Available online at Procedia Engineering 200 (2010) (2009)

Transcription

1 Available online at Procedia Engineering 200 (2010) (2009) Procedia Engineering 8 th Conference of the International Sports Engineering Association (ISEA) Contribution of Swimsuits to Swimmer s Performance Hazim Moria a, *, Harun Chowdhury a, Firoz Alam a, Aleksandar Subic a, Alexander John Smits b, Rahim Jassim c and Nasser Suliman Bajaba c a School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Melbourne, Australia b Department of Mechanical and Aerospace Engineering, Princeton University, USA c Department of Mechanical Engineering, Yanbu Industrial College, Kingdom of Saudi Arabia Received 31 January 2010; revised 7 March 2010; accepted 21 March 2010 Abstract Swimsuit is believed to play an important role in swimmer s performance. In competitive swimming (national, world and Olympic events) it is usually a very short winning time margins that often requires the help of advanced technology to determine the time difference between the winner and loser. Almost over 90% of swimmer s energy is spent to overcome hydrodynamic resistance during forward motion. Hence, the swimsuits might play an important role in reducing the hydrodynamic resistance and its associated energy loss during the swimming and can contribute positively to the final outcome. Development of efficient swimsuits is an on going process and the performance of swimsuit is believed to be getting better progressively. Currently, swimsuit manufacturers spend huge resources to design swimsuits using new materials and techniques. Very often swimsuit manufacturers claim and counterclaim about the performance of the swimsuits. However, there is no independent study that can verify these claims and counter claims. This paper describes a hydrodynamics comparative evaluation of two commercially available swimsuits and their role that might be played in swimsuit aerodynamics. c Published by Elsevier Ltd. Keywords: Swimsuit, aerodynamics, hydrodynamic, drag, performance; 1. Introduction Hydrodynamics plays an essential role in swimming performance regardless of the particular event (freestyle, butterfly, breaststroke or backstroke). Studies estimate that over 90% of the swimmer s power output is spent overcoming hydrodynamic resistance [2, 9]. The hydrodynamic resistance can be divided approximately into three, almost independent components: wave drag, form drag, and skin friction drag. The wave drag is associated with the work required to generate waves, form drag is the resistance to motion due to the shape of the body, and skin friction is the resistance to motion due to the area of the body with the water (the wetted area). The form drag is believed to constitute almost 90% of the total drag [2]. All three components are time-dependent as the swimmer * Corresponding author. Tel.: ; fax: address: hazim.moria@student.rmit.edu.au c 2010 Published by Elsevier Ltd. doi: /j.proeng

2 2506 H. Moria et al. / Procedia Engineering 2 (2010) H. Moria et al. / Procedia Engineering 00 (2010) completes the stroke, and all three components depend on the speed of the swimmer, as well as his/her shape, length, and style. Historically, the people used to swim nude and it was socially accepted. Today s swimsuit has travelled a long path and gone through a series of changes of styles and designs. Notably, in the early 18th century, wool and flannel were chosen as a suit fabric covering almost the entire skin of the swimmer. However, this suit became bulky when it came to contact with water. In 1908, the Australian swimmer, Annette Kellerman created the first practical swimsuit made of one piece plus bathing socks. This suit exposed the knees and arms of the swimmer for the first time in the history of swimming. Officially, the women s swimming events were added to Olympic game in 1912 and swimmers were allowed to use relatively shorter swimsuits. In 1920s, swimsuits were shortened even more, but women had to wear a short skirt called modesty panel and by this time a two-piece swimsuit became very common. In 1930s, bikini was introduced as an innovative swimwear. In 1950s, the bikini became more popular due to the economic boom and tranquility and revamped the traditional one-piece swimsuit. After the World War II, Nylon replaced the silk and wool in major events competitive suits and the colour was allowed in 1964 while the modesty panel was eliminated in In 1990s, swimsuits continue to evolve to mimic skin and the Lycra was introduced and quickly became popular. In 2000s, Speedo lunched the full-body Fastskin swimsuit based on so called shark s skin pattern and mimicked in V-shape ridges [6]. More recently, many other commercial swimsuit manufacturers have claimed and counterclaimed about their swimsuits performance by reducing aerodynamic drag and enhancing buoyancy. Since Beijing Olympic 2008, almost all major manufacturers introduced full-body swimsuits made of semi- and- full polyurethane combined with Lycra fabric. One of the most publicised swimsuits of these categories is Speedo LZR. The manufacturers claimed these suits have features such as ultra-light weight, water repellence, muscles oscillation and skin vibration reduction by compressing the body. Recently, swimsuits have been aggressively marketed principally as a means for reducing the skin friction component of the total drag, thereby conferring a competitive advantage over other swimmers. Some manufacturers have claimed significant reduction of drag, but it is difficult to find independent research in the open literature that supports these claims and counter claims [9]. Technologically, Strangwood [1] points out that the close interplay of design and sports materials brought about by engineering modelling is only as good as the data on which it is based. Also, the technological innovation in both design and materials has played a crucial role in sport achieving its current standing in both absolute performance and its aesthetics. Chowdhury et al. [5, 7, 8] clearly revealed that textiles can play a vital role in high performance sports where speed is a dominating factor. The aerodynamic properties such as drag and lift can play a dominant role in swimming especially in swimsuit design. The swimmers usually involve very short winning time margins in events that often have much longer timescales, making hydrodynamic resistance and its associated energy loss during the event significant in the outcome. In order to find answers of many contemporary questions on swimsuits, a large research project on swimsuit aerodynamics/hydrodynamics has been undertaken in the School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University. As part of this large research project, we have undertaken a comparative study of commercially acclaimed swimsuits. The study was conducted experimentally using wind tunnel facilities and specially developed testing methodology. 2. Testing Methodology and Experimental Procedure 2.1. Description of Standard Cylinder and Experimental Arrangement In order to obtain aerodynamic properties experimentally for a range of commercially available swimsuits made of various materials composition, a 110 mm diameter cylinder was manufactured. The cylinder was made of PVC material and used some filler to make it structurally rigid. The cylinder was vertically supported on a six component force sensor as shown in Figure 1. The aerodynamic forces and their moments were measured for a range of Re numbers based on cylinder diameter and varied wind tunnel air speeds (from 10 km/h to 120 km/h with an increment of 10 km/h). Each test was conducted as a function of swimsuit fabric orientation and seam positions.

3 H. Moria et al. / Procedia Engineering 2 (2010) H. Moria et al. / Procedia Engineering 00 (2010) (a) Experimental bare cylinder in wind tunnel (b) Schematic CAD model Fig 1. Experimental cylinder used to test the surface friction of swimsuit fabrics and CAD model 2.2. Description of Swimsuit Fabrics Two brand new full-body swimsuit materials have been selected for this study as they are officially used in the world and Olympic events. These swimsuits are: a) Speedo LZR Racer and b) Speedo Fast Skin-II (FS-II). In order to benchmark the aerodynamic performance of the swimsuits, the bare cylinder was tested initially. Later, the cylinder was wrapped with the swimsuit fabrics that were tested with the same test conditions as was in the case of bare cylinder. The Speedo LZR Racer swimsuit composed of 70% Polyamide (polyurethane) and 30% Elastane (Lycra) with ultrasonic weld seam which is located on sides (90 ). The polyurethane panels were superimposed on the Polyamide [6]. On the other hand, the Speedo FS-II is made of 75% Polyamide and 25% Elastane with 26 stitches per every 3 cm of seam [6]. The Speedo FS-II was tested at several fibre orientations including V-pattern and the reverse direction of V-pattern (e.g. Λ-shape). Additionally, the FS-II materials were also tested as a function seam positions. The Speedo LZR fabric was tested as a function of seams positions (i.e., ultrasonic weld seam) only as this fabric visually does not have V-pattern. Frontal view of swimsuit fabrics facing the wind, the left image shows the FS-II V-shape, FS-II vertical orientation, FS-II Λ-shape, Speedo LZR polyurethane panel and Speedo LZR fabric respectively. (a) Speedo Fast Skin-II (b) Speedo LZR Racer Fig 2. Experimental set up of swimsuits orientations in RMIT industrial wind tunnel

4 2508 H. Moria et al. / Procedia Engineering 2 (2010) H. Moria et al. / Procedia Engineering 00 (2010) Experimental Facilities The RMIT Industrial Wind Tunnel was used to measure the aerodynamic properties of swimsuit fabrics. The tunnel is a closed return circuit wind tunnel with a turntable to simulate the cross wind effects. The maximum speed of the tunnel is approximately 150 km/h. The rectangular test section dimensions are 3 m wide, 2 m high and 9 m long, and the tunnel s cross sectional area is 6 square meter. A plan view of the tunnel is shown in Figure 3. The tunnel was calibrated before conducting the experiments and tunnel s air speeds were measured via a modified National Physical Laboratory (NPL) ellipsoidal head Pitot-static tube (located at the entry of the test section) connected to a MKS Baratron pressure sensor through flexible tubing. The mounting strut (sting) holding the cylinder was mounted on a six component force sensor type JR-3 which measures all three forces (drag, lift and side forces) and three moments (yaw, pitch and roll moments). The data acquisition was recorded using ten second snaps. Computer software samples the forces at a frequency of 2000 Hz ensuring electrical interference is minimised. Multiple snaps were collected at each acquisition point and the results were averaged thus minimising possible errors in the data further. Further details about the wind tunnel can be found in Alam et al. [4]. Fig. 3. A plan view of RMIT Industrial Wind Tunnel [3] 4. Results and Discussion In this paper, only drag data in the form of non-dimensional drag coefficient (C D ) is presented. The C D was calculated using the following formula: C D =D/0.5ρV 2 A. The Reynolds Number was estimated by using Re=ρVd/μ which was varied by tunnel speeds only. The C D as a function of Reynolds numbers (Re) under a range of materials and fabric orientations of the swimsuits is shown in Figures 4 to 6. In order to compare the results of swimsuits materials, the C D of the bare cylinder was also shown in all figures. Figure 4 illustrates the C D variation with Reynolds number (Re) for the three fibre orientation patterns (V, reverse V & straight) of FS-II suit and the bare cylinder. At 70 km/h (corresponding speed in water 1.3 m/s), the airflow over the V and reverse V pattern fibre orientation of the materials under goes transition from laminar to turbulent and completes the transition at 90 km/h (1.7 m/s in water). However, the airflow over the bare cylinder and the material with straight fibre orientation does not undergo any transition and has the similar C D value (0.78). The reverse V pattern material has demonstrated the lowest C D (0.60) whereas the V pattern material possesses C D value of It may be noted that in most competitive swimming events, the swimmer s speed is in between 1.5 m/s (5.4 km/h) to 2.2 m/s (7.9 km/h) [9]. The C D variation with Re is shown in Figure 5 for the Speedo LZR swimsuit with a range of weld seam orientations. As mentioned previously, this suit is made of polyurethane and Lycra materials. The C D value for the polyurethane material is also shown in the figure. Unlike FS-II, the LZR material regardless of its seam weld positions undergoes transition at 90 km/h (1.7 m/s in water) and the transition ends at speeds over 110 km/h. No variation in C D value was noted. However, a small transition was observed for the bare cylinder and the polyurethane material at 90 km/h (see Figure 5). But, it was not clear if the flow becomes fully turbulent at speed 120 km/h for the bare cylinder and the polyurethane material. In order to clarify this, a further testing is underway. It

5 H. Moria et al. / Procedia Engineering 2 (2010) H. Moria et al. / Procedia Engineering 00 (2010) is clearly evident that the orientation of seam weld of the LZR suit does not have any effect on aerodynamic drag due to the fact that the seam weld is very flat and has no obtrusion CD Bare cylinder 0.40 Normal V-shape 0.20 Reverse V-shape Straight E E E+06 Re Fig. 4. C D variation with Re of Speedo Fast Skin-II CD Bare cylinder Polyurethane panel Ultrasonic weld seam_face air_0 deg Ultrasonic weld seam_face air_45 deg Ultrasonic weld seam_face air_90 deg Ultrasonic weld seam _not face air_180 deg E E E+06 Re Fig. 5. C D variation with Re of Speedo LZR Racer suit CD Bare cylinder Normal V-shape Polyurethane panel Ultrasonic weld seam_face air_90 deg E E E+06 Re Fig. 6. C D variation with Re between Speedo LZR Racer and FS-II

6 2510 H. Moria et al. / Procedia Engineering 2 (2010) H. Moria et al. / Procedia Engineering 00 (2010) Figure 6 shows a comparison of C D variation with Re for the Speedo FS-II and Speedo LZR Racer swimsuits. No apparent variation in C D value for the bare cylinder and polyurethane material as mentioned earlier. In contrast, the FS-II material with V shape pattern undergoes transition at 70 km/h and completes the transition at 90 km/h. The LZR material (not polyurethane) undergoes transition at 90 km/h and completes at 110 km/h. Although the LZR undergoes transition late compared to FS-II, it possesses the lowest C D value (0.56) compared to the FS-II (0.64). Nevertheless, this C D value at swimmer s average speed in water can significantly be higher if the polyurethane material is superimposed on the textile material. The C D could be at 0.75 as shown in Figures 5 and 6. The results indicate that the use of polyurethane will not assist the swimmer with the drag reduction. However, it might have some other advantages. 5. Conclusions The following conclusions are drawn, based on the experimental work presented here: The average drag coefficient of FS-II material at high speeds (over 70 km/h) is approximately 0.62 and the average drag coefficient for LZR material (without polyurethane) at high speeds (over 90 km/h) is approximately The fibre orientation has significant effect on aerodynamic drag and the optimal orientation can reduce the hydrodynamic drag. The seam weld of LZR has minimum or no effect on aerodynamic drag The polyurethane material and the bare cylinder display the similar aerodynamic drag. Acknowledgements The authors would express their sincere thanks to Mr. Patrick Wilkins and Mr Gilbert Atkin, the School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University for their assistance in experimental set up. References [1] Strangwood M, Subic A. modelling of materials for sports equipment. Materials in Sports Equipment, Volume 2, Woodhead Publishing Ltd., Cambridge, UK; [2] Vorontsov A R, Rumyantsev V A. Resistive Forces in Swimming & Propulsive Forces in Swimming. Biomechanics in Sport edited by Zatsiorsky Blackwell, UK;2000. [3] (accessed on 14 January 2010). [4] Alam F, Zimmer G, Watkins S. Mean and time-varying flow measurements on the surface of a family of idealized road vehicles. Journal of Experimental Thermal and Fluid Sciences 2003;27 (5): [5] Chowdhury H, Alam F, Mainwaring D E, Subic A, Tate M, Forster D. Methodology for aerodynamic testing of sports garments. The Proceedings of the 4th BSME-ASME International Conference for Thermal Engineering 2008;1: [6] (accessed on 20 January 2010). [7] Chowdhury H, Alam F, Mainwaring D, Subic A, Tate M, Forster D, Beneyto-Ferre J. Design and Methodology for Evaluating Aerodynamic Characteristics of Sports Textiles. Sports Technology, Wiley/Blackwell. (DOI: /jst.92), [8] Chowdhury H, Alam F, Mainwaring D, Beneyto-Ferre J, Tate M, Forster D, Subic A. Aerodynamics of Textiles for Elite Cyclist. Proceedings of the 8th International Conference on Mechanical Engineering (ICME2009), Dhaka, Bangladesh 2009;Paper No. ICME09-FM-20 pp1-6. [9] Nakashima M, Sato Y. Optimization of arm stroke in freestyle swimming by Simulation. Engineering of Sports III 2009:1: