INDUSTRIALFILTER SCREENWITHANINCREASEDSURFACEAREAANDA FILTRATIONASSEMBLY COMPRISINGTHESAME TechnicalFieldof theInvention The present invention generally relates to a filter screen for filtrating a liquid and screening of impurities and contaminant particles in a stream of liquid. The present invention particularly relates to a corrugated filtration screen designed for an industrial filter assembly and an industrial filter assembly as such. Background f theInvention Filtration assemblies are often used in a wide variety of industries pertaining to irrigation, cooling towers, fish farms, power generation plants, sea water treatment systems, steel industry, ships, etc. where it is required to supply a liquid, such as water from a source to a system. These filter assemblies generally accommodate a filter screen inside their body to filter the impurities and contaminant particles flowing into the filter in order to supply clean water to a system through its output. An assembly disclosed in CN 206285563 U suggests a water filter with a cylindrical body, a water inlet, a water outlet, and a cylindrical filtration screen arranged inside the body, comprising a cylindrical sieve, screen openings and a plurality of support rings. A further arrangement disclosed in WO 2015 130253 A1 provides a filtration assembly comprising a filter body, an inlet, an outlet, and a pair of cylindrical filter screens having screen openings. Similarly, KR 20130063563 A proposes a filtration assembly with a body, an inlet formed at one side of the body, an outlet formed at the other side of the body, and a cylindrical filtration screen built in the body so as to filter the water flowing into the assembly through screen openings. As the above-mentioned prior art documents indicate, the conventional filtration screens used in filtration assemblies provide a basic cylindrical shape with a flat surface to retain impurities and contaminant particles by means of screen openings. In large-scale industrial applications, this approach necessitates the implementation of substantially bigger filtration screens and thus bigger filtration systems, therefore increasing the production cost of the filtration screen and accordingly the whole filtration system accommodating the screen, and the complexity of the overall assembly. In addition, filtration systems with built-in cleaning means and mechanisms INDUSTRIALFILTER SCREEN^WITH^AN^INCREASED^SURFACE^AREA^AND^A^ FILTRATION^ASSEMBLY COMPRISING^THE^SAME Technical^Field^of^the^Invention The present invention generally relates to a filter screen for filtrating a liquid and screening of impurities and contaminant particles in a stream of liquid. The present invention particularly relates to a corrugated filtration screen designed for an industrial filter assembly and an industrial filter assembly as such. Background^of^the^Invention Filtration assemblies are often used in a wide variety of industries pertaining to irrigation, cooling towers, fish farms, power generation plants, sea water treatment systems, steel industry, ships, etc. where it is required to supply a liquid, such as water from a source to a system. These filter assemblies generally accommodate a filter screen inside their body to filter the impurities and contaminant particles flowing into the filter in order to supply clean water to a system through its output. An assembly disclosed in CN 206285563 U suggests a water filter with a cylindrical body, a water inlet, a water outlet, and a cylindrical filtration screen arranged inside the body, comprising a cylindrical sieve, screen openings and a plurality of support rings. A further arrangement disclosed in WO 2015 130253 A1 provides a filtration assembly comprising a filter body, an inlet, an outlet, and a pair of cylindrical filter screens having screen openings. Similarly, KR 20130063563 A proposes a filtration assembly with a body, an inlet formed at one side of the body, an outlet formed at the other side of the body, and a cylindrical filtration screen built in the body so as to filter the water flowing into the assembly through screen openings. As the above-mentioned prior art documents indicate, the conventional filtration screens used in filtration assemblies provide a basic cylindrical shape with a flat surface to retain impurities and contaminant particles by means of screen openings. In large-scale industrial applications, this approach necessitates the implementation of substantially bigger filtration screens and thus bigger filtration systems, therefore increasing the production cost of the filtration screen and accordingly the whole filtration system accommodating the screen, and the complexity of the overall assembly. In addition, filtration systems with built-in cleaning means and mechanisms - forming an undulated pattern on the sheet (6) defining a plurality of ridges and valleys continuously adjacent to each other, - reshaping the so formed sheet (6) to form a cylindrical shape with a filtration volume (3), - joining the meeting ends of the reshaped sheet (6) and obtaining a filter screen (1). In this method the said at least two layers of materials having different properties from one another can be simultaneously pressed in the press die (7). In a further aspect, the present invention provides a novel filtration assembly comprising the filter screen (1) as defined hereinabove. Such an industrial filtration assembly can be used for supplying filtrated water in irrigation, cooling towers, fish farms, power generation plants, sea water treatment systems, waste water treatment systems, steel production facilities and ships. Brief Descriptionof theFigures The figures, whose brief explanations are herewith provided, are solely intended for providing a better understanding of the present invention and are as such not intended to define the scope of protection or the context in which said scope is to be interpreted in the absence of the description. Fig.1 shows a perspective view of the filtration screen according to the present invention. Fig.2 shows a perspective view of the pressing apparatus and the sheet according to the present invention before the sheet is pressed. Fig.3 shows a perspective view of the pressing apparatus and the sheet according to the present invention after the sheet is pressed. Fig.4 shows a perspective view of the sheet according to the present invention after the sheet is pressed. Fig.5 shows an embodiment according to the present invention wherein the sheet is formed by a plurality of layers. Fig.5 is a perspective view of the filtration assembly comprising the filter screen according to the present invention. Fig.6 shows a cross-section and inner structure of the filtration assembly as shown in Fig.5. References 1. Filter screen 2. Screen openings 3. Inner surface of the screen 4. Outer surface of the screen 5. Flat portion of the screen 6. Sheet 7. Die press 8. Die 9. Flat portion of the die 10. Liquid inlet of the filtration assembly 11. Liquid outlet of the filtration assembly 12. Cleaning means 13. Nozzle 14. Collecting pipe 15. Discharge valve 16. Actuation unit 17. Motor 18. Brush V. Filtration volume DetailedDescriptionof theInvention The present invention relates to a novel filter screen for filtrating a liquid and screening of impurities and contaminant particles in a stream of liquid to solve the above-mentioned problems, overcome the shortcomings of the relevant prior art and provide further advantages. The present invention is disclosed in more detail with reference to different embodiments hereinbelow. As seen in FIG. 1, which shows a perspective view of the filter screen according to the present invention, a filter screen (1) for screening of particles in a stream of liquid is provided, having an outer surface (4), an inner surface (3), screen openings (2) and a filtration volume (V). The filter screen according to the present invention (1) is in the form of a cylinder with a varying diameter in cross-section wherein the filter screen’s (1) diameter is alternating between a maximum diameter and a minimum diameter along at least part of the longitudinal axis (x) of the cylinder so as to form ridges and valleys continuously adjacent to each other on both surfaces thereof. More preferably, the inner surface (3) and outer surface of the filter screen (1) is in a corrugated form undulating through the longitudinal axis (x). The filter screen (1) may further comprise at least one flat portion (5) with a fixed diameter at its top end and/or its bottom end. The minimum diameter and the maximum diameter values, and correspondingly the radii of curvatures of the ridges and the valleys may be chosen by a person skilled in the art according to the scale of the application. Preferably, the maximum diameter is at most 10% larger than the minimum diameter. At a point where the cylinder has a minimum diameter, the corresponding corrugation defines a valley on the outer surface (4) and a ridge on the inner surface (3). Likewise, at a point where the cylinder has a maximum diameter, the corresponding corrugation defines a ridge on the outer surface (4) and a valley on the inner surface (3). Accordingly, at least one of the top and the bottom ends of the screen in cylinder form embodies a flat portion (5) in order to allow the filtration screen (1) to be seamlessly and conveniently incorporated into a filtration assembly. The size of the flat portion(s) (5) may be chosen such that only the portion that is to be used for the installation of the filtration screen (1) is flat, and the rest of the filtration screen (1) comprises undulations as described hereinabove in order to obtain a filtration screen (1) with as much surface area as possible. Thereby a filtration screen (1) that is capable of screening a larger amount of impurities and contaminant particles compared to the conventional filtration screens, which would occupy an equivalent space within a filtration assembly, is provided by means of the increased surface area of the filter screen obtained by virtue of the combination of the features described. For this reason, the filter screen (1) according to the present invention is more space-efficient compared to the filtration screens proposed in the prior art and has reduced costs. Further, since a filtration assembly comprising the filter screen (1) would not have to be as big as it would otherwise have to be, a filtration assembly comprising the filter screen (1) according to the present invention has reduced energy consumption as well as reduced complexity. In a preferred embodiment, the filter screen (1) according to the present invention may comprise at least two or more superposed layers of materials as shown in FIG.5, having different properties from one another. These may include but are not limited to, for instance, permeable membranes, metal sheets with openings (i.e., mesh), porous polymers, composites, etc. In another aspect of the present invention, a method for producing a filter screen (1) according to any of the embodiments described hereinabove is provided, as illustrated in detail within FIGS.1 to 4. In the method, a die press (7) having a pair of dies (8) corresponding to each other is provided as shown FIG 2. Each of the dies (8) has a plurality of convex and concave portions continuously alternating on at least a part of each die’s (8) surface. Each of the dies (8) may further comprise a flat portion (9) in order to form the flat portions (5) on the filter screen (1). The method according to the instant invention comprises placing of the sheet (6) constituting the screen material inbetween the dies (8), in such a manner that the concave portions of the first die (8) would face the convex portions of the other die (8). Thus the sheet (6) is subsequently pressed and sandwiched between the pair of dies (8) forming an undulated pattern and defining a plurality of ridges and valleys continuously adjacent to each other on both surfaces of the sheet (8). The so formed sheet (8) is then reshaped to form a cylinder with a filtration volume (V) and lateral ends thereof are fixed to obtain the filter screen (1) according to the present invention. Therefore, a method for producing a filter screen (1) with reduced production costs and a facilitated process is obtained. In a preferred embodiment of the method according to the present invention, the method further comprises superposing at least two layers of materials having different properties from one another to obtain a sheet (6) with multiple layers. These layers can be pressed simultaneously within the die press (7) by superposing them one on another such that they behave as a single sheet (6). In a further aspect, the present invention relates to a filtration assembly as shown in FIG. 6 comprising the filter screen (1) according to any of the embodiments described hereinabove. As mentioned above, a filtration assembly comprising the filter screen (1) according to the present invention is more efficient compared to the conventional assemblies of the same size due to the filter screen (1) having an increased surface area as compared to other cylindrical screens, and thus the filtration assembly according to the present invention has reduced costs as the assembly can be constructed in a more compact manner, and featuring reduced energy consumption and reduced complexity. In a preferred embodiment of the filtration assembly according to the present invention, the filtration assembly further comprises a liquid inlet (10) that is in liquid communication with the filter screen (1). The liquid inlet (10) is arranged to allow the incoming liquid to flow into the filtration volume (V) of the filter screen (1) and towards the inner surface of the filter screen (1). The filtration assembly comprises also a liquid outlet (11) that is in liquid communication with the outer surface of the filter screen (1) for the filtered liquid to be discharged through. A more preferred form of the filtration assembly according to the present invention is shown in FIG 7. Accordingly, the assembly may further comprise a cleaning means (12) that is suitable for cleaning the inner surface (3) of the filter screen (1). The cleaning means (12) preferably comprises at least one nozzle (13) disposed in fluid communication with a collecting pipe (14) to suck and remove the particles from the inner surface (3) of the filter screen (1) under a negative pressure. For this purpose, the collecting pipe (14) is connected to a discharge valve (15) such that a negative pressure is created in opening ends of the nozzles (13). The collecting pipe (14) can be rotatably arranged in the longitudinal axis of the filtration assembly which rotation is provided by an actuation unit (16) driven by a motor (17). Alternatively, the cleaning means (12) can be equipped with at least one brush (18) to swipe and clean inner surface (3) of the filter screen (1). Nevertheless, a combination of at least one nozzle (13) and at least one brush (18) disposed on the collecting pipe (14) is more preferred because of the undulations on inner surface (3) of the filter screen (1). Due to these irregularities, nozzles (13) may have limited abutment to the inner surface (3) but the brushes (18) extending to the valleys of the inner surface (3) compensate shortcomings of the nozzles (13). In a further aspect, the present invention relates to use of the filtration assembly according to any of the embodiments described hereinabove for supplying filtrated water in irrigation, cooling towers, fish farms, power generation plants, sea water treatment systems, waste water treatment systems, steel production facilities and ships. Further advantages, the possible embodiments and uses of the invention shall be apparent for those skilled in the art in view of the claims and exemplary drawings appended to the present description.