Stories with Tag hydrodynamics

• How a yacht works: sailboat physics and design

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  Posted: 2025-04-15 21:19:33

  Verbose tl;dr

  Sailboats harness the wind to generate propulsive force through aerodynamic principles. The sails, acting as airfoils, create a pressure difference, generating lift perpendicular to the wind. This lift force can be resolved into two components: one pushing the boat sideways (leeway), and the other propelling it forward. The keel or centerboard counteracts leeway, allowing the boat to move efficiently against the wind by sailing at an angle. Sail shape, hull design, and appendage configuration are crucial for optimizing performance, balancing stability and speed. Different sail types and trims are used depending on the wind direction and strength, allowing sailors to adjust to varying conditions and desired points of sail.

  This comprehensive article delves into the intricate world of sailboat design and the underlying physics that govern their movement, exploring the delicate interplay of forces that allow these vessels to harness the power of the wind for propulsion. It begins by elucidating the fundamental principle of sailing: generating lift through the interaction of the sail and the wind, analogous to the aerodynamic principles that enable airplane flight. The sail, acting as an airfoil, curves the airflow around its surface, creating a pressure difference – lower pressure on the leeward side and higher pressure on the windward side. This pressure differential results in a net force perpendicular to the apparent wind direction, a force that can be resolved into two components: thrust, which propels the boat forward, and heeling force, which pushes the boat sideways.

  The article then meticulously dissects the different types of sails and their specific functions, differentiating between the mainsail and the jib, and explaining how their combined operation contributes to generating the necessary lift. It emphasizes the importance of sail shape and trim in optimizing performance, illustrating how adjustments to sail controls like the halyard, sheet, and outhaul can influence the curvature of the sail and thus the lift generated. Furthermore, it underscores the role of the center of effort, the point where the resultant force from the sails acts, and the center of lateral resistance, the point where the hydrodynamic resistance of the hull and keel opposes the heeling force, in maintaining equilibrium and preventing capsize.

  The article further elaborates on the significance of keel design in providing stability and counteracting the heeling force. It distinguishes between different keel configurations, explaining how fin keels, bulb keels, and bilge keels contribute to hydrodynamic lift, which opposes leeway, the sideways drift of the boat. This lateral resistance, coupled with the righting moment generated by the keel's weight and its distance from the centerline, allows the sailboat to maintain an upright position even under strong winds.

  Moreover, the piece explores the complex interplay between apparent wind, the wind experienced by the boat while in motion, and true wind, the actual wind direction and speed. It describes how the apparent wind shifts forward as the boat gains speed, enabling sailboats to sail at angles closer to the wind than one might initially expect. This "sailing close-hauled" is crucial for navigating upwind and is a testament to the sophisticated interplay of aerodynamic and hydrodynamic forces at play.

  Finally, the article touches upon other design considerations, including hull shape and rudder design, highlighting how these elements contribute to the overall performance and maneuverability of the sailboat. It elucidates the importance of minimizing drag and maximizing efficiency in hull design, and the role of the rudder in controlling the direction of the boat. In essence, the article provides a thorough and insightful overview of the physics and design principles that underpin the art of sailing, demonstrating the intricate balance of forces that allows these vessels to harness the wind and navigate the waters with grace and precision.

  • yacht
  • sailboat
  • sailing
  • physics
  • design
  • naval architecture
  • hydrodynamics
  • aerodynamics
  • keel
  • rudder
  • sail
  • mast
  • hull
  • Marine Engineering
  • boat design

  Summary of Comments ( 1 )
  https://news.ycombinator.com/item?id=43698522

  Verbose tl;dr

  HN commenters largely praised the article for its clear explanations of complex sailing concepts like apparent wind, sail trim, and heeling forces. Several appreciated the interactive diagrams, highlighting their effectiveness in illustrating how these forces interact. Some commenters with sailing experience shared personal anecdotes and added further details, expanding upon points made in the article, such as the importance of sail shape and the challenges of heavy weather sailing. A few mentioned the site's outdated design but emphasized that the quality of the content outweighed the aesthetic shortcomings.

  The Hacker News post "How a yacht works: sailboat physics and design" linking to onemetre.net sparked a moderate discussion with 16 comments. Several commenters praised the clarity and comprehensiveness of the linked article. One user, pjmlp, appreciated the "excellent diagrams and explanations" particularly regarding apparent wind, a concept they found often poorly explained elsewhere. Another, sp332, simply stated it was a "great explanation." throwaway30012 agreed, specifically highlighting the explanation of heeling force and righting moment as being "well explained."

  A recurring theme in the comments was the comparison of different sailboat designs. toomuchtodo pointed out the advantages of multihulls over monohulls in terms of speed and stability, referring to monohulls as "slow and tippy." This spurred a small discussion about the trade-offs, with yters countering that monohulls offer a more engaging and "fun" sailing experience, despite their performance disadvantages. They elaborated that the heeling and responsiveness of a monohull provides more feedback and a closer connection to the forces at play. sp332 further contributed to this comparison by mentioning the reduced wetted surface area of multihulls as a key factor in their speed.

  The discussion also briefly touched on the complexities of sail trim. throwaway30012 noted the subtleties involved in adjusting sail shape for optimal performance in varying wind conditions. However, this point wasn't elaborated on further by other commenters.

  Finally, there was a minor tangential discussion about the use of computational fluid dynamics (CFD) in modern yacht design, initiated by pjmlp. They mentioned the prevalence of CFD analysis in optimizing hull shapes and sail designs, acknowledging its significance in pushing the boundaries of performance.

  Overall, the comments on the Hacker News post generally praised the linked article for its accessible explanation of sailing principles. The discussion also touched upon some broader topics within sailing, such as the advantages and disadvantages of different hull designs, the intricacies of sail trim, and the role of modern technology like CFD in yacht design.

• New technique generates topological structures with gravity water waves

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  Posted: 2025-02-15 19:36:31

  Verbose tl;dr

  Researchers have developed a new technique to create topological structures in water waves using a sort of "acoustic tweezer." By strategically placing vibrating sources beneath a water tank, they generate specific wave patterns that exhibit topological properties, meaning certain features are protected and robust against perturbations. This method allows for the precise control and manipulation of these topological gravity waves, potentially opening new avenues for studying wave phenomena and their interactions in fluids.

  Researchers from the University of California, Berkeley, have pioneered a novel experimental technique to generate topological structures within gravity-capillary waves, a common type of water wave influenced by both gravity and surface tension. These waves, ubiquitous in nature from ripples in a pond to ocean swells, have now been manipulated in the laboratory to exhibit unique topological characteristics, opening exciting new avenues in wave physics and potential applications in diverse fields.

  The team's innovative method employs what they describe as "wave tweezers," a sophisticated setup involving carefully arranged wave generators strategically positioned around a circular basin. These generators, by emitting waves with precisely controlled frequencies and amplitudes, can effectively sculpt the wave field within the basin. This meticulous control allows them to create specific wave patterns exhibiting topological defects, points where the wave amplitude drops to zero and the wave phase becomes undefined. These defects are analogous to topological defects found in other areas of physics, such as condensed matter physics, and carry quantized topological charges, meaning they can only take on specific discrete values.

  The generated topological structures are robust and stable due to the underlying topological protection. This protection arises from the inherent geometric properties of the wave field, making the topological defects impervious to small perturbations or imperfections in the experimental setup. This inherent stability is a crucial aspect of topological phenomena and is a key reason for their growing interest across various scientific disciplines.

  Furthermore, the researchers demonstrated the ability to manipulate and control the movement of these topological defects within the wave field. By finely adjusting the wave generators, they can steer the defects along predefined paths, highlighting the dynamic nature of these topological structures. This controlled manipulation could pave the way for future applications in wave-based information processing or the creation of complex hydrodynamic circuits, analogous to electronic circuits.

  This breakthrough in generating and manipulating topological structures in gravity-capillary waves offers a powerful new platform for exploring fundamental concepts in wave physics, particularly concerning the interplay of topology and hydrodynamics. The ability to create, control, and study these robust topological defects in a readily accessible laboratory environment promises to deepen our understanding of topological phenomena and their potential applications in various fields, ranging from fluid dynamics to materials science. This research opens exciting new possibilities for future investigations, including exploring the interaction of multiple topological defects, studying the effects of non-linear wave dynamics, and investigating the potential for creating more complex topological structures in wave fields.

  • physics
  • fluid dynamics
  • water waves
  • gravity waves
  • topological structures
  • wave generation
  • experimental physics
  • optical tweezers
  • nonlinear dynamics
  • hydrodynamics

  Summary of Comments ( 10 )
  https://news.ycombinator.com/item?id=43061521

  Verbose tl;dr

  Hacker News users discussed the limitations of the "topological gravity" created with water waves, emphasizing that it's an analog simulation, not true gravity. Several commenters pointed out that while interesting, this doesn't offer new insights into actual gravity or quantum gravity. The analogy was compared to using water waves to simulate traffic flow – insightful for specific behaviors, but not fundamentally altering our understanding of cars. Some questioned the use of "topological" and "gravity" in the title, finding it misleadingly sensationalized. A few appreciated the elegance of the experiment, acknowledging the challenges of simulating complex physics, even in analog form. There was also brief discussion on the potential applications of such simulations in other fields.

  The Hacker News post titled "New technique generates topological structures with gravity water waves" (linking to a phys.org article) has a modest number of comments, generating a brief discussion rather than an in-depth exploration of the topic. The comments do not delve deep into the physics or mathematics of the research. Instead, they primarily focus on clarifying the meaning and implications of "topological" in this context.

  One commenter highlights the distinction between the everyday use of "topology" (referring to physical layout or connectivity) and its more rigorous mathematical definition in the context of the experiment. They explain that the water waves' behavior mimics aspects of topological insulators in solid-state physics, possessing properties that are robust against certain types of perturbations. This commenter also notes the broader trend of finding analogs of condensed matter phenomena in other physical systems.

  Another comment questions the significance of the research, wondering if it's merely a "cool demo" or has more fundamental implications. They express skepticism about the practical applicability of generating topological structures in water, particularly given the already intricate nature of fluid dynamics.

  A further comment chain discusses the concept of a topological charge, trying to elucidate its meaning and relevance to the experiment. One participant suggests thinking of it as a conserved quantity related to the swirling motion of the water. They also mention the connection to topological defects, which are stable configurations with unique properties.

  Finally, there's a brief exchange about the potential applications of this research. While some remain skeptical, others suggest potential links to understanding wave propagation in complex environments or designing novel waveguides. However, these suggestions are speculative and not explored in detail.

  Overall, the comments reflect a mixture of curiosity and skepticism about the research. While acknowledging the interesting nature of the experiment, commenters express reservations about its practical importance and struggle to fully grasp the implications of the "topological" aspects. The discussion remains primarily at a conceptual level, without venturing into the specifics of the experimental setup or the underlying theoretical framework.