such as
wind, hydropower, solar, geothermal. For the past few decades, renewable energy sources have been
in a state of continual growth. Among all renewable energy branches, one of the most popular and
fastest growing sources is wind energy. Use of this type of energy eliminates emission of CO2, SO2
and other harmful gases. According to Tong (2010), in 2009, global annual installed wind generation
capacity reached 37 GW, bringing the world total wind capacity in 2010 to 158 GW. Taking into
account that this “green” energy source is the most promising and reliable, wind power is believed to
play a critical role in global power supply in the 21st century.
Wind turbine technology has gained great development over the last decades. Traditional windmills
have been used for centuries, but owning to discovery of internal combustion engine and development
of electrical technology, traditional windmills started to disappear and development of modern wind
turbines began. Nowadays, it is not unusual to use wind turbines for electricity production. While wind
turbine technology is mainly concentrated on large turbines and offshore wind farms, this paper aims
to emphasize the importance of development and installation of small wind turbines which are
LUČIĆ Sanda, KRAUS Ivan / FE 2016 2
adequately safe and easy to run and maintain on individual buildings for independent power
production. Unlike large wind turbines, small wind turbines can be installed in urban areas, near to
buildings or at the top of them. These machines are operating in areas where people work and live thus
strict requirements concerning the safety of people and serviceability of the structure must be fulfilled.
Small wind turbines are usually designed with high tip-speed ratio hence their rotational speed
becomes very high. They also usually have fixed pitch type blades while their rotational surface can be
furled upward or side wards to prevent the over-rotation. As a result, these ferocious green energy
collectors can often be noisy and dangerous under strong winds. They also produce vibrations which
can be harmful for both structures and living beings (Ameku et al., 2008).
2. Vibrations
Vibrations in structures can have negative impact on both living beings and structures - they can cause
serviceability problems reducing comfort of people inside the building to an unacceptable level or
safety problems with danger of collapse of either structural or non-structural elements. Vibrations may
be caused by many different sources: human body motions, wind flow, traffic, working machines etc.
In this paper, only dynamic actions induced by rotating machines (wind turbines) are considered.
Vibrating machines, such as wind turbines, can affect different parts of engineering structures:
foundations, slabs, beams or even the whole structure. Operating machines can cause dynamic forces
that primarily depend on the type of the motion the machine describes – in case of wind turbine it is
rotation. Effects of machine-induced vibrations can be various; they can affect structures and structural
elements or people and other living beings. Effects on structures may include appearance of cracking,
crumbling plaster, loss of load-bearing capacity, fatigue problems. People, who spend time near to
machines emitting vibrations could be affected in various degrees - the intensity may range from
barely perceptible to slightly or strongly disturbing to harmful and they can manifest in three different
ways: as mechanical effects (vibration of floors or ceilings), an acoustic effects (noise from
installations or equipment motion) or as optical effects (visible motion of building elements of other
objects inside the building). Tolerable values of vibrations are different for different criteria:
structural, psychological and production-quality criteria. Vibration can be limited by given values of
physical quantities such as displacement amplitude, velocity amplitude and acceleration amplitude or
by other quantities such as KB intensity defined in German standard (Bachmann et al., 1994).
2.1. Human response to vibrations
All living beings are highly sensitive to vibration. People can sense vibration displacement amplitudes
as low as 0,001 mm, while finger-tips are even 20 times more sensitive. Human reaction to vibrations
is individual and depends on personal attitude and situation in which a person is. For instance, level of
discomfort is different while reading from driving in public transport. Sensitivity depends on many
different circumstances like personal dedication to a task, position (standing, sitting..), personal
activity, age, direction of incidence with respect to the spine, frequency of occurrence, time of day and
many others (Bachmann et al., 1994).
Table 1. Human perception of vibration level (The Engineering ToolBox, 2016)
Vibration level – acceleration [m/s2] Human Perception
< 0,315
0,315 – 0,63
0,50 – 1,00
0,80 – 1,60
1,25 – 2,50
> 2,00
Not uncomfortable
A little uncomfortable
Fairly uncomfortable
Uncomfortable
Very uncomfortable
Extremely uncomfortable
LUČIĆ Sanda, KRAUS Ivan / FE 2016 3
The intensity of perception is depended upon displacement, velocity and acceleration amplitudes,
duration of exposure and vibration frequency. According to Bachmann et al. (1994), perceptibility in
the range 1 to 10 Hz is proportional to acceleration, while in the range 10 to 100 Hz perceptibility is
proportional to velocity. Human perception of vibration depending of peak acceleration amplitude is
shown in Table 1.
2.2. Building response to vibrations
Vibrations in engineering structures are restricted by serviceability limit states. Recommended values
are mainly given for particle velocity. Those values are empirical and they depend on the type of the
structure, type of soil, type of excitation, frequency content and duration of exposure. Tolerable values
vary for different countries and structures and there is no criterion that can satisfy all requirements.
Most of the criteria reduce probability of appearance of damage to acceptably low levels but do not
guarantee total absence of it. Examples of recommended values are shown in Tables 2 and 3.
Table 2. Standard values for piling, sheet piling, vibratory compaction and traffic (Bachmann et al., 1994)
Building class
Frequency range where the
standard value is applicable
[Hz]
Max. resultant
velocity vi
[mm/s]
Estimated max. Vertical
particle velocity vmax
[mm/s]
Class 1 – Industrial buildings
of reinforced concrete, steel
construction
Class 2 – Buildings on
concrete foundation with
concrete or brick walls
Class 4 – Buildings with brick
cellar walls, upper apartment
floors on wooden beans
Class 4 – Especially sensitive
buildings and historical
buildings
10-30
30-60
10-30
30-60
10-30
30-60
10-30
30-60
12
12-18
8
8-12
5
5-8
3
3-5
7,2-12
7,2-18
4,8-8
4,8-12
3-5
3-8
1,8-3
1,8-5
Table 3. Recommended values for vibratory compactor (Bachmann et al., 1994)
Maximum vertical particle
velocity [mm/s] Effect on building
2
5
10
10-40
Risk of damage to ruins and buildings of great historical value
Risk of cracking in normal residential buildings with plastered walls and ceilings
Risk of damage to normal residential buildings (no plastered walls and ceilings)
Risk of damage to concrete buildings, industrial premises, ect.
3. Material
Floor and roof slabs and frame elements (beams and columns) were made from normal conventional
C30/37 concrete with characteristic compressive cylinder strength at 28 days fc = 30 N/mm2, secant
modulus of elasticity Ecm = 32 000 N/mm2 and density ρc = 2 400 kg/m
3 (CSI, 2009).
Tower of the wind turbine is made from normal conventional C40/50 concrete with characteristic
compressive cylinder strength at 28 days fc = 40 N/mm2, secant modulus of elasticity Ecm = 35 000
N/mm2 and density ρc = 2 400 kg/m
3 (CSI, 2009). Poisson’s ratio is taken equal to 0,2 (CEN 2002).
LUČIĆ Sanda, KRAUS Ivan / FE 2016 4
4. Geometry
Geometry of structural elements is provided in Table 4. Floor and roof solid reinforced concrete slabs
are 18 cm thick. Height of each level is equal 3 m while total height of structure is 33 m. Plan
dimensions of square plan shaped structure are 18x18 m (building Q) while rectangular shaped
structure has plan sides ratio 1:2,5 (18x45 m – building R).
Table 4. Geometry of structural elements
Element Geometry [cm]
Beam bb/hb
Beam length
Column bb/hb
Column height
Wind turbine’ pole Dbottom;Dtop
Wind turbine’ pole height
Slab thickness
30/50
300
50/50
300
40;20
300
18
5. Loading
5.1. Dead load
The structural analysis program SAP2000 (CSI, 2009) calculates the self weight of all structural
elements. Weight of floor layers for floor slabs was taken into account by uniformly distributed load
equal to 2,5 kN/m2, while uniformly distributed load added on roof slab is 4 kN/m
2. Those values are
taken as proposed by Džakić, Kraus and Morić (2012).
5.2. Live load
Live loads are also taken as suggested by Džakić, Kraus and Morić (2012). Characteristic values of
uniformly distributed load are determined according to category of use - 3 kN/m2 for floor slabs
(classrooms and offices) and 0,75 kN/m2 for roof slab.
5.3. Wind turbine loads
Wind turbine selected for this project is Bergey Excel 1kW wind turbine with power rating of 1000 W
and 2,5 m diameter. It is horizontal, upwind and has three fixed pitch fibreglass blades. Blades are
exceptionally strong because they are densely packed with glass reinforcing fibers that run the full
length of the blade (Bergey, 2003). Major components of the Excel 1 wind turbine are shown in Figure
1 and main characteristics of turbine are shown in Table 5. Turbine is mounted on concrete pole and
the rotational centre of the turbine blades is 3 m above the roof of the building.
Figure 1. Major components of Bergey Excel 1kW (Bergey, 2003)
LUČIĆ Sanda, KRAUS Ivan / FE 2016 5
Table 5. Characteristics of Bergey Excel 1kW (Bergey, 2003)
Bergey Excel 1 kW
Start-up wind speed
Cut-in wind speed
Cut-out wind speed
Max. design wind speed
Rated rotor speed
Rated power
Type
Rotor diameter
Turbine weight
Blade pitch control
Overspeed protection
3 m/s
2,5 m/s
None
54 m/s
490 RPM
1000 kW
3 blade upwind
2,5 m
34 kg
None, fixed pitch
AUTOFURL
Process of wind turbine modelling consists of several stages. Primarily, it was necessary to make a
model of wind turbine which was done using program Ashes 1.2 (Simis, 2013). Main purpose of wind
turbine modelling was to get output signal in form of time history which will be applied at the top
node of the wind turbine’ pole placed a top of the structure. Output signal generated in program Ashes
1.2 was in form of acceleration in time with time step of 0,1 s for two different wind load cases (Table
6). Both load cases are defined as recommended by CEN (2006) to assess dynamic behaviour of the
turbine in order to ensure that the system does not exhibit excessive vibrations. The input signal for
each load case is filtered so it covers frequency range of possible vibrations produced by small-scale
urban wind turbines. This way we cover all possible vibrations that may result from vibration of the
pole, vibration of the blades or wind flow.
Table 6. Wind turbine load cases
Load Case Wind Speed [m/s] Time of Simulation [s]
Case 1- normal operating wind speed
Case 2 – maximum wind speed
5
20
300
300
Wind turbine operating load is applied on the top node of the wind turbine pole placed on the building
roof. Input signal for SAP2000, generated using Ashes 1.2, was defined by records of acceleration in
time for three different directions. For the sake of brevity, Figures 2 and 3 show time histories for
direction x and z. Flow of wind in direction x is of particular interest since that is the direction of
attack of wind while the vibrations acting in z direction influence the behaviour of slabs and thus
influence humans.
Figure 2. Displacement of top node of tower for Case 1: direction x
-4
-3
-2
-1
0
1
2
3
0 5 10 15 20 25 30 35 40 45 50 55 60
Dis
pla
cem
ent [
mm
]
Time [s]
LUČIĆ Sanda, KRAUS Ivan / FE 2016 6
Figure 3. Displacement of top node of tower for Case 1: direction z
6. Numerical models
The numerical analysis of structures and soil-structure-wind turbine system was performed using
structural analysis program SAP2000. Buildings selected for this project are two eleven-story frame
structures regular in plan and elevation (Image 4). The buildings are shallow-founded and modelled as
linear-elastic. The foundation ground is modelled in two ways, namely by using: i) springs and ii) the
fixed-base assumption. Soil modelled by fixed supports represents soil category A (solid rock) while
the one modelled by springs correspond to the ground category C. Vertical and horizontals springs are
defined using expressions given by Gazetas (1983). Moreover, two cases of live loads are considered:
live load in 50% and 100% amount.
Figure 4. Cases modelled in SAP2000
In further text, results will be presented for different models named e.g. RF50 or QS100, where first
letter indicates plan shape of building (Rectangular or Quadratic), the second one marks foundation
model or type of the soil (Fixed or Spring), while the number corresponds to amount of live load
applied on model (50% or 100%).
-0,004
-0,0035
-0,003
-0,0025
-0,002
-0,0015
-0,001
-0,0005
0
0 5 10 15 20 25 30 35 40 45 50 55 60
Dis
pla
cem
ent [
mm
]
Time [s]
Model structure
Building Q
Soil A; 100% live load
Soil A; 50% live load
Soil C; 100% live load
Soil C; 50% live load
Building R
Soil A; 100% live load
Soil A; 50% live load
Soil C; 100% live load
Soil C; 50% live load
LUČIĆ Sanda, KRAUS Ivan / FE 2016 7
7. Results and discussion
Parametric analysis provides results in light of displacement response spectrums and acceleration
response spectrums taken from characteristic structural elements (slabs) on different floors. In this
chapter, characteristic values for nodes shown at Figure 5 are presented and compared with code-
based thresholds.
Figure 5. XY view (top) and XZ view (bottom) of building
LUČIĆ Sanda, KRAUS Ivan / FE 2016 8
7.1. Resulting vibrations for Load Case 1
Considering that acceleration values (Figure 6) in nodes “A” are higher than in nodes “B”, it can be
concluded that vibrations caused by wind turbine are more disturbing for people near building edges.
However, this does not apply on QF50 and RF50 models. In these two cases, acceleration values are
getting higher while approaching the centre of the building. In all modelled cases, vibrations are the
strongest in 10th floor, second from the top.
Figure 6. Maximum acceleration values
Red line (see Figure 6) represents limit value of 0,315 m/s2. For acceleration amplitude bigger than
this value, living beings are feeling a small degree of discomfort. However, maximum amount for Q
shaped model on springs with full amount of live load does exceed value of 0,5 m/s2 – value that
represents boundary between small and fairly amount of discomfort (see Table 1).
Figure 6 shows that vibration level is higher for buildings based on soft ground. Also, it can be noted
that for Q shaped building based on solid rock with decrease of live load amount, vibrations are
raising, while for same shape structure based on soil category C decreasing amount of live load
implicates lower particle acceleration values. For R shaped structure, regardless of the soil type,
vibrations are more disturbing for people for lower-intensity load.
Values of velocity amplitude are presented on Figure 7. As well as in case of acceleration, the highest
values for each node are recorded at 10th floor. Red line (see Figure 7) marks maximum tolerable value
of particle velocity. Maximum velocity for Q shaped structure on springs with full amount of live load
goes beyond 10 m/s which means that this kind of vibrations are dangerous for structure and its
structural and non-structural elements. Irrespective of soil category, higher amount of load acting on
structure influences differently on structures with different plan shape: for Q shaped building, velocity
drops while for R shaped structure velocity values are raising.
0,21
0,26
0,57
0,38
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0,4
0,45
0,5
0,55
0,6
0,65
Max
imum
acc
eler
atio
n [m
/s²]
Q-fixed-100 - A2 Q-fixed-50% - B2Q-spring-100% - A2 Q-spring-50% - A2
Q Building
0,09
0,16
0,25 0,25
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0,4
0,45
0,5
0,55
0,6
0,65
R-fixed-100 - A2 R-fixed-50% - B2
R-spring-100% - A2 R-spring-50% - A2
R Building
0,21
0,26
0,57
0,38
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0,4
0,45
0,5
0,55
0,6
0,65
Max
imum
acc
eler
atio
n [m
/s²]
F100 F50 S100 S50
LUČIĆ Sanda, KRAUS Ivan / FE 2016 9
Figure 7. Maximum velocity values
Elastic acceleration spectra in view of plan shape and soil category for z direction and full amount of
live load for Load Case 1 are presented at Figures 8 and 9. It can be generally noticed that acceleration
values are higher for structures based on soft soil when compared to the counterpart founded on rock.
Considering the fact that frequency is inversely proportional to period, these graphs can be used to
discuss sensitivity of structural elements to vibrations of certain frequency. These spectra show that
slabs on same verticals are sensitive to similar frequencies. Figure 8 (left, soil category A) shows that
“A” slabs (those near building edges) are particularly sensitive to frequency of 2,5 Hz while for “B”
slabs peak acceleration value is reached at approximately 1 Hz. “A” slabs of building based on soft
ground (Figure 8, right) will be most affected by vibrations with frequency value of 1,67 Hz and for
“B” slabs the critical value is 2,5 Hz.
Figure 8. Spectrum for building Q with 100% load: soil category A (left), soil category C (right)
4,64 4,51
15,11
10,18
0
2
4
6
8
10
12
14
16
Max
imum
vel
ocit
y [m
m/s
]
Q-fixed-100 - A2 Q-fixed-50% - B2
Q-spring-100% - B2 Q-spring-50% - A2
Q Building
1,75
3,60
6,01
8,13
0
2
4
6
8
10
12
14
16
R-fixed-100% - A2 R-fixed-50% - B2
R-spring-100% - A2 R-spring-50% - B2
R Building
0,21
0,26
0,57
0,38
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0,4
0,45
0,5
0,55
0,6
0,65
Max
imum
acc
eler
atio
n [m
/s²]
F100 F50 S100 S50
0
200
400
600
800
1000
0 0,4 0,8 1,2 1,6 2 2,4 2,8
Acc
ele
rati
on
[mm
/s²]
Period [s]
0
500
1000
1500
2000
2500
3000
3500
4000
0 0,4 0,8 1,2 1,6 2 2,4 2,8
Akc
ele
raci
ja [m
m/s
²]
Period [s]
A1
A2
A3
B1
B2
B3
LUČIĆ Sanda, KRAUS Ivan / FE 2016 10
Figure 9. Elastic spectrum for building R with 100% load: soil category A (left), soil category C (right)
Figure 9 shows nearly equal critical values for both verticals and for both ground types: for soil
category A relevant value is 2,5 Hz, while the corresponding value for soil category C is around 1,67
Hz.
Further, elastic acceleration spectra for nodes A1, A2 and A3 for different soil categories and different
live load amount in z direction and Load Case 1 are presented at Figures 10 and 11. It can be seen that
critical values are different for different soil categories what demonstrates importance of soil type and
its impact on building behaviour. Structure founded on solid ground modelled by fixed joints has
higher stiffness value when compared to the same building model on soil of category C which is
modelled using springs. Due to higher stiffness, vibrations are less perceptible; therefore acceleration
values are significantly lower. Also, apart from Q shaped structure with half amount of live load, peak
acceleration for fixed based structure is reached by lower value of period, hence higher frequency,
than in case of structure on springs.
Figure 10. Elastic spectrum for building Q on A and C soil category: 100% live load (left), 50% live load (right)
Figure 11. Elastic spectrum for building R on A and C soil category: 100% live load (left), 50% live load (right)
0
100
200
300
400
500
600
0 0,4 0,8 1,2 1,6 2 2,4 2,8
Acc
ele
rati
on
[mm
/s²]
Period [s]
0
200
400
600
800
1000
1200
1400
1600
1800
0 0,4 0,8 1,2 1,6 2 2,4 2,8
Period [s]
A1
A2
A3
B1
B2
B3
0
500
1000
1500
2000
2500
3000
3500
4000
0 0,4 0,8 1,2 1,6 2 2,4 2,8
Acc
ele
rati
on
[mm
/s²]
Period [s]
0
500
1000
1500
2000
2500
3000
3500
4000
0 0,4 0,8 1,2 1,6 2 2,4 2,8
Akc
ele
raci
ja [m
m/s
²]
Period [s]
A1 (F)
A2 (F)
A3 (F)
A1 (S)
A2 (S)
A3 (S)
0
200
400
600
800
1000
1200
1400
1600
1800
0 0,4 0,8 1,2 1,6 2 2,4 2,8
Acc
ele
rati
on
[mm
/s²]
Period [s]
0
200
400
600
800
1000
1200
1400
1600
1800
0 0,4 0,8 1,2 1,6 2 2,4 2,8
Akc
ele
raci
ja [
mm
/s²]
Period [s]
A1 (F)
A2 (F)
A3 (F)
A1 (S)
A2 (S)
A3 (S)
LUČIĆ Sanda, KRAUS Ivan / FE 2016 11
In Figure 11 it can be seen that spectra for building with R shaped plan based on soft soil are different
for different load amount applied on slabs, while for building on solid rock amount of load does not
significantly impact on spectral acceleration values or spectrum shape. Even though acceleration
values for model on springs are generally higher for higher load, for period of 0,8 s, acceleration is
lower for building with higher load value while at period of 1 s, acceleration values are the same for
both load amounts.
7.2. Comparison of Load Case 1 and Load Case 2
Observing the resulting vibrations for two load cases defined in Table 6, it can be concluded that
values of both acceleration and velocity are multiple rising with increasing of wind speed. Figure 12
provides comparison of maximum acceleration values for two different wind speeds: 5 m/s (Load Case
1) and 20 m/s (Load Case 2). In cases where values are crossing over the red line, vibrations are
extremely uncomfortable for human beings.
Figure 12. Comparison of maximum acceleration values: Load Case 1 (left) and Load Case 2 (right)
Figure 13 shows maximum velocity values for mentioned load cases for fixed base structure. Load
Case 1 gives acceptable results from the standpoint of the serviceability with maximum velocity value
significantly below the permissible level. Analysis for wind speed of 20 m/s gives more than six times
higher value of particle velocity than allowed hence there is a serious danger of failure of structure
exposed to wind turbine operating load.
Figure 14 provides transfer functions for node with maximum recorded acceleration values – node A2
on Q shaped building with full amount of load based on soft soil. Functions for each direction are
calculated by dividing output (structural vibration) and input (vibration of the top of the turbine)
signals pointing out amplified frequencies by structural members. The effect of amplification is
extremely high in vertical direction and it is most prominent for frequencies near to 1 Hz. For x
direction, vibrations of the top of the tower are lower or the same as the vibrations of the slabs, while
amplification for y direction rises until reaching the period value of 0,6 s (1,67 Hz), than drops till 1 s
period (1 Hz), and after this point, it keeps raising with increasing the period value.
0,21 0,26
0,090,16
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
Max
imum
acc
eler
atio
n [m
/s²]
Q-fixed-100 - A2 Q-fixed-50% - B2
R-fixed-100% - A2 R-fixed-50% - B2
5 m/s
3,39
4,29
1,40
2,55
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
Q-fixed-100 - A2 Q-fixed-50% - B2R-fixed-100% - A2 R-fixed-50% - B2
20 m/s
0,21
0,26
0,57
0,38
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0,4
0,45
0,5
0,55
0,6
0,65M
axim
um a
ccel
erat
ion
[m/s
²]
QF100 QF50 RF100 RF50
LUČIĆ Sanda, KRAUS Ivan / FE 2016 12
Figure 13. Comparison of maximum velocity values: load Case 1(left), load Case 2 (right)
Figure 14. Amplification of frequency for node A2: x and y direction (left), z direction (right)
8. Conclusion
Although wind turbine installation in urban areas contributes to production of “clean” energy, this
trend has its undesirable consequences too. Owning to its high tip-speed ratio, therefore high rotational
speed, small wind turbines can be dangerous at high wind speed conditions. Additionally, they often
produce loud noise and cause vibrations of structure elements. In this case study, we have come to a
conclusion that vibrations caused by only one small-scale wind turbine placed on the roof edge of 11
story building can cause serious problems for both structure and people who spend time inside it. For
normal operational wind speed (5 m/s), vibration will not have significant negative effect on people
but they will cause serviceability problems in structure. However, by increasing wind speed, vibration
level will also get higher. In case that wind turbine operates at maximum wind speed given for Osijek
4,64 4,511,75
3,60
0
10
20
30
40
50
60
70
80
Max
imum
vel
ocit
y [m
m/s
]
Q-fixed-100 - A2 Q-fixed-50% - B2R-fixed-100% - A2 R-fixed-50% - B2
5 m/s
74,6473,33
28,58
59,32
0
10
20
30
40
50
60
70
80
Max
imum
vel
ocit
y [m
m/s
]
Q-fixed-100 - A2 Q-fixed-50% - B2R-fixed-100% - A2 R-fixed-50% - B2
20 m/s
0,21
0,26
0,57
0,38
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0,4
0,45
0,5
0,55
0,6
0,65
Max
imum
acc
eler
atio
n [m
/s²]
QF100 QF50 RF100 RF50
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
5
0 0,4 0,8 1,2 1,6 2 2,4 2,8
Acc
ele
rati
ons
rat
io
Period [s]
X direction Y direction
0
2000
4000
6000
8000
10000
12000
14000
0 0,4 0,8 1,2 1,6 2 2,4 2,8
Acc
ele
rati
on
+s
rati
o
Period [s]
Z direction
LUČIĆ Sanda, KRAUS Ivan / FE 2016 13
area, it will generate vibrations seriously harmful for people as well as for the structure and its
structural and non-structural elements. Vibrations caused by small wind turbine are most disturbing for
people who are on 10th floor, second from the top. Also, vibration level rises while approaching edges
of building. They are generally more noticeable for building with Q shaped plan and for buildings
based on soft soil. Since vibration level for maximum wind speed (20 m/s) is overly high, it is
necessary to discuss and install optimal type of damper device in order to decrease vibration level to
acceptable level. In order to fully define all consequences of wind energy harvesting in urban areas
and the way each of them affect buildings and people, it is necessary to carry out further researches
varying different parameters such as soil type, plan shape, wind speed, position of wind turbine.
Acknowledgment
Authors of this paper would like to express their gratitude to COST Action TU1304 (WINERCOST)
for their support and for creating opportunities for research in the field of wind power technology.
Furthermore, thanks to Dr. Thomassen who generously allowed the use of program Ashes 1.2.
Without their support, this research would not be possible.
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