Standby Period Research Articles

Experimental study on mooring system of tunnel element subjected to current loading during the standby period before its immersion

ABSTRACT The safety of mooring system during the standby period is important for the follow-up immersion of tunnel elements. In this study, performance of a typical four-point mooring system, subjected to the current loading alone, was experimentally investigated. The latter is characterised by different direction, tidal elevation, and velocity, reaching the magnitude up to 2.5 m / s . The experimental results of motions of the tunnel element and tensions of the mooring lines were presented, based on which the safety of the mooring system and its correlation with the motions of the tunnel element are discussed. The results indicate that the magnitude of both the tensions of the mooring lines and the motions of the tunnel element increase with increasing current velocity, which is particular visible after reaching the 1.5 m / s -threshold. Whereas their relative values are governed by the current direction. The current loading is mainly carried by the mooring lines on the front side of the incoming current, among which the auxiliary lines generally governs the safety status of the mooring system. In this study, the maximum allowable current velocity can reach 1.5 m / s at the low tidal elevation of 12.016 m , where the safety factor of the mooring system keeps no smaller than 1.0, irrespective of the current direction. However, the maximum current speed is limited to 1.0 m / s at the high tidal elevation of 20.084 m . This maxima can be increased by strengthening the auxiliary mooring lines, in order to prolong the time window for construction of the immersed tunnel.

Numerical and experimental analysis of instability in high temperature packed-bed rock thermal energy storage systems

Due to heat losses of preferential areas of packed-bed energy storage systems, transverse temperature variations may occur during the charging, discharging and standby processes. Furthermore, the heat losses of preferential areas of the storage tank cause a lower pressure drop in these areas resulting in an increased mass flow rate and further cooling, and thereby an enhanced transverse temperature variation, in a positive feedback loop – a phenomenon called instability. The transverse temperature variations may deteriorate the performance and thereby the economic feasibility of packed-bed energy storage systems. In this paper, numerical and experimental investigations of an air-based packed-bed rock thermal energy storage system for large-scale high temperature applications are presented. The objective of the study is to predict the instability and to analyze the effect of different standby durations and storage size on the instability of the air-based packed-bed system. Transient axisymmetric computational fluid dynamics models were developed for the standby and discharging processes of the packed-bed thermal energy storage systems. In addition, experimental investigations were carried out at a test facility located at Stiesdal Storage, Denmark, using magnetite rocks as heat storage material and air as heat transfer fluid. The results suggest that the numerical predictions are in good agreement with the test data. The instability phenomenon is found to increase with the standby duration, resulting in a maximum difference of 161 K between the maximum rock temperature and the outlet air temperature for a standby period of 10 h followed by a discharging process. Moreover, the results indicate that the maximum difference between the rock temperature and outlet temperature is 73 K and 56 K for a reduced-scale and a full-scale system (no standby period), respectively.

Compact, efficient, and affordable absorption Carnot battery for long-term renewable energy storage

The growing penetration of renewable energy poses significant challenges to the stability of the power grid, necessitating the development of advanced energy storage systems to facilitate power grid decarbonization with enhanced flexibility. Nonetheless, current energy storage technologies face obstacles including geographical constraints, high expenses, and short lifespans. In this work, a novel Carnot battery (power-heat-power conversion) based on absorption-desorption processes of hygroscopic salt solutions, absorption Carnot battery (ACB), is proposed for large-scale renewable energy storage with remarkable energy storage density (ESD), competitive round-trip efficiency (RTE), and negligible self-discharging rate (SDR). Through the integration of heat-generation, heat-storage, and power-generation sub-cycles into a single compact system, the ACB can save space and cost compared to previous Carnot batteries. A dynamic model is established with high accuracies to explore the characteristics of the proposed system. The dynamic temperatures, pressures, concentrations, mass flow rates, powers, and efficiencies of the ACB are analyzed to elucidate its energy conversion/storage mechanism. Based on the multi-objective optimization, the optimum operating concentration range of [45%, 60%] is determined, demonstrating the best comprehensive performance with an RTE of 45.80% and an ESD of 16.26 kWh/m3. Compared to the existing energy storage systems, the ACB stands out due to the competitive RTEs (30.5%–48.4%) and higher ESDs (7.6–21.8 kWh/m3). Even during an 80-day standby period, the ACB exhibits a small SDR of only 0.74%, which is significantly lower than that of Rankine pumped thermal energy storage (RPTES) at 33.01%. Despite the ACB yields a higher initial cost, it demonstrates a markedly lower levelized cost of storage (0.342 $/kWh) compared to the RPTES (0.749 $/kWh) because of its higher ESD, thus confirming the economic feasibility of the proposed system.

Research on Green Vehicle Path Planning of AGVs with Simultaneous Pickup and Delivery in Intelligent Workshop

In this study, we present and discuss a variant of the classic vehicle routing problem (VRP), the green automated guided vehicle (AGV) routing problem, which involves simultaneous pickup and delivery with time windows (GVRPSPDTW) in an intelligent workshop. The research object is AGV energy consumption. First, we conduct a comprehensive analysis of the mechanical forces present during AGV transportation and evaluate the overall operational efficiency of the workshop. Then, we construct a green vehicle path planning model to minimize the energy consumption during AGV transportation and the standby period. Hence, the problems considered in this study are modeled based on asymmetry, making the problem solving more complex. We also design a hybrid differential evolution algorithm based on large neighborhood search (DE-LNS) to increase the local search ability of the algorithm. To enhance the optimal quality of solutions, we design an adaptive scaling factor and use the squirrel migration operator to optimize the population. Last, extensive computational experiments, which are generated from the VRPSPDTW instances set and a real case of an intelligent workshop, are designed to evaluate and demonstrate the efficiency and effectiveness of the proposed model and algorithm. The experimental results show that DE-LNS yields competitive results, compared to advanced heuristic algorithms. The effectiveness and applicability of the proposed algorithm are verified. Additionally, the proposed model demonstrates significant energy-saving potential in workshop logistics. It can optimize energy consumption by 15.3% compared with the traditional VRPSPDTW model. Consequently, the model proposed in this research carries substantial implications for minimizing total energy consumption costs and exhibits promising prospects for real-world application in intelligent workshops.

Defining working time versus rest time: An analysis of the recent CJEU case law on stand-by time

The article explores the evolution of the CJEU jurisprudence following on from the Matzak case. It provides an analysis of the most recent judgments on stand-by time, including those in case C-344/19 Radiotelevizija Slovenija, case C-580/19 Stadt Offenbach am Main, case C-107/19 Dopravní podnik hl. m. Prahy, and case C-214/20 Dublin City Council. The disputes concerned workers on stand-by duty who were not required to be physically present at the location expressly designated by the employer, but were expected to resume work within a short or very short period of time if necessary. In order to classify stand-by periods as working time or rest periods under the Directive 2003/88, the CJEU analyses whether the constraints imposed on the worker are such as to affect, objectively and very significantly, the possibility for the latter freely to manage the time during which his or her professional services are not required and to pursue his or her own interests. Moreover, the CJEU requires that employers cannot establish periods of stand-by time that are so long or so frequent that they constitute a risk to the safety or health of workers, irrespective of those periods being classified as rest periods. In the author's opinion, the required response time is a decisive and most important factor in the assessment. If the reaction period is very short, then in principle the stand-by time constitutes working time. Where the situation is not prima facie clear, additional secondary criteria should be taken into account. The factors that fall within the scope of an employer's managerial competences and pertain to an organisation's operational needs, and also the type of work performed by the worker, are relevant in assessing the legal characterisation of a particular stand-by period. The evaluation should not be affected by factors that remain beyond employer's control, e.g., the location of the workplace, the worker's residence, and distance between them.

Designing and producing a bird-inspired unmanned sailplane

PurposeIncreasing endurance was a very appropriate subject for the biomimetic approach. The study aims to design and manufacture a long-lasting mini unmanned aerial vehicle (UAV) using active gliding and soaring.Design/methodology/approachThe endurance of mini UAVs is limited by battery or fuel capacity, and it is not always possible to increase these energy sources due to the fuselage size. Long endurance aircraft are required in various areas such as silent environment and traffic monitoring or search and rescue. Literature research on bird flight performance conducted to determine design parameters. These parameters are used in the theoretical design of the UAV for optimization. Computational fluid dynamics simulation and flight tests of the UAV performed to figure out the success of the design.FindingsFor a mini UAV to be produced in this class, it has been observed that it is more accurate to examine birds instead of gliders due to the size similarity. The UAV design reaches a 27.5 L/D (Glide ratio) ratio in the theoretical approach. However, flight results approved max L/D ratio is around 25 at the sea level. This flight performance is enough to outperform in glide ratio of Wandering albatrosses.Practical implicationsSailplanes are known as sport aircraft. However, recent projects focus on glider designs due to fuel efficiency and silent tracking. Stemme S-14 that carries a high-resolution camera is one of the examples of these projects. The unmanned glider design can lead to these implications in the UAVs at least during the stand-by period in the air. Thanks to low weight, UAVs do not require strong thermals, which allows flying almost all over the world.Originality/valueResearchers generally focus on increasing the battery capacity or the performance of the UAV. However, this study’s concentration is to increase the flight duration of the UAV by using geographical currents. For this purpose, taking advantage of bird morphology is quite a new topic. Also, glider type designs are rarely found in the field.

A Study on The Safety Measures Against Fire Through An ESS Fire Analysis

Due to the increase in the frequency of fires due to the mass distribution of energy storage devices, following the introduction and operation of eco-friendly power generation facilities around the world, there is an urgent need to analyze the causes of such fires and to devise countermeasures against them. By analyzing the occurrence of ESS fires and reviewing the definition of ESS terminology, we intend to suggest some safety measures against ESS fires by understanding the related facilities and analyzing the causes. We would also like to propose new measures to prevent the spread of ESS fires. ESS fires occur most frequently during the discharge standby period after charging is completed in connected solar and wind power facilities. In addition, when we investigated the problems with the batteries, PCS manufacturing, ESS design, installation and construction, and the factors related to their usage and operation, we found such causes of fire as battery system defects, unsatisfactory protection systems against electrical shock, improper operations and environmental management, careless installations, and a lack of ESS integrated management systems. Therefore, a new approach is needed through the application of new technologies and safety measures including manufacturing standards, installation standards, operation and management standards, and firefighting standards for the purpose of ensuring the safety of these facilities and their operations, in order to prevent ESS fire accidents and the spread of fire.

A Single-Inductor–Multiple-Output (SIMO) 0.8-V/1.8-V/12-V Step-Up/Down Converter With Low-Quiescent Current for Implantable Electroceutical SoCs

This letter presents a single-inductor multiple-output (SIMO) step-up/down DC-DC converter for an implantable electro-ceutical system-on-chip (SoC), which generates the supply voltages of 0.8 V, 1.8 V, and 12 V from a battery (3 -4.2 V). To extend the battery life-time during a long standby period, the load-adaptive frequency-scaling (LAFS) without an active load sensor is proposed, effectively reducing the quiescent current under light loads at no expense of tran-sient response performance. Also, this paper introduces a new design of a low-power adaptive on-time (AOT) generator to achieve a consist-ently low output ripple regardless of battery voltage variation. The proposed chip fabricated in 0.18-mum BCD consumes a quiescent cur-rent of only 217 nA and offers the output recovery time of ≤ 1 ms at a zero-to-full load transition. The measured efficiency was 86% with a load of 500 muA and 55% even with an ultra-light load of 1 muA.

Effect of the co-treatment of synthetic faecal sludge and wastewater in an aerobic granular sludge system

The co-treatment of two synthetic faecal sludges (FS-1 and FS-2) with municipal synthetic wastewater (WW) was evaluated in an aerobic granular sludge (AGS) reactor. After characterisation, FS-1 showed the following concentrations, representative for medium-strength FS: 12,180 mg TSS L−1, 24,300 mg total COD L−1, 93.8 mg PO3-P L−1, and 325 mg NH4-N L−1. The NO3-N concentration was relatively high (300 mg L−1). For FS-2, the main difference with FS-1 was a lower nitrate concentration (18 mg L−1). The recipes were added consecutively, together with the WW, to an AGS reactor. In the case of FS-1, the system was fed with 7.2 kg total COD m−3d−1 and 0.5 kg Nitrogen m−3d−1. Undesired denitrification occurred during feeding and settling resulting in floating sludge and wash-out. In the case of FS-2, the system was fed with 8.0 kg total COD m−3d−1 and 0.3 kg Nitrogen m−3d−1. The lower NO3-N concentration in FS-2 resulted in less floating sludge, a more stabilised granular bed and better effluent concentrations. To enhance the hydrolysis of the slowly biodegradable particulates from the synthetic FS, an anaerobic stand-by period was added and the aeration period was increased. Overall, when compared to a control AGS reactor, a lower COD consumption (from 87 to 35 mg g−1 VSS h−1), P-uptake rates (from 6.0 to 2.0 mg P g VSS−1 h−1) and NH4-N removal (from 2.5 to 1.4 mg NH4-N g VSS−1 h−1) were registered after introducing the synthetic FS. Approximately 40% of the granular bed became flocculent at the end of the study, and a reduction of the granular size accompanied by higher solids accumulation in the reactor was observed. A considerable protozoa Vorticella spp. bloom attached to the granules and the accumulated particles occurred; potentially contributing to the removal of the suspended solids which were part of the FS recipe.

Mission Reliability Modeling and Prediction of an Automatic Sprinkler System

If the sprinkler system cannot be started at the time of need, it may cause huge economic losses. The system needs to have high reliability. Therefore, in the design stage of sprinkler system, it is necessary to carry out reliability modeling and prediction to ensure that the system reliability can meet the requirements. In this paper, the design scheme of a building sprinkler system is analyzed in depth, and then a task reliability model considering maintenance strategy, stand-by period failure and task period failure is established, and the reliability is predicted to evaluate whether the design scheme of the system can meet the design needs.

A case of lymphangioleiomyomatosis with maintained muscle strength by rehabilitation during lung transplantation standby period

A case of lymphangioleiomyomatosis with maintained muscle strength by rehabilitation during lung transplantation standby period

Influence of the storage period between charge and discharge in a latent heat thermal energy storage system working under partial load operating conditions

The supply intermittency of energy sources like solar energy or industrial waste heat should be properly addressed when studying latent heat thermal energy storage (TES) systems, since it might cause an incomplete melting/solidification of phase change materials (PCM). In the present paper, and experimental study was performed to analyse the storage period (also known as stand-by period) in a latent heat TES system working under partial load operating conditions and the effect of its duration on the subsequent discharging process. In the experimental set-up, 99.5 kg of high density polyethylene (HDPE) was used as PCM in a 0.154 m3 storage tank based on the shell-and-tube heat exchanger concept. Four different percentages of charge were evaluated: 58%, 73%, 83% (partial charge), and 97% (full charge). Each charging level was followed by three different periods of storage: 25 min, 60 min, and 120 min. The fact of working at different levels of charge caused that in some regions of the TES system the PCM was not completely melted. Thus, at the end of the charging process different levels of thermal homogenisation were observed. However, during the storage period, the PCM temperature showed a tendency to homogenisation, which was influenced by the energy distribution within the PCM, the heat losses, and the duration of the storage period. Focusing on the discharging period, it was observed that the duration of the storage period slightly affected the temperature and heat transfer profiles, causing the main differences of performance during the first 30 min of process.

Energy-saving management of steam sterilizers in hospital′s sterilization and supply center

Objective To reduce the energy consumption and cost of steam sterilizers at sterile supply centers. Methods Routine data of the steam sterilizers from January to June of 2016 were collected from one hospital in Changchun. Usage by timeframe of these sterilizers was analyzed, including their performance when they are powered on, standby (idle), and powered off and their energy expenditure at such states. Sustainable and stepwise energy saving strategy was developed, with the reduction of standby (idle) period and energy saving amount of energy and cost. Results Usage of sterilizers was found with obvious peak and valley hours, while their standby hours during the latter were long and in a few timeframes. After implementation of the energy saving management strategy, their standby hours at various timeframes averaged ≤3 h (P<0.001). For six months, we reduced 5 818 hours of standby time, 97 tons of steam, 2 910 kW·h of electricity, saving cost over 30 000 yuan (17%). Conclusions The energy-saving management strategy could reduce the consumption of energy and cost effectively. Key words: Sterile supply center; Steam sterilizer; Energy saving management; Stepwise

Acute Kidney Injury in Elderly Population: A Prospective Observational Study

Background/Aims: Acute kidney injury (AKI) has been reported as a recognized condition among the elderly population; however, its clinical epidemiology is still poorly evaluated. We propose to evaluate the epidemiological profile of AKI in hospitalized elderly patients and the variables associated with renal replacement therapy (RRT) dependency at discharge after an episode of AKI. Methods: This prospective observational study enrolled 286 elderly patients (aged ≥60 years), who had a diagnosis of AKI and were admitted to a tertiary care hospital. Clinical data were analyzed, which included RRT indication, referral time to nephrologist support, standby period in the emergency care units (ECU) before a transfer to an intensive care unit, staff criteria used to indicate palliative care, and the incidence of patients who stayed on chronic dialysis for at least 6 months after discharge. Results: The overall hospital mortality was 56.3%. Acute Kidney Injury Network (AKIN) 3 at the time of admission was significantly higher in patients who underwent RRT. Intrinsic AKI (p < 0.001), AKIN 3 (p < 0.001), RRT (p < 0.001), and increased length of stay in ECUs (p = 0.01) all had a significantly higher prevalence among non-survivors. On multivariate analysis, however, only renal aetiology (intrinsic AKI) was independently associated with mortality (OR 2.88; 95% CI [1.29–6.13]). Approximately 85% of the discharged patients (n = 125) were dialysis free and 36.4% of them who had a previous diagnosis of chronic kidney disease (CKD) upon admission had a worse renal function. Age, AKIN 3, RRT, prior history of CKD, diabetes mellitus, and the number of hemodialysis sessions showed to have an impact on dialysis dependence. Furthermore, 24 of 161 patients who had a dialysis indication were placed on palliative care. Conclusions: The severity of AKI and the need for RRT were risk factors for mortality and dependence on dialysis. Antecedents of CKD seem to be associated with a poor renal outcome following an AKI episode. Starting RRT had an impact on the clinical decision to enroll these patients into palliative care.

Material and energy loss due to human and machine error in commercial FDM printers

Additive manufacturing is thought to have environmental benefits. However, material waste and energy consumption could be larger than expected due to human or printer error. In general, fused deposition modeling (FDM) printers using ABS plastic have three stages for parts fabrication: the standby period, preheating process and the printing process. In practice, the quantity of support material is influenced by the part orientation and settings of the printing. Material waste and energy consumption for commercial FDM printers using ABS material in a heavily utilized open shop were analyzed. The failed prints were classified into 9 different categories and analyzed. The data indicated that about 34% of the plastic used in the open studio was wasted. Only considering the failed prints as the extra amount of material consumed under realistic conditions, the mass of material lost to failed builds was about 2.22 times what might be estimated in a controlled process study. For energy consumption, the standby period and preheating time vary for every job, which results in variability of energy consumption. The printing time is based on the geometry of parts being built, the part printing orientation and setting of that print. From collected data, the preheating energy consumption is 0.835 MJ/kg, the printing is 21.5 MJ/kg, and the standby is 9.5 MJ/kg. Moreover, suggestions to reduce the building cost for each failure type are given. A life cycle inventory (LCI) combining the material waste and energy consumption data of FDM reveals that actual energy consumption may be 50% more than under ideal conditions.

誘導加熱を用いたウエルドボンド工法の基礎的研究

The weld-bonding method uses adhesion and spot welding it has the advantages of high fatigue resistance, high rigidity, no need of a jig for adhesion, and so on. However, the conventional adhesive is an epoxy resin, which is cured by a chemical reaction. Therefore, the adhesive needs a long curing time. In an automobile assembly factory, the adhesive is cured by drying during the body painting process. The standby period before the drying process influences the quality of the adhesive. To solve this problem, we propose a new method that uses an epoxy resin with a thermal agent added and induction heating (IH) for quick curing. We obtained the fundamental data of IH coil heating steels for practical application of the new method. Based on the experimental and analytical results, suitable conditions regarding the frequency and IH coil position for automobile steel models were selected. Finally, we determined a semi-cured heating temperature for the adhesive of more than 120°C and IH coil movement of 10cm/s for practical application.

In situ restoring of aged thermally rearranged gas separation membranes

Physical aging in high free-volume polymer membranes is one of the main hurdles limiting their application in gas separation. The recovery of membrane separation properties without the need to disassemble the module, although challenging, would provide significant advantages for applications in various fields. In this work, an in situ restoring procedure for the recovery of mass transport in aged membrane modules made of thermally rearranged polymer membranes was developed in which the modules were exposed to methanol at 80°C. The thermally rearranged hollow fiber membrane modules were subjected to long-time operation to investigate their aging: the CO2 and N2 permeances were monitored at different temperatures, pressures, and feed compositions over a total period of 727 days with two long-time runs of 185 and 263 days, interspersed by a stand-by period of 240 days, and with each run followed by a restoring. In both long-time runs, CO2 and N2 permeance dropped as a result of aging, whereas the selectivity remained nearly constant. The permeances were fully recovered after the proposed restoring procedure was applied, demonstrating its efficacy and repeatability for membrane aging recovery, even for an extremely aged membrane exposed to various conditions for nearly two years.

Transient analysis of the cooling process of molten salt thermal storage tanks due to standby heat loss

Molten salts consisting of 60% sodium nitrate and 40% potassium nitrate have been used successfully as a thermal energy collection and storage fluid in different solar thermal plants. However, the relatively high melting point of this mixture (221°C) represents an important risk of local solidification in the operation of the solar power plants during standby periods. In this work, a computational fluid dynamics (CFD) model is developed to analyze the cooling process of representative state-of-the-art molten salt thermal storage tanks during these standby periods. A comprehensive set of operating conditions is analyzed, covering both hot and cold storage tanks, charging levels, and heat losses. Results show that the onset of local crystallization is highly influenced by the tank charging level. While the risk is relatively high in the case of the minimum charging level, in the case of maximum charging level the risk is minimal as it would require a very long standby period. To summarize the results, this work presents a safe charging level calculation, as a function of the operation temperature and the expected standby duration, which could be used as part of an appropriate operational strategy to avoid the risk of freezing for long standby periods. The model assumptions, the different configurations studied and their results are presented and discussed in detail.

Characterization of Battery Behavior for Battery-Aware Design of Wireless Sensing Networks

In battery-aware design, knowledge of the interaction between the duty cycle and battery performance is used to provide improvements in battery life beyond those achievable through low-power design alone. To that end, this study examined experimentally the influence of wireless sensing duty cycles on battery performance and capacity for small autonomous sensing nodes. A simple model of the physical processes that control battery behavior was used to understand and quantitatively describe our observations. The model was found to accurately describe and predict battery rate-capacity and recovery effects for a range of duty cycles. In particular, battery life was found to be a strong, predictable function of key operating parameters including the peak current, standby current, pulse length, and length of the standby period. The results and methods from this study help to enable battery-aware design by making it possible to assess the suitability of batteries for a variety of autonomous sensing applications based on their duty cycle requirements.

Study of the influence of inner lining material on thermal stratification in a hot water storage tank

The present study has analysed the influence of thermal conductivity of the inner lining material on the stratification process in a hot water tank during thermal charge and the later standby period. This analysis has been carried out numerically by a three-dimensional Computational Fluid Dynamics (CFD) model. Experimental measurements of temperature profiles are used to select and verificate the model, and to later validate CFD simulations. With the validated model, temperature over time at several heights, temperature profiles, velocity contours, water streamtraces and temperature contours, are studied and compared for three different inner lining materials. The obtained results confirm that a weak conducting lining material favours energy storage in the tank and the thermal stratification of water during charge and subsequent standby period. The effect of the inner lining material on the energy accumulated in water and on the moment of energy (stratification) is potentially enhanced when the material's thermal conductivity diminishes. The use of insulating paints as inner lining for water storage tanks could be a possible solution to be studied and subsequently adopted in practice to improve the efficient use of energy in stored water. The analysis techniques employed prove most useful and enable the results to be compared and presented in a novel way.