Smart Materials Finishing and Insulation Solutions applied to the Interior Design of a Cruise Ship Cabin

2.1. Thermo-acoustic material selection outlines

The research activity has started with a classification of the main insulating materials applied in the shipbuilding sector, considering the constituent type of the fibres (Fig. 1). A main difference between Natural-based and Petrolchemical materials is taken into account, each of them further divided into organic (Table 1, 2) and inorganic groups (Table 3, 4).

[2] Referred values for Bacchi Spa™ lightweight panel; [3] Hongisto et al. (2022); [4] Rockwool ™ database; [5] Reference value for mineral wools from Isover ™ Database

Composed of hydrated laminar magnesiun-aluminium64–160 0.058–0.070 840–1080 630–1360 Hard-core Thermal insulation in ironsilicate which resembles mica. It is most used in its panels, structural elements for exfoliated (expanded) form boards large public spaces. Acoustic-fireproofing panels

Insulating material made from natural or recycled stone The stone is melted and spun into fibres

Wall insulation and HVAC (Heating Ventilation and Air Conditioning) system

Insulating material made from fine fibres of glass. 11–70 0,033–0.040 1030 180 Boards, Glass wool is produced by melting glass and then [3] [3] [3] [5] rolls spinning it into fibres

High-temperature insulation and fireproofing. Acoustic tiles and insulation in ducts a non-combustible autoclaved calcium silicate board

Inorganic material composed of calcium, silica, and 280-320 0.07 1100 – Boards reinforcing fibres. The material is formed through a chemical reaction and heat treatment process, resulting in rigid and fire-resistant boards

Technical Density Thermal description [kg/m3] conductivity [W/m°C]

[1] Referred values for CFAB™ Cellulose-based, thermo-acoustic panels

Derived from the bark of cork oak trees, specifically quercus suber. It undergoes expansion through heating and pressure treatment

Cellulose-based products made primarily from post48–128 0.037 2000 – Panels consumer and industrial paper, with recycled newspaper being the main raw material

Technical Density Thermal conductivity description [kg/m3] [W/m°C]

Table 1. Natural-based organic materials Seatific, Vol. 3, Issue. 2, pp. 89–110, December 2023

Polyethylene Terephthalate Foam (PET) Polymethyl Methacrylate (PMMA)

Open-cell foam composed of melamine resin, a 9–12 0.032–0.035 1650–1800 95.5–142 Sheets, thermosetting polymer derived from melamine panels and formaldehyde. It is high porous Thermosetting plastic foam made from phenol 32–38 0.02 1850–1910 334–455 Sheets, formaldehyde resin. The foam structure consists (closed cell boards of a network of cells, providing low thermal 0.035) conductivity and fire-resistant properties Transparent thermoplastic known for its high 1190–1210 0.19–0.22 1150–1250 1390–1430 Sheets, impact resistance, optical clarity, and UV stability panels It can be extruded into sheets or molded into panels with varying thicknesses and shapes Closed-cell foam made from polyethylene, 75–110 0.033–0.035 1140–1260 687–821 Sheets, a thermoplastic polymer. Lightweight, flexible, boards and resilient material with closed cells Transparent thermoplastic known for its optical 1160–1220 0.19–0.21 1400–1480 1410–1800 Sheets, clarity, scratch resistance, and UV stability. panels It is typically extruded into sheets or molded into panels High-temperature resistant foam made from 15–32 0.032–0.304 1390–1450 119–173 Sheets, polyimide resin, which is known for its excellent rolls thermal stability and resistance to heat, chemicals, and radiation Synthetic polymer made from monomers of the 28–32 0.032–0.036 1200–1220 468–616 Sheets, aromatic hydrocarbon styrene. Closed-cell boards structures provides thermal insulation and buoyancy Foam formed by reacting polyols and 30–34 0.03–0.035 1650–1700 35.1–43.7 Spray foam, isocyanatesopen-cell or closed-cell structure with boards varying densities Thermoplastic known for its versatility and 36–44 0.02–0.03 1120–1140 745–871 Sheets, durability. PVC is produced in various forms pipes through polymerization of vinyl chloride monomer

High-temperature insulation and in electronics. Acoustic insulation in machinery spaces Insulation boards,walls soundproofing

Core material for sandwich panels, acoustic insulation walls, ceilings, and floors of cabins Windows and decorative panels, transparent partitions

Cabin ceiling/floors and accomodation areas. HVAC insulation, noise barriers and acoustic absorbers Refrigeration and pipes insulation, acoustic panels

It could be possible thanks to the application of Granta EduPack Software, currently used in an interdisciplinary matter in the academic field to perform complex analysis which can synoptically consider engineering, design and sustainable development aspects. The user can perform analysis based on three stages. Level 1 database contains an introductory approach of more than 60 records or common engineering materials (metals, plastics, ceramics, glasses, composites and natural materials). A limited set of attributes is linked to records for processes that are used to shape, join or finish them.

Level 2 contains a comprehensive set of mechanical, thermal and electrical properties, as well as Eco Properties and Durability Information, for more than 100 common materials. The materials and the content of the records enable a wide range of selection studies and environmental audits of products. The process records include a simple cost model that allows cost-comparisons between alternative processes. Belonging to this level is the Building Environment repository, which contains more than 120 materials commonly used in Architectural applications. A set of mechanical, thermal, electrical, hygro-thermal, acoustic is provided, along with durability information. Level 3 contains a comprehensive set of the previous data, together with mechanical, optical, magnetic and environmental properties for over 4,000 engineering materials. Eco Design database also encompasses environmental properties such as whether a material is restricted, NOx and SOx values, water usage, carbon footprint, embodied energy, and end of life information. A crossed use of the second and the third level, together with a scoping review activity of the cutting-edge solutions actually present on the market and the support of the scientific literature, helped to create the material classification. It should be stressed that specific heat and thermal conductivity are related to an ambient temperature set at 23°C. In order to further characterise each substance, the acoustic velocity variable (m/s) has been used, as measure of the speed of longitudinal sound waves in a solid. It is calculated as follows (Equation 1): [6] Reference values for Zoltex Carbonized PX 35 felt

Material derived from 100 0.031 700–750 – Sheets, polyacrylonitrile polymer. rolls It undergoes preoxidation and stabilization processes to enhance its thermal stability and fire resistance Oxidized Poly-Acrylonitrile (OPAN) [6]

where E is Young Modulus (Pa) and ρ is the material density (Kg/m3). The speed of sound in a solid material can be used as a further indicator of its insulating properties. It depends on the density and compressibility of the matter through which it propagates. In general, in denser and more rigid materials, such as metals, the speed of sound is higher, while in less dense and more flexible ones, such as thermal insulators like wool, fiberglass and foam, the speed of sound is slower. The parameters considered are related to the substances used and not to the finishes applied, as they could undergo variations in their weight, depending on the different thicknesses applied and their relative stratigraphy. In many

Thermal conductivity Cryogenics test laboratory Non-destructive method Diametral compression test for mechanical properties Mechanical properties Micro-indentation technique of silica aerogels Dynamic compressive test Fracture toughness tests Single-edge-notch bending (SENB) Density measurement Torsional oscillator measurements Hydrophobicity and Contact Angle Measurement Hydrophilicity Aging and Stability Tests Long-Term Stability Environmental Resistance Optical absorption UV–Vis tests

solutions on the market these materials often constitute the core of sandwich and honeycomb compounds to combine the aforementioned properties with structural capacity.

3.1. Aerogels (HPM)

Aerogels are highly porous, ultra-lightweight substances with very low thermal conductivity (0.017 W/m°C) (Aegerter et al., 2011), primarily composed of air. They are manufactured through a supercritical drying process that removes the liquid content of a gel. Various materials have been implemented,

Used to determine apparent thermal conductivity (k-value) of thermal insulation systems Application of stress load or force to the point where a material object is split in half (down the diameter of the object) The sample material is indented using a sharp, pointed probe, with a controlled force application Tests of cross-linked silica aerogel using a split Hopkinson pressure bar (SHPB) for Poisson's ratio determination Specimen is subjected to three-point bending loads Body suspended by a thread or wire which twists first in one direction and then in the reverse direction, in the horizontal plane Determine the contact angle of water on the aerogel surface to assess its hydrophobic or hydrophilic properties. Subject the aerogel to aging tests to simulate real-world conditions and evaluate its stability over time. Proton irradiation tests Test the aerogel's resistance to ultraviolet (UV) radiation

Moner-Girona et al. (1999) Luo et al. (2006) Ehrburger-Dolle et al. (1995) Crowell et al. (1990)

with silica being the most commonly used (Pierre, Anderson, 2011). Historically, aerogels production has been relatively costly, constraining its usage to advanced aerospace operations (Jin et al., 2023). However, as manufacturing expenses decline, they are finding their way into a wider array of applications, including their incorporation into composite materials such as laminated glazing for thermal insulation or integration into blankets for heat protection and acoustic absorption. The following table show the test methods aimed at characterizing aerogels main properties (Table 5). In cruise ship design, suitable features and applications can include: •

Internal cabin insulation: it can be used aerogels low thermal conductivity helps maintain comfortable inside temperatures, reducing the reliance on heating and cooling systems. This can lead to energy savings and lower operational costs;

Energy-Efficient Windows: aerogels can be integrated into windows frames to enhance their thermal insulation properties. This helps reduce heat gain during sunny days and heat loss during cold weather, contributing to energy savings in the ship's overall HVAC system;

Soundproofing: in addition to thermal insulation, aerogels can provide soundproofing benefits. Installing aerogel-based insulation in cabin walls and ceilings can help minimize noise transfer between cabins and common areas;

Table 6. Vacuum Insulation Panels (VIPs) test methods Testing category

Standard specification for ASTM C1484-10(2018) Specification covers the general Vacuum Insulation Panels requirements for vacuum insulation panels Thermal testing DIN EN 12667:2001 Determination of thermal resistance Fire test method ISO 834-11:2014 One side of the specimen is exposed to the furnace and measured according to its appearance and ignition Insulation performance

3.2. Vacuum Insulation Panels (VIPs) – (HPM)

VIPs consist of a core material (typically a rigid, porous material like fiberglass or silica aerogel), enclosed in a vacuum-sealed panel, which minimizes heat transfer by eliminating air molecules. They provide high insulation efficiency in a thin profile, making them suitable for spaceconstrained applications (Baetens, 2010). Here's how VIPs work and why they can be effective also in the maritime field: •

Vacuum Core: core material is placed in a vacuum or near-vacuum environment, which reduces the conduction and convection of heat;

Airtight Encapsulation: core material is sealed within a gas-tight envelope made of high-quality barrier materials, often metallic or laminated films. This envelope prevents air from entering and disrupting the vacuum, ensuring long-term insulation performance;

Longevity: if properly maintained and protected from physical damage or perforations, VIPs can maintain their insulation properties for an extended period, making them a durable and cost-effective insulation solution over the long term.

Nikafkar and Berardi (2020) Davraz and Bayrakçı (2013) Y. U. Kim et al. (2021)

and architecture sectors, the term "PCM" has gained relevance concerning materials and products utilized for temperature regulation purposes. PCMs store and release heat energy during phase transitions, such as from solid to liquid or vice versa. They can absorb excess heat during the day and release it at night, helping to maintain a stable indoor temperature. PCMs can be embedded in insulation materials or used as standalone panels. The following table show the test methods aimed at characterizing PCMs main properties (Table 7). Potential applications aboard cruise ships may include: •

Temperature Control: PCMs are effective at stabilizing indoor temperatures by absorbing and releasing heat during phase transitions. In cruise ship cabins, PCMs can absorb excess heat during the day when the sun is intense and release it at night when temperatures drop, ensuring a consistent and comfortable environment for passengers;

Space Efficiency: they are typically applied as thin layers within walls or ceilings, making them ideal for cruise ship cabins with limited space. Their slim profile allows for efficient insulation without sacrificing valuable cabin space;

Condensation Prevention: PCMs can help prevent condensation on cabin surfaces, which is essential for maintaining a healthy and comfortable indoor environment. Condensation can lead to moisturerelated issues like mold growth and corrosion;

Retrofitting Capabilities: in some cases, existing cruise ships may undergo renovations or upgrades to improve energy efficiency and passenger comfort. PCMs can be integrated into cabin insulation during retrofitting projects to enhance insulation properties;

Emergency Energy Backup: in the event of a power outage or HVAC system failure, PCMs can temporarily maintain indoor temperatures, ensuring passenger safety and comfort until normal operations are restored.

The following table show the test methods aimed at characterizing VIPs main properties (Table 6).

3.3. Phase Change Materials (PCMs) - (SM)

This category includes all smart materials capable of undergoing reversible changes in response to external stimuli, in particular they exhibit phase changes dependent on temperature (Delgado et al., 2018). In the construction

Table 7. Phase Change Materials (PCMs) test methods Testing category

Latent Heat of Fusion Calorimetry Measure the heat absorbed or released during the phase transition Thermal Cycling Stability Repeated Heating and Assess the stability of the material over Cooling Cycles multiple cycles, checking for performance degradation Thermal Conductivity Standardized Methods Measure the material's ability to conduct heat during solid and liquid phases Encapsulation Efficiency Encapsulation Assessment Evaluate the efficiency of the encapsulation process, ensuring containment and leak prevention Durability and Long-Term Extended Testing Periods Conduct long-term tests to assess durability Performance and performance over extended periods Material Compatibility Compatibility Tests with Investigate how well the PCM interacts Other Materials with materials commonly used in specific applications Environmental Impact Environmental Assessment Evaluate the environmental impact, considering factors like recyclability and potential hazards

3.4. Shape Memory Materials (SMMs) – (SM)

These materials have the remarkable ability to "remember" a specific shape and return to it when exposed to a certain stimulus, typically heat (Sun et al., 2012) (Vili, 2007). Shape-memory alloys (SMA’s) exhibit two distinct crystal structures linked to a phase transformation between a lowtemperature, martensitic phase and a high-temperature, austenitic phase. In the first configuration, the metal can easily be deformed into any shape; when the alloy is heated the memory metal is able to recall the shape it had before the deformation. This property enables the creation of dynamic, shape-changing structures and components like self-opening/closing windows and furniture mechanisms that can change their shape or configuration based on temperature changes (Jani et al, 2014). Stimulus-responsive configurations refer to the ways in which shape memory materials (SMMs) can be triggered or activated to exhibit their shape-changing properties. Different types of shape memory materials respond to various stimuli, allowing for a range of applications in diverse fields. Here are some common stimulus-responsive configurations: •

Thermal Activation: the most common stimulus for shape memory materials is temperature change. For shape memory alloys (SMAs), heating above a certain transition temperature (often called the austenitic finish temperature) causes a reversible phase transformation, allowing the material to recover its original shape; Light Activation: some shape memory materials, particularly polymers, can be activated by exposure to light. Photothermal heating induces the required temperature change for triggering the shape memory effect. This feature is often exploited in biomedical applications where light can be precisely controlled; Electrical Activation: Applying an electric current to shape memory alloys can generate Joule heating, causing the

References Kotzé et al. (2014) Putra et al. (2019) C. Xu et al. (2022) Y. Huang et al. (2023) Egea et al. (2022) Ostrý et al. (2019) Di Bari et al. (2020)

material to undergo the phase transformation and recover its original shape. This electrical activation is useful in micro actuators and other electronic applications; •

Magnetic Activation: certain shape memory alloys, such as nickel-titanium, are responsive to magnetic fields. This latter induces mechanical deformation, making it possible to control the shape memory effect remotely;

Chemical Activation: reversible chemical reaction, leading to a change in the polymer's structure and, consequently, in its shape;

pH Activation: they can to respond to changes in pH. The pH-induced changes can alter the polymer's structure, leading to a reversible shape change;

Moisture Activation: particularly in hydrogels They can react to changes in moisture levels. Absorption or loss of water can induce a change in the material's conformation and trigger the shape memory effect;

Mechanical Activation: in some cases, shape memory materials can be activated by applying mechanical stress. This might involve stretching, compression, or other mechanical deformation to initiate the shape memory response;

Dual/Multi-Stimulus Activation: some advanced configurations involve materials that respond to multiple stimuli simultaneously or sequentially.

The following tables show the test methods aimed at characterizing SMM main properties (Table 8, 9). Between the possible application we can list the following cases: •

Adaptive Insulation: since SMM can change shape or thickness in response to temperature fluctuations, during colder periods they can expand to provide additional insulation and during summer, they could contract to allow better ventilation. This adaptability can

Fulcher et al. (2010) Ibarra et al. (2022) Mohamed et al. (2022) Azra et al. (2013) Wang et al. (2023) Jacobson and Iroh (2021) B. Wang et al. (2023) Gall et al. (2002) Goda et al. (2020) X. Huang et al. (2021) Rybak et al. (2021) Pradhan et al. (2022)

Shape Memory Effect (SME) Shape Fixity and Recovery Test Subject the material to a deformation at a certain temperature, then allow it to recover its original shape upon heating Programming and Recovery Cycles Assess the material's ability to go through multiple shape memory cycles without significant degradation Thermal Characterization Differential Scanning Calorimetry (DSC) Measure the heat flow associated with the phase transitions in the SMP, such as the glass transition and melting temperatures Mechanical Testing Tensile Testing Assess the tensile properties of SMPs, such as modulus, strength, and elongation, both below and above their transition temperatures Compression Testing Investigate SMP response to compressive forces and shape recovery Thermo-Mechanical Analysis (TMA) Coefficient of Thermal Expansion (CTE) Evaluate dimensional changes in response to temperature variations Rheological Testing Shear Testing Study flow and deformation behavior under shear stress Dynamic Mechanical Analysis (DMA) Frequency Sweep Measure viscoelastic properties under dynamic loading conditions Chemical Resistance Testing Exposure Tests Expose SMP to different chemical environments for stability assessment Microscopic Analysis Scanning Electron Microscopy (SEM) Examine microstructure effects of deformation and recovery Electrical and Thermal Conductivity Testing Electrical Resistance Measurement Assess electrical conductivity in deformed and recovered states Thermal Conductivity Testing Evaluate thermal conductivity and heat transfer characteristics

Tcharkhtchi et al. (2014) Zhou and Huang (2015) Abdullah et al. (2012) Li & Wang, (2016) Zhao et al. (2015) Lendlein (2010) Martins (2019) McKinley (2004) Staszczak et al. (2022) Fisher et al. (2020) Kim et al. (2021) Ohki et al. (2004) Tobushi et al. (2015

help maintain optimal cabin temperatures without relying entirely on HVAC systems; • Sealing and gasketing: SMMs can be employed in sealing and gasketing applications to ensure airtight seals around doors, windows, and other openings. They can change their shape or compress when necessary to maintain a tight seal, preventing drafts and heat loss. It is important to note that SMMs are not commonly used for large-scale applications like cruise ship design at present. While they offer peculiar advantages, their adoption has to be assessed by factors such as cost, complexity, and the need for reliable control mechanisms.

3.5. Thermochromic materials (TMs)–(SM)

Thermochromic materials can be integrated into cruise ship cabin design to enhance insulation and improve the overall passenger experience (Boscolo et al., 2007). They change colour or optical properties in response to temperature variations, which can be used to create adaptive insulation systems and achieve energy efficiency in cruise ship cabins: • Smart Window Systems: thermochromic coatings or films can be applied to cabin windows to control solar heat gain and glare. When exposed to sunlight or high temperatures, these materials darken, reducing the amount of heat and light entering the cabin. In cooler conditions or at night, they become transparent, allowing natural light to enter and potentially aiding in passive solar heating. • Temperature-Responsive Surfaces: they can be used on cabin walls, ceilings, or other surfaces to visually indicate temperature changes. When the temperature inside the cabin rises or falls, these surfaces change colour or appearance, providing passengers with a visual cue about the thermal conditions. This can help passengers make informed decisions about adjusting the cabin temperature and HVAC settings. • Customized Cabin Experience: cruise ship cabins often host passengers with varying preferences for temperature and lighting. Thermochromic materials can be incorporated into cabin controls, allowing passengers to adjust the cabin environment to their liking. For example, passengers can control the tint level on windows or the colour of cabin surfaces. The test methods aimed at characterizing TH main properties are included in the following section table, since both smart materials acts in a similar way (Table 10).

Shape Memory Effect (SME) One-way Shape Memory Effect Deform material at a certain temperature and observe recovery Two-way Shape Memory Effect Assess ability to recover different shapes upon cooling and heating Thermal Characterization Martensitic Transformation Temperature Determine critical temperatures using DSC or Differential (Ms) Thermal Analysis Austenitic Finish Temperature (Af) Measure temperature associated with complete phase transformation Heat Treatment Analysis Differential Scanning Calorimetry (DSC) Study phase transformations and thermal behavior during heat treatment Metallography after Heat Treatment Examine changes in microstructure due to heat treatment processes Mechanical Testing Tensile Testing Measure strength, yield strength, elongation, and modulus of elasticity Compression Testing Evaluate compressive strength and deformation behavior Hardness Testing Assess material hardness using Brinell, Vickers, or Rockwell tests Impact Testing Evaluate toughness and resistance to impact loading Chemical Composition Analysis X-ray Fluorescence (XRF) Determine elemental composition of the alloy Atomic Emission Spectroscopy (ICP-AES) Analyze element composition, especially traces Non-Destructive Testing (NDT) Ultrasonic Testing (UT) Detect internal defects or flaws in the alloy Radiographic Testing (RT) Use X-rays or gamma rays to inspect the internal structure Eddy Current Testing Detect surface and near-surface flaws in conductive materials Corrosion Testing Salt Spray Test Evaluate corrosion resistance in a saline environment Electrochemical Corrosion Testing Measure corrosion rate under controlled electrochemical conditions Fatigue Testing Rotating Beam Fatigue Test or Axial Assess fatigue strength and behaviour under cyclic loading Fatigue Test

Testing high performance small diameter Nitinol wire the largest portal of nondestructive testing (NDT). https://www.ndt.net/search/ docs.php3?id=22368 Charfi et al. (2009) Sampath et al. (2023) Rondelli (1996) Soltan et al. (2023)

Liu and Huang (2006) Kožuh et al. (2018) Lavernhe-Taillard et al. (2009) Hashemi et al. (2023) Arciniegas et al. (2008) Sofocleous et al. (2013) Alım et al. (2018) G. Fisher (2003) Fink et al. (2023) Lee et al. (2023) Meir et al. (2011)

Naresh et al. (2016) Lexcellent et al. (2000) Meddour and Brek (2018) Gan et al. (2012)

Optical Properties Transmittance Spectroscopy Measure transparency in visible and near-infrared regions Coloration Efficiency Quantify color change per unit of applied charge Electrochemical Properties Cyclic Voltammetry (CV) Examine redox behavior through potential sweeps Chronoamperometry Study electrochemical response over time Impedance Spectroscopy Analyze electrical impedance as a function of frequency Mechanical Properties Durability Testing Evaluate stability under repeated cycling Adhesion Strength Assess adhesion between electrochromic layer and substrate Environmental Stability Chemical Resistance Test resistance to moisture, chemicals, temperature Long-Term Stability Assess performance over an extended period Colour retention test Examines how well the material retains its original color after multiple thermal cycles Color transition temperature (TM) Differential Scanning Calorimetry (DSC) Measure the heat flow associated with the material's phase transitions, providing information on the color transition temperature Thermal Conductivity (TM) Thermal Conductivity Measurements Evaluate the material's ability to conduct heat, which can impact its response time to temperature changes Morphological Changes (TM) Scanning Electron Microscopy (SEM) Examine the material's surface morphology to understand any structural changes induced by temperature variations Electrochromic Device Switching Speed Measure transition time between colored and bleached states Performance Cycling Stability Evaluate performance over numerous coloration/bleaching cycles Response to external stimuli Assess material's response to factors like light intensity or temperature changes Energy Efficiency Energy consumption Evaluate energy efficiency during coloration and bleaching

Table 10. Thermochromic (TMs) and electrochromic (ECMs) materials test methods

Bessinger et al. (2021) Xu et al. (2016) Padilla et al. (2023) Fiksman (1997) (TM) Wu et al. (2023) R. Li et al. (2021) Hassab et al. (2018) Park et al. (2021)

Rai et al. (2020) Jelle and Hägen (1993) Fabretto et al. (2007) Elgrishi et al. (2017) K. Zhou (2020) Pehlivan et al. (2021) Tracy et al. (1999) Ko et al. (2022) Fan et al. (2020) Jensen et al. (2013) Borui et al. (2022) Ye et al. (2018) Chang et al. (2018) (TM) Y. Liu et al. (2023) (TM) Wałęsa-Chorab and Skene (2020) Fu and Hu (2017) Strbac (2022) (TM) Viková and Vik (2023) Ning et al. (2023)

3.6. Electrochromic materials (ECMs) – (SM)

Electrochromic materials change their optical properties in response to an applied electrical voltage quicker than the previous class. To manage solar heat gain and reduce heating or cooling, windows can be controlled by controlling their transparency or reflectivity (Somani, Radhakrishnan, 2003). However, they can contribute to energy efficiency and passenger comfort in cruise ship cabins through the control of natural light and glare (Granqvist et al., 2018). Here's how electrochromic materials can be applied in cruise ship design: •

Smart Windows: cruise ship cabins can incorporate electrochromic windows to control the amount of incoming natural light and reduce glare. They provide passengers with control over their cabin's lighting conditions, allowing them to adjust the opacity of the windows to control visibility from outside the cabin, thus enhancing privacy.

Energy Efficiency: while not a direct insulation material, electrochromic windows can contribute to energy efficiency by reducing the need for artificial lighting and shading in cabins. By optimizing natural light levels, cruise ships can lower their energy consumption for lighting and cooling, resulting in cost savings and reduced environmental impact.

The following tables show the test methods aimed at characterizing TM and EM main properties (Table 10).

3.8. Dynamic insulation systems

They can be designed to mitigate the effects of vibrations and motions experienced by passengers in their cabins. These systems use sensors, actuators, and control algorithms to counteract ship motions caused by waves, engine vibrations, and other factors, thereby enhancing passenger comfort (Fawaier, Bokor, 2022). Here's how active vibration control works in cruise ship cabins: •

Sensors: vibration sensors are strategically placed in the cabin to detect any vibrations and motions. These sensors continuously monitor the cabin's movement in multiple axes, capturing data about the ship's vibrations and oscillations; Control Algorithms: advanced control algorithms process the sensor data in real-time. They calculate the optimal corrective actions needed to counteract the vibrations and motions and maintain a stable and comfortable environment inside the cabin;

Actuators: devices able to generate forces to counteract the detected vibrations and motions. They are typically located beneath the cabin's floor or within the cabin's structure. These actuators can include hydraulic pistons, electromechanical devices, or other mechanisms capable of applying forces in various directions;

Feedback Control: it uses feedback from the sensors to adjust the actuators' output. By applying forces in the opposite direction to the detected vibrations and motions, the system effectively cancels out or dampens the cabin's motions;

Adaptive Control: some advanced systems use adaptive control techniques that continuously adapt to changing ship conditions and passenger preferences. They can optimize their performance based on real-time data and adjust to different sea conditions, cruise speeds, and passenger activities; • User Interface: passengers may have control over the system through a user-friendly interface in the cabin. They can adjust the level of vibration control or turn it off if they prefer a more natural experience. Potential benefits of applicating active vibration control in cruise ship cabins can include: • Improved Comfort: Guests experience less discomfort and motion sickness, especially during rough sea conditions or when the ship is manoeuvring. • Safety and Structural Benefits: These systems can also help protect the structural integrity of the ship by reducing the wear and tear caused by vibrations over time.

4.1. Self-cleaning surfaces

Often referred to as "hydrophobic" surfaces, are designed to repel dirt, water, and other contaminants, making them resistant to staining and facilitating easier cleaning. These can be achieved through the use of various technologies and materials (Liu, Jiang, 2012) like:

Hydrophobic Coatings: designed to repel water, preventing water droplets from adhering to the surface. This not only prevents water spots but also helps to carry away dirt and contaminants as water rolls off (Schmidt et al., 1994);

Photocatalytic Coatings Surfaces: when exposed to light, they can break down organic compounds and pollutants on the surface. This process helps to keep the surface clean by decomposing dirt and organic matter (Yoshida et al., 2016). Furter characterization will be provide in the next paragraph, with a specific focus on their application in HVAC components;

UV light. UV-C LEDs lamps emit ultraviolet light with a wavelength in the range of 254 to 365 nanometres, coinciding with the peak UV absorption of virus RNA (Nunayon et al., 2019). When this latter interacts with the photocatalyst, it triggers a photocatalytic reaction, generating highly reactive oxygen radicals, which break down and oxidize a wide range of indoor air pollutants, including volatile organic compounds (VOCs), bacteria, viruses, and odorous compounds (Zaleska et al., 2010); •

Air-Purifying Paints: these paints contain photocatalytic materials that react as described in the previous topic. Among paints currently available on the market them we can find also Activated Carbon Paints, which can adsorb and trap volatile organic compounds (VOCs) and odours from the air and Mineral-Based paints, which incorporate natural minerals like zeolites, which can neutralize certain pollutants, including ammonia and formaldehyde;

Active Ventilation Systems: smart materials can be integrated into ventilation systems to actively filter and purify incoming air, removing contaminants before they enter the room.

Intelligent Air Quality Sensors: smart sensors that detect pollutants, allergens, and other air quality parameters can trigger ventilation or purification systems for realtime air improvement.

Superhydrophobic Coatings: they go beyond hydrophobic coatings by creating a surface with extreme water-repellent properties. These coatings can cause water droplets to form near-perfect spheres and easily roll off the surface, taking dirt and contaminants with them (Wang et al., 2020);

Self-Cleaning Glass: it is coated with a photocatalytic and hydrophobic layer that breaks down organic matter and allows rainwater to wash away dirt and debris (Chabas et al., 2008);

Electrodynamic Surface Cleaning: some surfaces can be designed to generate an electrostatic charge that repels dust and particles, helping to keep the surface cleaner over time (Deputatova et al., 2018);

Anti-Static Coatings: they can help preventing the arise of static charges able to attract dust and dirt, keeping the surface cleaner for longer (Al-Dahoudi et al., 2001).