dynamic architecture and analysis of wind loads

Dynamic Architecture And Analysis Of Wind Loads Loads On High Rise Structures

1. INTRODUCTION

Wind is air in motion relative to the surface of the earth. The primary cause of wind is traced to earth‘s rotation and differences in terrestrial radiation. The radiation effects are primarily responsible for convection either upwards or downwards. The wind generally blows horizontal to the ground at high wind speeds. Since vertical components of atmospheric motion are relatively small, the term ‗wind‘ denotes almost alm ost exclusively the horizontal wind, vertical winds are always identified as such. The wind speeds are assessed with the aid of anemometers or anemographs which are installed at meteorological observatories at heights generally varying from10 to 30 metres above ground. Wind has two aspects. The first a beneficial one, that its power can be used to generate power, sail boats and to cool down temperature on a hot day. The other a parasitic one, that it loads any and every object that comes in its way. The latter is an aspect a civil engineer is concerned with, since the load caused has to be sustained by the structure with the specified safety. All civil and industrial structures s tructures have thus to be designed to resist wind loads. Buildings are defined as structures utilized by the people as shelter for living, working or storage. As now a days there is shortage of land for building more buildings at a faster faste r growth in both residential and industrial areas the vertical construction is given due importance because of which Tall Buildings are being built on a large scale. Wind in general has two main effects on the Tall buildings: 

Firstly it exerts forces and moments on the structure and its cladding



Secondly it distributes the air in and around the building mainly termed as Wind Pressure

Wind load on a Tall building can be determined by:



Analytical Method given in the code IS 875: part 3-1987 which is given by

A.G.Davenport. 

Estimation of Wind Load through Wind tunnel testing with a scaled building model

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Dynamic Architecture And Analysis Of Wind Loads Loads On High Rise Structures Sometimes because of unpredictable nature of wind it takes so devastating form during some Wind Storms that it can upset the internal ventilation system when it passes into the building. For these reasons the study of air -flow is becoming integral with the planning a building and its environment.

One of the main beneficial aspects of wind is that it is a renewable source of energy. The adverse effect of wind loading on a building can be used to harness sustainable energy .

Dynamic architecture is an innovative technology which has been proposed to make this possible.

The Dynamic Architecture project is innovative in design and building sustainability, therefore the project recognizes environmental care and industrial production process as key points in the buildings of the future.

In particular, it is based on three fundamental concepts: it is DYNAMIC because each floor can rotate independently from others allowing the building to change its shape continuously, it is GREEN because it produces its own energy from the wind and from the sun; it is INDUSTRIALLY PRODUCED being made of pre-fabricated modules, then assembled on site

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Dynamic Architecture And Analysis Of Wind Loads On High Rise Structures 2.General

Wind is air in motion relative to the surface of the earth. The primary cause of wind is traced to earth‘s rotation and differences in terrestrial radiation. The radiation effects are primarily responsible for convection either upwards or downwards. The wind generally blows horizontal to the ground at high wind speeds. Since vertical components of atmospheric motion are relatively small, the term ‗wind‘ denotes almost exclusively the horizontal wind, vertical winds are always identified as such. The wind speeds are assessed with the aid of anemometers or anemographs which are installed at meteorological observatories at heights generally varying from 10 to 30 metres above ground. Very strong winds (greater than 80 km/h) are generally associated with cyclonic storms, thunderstorms, dust storms or vigorous monsoons. A feature of the cyclonic storms over the Indian area is that they rapidly weaken after crossing the coasts and move as depressions/lows inland. The influence of a severe storm after striking the coast does not, in general exceed about 60 kilometres, though sometimes, it may extend even up to 120 kilometres. Very short duration hurricanes of very high wind speeds called Kal Baisaki or Norwesters occur fairly frequently during summer months over North East India. The wind speeds recorded at any locality are extremely variable and in addition to steady wind at any time, there are effects of gusts which may last for a few seconds. These gusts cause increase in air pressure but their effect on stability of the building may not be so important; often, gusts affect only part of the building and the increased local pressures may be more than balanced by a momentary reduction in the pressure elsewhere. Because of the inertia of the building, short period gusts may not cause any appreciable increase in stress in main omponents of the building although the walls, roof sheeting and individual cladding units (glass panels) and their supporting members such as purlins, sheeting rails and glazing bars may be more seriously affected. Gusts can also be extremely important for design of structures with high slenderness ratios. The liability of a building to high wind pressures depends not only upon the geographical location and proximity of other obstructions to air flow but also upon the characteristics of the structure itself. The effect of wind on the structure as a whole is determined by the combined action of external and internal pressures acting upon it. In all cases, the calculated wind loads act normal to the surface to which they apply. 3

Dynamic Architecture And Analysis Of Wind Loads On High Rise Structures The stability calculations as a whole shall be done considering the combined effect, as well as separate effects of imposed loads and wind loads on vertical surfaces, roofs and other part of the building above general roof level. Buildings shall also be designed with due attention to the effects of wind on the comfort of people inside and outside the buildings. 2.1. WIND SPEED AND PRESSURE 2.1.1 Nature of Wind in Atmosphere —

In general, wind speed in the atmospheric boundary layer increases with height from zero at ground level to a maximum at a height called the gradient height. There is usually a slight change in direction (Ekman effect) but this is ignored in the code. The variation with height depends primarily on the terrain conditions. However, the wind speed at any height never remains constant and it has been found convenient to resolve its instantaneous magnitude into an average or 2.1.2 Importance of Wind Loads on the Tall Buildings

Buildings are defined as structures utilized by the people as shelter for living, working or storage. As now a days there is shortage of land for building more buildings at a faster growth in both residential and industrial areas the vertical construction is given due importance because of which Tall Buildings are being build on a large scale.

Wind in general has two main effects on the Tall buildings:

Firstly

it exerts forces and moments on the structure and its cladding

Secondly

it distributes the air in and around the building mainly termed as Wind

Pressure

Sometimes because of unpredictable nature of wind it takes so devastating form during some Wind Storms that it can upset the internal ventilation system when it passes into the building. For these reasons the study of air -flow is becoming integral with the planning a building and its environment.

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Dynamic Architecture And Analysis Of Wind Loads On High Rise Structures Wind forces are studied on four main groups of building structures :

i. Tall Buildings ii. Low Buildings iii. Equal-Sided Block Buildings iv. Roofs and Cladding

Almost no investigations are made in the first two categories as the structure failures are rare, even the roofing and the cladding designs are not carefully designed, and localised wind pressures and suctions are receiving more attention. But as Tall buildings are flexible and are susceptible to vibrate at high wind speeds in all the three directions(x, y, z) and even the building codes do not incorporate the expected maximum wind speed for the life of the building and does not consider the high local suctions which cause the first damage. Due to all these facts the Wind Load estimation for Tall Buildings are very much important .

2.2 Codal criteria for the buildings to be examined for Dynamic Effects of Winds [BIS (1987)]

Flexible slender structures and structural element s shall be investigated to a certain the importance of wind induced oscillations or excitations along and across the direction of wind. In general, the following guidelines may be used for examining the problems of wind Induced oscillations:

a) Buildings and closed structures with a height to minimum lateral dimension ratio of more than about 5.0, and b) Buildings and closed structures whose natural frequency i n the first mode is less than1.0 Hz.

Any building or structure which satisfy either of the above two cri teria shall be examined for dynamic effects of wind.

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Dynamic Architecture And Analysis Of Wind Loads On High Rise Structures 2.3.Response Parameters

Wind induced response of a tall building is a function of many parameters. These include the geometric and dynamic characteristic of building as well as the turbulence characteristic of the approach flow. A few analytical approaches are available for the estimation of the wind induced response of the tall buildings in along and across wind direction.

Wind Direction

Along Wind

Across Wind

Fig. 1 Along and Across Wind Response

Under the action of wind flow, structure experience aerodynamic forces that include the drag force and lift force. Drag (along -wind) force acting in the direction of the mean wind and the lift (across -wind) force acting perpendicular to that direction as shown in Fig 1.1. The Along-wind motion primarily results from pressure fluctuations in the windward and the leeward faces, which generally follow the fluctuations in the approach flow; at least in the low frequency range. The Across -wind motion is introduced by pressure fluctuations due to vortex shedding in the separated shear layers and wake flow field.

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Dynamic Architecture And Analysis Of Wind Loads On High Rise Structures 3.Estimation of the Wind load on Tall Buildings

Wind load on a Tall building can be determined by:

1. Analytical Method given in the code IS 875: part 3-1987 which is given by A.G.Davenport. The analytical method is usually acceptable for a building with regular shape and size and is almost based on the geometric properties of the building and without incorporating the effects of the nearby buildings. 2. Secondly the Estimation of Wind Load through Wind tunnel testing with a scaled building model used. In Wind Tunnel Testing for the structural design the Dynamic analysis of the scaled model building is done with Balendra‘s approach and for the cladding design the Surface Pressure Measurement analysis with Pressure Measurement system is done. Also the effects of the nearby buildings have been taken into consideration as the Interference effects on the buildings in a same procedure being used for an isolated building model. Wind Tunnel testing of an aero elastic model of a building can be used to find out wind loads. Moreover it is very difficult to fabricate an aero elastic model (because of its mass and stiffness distribution), an alternative approach given by Balendra (1996) can be used. As per this procedure a rigid model of the building is mounted on a high sensitive stiff force balance (HFFB), High frequency force balance (HFFB) measurements are utilized to measure the varying fluctuating wind loads on buildings in form of the forces FX, FY their corresponding moments MX, MY and the generalized torque MZ required for the determination of the Base Forces and Base Moments on the building in the Standalone condition and with the same method but with also incorporating the models of the nearby buildings, the Interference effects are taken in form of the values for Forces and Moments.

In the Surface Pressure Measurement analysis the Rigid Model Studies with pressure tapings or transducers have been used in the Wind Tunnel Testing. A Pressure Measurement system is used which records the values of the Pressure Coefficients on their respective taping locations on the building model in the Wind Tunnel. These Pressure distribution i.e., either pressure or suction on the faces of the building required for the cladding designs of the building. The pressure variations on the building models are also taken for both the conditions of Standalone and Interference effects.

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Dynamic Architecture And Analysis Of Wind Loads On High Rise Structures 3.1.Analytical Method given in the code IS 875: part 3-1987

b ) for any site shall be obtained from Design Wind Speed ( Vz ) — The basic wind speed ( V Fig. 1 and shall be modified to include the following effects to get design wind velocity at any height ( V z ) for the chosen structure: a) Risk level; b) Terrain roughness, height and size of structure; and c) Local topography. It can be mathematically expressed as follows: V z = V b k 1 k 2 k 3 where V z = design wind speed at any height z in m/s; k 1 = probability factor (risk coefficient) k 2 = terrain, height and structure size factor; and k 3 = topography factor. NOTE — Design wind speed up to 10 m height from mean ground level shall be considered constant. Risk Coefficient ( k 1 Factor ) — Figure 1 gives basic wind speeds for terrain Cat egory 2 as applicable at 10 m above ground level based on 50 years mean return period. The suggested life period to be assumed in design and the corres ponding k 1 factors for different class of structures for the purpose of design is given in Table 1. In the design of all buildings and structures, a regional basic wind speed having a me an return period of 50 years shall be used except as specified in the note of Table 1. Terrain, Height and Structure Size Factor ( k 2 Factor ) Terrain — Selection of terrain categories shall be made with due regard to the effect of obstructions which constitute the ground surface roughness. The terrain category used in the design of a structure may vary depending on the direction of wind under consideration.

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Dynamic Architecture And Analysis Of Wind Loads On High Rise Structures Wherever sufficient meteorological information is available about the nature of wind direction, the orientation of any building or structure may be suitabl y planned. Terrain in which a specific structure stands shall be assessed as being one of the following terrain categories: a) Category 1 — Exposed open terrain with few or no obstructions and in which the average height of any object surrounding the structure is less than 1.5 m. NOTE — This category includes open sea-coasts and flat treeless plains.

b) Category 2 — Open terrain with well scattered obstructions having heights generally between 1.5 to 10 m. NOTE — This is the criterion for measurement of regional basic wind speeds and includes airfields, open parklands and undeveloped sparsely built-up outskirts of towns and suburbs. Open land adjacent to sea coast may also be classified as Category 2 due to roughness of large sea waves at high winds.

c) Category 3 — Terrain with numerous closely spaced obstructions having the size of building-structures up to 10 m in height with or without a few isolated tall structures. NOTE 1 — This category includes well wooded areas, and shrubs, towns and industrial areas full or partially developed. NOTE 2 — It is likely that the next higher category than this will not exist in most design situations and that selection of a more severe category will be deliberate. NOTE 3 — Particular attention must be given to performance of obstructions in areas affected by fully developed tropical cyclones. Vegetation which i s likely to be blown down or defoliated cannot be relied upon to maintain Category 3 conditions. Where such situation may exist, either an intermediate category with velocity multipliers midway between the values for Category 2 and 3 given in Table 2, or Category 2 should be selected having due regard to local conditions.

d) Category 4 — Terrain with numerous large high closely spaced obstructions. NOTE — This category includes large city centres, generally with obstructions above 25 m and well developed industrial complexes.

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Dynamic Architecture And Analysis Of Wind Loads On High Rise Structures

FIG. 2 BASIC WIND SPEED IN m/s (BASED ON 50-YEAR R ETURN PERIOD)

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3.2 WIND TUNNEL

3.2.1 Wind Tunnel Instrumentation

Because most of the instruments used in wind tunnel tests are standard equipment discussed in many fluid mechanics texts, only a brief discussion of certain salient features of each important instrument will be given in this chapter.

3.2.2 Pitot tube

Pitot tube is the basic instrument used for measuring wind speed in a wind tunnel. It is based on the principle of conversion of kinetic energy to pressure at a stagnation point-the tip of the Pitot tube. The pressure differential sensed by the tube is proportional to the square of the velocity. This instrument is accurate, reliable, convenient, and economical. Furthermore, it does not require calibration. However, the Pitot tube is inaccurate at low speeds (about less than 5 m/s) and unsuitable for measuring turbulence.

3.2.3 Hot-Wire Anemometer

The sensing element of a hot-wire anemometer is a fine wire made of tungsten, platinum, or a special alloy. The wire is finer than human hair, and its length is only about 1 mm. The two ends of the wire are welded to two pointed electrodes (support needles) connected to a source of electricity. The turbulence in the wind causes changes of heat transfer from the wire, which in turn causes the resistance of the wire to fluctuate. The electronic circuit automatically adjusts the current going through the wire to keep the wire at constant temperature. Consequently, the velocity fluctuations (turbulence) can be determined from the fluctuations of the current through the wire. A variant of the hot wire anemometer is the hotfilm anemometer. The sensing element of a hot film is a coated metal film laid over a tiny glass wire. The rest are the same as for hot wires. The device is more robust than the hot wires and hence can be used not only in air but als o in water and contaminated environments. Hot-wire or hot-film anemometers can be used to measure both mean velocity and turbulence. They can measure rapid changes of velocities with frequency response higher than I kHz. Due to the small size of its sensing element, the velocity measured by a hot wire is often considered as the point velocity. Calibrations of hot wires are done by using a Pitot tube placed alongside a hot wire in a wind tunnel having approximately a uniform flow.

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Dynamic Architecture And Analysis Of Wind Loads On High Rise Structures 3.2.4 Manometers

Manometers are the standard equipment for measuring mean (time-averaged) pressure and for calibrating pressure transducers. Like Pitot tubes, manometers are accurate, reliable, and economical, and do not require calibration.

3.2.5 Pressure Transducers

Pressure transducers can measure both mean and fluctuating pressures and are discussed in section 3.4 for Surface Pressure Measurements.

3.2.6 Other Sensors

Many other transducers (sensors) may be needed in a wind tunnel study. These include strain gauges for measuring strain, accelerometers for measuring the accelerometers of models, and so on. They are standard sensors familiar to most structural engineers and hence not explained here.

3.2.7 Data Acquisition Systems

Modern data acquisition systems for wind tunnel tests consist of on-line processing of data by digital computers. Many mini and micro computers equipped with an analog to digital converter can perform such duties. The computer records the signals from various transducers, analyzes the signals, and prints or plots the results in desired forms. Such systems have brought great convenience to wind tunnel testing.

3.2.8 Flow Simulation

An issue for prime importance for experimental work with building models in a wind tunnel is the modeling of the characteristics of the atmospheric boundary layer (ABL) is to be modeled in the wind tunnel in order that structure models respond as closely as possible to their prototype behavior. The general criteria for ABL simulation include the duplication of vertical distribution of mean wind speed, longitudinal turbulence intensity as per the distribution in the field, and the integral scale of longitudinal turbulence, as closely as possible at the same geometric scale used for the building model. For tall buildings models, scale ratio of the order of 1:250 to 1:500 is appropriate.

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Dynamic Architecture And Analysis Of Wind Loads On High Rise Structures 3.2.9 Velocity Measurement in the Wind Tunnel

Measurements of the fluctuating velocity of the incoming flow in the wind tunnel have been made using a single hot wire probe. The hot wire probe and the associated instrumentation have been calibrated to give a voltage velocity relationship, to enable the conversion of the acquired voltages to the wind velocities. The calibration has been carried out in smooth flow, with turbulence level not exceeding 0.5% at 1m height in the test section. Static velocity head has been measured using a standard pitot-tube, connected to KBS Baratron Transducer and its digital display unit. Corresponding head has been converted to velocities and simultaneous values of voltage output at mean value unit of hot-wire s ystem were recorded for a range of wind speed between 2m/s and 20m/s

3.2.10 Establishing Flow Conditions

For flow measurements with the hot-wire system, a sampling frequency beyond 1 KHz and a 4-second length of record was adopted as minimum requirement (Gupta 1996). In the present study, instantaneous velocity fluctuations have been recorded using hot-wire probe at a sampling frequency of 4 KHz for a duration of approximately 4 seconds viz. a total of 16384 samples are recorded at each point for flow characteristic measurement. The mean velocity and longitudinal turbulence intensity variation obtained in the wind tunnel are presented in Fig 3. Theoretical velocity profile variation (solid line), corresponding to α = 0.18, is in good

agreement with measured values. The theoretical curve, which is called power law, is given as ( VZ / VO ) = ( Z / ZO ) α Where α = 0.18 VO is the velocity at ZO = 1m height from the tunnel floor. For different values of ( Z / ZO ), ( VZ / VO ) values are calculated. The values of mean velocity and longitudinal turbulence intensity at the topmost height of the building model have been found to be 10.78 m/sec.

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FIG 3 Variation In Velocity With Height During Flow Conditions

3.2.11 Surface pressure measurements

Holmes and Lewis (1986, 1987 and 1989) performed extensive experimental work on the fluctuating pressure measurements using a small diameter connecting tube to transmit the pressure from the connecting point, or tap, to the pressure transducer. Their authentic work has provided sufficient guidelines to develop a range near optimum systems for the measurement of fluctuating pressure on models of the buildings in wind tunnels. In the present study the choice of tubing system for pressure measurements is largely based on the work of Holmes and Lewis (1987). Surface pressure on the faces of the building models have been measured by providing steel taps of 1-mm internal diameter are flushed to model surface, which in turn are connected to small diameter tubing. Two stage restricted tubing has been used to measure pressure on each tap. Pressure measuring system consists of 500mm

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Dynamic Architecture And Analysis Of Wind Loads On High Rise Structures Vinyl tube with 40mm restrictor at 400mm from pressure point and a ZOC22 Scanivalve pressure scanner. Internal diameter of Vinyl tube is 1.5mm and internal diameter of the restrictor is 0.4 mm. This system is close to system suggested by Holmes and Lewis (1987) who obtained a linear response up to 200 Hz. The system used has therefore been considered suitable for study made and reported in this thesis. Reference static pressure has been measured in the tunnel floor at 1.5 m from the centre of test building. A 32 channel ZOC22 pressure scanner from Scanivalve Corporation Ltd. is used to measure pressure. The output signal in the form of voltage from pressure scanner has been recorded using PCL206 ADC Card. A computer program is developed to acquire the voltage signal from Scanivalve through PCL206 ADC Card Data has been recorded at a sampling of 1000 samples/sec/channel. 8192 samples of pressure data from each channel have been recorded, thus giving a record of approximately 20 seconds. All the readings have been repeated once to ensure repeatability In wind tunnel testing Rigid Model Studies with pressure tapings or transducers have been used. In which Rigid models are used to determine the fluctuating local pressures on the exterior surfaces of the building. Fig 4 shows the model of a building being tested in Wind Tunnel.

Fig 4 Model Of A Building Being Tested In A Wind Tunnel 16


It is common to use Perspex as the construction material. The exterior features of the building that are considered to be important with regard to the wind flow are simulated to the correct length scale; using architectural drawings. The model is instrumented with a large number of pressure taps (500 to 800) around the model surface to obtain a good distribution of pressures. More tapings are required in regions of high-pressure gradients, such as corners, Slits opening etc. The pressure tapings are connected by plastic tubing to miniature electronic pressure transducers which can measure the fluctuating pressures. The length of plastic tubing is kept as short as possible to minimize the damping of fluctuating pressures in the tubing. As it is uneconomical to use a single transducer for each pressure tapping, the transducer is mounted onto a pressure-scanning device, such as a Scanivalve, which automatically switches the pressure transducer between 40 to 50 pressure taps, one at a time. Pressure data is acquired by an on-line computer system capable of sampling data at a high speed. The setup is shown in the Fig 5

Fig 5 Setup on which Pressure data is acquired by an on-line computer system

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Dynamic Architecture And Analysis Of Wind Loads On High Rise Structures 4.DYNAMIC ARCHITECTURE

Fossil fuels make up more than two-thirds of the total world electrical energy consumption. A majority of the world‘s renewable energy is obtained from the sun, but a good percentage is also obtained by harnessing natural wind. In terms of wind technology, there are two major types of power producing turbines in operation. These are classified as the horizontal axis wind turbines (HAWT) and the vertical axis wind turbines (VAWT). Horizontal axis wind turbines are the most common type of wind turbines. In these turbines, the focus rotor shaft is pointed parallel to the direction of the wind while the blades move perpendicular to that direction, thus providing high overall efficiency. However, these turbines require a yaw mechanism in order to keep the hub pointing towards the wind flow direction. Vertical axis wind turbines orientate on the vertical axis where the focus rotor shaft is aligned vertically. These turbines are more compact in size and therefore allow easier maintenance since the nacelle components (gear box, generator, controller, and brake) are not mounted on the high tower unlike in the case of the horizontal axis wind turbines. The major difference aesthetically between these two types of wind turbine technologies lies in the working altitude. The horizontal axis wind turbines operate at a greater altitude, thus utilizing most of the available wind energy compared with the vertical axis wind turbine which operates at low altitude at variable wind speeds, shown in Fig. 1. Owing to the increasing urbanization rate in Dubai, significant energy consumption is utilized by high rise building structures. However, with the advances in research into new technology for more efficient energy production using renewable resources to cater for growing demand and to counter the dependency on the fossil fuels, the need for new low-energy consuming buildings is prominent. One such proposal is to incorporate horizontal axis wind turbines between floors of high-rise structures. The proposed arrangement utilizes the power generated to supply each residential apartment and also to rotate the floors, thus creating a dynamic structure.

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Fig 6 Schematic illustration of the two orientation types of wind turbine

Buildings utilize energy in two primary methodologies, first, to keep the interior as contented

as

achievable

through

optimizing

Heating,

Ventilation

and

Air-

Conditioning(HVAC) and secondly, to generate power to run the required domestic applications, all of which leading to an increase in resultant global CO2 emissions. Buildings are accountable for almost 40% of the global energy consumption and are responsible for approximately half of the world‘s greenhouse gas emissions. The majority of the world‘s renewable energy is directed from the sun, but a good percentage is also made up by harnessing the resource of natural wind. The potential of utilizing wind energy in India demands concentrated research planning, in order to estimate the vast benefits that can be achieved using this natural resource. Utilizing natural ventilation for maintaining satisfactory air quality in the interior is dependent on the supply of fresh air. The quantity of ventilation needed to ensure an adequate air quality indoors depends on the amount of the pollutant in a space. It is knows that the pollution level decreases exponentially with the airflow rate. Hence, the ideal airflow rate can be calculated by knowing the pollution intensity of the system. Due to the increasing urbanization rate in India, significant energy consumption is utilized by high-rise building structures. However, with the advances in research into new technology for more efficient energy generation using renewable resources to cater for growing demand and to counter the dependency on the fossil fuels, the need for this study has arisen in this India. Suitable planning of energy cognizant buildings requires a balance between the thermal performance of the building and the appropriate selection of techniques

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Dynamic Architecture And Analysis Of Wind Loads On High Rise Structures for heating and cooling. It also necessitates thermal comfort which comes from an adequate quality of the indoor climate. 4.1 DYNMIC TOWER, DUBAI

The tower consists of a tubular concrete core, layered with smooth triangular floors which can move at varying speeds and so create a vast combination of different shapes. The floors will comprise more than 2,000 prefabricated steel and aluminium pods, which will be manufactured in Italy. The pods will then be lifted into place with between 30 and 42 per floor and will appear to cantilever out from the core.

Fig 7 3D Model Of Rotating Tower, Dubai 20

Dynamic Architecture And Analysis Of Wind Loads On High Rise Structures A 360 degree rotation of each floor will take approximatel y an hour and a half, and the owners of each floor will be able to set the speed. The Dynamic Tower is the first skyscraper to be built entirely from prefabricated parts that are custom made in a workshop, resulting in fast construction and substantial cost savings. This approach, known as the Fisher Method, also requires far less workers on construction site while each floor of the building can be complete d in only seven days. The Dynamic Tower is also environmentally friendly, with the ability to generate electricity for itself as well as other buildings nearby making it the first building designed to be self powered. It achieves this feat with wind turbines fitted between each rotating floor. The 80story building will have up to 79 wind turbines, making it a true green power plant. The rotating tower is one of the green projects scheduled to be built In Dubai. Once completed, it will stand at 420mand will comprise 78 floors, each with the freedom to rotate about its own axis. The design (CAD) for this investigation comprises Fig. 10 CAD 1:200 scale model of the rotating tower Design eight individual floors from ground level in a 1:200 ratio, shown in Fig. 3. Detailed information about the dimensions of the structure is scarce. One important aspect is the spacing between individual floors which is 20 per cent of the floor height itself. This spacing is for accommodating the wind turbine blades integrated inside the building structure. The height of each floor is 5.2 m and; hence, the spacing is approximately 1 m.

Fig 8 Horizontal Axis Turbines Placed Between Floors 21

Dynamic Architecture And Analysis Of Wind Loads On High Rise Structures 4.1.1 Winwind 3.0 MW Wind Turbine

Fig. 9 Schematic of theWinWind 3.0MWwind turbine showing the major components

Fig. 9 is a schematic of the nacelle of the WinWind 3.0MW wind turbine showing its major components. A tapered roller bearing is used to connect the rotor hub to the gearbox casing. The bearing transfers the rotor loads directly to the main casing, in process keeping the drive train free from excessive rotor loads. The planetary gear train increases the rotating speed and transfers the torque to the low-speed permanent magnet generator. The frequency converter transfers the full generator power. The machine produces efficient and reliable power even at low to moderate wind speeds. The WinWind 3.0 MW Wind turbine operates on Multibrid technology. Multibrid is an upcoming and advanced concept in the performance of wind turbines which uses a planetary gear system along with a low-speed permanent magnet generator. The conceptual model consists of a single-stage planetary gear along with a low speed generator and a frequency convertor, with the main advantages being the elimination of high speed components thus keeping a higher strength to weight ratio. The mechanical forces are managed with the main bearing which is designed to undertake all the rotor loads. The turbine supports an all enclosed structure to shield the components from dust particles. This technology results in high efficiency starting from low wind speeds. Since the overall method is automatic, the power production and the generator control system are optimized and the maintenance levels required are significantly lower compared to the traditional system .

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Fig. 10 CAD 1:200 Scale Model Of The Rotating Tower Design 4.1.2 CFD MODEL

The CFD analysis was carried out using the ANSYS v12.1 commercial software package. The CAD model was imported directly and an enclosure created to provide the external wind environment. The enclosure was set with boundary walls of the macroclimate (the flow domain) at 2.5 times the distance from the nearest geometrical face to avoid reversed flow in the region, a methodology widely used and validated for natural ventilation [ 10, 11]. To establish the velocity entering and exiting the integrated wind turbine, two vertex points were created. The points were based on the entrance location of the air having the co-ordinates of (

−110, −50, 105) and the exit location of the air having the co-ordinates ( −80, −50, 105). The vertex points were created on the middle floor of the building geometry and are shown in Fig.

Fig. 11 Location of vertex measurement points for CFD results 23


Fig. 12 CAD model dimensions, front and top view 4.1.3 Boundary conditions

The geometry was analysed with varying wind speeds to ensure the precision of the results remain in accordance. The geometry was modelled as a solid structure to allow the air to pass around it, rather than through it in order to determine the variation in wind velocity from inlet to outlet. The k -epsilon turbulence model was used for each simulation as this is the most appropriate turbulence model for natural ventilation wind speeds of 5 m/s and less. The boundary conditions for the CFD model are displayed in Table 2. The flow inlet and outlet conditions were assigned as follows: the velocity inlet was used on the left hand side of the macroclimate (upstream), set at the operating velocity (as defined in Table 2). Pressure outlet was assigned to the opposing boundary wall (downstream). The remaining boundary walls of the macroclimate were set as symmetry to avoid recirculation of the flow shown in Fig. 6. Any unmeshed geometry, namely the building and turbine components, was named as wall, and the scheme used is the standard wall function, based on the proposal of Launder and Spalding. 4.1.4 CFD calculated flow visualization

Figure 7 is based on the front view of the geometry and displays the velocity contour obtained at a free-stream velocity of 3.67 m/s. As seen from the figure, there is a decrease in

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Dynamic Architecture And Analysis Of Wind Loads On High Rise Structures velocity as it approaches the turbine blades located in the gap between floors. The flow streamlines distribution is displayed in Fig. 8.The flow enters uniformly before shearing across the building windward façade creating an area of turbulence across the leeward façade. The velocity vectors are displayed in Fig. 9, with the flow direction coming in from left- to right-hand side of the figure. The flow is significantly reduced when leaving the structure between the floors, thus the mathematical model would not be accurate for the analysis.

Fig. 13 Velocity contours with external velocity of 3.67 m/s

Fig. 14 Velocity streamlines distribution with top view (external velocity of 3.67 m/s) 25


Fig.15 Velocity vectors representation with cross sectional view (external velocity of 3.67 m/s) 5.Conclusion

This report demonstrated the scope of generating power by implementing wind turbines inside the rotating tower geometry. The investigation proved that, by integrating the wind turbines inside the building configuration, a significant reduction in land set-up area for a horizontal axis wind farm was possible. With respect to electricity generation capability, the study revealed that the standard horizontal orientation of the wind turbine yielded 80% better results. On the other hand, similar power production is possible using the vertical orientation, at the expense of installing more number of equipment. Since the rotating tower will comprise of 78 floors, the investigation concluded that 46 scaled wind turbines in the vertical orientation would be sufficient to accommodate itself inside the building structure and therefore provide the essential power for the respective.

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Dynamic Architecture And Analysis Of Wind Loads On High Rise Structures REFFERENCE

[1] M. Asif, T. Muneer, R. Kelley, ―Life cycle assessment: a case study of a dwelling home in Scotland‖, Building and Environment 42 (2007) [2] WWD-3 Technical Specification. [Online] 2009. [Cited: September 24, 2009] Available from http://www.winwind.fi. [3] H. David Fisher, Rotating Tower Dubai, Rotating Tower Technology International Limited (UK) 2008 [4] F. Allard, ―Natural Ventilation in Buildings‖ – A design handbook (p1- 3), European Commission Directorate general for Energy Altener Program [5] B.R. Hughes and S.A.A. Abdul Ghani, ― Investigation of a windvent passive ventilation device against current fresh air supply recommendations‖, Energy and Buildings, 2008 [6] H.N. Chaudhry and B.R. Hughes, ―Computation al Analysis of Dynamic Architecture‖, Journal of Power and Energy, Article in press [7] G. Muller, F. Jentsch Mark and E. Stoddart, ― Vertical axis resistance type wind turbines for use in buildings‖, Renewable Energy 2008 [8] N. Mithraratne, ―Roof -top wind turbines for microgeneration in urban houses in New Zealand‖, Energy and Buildings 2009 [9] S. Shun, and A. Ahmed Noor, ―Utilizing wind and solar energy as power sources for a hybrid building ventilation device‖, Renewable Energy 2007 [10] A.S Bahaj, L. Myers, and P.A.B. James, ―Urban energy generation: Influence of micro wind turbine output on electricity consumption in buildings‖, Energy and Buildings 2006

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dynamic architecture and analysis of wind loads

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