Magic of Water: Exploration of Production Process with Fluid Effects in Film and Advertisement in Computer-Aided Design ^†

Abstract

Fluid effects are important in films and advertisements, where their realism and aesthetic quality directly impact the visual experience. With the rapid advancement of digital technology and computer-aided design (CAD), modern visual effects are used to simulate various water-related phenomena, such as flowing water, ocean waves, and raindrops. However, creating these realistic effects is not solely dependent on advanced software and hardware; it also requires an understanding of the technical and artistic aspects of visual effects artists. In the creation process, the artist must possess a keen aesthetic sense and innovative thinking to craft stunning visual effects to overcome technological constraints. Whether depicting the grandeur of turbulent ocean scenes or the romance of gentle rain, the artist needs to transform fluid effects into expressive visual language to enhance emotional impact, aligning with the storyline and the director’s vision. The production process of fluid effects typically involves the following critical steps. First, the visual effects artist utilizes CAD-based tools, particle systems, or fluid simulation software to model the dynamic behavior of water. This process demands a solid foundation in physics and the ability to adjust parameters flexibly according to the specific needs of the scene, ensuring that the fluid motion appears natural and smooth. Next, in the rendering stage, the simulated fluid is transformed into realistic imagery, requiring significant computational power and precise handling of lighting effects. Finally, in the compositing stage, the fluid effects are seamlessly integrated with live-action footage, making the visual effects appear as though they are parts of the actual scene. In this study, the technical details of creating fluid effects using free software such as Blender were explored. How advanced CAD tools are utilized to achieve complex water effects was also elucidated. Additionally, case studies were conducted to illustrate the creative processes involved in visual effects production to understand how to seamlessly blend technology with artistry to create unforgettable visual spectacles.

1. Introduction

In the digital imaging production process, creating visual effects (VFX) and seamlessly integrating them with live-action footage requires multiple critical steps. VFX animators design the effects based on the film script, using fluid simulations or particle systems to generate elements such as smoke, fire, or water flow. They adjust parameters to ensure natural and smooth effects. Next, lighting and material settings are matched to the live-action footage, including light direction, reflections, and material details, including transparency and refractive index, to enhance realism. In the rendering phase, high-quality images are generated, with initial baking performed to reduce the computational load in later stages. Finally, compositing software is used to blend the effects with the footage seamlessly. Compositors apply multilayer overlays, color corrections, and flaw fixes to balance tones and brightness, ensuring the effects integrate naturally into the overall scene. As a result, a realistic visual effect is created to immerse audiences in a world of virtual imagery and portray phenomena impossible to capture in the real world. This process involves several critical steps. First, VFX artists must thoroughly understand fluid dynamics and master the software tools, particularly fluid simulation and effects nodes. Using professional software such as Houdini or Blender, they generate the motion of water, including flow speed, ripples, and shape variations, ensuring natural and realistic movement. Subsequently, lighting and material settings are aligned with the live-action footage to achieve realistic lighting effects. The artist adjusts the water’s transparency, refraction, and reflection properties, integrating it seamlessly into the scene. In rendering, high-quality images are produced while balancing baking and rendering times. Finally, compositing software is used to combine the water effects with live-action footage, applying color corrections and flaw adjustments. This process requires a combination of technical skill and artistic vision. While computer software accelerates the creation of these visual effects, the ultimate success depends on the creator’s aesthetic judgment and technical expertise. The artistic and technical aspects of this process are discussed in this article.

2. Aesthetic Requirements

Understanding the forms and characteristics of water is crucial for creating realistic water fluid effects. While general computer software can create basic water shapes, professional software offers dozens of different water fluid types that can be applied to various themes and scenarios. Although modern technology provides these conveniences, vivid and realistic effects that seamlessly integrate with the film require VFX artists to thoroughly understand the properties and behaviors of water in the natural world. This understanding is key to producing visually impressive effects.

2.1. Forms of Water

To effectively present the characteristics of water, creators must regularly observe different types of water forms in two scenarios.

• Large-scale scenarios: Waterfalls, ocean waves, foam, splashes, shorelines, and fountains;
• Small-scale scenarios: indoor scenes featuring water droplets, crowns, and splashes.

With detailed observation and study of these forms, creators can better understand the behavior of water to heighten realism in visual effects creations. This observation enhances technical skills and the aesthetic appreciation of water, ultimately influencing the quality and vitality of their work. As many experts emphasize, familiarity with the various manifestations of water is critical in visual effects creation. For example, in the 2017 Russian sci-fi film Attraction, the visual effects team utilized advanced fluid simulation technology to replicate water’s physical properties as follows.

• Flow speed and dynamics: By controlling the speed and direction of water flow, the team recreated realistic water behaviors, such as rapids, ripples, and vortices.
• Interaction effects: The reaction of water when encountering different objects (such as spaceships or characters) was carefully simulated to enhance realism. For instance, when water flowed past certain obstacles, the resulting splashes and reflection effects became crucial details (Figure 1).

2.2. Characteristics of Water

In addition to its various external forms, water possesses numerous intrinsic properties, such as volume, vitality, speed, viscosity, collision behavior, and surface tension. These properties, combined with its shape, enable water to exhibit dynamic and vivid behavior. Standard visual effects software generates natural fluid forms, such as ocean waves or waterfalls, while emphasizing the visual impact of fluid properties. For example, in advertisements, the stacking effect of viscous liquids—such as pouring honey or squeezing toothpaste—leverages these physical properties. The crown-like shape formed by a droplet of water is an example. This is a physical phenomenon related to surface tension. Capturing the aesthetic of such a moment using traditional methods is challenging due to the many influencing factors, including the droplet’s volume, height, and potential for creating different visual effects, such as internal or external crowns. Factors affecting visual appeal also include the crown’s diameter, height, and the number of suspended droplets. Due to the difficulty of capturing water droplets authentically and the challenge of manipulating droplet shapes or directing their motion along a specific path per a script, modern visual effects technology relies on computer-generated solutions. This approach enables precise control over the effects and creative ideas to be realized more efficiently, as shown in Figure 2.

The combination of water’s characteristics and its forms enables a variety of dynamic shapes. When designing according to the script’s requirements, finding the most appropriate production method is crucial. This often involves utilizing the various features provided by different software to quickly achieve the desired effect. However, aesthetic requirements are a prerequisite for visual effects. Relying solely on the operation of computer software without the necessary aesthetic understanding often results in creations that appear stiff and lack vitality. Therefore, VFX artists must possess technical skills and artistic literacy to truly bring visual effects to life.

3. Technical Requirements

In creating realistic fluid visual effects, it is essential to first master the physical properties that the software can accurately simulate. This involves understanding different resolutions, mastering time scales, and setting liquid diffusion. Next, it is crucial to fully understand and utilize the use of nodes. Nodes are an indispensable key technology in visual effects production, typically including effect nodes and material nodes, among others. Different software has various methods of operation and focal points.

3.1. Physical Properties

3.1.1. Resolution

Resolution encompasses the level of detail in object models, the clarity of baking or rendering, and the final video output resolution. The higher the resolution, the richer the details, making the liquid’s appearance more realistic. This also means higher demands on the same computer hardware. In terms of fluid performance, resolution is a critical factor in determining the perfection of the effect. If hardware conditions allow, the higher the resolution, the better. Resolution can be analyzed through various production processes, with the key to fluid performance being the level of detail on the liquid surface. Fluids are usually subdivided into units called “voxels,” which collectively make up the “pixels” of the fluid. The process of generating fluid within a certain size range is called the “domain.” Within this domain, controlling the number of subdivisions is crucial. A higher number of subdivisions is an effective method for creating high-resolution fluids. These subdivisions directly affect the computer-generated effect. Since resolution is defined by subdivision, larger domains need more divisions to match the resolution of smaller domains. For example, a 1 m³ domain with 64 resolution divisions would require 128 subdivisions to match a 2 m³ domain. In practical application, the size of the voxels is visualized and adjusted according to specific needs [1]. Figure 3 illustrates the performance of fluids at different resolutions.

3.1.2. Time Scale

Time scale is one of the key factors influencing fluid performance, especially when simulating water flow speed. The motion speed of water affects the appearance of the liquid and its realism. In computer simulation, the speed of time determines the rate of change in water flow patterns, directly affecting the simulation results. By adjusting the time scale, the speed of the simulation can be controlled. Lower time scale values result in a “slower motion” effect, where the water flows slowly, while higher values speed up the simulation, quickly showcasing the dynamic behavior of the water. Setting the correct water flow speed is a key element in liquid effects; if the speed does not accurately reflect real-world behavior, the final result is significantly diminished. Therefore, appropriately setting the time scale is essential for achieving realistic effects in fluid simulations. Researchers need to understand the physical properties of water and its behavior under different time scales to ensure that the generated fluid effects meet viewers’ expectations. Only by mastering the time scale can the realism and visual impact of liquid effects be enhanced, leading to high-quality visual effects.

3.1.3. Liquid Diffusion

Liquid diffusion is a critical physical property to determine how the liquid interacts with its environment. The main factors affecting diffusion include viscosity and surface tension, which are adjusted to simulate the behavior of various liquids, such as water, oil, or honey. Viscosity measures the “thickness” of a fluid and reflects the force needed to move an object at a given speed over a specific surface area. Specifically, in software such as Blender, the kinematic viscosity (or dynamic viscosity) is measured in Pa·s (Pascal seconds), divided by density (measured in kg·m⁻³), with the result expressed in m²·s⁻¹. For example, at room temperature, water has a viscosity of 1.002 cP (centipoise), which is equivalent to 0.001002 Pa·s, and its density is about 1000 kg·m−³. Therefore, the kinematic viscosity of water is 0.000001002 m²·s⁻¹. Based on this, input parameters are represented as 1.002 × 10⁻⁶ [2].

Table 1. Blender viscosity unit and conversion.

Fluid	Dynamic Viscosity (in cP)	Kinematic Viscosity (Blender, in m2/s)
Water (20 °C)	1.002 × 100 (1.002)	1.002 × 10−6 (0.000001002)
Oil SAE 50	5.0 × 102 (500)	5.0 × 10−5 (0.00005)
Honey (20 °C)	1.0 × 104 (10,000)	2.0 × 10−3 (0.002)
Chocolate Syrup	3.0 × 104 (30,000)	3.0 × 10−3 (0.003)
Ketchup	1.0 × 105 (100,000)	1.0 × 10−1 (0.1)
Melting Glass	1.0 × 1015	1.0 × 100 (1.0)

(https://docs.blender.org/manual/zh-hant/dev/physics/fluid/type/domain/liquid/diffusion.html, accessed on 31 June 2024).

shows the viscosity units of different liquids in Blender 5.0 software and compares their values under normal conditions. This comparison helps users select appropriate viscosity and surface tension parameters in virtual liquid simulations, enabling accurate reproduction of the physical properties and behavior of various liquids.

3.2. Material Node Editor

Each 3D effects software has its unique method for creating fluid effects. For instance, with material nodes, in addition to adjusting various settings in the material panel to create materials, users can merge different basic material nodes using the node editor window to form complex effects. Each node performs a specific material operation, creating a grid-like structure where one node can pass information to multiple nodes, or multiple nodes can feed into the next one. The introduction of this node system makes material design more flexible, enabling creators to control and create more complex and stunning material effects. When building a node system, effects are viewed as a combination of data processing pipelines: nodes include “source” nodes (representing data origins), “process” nodes (which filter and adjust data), and “output” nodes (leading to the final effect). Users can connect nodes in various ways and adjust each node’s attributes or parameters to flexibly generate various material effects. Material nodes are divided into shading nodes and texture nodes, which, through these functions, allow fluid effects like water flow to be presented in a more realistic and detailed manner.

3.2.1. Texture Mapping

Texture mapping is used to enhance the surface detail of objects by projecting images or patterns onto the surface, making it visually richer. This technique alters the surface’s color and adjusts properties such as specular reflection, transparency, and pseudo-3D depth, allowing 2D images to present a more 3D effect in a 3D environment. Texture mapping plays a crucial role in the rendering process as it layers the designed patterns on the surface to achieve a natural and realistic visual effect. Additionally, texture mapping is widely used in digital sculpting, painting, and deformation operations to enhance the realism and richness of surface details. Figure 4 demonstrates the effect of applying multiple layers of textures on an object. By stacking different textures, the surface of the object acquires intricate detailing, thereby enhancing its visual depth and realism. These layered structures typically include different types of textures, such as diffuse textures controlling color, specular textures controlling glossiness, and normal or displacement textures simulating bump effects. Through this layered texture mapping technique, creators can create complex and realistic visual effects, making the object’s presentation in a virtual environment more vivid and detailed.

3.2.2. Procedural Textures

Procedural textures refer to the advanced texture generation technique that does not rely on external image files but instead automatically generates textures through a series of algorithms and mathematical formulas. Procedural textures maintain their quality at different scales, created based on mathematical computations rather than fixed-pixel images. Moreover, users can adjust the parameters of procedural textures at any time, enabling real-time visual changes with significant flexibility and control in the creative process. Procedural textures are especially appropriate for simulating natural materials such as wood, stone, and metal, as these materials often have complex and irregular surface characteristics. With procedural textures, artists can create high-quality, detailed materials without requiring large amounts of storage space since these textures do not need to be saved as large image files. In Blender, users can utilize its powerful node system to create and modify procedural textures. This system allows users to connect various texture nodes and combine them with other materials and textures for complex visual effects. For example, users can blend procedural textures with mapping, color, reflection, and transparency properties to produce unique and diverse results. Procedural textures enhance the diversity of materials and the visual expressiveness of models, allowing designers to explore various creative possibilities. Due to their flexibility and adjustability, procedural textures have become an indispensable tool in 3D modeling and material design, particularly for projects requiring a high degree of realism and complexity.

3.2.3. Ocean Modifier and Foam Node

The Ocean Modifier in Blender is a powerful tool used to simulate large bodies of water, such as oceans and waves, and generate realistic wave effects. The Foam Node enhances the rendering’s realism by adding foam effects to the water surface.

The Ocean Modifier offers the following adjustable parameters:

• Resolution by controlling the detail level of the waves: the higher the values, the more detailed the results, and the longer the computation time;
• Physical size of the ocean;
• Time for animation effects: the more time, the more the waves move;
• Wind velocity that affects the height and speed of the waves;
• Choppiness, which sharpens the waves, making the peaks more pronounced;
• Foam data, which enables foam effects and generates a foam image sequence.

The Foam Node is not an independent node, but a property mask generated based on the foam data in the Ocean Modifier. This mask can be used in the material settings to control foam distribution.

To set up the foam effect, foam data is required in the Ocean Modifier. An attribute node needs to be added in the Shader Editor to input “foam” (case-sensitive) in the name field. Optionally, the vertex data layer is added as a data layer. The Ocean Modifier stores the foam data as a color attribute for accessing foam details in the renderer. The coverage setting is adjusted to control the amount of foam on the wave surface. Negative values indicate a reduction in foam coverage (limiting it to the wave peaks), while positive values mean an increase. The typical range is from −1.0 to 1.0. As shown in Figure 5, these steps illustrate the implementation and adjustment of foam effects. In Figure 6, an example created and rendered in Blender5.0 demonstrates the foam effect, where the wave crests appear white due to the foam data.

4. Output

It is possible to create realistic visual effects by mastering the software’s features and practicing extensively. Using the software, the functions to represent specific water states can be identified. However, testing is required to determine the features that yield the desired results. Once testing is completed, the most appropriate effect is selected and fine-tuned. This refinement process enhances the effect’s quality to adjust the size and position of water droplets, the flow speed, and lighting contrasts, and to seamlessly integrate rendered footage into videos. Every production stage demands careful review to ensure that each frame is created and previewed individually during the creation process. Multiple revisions are necessary before exporting the final video to guarantee quality. Although this process is time-consuming, attention to detail is crucial. For instance, Figure 7 captures the fleeting beauty of a wave’s spray at its peak. This effect, although impossible to capture with a conventional camera, requires a top-down perspective to freeze the spray mid-air, embodying the concept of eternity in a moment. In the creation process, an object moving in a circular path is generated to create a water surface for the object to skim across, causing splashes. Achieving the ideal visual effect necessitates numerous experiments and adjustments. While computer-generated effects enable desired results, they also introduce randomness and unpredictability. These random elements often inspire creators, enabling them to discover their perfect design. Other than the wave spray’s shape, the work emphasizes secondary factors, such as the atmosphere, which enhance the overall effect. A key light source is positioned laterally, penetrating the liquid surface of the spray to create a translucent, crystalline appearance. This illuminates the spray against a tranquil setting, producing a serene and stunning image that perfectly encapsulates the eternal beauty of a fleeting moment.

5. Conclusions

Computer-generated effects offer immense commercial benefits by creating visuals that cannot be achieved in traditional filming. Their widespread adoption becomes more prominent. Particle effects in computer graphics enable highly realistic visuals, bringing a new dimension to content that traditional film techniques cannot convey. To effectively utilize computer-generated effects, clear workflows and precise control of these tools are required. Achieving realism is a fundamental goal for creators. Water fluid effects are common visual effects, but their methodology can be applied to other types of effects. As visual effects technology becomes increasingly accessible, many effects once excluded from the big screen are now created on personal computers. The ability to craft realistic effects using personal computers is a trend that significantly impacts the film industry. For production companies and individual creators, cultivating an aesthetic sensibility and mastering software tools is crucial to enhancing the quality of their work.