Designing nature-inspired swimming gloves: a biomimicry design spiral approach

Abstract

This study aims to present a comprehensive overview of the technical steps in the biomimicry design spiral and endeavours to apply these steps in the design of a swimming gloves. This involves five steps in the biomimicry design spiral as distillation, translation, discovery, emulation and evaluation. The study then provides four alternative designs inspired by the morphology of crab-eating frog legs (Fejervarya cancrivora). Computational fluid dynamic (CFD) simulation is conducted to assess drag and lift forces. The simulation incorporates parameters such as fluid density, flow speed, water pressure, turbulence intensity and viscosity. The result reveals that the full-cross (FC) swimming glove design exhibits the highest drag force, while the full-straight (FS) design achieves the highest lift force. The usability test is conducted to evaluate the designs by considering five aspects, i.e. material comfort, ease of use, ease of swimming and non-swimming activities, as well as aesthetics. The potential benefits for the industry are also provided in the end of the article.

Public Interest Statement

Finding innovative ideas in new product development is critical because designer creativity is required to meet market demands. Nature can be a source of inspiration. Biomimicry is an interdisciplinary approach to studying and transferring principles or mechanisms from nature to solve design challenges. This article explains how to design swimming gloves using the Biomimicry design spiral approach. Training arm muscles and swimming faster have become necessary for professional swimmers to improve their swimming performance. The idea of a membrane addition resembling a crab-eating frog’s (Fejervarya cancrivora) leg to the section of the hand used for paddling while swimming aims to increase thrust. Biomimicry consists of five steps as distillation, translation, discovery, emulation and evaluation. This study serves as an illustrative example of how biomimicry can be employed in product design, spanning from the initial idea generation phase to product testing, to achieve a product that effectively addresses design challenges.

Keywords:

• Biomimicry design spiral
• computational fluid dynamic simulation
• drag and lift force simulation
• nature-inspired design
• swimming gloves

Review Editor:

• Pham D T
• Chance Professor of Engineering
• School of Mechanical Engineering
• University of Birmingham
• Birmingham B15 2TT
• UNITED KINGDOM

Subjects:

• Computer Science
• Computation
• Simulation and Modelling
• Industrial Engineering and Manufacturing
• Industrial Design
• Manufacturing Engineering
• Sustainable Engineering and Manufacturing
• Arts and Humanities
• Arts
• Art and Visual Culture
• Design
• Product Design

1. Introduction

New product designs are not always successful, as the failure rate for these designs ranges from 25% to 45% (Cooper, 2001; Crawford, 1979). Out of seven new product design ideas that enter the development stage, only half are launched, with only one proving successful (Booz et al., 1982). Therefore, the creative process plays a critical role in developing ideas for product design.

Nature serves as a wellspring of inspiration when developing creative ideas for product design. Nature not only embodies perfection but also offers a myriad of sustainable solutions to problems. The challenges observed in nature often mirror those encountered by humans as we strive to devise new ways for sustainable design and living (Rao, 2014). Nature’s evolution into something superior over time provides a tested solution, honed over hundreds or thousands of years. Consequently, Earth has yielded numerous ingenious solutions that may surpass our initial imagination.

Biomimicry is a design development model proposed by Benyus (1997) in which utilizes nature as a model, measure and mentor. It involves mimicking or imitating natural models, systems and elements to address complex human problems (Benyus, 1997). Biomimicry aids in generating product concept designs by learning how nature solves design problems (Rossin, 2010). Nature not only provides ideas for problem-solving but also serves as a measure by offering examples of what is possible. Moreover, it acts as a mentor, fostering the realization that we are part of an extensive system.

Research in biomimicry is a burgeoning field, particularly in design and architecture (Austin et al., 2020). This interdisciplinary approach extends to various domains, such as concrete design (Nalcaci & Nalcaci, 2020; Radwan & Osama, 2016), civil engineering (Sani et al., 2013), furniture innovation (Tavsan & Sonmez, 2015), lightweight constructions, nanoscale tissue, the aerospace industry (Rashidi et al., 2019) and the transportation sector (Chowdhury et al., 2019).

Despite its widespread applications, one of the primary challenges of adopting biomimicry as a design approach lies in (Reiter, 2008) the difficulty of translating biological ideas into design concepts. Notably, this involves fostering collaboration across diverse knowledge domains and developing and evaluating design principles inspired by biological systems. The specific shapes, materials, production methods, behaviours and scales observed in biological models are often not directly replicated in designed solutions. Instead, practitioners of biomimicry must identify the functional principles underlying biological mechanisms and employ them as a guide for effective imitation (Rovalo & McCardle, 2019).

Over the past two decades, there has been a notable increase in global interest in biomimicry, yet public awareness of this field remains limited (Oguntona & Aigbavboa, 2019). While the interest in biomimicry is on the rise, there is a shortage of literature that discusses methods or steps for applying biomimicry in design. Notable exceptions include works by Blok and Gremmen (2016), Mathews (2011) and Rovalo and McCardle (2019). This condition is motivated by the fact that product designs applying biomimicry were often patented (were not published). A study conducted by Bae (2023) analyzed patent trends in Korea, the United States, Japan and Europe from 1975 to 2021, revealing that biomimicry technology is currently in a growth phase and is expected to continue flourishing in the future. Therefore, this article aims to bridge the gap by providing a clear explanation of the design steps in the application of biomimicry.

The biomimicry Institute has formulated the biomimicry process design which outlines steps to translate problems into biological terms, opening up opportunities for biologists to identify innovative solutions in nature. These steps are visually represented in what is known as ‘The Biomimicry Design Spiral’ (Hastrich, 2006), i.e. distillation, translation, discovery, emulation and evaluation (Baumeister et al., 2012) see Section 2.1 for more detailed description.

There are only a few studies on biomimicry applications, particularly those focused on products directly used by humans. In this study, the biomimicry design spiral is employed to design swimming gloves (Section 2.3 provides a brief literature review, showing that no research applied the biomimicry into the swimming gloves). The conceptual design involves incorporating a membrane resembling crab-eating frog (Fejervarya cancrivora) legs onto human hands. This membrane is utilized for paddling during swimming to enhance thrust (Fan et al., 2017; Purwaningsih et al., 2018). In addition, during practice, swimmers can wear swimming gloves to assist their training to increase water resistance. The added resistance provides more work for the upper body, giving the shoulders, arms, chest and back an intense workout and toning muscles well beyond normal swimming. The use of gloves increases the surface area of hand propulsion, impacting swimming kinematics, including speed, paddle frequency and paddle length (Gourgoulis et al., 2006). The greater the propulsion area, the greater the thrust, influencing the need to balance increased thrust and reduced resistance for accelerated swimming (Sato & Hino, 2013).

The inspiration for this design arose from observing crab-eating frog legs during swimming. The frogs possess membranes between their toes, facilitating efficient swimming. The widened section of their legs enhances the push force against water. Applying this principle aims to assist humans in achieving faster swimming speeds. Consequently, biomimicry swimming gloves were developed to maximize the drag force of the hands underwater, enhancing overall swimming speed (Purwaningsih et al., 2018).

This study not only offers a step-by-step guide to designing swimming gloves using the biomimicry approach but also investigates the enhancement of swimming speed. The latter is achieved through the application of computational fluid dynamics (CFD) simulation. Since the late 1990s, there has been a growing interest in utilizing CFD simulation to study the flow around a swimmer’s hand. A study of López-Plaza et al. (2012) utilized CFD simulation on hand strokes during swimming with assistive devices. The study aimed to assess differences in kinetic parameters (i.e., average swimming speed, stroke rate and stroke length, based on variations in the size of hand paddles). Elite swimmers were observed swimming the 100 m distance, and the results indicated that speed and stroke length increased with the area of the hand paddles, while stroke rate decreased. Building on López-Plaza et al. (2012), this research further explores how area affects drag and lift forces in swimming. Moreover, other previous studies (see Section 2.2) have collectively concluded that a tighter or more solid hand position results in increased drag force. However, whether the surface area of the hand interacting with water also affects the rise in drag force or lift force remains an unanswered question in the previous studies. This question will be addressed in this present study, wherein we explore the design variations of full and half-height glove membranes.

This research generates four alternative designs of the swimming gloves, we named them as: full-cross (FC), full-straight (FS), half-cross (HC) and half-straight (HS). Assessment of these designs, carried out via CFD simulation to quantify drag and lift forces, unveiled significant observations. The FC alternative design consistently displayed the most substantial drag force across different hand positions, whereas the FS alternative design showcased the highest lift force during the sweep position. These results highlight the impact of surface area on the lift and drag forces exerted by the gloves, emphasizing that larger surface areas play a pivotal role in augmenting thrust generation.

The article is structured as follows. The next section outlines the theoretical foundation (i.e. the biomimicry design spiral and CFD simulation) as well as literature review. Section 3 details the methods employed in this study, followed by Section 4, which presents the results and discussion. Section 5 provides limitations of the research and future research direction. Finally, Section 6 concludes.

2. Theoretical foundation and literature review

2.1. The biomimicry design spiral

The biomimicry design spiral outlines a step to translate problems into biological terms, offering more opportunities for biologists to identify innovative solutions in nature. The steps are graphically represented resembling a snail’s shell. The snail shell, specifically the Nautilus shell, serves as a symbolic representation due to its spiral design, which is a prevalent pattern in both natural and human design. This redesign pattern adheres to the Fibonacci sequence, known as ‘The Golden Ratio,’ resulting in a series of inherently productive measurements.

The biomimicry design spiral comprises five essential steps: distillation, translation, discovery, emulation and evaluation (Baumeister et al., 2012). The initial step, distillation or identification, involves identifying user needs. The second step is the translation of solutions from nature into product ideas, where natural biological solutions are filtered and developed into design functions. The third step, discovery, entails studying and identifying natural models for product design. Emulation, the fourth step, is the process of imitating natural models by replicating shapes, colours, motions or procedures found in nature. This stage involves discussing alternative design solutions. The final step is evaluation, where the proposed alternative design is rigorously assessed to determine if it adequately fulfils its designated function. The results from this stage serve as inputs to refine and enhance the final product design. Scientifically conducted product testing and evaluation are essential at this stage (Hastrich, 2006).

The spiral model is a flexible process that can be initiated from any step. For those aiming to create a new design, researchers may commence from the distillation step. If the focus is on advancing innovation, particularly in areas like sustainable design and providing solutions, the process can start from the translation step. When the goal is fostering creativity, initiation can begin from the emulation step. Alternatively, for those beginning with assessing and concentrating on the concept of sustainability for existing products, researchers can start from the evaluation step.

2.2 Computational fluid dynamics simulation

CFD is a computational method used to study fluid dynamics. This method simultaneously provides information on various fluid dynamics parameters, including fluid velocity, flow direction, pressure, temperature and concentration. Fluid dynamics during fluid movement are influenced by material properties, operating conditions, reactions and the geometric shape of space. The results of CFD can be visually represented through colours, contour plots or velocity vectors.

CFD holds advantages over other methods for studying fluid dynamics due to its cost-effectiveness, ability to conduct repeated simulations, provision of systematic and comprehensive results, and the capability to visually display fluid flow (Fan et al., 2017). It is a reliable and valid method for studies on swimming hydrodynamics. For instance, in a study by Bixler et al. (2007), the total lift forces of professional swimmers, digital CFD models of the same swimmers, and mannequins based on digital models were compared. The results indicated that the drag force determined by the digital model using the CFD approach closely matched the experimentally assessed value for the mannequin, differing by only 4%. However, the drag force on the mannequin was 18% less than that on the actual swimmer. CFD replaces complex Navier–Stokes fluid flow equations with discretized algebraic expressions solvable through repeated computerized calculations. Apart from avoiding surges, ventilations and obstructions, CFD can reveal detailed fluid flow characteristics around the hands and arms (Bixler & Riewald, 2002).

Bixler and Riewald (2002) conducted an investigation into the drag and lift forces acting on a hand in a steady-state equilibrium using commercially available CFD simulation. They visualized the pressure distribution and streamlines surrounding a hand and found that the computed fluid forces at different angles of attack strongly agreed with experimental results. In a study by Lauder et al. (2001), a simulation using CFD was performed to analyse the flow around an arm under steady-state conditions. The simulation results exhibited a close agreement between computed drag and lift forces and experimental data obtained from wind tunnel measurements. Minetti et al. (2009) utilized CFD to investigate the optimal finger spacing in a steady flow state. Their findings suggested that optimizing finger spacing could lead to an approximate 10% rise in the drag coefficient. Marinho et al. conducted several studies on flow patterns around the hand of an Olympic swimmer under steady-state conditions. They explored the effects of different thumb positions (Marinho et al., 2009), varying degrees of small-finger spread (Marinho et al., 2010), and analyzed the flow around the hand and forearm of an elite swimmer (Marinho et al., 2011). Another study by Bilinauskaite et al. (2013) investigated the impact of finger position and hand orientation on drag and lift forces.

These previous studies have collectively concluded that a tighter or more solid hand position results in increased drag force. However, whether the surface area of the hand interacting with water also affects the rise in drag force or lift force remains an unanswered question in the previous studies. This question will be addressed in this study, wherein we explore the design variations of full and half-height glove membranes. Furthermore, the angle or inclination of the interaction surface also plays a role in the drag and lift forces. This will be represented by the straight and cross designs on the glove membranes in our simulation. The primary question driving this research is the impact of surface area, and whether a straight or cross membrane design will yield a greater force.

2.3. Literature review

Literature about biomimicry applications, particularly those focused on products directly used by humans is quite limited. A literature review is conducted in the Scopus database with the following search query: TITLE-ABS-KEY (biomimicry AND design AND (human OR people OR person) AND product). It means that articles which contain this search query in the title, abstract or keywords are extracted. The period of time is not limited. For the sake of quality assurance, the document type is restricted to peer-reviewed research article published in a journal. From a pragmatic point of view, only articles published in English are included.

The search yields only eighteen articles. The screening is then performed by reading the title and abstract to verify the relevance of the extracted articles. In this way, 14 articles are excluded since they did not discuss a case study of designing a product for human by applying biomimicry. This low number of pertinent articles indicates that this research area is under-studied. All four articles from the screening are eligible to be further analysed as follows.

Kennedy (2014) presented a case study wherein nature-inspired design was used successfully as a tool to help develop novel, viable and product concepts for a packaged-goods industry client. Consumer packaged goods include any substance that is used and replaced frequently: cleaning products, personal care items, cosmetics, food and beverages and so on. Lizoňová and Tončíková (2019) showed how to apply the principles of biomimicry to design furniture and interior equipment. The objects then were abstracted using geometric knowledge and constructions. These constructions have been thoroughly analysed and have become the basis for product development. A study by El-Mahdy and Gabr (2017) aims to explain the organism’s behaviour when producing the material and translating it by using a digital tool by mimicking its behaviour in construction. Finally, Zinger et al. (2021) discussed biomimetic nano drug delivery carriers for treating cardiovascular diseases. They showed that systemic delivery of free drugs has limitations, including rapid systemic clearance, inadequate levels of drug in the target tissue, poor solubility of some drugs and increased off target toxicity. Much effort has been invested into the development of different synthetic drug carriers. Biomimetic carrier systems hold great therapeutic potential in addressing these challenges. Inspired by native cells’ biological functions, they showed that biomimetic nano-carrier platforms possess favourable properties such as: longer circulation times, mononuclear phagocyte system evasion and favourable interactions with target cells.

As evident from the literature review, there are a limited number of publications related to applying biomimicry in product design for humans. This scarcity may be attributed to instances where designs, though not published, have been patented. In contrast, this study provides step-by-step guidance for designing swimming gloves using the biomimicry approach. We expect that this endeavour will not only contribute to the existing literature but also benefit practitioners, particularly designers seeking to implement the biomimicry approach in their designs.

3. Method: step-by-step

In the context of developing nature-inspired swimming gloves, the application of the biomimicry design spiral involves a systematic and iterative process that draws inspiration from nature’s solutions. The biomimicry design spiral comprises five essential steps (i.e., distillation, translation, discovery, emulation and evaluation), each contributing to the development of a functional and efficient design.

3.1. Distillation

The primary objective of the distillation step is to identify user needs. In the context of the swimming gloves design with the primary objective of augmenting swimming speed, the focal point is the reinforcement of thrust generated through hand movements in the water. In practical application, swimmers can leverage swimming gloves as valuable training aids to intensify their workout and enhance overall performance. The incorporation of swimming gloves into training sessions introduces an additional element of water resistance, requiring swimmers to exert more effort and engage their upper body muscles in a more demanding manner. This heightened resistance not only contributes to an intense workout for the shoulders, arms, chest and back but also extends the toning effects well beyond what is achieved in normal swimming.

The use of swimming gloves strategically amplifies the surface area of hand propulsion, influencing key aspects of swimming kinematics. Studies, such as those conducted by Gourgoulis et al. (2006), have elucidated the significant impact of gloves on swimming dynamics. The increased surface area results in notable alterations in swimmer kinetics, affecting parameters such as speed, paddle frequency and paddle length. Research findings suggest that the greater the propulsion area facilitated by swimming gloves, the more substantial the thrust generated. This nuanced relationship between increased propulsion and its effect on swimming performance underscores the delicate balance required to optimize swimmer efficiency. Notably, the work of Sato and Hino (2013) emphasizes that while a larger propulsion area contributes to greater thrust, it simultaneously necessitates a careful consideration of reduced resistance for achieving accelerated swimming.

The practical integration of swimming gloves into training regimens thus becomes a nuanced strategy, emphasizing the need for swimmers to master the interplay between increased thrust and streamlined resistance. The utilization of gloves serves not only as a means to enhance strength and toning but also as a method to refine swimming technique, fostering a dynamic connection between the swimmer, the water and the ergonomic design of the gloves.

The pivotal challenge lies in deciphering how to amplify this propulsive force and identifying natural mechanisms employed by aquatic creatures to achieve optimal thrust. The initial phase involved a comprehensive examination of diverse living creatures, with a keen emphasis on animals renowned for their swimming prowess. The primary goal was to gain profound insights into their physiology, specifically pinpointing the body parts intricately involved in the swimming process. A range of aquatic animals, including fish, ducks, and frogs, showcases distinctive mechanisms for efficient swimming. Of particular interest is the crab-eating frog (Fejervarya cancrivora), notable for its physiological resemblance to humans in the configuration of both legs and arms. Notably, the larger feet of these frogs were observed to exert substantial pressure on the surrounding water, leading to the stretching of the membrane and a consequent increase in the power generated during swimming. This frog species presents a unique opportunity for biomimicry, as its evolutionary adaptations are tailored to navigating aquatic environments.

3.2. Translation

As we delve into the exploration of a biological approach for our product concept, the objective is to seamlessly translate nature’s ingenious solutions into tangible product concepts. At the heart of this step is a focused effort to comprehend how nature adeptly tackles our design challenge – the enhancement of swimming thrust through the development of innovative swimming gloves.

To unravel the secrets of optimal thrust generation, a comprehensive examination of the crab-eating frog’s biomechanics is imperative. Focus on how the frog’s limb movements interact with the water to produce efficient propulsion. Additionally, explore the surface textures, appendage shapes and coordination of movements that contribute to its streamlined swimming ability. The abstraction of principles from the crab-eating frog’s swimming mechanics becomes a crucial step in the biomimicry design spiral. By understanding and emulating the biomechanical features that enable the frog to navigate water with agility, designers can integrate these insights into the conceptualization and development of swimming gloves.

3.3. Discovery

The pivotal discovery step in our design process revolves around the meticulous identification of natural models, with a keen focus on unravelling the secrets of how the membrane of the crab-eating frog can be harnessed to enhance swimming. Our exploration delves into an in-depth investigation of the frog’s swimming motion, seeking to understand the nuanced mechanisms that contribute to its aquatic prowess.

To capture a comprehensive understanding of the crab-eating frog’s swimming dynamics, our process involves the meticulous recording of footage showcasing the frog’s intricate movements in water. Frogs showcase proficient swimming abilities attributed to their anatomical adaptation of webbed feet. Research by Pandey et al. (2013) highlights that the webbed feet, when in motion, generate the most thrust during swimming. The propulsive performance is significantly influenced by the size and shape of the frog’s webbed feet, as elucidated in a study by Jizhuang et al. (2017). Furthermore, Shimizu et al. (2017) propose in their study that the webbed foot structure of a swimming frog cyborg establishes an advantageous interaction between musculoskeletal elements and the underwater environment, contributing to the frog’s locomotion. Consequently, the webbed feet of frogs play a crucial role in enhancing their swimming capabilities.

This invaluable visual data provides profound insights into the potential applications of the frog’s membrane to human fingertips. The observations bring to light a fascinating aspect of the frog’s anatomy – the extension of membranes to the very tips of their fingers, with some membranes measuring only half the height of their fingers. These observations serve as a cornerstone in informing the design process, particularly in considering the form and application of the membrane. Understanding that frogs possess membranes that extend to the fingertips opens a realm of possibilities for translating this natural adaptation into our product concept.

3.4. Emulation

In the emulation step efforts are directed towards replicating the natural solution into the design of the product concept. This step also involves discussing alternative design solutions.

Drawing from the findings of frog anatomy research and literature on the thrust produced by frog leg membranes, the emulation step lead to the creation of four concept designs. First, two fundamental orientations are considered: crosswise placement or horizontal positioning between fingers, commonly referred to as slips. The attachment point of the oblique membrane is strategically positioned at the top of the finger, with the other end securely affixed at the bottom. Second, the height of the membrane becomes a pivotal factor, and two variations are considered – half and full. Simultaneously, the placement of the membranes linked to the fingers is explored in two configurations – straight and cross. The combination of these variables results in the emergence of four unique designs, each possessing its own set of characteristics and potential benefits. The concepts are shown in Figure 1 and are identified through a letter abbreviation reflecting the membrane’s form, the breadth of a closed finger, and whether it is a FC, FS, HC or HS attachment. The emulation step results in alternative design concepts that, as product prototypes, closely mimic the size, shape, flexibility and ergonomic aspects of the frog’s membrane.

Figure 1. Four design concepts.

This innovative approach underscores the central role of creativity in the product design process. By exploring different combinations of membrane height and finger attachment shapes, we can successfully generate diverse alternatives. The realization that the membrane’s height and orientation could be flexibly combined paved the way for a more comprehensive understanding of the design space. Notably, the amalgamation of membrane height (full and half) with the shape of the membrane attached to the fingers (straight and cross) showcases the dynamic interplay between nature-inspired observations and human ingenuity. This creative synthesis reflects the essence of the design process – transforming inspiration from the natural world into practical, functional and innovative solutions. Moreover, this inventive journey aligns with the recommendations of Hsiao and Chou (2004), emphasizing the importance of incorporating creativity techniques into the product design process. The deliberate application of creative methodologies not only enriches the ideation phase but also contributes to the overall performance of innovative product design, fostering a culture of exploration, experimentation and imaginative problem-solving.

3.5. Evaluation

In the evaluation step, the objective is to identify the optimal design that best meets user requirements for product functionalities, specifically focusing on enhancing swimming propulsion.

To test the alternative designs (see again Figure 1), the CFD simulation is used. This simulation allows for precise calculations of the drag force generated by the utilization of frog leg membranes in the water. This simulation-based approach provides a comprehensive understanding of the product’s performance in diverse conditions. First, we specify the size of the swimming gloves which is crafted based on Indonesian hand anthropometric data on individuals aged 18–22 years old (Purnomo, 2014). The size of the gloves remains consistent across all design types. The distinguishing features among the design concepts are the height and shape of the membrane between fingers. Each design type exhibits varying two side surface areas. The FC design boasts the largest surface area at 437.66 cm², followed by the FS design with an area of 422.14 cm². The HC design featured an area of 402.07 cm², while the HS design had the smallest surface area at 394.05 cm². In the absence of gloves, the natural hand surface area was measured at 349.5 cm².

Next, CFD simulation is employed to investigate two different hand movement positions during breaststroke swimming, i.e. out-sweep position, and in-sweep position as the following:

• Out-sweep position:

  Movement: The out-sweep position is characterized by a 40° angle of attack. This position represents the initial hand movement in breaststroke swimming (see Figure 2).

  Orientation: The water’s direction is perpendicular to the hand.

  Purpose: This position is specifically used to measure the drag force resulting from the hands pushing against the water.

• In-sweep position:

  Movement: The in-sweep position is characterized by a 0° angle of attack.

  Orientation: The water’s direction forms the bottom of the swimmer, perpendicular to the surface of the hand, as shown in Figure 2.

  Purpose: This position is employed to measure the lift force, as the hands push down to lift the body.

Figure 2. Hand position.

The chosen hand positions play a decisive role in determining the specific movements that generate thrust during breaststroke swimming, allowing for a comprehensive analysis of fluid dynamics and forces in aquatic environments. CFD proves to be particularly suitable for fluid and air flow visualization, as highlighted by Reno et al. (2022), and for analyzing thrust in open water conditions, as explored by Darmawan et al. (2022).

The angle of attack in hand positions during swimming has been a subject of discussion in various research studies, including those by T. M. Barbosa et al. (2011), Bixler et al. (2007) and Marinho et al. (2011). Notably, Marinho et al. (2009) found that the thumb abducted position exhibited greater values than positions with the thumb partially abducted and adducted at angles of attack of 0° and 45°. Additionally, the position with the thumb adducted displayed the highest resultant force at a 90° angle of attack.

The CFD simulation then uses water as the fluid under steady-flow conditions. Key parameters for the simulation include:

• Fluid flow velocity: 4.0 m/s (Lauder et al., 2001).

• Water turbulence: 1% intensity with a scale of 0.1 m.

• Water density: 998.2 kg/m³.

• Water viscosity: 0.001 kg/ms (Bixler & Riewald, 2002).

The thrust force in this study is determined by applying Newton’s second and third laws of motion. The estimation of thrust force results is derived from drag and lift forces and their respective coefficients (Lauder et al., 2001).¹ The direction of drag and lift forces is illustrated in Figure 3.

Figure 3. Force direction.

The force (Fi) is calculated as follows (Bixler & Riewald, 2002): (1) $$F_i=0.5’\times C_i\rho A{v}^2,$$(1) where Fi is the force (drag or lift), Ci is the coefficient of the force, ρ is the density of the fluid, A is the projection of the surface area of the swimming glove and v is the constant velocity of the fluid flow towards the hand. Equation (1)(1) $$F_i=0.5’\times C_i\rho A{v}^2,$$(1) demonstrates that the force is linearly related to the surface area, highlighting the significance of surface area in influencing thrust force. This methodological approach ensures a comprehensive understanding of the forces involved in swimming, particularly how drag and lift forces contribute to the overall thrust force. The linear relationship with surface area emphasizes the importance of surface area considerations in optimizing thrust during swimming.

4. Results and discussion

4.1 Drag force

Figure 4 presents the 3D simulation results for the out-sweep hand position across four swimming glove design concepts. A notable observation is that the FC concept design exhibits maximum pressure along the finger, evident in the image comparisons. Further scrutiny reveals that this FC design generates the highest pressure, reaching 109.8 kPa. Correspondingly, the drag force at FC peaks at 167.604, with a force coefficient (Cd) of 0.497.

Figure 4. Outsweep's simulation result.

Interestingly, the results underscore that designs with larger surface areas (FC and FS) contribute to increased drag forces compared to those with smaller surface areas (HS and HC). The 40° angle formed during the out-sweep hand position results in a substantial upward force, particularly when contrasted with other in-sweep positions parallel to the fluid flow. Notably, the dominant drag force can be interpreted as a thrust force, given its significant value (van Houwelingen et al., 2017). The FC alternative design emerges as a potent contributor to thrust, generating substantial drag force compared to other designs. These findings provide valuable insights into the nuanced effects of hand position and design concepts on drag forces, shedding light on the potential for optimizing thrust in swimming motions.

4.2. Lift force

During the propulsion of hands and arms through water, the surrounding water exerts a resistive pressure known as the lift force. This resistive pressure acts perpendicular to the surface of the arm. Bernoulli’s Principle illuminates a crucial relationship between fluid speed and pressure, positing that as fluid speed increases, the pressure decreases. This principle, proposed by Sanders (1998), serves as a foundational understanding of the mechanism for generating lift during swimming.

The simulation of lift force is conducted in the in-sweep hand position, characterized by a 0° angle of attack, with water pressure set at 101.325 kPa. Notably, the FS design yields the most substantial lift force, measuring 276.927 N, with a force coefficient (Cl) of 0.821. Figure 5 presents the 3D simulation results for the in-sweep hand position across four swimming glove design concepts. Within the in-sweep position, the FC design stands out, demonstrating the most significant lift force values, notably reaching 108 kPa. These observations offer valuable insights into the dynamics of lift force generation during swimming, emphasizing the role of design concepts in optimizing lift and overall propulsion.

Figure 5. Insweep's simulation result.

4.3 The effect of membrane area to drag and lift force

In the propulsion phase of front crawl, back crawl, and butterfly styles, empirical research by Guo et al. (2020), Norton et al. (2007) and Yang et al. (2019) highlighted the dominance of drag force over lift force. Notably, not all movements generating thrust and lift forces succumb to drag force predominance, particularly when swimmers exert strength and acceleration (Maglischo, 2003). Drag consistently prevails over lift, opposing the swimming motion (van Houwelingen et al., 2017). The study results further reveal a close proximity between lift force values (in-sweep) and drag force (out-sweep).

In examining alternative designs, FC emerges with the largest surface area at 437.66 cm², succeeded by FS (422.14 cm²), HC (402.07 cm²) and HS (394.05 cm²). This variance in surface size significantly influences kinetic parameters, including average swimming velocity, stroke rate and stroke length. Research by López-Plaza et al. (2012) underscored that increased surface area of hand paddles correlated with elevated swimming velocity and stroke length, coupled with a decrease in stroke rate.

The use of paddles in swimming brings forth noteworthy advantages. Gourgoulis et al. (2006) established a connection between larger paddle surface area and enhanced force production, resulting in faster swimming times. Paddle usage increases propulsion force, subsequently elevating swimming speed (Tsunokawa et al., 2019). The adoption of paddles contributes to increased average stroke length and swimming velocity, accompanied by a reduction in average stroke rate and hand velocity in the water (Telles et al., 2011). Moreover, the impact is more pronounced with oversized paddles, as evidenced by Gourgoulis et al. (2006). This performance enhancement is not solely attributed to increased energy production but is driven by heightened propulsion efficiency stemming from the expanded surface area of the hand paddle (Ogita & Tabata, 1993). Multiple studies, including those by Barbosa et al. (2013) and Gourgoulis et al. (2008), corroborated the significant impact of paddle usage on augmenting swimming velocity. Table 1 provides insight into the force magnitude on the swimming gloves during out-sweep and in-sweep positions.

Table 1. Force simulation result of four design concepts.

Hand position	Alternative designs	Force (N)	Cd or Cl
Out-sweep/Drag force	FC	187.46	0.54
	HC	152.47	0.48
	FS	167.60	0.50
	HS	154.77	0.49
In-sweep/ Lift force	FC	251.53	0.72
	HC	236.91	0.74
	FS	276.93	0.82
	HS	249.03	0.79

Table 2 vividly illustrates that the FC design commands the largest drag force value, while the FS design dominates with the highest lift force value. These findings underscore a pivotal correlation between the area of the swimming gloves and the magnitude of drag and lift forces. Paddle usage further amplifies pressure on the hand during swimming, creating a nuanced distribution of forces. Specifically, the pressure on the palm side escalates, while the back side experiences a decrease. This pressure differential generates an active forward force from the hand, with larger surface areas yielding greater pressure on the palm’s side. This phenomenon culminates in increased forces, and as this force intensifies, it ultimately enhances average velocity and energy efficiency during swimming (Tsunokawa et al., 2017).

Table 2. Membrane dimension.

Dimension	FC	HC	FS	HS
Thumb to the index finger (cm)	7	6.5	8	7
Index finger to middle finger (cm)	3.5	2.5	4	2
Middle finger to ring finger (cm)	3	2.5	3	2
Ring finger to little finger (cm)	3	2.5	3	2
Area (cm^2)	437.66	402.08	422.14	394.05

Beyond surface area, the material’s density plays a critical role, and for this study, Neoprene, a solid material with a mass density of 1292 kg/m³, is chosen. Neoprene, derived from carbon, hydrogen and chlorine polymers, is a vulcanized rubber renowned for its high tensile strength, stretchability and resistance to water, degradation and temperature fluctuations (Ciullo & Hewitt, 1999). Its insulating properties make it a staple material in wetsuit production, minimizing convective heat loss while providing thermal insulation (Naebe et al., 2013). In this study, material types remain constant across prototypes, and the focus shifts solely to the height of the membrane, driving variations in glove surface areas.

An exploration of the area’s impact on drag and lift forces reveals a direct relationship between surface area and force generation. Figure 6 visually presents this correlation, depicting the average force across all positions for each alternative. The thrust, as indicated by drag force, exhibits a consistent increase with expanding surface area. These outcomes align with previous research elucidating the influential role of surface area in augmenting thrust, consequently boosting swimming velocity. The rise attributed to differences in water pressure and volume transferred by the hand is a direct result of increased surface area (Tsunokawa et al., 2017). CFD test results conclusively assert the gloves’ efficacy in enhancing thrust. Notably, the FC design emerges as the optimal concept, demonstrating unparalleled thrust force production compared to other designs.

Figure 6. Comparison of surface area with force.

Next, Figure 7 visually captures the nuances of hand positions in determining drag and lift forces, with out-sweep representing the former and sweep determining the latter. Notably, the force coefficient for lift surpasses that of drag, with a lower Cd signalling superior aerodynamic performance compared to a higher drag coefficient. In the context of Cl, a positive value signifies upward lift, while a negative value denotes downforce. The visualization in Figure 7 unveils that all Cd values are smaller than Cl values, indicative of enhanced aerodynamics in the out-sweep position where drag force outperforms lift force.

Figure 7. Force coefficients.

Aligning with Marinho et al.'s (2010) findings, this research affirms that a hand model with a small finger spread during water paddling generates greater thrust compared to fingers spaced farther apart. This parallels the study’s outcomes, where fully covered gloves yield greater drag force than those with only half the finger height.

A comparative analysis with research by Vilas-Boas et al. (2015), conducted without gloves, measured drag and lift forces of swimmers at a velocity of 2 m/s, showcasing similar parameters to this study. Their research unveiled that the highest drag force coefficient is attained at a 90⁰ angle of attack with a coefficient close to 1, while the highest lift force coefficient occurs at a 45⁰ angle of attack with a coefficient of 0.5 at an orientation angle of 270⁰ (pressure direction from under the hand). While the force coefficient values in this study are slightly lower than those in Vilas-Boas’s results, the employment of swimming gloves emerges as a factor enhancing the aerodynamic performance of hands during swimming. Kudo et al. (2008) delved into the quantification of wave drag effects due to surface penetration on drag and lift forces (Cd and Cl) acting on a hand model. Their study revealed a Cd value of 0.53 at a 30⁰ angle of attack, with a flow speed set at 1.5 m/s. These findings collectively underscore the significance of hand position, force coefficients and the positive impact of swimming gloves on aerodynamic efficiency in aquatic propulsion.

Convergence testing in CFD simulation is conducted to ensure numerical solutions from fluid flow modelling remain consistent and independent of grid size or density (mesh).² This testing enhances confidence in the reliability of CFD simulation results. Each simulation case undergoes a convergence test using Solid Work 2020 flow simulation, optimizing mesh size and computational domain. For instance, in the FC design at the out-sweep hand position, the convergence test yielded a mesh size of 340,382 and 149,740 fluid cells contacting solid after 196 iterations. Similarly, for the FS design at the in-sweep hand position, the mesh size was 237,814, and fluid cells contacting solid were 92,244 after 194 iterations. The iteration number was defined by the software as the force coefficient approached the minimum value. Noteworthy comparisons with prior research include Sato and Hino (2013) using 5401 cells for the convergence test in their simulation of hydrodynamic forces on a swimmer’s hand, and Bixler and Riewald (2002) employing 215,000 mesh. These considerations underscore the meticulous approach taken in the simulation process, acknowledging limitations and emphasizing the reliability and consistency of the obtained results.

4.4 Usability testing

Usability testing is considered to be one of the most important and most widely used methods to evaluate product designs (Lewis, 2006). It aims to assess the usability of a product by simulating the user-product interaction under controlled conditions. In this study, 25 swimmers as respondents of this study will evaluate the characteristics of the four alternative designs based on their individual perceptions. There are five aspects that respondents will assess, namely material comfort, ease of use, ease of non-swimming activities, ease of swimming activities and aesthetics. Material comfort means that the feelings generated from using a product are influenced by the materials used. Ease of use means the level of ease of use when putting on and taking off the glove; ease of non-swimming activities means that level of ease when the glove is used to stretch, contract and bend the fingers; while ease of swimming activities means the level of ease experienced in the water while swimming. Lastly, aesthetics refers to the objective design aspects of a product, including form, tone, colour and texture (Postrel, 2003). The assessment criteria use a Likert scale ranging from 1 to 5 (1 is the least preferable and 5 is the most preferable).

In general, respondents do not exhibit significant variations in their evaluations concerning the membrane length in the design. This implies that there is a similarity between the FS and HS designs, both featuring a straight membrane, as well as the FC and HC designs with a cross membrane. The most apparent disparity in perception is observed in the characteristics of the membrane design, particularly in the distinction between straight and cross designs. Regarding the straight membrane design, respondents expressed that the use of materials provides sufficient comfort. Regarding ease of use, some respondents mentioned a bit of difficulty, especially in the finger joint area of the glove. Regarding the ease of swimming and non-swimming activities, respondents stated that the gloves are less flexible in stretching the fingers and are too heavy when used for swimming. This is attributed to the membrane layer (between the fingers) having the same connection as the finger part. The thick membrane layer results in the gloves being less flexible and heavier during swimming activities. In terms of aesthetics, respondents believed that the choice of glove colour is suitable as it blends with the water colour, and the use of a single colour (blue) is preferable to colour combinations in the cross design. The summary of the results is shown in Table 3.

Table 3. Result of the usability testing.

Design concept	Aspect
	Material comfort	Ease of use	Ease of non-swimming activities	Ease of swimming activities	Aesthetics
FS	The material is quite comfortable	A bit challenging due to the narrow finger joints	Finger movement is restricted or limited	Slightly heavier due to the thick membrane	Good because the colour resembles water
HS	The material is quite comfortable	A bit challenging due to the narrow finger joints	Finger movement is restricted or limited	Slightly heavier due to the thick membrane	Good because the colour resembles water
FC	The material is quite comfortable	Easier	Finger movement is easier	Lighter due to the thinner membrane	The choice of two colours (blue and white) is not really suitable
HC	The material is quite comfortable	Easier	Finger movement is easier	Lighter due to the thinner membrane	Not good, better just only one colour.

Next, regarding the cross membrane design’s material comfort, respondents acknowledged that the use of materials provides ample comfort. When it comes to ease of use, respondents conveyed that this design is more user-friendly compared to the straight design, albeit still slightly more challenging than typical gloves. In terms of ease during swimming and non-swimming activities, respondents perceived this design as superior to the straight design. The cross design demonstrates greater flexibility when stretched and feels lighter when used for swimming. This is attributed to the cross design’s membrane layer comprising only one layer of neoprene (thinner than the straight design), and the membrane layer is separate from the finger part. These factors contribute to gloves with this design being more flexible and lighter when used in water. Regarding aesthetics, respondents generally found the choice of different colours (blue and white) less suitable and suggested that opting for a single colour is preferable.

We also evaluate the material used: our nature-inspired swimming glove which uses Neoprene is compared with other swimming glove which uses Lycra (also called Spandex or elastane). According to user perception assessments, Neoprene materials generally received positive ratings for material comfort, ease of swimming and non-swimming activities, as well as aesthetics. However, the ease of use aspect draws numerous complaints from respondents due to a mismatch with the size of the glove’s fingers, making it challenging to insert fingers. In contrast, gloves made from Lycra face challenges in the aspects of ease of use and non-swimming activities. Respondents noted that the fingertips are slightly short, and the membrane is too wide, resulting in less comfort when fingers do not stretch.

5. Limitations and future research directions

The study of a swimmer can be undertaken in two states, namely steady and unsteady, as fluid can exhibit both steady and turbulent characteristics simultaneously (Rouboa et al., 2006). Fluid is considered steady when the average flow remains constant over time, assuming an absence of turbulent fluid. One limitation of this research pertains to the analysis of why the FC design exhibits the largest drag and lift forces. We acknowledge a speculative focus on the area alone, disregarding the potential impact of the slope angle of the membrane, which could influence water current direction during interaction. Another drawback lies in the absence of validation for the simulation. However, the study aligns with previous research in swimming simulations using CFD, indicating consistent results. Further research avenues could explore additional factors influencing drag and lift forces in swimming, such as hand shape, swimmer’s technique and fluid flow characteristics. Subsequent research with a market-oriented perspective could employ tools, like the House of Quality (HOQ) to map user needs and competitor product specifications, identifying unique competitive advantages to enhance swimming glove design (Angie et al., 2021). Leveraging force coefficient data, design improvements could be pursued by optimizing the design to achieve smaller force coefficient values.

Mesh size is a critical aspect of CFD simulation. Contrary to the notion that a larger number of meshes always leads to increased validation, convergence analysis studies have yielded varying insights. Sitio et al. (2013) conducted convergence analysis with mesh ratio, revealing that changes in computed lift and drag coefficients decrease monotonically with an increasing grid resolution. However, challenging this assertion, Yahya et al. (2018) found that a medium grid scheme could be utilized to produce high-accuracy results in CFD simulation. In contrast, Reiter (2008) reported relative errors of 40% or more between values measured at specific points in wind tunnel tests and those predicted at the same points by CFD simulations. It is essential to note that, in many instances, a finer mesh (smaller size) tends to offer more accurate results, particularly as it enables better capture of details in complex flows and phenomena. While considerations of mesh size are crucial in achieving accurate simulations, the choice may vary based on the specific characteristics of the simulated flow. Future research direction could explore modelling with higher accuracy, encompassing simulations that consider the surface’s slope angle. This would contribute to advancing the precision and reliability of CFD simulation, offering a more nuanced understanding of fluid dynamics in complex scenarios.

6. Conclusion

The biomimicry design spiral has proven to be a systematic and replicable design process for developing products inspired by the mother earth. Each step of the biomimicry has been outlined, providing a clear roadmap for translating ideas or solutions from nature into effective design strategies. The method’s advantage lies in its ability to facilitate the identification and application of nature-inspired solutions to design challenges.

In the emulation step, four alternative designs are generated. Evaluation of these designs, conducted through CFD simulation measuring drag and lift forces, revealed notable insights. The FC alternative design consistently exhibited the most substantial drag force across various hand positions, while the FS alternative design demonstrated the highest lift force in the sweep position. These findings underscore the influence of surface area on the lift and drag forces of the gloves, with larger surface areas contributing to increased thrust generation. The FC design, characterized by the highest drag force of 187 N and a force coefficient of 0.537, exemplifies the impact of surface area on drag. On the other hand, the FS design stands out for achieving the highest lift force at 276.9 N, with a force coefficient of 0.821. Notably, the force coefficient for lift force consistently surpassed that of drag force across all design types, indicating superior aerodynamic performance in the out-sweep compared to the in-sweep. These outcomes emphasize the potential of biomimicry in optimizing product design, showcasing how insights from nature, specifically crab-eating frog membranes, can be leveraged to enhance the performance of swimming gloves.

This research holds several potential benefits for the industry as follows:

• Enhanced performance: By mimicking natural processes, such as the crab-eating frog’s membrane, the swimming glove design has the potential to enhance performance in terms of drag reduction, lift generation and overall swimming efficiency. This can be particularly valuable for competitive swimmers and athletes seeking to improve their speed and technique.

• Innovation and competitive edge: Embracing the biomimicry in product design demonstrates a commitment to innovation. An industry that adopts nature-inspired solutions gains a competitive edge by offering unique and potentially superior products in the market. This innovation can attract customers seeking cutting-edge and high-performance swimming gear.

• Improved ergonomics: The biomimicry allows for the integration of natural designs that have evolved for efficiency and functionality over time. Applying these principles to swimming glove design can result in improved ergonomics, ensuring a better fit, comfort and ease of movement. This can lead to increased customer satisfaction and loyalty.

• Sustainability: Nature-inspired designs often align with sustainable practices, as they leverage efficient and optimized solutions developed by ecosystems over time. Utilizing the biomimicry in product design can contribute to more sustainable and eco-friendly manufacturing processes, aligning with the growing demand for environmentally conscious products.

• Consumer appeal: Consumers are increasingly drawn to products that reflect a connection with nature and innovative design approaches. A swimming glove designed with inspiration from natural mechanisms may resonate with environmentally conscious consumers and those seeking state-of-the-art equipment.

• Technological advancements: Research into the biomimicry for swimming gloves can lead to advancements in materials science, fluid dynamics, and manufacturing processes. These technological innovations can have broader applications beyond swimming gear, influencing advancements in related industries.

• Research collaboration: The pursuit of the biomimicry in product design encourages collaboration between industries and scientific disciplines. This interdisciplinary approach can foster partnerships between sportswear manufacturers, biologists, engineers and materials scientists, contributing to a holistic and innovative research ecosystem.

In summary, incorporating the biomimicry concept into the swimming glove design not only has the potential to revolutionize the sportswear industry but also aligns with broader trends in sustainability, innovation, and consumer preferences. It positions the industry at the forefront of technological and design advancements, fostering a reputation for forward-thinking and environmentally conscious practices.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

There is no associated data for this manuscript.

Additional information

Funding

This research was funded by the Directorate General of Research and Community Service, Ministry of Research, Technology and Higher Education of Indonesia, under the scheme of ‘Penelitian Terapan Unggulan Perguruan Tinggi’ in 2018.

Notes on contributors

Ratna Purwaningsih

Ratna Purwaningsih is an Associate Professor in the Department of Industrial Engineering, Faculty of Engineering, Diponegoro University, Indonesia. She obtained her bachelor’s degree in Industrial Engineering and doctoral degree in Marine Technology from Sepuluh Nopember Institut of Technology, Indonesia. Her research interests include product design and development, design for sustainability, and industrial sustainability.

Denny Nurkertamanda

Denny Nurkertamanda is an Associate Professor in the Department of Industrial Engineering, Faculty of Engineering, Diponegoro University, Indonesia. He finished his doctoral degree in Occupational Safety and Health from Udayana University, Indonesia. His research interests include ergonomics, occupational safety and health, and product development.

M. Mujiya Ulkhaq

M. Mujiya Ulkhaq is a Lecturer in the Department of Industrial Engineering, Faculty of Engineering, Diponegoro University, Indonesia. He finished his doctoral degree in Analytics for Economics and Management from University of Brescia, Italy. He obtained his bachelor’s degree in Industrial Engineering at Diponegoro University, Indonesia, and master’s degree in Engineering Management at Jönköping University, Sweden. His research interests include performance measurement, impact evaluation, service and quality management, as well as data analytics.

Faradhina Azzahra

Faradhina Azzahra is a Lecturer in the Department of Industrial Engineering Department, Faculty of Engineering, Diponegoro University, Semarang, Indonesia. She gained her master’s degree in Industrial Engineering at Universitas Gadjah Mada, Indonesia. Her research interests include Ergonomic Cognitive, Agent-based Model, as well as Environmental and Sustainability-related Issue.

Daffa Alyaa Musyaffa

Daffa Alyaa Musyaffa is an industrial engineering graduate from Department of Industrial Engineering, Diponegoro University. His research interest is product design.

Notes

1 The drag force is the force acting parallel to the direction of fluid flow; where the lift force is the force acting perpendicular to the drag force on the horizontal plane x–y (Bixler et al., 2007).

2 Mesh size denotes the size of discretization elements or cells used to partition the flow domain.