FIELD OF THE INVENTION

The present invention relates to the manufacture of a blade, such as for a wind turbine generator (WTG), and in particular to a blade assembly, and a method of monitoring blade assembly .

BACKGROUND

Conventionally, wind turbine blades comprise two shells (which may also be referred to as shell-halves) that are joined together, one shell defining one surf ace of the blade, and the other shell defining a surface on the opposite side of the blade. The two shells may also be referred to as the upper shell and lower shell (depending on the orientation in which the blade is fabricated), or the leeward shell and windward shell , or the pressure side (PS) shell and the suction side (SS) shell, based on the aerodynamic shape of the blade. The shells define a relatively thin surface or skin of the blade. The interior of the blade is generally hollow, except for one or more longitudinal structural components that provide the blade with stiffness.

To manufacture a blade, a shell mold is provided for each of the upper shell and the lower shell. Each mold defines the shape of the exterior aerodynamic surf ace of the respective shell. Dry fiber materials are laid up in each mold ; each mold is bagged; and liquid resin is infused into the fiber. The resin is cured to form each solid shell. One or more structural components (such as spars, webs, and/or web assemblies are bonded into the lower shell). Adhesive is applied to the leading edge (LE) and trailing edge (TE) of the lower shell, as well as to the tops of the structural components. The upper shell is then lifted and rotated into position above the lower shell. The upper shell is lowered into position on the lower shell and the adhesive is cured to an appropriate level such that the two shells are bonded together to form the blade. The upper mold is removed and the blade is lifted from the lower mold, so that the blade can be taken to a finishing area. There are a number of problems with this process. For modern blades that can be many tens of metres long, even over 100 m, and multiple metres wide, each mold is very large and expensive to make, such as several million dollars. While the adhesive is curing, the very expensive molds are effectively idle, such that fabrication of the next blade cannot be started. This slows the rate at which blades can be produced. For this reason, curing of the adhesive is often performed at an elevated temperature , such as 80 to 120 degrees C. This is far outside the normal operating conditions of the blade in the field, so can cause thermal expansion effects in the blade that can be deleterious to the formation of the adhesive bond. Furthermore, after the shells have been bonded together, it is difficult to inspect the bonding of the internal structural components to the shell. This means that quality control inspection is slower and more costly, requiring, for example non-destructive testing (NDT) and indirect inspection techniques. It is also costly to repair any defects that are found in the blade. Any defects that are not found may lead to catastrophic blade failure.

The present invention aims to alleviate, at least partially, some or any of the above problems.

SUMMARY

According to one aspect of the invention there is provided a blade assembly for one of a wind turbine blade and a sea transportation vessel blade, the assembly comprising: a first shell and an opposing second shell; a structural component within the blade; wherein the structural component is joined to the first shell, and wherein the assembly further comprises a monitoring device within the blade arranged to monitor displacement of the second shell with respect t o the structural component while an adhesive located between the structural component and the second shell cures.

Another aspect of the invention provides a method of monitoring blade assembly for one of a wind turbine blade and a sea transportation ves sel blade , the method comprising: providing a first shell joined to a structural component; providing a second shell; applying adhesive to at least one of the structural component and the second shell for forming a bond between the structural component and the second shell; uniting the first and second shells to create an adhesive bond line between the structural component and the second shell; and monitoring from within the blade assembly the displacement of the structural component with respect to the second shell while the adhesive between the structural component and the second shell cures Further optional aspects of the invention are defined in the dependent claims . BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of non -limiting example, with reference to accompanying drawings, in which:

Figure la is an illustration in cross-section of a portion of a blade assembly, showing a blade internal structural component, with a bead of adhesive applied to a flange, and ready to be bonded to a shell according to an embodiment of the invention;

Figure lb is a transverse cross-section of a blade according to an embodiment of the invention;

Figure 2 is an illustration in cross-section of the components of figure 1 with the adhesive bead now compressed between the flange and the shell ;

Figure 3 is an illustration in cross-section of the components of figure 1 during curing, with thermal expansion causing the shell to lift away from the wet adhesive; and

Figure 4 is an illustration in cross-section of the components of figure 1 after curing, with the shell now in contact with the hard adhesive.

In the drawings, like parts are indicated with like reference numerals, and, for conciseness, description thereof will not be repeated.

DETAIFED DESCRIPTION

Fig. l a shows, in cross-section, a portion of a wind turbine blade assembly according to one embodiment of the invention. A plurality of structural components 10 are provided within the blade. In the illustrated embodiment, the structural components are in the form of an I-beam. Each structural component comprises a web 12 and a flange 14, 16 along each edge of the web. As shown in Fig. lb, the edge of the web 12 distal from the upper flange 14 has a second flange 16 that is j oined to a first (lower) shell 18 of the blade. Referring to Fig. l a, a bead of adhesive 20 has been applied along the upper flange 14. A second (upper) shell 22 is positioned to be closed onto each bead of adhesive 20. Adhesive has also been applied along the leading edge and trailing edge of one of the shells to bond those edges to the respective leading and trailing edges of the opposite shell when the shells are united together (closed). In this embodiment, the structural components and the shells comprise resin- fiber composite material, such as carbon fiber reinforced polymer (CFRP), or glass-fiber reinforced plastic (GFRP). Fig. 2 shows the components of Fig. l a with the shell 22 having been closed (as in Fig. lb). The adhesive bead 20 is compressed between the shell 22 and the flange 14 to create a bond-line. A monitoring device 30 is provided to monitor displacement of the shell 22 with respect to the structural component. In this embodiment the monitoring device comprises a body 32 rigidly fixed via an arm 34 to the web 12. The arm 34 can be chemically fixed to the web 12 (e.g. glued) or can be mechanically fixed to the web 12 (e.g. bolted). The monitoring device has a probe 36 that is spring-loaded and moveable with respect to the body 32. When the shell is closed, the probe 36 contacts the shell 22 and is pushed into the body 32.

In this specific embodiment, the monitoring device 30 comprises a linear potentiometer. The electrical resistance between two terminals in the device depends on the position of the probe 36 withrespect to the body 32. As the probe 36 slides with respect to the body 32, that resistance changes. In this way , the resistance is related to the separation between the flange 14 and the shell 22. Circuitry in the body 32 produces a monitoring output that is based on the resistance of the potentiometer.

When the shell 22 is first closed to form the blade, as in Fig. 2, the monitoring output of the monitoring device 30 has a particular value. During the curing process , if that monitoring output stays substantially constant, or deviates by an amount less than a predetermined threshold, then the bonding is successful.

In contrast, as shown in Fig. 3, if thermal expansion effects cause the shell 22 to lift from the adhesive, then the probe 36, which is spring biased against the shell, moves with respect to the body 32, and the monitoring output value changes. If this occurs before the adhesive has gelled, then the compressed adhesive 20 may loose contact with either the shell 22 (as illustrated in Fig. 3) or with the flange 14. As the curing continues, the adhesive hardens, but there is an air gap between one of the components and the adhesive. Then, on cooling , the gap closes , as illustrated in Fig. 4, but on hardened, cured (or partially cured) adhesive. This results in a so-called “kissing bond” along the line 40, in which there appears to be intimate contact between the surfaces, but there is actually no adhesion, and so no structural integrity. This is particularly problematic because it is difficult to detect by inspection of the blade. Of course, the monitoring output of the monitoring device 30 tracks the opening and closing of this gap. If the change in monitoring output exceeds a predetermined threshold during the curing, then an alert is genera ted, either by the monitoring device directly, or by an external apparatus in communication with the monitoring device that analyses the output. Further embodiments

The monitoring device 30 described above comprises a potentiometer that uses mechanical contact to detect displacement, but that is merely one example . Other forms of transducer, or linear transducer, can be used thatrely on contact or can be contactless. For example the displacement can be monitored optically (e .g. using a laser range sensor), acoustically (e.g. using an ultrasound proximity sensor), or inductively /magnetically using a coil to sense proximity .

The monitoring device produces a monitoring output based on the relative position and/or displacement of the parts being bonded. The monitoring output can be analog or digital. The monitoring device can communicate the monitoring output to an external apparatus for further processing. The communication can be wired or preferably wireless. During curing, the monitoring device c an communicate the monitoring value continuously in real time, or the monitoring device can store the monitoring value time sequence locally, and upload the values to the external device at a later time. In a preferred embodiment, the monitoring device 30 comprises a battery, microprocessor, memory, and wireless transmitter.

In the illustrated embodiment, the monitoring device 30 is fixed to the web 12, but in alternative embodiments it can he fixed to the flange 14 or the shell 22 , or to more than one part. In the illustrated embodiment, the web 12 is firstly fixed to a lower shell 1 8 , and then the upper shell 22 is bonded to the upper flange 14 of the web. However, an alternative embodiment is to fix the web 12 to what will become the upper shell, a nd then to close this assembly onto the lower shell, so that the bondbeing monitored is between the bottom flange and the lower shell. In other words Figs l a and 2 would be upside-down, and the bead of wet adhesive could be applied to the shell rather than to the flange. In principle the invention could be applied in any orientation.

A further embodiment of the invention is for the m onitoring device 30 to include a temperature sensor for monitoring the local temperature during the curing cycle. This could take the form of a thermocouple embedded in the adhesive bead 20. The temperatures values are communicated to the external apparatus for analysis along with the displacement transducer monitoring output.

Thermal expansion effects are particularly relevant as blades get bigger. S o the invention is particularly useful for blades with a width (from leading edge to trailing edge, or ‘ chord’) of at least 3 m, such as at least 5 m, and even at least 6 m ; and for blades with a length of at least 30 m, such as at least 50 m, including at least 70 m.

The figures show a blade with multiple webs, one of whichhas a monitoring device 30; this is purely illustrative. The blade may have a single web or multiple webs as structural components, and the structural components can take various forms , not just I-beams, such as box girders, spars, multiple webs sharing a common flange, and so forth. All structural components could be provided with monitoring devices, or only some of them. A structural component can have multiple monitoring devices distributed along its length. If there are multiple monitoring devices in a blade , they could each be autonomous, or they could share a common unit that handles aspects such as any data processing, storage, and external communication.

Uses

There are several ways in which the invention can be used. S ome examples embodying the invention are as follows.

( 1) Commissioning

When a new mold (such as for a new blade design, or for an existing blade design) is initially being set-up and commissioned, or a new curing cycle or new adhesive is being used to manufacture a blade, then the monitoring output of the one or more monitoring devices can be analysed to check that displacement of the shell with respect to the structural component does not occur, or is within a tolerance threshold. This provides an indication that the mold/process is satisfactory and can be passed for serial production without using monitoring devices. P eriodically a blade can be manufactured incorporating monitoring device(s) to check that the mold/process still meets the specification.

(2) Process Optimization

Process parameters, such as rate of change of temperature, peak temperature, and temperature distribution, can be adjusted to try to optimize both speed of cure and bond quality. Using monitoring devices in an assembly according to the invention enables it to be rapidly determined when the process is satisfactory or not.

When there is some detected displacement, destructive testing can be used to assess the bond, e.g. to see whether there is a kissing bond or not, and this can be used to determine a threshold of permissible displacement at a specific blade location and part of the cure cycle such that a satisfactory bond is still formed.

By manufacturing a blade with multiple monitoring devices, a map of high-risk areas prone to displacement and bonding failure can be obtained. The number of monitoring devices can then be reduced and/or relocated to those areas only, or the process corrected and monitoring devices removed entirely.

(3) Serial Production

Monitoring devices can be used in the routine manufacture of every blade, not just on runs when the mold/process is being commissioned or optimized. For example , the monitoring device or devices can be retrieved from within the blade, particularly at the root end of the blade, whichhas a larger cross-section so is more accessible, and which is more prone to differential thermal expansion ef fects . Alternatively or in addition, monitoring devices can be left within the finished blade. The monitoring devices can weigh only a few grams and cost a few cents, so do not affect the performance or cost of the blade.

Although the above description has specifically mentioned manufacturing a blade for a wind turbine, the invention can also be applied in other embodiments to assembling blade structures such as for wind assisted propulsion of sea transportation vessels. One or more of these blades can typically be vertically mounted on top of the vessel, and is rotatable about the vertical axis. The vessel can be, for example , a cargo container, oil/gas tanker, or grain tanker. The aerodynamic blade or blades utilises wind assistance to augment the conventional propulsion of the vessel, thereby reducing fuel costs and emissions. In this context, a blade may also be called a wing or a sail, but the term ‘blade’ is used herein to encompass these alternative terms.