Design Working Conditions Research Articles

Joint modeling and dynamic analysis of the microenvironment and life support performance of extravehicular spacesuits

The ability to maintain the microenvironment and life-support systems of an extravehicular spacesuit is an important factor in determining the duration of extravehicular activity (EVA). This paper introduces a joint human-spacesuit microenvironment dynamic model. The paper presents novel simplified human body models and analyzes expendable substances. These models can reasonably predict spacesuit safety performance, correctly respond to changes in loads, and aid in the optimization of the intensity of EVAs. According to the simulations, an 8-h EVA consumes approximately 1 kg of LiOH and 2.7 kg of water under the designed working conditions. Liquid cooling systems are the primary thermal management devices in microenvironments. Activity intensity and liquid cooling system flow rate are two important factors that influence the spacesuit microenvironment and life support material consumption. Activity intensity has a significant impact on LiOH consumption, with a threefold increase in metabolic heat increases LiOH consumption by about 2.5 times. Activity intensity plays an important role in the life-support performance of a spacesuit, and proper scheduling is critical to the efficiency and safety of EVAs. The material consumption model can estimate material consumption during the mission scheduling phase, resulting in efficient and dependable operation of the life support system.

Thermodynamic evaluation of a combined cooling, heating, hydrogen, and power multi-generation system for full-spectrum solar energy utilization

Solar photovoltaic/thermal (PV/T) hybrid systems are considered energy-efficient and eco-friendly. However, conventional PV/T systems generate electricity with high power fluctuations and low-grade thermal energy. In this paper, dry reforming of methane (DRM) is introduced to convert low-grade thermal energy through chemical reaction and enhance the dispatchability of the PV/T system. A combined cooling, heating, hydrogen and power (CCHHP) multi-generation system that integrates the PV/T, DRM and CCHP (combined cooling, heating and power) is proposed to use the full-spectrum solar energy. Energy and exergy analysis under design and variable working conditions are conducted to analyze the system performance. The results reveal that the proposed system can achieve a high energy conversion efficiency of 61.34 % and 18.8 % energy storage ratio at direct normal irradiance (DNI) of 800 W·m−2. In addition, the system can save up to 81.78 % primary energy when compared with the reference system. This study can facilitate the better design and performance evaluation of PV/T hybrid systems.

Dinka Jeričević – the Iron Lady of Croatian Scenic Design

The paper examines the theatrical career and artistic expression of Dinka Jeričević (Vukovar, 26 September 1947), a distinguished Croatian scenic designer and one of the few women in the profession, especially at the time of her formative years, when she also served as the only female technical director in Croatian theatres. Creating over six hundred scenic designs, collaborating with the most prominent Croatian theatrical directors, and working in almost all Croatian theatres, as well as several theatres abroad, as both an in-house and guest designer, Jeričević significantly influenced and personally marked the history of Croatian scenic design over the last fifty years. Furthermore, her long-standing educational work with directors and producers at the Academy of Dramatic Arts in Zagreb and her passionate mentoring of emerging designers in theatre practice contributed greatly both to the education of numerous young theatre professionals and to shaping contemporary Croatian scenic design. Finally, by becoming actively involved in continuous and pertinent efforts of the Croatian Association of Artists of Applied Arts (ULUPUH) to improve the professional and legal status and working conditions of Croatian designers, she actively participated in the social betterment of Croatian scenic design(ers). Even though she is recognized and acknowledged in her professional environment, and presented with numerous prizes and awards, her career in the theatre has never been the subject of any scholarly analysis. The paper therefore attempts to address some of her design principles and contribute to the systematisation, valorisation and contextualisation of her multiple, diverse and outstanding artistic and professional accomplishments in national theatre.

Relationships between leadership style and organizational commitment: The moderating role of the system of work

The article fills a crucial gap in the literature in the area of relationships between leadership style and organizational commitment. In spite of the actuality of the theoretical nature and growing practical importance of the issue, no attempt has been made to examine the relationship in the context of its moderation by the work system in light of the widespread increase in remote working in response to the COVID-19 pandemic and post-Covid digitalization of the working environment by now. As a result, the key purpose of the paper is to investigate the moderating role of the work system in the relationship between leadership style and organizational commitment. The work system is understood as remote or onsite working. The empirical research is based on the survey done for Poland in the year 2022. The obtained primary data were analyzed within the Structural Equation Model (SEM) analytical framework. The main findings prove that transactional leadership has a greater impact on the organizational commitment of remote workers, while transformational leadership has a stronger impact on the organizational commitment of employees who work onsite. Therefore, from the practical perspective, organizations can increase the organizational commitment of their employees by adopting appropriate leadership behaviors by leaders. These behaviors should be adapted to the work system, depending on whether employees work remotely or on-site. Based on these results, organizations can better design working conditions contributing to greater employee commitment, which in turn will translate into organizational performance.

Creep damage and crack propagation behavior of printed circuit heat exchanger manufactured by diffusion welding: from material to structure

The printed circuit heat exchanger (PCHE) is extensively used in several applications due to exceptional compactness and heat transfer efficiency. However, the dominant failure mode of PCHE is creep fracture in its diffusion welding joints. Therefore, an accurate prediction of the creep crack propagation behavior for diffusion welding joints is essential for assessing the life of PCHE. In this paper, based on the research route from material to structure, the creep properties of 316L stainless steel base metal and its diffusion welding joint are firstly measured. On this basis, a constitutive model incorporating a time-hardening term for describing the creep damage is established. Furthermore, the creep damage and service life of the PCHE structure under working conditions (600 °C, 20 MPa) are analyzed, along with the effects of structure factors on the creep crack propagation behavior. The results show that the initial decelerating stage and the steady state stage play a dominate role in the creep curve of the diffusion welding joint, differing from the base metal's creep curve. Besides, the creep rate of the joint is approximately 30 times that of the base metal. The established creep damage constitutive model effectively characterizes the creep crack propagation behavior of diffusion welding joints. The maximum creep strain occurs at the weld metal and continuous operation for 100,000 h can be achieved at the designed working condition (600 °C, 20 MPa). For the purpose of lifetime extension by restraining the creep crack, it is recommended to increase the spacing and fillet radius while reducing the diameter during design process.

Multi-scale modeling and fast inference for thermal environment analysis of air-cooled data center

Both the thermal environment of a data center room and the internal thermal environment of a server are of great concern, but it is extremely difficult to build and solve full-scale computational fluid dynamics (CFD) simulation models from room scale to chip scale. In this paper, a multi-scale simulation method for data centers is proposed to achieve this aim by coupling room-level, rack-level, and server-level models. Simulations of the designed working conditions were carried out. The results showed that aisle containment systems improve the server's thermal environment, resulting in a drop in the maximum temperature of the server from 87.5 °C to 73.1 °C. A multi-scale model of the data center can be used to optimize system operation parameters conveniently and accurately. In this simulation, air conditioning parameters that contribute to energy savings with higher supply air temperatures and lower supply air volumes while guaranteeing safe server operation were determined. Moreover, fast and accurate prediction of chip temperature by radial basis function (RBF) networks has been proven to be feasible.

Experimental and Numerical Study on the Ablation Analysis of a Pintle Injector for GOX/GCH4 Rocket Engines

In the present study, the ablation of a pintle injector on a 500N GOX/GCH4 rocket engine under different working conditions is studied experimentally and numerically. The temperature of the pintle tip and the combustion gas in the head zone was measured in a series of experiments by the thermocouples. Moreover, a three-dimensional model was established to simulate combustion and heat transfer concurrently and analyze the ablation state of the pintle injectors. The obtained results indicate that under a low chamber pressure (pc=0.25 MPa) and an increasing O/F ratio from 0.8 to 2, the tip temperature declines first, and then rises. At the designed working condition (pc=1.05 MPa and O/F = 3.2), the pintle tip suffered serious ablation, and the microstructure analysis indicates that the ablation failure of the stainless steel pintle tip originates from chromium precipitation. This phenomenon is especially more pronounced when the temperature exceeds 1273 K, which makes the structure fragile and vulnerable. This article helps to provide an understanding of the ablation failure of the pintle injectors, and the established model is capable of giving a prediction on the ablation status of the pintle tips consistent with the experiment.

Dökme yük gemisi için Rejeneratif Organik Rankine Çevrimi Sisteminin Dekarbonizasyon Üzerindeki Etkisinin Araştırılması

Shipping has a very important share in world trade. However, it has an inevitable effect on global greenhouse gas emissions. Therefore, there is a great motivation for the reduction of fuel consumption and exhaust emissions. Waste heat recovery systems based on Organic Rankine Cycle (ORC) technology have a significant potential to reduce fuel consumption and exhaust emissions. In this study, the optimization of the regenerative ORC was carried out for a bulk carrier. Multi-objective optimization was performed using a Grey Wolf Optimization algorithm that is a powerful and novel algorithm. Thermo-economic evaluations were carried out by considering the design and off-design working conditions of the ship. In addition, the impact of the optimized ORC system on decarbonization was investigated. The results showed that the annual average Wnet was determined as 372.78 kW. The annual average fuel saving and the annual average CO2 reduction were calculated as 522.83 tfuel/year and 1628.09 tCO2/year, recpectively. The findings indicated that using the RORC system on ships is a promising solution for increasing emission restrictions and environmental concerns.

An Analysis of Energy and Internal Flow Characteristics of Open Inlet Channel Axial Flow Pumping Devices

For the purpose of studying the dynamic and inner flow features of an open inlet channel axial flow pump unit, in the present study, numerical calculations using the SST k-ω turbulence model are applied to an open inlet channel axial flow pumping unit based on the NS equation, and experimental validation is then performed. The experimental output indicates that the designed working conditions are Q = 350 L/s, head H = 5.065 m, efficiency η = 79.56%, and the maximum operating head is H = 9.027 m, which is about 1.78 times that of the design head; further, the pump device can operate in a wide range of working conditions. In addition, the design working conditions are within the range of high-efficiency operating conditions. The calculated values and the experimental comparison are all within a 5.0% margin of error; further, the numerical calculations are reliable. The hydraulic loss of the inlet channel under the design condition Q = 350 L/s is 0.0676 m, which satisfies the relationship of the quadratic function. The uniformity of the impeller inlet velocity is 80.675%, and the weighted average angle of the velocity is 79.223°. The hydraulic loss of the outlet channel under the design condition Q = 350 L/s is 0.3183 m, and the hydraulic loss curve is a parabola with an upward opening. The flow state of the pump device is sensitive to changes in the working conditions; additionally, the flow state is optimal under the design working conditions. In this study, the energy and inner flow features of the open inlet axial flow pumping units are revealed, and the research outcomes can be used as a reference for the design and operation of similar pumping units.

Numerical simulation of hydrodynamic and noise characteristics for a blended-wing-body underwater glider

The present study compares the hydrodynamic and noise characteristics of a second-generation underwater glider, i.e., the blended-wing-body glider, and a traditional Slocum glider, based on large eddy simulation and Ffowcs–Williams and Hawkings equation. Results shows that the blended-wing-body glider has a maximum lift/drag ratio of 15.38, which is significantly higher than that of the traditional glider (5.84 for the Slocum), suggesting that the blended-wing-body glider is lower-energy-cost. In terms of the underwater radiated noise, the maximum noise of both gliders is located in the direction above/below the glider. In the designed working conditions, the maximum sound pressure level of the blended-wing-body glider is found to be 64.78 dB, which is significantly lower than that of the Slocum (91.49 dB). This finding indicates that the blended-wing-body glider is suitable for ocean acoustic observation tasks compared with the traditional glider (a revolving body combined with two wings, such as the Slocum glider), thanks to its excellent low-noise performance.

Numerical analysis of environment-friendly solar aided coal-fired supercritical thermal power plant cycle integrated with dual heat exchangers

The hybrid solar-coal supercritical steam thermal system has been developed in current research work. The proposed system uses a double-tank heat storage system to increase the stability of the solar tower system, and two heat exchangers to transfer heat from molten salt in the solar tower system to steam in a supercritical coal-fired thermal system. TRNSYS software has been used as a platform to build a model of the solar coal-fired hybrid supercritical steam thermal system. Local weather data is imported to simulate the characteristic year’s operation of a hybrid system under design and off-design working conditions. The variation of heat transferred from solar system to supercritical steam thermal system, power generated from supercritical steam thermal system, solar-electrical generation capacity, efficiency and proportion of solar power generation are compared and analyzed. The results show that after the system is integrated, the tower solar steam production mechanism will increase the output power of supercritical steam thermal system and reduce thermal efficiency of the integrated system. When boiler steam flow rate is kept at less than reference flow rate after joining with solar steam flow rate, total steam flow rate exceeds the reference flow rate, while solar steam flow rate increases.

MODELLING AND ANALYSIS OF MECHANICAL PULLER

In this work, a simple, inexpensive, lightweight, low energy consumption mechanical extractor was developed to operate. The puller screw shaft was first designed and followed by the nut and then its collar top. Non-conventional shapes were assumed for the collars and handles. Finite element analysis was used to evaluate the stress in the arm and collar which had complex shapes. Finite element analysis reveals that pullers are less likely to fail under design working conditions. A designed 3 arm mechanical bearing puller was fabricated and used to remove many bearings stuck in the shaft. Attempting to remove a component mounted on a shaft without using the correct type of puller can be frustrating and time consuming. A snug fit, dirt, or corrosion can make the removal process difficult. Trying puller alternatives such as cutting, blow torch, and hammer poses obvious safety risks. There is also a risk of damaging the components of the machine you are trying to repair. Mechanical pullers are a great tool for removing components from different industries. Small types of pullers are widely used by technicians such as small car stores. Larger and higher tonnage models are used in heavy industry. This project, which requires the use of a puller, generally involves the maintenance of rotating equipment. Common components to remove include bearings, gears, wheels, pins, bushings, sleeves, couplers, sprockets and pulleys. Keywords: - Mechanical puller, collar, shaft, linkage arm, Design and analysis.

Experimental study on the thermal comfort and physiological responses of the elderly in unstable environments

In this study, the investigators used comparative experiments in order to study the age differences and the effects of temperature changes on physiological responses. Firstly, This paper analyzed the thermal sensation differences and the trend of changes in the design working conditions in different age groups. The researchers found that the thermal sensation of elderly people was lower than that of young people in the hot environment and higher than that of young people in the cold environment. On this basis, the heart rate changes of the elderly in the dynamic environment and the differences with the young people were studied. The results showed that the heart rate of the elderly and the young people increased with the increase of temperature in the temperature rise condition, but there was no significant difference between the two groups. In the temperature drop condition, the heart rate decreased with the decrease of temperature. Finally, an equation was developed to quantitatively predict heart rate parameters. The equation predicts human heart rate by ambient temperature, and the results show that the least square error of the prediction equation for elderly people is 46, while the average difference between the actual and predicted values is 1.2. Therefore, it is recommended to use the proposed heart rate prediction equation when predicting the healthiness of heart rate in elderly people.

An agent-based dynamic reliability modeling method for multistate systems considering fault propagation: A case study on subsea Christmas trees

The fault propagation of multistate systems (MSSs) with various operational modes is a critical factor affecting the reliability and safety of systems. However, traditional methods have difficulty describing the influence of function transitions and multiple faults of components on fault propagation, and are inapplicable for accurately evaluating the dynamic reliability of MSSs. To solve these issues, an agent-based method is developed to evaluate the dynamic reliability of MSSs. This study proposes a reliability modeling framework that consists of a management agent and several system agents. Combined with different agents, two types of models are established to describe the logical relationships among components. Moreover, Monte Carlo simulation is used to evaluate the dynamic reliability of MSSs, and a visual failure paths analysis method is proposed to inhibit potential risk. The LH4–1 horizontal Christmas tree is used to verify the effectiveness of proposed method. Under the designed working condition, the dynamic reliability curve of system with three operational modes and the visual failure paths including 15-node are obtained. By comparing the influence of failure rates, it is found that the production choke valve, flowlines, tree cap and MEG chemical control valve have a great impact on the system reliability.

Influence of Inlet Angle of Guide Vane on Hydraulic Performance of an Axial Flow Pump Based on CFD

Axial flow pump has been widely used in hydraulic engineering, agriculture engineering, water supply and sewerage works, and shipbuilding industry. In order to improve the hydraulic performance of pump under off-design working conditions, the influence of the inlet segment axial chord and inlet angle adjustment of the guide vane on the pump segment efficiency and flow filed was simulated by using the renormalization group (RNG) k − ε turbulent model based on the Reynolds-averaged Navier–Stokes equations. The results indicate that the inlet segment axial chord and inlet angle adjustment of guide vane have a strong influence on the pump segment efficiency. Considering the support function and hydraulic loss of the guide vane, the inlet segment axial chord is set to 0.25 times the axial chord of guide vane. On the basis of the inlet angle of the guide vane under design conditions, when the inlet segment angle is turned counterclockwise, the pump segment efficiency is improved in the lower flow rate region; moreover, the pump segment efficiency is improved in the larger flow rate region when the inlet segment angle is turned clockwise. As the conditions deviate from the design working conditions, the influence of the guide vane inlet angle on the pump segment efficiency increases. If the inlet segment angle is properly adjusted under off-design working conditions, the flow pattern in the guide vane is improved and the hydraulic loss is decreased, because the inlet segment angle matches with the flow direction of impeller outlet; consequently, the pump segment efficiency is increased.

Numerical study on solar spouted bed reactor for conversion of biomass into hydrogen-rich gas by steam gasification

A solar-powered biomass steam gasification system was developed, in which heat transfer model, flow model and chemical model were constructed to predict the distributions of temperature, pressure, mole fraction of syngas, and solar incident flux. Several key parameters of gasifier were designed to ensure the fluidization stability. Based on the model validation, gasifier performance simulations in the design working conditions were obtained. The effects of the key variable parameters, including the rim angle of the dish collector, steam-to-biomass mass flow ratio, biomass feeding rate and the solar irradiance in the different operation working conditions on the composition of syngas, lower heating value, and efficiencies were investigated. The results reveal that the coupled system implements the best gasification performance in the design conditions which the rim angle, steam-to-biomass mass flow ratio, and biomass feeding rate are set at 60°, 0.4, and 2.5 g/min, while the LHV, carbon conversion, and gasification energy efficiencies are 11.51 MJ/m3, 78.17%, and 93.01%, respectively. The overall energy efficiency considering solar energy is 30.79%.

Comparison the start-up time of the key parameters of aqua-ammonia and water–lithium bromide absorption chiller (AC) under different heat exchanger configurations

The time that an absorption chiller needs to reach the designed working condition is called start-up. During this time, energy is consumed through the system while efficient refrigeration is not available. So, it’s too important to consider the influencing parameters on this period of time so that reduction in energy consumption is achieved. Also, dynamic analysis is used to reduce the startup time and increase system performance in addition to strategic control purposes. Optimizing an absorption cycle during transient operations, such as start up or shut down is very important. The aim of this study is to investigate and compare the effect of employing refrigerant and solution heat exchangers (RHX and SHX) on dynamic performance of both NH3–H2O and H2O–LiBr absorption chillers (ACs). Also, the effect of solution heat exchanger’s efficiency on the start-up time of the key parameters of both ACs is investigated. To diminish the effect of approximate relations on the results, thermodynamic properties of NH3–H2O and H2O–LiBr solutions are extracted from the EES software. By making a link between MATLAB and EES software, a set of differential equations is solved in MATLAB software. The fourth order Runge–Kutta method is employed to solve the differential equations system. This process is continued until convergence criteria are satisfied. The results show that removing SHX from the cycle increases the start-up time of both NH3–H2O and H2O–LiBr AC’s COPs by 11.76% and 45.16% respectively. The start-up time of the COP of H2O–LiBr absorption chiller is highly affected in comparison with the NH3–H2O absorption cycle, by removing SHX or increasing the SHX efficiency. Also, utilizing the RHX does not affect the dynamic response of the key parameters of the both absorption chillers.

Frequency domain analysis of two-phase flow instabilities in a helical tube once through steam generator for HTGR

Two-phase flow instabilities will disturb the control systems and cause mechanical vibrations and failure of components, which should be avoided. Two-phase flow instabilities in a helical tube Once Through Steam Generator (OTSG) for High Temperature Gas-cooled Reactor (HTGR) were investigated. First, a linear frequency domain model of the helical tube OTSG was developed. The convective evaporation process was divided into single phase water region, two-phase flow boiling region and superheated steam region. Incompressible assumptions were adopted in the single phase water and superheated steam regions. Homogeneous flow model was used in the two-phase region. Small perturbation linearization and Laplace transform were performed to analyze the governing equations in the three regions. The corresponding frequency domain transfer functions describing the flow pulsation and pressure drop pulsation of the two-phase flow systems were derived. By solving the Nyquist curve of the transfer function with matlab software, the two-phase flow instabilities and the stable boundary of the evaporation process in helical tubes can be determined. The new model in this paper was verified using previous experimental results. The two-phase flow stability in the helical tube OTSG of High Temperature Gas-cooled Reactor Pebble-bed Module (HTR-PM) was analyzed using the developed frequency domain model at the design power levels. The stability boundary of the two-phase flow and effects of various parameters on flow instabilities were also investigated. Then an accumulator was added to this linear frequency domain model, which was used to study the effect of compressible volume or accumulator on DWO and PDO. Using this model, the effects of throttle valves at different locations on the stability of the system with an accumulator were also studied. The results show that the helical tube OTSG for HTR-PM can operate stably under the designed working conditions with enough margin.

Study on economics of depth peak-shaving for 1000MW ultra supercritical unit

With the increase of the demand for deep peak regulation of power grid, large-capacity units have the advantages of strong peak regulation capacity. 1000MW units have been widely involved in deep peak regulation. In the process of deep peak regulation, the actual working condition of the unit deviates greatly from the designed working condition, and the unit efficiency decreases significantly, making the unit economy deteriorate seriously, especially in the 1000MW grade unit. In this paper, a 1000MW unit depth peak adjustment is experimentally studied and its economic indexes are calculated. Then, by analyzing the test data, the optimization Suggestions for the operation of the unit during the depth peak adjustment are put forward:(1)Improve the opening of the high pressure switch of the unit to reduce throttling loss and improve the unit efficiency; (2)Increase the reheat steam temperature to ensure the stable operation of the reheat steam temperature at 620 °C of the full load section; (3) Keep a circulating pump running at a low speed during deep peak adjustment to reduce power consumption.

Professional stress in miners depending on the education and period of service in mining

Stress is one of the many potential determinants of health. It is not a new phenomenon and it accompanies people from the very beginning of their lives. One special place where many stimuli (stressors) causing stress conditions in humans occur, is the work environment. In the study, a questionnaire was used regarding the professional stress among the employees of one of the coal mines [1]. It comprised of three parts encompassing the following problem areas: the physical properties of the work environment, the social factors of the work environment and stress-inducing factors caused by poor organization of work. In the study of questionnaires filled by the respondents in one of the coal mines, it was found that the stressors are located both in the physical and social environment of work and their occurrence is in relation to the errors in the organization of the plant and managing human resources. The basic step preceding the proper prophylactic activities should be noticing the stress as a problem concerning both the individual employees as well as the entire plant. One should thus identify and eliminate the professional stressors occurring in the mining plant. It is necessary to design working conditions with a limited potential of inducing stress.