•A procedure for the estimation of the lifetime reduction is proposed.•The plant dynamic model is the core of the proposed procedure.•A three pressure level combined cycle power plant is selected as ...test case.•Different transient conditions are analyzed.•The lifetime reduction of the high pressure superheater and drum is computed.
The liberalization of the European energy markets combined with the rapid spread of unpredictable renewable energy sources have stressed the need of improving the traditional power units flexibility. Fast start-ups/shut downs and rapid load variations have become priority objectives because they guarantee high profits in the short term but cause a lifetime reduction due to thermo-mechanical fatigue, creep and corrosion. To this purpose, in the present work, an innovative procedure, able to predict the power plant dynamic behaviour during load variations, identify the most stressed components and estimate their lifetime reduction is presented and tested. Being combined cycles the most efficient, flexible and widespread technologies, the selected test case is a 380MW combined cycle unit. To predict the plant dynamic performance a dynamic model has been built in Modelica language and several transient conditions investigated. The high pressure steam drum and superheater are the most stressed components. Results show a 52.9% reduction in superheater collectors life if the load variation is 50% faster than the reference case. On the contrary, a 35.8% lifetime increase is observed if the load variation is 50% slower. For the same conditions the high pressure steam drum life is reduced by 31.9% and increased by 16.3%, respectively. Also the superheater tube bank lifetime reduction is computed. The proposed procedure can be considered a valuable innovative tool to assist power plant designers and operators.
•Optimal waste heat recovery technology for offshore platforms.•Organic Rankine cycle, air bottoming cycle and steam Rankine cycle as waste heat recovery units.•Multi-objective design-point ...optimization approach to compare the three alternatives.•Three objective functions considered: yearly CO2 emissions, weight and net present value.•Case study: Draugen offshore oil and gas platform in the Norwegian Sea.
This article aims at finding the most suitable waste heat recovery technology for existing and future offshore facilities. The technologies considered in this work are the steam Rankine cycle, the air bottoming cycle and the organic Rankine cycle.
A multi-objective optimization approach is employed to attain optimal designs for each bottoming unit by selecting specific functions tailored to the oil and gas sector, i.e. yearly CO2 emissions, weight and economic revenue. The test case is the gas turbine-based power system serving an offshore platform in the North Sea.
Results indicate that the organic Rankine cycle technology presents larger performances compared to steam Rankine cycle units, whereas the implementation of air bottoming cycle modules is not attractive from an economic and environmental perspective compared to the other two technologies.
Despite the relatively high cost of the expander and of the primary heat exchanger, organic Rankine cycle turbogenerators appear thus to be the preferred solution to abate CO2 emissions and pollutants on oil and gas facilities.
As a practical consequence, this paper provides guidelines for the design of high-efficiency, cost-competitive and low-weight power systems for offshore installations.
In the present work, a numerical study aimed to analyse the effect of an extreme loading event on a Horizontal Axis Wind Turbine (HAWT) is performed. A 3D unsteady CFD model of the NREL Phase VI ...small-sized wind turbine is validated against experimental data, with the incompressible solver of ANSYS Fluent and an unstructured moving mesh strategy. Then the Extreme Operating Gust (EOG) model from IEC 61400-2 is considered as the inlet condition. The results of the aerodynamic response and of the structural ultimate check, based on the IEC guidelines, are presented for both the operating and the parked turbine, in order to underline the benefit of the safety position in terms of lower stress transferred to the critical root section.
•An unsteady CFD model of small-sized wind turbine has been developed.•The EOG gust model presented in IEC-61400 has been used as reference.•The NREL Phase VI HAWT has been considered as case study.•Both aerodynamic and structural analyses have been performed.
Purpose
Sylvian arachnoid cysts (SACs) are the most common type of arachnoid cysts and the most prone to undergo a rupture. This event is considered rare but potentially severe. No definite ...information is available on its occurrence or management. The goal of the present article is to provide an update on the epidemiological, etiological, and clinical aspects and the management of this peculiar clinical condition.
Methods
A comprehensive review of the English literature of the last 40 years on this topic has been realized. Moreover, a personal series of children investigated and treated in the last 20 years is presented. These patients were managed as follows: (1) treatment of the subdural collection; (2) identification of candidates for surgical treatment of the residual cyst (brain MRI, perfusion brain MRI, prolonged invasive ICP monitoring (selected cases), EEG, neuropsychological tests); (3) surgical treatment of the cyst in the patients with pathological perfusion MRI and/or ICP measurement and/or clear neurophysiological and neuropsychological correlations.
Results
A total of 446 patients (430 from the literature and 16 from the personal series), mainly children, adolescents, and young adults, have been analyzed leading to the following results: (1) SAC rupture is rare but not negligible (yearly risk of rupture: 0.04%; overall risk up to 10% in children affected by SCAs). Prophylactic surgery in asymptomatic cases is not advisable. (2) The mechanism of rupture is not known but an impact of SAC against the sphenoid wing and/or a direct injury on SAC through a thinned temporal bone, with possible laceration of the cyst wall vessels and/or tear of the bridging veins, can be hypothesized. A head injury is often not reported (may be misdiagnosed). (3) Subdural collection (hygroma > chronic hematoma) is the most common finding followed by intracystic bleeding, extradural hematoma, and other types of bleeding. Signs or symptoms of raised intracranial pressure are the most frequent ones. (4) The complication of the rupture is usually treated in emergency or in the acute period by burr hole or craniotomic evacuation of the subdural collection, although a conservative management is possible in some cases. Following the rupture, the majority of SACs are treated (70%), often at the same time of the complication, but no specific investigations are routinely performed to select candidates. According to our protocol, only 43.7% of SACs needed to be treated.
Conclusions
The “spontaneous” or posttraumatic rupture of SACs is a rare but potentially significant complication followed by a generally good outcome. The course of the cyst is independent from the outcome of the complication, consequently requiring specific investigations for individuating those lesions interfering with CSF dynamics and/or cerebral blood flow.
Microtunnelling is an excavation technique capable of positioning underground pipes with considerable advantages from the point of view of the environment, safety, construction times and also total ...costs, when the lengths are significant. The technology used is now reliable and is suitable for use in different types of soils and rocks without particular problems. The installation of the concrete lining of the micro-tunnel takes place behind the excavation machine starting from a thrust shaft. A filling material must be injected between the outer surface of the lining and the tunnel wall. This filling material plays a very important role, because it conditions the overall stiffness of the support system and, therefore, influences the radial load applied by the ground to the support system. Therefore, it is necessary to take into account the presence of the filling material in order to correctly size the support system of the micro-tunnel. This paper illustrates a new procedure for analyzing the behavior of the micro-tunnel support system, based on widely used and tested analytical calculation methods. This procedure was applied to a real case, underway in Northern Italy. The results obtained were then compared with those of numerical modeling, which made it possible to simulate the micro-tunnel in detail. From the comparison it was possible to note how the analytical calculation procedure leads to stress states similar (slightly higher) to those of numerical modeling; the first, therefore, can be effectively used in the preliminary stages of the design of micro-tunnels to obtain useful information on the characteristics of the support systems to be adopted to ensure the stability.
A new empirical formulation is presented which can be used to estimate the penetration-per-revolution for TBM tunneling, derived from TBM monitoring data of alpine tunnels in the North-West of Italy. ...This formulation is easy to use and allows the contribution of both the intact rock and of the rock mass characteristics to be taken into account. The contribution of the intact rock is taken into consideration through the use of the uniaxial compression strength, while the influence of the rock mass is considered through the use of the GSI. A statistical interpretation procedure of numerous operative data from TBMs used for the excavation of tunnels in rock, and of the characterization of intact rock and of the rock mass, has been developed to determine the proposed formulation. In particular, the penetration-per-revolution (p) recorded during excavation, the forces applied to each disk (FN), the Geological Strength Index (GSI) and uniaxial compression strength of the intact rock (σc) along the stretch have been compared.
The set-up formulation is simple to use and reliable for tunnels excavated in metamorphic rock, as it has successfully been compared with the TBM net advancement speed data of a well-known case history taken from the literature (the Maen tunnel in Italy). Comparisons with results obtained with the Norwegian School method (NTNU) and Barton׳s calculation model have also led to positive results.
•An important aspect in the design of a tunnel is the evaluation of TBM speed•Some formulations which predict the penetration per revolution are complex•A new formulation is presented to estimate the penetration per revolution•The proposed formulation is simple and requires a small number of parameters•A comparison between the existing formulations and the one proposed is presented•The results obtained with the new formulation are compared with a case history
Persimmon production in Brazil is concentrated from February to June. The large amount of this fruit available in the market influences its price during this period. This study was carried out to ...evaluate the effect of different packaging plastic materials on extending the storage life of ‘Fuyu’ persimmons kept under refrigeration. ‘Fuyu’ persimmon fruits were harvested on the mature-green stage and enclosed in groups of three (750
±
30
g) in different packaging materials: 58-μm multilayer polyolephynic film (PO); 50-μm low density polyethylene film (LDPE) and 38-μm microperforated PO. Unpacked fruit stored in corrugated cardboard boxes were used as control. Fruit were stored at 1
±
1
°C/90
±
5% RH for 90
d. Every 7
d, five replicates of each treatment were evaluated for headspace gas composition (O
2, CO
2) and then transferred to 25
±
1
°C/70
±
5% RH for five more days. Then they were evaluated as to headspace gas composition (O
2, CO
2, acetaldehyde and ethanol), firmness, weight loss, skin and flesh color, total soluble solids, titratable acidity, pH, decay, discoloration and sensory attributes. The gas composition in the steady-state established in the 58-μm PO and 50-μm LDPE films extended the storage period up to 84
d at 1
°C plus 5
d at 25
°C differing significantly (
P
≤
0.05) from the control fruit as well as from those in the 38-μm microperforated PO, which were stored for 21 and 28
d, respectively. Off-flavors were not detected by sensory analysis. These results suggest that the 58-μm PO and 50-μm LDPE films are suitable for atmosphere modification and packaging of ‘Fuyu’ persimmon fruit stored under refrigeration with an additional period of time at ambient temperature.
•The flexibility of traditional power plants have become of primary importance.•Three dynamic models of the same single pressure HRSG are built.•The plant dynamic behaviour is predicted.•A lifetime ...calculation procedure is proposed and tested.•The drum lifetime reduction is estimated.
The energy markets deregulation coupled with the rapid spread of unpredictable energy sources power units are stressing the necessity of improving traditional power plants flexibility. Cyclic operation guarantees high profits in the short term but, in the medium-long time, cause a lifetime reduction due to thermo-mechanical fatigue, creep and corrosion. In this context, Combined Cycle Power Plants are the most concerned in flexible operation problems. For this reason, two research groups from two Italian universities have developed a procedure to estimate the devices lifetime reduction with a particular focus on steam drums and superheaters/reheaters. To assess the lifetime reduction, it is essential to predict the thermodynamic variables trend in order to describe the plant behaviour. Therefore, the core of the procedure is the power plant dynamic model. At this purpose, in this paper, three different dynamic models of the same single pressure Combined Cycle Gas Turbine are presented. The models have been built using three different approaches and are used to simulate plant behaviour under real operating conditions. Despite these differences, the thermodynamic parameters time profiles are in good accordance as presented in the paper. At last, an evaluation of the drum lifetime reduction is performed.
The effect of phosphine on Salmonella enterica serotype Enteritidis inoculated in culture medium and in black pepper grains (Piper nigrum), as well as on the reduction of the microbial load of the ...dried and moisturized product, was verified. The postfumigation effect was verified in inoculated samples with 0.92 and 0.97 water activity (a(w)) exposed to 6 g/m(3) phosphine for 72 h, dried to 0.67 a(w), and stored for 24, 48, and 72 h. No decreases were observed in Salmonella Enteritidis populations in culture medium when fumigant concentrations up to 6 g/m(3) were applied for 48 h at 35°C. However, the colonies showed reductions in size and atypical coloration as the phosphine concentration increased. No reduction in Salmonella counts occurred on the inoculated dried samples after fumigation. On the other hand, when phosphine at concentrations of 6 g/m(3) was applied on moisturized black pepper for 72 h, decreases in Salmonella counts of around 80% were observed. The counts of total aerobic mesophilic bacterium populations of the dried and moisturized black pepper were not affected by the fumigant treatment. The results of the postfumigation studies indicated that Salmonella Enteritidis was absent in the fumigated grains after drying and storage for 72 h, indicating a promising application for this technique. It was concluded that for Salmonella Enteritidis control, phosphine fumigation could be applied to black pepper grains before drying and the producers should rigidly follow good agricultural practices, mainly during the drying process, in order to avoid product recontamination. Additional work is needed to confirm the findings with more Salmonella serotypes and strains.
•Engine performance is highly influenced by transmission layout and control.•Power Split transmission allows a direct control of the engine operation point.•Numerical simulations of an urban bus are ...used to compare control strategies.•Control strategies are discussed in terms of both fuel consumption and emissions.•Results on a standard test cycle are compared to the Euro V regulations.
The continuously variable hydromechanical transmission is an interesting solution for high power vehicles subject to frequent changes of speed, in which the comfort is a significant requirement.
Despite their low average efficiency with respect to the mechanical transmissions, the hydromechanical transmissions allow to release the engine speed by the vehicle speed, and to open the possibility for the optimal control of the engine. It follows that the performance and emissions of the powertrain is heavily affected by the logic control.
The aim of the paper is to investigate the emission reductions that can be obtained using a Power-Split transmission.
Therefore, a hydromechanical transmission has been sized and tested on a 12-ton-city bus by using a one-dimensional model developed in an AMESim environment. Four different control strategies of the powertrain were applied to the model. The CUEDC-ME standard cycle for the characterization of emissions in heavy vehicles was used as a reference mission.
The simulation results showed that the hydromechanical transmission reduces consumption or the emission levels with respect to the traditional transmission when managed according to appropriate control strategies. By means of emission values normalized with respect to the standard limits, it is possible to identify a control strategy that allows the reduction of emissions in every usage condition of the vehicle at the expense of a slight increase of consumption.
The suggested procedure could help the manufacturer to satisfy the emission standard requirements.
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