This paper presents a method for enabling autonomous navigation of a legged underwater robot designed to perform targeted exploration missions on the seafloor. Unlike traditional underwater vehicles, which rely on thrusters or tracks and often struggle with stability and precise movement on uneven terrain, the proposed system leverages a hybrid locomotion strategy-including walking, jumping, swimming, and sinking gaits-to adapt to diverse and unstructured environments while minimizing disturbance to the seafloor. Experimental results demonstrate that the robot is capable of generating multi-modal trajectories, dynamically choosing between swimming, jumping, descending and walking gaits. Both local and global motion plans are generated to achieve either distance or energy optimal motions around or over seafloor obstacles.

A dynamic mathematical model is developed to study the flexible cryostat for high temperature superconducting (HTS) cable. The physics-based model aims to obtain the optimal internal geometry for minimum total power consumption during the circulation of gaseous cryogenic fluids such as hydrogen and helium used to cool HTS cables. The volume element method (VEM) was used to construct a set of time dependent ordinary differential equations (ODE) for the cable temperature map. The analysis included the cable fluid pressure drop in the channels and spatial temperature distribution in the flow direction. A parametric study was reported to optimize design and operating parameters for minimum total power consumption, combined cable heat leak rate, and pumping power under a constant cable cross sectional area as the constraint. Two-way optimized (2wo) aspect ratios of cryostat are obtained. The dimensionless model is suitable for obtaining the optima agnostic to cooling gas medium and can be used for both hydrogen and helium-cooled HTS cable systems of electric aircraft and ships.

The seafloor is a complex environment and it is challenging to conduct detailed mapping, soil composition sampling, and habitat characterization missions in this benthic region. As a step toward overcoming these challenges, we present a quadruped robot capable of walking on the seafloor and maneuvering via midfluid swimming. SELQIE, the Seafloor Environment Legged Quadruped Intelligent Explorer, is capable of walking underwater at speeds up to 0.2 m/s, swimming at over 0.16 m/s, and transitioning between modes. We also introduce a path planning algorithm that can account for both swimming and walking gaits to efficiently navigate around or over obstacles, and demonstrate the robot executing such a multi-modal trajectory.

The world population is expected to reach 9.8 billion by 2050 according to a report by the United Nations. The global demand for alternative proteins from different sources, such as microalgae, mycoproteins, insects, cell-based, cultured meat, meat substitutes, dairy alternatives, and fungi-based proteins, is projected to reach USD 290 billion by 2035. Due to their similar characteristics, offered at a relatively more affordable cost than animal proteins, alternative plant-based proteins are experiencing significant global demand. In recent years, industrial production of microalgal biomass has received attention due to its rich content of quality proteins, lipids, fatty acids, and pigments, whose products are of commercial interest in the field of food technology and engineering. Microalgae can be grown easily in open and closed systems for biomass and high-value products. Spirulina and Chlorella have the outstanding ability to accumulate protein and have already been used in meat substitutes, food products, feed, nutraceuticals, and pharmaceuticals. Here, we review the current literature, including new insights into the patent landscape about algal protein wholistically for its quality, culture conditions, recovery, and potential applications for food uses, and discuss its potential to find alternative protein sources for global needs.

This paper presents an overview of thermal management solutions that are being investigated for power electronic building blocks and their integration into power corridors, both of which are seen as enablers of flexible and reconfigurable power distribution systems in the next generation Navy ships. Air, liquid, two-phase, and indirect cooling approaches are discussed in the context of specific building block configurations built and designed at CPES (Virginia Tech). The paper concludes with an overview of ongoing efforts towards the design, construction, and testing of technology prototypes.

Bipedal robotic systems open up distinctive opportunities to aid individuals with reduced mobility in daily activities such as walking, rising from a seated position, and engaging in fundamental tasks that involve standing, such as bathing or getting dressed. This paper proposes a real-time framework to perform assisted sit-to-stand maneuvers through collaboration with a legged robot. The study develops a reduced-order model and presents preliminary simulation results, showcasing the realtime performance of the control framework while accomplishing a sit-to-stand maneuver. Additionally, the framework incorporates critical system constraints aimed at preventing robot falls and mitigating the over-extension of joints.

Microalgae biomass products are gaining popularity due to their diverse applications in various sectors. However, the costs associated with media ingredients and cell harvesting pose challenges to the scale-up of microalgae cultivation. This study evaluated the growth and nutrient removal efficiency (RE) of immobilized microalgae Tetradesmus obliquus in sodium alginate beads cultivated in swine manure-based wastewater compared to free cells. The main findings of this research include (i) immobilized cells outperformed free cells, showing approximately 2.3 times higher biomass production, especially at 10% effluent concentration; (ii) enhanced organic carbon removal was observed, with a significant 62% reduction in chemical oxygen demand (383.46-144.84 mg L-1) within 48 h for immobilized cells compared to 6% in free culture; (iii) both immobilized and free cells exhibited efficient removal of total nitrogen and total phosphorus, with high REs exceeding 99% for phosphorus. In addition, microscopic analysis confirmed successful cell dispersion within the alginate beads, ensuring efficient light and substrate transfer. Overall, the results highlight the potential of immobilization techniques and alternative media, such as biodigested swine manure, to enhance microalgal growth and nutrient RE, offering promising prospects for sustainable wastewater treatment processes.

This work uses an experimentally validated mathematical model to maximize alkaline membrane fuel cell (AMFC) stacks net power output. Temperature distribution, efficiency, polarization, and power output curves are obtained. Fundamental optimization opportunities exist for the internal and external structure, which led to a two-way optimized AMFC stack for maximized net power. After system optimization, a parametric analysis was carried out for electrolyte KOH mass fraction, stoichiometric ratios and total fuel cell stack size (volume). KOH content was shown to lead to a third optimum, i.e., 40 wt %. The three-way optimized AMFC stack (xi(s) = 1.37 x 10(-3), y = 40 wt% KOH)(opt) was shown to be independent of the stoichiometric ratio and stack size variation, but (xi(y)/xi(x )= xi(z)/xi(x))opt was affected by total stack volume (or size). In fact, it was found that the three-way maximized dimensionless AMFC stack net power output rises as the stack volume rises in a path that is well correlated by W(net,mmm )x 10(-3) = 36.266V(T)(0.74), which is similar to the allometric law of nature that correlates basal metabolic rate (BMR, W) and body mass (m(b),kg) for living beings, i.e., BMR similar to m(b)(0.74), that could be understood as an indication that inanimate and animate systems follow the same evolution laws.(c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

The International Maritime Organization has expressed its concern about the pollution caused by ships by putting in place regulations to decrease greenhouse gas emissions. As a result, ships must evermore be fi tted with efficient and environmentally friendly engines, and one of the most essential selection parameters to consider is the specific fuel consumption. This parameter can be obtained by means of simulation models with various levels of sophistication, which can be either coded in basic programming languages or run in dedicated packages. The aim of the present study is to conceive a facilitated model to calculate the specific fuel consumption of low-speed dual-fuel engines with low-pressure gas injection driving either fi xed or controllable pitch propellers. Clear specific fuel consumption trends were revealed when a normalization process was employed and then polynomials were obtained by numerical regression. This model requires very limited input data to predict the specific fuel consumption of an engine at any contractual maximum continuous rating, including part load operation. Results showed very close qualitative behavior and the highest deviations occurred for the brake-specific pilot consumption, peaking at about 5%. At last, the developed approach was concluded to be an easy-to-implement and fast-to-run model with promising usage for optimization studies.

This paper introduces a first and second law based transient mathematical model for 4-stroke compression ignition internal combustion engines (CI-ICE) driven by diesel/biodiesel/biogas mixtures to allow for the maximization of system performance. In this way, the CI-ICE morphology that provides easier access to the currents that flow through it is sought, according to constructal law. The total entropy generated in the CI-ICE cycle was calculated by adding the entropy generation in all strokes. An optimization problem was formulated based on the variation of operating and geometric parameters, and the objective functions were the effective and 2nd law efficiencies, n ef and nII, II , as well as the destroyed exergy fraction, y D . The optimal ranges found for the bore-stroke, compression and conrod-crank ratios were 0.51 <= B opt <= 1.25; 2.07 <= ( ROD / CS ) opt <= 4.14, and 10.23 <= CR opt <= 33.44 in which ( nef, ef , nII) II ) max c (0.33, 0.37) with y D , min c 0.66 for D100 (pure diesel), and ( nef, ef , nII) II ) max c (0.31, 0.35) with y D , min c 0.64 for B50D25NG25 (biodiesel/diesel/natural gas blend). The maxima and minimum found were sharp, since n ef and n II varied up to 71% and 69% in comparison to their maximum values, respectively, and yD D up to 45% in comparison to its minimum value within the adopted ranges of variation of the optimized parameters. Such large variations stress the importance of considering the optimized CI- ICE morphology in actual design, i.e., CI-ICE constructal design.

This paper presents design, modeling, and simulation considerations for an underwater glider. The design section covers strategies for buoyancy control, packaging of electronics, and placement and integration of energy harvesting systems. The modeling efforts covers the glider dynamics and the energy harvesting, which relies on use of solar energy, phase changing materials, and thermoelectric units. The dynamics and energy harvesting models are integrated to a motion planning algorithm that uses a Sampling-Based Model Predictive Optimization approach to plan glider's trajectories that satisfy imposed constraints and generate optimal trajectories. The power requirements for the missions considered are within the power generation range of the thermoelectric units.

This paper introduces a mathematical model for the design and fundamental optimization of steam Rankine cycle (SRC) power plants. The model assumes that the plant irreversibilities are predominant in the heat exchangers, thus exergy destruction in the turbine, pump, fittings, tubes and other internal components are neglected. The NTU-effectiveness method was utilized to model the heat exchangers, and water was considered as the working fluid, which changes phase in both heat exchangers. Acknowledging that entropy is generated in any physical system, the fundamental optimization problem selected the dimensionless net power output, and second law efficiency as the objective functions to be maximized, after the identification of plant geometric and operating parameters to be optimized based on the intersection of asymptotes method, subject to a fixed total heat exchangers area realistic physical constraint, i.e., for a finite size plant. As a result, two levels of optimization were identified: i) the working fluid to hot stream mass flow rate ratio, M, and ii) the steam generator, xH, and condenser, xL, area fractions of the plant fixed total heat exchangers area. The model was experimentally validated for a heat recovery driven power plant. Sharp maxima were obtained in both levels, which is illustrated with a base case by - 60 % second law efficiency variation in comparison to the obtained maximum for 0.05 < M < 0.25 in the first optimization level, and - 30 % for 0.2 < xH < 0.7 in the second optimization level, so that (xf,H, xfg,H, xg,H)2wo = (0.14, 0.13, 0.23), with (M, xH)2wo = (0.16, 0.5), in the base case considered in this study. The two-way optima results sensitivity to several plant geometric and operating parameters were thoroughly investigated. The optimized parameters are shown to be robust with respect to several system's design and operating conditions. Therefore, the herein reported fundamental optimization results are important for whatever actual SRC power plant.

The advancement towards all-electric transportation brings increasing demands for high power density motor drive. In this paper, a high power density SiC motor drive is proposed for a 6-phase PMSM machine. In order to achieve both the high efficiency and high power density, an electrical-thermal co-design is implemented to balance the system level trade-offs and achieve the design targets. A 6-pack 1.7 kV SiC module is selected and a compact cold plate is optimized based on the co-design method. Finite element method (FEM) simulations of the fluid and thermal domains are used to determine the efficacy of the design before performing experiments on it.

Thermoelectric materials hold tremendous promise for advances in fundamental science and practical applications, particularly for robust electricity generation in extreme and remote environments. Despite this, for most materials the energy conversion efficiency is limited by the proportionality between the electrical and thermal conductivities and small values of the Seebeck coefficient for metals. It was previously reported that the heavy-fermion compound YbIr2Zn20 exhibits large Seebeck coefficient [E. Mun et al., Phys. Rev. B 86, 115110 (2012)] and thermoelectric figure of merit ZT at 35 K [K. Wei et al., Sci. Adv. 5, eaaw6183 (2019)]. This behavior is primarily associated with strong hybridization between the f- and conduction electron states. Here, we seek to improve the thermoelectric properties through chemical substitution on the Yb site using Ce and Sm. By surveying different levels of substitution, we find that the thermoelectric properties vary strongly with the f-element ratio. This confirms that electronic hybridization dominates the thermoelectric properties and clarifies directions for optimizing these materials for applications. We also investigate the impact of the disorder on the thermal conductivity, where we find only weak variation with lanthanide content.

This study investigates the possibility of hydrogen production from microalgae depending on temperature, and cultivation medium microalgae, oxygen and carbon dioxide concentrations in compact photobioreactors (PBR). A mathematical model generated a system of time dependent ordinary differential equations (ODE) to predict hydrogen generation in the indirect biophotolysis process originating from microalgae cultivation in tubular compact PBR. The indirect biophotolysis consists of two stages: i) aerobic (microalgae growth with air supply) and ii) anaerobic (consumption of microalgae biomass with hydrogen generation without air supply). A Michaelis-Menten type expression was used to model the rate of H2 generation considering that oxygen and sulfur could inhibit the process. The model was adjusted and experimentally validated against measured H2 production from green microalgae. The maximum rate of hydrogen production from local wild microalgae Tetradesmus obliquus was 6.8 x 10-7 kgH2 kg-med1 d-1. The thermodynamic optimization of the system determined that the optimum time of the anaerobic stage was 11 days and 13 h. The herein obtained results demonstrated that it is reasonable to state that a fundamental anaerobic stage optimum time for maximum large-scale H2 production should be expected in any indirect H2 biophotolysis process, no matter the complexity of the actual system.

Mission endurance is a critical factor for mobile robots deployed for space exploration purposes and other challenging missions in remote locations. The mission endurance is highly correlated with thermoregulation, and exposure to solar radiation which affects both the robot integrity and its access to power. There is an increased interest in developing temperature aware motion planning strategies due to efforts from governments and private companies to expand exploration of the moon and other celestial bodies. One key step to achieve thermally informed motion planning is the development of time varying thermal maps that can be used by both robots and human teammates that collaborate on the exploration missions. This paper develops an approach to produce thermal maps that are dependent on the incidence direction of solar rays and terrain surface geometry. The paper also discusses integration of the generated maps with motion planners that consider thermal information.

In face of the current high energy consumption and demand worldwide, a change to a sustainable energy matrix became one of the pillars for global sustainability. The use of renewable energy has been one of the most attractive subjects in recent years. Several public policies in this matter have been suggested and there are ongoing efforts toward their implementation. The United Nations (UN) proposed what is called the 2030 Agenda, which considers 17 Sustainable Development Goals (SDG) to be achieved by the year 2030. In support of the 2030 Agenda, research on the production of fuels from clean and sustainable sources is being conducted by the scientific community around the world. Fossil fuels are finite and also a major source of environmental pollutants, therefore the choice of using renewable sources of energy tends to be an increasingly growing and attractive alternative. Hydrogen is a fuel with a high heating value and is known as the most abundant gaseous element and simplest in chemical structure. The scientific community researching fuel cells has given much attention to the generation and storage of hydrogen. Besides the electrolytic hydrogen production and the reforming of fossil fuels (e.g., natural gas), hydrogen can be generated by metallic means, for example, by oxidation of aluminum in an alkaline solution. The use of recyclable metals, such as aluminum in this study, is an option for sustainable hydrogen generation processes. Nevertheless, like any chemical reaction, part of the products generated are waste, and some are even harmful to the environment, which makes the production of sustainable fuels unfeasible in case of not finding an appropriate technological industrial destination for such waste. The herein study comprises the investigation of the industrial and technological applications of the products of the hydrogen generation reaction from aluminum. Mastering the chemical reaction parameters of that reaction is paramount for the optimal design of a hydrogen generation system. The disposal of the waste is relevant since it makes the energy supply chain complete and sustainable.

The increase in human population results in high demand for clean and potable water and large municipal solid waste (MSW) generation. At the same time, a global scenario of freshwater shortage is expected. This paper presents an exergetic analysis and optimization of an integrated MSW incineration and wastewater treatment plant, in which thermal energy generated by incinerating MSW is recovered for wastewater treatment. The methodology consists of assessing the viability of the system through an exergetic analysis. The system is divided into three modules: (i) incinerator, (ii) heat exchanger, and (iii) microalgae-based photosynthetically driven emissions filter. A mathematical model is presented for steady-state operation based on the conservation laws and the second-law of thermodynamics. The system's exergetic efficiency is optimized for operating parameters (e.g., incineration rate and air-fuel ratio). The integrated plant enables heat recovery for steam generation and provides microalgae bioproduct that can be processed for high-value products (e.g., animal feed, nutraceuticals, pharmaceuticals).

Algae are ubiquitous organisms whose capabilities have drawn much attention as of late in the bioengineering field due to their potential to enable a wide range of bioproducts. Microalgae are ideal organisms for the application of the biorefinery concept since they can be grown in wastewater and, at the same time, produce many products of commercial interest. These microorganisms are also known for their resilience to extreme environmental conditions and suitable cell growth rates. Beyond the known potential for biofuel production, these microorganisms can still produce other compounds, being lipids, pigments, vitamins, proteins, and polysaccharides, whose applications go from pharmaceutical to agricultural industries. Recently, the research focus has been directed to the biopolymer-producing ability of both micro- and macroalgae, as they can be rather varied and useful to many applications. However, this is still an ongoing research field, and new data are frequently added in the literature, notably on biomass processing, which can be done with the intent of use into dyes, bioplastics, paints, and even as biochar in solid fuel cells. Microalgae-based biopolymers can be used in a wide range of products, nevertheless, the resulting process efficiency and yields depend on the extraction process utilized, as well as on the microalgae species used and the culture conditions. Furthermore, the polymer extraction can be done directly with common solvents at atmospheric pressure or with other fluids, such as supercritical CO2 or subcritical solvents, and assisted by specific treatments, e.g., ultrasound and microwave. The residual biomass can still be used to produce other less valuable products, such as feedstock, and energy via combustion. In this sense, the present work aims to provide a state-of-the-art review on microalgae biopolymers. Issues related to the efficiency of current treatment methods, industrial applications, and environmental performance are presented and discussed. Besides, the perspectives in this area of knowledge are also a contribution of the present work, the extent to which scientific research is still under development.