Constantinos Tsanaktsidis  Konstantinos Spinthiropoulos  George Tzilantonis  Christos Katsaros 《Petroleum Science and Technology》2016,34(13):1121-1128

The use of biodiesel fuel is becoming increasingly imperative nowadays and it is necessary to know the change of density. In this work the variation of density of diesel-biodiesel blends across the scale of 0–100% by adding each time 2% biodiesel and then measuring the density of three different temperatures (5, 15, 25°C) covering and the usual scale of temperatures the use of mixtures of diesel-biodiesel. Through the extraction of equations can be known in advance the relationship of density of diesel-biodiesel blend, and temperature that is used.  相似文献   

    

Konstantinos C. Bacharoudis  Theodore P. Philippidis 《风能》2015,18(5):783-796

A probabilistic stress analysis tool predicting reliability of composite wind turbine rotor blades was developed and validated by comparing with results from a three‐dimensional shell finite element model of a blade. Stress analysis was based on thin wall multicellular Euler–Bernoulli beam theory using as input section stress resultants directly from aeroelastic simulations; a finite strip method was implemented for elastic stability calculations. Reliability analysis was performed at the ply level of the multidirectional laminates implementing various methods such as the response surface method, β‐index and crude Monte Carlo simulation. Physical and statistical uncertainties of the basic variables was taken into account while several model uncertainties related to the material properties were further introduced and quantified in the light of appropriate test results. To prove the efficiency of the code as a design tool, the effect of various probabilistic assumptions concerning the material properties was directly investigated on the estimated reliability β‐index values for two rotor blade design cases typical of stall‐regulated and pitch‐regulated wind turbines. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

    

Konstantinos Agathos;Konstantinos Vlachas;Anthony Garland;Eleni Chatzi; 《International journal for numerical methods in engineering》2024,125(10):e7445

In this work, a novel approach is introduced for accelerating the solution of structural dynamics problems in the presence of localised phenomena, such as cracks. For this category of problems, conventional projection-based Model Order Reduction (MOR) methods are either limited with respect to the range of system configurations that can be represented or require frequent solutions of the Full Order Model (FOM) to update the low-dimensional spaces, in which solutions are represented. In the proposed approach, low-dimensional spaces, constructed for the healthy structure, are enriched with appropriately selected columns of the flexibility matrix of the system. It can be shown that these spaces contain the solution to the original problem for the static case, while their dimension is much smaller. In order to allow their online construction for arbitrary localised features, the full flexibility matrix of the system should be available. To this end, a hierarchical representation is used for the matrices involved, allowing to compute the flexibility matrix efficiently and with reduced memory requirements. The resulting method offers significant speedups, without sacrificing the flexibility and accuracy of the full order model. The performance and limitations of the approach are studied through a series of examples in structural dynamics.  相似文献   

    

Mohammed A. Zaki;Hayder A. Rasheed;Konstantinos Mitsios; 《Structural Concrete》2024,25(3):2206-2221

This research provides a study for an experimental program using sand-perlite-lightweight reinforced concrete (RC) beams strengthened and anchored with carbon fiber reinforced polymer (CFRP) materials. The main objective of this work is to showcase the efficiency of using U-wrap anchors to secure the externally applied CFRP sheets on lightweight RC beams. A series of six full-scale T-beams with an increasing number of CFRP U-wraps per shear span was prepared and tested. The use of U-wrap anchorage enhanced the flexural performance of the sand-lightweight concrete beams by progressively delaying the premature debonding of CFRP sheets as a direct function of the number of U-wraps used per shear span. The beam flexural capacity gradually improved from 116 kN without the use of U-wrap anchors to 182 kN when using six U-wraps per shear span, which reflects a significant enhancement. Similarly, the ultimate deflection gradually improved from 56 mm for the beam without U-wrap anchors to 94 mm when applying six U-wraps per shear span. A design model established earlier, for normal weight concrete, has been successfully qualified to yield accurate findings against the experimental results. Also, the outcome of this study interestingly showed that the ultimate strength results of the anchored beams were close to their counterparts of normal weight concrete conducted on identical beams. This finding shows that U-wrap anchors performed efficiently despite the lack of coarse aggregate interlock in the concrete mix.  相似文献   

    

Konstantinos?Kiritsakis  Eleni?Melliou  Prokopios?Magiatis  Dimitrios?Gerasopoulos  "mailto:dgerasop@agro.auth.gr  " title=  "dgerasop@agro.auth.gr  " itemprop=  "email  " data-track=  "click  " data-track-action=  "Email author  " data-track-label=  "  ">Email author 《Journal of the American Oil Chemists' Society》2017,94(8):1077-1085

Mature ‘Chondrolia Chalkidikis’ olives were processed in an industrial olive oil mill equipped with a three‐phase decanter. Water was added to the decanter at a 1:2 water‐to‐paste ratio. Olive mill waste water (ΟΜWW) was used to replace the added water at a rate of 50 or 100%. Following the final separation, the obtained oil was used for chemical analysis and sensory evaluation. All oils had similar acidity, peroxide and Κ values. OMWW‐treated olive oils presented higher total phenolic content and higher antioxidant activity based on DPPH and oven tests, but lower chlorophyll and carotenoids content. However, there was no significant difference between the 50 and 100% replacement. The phenolic profile of the treated olive oils analyzed by quantitative ¹Η NMR revealed more than twofold oleocanthal and oleacein as well as oleuropein and ligstroside aglycone contents than in the control. Sensory evaluation of treated oils also showed an enhancement of fruity, bitter and pungent attributes compared to the control.  相似文献   

    

Konstantinos T. Panourgias  John A. Ekaterinaris 《International journal for numerical methods in engineering》2017,112(11):1687-1711

The discontinuous Galerkin FEM is used for the numerical solution of the three‐dimensional Maxwell equations. Control of errors in the numerical level for the divergence‐free constraint of the magnetic field can be obtained through the use of divergence‐free vector bases. In this work, the so‐called perfectly hyperbolic formulation of the Maxwell equations is used to retain both divergence‐free magnetic field and in the presence of charges to satisfy the Gauss constraint for the electric field at the numerical level. For both approaches, it is found that higher‐order approximations have favorable effect on the preservation of the divergence constraints and that the perfectly hyperbolic formulations retains these errors to a lower level. It is shown that high‐order accuracy in space and time is achieved in unstructured meshes using implicit time marching. For nonuniform meshes, local resolution refinement is used using p‐type adaptivity to ensure accurate electromagnetic wave propagation. Thus, the potential of the method to reach the required higher resolution in anisotropic meshes and obtain accurate electromagnetic wave propagation with reduced computational effort is demonstrated.  相似文献   

    

Constantinos Tsanaktsidis  Spiros Bousios  Konstantinos Spinthiropoulos  George Tzilantonis  Apostolos Scaltsoyiannes 《Petroleum Science and Technology》2018,36(17):1332-1339

One of the important stages in the preparation of fuel for the smooth progress of combustion is to remove humidity from it. Natural resin, a natural product from Pinus nigra and Pinus halepensis were used in order to remove water residues from petroleum fuels. The mass of resin (P. nigra and P. halepensis) was mixed with diesel fuel and the humidity eliminated, 38% and 69% of diesel fuel also. The proposed method can be used in a simple fuel cleaning process using a metal mesh vessel consisted of the natural resin of P. nigra sample.  相似文献   

    

Konstantinos Bampalioutas  Anestis Vlysidis  Gerasimos Lyberatos  Apostolos Vlyssides 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2019,94(1):265-275

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Konstantinos Tserpes  Ioannis Floros 《Fatigue & Fracture of Engineering Materials & Structures》2019,42(7):1430-1440

A numerical model has been developed for simulating fatigue crack growth (debonding) in adhesively bonded composite joints subjected to mode‐I, mode‐II, and mixed‐mode I + II loading conditions. The model employs a cohesive zone model described by a modified bilinear traction‐separation law. Fatigue damage in the composite adherends is not considered in the model. To account for crack divergence and reduce sensitivity of numerical results on mesh density, a crack front detection algorithm based on the effective element's length was employed. The model is implemented as a user‐defined subroutine (UMAT) in the commercial FE code LS‐DYNA. The model's input parameters, in the form of a modified Paris law, and the validation data were obtained from experimental tests conducted by the authors. It was found that the model is able to successfully simulate crack growth in the regime of the experimental data.  相似文献   

    

Neil Maiden  Kristine Pitts  Kevin Pudney  Konstantinos Zachos 《International journal of human-computer interaction》2019,35(7):605-619

There has been little research to investigate the impact of software to support the care for older people with dementia care. This article reports the evaluation of software adapted to support one key person-centered task for the care of older residents with dementia – recording and sharing daily care notes. The evaluation on the dementia wing of 1 residential home for over 6 months revealed that use of the software on mobile devices carried by the carers increased the number and volume of daily care notes recorded, but only for the types of content that were already being recorded by carers. Carers reported more advantages that resulted from daily care notes once in digital form than from the documenting task, as well as barriers to the use of mobile digital software to record daily care notes.  相似文献