Field of the Invention

The present invention relates to a connection guidance system. In particular, but not exclusively, the present invention relates to a connection guidance system for assisting in the connection and disconnection of catenary hoses transferring liquids or gases such as hydrocarbon fuels, for example liquid natural gas (LNG), between bodies in relative motion. The present invention finds particular utility in a marine environment. Background to the Invention

In many environments it is required to transfer fluid between bodies in relative motion to one another. For example, in a marine environment, fluids such as hydrocarbon fuels are often loaded onto ships. In such an environment, the movement of the floating ship must be accommodated when transferring the fluid. Such issues occur when a ship is supplied from the shore and also when ships are supplied by other floating vessels. For example, a bunker vessel may be used to refuel a larger ship.

The transfer of fluid between two bodies occurs through fluid paths coupled to each vessel, which should be able to be connected and disconnected under a range of circumstances. In recent years, the use of liquid natural gas (LNG) as a fuel for maritime vessels has increased in popularity, meaning that the provision of a system for a safe, flexible, and controllable connection of fluid paths between bodies acting in relative motion, such as the movement between two vessels, is increasingly desirable. Some prior art approaches comprise coupling systems which utilise a cable, coupled between the two bodies, and maintained at a nominal tension. The manifold of a first vessel moves along a trajectory guided by the cable until it reaches a manifold of a second vessel. An approach of this kind is described in US7954512. While the use of a guidance cable may reduce the risk of impact between the manifold and the coupling system, there remain difficulties with ensuring a correct alignment in difficult meteorological conditions. If a large movement of one of the vessels occurs whilst the manifolds are relatively close, for example, an impact may occur leading to damage or uncontrolled fluid delivery. An alternative approach is described in US7147022. In this approach, two cables are provided, one cable secured between the base of a transfer boom and the transfer manifold and the other cable wound upon a winch disposed on that manifold. This connection system uses a balanced loading and unloading arm as the transfer boom for transferring the fluid lines, and may allow for the connection or disconnection of the loading arm to or from a vessel in difficult sea conditions. The loading arm of US7147022 is a rigid arm balanced around a pivot by a counter weight. The cables together form a lateral path to guide the rigid arm across the distances between the two bodies in a similar way to the coupling system described above with reference to US7954512. However, it remains challenging to handle in difficult weather conditions or when relative movement is large. It is particularly important to prevent impacts when using LNG as LNG is extremely volatile, meaning that any spark caused by the impact would risk explosion. This applies both when connecting the manifolds together and in any emergency disconnection scenario. Summary of the Invention

According to a first aspect of the present invention, there is provided a connection guidance system, comprising:

a support member;

a transfer manifold suspended from the support member;

a receiving manifold for coupling to the transfer manifold to form a fluid path therewith;

a winch fixed to either the transfer manifold or the receiving manifold;

a guide wire extending from the winch;

a male connecting element and a female connecting element, wherein the male connecting element is fixed to one of the transfer manifold and the receiving manifold and the female connecting element is fixed to the other of the transfer manifold and the receiving manifold; and

a tensioning member for applying a tensile force to the transfer manifold during a transfer operation, wherein the transfer manifold is suspended from the support member by the tensioning member.

The system of the present invention can assist in providing both flexibility and control to a fluid transfer operation. In particular, the use of a guide wire fixed via the winch to the transfer manifold can enable a female connecting element fixed to the transfer manifold to be brought into alignment with a male connecting element fixed to the receiving manifold. Preferably, the guide wire extends through a guide hole in the female connecting element, which may facilitate a more controlled alignment of the male and female connecting elements. In this manner, the transfer manifold can be guided into position for coupling to the receiving manifold. Alternatively, the guide wire can be fixed via the winch to the receiving manifold and can enable a male connecting element on the transfer manifold to be brought into alignment with a female connecting element on the receiving manifold. Alternatively, other combinations of the position of the winch and the male and female connecting elements with respect to the transfer and receiving manifolds are possible. These arrangements may also facilitate the guiding into position of the transfer manifold for coupling to the receiving manifold.

The tensile force provided by the tensioning member can provide particular advantages in an emergency disconnection scenario. Rather than allowing the manifold to fall away from the receiving vessel in an uncontrolled manner, the tensioning member may provide a sufficient tensile force such that the transfer manifold is moved in a predefined direction. Preferably, the tensioning member provides a sufficient tensile force to lift the transfer manifold upwards if a disconnection with the receiving vessel occurs. By maintaining a tensile force of at least this magnitude throughout the transfer operation, at no time is there a risk of uncontrolled disconnection. Preferably, the tensioning member is extensible. That is to say, the tensioning member may vary in length, both increasing and decreasing as desired. More preferably, the tensioning member is flexible. This can allow the position of the transfer manifold relative to other elements of the system to vary within desired parameters. A tension drive mechanism may be provided to maintain tension in the tensioning member during the transfer operation. The tension drive member may be a tension winch or a hydraulic drive system, for example. The tensioning member is preferably maintained under constant tension during the transfer operation. For example, the tension drive member may be designed to maintain constant tension in the tensioning member during the transfer operation.

In preferred embodiments, the system further comprises at least one catenary hose having a proximal end suspended from the support member, wherein the transfer manifold is coupled to a distal end of the support member. The catenary hose can flex to accommodate relative motion between the transfer manifold and the counter-party to which the transfer manifold is attached. Preferably, the transfer manifold is suspended from the support member independently of the catenary hose (for example, by the tensioning member). Accordingly, the hose itself need not be under tension. This is found to increase the reliability of suitable hoses for fluid transfer, particularly when repeated flex of the hose is incurred. Preferably, the support member further comprises one or more rigid pipes coupled to the or each catenary hose. This allows fluid to be carried to the or each catenary hose through a rigid and reliable connection.

In preferred embodiments, the female connecting element comprises a flared end section. Accordingly, initial engagement between the female connecting element and the male connecting element can be achieved with a relatively large margin for error in the alignment of these elements, but as the elements are brought closer together the tightening of the flared section brings the elements into closer alignment. Preferably, the flared end section comprises an enlarged bottom section having a greater radial extent than an upper section. Thus, a greater margin of error can be provided if the transfer manifold is brought into contact from above the receiving manifold, without unnecessarily increasing weight of the system by providing an enlarged top section. Bringing the transfer manifold in from a relatively high position minimises the opportunity for accidental collisions during the connection process.

In preferred embodiments, the transfer manifold comprises a distal part and a proximal part suspended from the support member, the distal part being removably coupled from the proximal part, wherein the winch is fixed to the distal part. Thus, if for any reason there is a requirement to disconnect the parts of the transfer manifold (for example, if an emergency disconnection is required), the winch and guide wire arrangement will remain with the part that is still fixed to the receiving manifold. This avoids any interference between the winch/guide wire and the emergency disconnection process. In some embodiments, the winch is fixed to the receiving manifold. The guide wire is then preferably fixed to the distal part of the transfer manifold. This arrangement similarly avoids any interference between the winch/guide wire and the emergency disconnection process. Alternatively, the winch or guide wire may be fixed to the proximal part of the transfer manifold.

Preferably, the transfer manifold further comprises an emergency disconnection system for preventing transfer of fluid in an emergency, wherein the distal part and the proximal part of the transfer manifold are coupled by the emergency disconnection system. The emergency disconnection system may be hydraulically powered. In preferred embodiments, the emergency disconnection system comprises a double isolation valve, such as a double ball valve. In preferred embodiments, the support member further comprises a support arm from which the tensioning member is suspended. Alternatively, the tensioning member may be suspended from another element of the support member. The support arm may comprise a plurality of rigid elements movable relative to one another. Movement of the support member may be controllable, for example by a hydraulic system. As such, the support member may be moved to control the position of the tensioning member, which can increase the operating envelope of positions in which the tensioning member can support the transfer manifold.

Preferably, the system further comprises a pedestal, and the support member is pivotally mounted to the pedestal. The tensile support arm may also be pivotally mounted to the pedestal. Preferably, the coupling of the support member and/or the support arm to the pedestal allows rotational movement around a substantially vertical axis. The pedestal movement may thus provide rotational movement in a horizontal plane, while the suspended tensioning member may provide movement along a vertical axis.

According to a second aspect, there is provided a fluid transfer apparatus comprising: a support member;

a transfer manifold suspended from the support member;

a winch fixed to the transfer manifold;

a guide wire extending from the winch;

a connecting element fixed to the transfer manifold; and

a tensioning member for applying a tensile force to the transfer manifold during a transfer operation, wherein the transfer manifold is suspended from the support member by the tensioning member.

According to a third aspect, there is provided a fluid transfer apparatus comprising:

a support member;

a transfer manifold suspended from the support member;

a connecting element fixed to the transfer manifold and comprising a connection point for receiving a guide wire; and

a tensioning member for applying a tensile force to the transfer manifold during a transfer operation, wherein the transfer manifold is suspended from the support member by the tensioning member. The fluid transfer apparatus of either aspect may have any of the features described above with reference to the connection guidance system, either alone or in combination with any other feature. The transfer manifold is suitable for coupling to a receiving manifold to form a fluid path therewith. In some embodiments, the receiving manifold comprises a male connecting element configured to engage with a female connecting element of the transfer manifold of the fluid transfer apparatus. In aspects where the transfer manifold comprises a winch and a guide wire, the male connecting element of the receiving manifold may comprise a connection point for securing the guide wire. The connection point may be located at the tip of the male connecting element. The guide wire may extend through a hole in the female connecting element and be configured to couple to the connection point. Alternatively, the connection point may be on the female connecting element of the transfer manifold and the winch and guide wire may be provided on the receiving manifold. In other embodiments, the connecting element of the fluid transfer apparatus is a male connecting element. The receiving manifold may comprise a winch, a guide wire extending from the winch and a female connecting element. The guide wire is configured to couple to the connection point of the male connecting element of the transfer manifold. Alternatively, a male connecting element may be fixed to the transfer manifold comprising a winch and a guide wire. The guide wire may then be secured to a connection point on a female connecting element of the receiving manifold.

According to a further aspect of the present invention, there may be provided a bunker vessel comprising the apparatus of the second or third aspects. A bunker vessel is a vessel designed to provide fuel to another vessel. As both vessels may be floating during the fuel transfer, it is important to provide adequate flexibility in the transfer apparatus, and as such the transfer apparatus of the present invention finds particular utility. Alternatively, the apparatus described above may be provided on a jetty, or any other suitable fluid transfer facility.

According to a yet further aspect, there is provided a method for carrying out fluid transfer, comprising

suspending a transfer manifold from a support member by a tensioning member; securing a guide wire extending from a winch fixed to either the transfer manifold or a receiving manifold to a first connecting element of a pair of male and female connecting elements, the first connecting element being fixed to the other of the transfer manifold and the receiving manifold; winching the guide wire to draw the female connecting element and the male connecting element together, wherein one of the male connecting element and the female connecting element is fixed to the transfer manifold and the other is fixed to the receiving manifold;

fixing the receiving manifold to the transfer manifold;

applying a tensile force to the transfer manifold by the tensioning member during a fluid transfer operation between the transfer manifold and the receiving manifold.

In some embodiments, the guide wire extends through a guide hole in the male or female connecting element which is fixed to the same manifold as the winch. The guide wire is secured to a connection point on the first connecting element of the pair of female and male connecting elements, which is fixed to the other of the receiving manifold or transfer manifold. Preferably, the transfer manifold is suspended in a position above the receiving manifold prior to the winching step. Preferably, the tensile force is constant during the transfer operation.

In preferred embodiments, the method further comprises maintaining the connection between the guide wire and the male connecting element during a fluid transfer operation between the transfer manifold and the receiving manifold.

Preferably, the fluid is a hydrocarbon fuel, more preferably liquid natural gas (LNG). In particular embodiments, there may be provided two catenary hoses. These may carry LNG to a receiving system and receive boil off gas (i.e. LNG which has evaporated) from the receiving system.

Brief Description of the Drawings

Embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a fluid transfer apparatus according to a preferred embodiment of the present invention;

Figure 2 is a side view of a connection guidance system according to the preferred embodiment of the present invention;

Figure 3 is a side view of the connection guidance system according to the preferred embodiment of the present invention showing the connection of the different elements of the connection guidance system;

Figure 4 is a perspective view of the preferred embodiment of the present invention; and Figure 5 is a perspective view of the preferred embodiment of the present invention. Detailed Description

With reference to Figure 1 , a perspective view of a fluid transfer apparatus 10 is shown. The fluid transfer apparatus 10 is designed to provide fluid, particularly liquid natural gas (LNG), to a receiving vessel and to receive boil-off gas (LNG vapour) therefrom. The fluid transfer apparatus is designed to accommodate movement of the receiving vessel.

The fluid transfer apparatus comprises two catenary hoses 11 each suspended from a support member 12 at an end of the fluid transfer apparatus proximal to the refuelling vessel or the jetty. The distal end of each catenary hose 11 is coupled to a transfer manifold 150. The manifold 150 can be coupled to the systems of a receiving vessel. As such, the apparatus 10 may transfer fluid to and from a receiving vessel through a path comprising the rigid pipe 13, the catenary hose 1 1 and the transfer manifold 150. The apparatus 10 allows the relative movement of the receiving vessel to be accommodated.

A tensioning member 16 is also provided. The tensioning member 16 comprises two wire elements which are maintained under constant tension by a tension drive element, in this embodiment a constant tension winch 17. In the embodiment shown, the tensioning member 16 is coupled to the transfer manifold 150, and exerts a tensile force on the distal end of each catenary hose 11 via the manifold 150. The tensioning member 16 is extensible, in the sense that its longitudinal extent may vary. In the preferred embodiment shown in Figure 1 , this is achieved through the constant tension winch which releases more or less wire according to the current level of tension. The tensioning member 16 is suspended from a support arm 18 comprising a plurality of rigid elements which are movable relative to one another and are hydraulically controlled. The movable elements are pivotally mounted to each other. In the preferred embodiment, the pivotal mounting of the rigid elements is around a horizontal axis, although other axes or forms of movement are possible. By controlling the support arm 18, the position of the tensioning member 16 and thus the transfer manifold 150 can be controlled.

The transfer manifold 150 comprises an emergency disconnection system 15, which is hydraulically powered via a hydraulic supply line 20, which is suspended from the support member 12. The emergency disconnection system comprises a double isolation valve, particularly a double ball valve for each fluid path which is activated to prevent transfer of fluid in the case of an emergency. With reference to Figure 2, a connection guidance system 100 comprises the apparatus 10 of Figure 1 and a receiving manifold 180. The receiving manifold is located on a receiving vessel. The connection guidance system is designed to connect the catenary hose to the systems of the receiving vessel and accommodate movement of the receiving vessel. A transfer manifold 150 of the connection guidance system 100 is suspended from a support member 18 of the fluid transfer apparatus described with reference to Figure 1. The manifold 150 incorporates two separate fluid paths as in Figure 1 , but only one is shown in Figure 2 due to the perspective of the figure. As mentioned above, the apparatus 10 comprises a tensioning member 16, which is maintained at a constant tension by the auto-tensioning constant tension winch 17 of the fluid transfer apparatus. In this embodiment, the tensioning member 16 is a wire element. The auto-tensioning winch 17 pays in or out to compensate for relative movements of the vessels, while maintaining a constant tension during fluid transfer operations. This arrangement is advantageous as if an emergency situation were to occur, the winch 17 draws the transfer manifold upwards, away from contact with either vessel.

As can be seen in Figure 2, the transfer apparatus 10 comprises a guide wire 104 which is an alignment cable designed to align the manifold 150 of the apparatus 10 and a manifold 180 of the receiving vessel. An end of the guide wire 104 is securely connected to a winch 152 and the guide wire 104 is wound around the winch 152. The auto-tensioning winch 17 of the fluid transfer apparatus is arranged to apply a positive tension to the tensioning member 16 until the guide wire 104 is in tension. A coupler 108 is securely connected to another end of the guide wire 104. The coupler 108 is arranged to couple to a fixing point 182 on a cylindrical male connecting element 184 of a manifold 180 of the receiving vessel. The coupler 108 may be a clip which clips onto a ring at the fixing point 182. In other embodiments, the coupler may connect to the fixing point by other means. For example, the coupler may be a threaded bolt which fixes to a corresponding threaded hole. The guide wire 104 is designed to align the relative positions of flanges on the manifold 150 of the apparatus 10 and the manifold 180 of the receiving vessel when the fluid transfer apparatus nears the receiving vessel. This design may facilitate a very controlled connection of the transfer manifold 150 to the receiving manifold 180.

The transfer manifold 150 is formed of a series of hollow pipes suitable for the transfer of fuel, for example LNG. The manifold 150 further comprises a flange 154 and a female connecting element 156. The flange 154 is arranged to couple to a flange 186 of the receiving manifold 180. The female connecting element 156 is a cylindrical hollow member. One end of the female connecting element 156 comprises a conical member 158 to form a flared end section. The female connecting element 156 is designed to receive the male connecting element 184. In this embodiment, the conical member 158 has a lower section of greater radius than an upper section. This is advantageous as it provides a larger margin for error as the transfer manifold 150 approaches the receiving manifold 180 from a relatively high position, while at the same time reduces the weight of the connection guidance system in comparison with an approach in which the top section is also enlarged.

The winch 152 is connected to the transfer manifold 150. The winch 152 is secured to the back of the female connecting element 156 on the transfer manifold 150. The guide wire 104 passes through the female connecting element. The tensioning member 16, the guide wire 104, the male connecting element 184 and the female connecting element 156 in combination assist with the connection of the transfer manifold to the receiving vessel manifold 180. Both the male connecting element 184, the female connecting element 156, and the winch 152 can be fitted and removed from their respective manifold assemblies. In some embodiments, the winch 152 can be fixed to the receiving manifold instead of the transfer manifold. Furthermore, the locations of the male and female connecting elements may be reversed; the male connecting element 184 may be fixed to the transfer manifold 150 and the female connecting element 156 may be fixed to the receiving manifold 180. As the male connecting element, the female connecting element and the winch are removable, the connection guidance system of this preferred embodiment can be fitted to an existing manifold. New manifolds are therefore not required, which would be expensive. The flanges 186 and 154 are removable and can therefore be sacrificial pieces, again preventing the need for a new manifold system. Furthermore, by integrating removable parts into the connection guidance system, the parts can be sacrificial in the event of any damage. This can be beneficial as it can further reduce costs.

The manifold 150 further comprises an emergency disconnection system 15. The emergency disconnection system 15 is designed to engage when a tension on the tensioning member 16 exceeds a prescribed safety threshold. When disconnection occurs, the transfer manifold 150 becomes two separate pieces. One piece is connected to the catenary hose and the other piece remains connected to the receiving vessel manifold 180. The emergency disconnection system 15 comprises valves which prevent the fluid in the catenary hoses from spilling onto a vessel or into the sea.

With reference to Figure 3, the connection process is described. In use, the apparatus 10 is brought to the vicinity of a receiving vessel. During a connection stage, the tension winch 17 may be configured to maintain a constant length of the tensioning member (rather than a constant tension) in order for the position of the transfer manifold 150 to be readily manoeuvred towards a receiving manifold 180 of the receiving vessel. The support arm 18 may be used to move the transfer manifold 150 close to the receiving manifold 180 of the receiving vessel. As the manifold 150 of the connection guidance system nears the manifold 180, the guide wire 104 is passed to the operators of the receiving vessel and the coupler 108 is secured to the fixing point 182 of the male connecting element 184. Once the manifold 150 and the manifold 180 are connected by the cable 104, the winch 152 acts in positive tension in order to compensate for the relative movements of the bodies. The winch 152 winds up the guide wire 104 to gradually draw the manifold 150 towards the receiving vessel manifold 180.

The male connecting element 184 of the receiving manifold 180 is arranged to fit inside the female connecting element 156 of the transfer manifold 150. Therefore, as the cable 104 is wound up, the male connecting element 184 is drawn through the female connecting element 156 towards the winch 152. The fit between the male connecting element 184 and the female connecting element 156 is such that when the male connecting element 184 is inside the female connecting element 156, a flange 186 of the manifold 180 is in alignment with a flange 154 of the manifold 150. Once the manifolds are in the connection position, they are held in alignment by the guide wire 104 acting in positive tension. An automatic or manual procedure can be followed to secure the flange 154 of the transfer manifold 150 to the flange 186 of the receiving manifold 180. The tension winch 17 may then be controlled to enter a mode in which tension in the tensioning member 16 is kept constant during a fluid transfer operation.

Once the transfer manifold 150 is secured to the receiving manifold 180 of the receiving vessel, transfer operations can begin. For example, LNG can be transferred to the receiving vessel through one of the catenary hoses while boil-off gas can be received through the other. If the receiving vessel moves during the transfer operation, this is accommodated by flexibility in the transfer apparatus 10. In particular, the catenary hoses 11 provide flexible fluid paths that can accommodate relative movement. Moreover, while the transfer manifold 150 is also coupled to the tensioning member 16, the extensible nature of the tensioning member 16 enables movement of the transfer manifold 150 as does the movable support arm 18 from which the tensioning member 16 is supported.

During the transfer of fluid, the tensioning member 16 applies a tensile force to the transfer manifold 150. In the preferred embodiment, the tensile force is constant throughout the transfer operation, although it may be variable in alternative embodiments. As a result, if the transfer manifold 150 should become disengaged from the receiving manifold 180 of the receiving vessel then the tensioning member 16 will act to pull the transfer manifold away, preferably upwards, from its current location.

Accordingly, in the case of an unexpected disengagement, the transfer manifold 150 will automatically move away from the receiving vessel. This fulfils a safety requirement during fuel transfer. In addition, in the case of an unexpected disengagement, the emergency disconnection system 15 will act to prevent the transfer of fluid through the transfer manifold 150. In particular, the double ball valve of the emergency disconnection system 15 is engaged using power from a hydraulic supply line 20 to close the fluid path through the transfer manifold.

The emergency disconnection system 15 may additionally or alternatively separate the transfer manifold 150 into a distal part and a proximal part. The proximal part of the transfer manifold is coupled to the tensioning member 16 and is thus drawn away from the receiving manifold 180. Preferably, the proximal part is coupled to the catenary hoses 1 1.

Preferably, the winch 152 is coupled to the distal part. In some embodiments, the guide wire 104 may be fixed to the distal part of the transfer manifold 150 and the winch 152 may be coupled to the receiving manifold 180. In either arrangement, the connection between the distal part of the transfer manifold 150 and the receiving manifold 180, including the action of the guide wire 104, is not interrupted.

With reference to Figure 4, a perspective view of the transfer manifold 150 is shown. From Figure 4 it can be clearly seen that the transfer manifold 150 comprises two fluid path assemblies, as described above with reference to Figures 1 to 3. Each fluid path assembly comprises a distal part and a proximal part connected by an emergency disconnection system 15. Furthermore, each fluid path assembly comprises the elements of the transfer manifold described above in relation to Figures 2 and 3, particularly winch 152, guide wire 104 and female connecting element 156. With reference to Figure 5, the two fluid paths of the transfer manifold 150 are connected to corresponding fluid transfer paths of the receiving manifold 180, each being provided with a male connecting element 184. The two fluid paths are used to connect two different catenary hoses. When transferring liquid natural gas (LNG), it is often necessary not only to transfer the LNG to the receiving vessel, but also to carry boil off gas (LNG vapour) away from that vessel. Therefore, there is a need to connect a vapour line in addition to the catenary hose carrying the LNG. As described above with reference to Figures 1 and 2, the tensioning members 16 are maintained at a constant tension and the guide wires 104 pulls the transfer manifold 150 towards the receiving manifold 180 to facilitate correct alignment of the flanges 154 and 186. The two fluid path assemblies of the transfer manifold 150 are joined by two spacer bars 370. In other embodiments, there may be more than two fluid path assemblies arranged in series and separated by a plurality of spacer bars. Alternatively, the assemblies 150 may be separated by one spacer bar 370. The spacer bars 370 are coupled to the assemblies, one above the emergency disconnection system 15 and one below. This ensures that if emergency disconnection of the transfer line manifold assemblies occurs, the two assemblies will not contact one another and possibly cause a spark. The spacer bars 370 in this embodiment are rigging screws (bottle screws), but another form of coupling between the spacer bars 370 and the assemblies can be used. The spacer bars enable the adjustment of the spacing between the two assemblies. Currently, there is no standard separation distance between the assemblies for bunkering vessels. Therefore, the present invention ensures that the connection guidance system can be adjusted for use with a range of receiving manifolds 180.

Other variations and modifications will be apparent to the skilled person. Such variations and modifications may involve equivalent and other features which are already known and which may be used instead of, or in addition to, features described herein. Features that are described in the context of separate embodiments may be provided in combination in a single embodiment. Conversely, features which are described in the context of a single embodiment may be also provided separately or in any suitable sub-combination.

It should be noted that the term "comprising" does not exclude other elements or steps, the term "a" or "an" does not exclude a plurality, a single feature may fulfil the functions of several features recited in the claims and reference signs in the claims shall not be construed as limiting the scope of the claims. It should be noted that the Figures are not necessarily to scale; emphasis instead generally being placed upon illustrating the principles of the present disclosure.