WO2013135246A1

WO2013135246A1 - A load application unit, a test bench including the load application unit, methods and uses of the load application unit

Info

Publication number: WO2013135246A1
Application number: PCT/DK2013/050066
Authority: WO
Inventors: Morten Nørgaard Storm PEDERSEN; Kent Frank PEDERSEN; Claus Odsbjerg BECK; Karl Åge MAJ
Original assignee: R&D A/S
Priority date: 2012-03-13
Filing date: 2013-03-13
Publication date: 2013-09-19

Abstract

A load application unit comprising a fixed part adapted for securing the load application unit to a base structure, a moveable load application means adapted for being operatively connected to a device under test by means of a series of actuators serves to simulate the load the device under test can be subjected to. The moveable load application means comprises a front ring part coaxially connected to the fixed part by means of a hexapod system of three angularly distributed pairs of independently controllable linear actuators selected to move the moveable load application means and the device under test, and a main bearing comprising an outer ring part secured coaxially to the front ring part, and an inner ring part adapted for engaging a rotary shaft.

Description

A load application unit, a test bench including the load application unit, methods and uses of the load application unit . The invention relates to a load application unit, comprising a fixed part adapted for securing the load application unit to a base structure, and a moveable load application means adapted for being operatively connected to a device under test by means of a series of actuators.

When testing for example a nacelle it is desired to simulate the dynamic and/or static forces acting on the main bearing, shaft and/or hub of the nacelle, as well as on the bearing of the yaw system. It is common practice today to mount the nacelle in a test bench and connect its main shaft with a wind simulator, for example consisting of an axially mounted, rotating disc and a number of hydraulic actuators, that can act on the disc and thus create axial and radial forces and bending moments about the centre axis of the main shaft. Such a system is known from international patent application no. WO2007/144003. Systems of this structure have five degrees of freedom (DOF) , namely axial forces along the x-axis, and radial forces along the y-, and z well as bending moments about the y- and z-axes. Bending moment and/or torque about the main axis, the x-axis, is provided by an external main engine. Such systems have considerable limitation regarding the dynamic in the system, because the rotating disc has a large mass. The large mass ensures rigidity against the forces, which the actuator applies to the disc, so that it is the components of the nacelle, which yield, and not the disc. The large mass also causes large inertia and thus less dynamic.

US patent application no. US2005172729A1 relates to another kind of test bench for testing wind turbines. This known test bench comprises a test bed on which an assembly to be tested is mounted. The test bench has load application means for applying loads on the assembly. In order to be tested the assembly is mounted to a cylindrical support anchored to a foundation. The foundation is provided, in the area on which the cylindrical support is situated, with rails running in a direction perpendicular to the area occupied by a load application means for applying loads on the assembly to be tested, the cylindrical support structure being able to move on these rails, so as to adjust its distance from the load application means. The cylindrical support structure includes a rotary flange for the anchoring of the assembly to be tested, a ring gear fixed to the rotary flange, a series of geared motors with pinions engaging with the ring gear in order to actuate the flange, and a series of brakes capable of acting on a brake disc which is solidly connected to the rotary flange. The load application means comprises a moveable structure suspended from a fixed structure through several cardan and ball-and-socket joints and the moveable structure is related to said fixed structure through a complicated system consisting of a plurality of hydraulic, linear static actuators and hydraulic, linear dynamic actuators, by means of which the static and dynamic loads will be applied to the assembly to be tested. The moveable structure is a three-dimensional structure adopting an approximately truncated pyramidal shape, on the major base of which the connection means to the assembly to be tested are situated in a central position, whilst the jointing points of the dynamic actuators are located in a position coinciding with the vertices of this major base. This known test bench has various shortcomings, including being unable to rotate components of a device under test.

These known systems and load application units are also complicated structures, which are time-consuming to set up for test of a given unit. These known systems and load application units rely heavily on the interaction of many interconnected components. The individual function of each component and the cooperation of all components must perform perfectly. Defects in or malfunction of one or more of the many components have impact on the final test result. Thus dependability of the many components, each let alone or in common, is essential to avoid false test results. Due to the complexity of the known systems and load application units maintenance becomes very time- comsuming and expensive. There is a need within the art for alternative systems and load application units that are less vulnerable to defects and malfunctioning than known systems, for alternative systems and load application units that are versatile in view of being configured for various devices under test, and for systems and load application units that provide the option of applying six Degrees of Freedom (DOF) of load or translation/rotation . It is a main aspect of the present invention to provide an alternative system for dynamic and/or static load testing.

It is a further aspect of the present invention to provide a unit for application of load in a test bench for testing components of a wind turbine, in particular a nacelle.

It is a further aspect of the present invention to provide a system for dynamic load and/or static testing which is easier and faster to adapt for testing different devices.

It is a further aspect of the present invention to provide a system for high precision of applied loads from the load application unit on a device under test. It is a further aspect of the present invention to provide a system for dynamic and/or static load testing, which provides reliable test results.

It is a further aspect of the present invention to provide a system for dynamic and/or static load testing which can simulate natural operation conditions. It is a further aspect of the present invention to provide a system for dynamic and/or static load testing in which the number of individual load application components is reduced compared to prior art systems and load application units.

It is a further aspect of the present invention to provide a system for dynamic and/or static load testing which is less susceptible to failure and malfunctioning than prior art systems.

It is a further aspect of the present invention to provide a system for dynamic and/or static load testing in which measurement errors are reduced, in particular measurement errors due to friction loss and/or rolling resistance in the main bearing.

It is a further aspect of the present invention to provide a test bench implementing the load application unit.

It is a further aspect of the present invention to provide a method of using the load application unit.

It is a further aspect of the present invention to provide a system for applying very high static and/or dynamic torques to a nacelle with or without rotation of the nacelle main shaft.

The novel and unique whereby these and other aspects are achieved according to the invention consists in that the moveable load application means comprises

a front ring part coaxially connected to the fixed part by means of a hexapod system of three angularly distributed pairs of independently controllable linear actuators selected to move the moveable load application means and the device under test, in a pair of linear actuators each linear actuator has first ends anchored to the fixed part and second ends anchored to the front ring part,

and

- a main bearing comprising an outer ring part secured coaxially to the front ring part, and an inner ring part adapted for engaging a rotary shaft.

The main component of the load simulator, the load application unit, is a manipulator based on the principles known from a "Stewart-Gough platform", which principles are discussed in e.g. D. STEWART, A platform with six degrees of freedom, Proc. of the Institution of Mechanical Engineers, 180 (1965-66), pp. 371-386; and US patent no. 3,295,224. The fixed part of the load application of the present invention constitutes the base of the Stewart platform and the moveable load application means constitutes the platform of the Stewart platform. The load application unit according to the present invention is statically and kinematically determinate. Very accurate loads and positions can be applied to the device under test.

In an idle state of the load application unit the first ends of the pairs of linear actuators are in a plane substantially parallel to the plane of the respective second ends.

The hexapod of the moveable load application means according to the invention utilizes three pairs of actuators, which is considerably fewer than utilized in the complex prior art test bench of US patent application no. US2005172729A1. By the above-mentioned known kinds of tests the primary objects are application of force in different directions, however regarding the correct application of force this is subject to some uncertainty because control of the movement of the actuator is given priority. According to the present invention the actuators move the front ring part, and thus also the main bearing, radially and axially in relation to the centre axis of the load application unit. The force components applied by the linear actuators on the front ring part are transmitted to the shaft rotating in the main bearing to test the load capacity of a device under test connected to the rotary shaft. Thus the invention utilizes the unique construction of the hexapod to create the axial and radial forces used on testing for example nacelles in order to simulate the effects of for example wind load. The load application unit of the present invention enables application of shaft rotation, torque, bending moments and shear forces similar to those encountered by the nacelle due to the wind load. Thus the invention may e.g. serve to simulate real time wind loads to analyze the dynamic operation behavior of nacelles. The novel load application unit has six degrees of freedom for application of load and is not limited for use with nacelle or nacelle components. It is possible to test e.g. complete drive trains and components making up the drive train. Thus it is possible to apply load to almost all features of a given system, including coupled dynamic dependencies, such as those relating to main shaft, main shaft support bearings, bearing housings, gearbox, yaw drive system, and brake assembly .

In one embodiment of the load application unit according to the present invention the distance between the first ends of two linear actuators of a pair of linear actuators may be smaller than the distance between their respective second ends, as in a usual Stewart-Gough platform, to provide appropriate high radial displacement of the moveable load application means when operating the actuators. The reverse arrangement is however not excluded and in another embodiment of the load application unit the distance between the first ends of two linear actuators of a pair of linear actuators are smaller than the distance between their respective second ends. Even combinations of these embodiments may be possible in consideration of the device under test.

The main bearing can advantageously be one or more roller bearings capable of both absorbing large radial loads across the rotary shaft, e.g. loads corresponding to the weight of the rotor, and large axial forces along the shaft, e.g. forces corresponding to the wind pressure on the rotor. The main bearing may be of the kind that comprises a plurality of load bearing elements, such as rollers or spheres disposed between the inner ring part, the inner race, and a separate outer ring part, the outer race, that permits the inner ring part and the outer ring part to rotate relative to each other with minimum friction. The inner ring part can be brought to rotate by means of the rotary shaft in relation to the outer ring part due to the outer ring part being fixed to the front ring part . Preferably the main bearing can be a slewing bearing. The inner ring part, the outer ring part and the rolling elements of the slewing bearing may advantageously serve to effectively absorb and support axial and radial forces during load testing. Alternatively the main bearing can be e.g. a pair of spherical roller bearings, e.g. of the kind used as main bearings of common modern wind turbines. Suitable rolling elements include but are not limited to balls. Thus rolling elements can have any suitable shape or configuration, e.g. cylindrical, tapered, spherical, or polygonal. These kinds of bearings can rotate very stable and are able to carry considerable thrust load in addition to a high radial load. Moreover frictional torque is low under most load conditions. Thus by using roller bearings number and amount of variables stemming from the load application itself are insignificant compared to data measurements obtained from the devices under test. Hydrostatic bearings may be another suitable alternative for some test set- ups . It is important that the configuration of a main bearing is selected in dependency of the predominant types of loads acquired by the load application unit. When used in the present application the term "torque" is to be understood as the tendency of a force to produce rotation or torsion about an axis. Torque between two components is e.g. transferred by friction or shear connection between these two components, and thus e.g. dependent upon friction, e.g between a main shaft of the wind turbine and another shaft.

The invention attempts to simulate the conditions which e.g. a wind turbine is subjected to during use, in order to test a.o. stress and fatique. To that aspect the centre axis of the load application unit can be substantially horizontal or close to the tilt angle of the wind turbine, and not substantially vertical as normal when using Stewart-Gough platforms. Preferably, the centre axis of the load application unit can be at an angle of less than 10° to horizontal, preferably less than 8° to horizontal, more preferred less than 7° to horizontal, and more preferred 6° or less, such as even 5° to horizontal to simulate the conventionally used positive angle used to tower clearance of a wind turbine. By tilting the load application unit in relation to horizontal it is possible to subject e.g. a nacelle to conditions very close to the external and operative load conditions the nacelle must be able to withstand when subjected to wind load to achieve power generation . External and operative possible load conditions may for example result from oceanographic or meteorological conditions, and any mechanically powered machinery, and may even relate to erection, transport and maintenance of some or all of the components of the nacelle. The load application unit may be suited for application of loads to many kinds of devices including but not limited to any kind of drive trains, vehicles and motors. A few examples are e.g. automobiles, trains, larger vehicles for transportation, ships, and marine engines.

The inner ring may have a load platform protruding coaxially towards the device under test and serving as an interface for coupling the load application unit to various devices to be tested, e.g. by operating the main shaft of the device under test using the rotary shaft, which passes through the inner ring part of the main bearing, and the linear actuators for application of static and/or dynamic loads and torque to said device. If the load platform does not fit together with the device under test, an adaptor means enabling coupling the load application unit to the device can be introduced between the load platform and the device under test,

The load application unit may comprise a prime mover for driving the rotary shaft, e.g. an electric motor capable of application of heavy loads. The load application unit can be operated with or without the rotary shaft rotating depending on what is tested, the set-up and the device under test.

The load application unit may comprise a device for locking the rotation of the main bearing in order to be able to apply a fixed static torque to the device to be tested without interference from the prime mover. In this embodiment load application is achieved by operating the hexapod system of linear actuators to apply load to the locked rotary shaft and thus to any device coupled to said locked rotary shaft. The load application unit may be connected to the prime mover via a drive shaft coupling. The drive shaft coupling connects the shaft of the prime mover and the inner ring part of the main bearing of the load application unit in order to transmit power from the prime mover to the load application unit. Some drive shaft couplings can be used to control torque. Five Degrees of Freedom (F_x, F , F_z, M , M_z) of load are applied by the linear actuators. The sixth Degree of Freedom, the torque (M_x) , can e.g be transferred by means of the drive shaft coupling from the drive components of the prime mover to the load platform via the inner ring part of the main bearing or directly from the prime mover.

In summary the load application units can apply six degrees of load or translation/rotation (F /S , F /S , F /S , M /Θ , M /θ , Μ_ζ/Θ_ζ) wherein the symbols have the meaning stated below.

F_x Axial force (Thrust) M_x Drive torque (Rotor)

F_y Radial force (Crosswind) M_y Bending torque (Tilt)

F_z Vertical force (Gravity) M_z Bending torque (Yaw)

S_x Axial displacement (Thrust) θ_χ Rotation angle (Rotor)

S_y Lateral displacement (Crosswind)

θ_γ Rotation angle (Tilt)

S_z Vertical displacement (Gravity)

θ_ζ Rotation angle (Yaw)

The position of the prime mover can be behind the load application unit or the load application unit can be modified for using a prime mover in front of the front ring part of the load application unit.

Drive shaft couplings are expensive and a drive shaft coupling may no longer be needed if the prime mover is located in front of the front ring part of the load application unit. Nor may a main bearing in the load application unit be needed because the bearings of the prime mover can be used instead. Although not suited for some devices the latter embodiment and set-up may still be preferred for other devices in view of cost consideration, if possible.

The length of the coupling has an influence on the magnitude of the restoring forces and restoring torque coming from the end flanges of the drive shaft coupling (restoring loads) . In most cases minimisation of the restoring loads from the coupling is of great importance. A short coupling means large restoring loads and by having a long coupling the restoring loads are reduced .

A very accurate establishing of the displacement and position of a cylinder of a linear actuator can be measured if at least one linear length transducer is operatively associated with at least one of the linear actuators.

Similarly, the load application unit may further comprise at least one pressure sensor and/or load cell operatively associated with at least one of the first end or the second end of at least one of the linear actuators to measure very accurate resulting force of the cylinders of the linear actuators.

For some load applications it may be beneficial to include a load measuring unit between the adaptor means and the load platform of the load application unit. The load measuring unit can operate as a redundant system together with the above load cells of the linear actuators in order to increase the loading accuracy of the system. The load measuring unit may e.g. consist of two interfacing ends, which preferably would be bolted connections, one at each ends where the loads are transferred either by means of friction and/or shear. In- between the two interfacing ends a measuring arrangement is positioned. The measuring arrangement can preferably be a tube with a precise uniform thickness where strain gauges and/or load cells are mounted in order to determine at least one of the loads going through the load measuring unit. The measuring arrangement could also be a solid shaft or a mechanical device, which incorporate strain gauges and/or load cells in an appropriate configuration for measuring at least one of the transferred loads. The load application unit according to the invention may further comprise that at least one of the first ends and/or the second ends of the linear actuators are anchored to the fixed part and the front ring part, respectively, by means of one or more anchor means selected from spherical bearings, Charnier joints, bolted connections, and/or cardan joints to allow the first ends and/or the second ends to move in response to independent actuation of the linear actuators, thus allowing a linear actuator to move along and somewhat about its longitudinal cylinder axis and to follow the angular displacement, tilting and moving of the front ring part imparted to it by operating the linear actuators one at the time . To minimize or even eliminate considerations of friction in the anchor means such anchor means preferably are low friction anchor means. Using such reduce factors from the load application unit to be taken into account when calculating the load components and torque components the device under test has been subjected to during test.

Depending on the amount of load to be applied to a certain device under test the linear actuators can be hydraulic, pneumatic, mechanical or electrical linear actuators, or combinations thereof. Hydraulic actuators are preferred for very heavy load applications whereas pneumatic linear actuators may suffice for less heavy loads.

In an embodiment, which is versatile to modifications in view of being useful for various load applications, the diameter of the outline of the fixed part can be larger than the diameter of the front ring part. In such embodiments the hexapod appears as a truncated cone wherein the linear actuators, at least in idle state, all have longitudinal axes inclined towards the front ring part. This embodiment is a.o. economical to upgrade for larger load application. Thus at least in an idle state of a set of linear actuators their respective longitudinal axes may converge towards the fixed part and intersect each other at an angle equal to or less than 100°, alternatively equal to or less than 90°, alternatively equal to or less than 80°, alternatively equal to or less than 70°, alternatively equal to or less than 60°, alternatively equal to or less than 50°, alternatively equal to or less than 40°, alternatively equal to or less than 30°, alternatively equal to or less than 20°, alternatively equal to or less than 10°. The appropriate angle of intersection of the converging axis of a pair of linear actuators depends a.o. on the device to be tested, the load to be applied and the conditions, which are intended to be simulated. For example an angle of about 100° is particularly suited for application of large radial forces and torsion, whereas an angle of intersection of just 10° applies large thrust load. The angle can be adjusted by altering the distance between the fixed part and the front ring part or by adjusting the diameter of same, or by changing the angles of the linear actuators interactions on the periphery of the front ring part and fixed part.

At least in an idle state of a set of linear actuators it may be appropriate that the respective longitudinal axes of the linear actuators of a pair converge towards the fixed part and intersect at an angle between 70° - 30°. It will however depend on the device under test and for some of such devices a more narrow interval may be preferred, e.g. between 65 - 35°, alternatively between 60° - 40°, alternatively between 55° - 45°, alternatively between 52° - 48.

It is expected that an all-round load application unit can, at least in an idle state of a set of linear actuators, be configured so that the respective longitudinal axes of the linear actuators of a pair converge towards the fixed part and intersect at an angle of 50° ± 5°.

Similar angular relationships are intended for the reverse arrangement of linear actuators where the distance between the first ends of two linear actuators of a pair of linear actuators are smaller than the distance between their respective second ends. In this reverse arrangement the linear actuators converges towards the front ting part instead.

In order to get a true and reliable representation of the load that a device under test is able to cope with, as many variables and parameters of the components of the test facility and of the load application unit, as possible are considered. Some can be ruled out either because their contribution and impact on load application is low due to deliberate structural precautions. However, some cannot be eliminated by structural means and need to be taken into consideration. To that aspect the load application unit may further comprise means for measuring friction loss and/or rolling resistance of the main bearing of the load application unit.

The load application unit may be secured directly or indirectly, e.g. via a test bench, to a foundation, a frame, and/or a frame secured to a foundation. A suitable foundation can e.g. be built as a reinforced concrete foundation. Within the foundation, steel anchors can be placed in order to transfer the loads from the drive components of the prime mover and load application unit through tooling plates to the reinforced concrete structure. The tooling plates can be grouted to the concrete foundation and fastened with tension bolts post-tensioned to full load. A damping means may be included between the foundation and the surrounding building foundation in order to decrease vibrations from the foundation to the surroundings. The load application unit is adapted for application of loads of at least 10,000 kN*m, more preferred at least 15,000 kN*m, and even more preferred at least 30,000 kN*m, which are much higher loads than the load application unit disclosed in US2005172729A1 is capable of.

The invention also relates to a test bench including the load application unit described above. In the test bench the load application unit may utilize the main shaft of the device under test as the shaft to be coupled to the prime mover. Thus the shaft passing through the main bearing of the load application unit could be the main shaft of the nacelle coupled to the drive shaft of the prime mover.

The rotation of the inner ring part can be locked by means of a locking means, a clamping means or a brake means, and the linear actuators be used to apply a torsion torque instead of the prime mover.

The load application unit and the test bench of the present invention is in particular designed to apply heavy load to test devices, which should be able to resist very heavy loads and perform under such very heavy loads. Such device under test can be a turbine, in particular a wind turbine, more particularly a nacelle. However, movers and drive trains for many kinds of vehicles are also contemplated within the scope of the present invention . The invention also relates to a method of applying a load on a device under test

The method comprises the steps of

providing a load application unit as described above, and providing a device under test in operative coupling with the load application unit with the rotary shaft extending through the main bearing,

operating the linear actuators and/or the rotary shaft, and

measuring data representing the applied load.

The steps of operating the linear actuators and/or the rotary shaft may advantageously comprise applying translation and/or rotational load, such as one or more of axial force, radial force, vertical force, axial displacement, lateral displacement, vertical displacement, drive torque, bending torque, and torsion torque. It may be convenient to provide the load application unit at an angle to horizontal to get the test set-up as close to natural conditions as possible.

By operating the prime mover some or all of the desired torque for a load application test can be applied.

The method may further comprises a calculation step, including subtracting the load contributions representing the friction loss, rolling resistance and weight of the load application unit from the measurement data to obtain true data for the load applied to the device under test.

A preferred use of any or all of the load application unit, the test bench, and the method is for testing a nacelle or testing components of a nacelle, however the invention is also suited for testing drive trains, for example drive trains for motors or vehicles .

The inventions are described in further details below with references to the accompanying drawing in which Fig. 1 schematically shows a test bench with a first embodiment of a load application unit according to the invention,

Fig. 2 shows the schematic load application unit seen in fig. 1 in an enlarged scale side view,

Fig. 3 shows, in perspective, the load application unit of fig. 2 seen slightly from the load platform,

Fig. 4 shows a second embodiment of a load application unit in a perspective exploded view,

Fig. 5 illustrates the mutual angular arrangement of the three pairs of hydraulic cylinders of the second embodiment of the hexapod of the load application unit seen in fig. 4, and the mutual angular arrangement of two individual hydraulic cylinders of a pair of hydraulic cylinders in idle state of the load application unit,

Fig. 6 is a side view of the second embodiment of the load application unit seen in fig. 3 in assembled state,

Fig. 7 is a perspective of the same seen oblique from the front with the load platform, Fig. 8 shows the second embodiment of the load application unit with a load measuring unit and an adaptor means,

Fig. 9 shows, seen from the side, a third embodiment of a load application unit having the prime mover in front instead of behind the load application unit, as previously described for the first and the second embodiment,

Fig. 10 is a sectional view of the load application unit and the prime mover of fig. 9, taken along line X - X in fig. 9, Fig. 11 is a perspective view of the second embodiment of a load application unit coupled to the prime mover by means of a drive shaft coupling, Fig. 12 shows a sectional view taken along line XII - XII in fig. 11,

Fig. 13 is a perspective view of a fourth embodiment of a load application unit secured to a vertical frame,

Fig. 14 is a perspective exploded view of the same in smaller scale, and

Fig. 15 shows the second embodiment of a load application unit in a test bench with a prime mover.

In the following detailed description the load application unit is as an example described in respect of testing wind load, in particular wind load on a nacelle. This should not be construed as limiting the scope of the appended claims. The load application unit can be used to simulate other kinds of loads on many kinds of devices under test (DUT) .

For the sake of convenience the load application unit for simulating wind load is denominated a Wind Load Unit, or a WLU, in the below detailed description. In the present case the exemplary device under test is the nacelle of a Horizontal Axis Wind Turbine. The linear actuators are for example hydraulic cylinders, but can be any other kind, depending on a.o. the DUT. It should be understood that the linear actuators can be connected to any suitable drive means (not shown), in the present case a hydraulic system including hydraulic pump, valves, controls, etc. Further, although not shown, emphasize is made that the power transmission system associated with the prime mover may include drive components such as a gear box, brakes, a clutch and additional shafts. Fig. 1 shows schematically the structural build-up of a complete test bench T, including a nacelle 1, the DUT, a prime mover 2, a foundation 3 and a Wind Load Unit 4, the WLU,

The WLU 4 has a fixed part 5 secured to a frame 6, which frame 6 again is secured to the foundation 3, and a moveable load application means 7 that applies load on the nacelle 1. A rotary shaft 8 extends through the WLU 4 and is in operative connection with the prime mover 2 via a gearbox G, a drive shaft coupling 9, and with the main shaft 10 of the drive train of the transmission system (not shown) of the nacelle.

The tilt angle between horizontal and the centre axis C of the WLU is, in this exemplary case, about 6°. A high power generation capacity of 7MW is indicated on the nacelle shown in fig. 1. Such nacelles are e.g. used in offshore wind turbines having rotor diameters between 100 - 180 m, while onshore wind turbines often are smaller. Use of the test bench serves a.o. to simulate the rough conditions, which the wind turbine should be able to handle at the location of use. The nacelle 1 is anchored to the foundation 3 via a socket 11, which socket 11 can be of any suitable kind able of providing connection to the foundation 3, preferable rigid connection.

Fig. 2 shows the schematic WLU 4 of the test bench T seen in fig. 1 in an enlarged scale side view. The moveable load application means 7 includes three pairs of linear actuators 12a, 12b; 13a, 13b; 14a, 14b, in the present case hydraulic cylinders, connected to the fixed part 5 via first anchor means 15a, 15b; 16a, 16b; 17a, 17b, e.g. spherical bearings, and to a front ring part 18 by means of second anchor means 19a, 19b; 20a, 20b; 21a, 21b to form a hexapod 22 based on the principles of a Stewart-Gough platform, as discussed above, in order to apply controlled load to the nacelle or components of the nacelle 1. Only a few of the hydraulic cylinders are visible in fig. 2. The front ring part 18 is retained, and its movement controlled, by these six hydraulic cylinders 12a, 12b; 13a, 13b; 14a, 14b. The first ends 12a ' , 12b ' ; 13a ' , 13b ' ; 14a', 14b' of the hydraulic cylinders 12a, 12b; 13a, 13b; 14a, 14b are moveably, e.g. pivotably and/or rotatably, anchored to the fixed part 5, i.e. bolted to the frame 6 via holes in footings 23a, 23b, 23c. The second ends 12a ' ' , 12b ' ' ; 13a ' ' , 13b ' ' ; 14a' ',14b'' are moveably, e.g. pivotably and/or rotatably, anchored to the front ring part 18. The footings 23a, 23b, 23c of the present embodiment include Charnier connections to which the first ends 12a ' , 12b ' ; 13a ' , 13b ' ; 14a ' , 14b ' are secured by pin bolts 25. The first anchor means 15a, 15b; 16a, 16b; 17a, 17b can be of same or different kind as the second anchor means 19a, 19b; 20a, 2 Ob; 2 la, 2 lb . Considerable attention needs to be given when designing the footings 23a, 23b, 23c to ensure that a wind turbine can be sufficiently restrained to operate efficiently. Other kinds of connections are also within the scope of the present invention, as discussed above. The hydraulic cylinders in the present embodiment are hydraulic actuators, but other kinds of hydraulic cylinders are also comprised within the invention.

Fig. 3 shows, in perspective, the WLU 4 of fig. 2 seen slightly from the load platform 29.

A second embodiment of a WLU 4' of the present invention is seen in a perspective exploded view in fig. 4. The preferred main bearing 24 for heavy load testing is a roller bearing 24, such as a slewing bearing. The roller bearing 24 is comprised substantially of an outer ring part 26, the supporting ring, secured to and arranged coaxially with the front ring part 18, and an inner ring part 27, the rotating part, connected to the outer ring part 26. An extra ring element 28 serves to adapt the diameter of the inner ring to be coupled to the front ring part part 18. The inner ring part 27 is the part of the main bearing 24 that retains and engages the rotary shaft 8, which is driven by the prime mover 2, for example an electric motor. The inner ring part 27 is further provided with a load platform 29 in form of a load platform flange for coupling the WLU to the DUT . The person skilled in the art of for example wind turbines are familiar with various kinds of main bearings and capable of selecting appropriate and suited main bearings when designing a WLU 4' for at given load task.

The main bearing 24 of the WLU 4' is connected coaxially to the front ring part 18 of the hexapod 22 so that the rotary shaft 8 of the prime mover 2 can pass through both the main bearing 24 and the hexapod 22, to e.g. test transmission system of the wind turbine of nacelle 1. Upon actuation of the prime mover 2 and the hydraulic cylinders 12a, 12b; 13a, 13b; 14a, 14b radial forces, thrust forces and torque are applied to the DUT to simulate a pattern of conditions, which the DUT is expected to be subjected to.

The three pairs of hydraulic cylinder 12a, 12b; 13a, 13b; 14a, 14b anchored in respective footings 23a, 23b, 23c are shown separately in fig. 5, to illustrate the angular arrangement of two hydraulic cylinder of a pair of hydraulic cylinders of the hexapod 22. In the present embodiment of the angle βΐ2, βΐ3, βΐ4 between the longitudinal axes L12 ' , L12 ' ' , L13 ' , L13 ' ' , LI 4 ' , LI 4 ' ' of two hydraulic cylinders are acute.

Other angles may be better for other DUTs and the optimum WLU is designed and tailored for a given task and DUT. The WLU can be modified in many ways without deviating from the general idea of using the principle of a Stewart-Gough platform in combination with a rotary shaft acting on a main bearing provided substantially concentric with the hexapod 22.

So, by adjusting, varying and selecting parameter of the WLU 4', for example the kind of linear actuators, the kind of main bearing, various mutual angles, distances and dimensions of the components of the WLU 4', WLUs can be designed and dimensioned for almost any task and DUT .

To obtain an angle of a hydraulic cylinder in relation to the centre axis C of the WLU the diameter D_ , of the circle CL. , taken through the first ends of the hydraulic cylinders is larger than the diameter D_Front of the circle C_Front taken through the second ends of the hydraulic cylinders, as is more clear from the side view of the WLU seen in fig. 6. The angular spacing of two hydraulic cylinders are also illustrated in fig. 5: By the angle pl3, as indicated by dashed lines between the first ends 13a', 13b' of the pair of linear actuators 13a, 13b viewed in relation to the circle C_Fixed, and by the angle γ13, as indicated by dotted lines, between the second ends 13a' ',13b'' of the same pair of hydraulic cylinders 13a, 13b viewed in relation to the circle C_Front The hydraulic cylinders 12a, 12b and 14a, 14b are similarly arranged at angles φ12 and φ14 at the respective first ends, and at angles angle γ12 and γ14 at the respective second ends in a similar manner, however for the sake of clarity of fig. 5 these angles are not indicated by reference numbers.

In the present embodiment the distance between the front ring part 18 and the fixed part 5, constituted by at least the footings 23a, 23b, 23c, is smaller than any of the diameters of the external perimeters or external diameters of the fixed part 5 and the front ring part 18, D_Fixed and D_Front, respectively, however this arrangement is also open to modification and may be modified as occasion requires. Due to the orientation of the cylinders of the hydraulic cylinders, the WLU makes it possible to measure the friction loss and rolling resistance of the main bearing 24. These losses of the main bearing can then be subtracted from the applied torque of the prime mover 2 and the resulting load on the DUT 1 can be accurately determined. Prior art WLUs are leaving most of the friction loss of the main bearing out of the equation by using low-friction hydrostatic bearings - for instance the "MTS Non-Torque Loading (NTL) System". However, this known system is very expensive and does not completely eliminate measurement errors due to friction loss in the main bearing.

The net weight of the hanging parts of the WLU according to the invention is compensated for in the algorithm controlling the hydraulic cylinders in order to ensure a precise load.

The second embodiment of the WLU 4' is seen in a perspective view in fig. 7 from the load platform 29.

Fig. 8 shows the second embodiment of the WLU 4' with a load measuring unit 30 and an adaptor means 31. If the load platform 29 does not immediately fit together with a certain DUT component, e.g. a coupling flange 32 of a main shaft 10 of a wind turbine 1, the adaptor means 31 is inserted as an intermediate coupling part 31 for enabling coupling of the DUT to the load platform 29, and thus to the inner ring part 27 of the main bearing 24, to transfer torque irrespective of the fact that the diameter of the load platform 29 does not fit exactly with the diameter of the coupling flange 32 of the component of the DUT. Adaptor means are contemplated for any embodiment of the load application unit according to the present invention. The load measuring unit 30 provide the possibility to obtain supplemental data and/or other data from the load test than those obtained from load cells (not shown) associated with the hydraulic cylinders 12a, 12b; 13a, 13b; 14a, 14b. The load cells can be any kind of device able to measure parameters related to the operation of the linear actuators .

Fig. 9 shows a third embodiment of a WLU 4'' having a prime mover 2' in front of the WLU 4'' instead of behind, as shown and described for the first and the second embodiments of WLUs 4 ; 4 ' .

In the third embodiment of the WLU 4'' the bearing(s) 33 of the prime mover 2' serve the purpose of the main bearing 24 of the first 4 and the second 4' embodiments.

As seen better in the sectional view of fig. 10 the prime mover 2' is an electric motor, e.g. an motor with a stator 33 and a rotor 34 arranged surrounding the bearing 35 of the motor 2'. The coupling length from prime mover 2' to DUT is substantially eliminated in this embodiment. Prime movers can be motors of any kind including synchronous motors and asynchronous motors able of applying the required load contribution for a given test.

Fig. 11 is a perspective view of the second embodiment of a WLU 4' coupled to the main rotary shaft 8 of the prime mover 2'' by means of a drive shaft coupling 9, as seen better in the sectional view of fig. 12. A first coupling flange 35 of the rotary shaft 8 is coupled to a second flange 36 provided on the drive shaft coupling 9 to rotate both about their longitudinal axes. At the end of the drive shaft coupling 9 opposite the second flange 36 the drive shaft coupling 9 has a third flange 37 coupled to the inner ring part 27 of the main bearing 24. In this embodiment the drive shaft coupling 9 becomes an extension of the rotary shaft 8 that is received in the main bearing 24. Thus the term "rotary shaft" includes any elongate part that rotates or can rotate about its longitudinal axis.

Fig. 13 is a perspective view of a fourth embodiment of a WLU 4''' secured to a vertical frame 35, which vertical frame e.g. can be bolted to a foundation (not shown), and fig. 14 is a perspective exploded view of the same. The fourth embodiment of a WLU 4''' corresponds substantially to the second embodiment of a WLU 4' and for like parts same reference numerals are used. The fourth embodiment of a WLU 4''' differs in the structural build-up of the main bearing 39 in that the main bearing 39 includes a tapered body 40 inserted between the inner ring part 27 of the main bearing 39 and the load platform 29. The tapered body compensate for differences in diameters of components of the WLU to be coupled together.

Fig. 15 shows the second embodiment of a WLU 4' in a second embodiment of a test bench T' for testing a nacelle 1''. A rotary shaft 8 passes through the centre opening 41 of the WLU 4' inside the main bearing 24 to the main shaft 10 of the wind turbine of the nacelle 1''. The rotary shaft 8 rotates inside the main bearing 24 operated by prime mover 2 ' ' . The nacelle 1'' is anchored to a first level 3a of the foundation 3 via socket 11. The WLU 4' is anchored, e.g. by means of bolts to a second level 3b of the foundation 3, which second level 3b is higher than the first level 3a, via frame 6. The prime mover 2 ' ' is anchored to a third and fourth level 3c, 3d of the foundation, which third and fourth levels 3c, 3d are higher than both the first level 3a and the second level 3b. This way the foundation 3 provides an angle to horizontal for the rotary axis to attack and apply load to the DUT 1''.

The load application unit according to the present invention has a substantially reduced inertia compared to the prior art load application units and thus a substantially improved ability to act dynamically.

In another embodiment the load application unit can also be made so that the hexapod rotates together with the DUT.

The invention provides a new method for dynamic and static testing of for example the main bearing and the yaw bearing of a nacelle. The construction of the Stewart platform means that by positioning the hydraulic cylinders in a given position a very clear picture of by which force and in which direction the platform affects another structure, is given. Thereby is obtained a possibility of very exactly creating the desired effects on the nacelle. The modern wind turbine is a complex and integrated system. Structural elements comprise the majority of the weight and cost. All parts of the structure must be inexpensive, lightweight, durable, and manufacturable, under variable loading and environmental conditions. Turbine systems that have fewer failures, require less maintenance, are lighter and last longer will lead to a reduction of the cost of wind energy.

The invention provides a new load application unit and a method to impact on a nacelles main bearing and yaw bearing via a hydraulic driven Stewart platform and a prime mover.

Due to the lower inertia in the system than in prior art systems the invention will have a considerable improved ability to act dynamically, and this provides the possibility of load scenarios not possible hitherto.

Due to the construction of the Stewart platform it is possible to control the load application unit's force application on the DUT much better than was possible hitherto.

Claims

A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) comprising

a fixed part (5) adapted for securing the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) to a base structure,

a moveable load application means (7) adapted for being operatively connected to a device under test by means of a series of actuators ( 12a, 12b; 13a, 13b; 14a, 14b) , characterised in that the moveable load application means (7) comprises

a front ring part (18) coaxially connected to the fixed part (5) by means of a hexapod (22) system of three angularly distributed pairs of independently controllable linear actuators ( 12a, 12b; 13a, 13b; 14a, 14b) selected to move the moveable load application means (7) and the device under test, in a pair of linear actuators ( 12a, 12b; 13a, 13b; 14a, 14b) each linear actuator has first ends (12a', 12b';13a', 13b';14a', 14b') anchored to the fixed part (5) and second ends ( 12a ' ' , 12b ' ' ; 13a ' ' , 13b ' ' ; 14a' ',14b'') anchored to the front ring part (18), and

a main bearing (24;39) comprising an outer ring part (26) secured coaxially to the front ring part (18), and an inner ring part (27) adapted for engaging a rotary shaft (8) .

A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to claim 1, characterised in that the distance between the first ends (12a', 12b';13a', 13b';14a', 14b') of two linear actuators of a pair of linear actuators ( 12a, 12b; 13a, 13b; 14a, 14b) are smaller than the distance between their respective second ends ( 12a ' ' , 12b ' ' ; 13a ' ' , 13b ' ' ;

14a' ' , 14b' ' ) .

A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to claim 1, characterised in that the distance between the first ends (12a', 12b ' ; 13a ' , 13b ' ; 14a ' , 14b') of two linear actuators of a pair of linear actuators

( 12a, 12b; 13a, 13b; 14a, 14b) are greater than the distance between their respective second ends ( 12a ' ' , 12b ' ' ; 13a' ' , 13b' ' ; 14a' ' , 14b' ' ) .

A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the claims 1, 2 or 3, characterised in that the main bearing (24;39) is one or more roller bearings (24) .

A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 1 - 4, characterised in that the main bearing (24;39) is a slewing bearing or a pair of spherical roller bearings.

A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 1 - 5, characterised in that the centre axis (C) of the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) is substantially horizontal, preferably the centre axis (C) of the load application unit ( 4; 4 ' ; 4 ' ' ; 4 ' ' ' ) is at an angle (a) of less than 10° to horizontal, preferably less than 8° to horizontal, more preferred less than 7° to horizontal, and most preferred 6° or 5° to horizontal.

A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 1 - 6, characterised in that the inner ring (27) has a load platform (29) protruding coaxially towards the device under test and serving for coupling the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) to the device under test, or for coupling to an adaptor means (31) enabling coupling the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) to the device .

A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 1 - 7, characterised in that the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) comprises a prime mover ( 2 ; 2 ' ; 2 ' ' ) for driving the rotary shaft (8).

A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 1 - 8, characterised in that the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) comprises a device for locking the rotation of the main bearing (24;39) .

10. A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 1 - 9, characterised in that the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) is connected to the prime mover ( 2 ; 2 ' ; 2 ' ' ) via a drive shaft coupling (9).

11. A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to claim 8, 9 or 10, characterised in that the prime mover ( 2 ; 2 ' ; 2 ' ' ) is behind the load application unit ( 4 ; 4 ' ; 4 " ; 4 " ' ) .

A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 8 - 10, characterised in that the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) is modified to insert the prime mover ( 2 ; 2 ' ; 2 ' ' ) in front of the front ring part (18) of the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) .

A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 1 - 11, characterised in that the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) further comprises at least one linear length transducer operatively associated with at least one of the linear actuators ( 12a, 12b; 13a, 13b; 14a, 14b) .

A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 1 - 13, characterised in that the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) further comprises at least one pressure sensor and/or load cell operatively associated with at least one of the first end ( 12a ' , 12b ' ; 13a ' , 13b ' ; 14a', 14b') or the second end ( 12a " , 12b " ; 13a " , 13b " ; 14a' ',14b'') of at least one of the linear actuators

(12a, 12b; 13a, 13b; 14a, 14b) .

A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 1 - 14, characterised in that the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) comprises a load measuring unit (30) between the adaptor means (31) and the load platform (29) of the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) .

16. A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 1 - 15, characterised in that the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) further comprises that at least one of the first ends ( 12a ' , 12b ' ; 13a ' , 13b ' ; 14a ' , 14b ' ) and/or the second ends ( 12a ' ' , 12b ' ' ; 13a ' ' , 13b ' ' ; 14a' ',14b'') of the linear actuators ( 12a, 12b; 13a, 13b; 14a, 14b) are anchored to the fixed part (5) and the front ring part (18), respectively, by means of one or more anchor means ( 15a, 15b; 16a, 16b; 17a, 17b) selected from spherical bearings, Charnier joints, bolted connections, and/or cardan joints.

A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to claim 16, characterised in that the anchor means ( 15a, 15b; 16a, 16b; 17a, 17b) are low friction anchor means.

A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 1 - 17, characterised in that the linear actuators ( 12a, 12b; 13a, 13b; 14a, 14b) are hydraulic, pneumatic, mechanical or electrical linear actuators, or combinations thereof.

A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 1 - 18, characterised in that the diameter of the outline of the fixed part (5) is larger than the diameter of the front ring part (18) .

A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 1 - 19, characterised in that at least in an idle state of a set of linear actuators ( 12a, 12b; 13a, 13b; 14a, 14b) their respective longitudinal axes (L12 ' , L12 ' ' ;L13 ' , L13 ' ' ;L14 ' , L14 ' ' ) converge towards the fixed part (5) and intersect at an angle (βΐ2, βΐ3, βΐ4) equal to or less than 100°, alternatively equal to or less than 90°, alternatively equal to or less than 80°, alternatively equal to or less than 70°, alternatively equal to or less than 60°, alternatively equal to or less than 50°, alternatively equal to or less than 40°, alternatively equal to or less than 30°, alternatively equal to or less than 20°, alternatively equal to or less than 10°.

A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 1 - 19, characterised in that at least in an idle state of a set of linear actuators ( 12a, 12b; 13a, 13b; 14a, 14b) their respective longitudinal axes (L12 ' , L12 ' ' ;L13 ' , L13 ' ' ;L14 ' , L14 ' ' ) converge towards the fixed part (5) and intersect at an angle (βΐ2, βΐ3, βΐ4) between 70° - 30°, alternatively between 65 - 35°, alternatively between 60° - 40°, alternatively between 55° - 45°, alternatively between 52° - 48°.

A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 1 - 21, characterised in that at least in an idle state of a set of linear actuators ( 12a, 12b; 13a, 13b; 14a, 14b) their respective longitudinal axes (L12 ' , L12 ' ' ;L13 ' , L13 ' ' ;L14 ' , L14 ' ' ) converge towards the fixed part (5) and intersect at an angle (βΐ2, βΐ3, βΐ4) of 50° ± 5°.

23. A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 1 - 22, characterised in that the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) further comprises means for measuring friction loss and/or rolling resistance of the main bearing (24;39) .

24. A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 1 - 23, characterised in that the base structure to which the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) is secured is a foundation (3), a frame

(6) , and/or a frame secured to a foundation (3) .

25. A load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 1 - 24, characterised in that the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) is adapted for application of loads of at least 10,000 kN*m, more preferred at least 15,000 kN*m, and even more preferred at least 30,000 kN*m.

26. A test bench (Τ;Τ') for a device under test comprising the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 1 - 25.

27. A test bench unit (Τ;Τ') according to claim 26, characterised in that the device under test has the rotary shaft (8) .

28. A test bench unit (Τ;Τ') according to any of the claims 26 or 27, characterised in that the device under test is a turbine, in particular a wind turbine, more particularly a nacelle ( 1 ) .

29. A method of applying a load on a device under test, characterised in that the method comprises the steps of

providing a load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) according to any of the preceding claims 1 - 25,

and providing a device under test in operative coupling with the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) with the rotary shaft (8) extending through the main bearing (24;39) ,

- operating the linear actuators ( 12a, 12b; 13a, 13b; 14a, 14b) and/or the rotary shaft (8), and

measuring data representing the applied load.

30. A method according to claim 29, characterised in that the steps of operating the linear actuators

( 12a, 12b; 13a, 13b; 14a, 14b) and/or the rotary shaft (8) comprise applying translation and/or rotational load.

31. A method according to claim 30, characterised in that applying translation and/or rotational load comprises applying one or more of axial force, radial force, vertical force, axial displacement, lateral displacement, vertical displacement, drive torque, bending torque, and torsion torque .

32. A method according to claim 29, 30 or 31, characterised in that the method comprises providing the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) at an angle to horizontal.

33. A method according to any of the preceding claims 29 - 32, characterised in that the method comprises operating the prime mover ( 2 ; 2 ' ; 2 ' ' ) .

34. A method according to any of the preceding claims 29 - 33, characterised in that the method further comprises a calculation step, including subtracting the load contributions representing the friction loss, rolling resistance and weight of the load application unit ( 4 ; 4 ' ; 4 ' ' ; 4 ' ' ' ) from the measurement data to obtain true data for the load applied to the device under test.

35. Use of the load application unit according to any of the preceding claims 1 - 25 and/or the test bench according to any of the preceding claims 26 - 28 and/or the method according to any of the preceding claims 28 - 34 for testing a nacelle or components of a nacelle.

Use of the load application unit according to any of the preceding claims 1 - 25 and/or the test bench according to any of the preceding claims 26 - 28 and/or the method according to any of the preceding claims 28 - 34 for testing drive trains.

37. Use according to claim 35 characterised in that the drive trains are drive trains for motors or vehicles.