54 research outputs found

    Termohaline properties and dynamical processes in the Adriatic sea simulated with regional climate models

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    Tijekom zimskog razdoblja, zbog izloženosti udarima hladne i snažne bure, na sjevernom i južnom Jadranu se stvaraju guste vodene mase, koje utječu na termohalinu cirkulaciju u istočnom Sredozemlju. Stvaranje guste vode u Jadranu utječu i na Jadransko-jonsku bimodalnu oscilaciju (engl. Adriatic-Ionian Bimodal Oscillating System, BiOS), koja određuje termohaline karakteristike Jadrana. U doktorskom istraživanju se ispituje koliko dobro regionalni oceanski klimatski modeli za Sredozemlje reproduciraju navedene procese kao i termohalina svojstva u Jadranu. Analizirano je sedam regionalnih klimatskih simulacija modelom NEMOMED. Cilj istraživanja je testiranje različitih modelskih postavki na ponašanje modela pri reprodukciji termohalinih svojstava jadransko-jonskog bazena te njihovih varijabilnosti. Simulacije su verificirane pomoću in situ hidroloških podataka prikupljenih na više klimatoloških postaja u razdoblju 1960. -2012., te pomoću podataka razine mora dobivenih altimetrijskim mjerenjima. Simulacije spregnutih modela su pokazale bolju sposobnost reprodukcije stvaranja guste vode u Jadranu, s nižim zabilježenim odstupanjima temperature i saliniteta, varijabilnosti te promjena vezane uz BiOS: promjena u cirkulaciji sjevernog Jonskog mora i povezanu dekadsku varijabilnost termohalinih svojstava Jadrana. Simulacije nespregnutih modela koji imaju višu vertikalnu rezoluciju oceanskog modela pokazuju bolju sposobnost reproduciranja svojstava i dinamike Levantinske intermedijarne vode. Upotreba veće rezolucije atmosferskog i oceanskog modela je rezultirala realističnijim prostornim obilježjima procesa stvaranja guste vode u kompleksnom području sjevernog Jadrana. Utjecaj riječnih forsiranja na termohalina svojstva jadransko-jonskog sustava nije izražen. Uključivanje trenda aerosola je poboljšalo reprodukciju promjene u cirkulaciji sjevernog Jonskog mora. Simulacije spregnutih modela u načelu imaju bolju sposobnost reprodukcije stvaranja duboke vode u Jadranu te BiOS-a i svojstava jadransko-jonskog sustava. Stoga je i analizirana simulacija buduće klime Jadrana pomoću potpuno spregnutog atmosfersko-morskog modela NEMOMED za Sredozemlje, pri čemu su pretpostavljena tri uobičajena scenarija emisije stakleničkih plinova (RCP2.6, RCP4.5 i RCP8.5). Projekcije za sva tri scenarija pokazuju porast površinske temperature i saliniteta u Jadranu i jačanje mehanizma BiOS-a do kraja 21. stoljeća, posebice izraženo u scenariju RCP8.5.Wintertime cooling on the shelf and deep convection process, common for the Adriatic Sea, are recognized as major drivers of the Adriatic-Ionian thermohaline circulation (Orlić et al., 2006). To observe, simulate and understand climate-scale variability of the thermohaline circulation and its drivers is still very challenging. Because of geographical position of the Adriatic Sea and the surrounding topography, the bursts of cold and dry Bora wind blowing over the basin (Grisogono and Belušić, 2009) are responsible for the Dense Water Formation (DWF) processes, in particular for: -Very cold and dense Northern Adriatic Dense Water (NAdDW) generated at shallow northern Adriatic shelf. After its formation, NAdDW is advected towards southeast inform of a bottom density current that travels along the western shelf and fills the deepest parts of the Adriatic (Jabuka Pit and South Adriatic Pit). - Adriatic Deep Water (ADW) that is formed through deep convection inside the South Adriatic cyclonic gyre. Joined with NAdDW, through Otranto Strait, ADW flows towards the Ionian Sea, where it fills the deepest layers of the Eastern Mediterranean (Zore-Armanda, 1963; Schlitzer et al., 1991; Artegiani et al., 1997a; Vilibić et al., 2004). Adriatic deep water masses are important for several reasons. As mentioned, they contribute to the Eastern Mediterranean circulation sustainability (Roether and Schlitzer, 1991; Manca et al., 2002) and refresh the deep layers of that area by bringing oxygenized waters (Malanotte-Rizzolii Robinson, 1988). They drive the thermohaline circulation of the Adriatic-Ionian basin (Orlić et al., 2006; Vilibić et al., 2013), and influence observed decadal oscillation of the northern Ionian Sea circulation (Borzelli et al., 2009), which in turn affects the dynamics of entire middle and eastern Mediterranean, especially of the Adriatic Sea (Gačić et al., 2010). The feedback mechanism between the Adriatic DWF and the circulation patterns of northern Ionian is called The Adriatic-Ionian Bimodal Oscillating System (BiOS), and is recognized as the main feature that drives the decadal variability of the Adriatic thermohaline properties (Mihanović et al., 2015). In this PhD research regional climate modelling approach is used to study thermohaline properties and variability of the Adriatic Sea. The research includes qualitative and quantitative analysis of the Adriatic thermohaline circulation and its variability, focusing on the processes of the DWF and the BiOS. Past experiences in modelling studies suggest the important issues to be implemented in order to properly reproduce the Adriatic-Ionian ocean processes, such as the DWF and the BiOS: -proper introduction of topography and bathymetry (Hendershot and Rizzoli, 1976), -high spatial and temporal resolution of the ocean (Pinardi et al., 1996) and atmospheric (Bergamasco et al., 1999; Beg-Paklar et al., 2001) components of a model, -proper introduction of buoyancy fluxes (Vested et al., 1998; Raicich et al., 2013) and river discharges (Janeković et al., 2014), and -appropriate boundary conditions (Mantziafou and Lascaratos 2004, 2008; Oddo and Guarnieri, 2011). However, all these researches were conducted with short-term numerical simulations, for which their results were limited only to the evaluation of the Adriatic-Ionian ocean processes on shorter timescales (up to 10 years). In order to quantify long-term changes of oceanographic properties related to the Adriatic-Ionian thermohaline circulation, and to test the performance of climate models with different setup in the basin (following previous suggestions), seven different regional hindcast simulations based on various configurations of NEMO–Mediterranean versions covering ERA-Interim period (1980-2012) were tested. This work is also testing the performance of coupled vs. non-coupled modelling approach. The chosen simulations of regional climate models are produced within the framework of the Med-CORDEX initiative (www.medcordex.eu), and are differing in their vertical and horizontal resolution, freshwater load, surface heat fluxes, air-sea interaction, and inclusion or not of the aerosol trend. The objective of this research is to evaluate the reliability of regional climate models for the Mediterranean region to reproduce the Adriatic-Ionian ocean dynamics, through their validation on in situ observations, and through detailed assessment of both Adriatic DWF processes and the BiOS, as well as their multi-decadal variability. The goal is to find the optimal model which will be the most reliable for quantification of Adriatic-Ionian thermohaline circulation in the future. Performance of all seven simulations is evaluated on the long-term in situ data collected over three northern Adriatic transects, along the Palagruža Sill transect, at Jabuka Pit and at South Adriatic Pit, as well as on the altimetry satellite observations. Detailed description of the Adriatic-Ionian thermohaline properties and dynamics is provided in Section 1. Section 2 covers the description of all used simulations, in situ and altimetry obtained data, and details of the performed analysis. A performance analysis of the NEMOMED8 ocean regional circulation model is given in Section 3. The analysis was undertaken for the Adriatic Sea during the period of 1961–2012, focusing on two mechanisms: the DWF and the BiOS, which drive interannual and decadal variability in the basin. The model was verified on sea surface temperature, sea surface height and long-termhydrographic in situ observations from several key areas. NEMOMED8 simulation qualitatively reproduces basin-scale processes, in particular: -thermohaline-driven cyclonic circulation and freshwater surface outflow along the western Adriatic coast, -dense water dynamics, and -the inflow of Ionian and Levantine waters to the Adriatic. However, positive temperature and salinity biases are reported; the latter particularly large along the eastern part of the basin, presumably because of the inappropriate introduction of eastern Adriatic rivers into the model. The highest positive temperature biases in the vertical direction were found in dense water collectors in the Adriatic, i.e. Jabuka Pit and South Adriatic Pit, indicating either inappropriate quantification of DWF processes or temperature overestimation of modelled dense water, especially of NAdDW. Moreover, much reduced model domain compared to the real bathymetry, which does not include entire coastal area of the northern Adriatic where the largest heat losses are found, i.e. the part of the Kvarner Bay (Janeković et al., 2014), also led to an underestimation of the cumulative surface heat losses during wintertime cold outbreaks, and therefore to the under representation of the NAdDW formation. As a consequence, the simulated NAdDW is of lower volume when it comes to the deep layers of South Adriatic Pit. Thus, an over estimation in vertical mixing of water column during deep convection process has been documented by the NEMOMED8 model. The DWF rates are qualitatively well reproduced by the model, being larger when preconditioned by higher basin-wide salinities. The decadal variability in the thermohaline properties is reproduced better than interannual variability, which is considerably underestimated. However, a key process that drives the Adriatic decadal variability, the BiOS, is not properly reproduced, in particular current reversals and outreach of the Northern Ionian gyre. The only appearance of anticyclonic circulation simulated by the NEMOMED8in the northern Ionian Sea was found only during the Eastern Mediterranean Transient. Next, performance analysis of seven regional ocean configurations based on NEMO has been carried out for the Adriatic Sea over a common period (1980-2012). The goal of the study was to test the model performances with different settings, particulary when it comes to reproduction of the Adriatic-Ionian thermohaline properties and variability. The analysis is given in Section 4. Simulations differ in resolution, model physics, atmospheric forcing (forced vs. coupled models) and river discharges imposed within the Adriatic Sea. Models have been evaluated on the long-term temperature and salinity measurements in all of the Adriatic sub-basins, in particular within dense water collectors (Jabuka Pit and South Adriatic Pit) and dense water formation sites (northern and southern Adriatic). Adriatic-wide salinity values are mostly linked to the proper introduction of the overall water budget, rather than to the local river forcing. Forced models mostly overestimate temperature and salinity values. On average, coupled models better reproduce the thermohaline properties and processes, in particular the BiOS reversals and its decadal variability. Wintertime heat losses are playing major role in defining the ADW transport rates in coupled models, while preconditioning in salinity is the most important factor in forced models. Further on, increase of resolution of the atmospheric forcing results in more realistic ocean dynamics, including the DWF in the complex coastal northern Adriatic. However, all models have large positive temperature biases at the dense water collector sites, indicating overall underrepresentation of the Adriatic DWF. Consequently, mixed-layer depth in the southern Adriatic is overestimated, reaching the bottom during some years and in some models. Ocean model resolution and river forcing seem to play a second-order role in defining the overall Adriatic-Ionian thermohaline properties, while inclusion of aerosol trend only slightly modified the reproduction of the BiOS. Lastly, a preliminary analysis of future projections which contain the very first attempt to quantify the processes of the DWF and the BiOSin the future climate, is described in Section 5. This also applies to the evolution of surface temperatures and salinities. The NEMOMED8 simulations were forced by three future scenarios of Representative Concentration Pathways (RCP, IPCC, 2013): RCP2.6, RCP4.5 and RCP8.5. The analysis is performed for the three future periods: near (2011-2040), middle (2041-2070), and far future (2071-2100), with respect to the last 30 years of the referent period simulated in historical simulation (1976 -2005). No significant trends in all analyzed parameters were found in control simulation covering the period 1950-2100. Towards the end of 21st century, under all three scenarios, gradual increase in basin-wide sea surface temperature (SST) was found, of which RCP8.5 is resulting with highest SST at the end of the 21st century, about 2.7 oC on average. All scenarios result also in an increased sea surface salinity (SSS), more pronounced at the coastal parts of the Adriatic, with highest increase found in RCP8.5. All three scenarios show a decrease in maximum mixed layer depth (MLD), suggesting a weakening of deep convection processes by the end of the 21stcentury. As for the analysis of the BiOS related processes, all scenarios are projecting an increase in intensity of the positive BiOS index (anticyclonic circulation in northern Ionian Sea), which favors the advection of less saline water masses coming from the Western Mediterranean to the Adriatic. The strengthening of the both positive and negative BiOS regimes is only projected with RCP8.5 scenario, more pronounced in the anticyclonic phase

    Termohaline properties and dynamical processes in the Adriatic sea simulated with regional climate models

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    Tijekom zimskog razdoblja, zbog izloženosti udarima hladne i snažne bure, na sjevernom i južnom Jadranu se stvaraju guste vodene mase, koje utječu na termohalinu cirkulaciju u istočnom Sredozemlju. Stvaranje guste vode u Jadranu utječu i na Jadransko-jonsku bimodalnu oscilaciju (engl. Adriatic-Ionian Bimodal Oscillating System, BiOS), koja određuje termohaline karakteristike Jadrana. U doktorskom istraživanju se ispituje koliko dobro regionalni oceanski klimatski modeli za Sredozemlje reproduciraju navedene procese kao i termohalina svojstva u Jadranu. Analizirano je sedam regionalnih klimatskih simulacija modelom NEMOMED. Cilj istraživanja je testiranje različitih modelskih postavki na ponašanje modela pri reprodukciji termohalinih svojstava jadransko-jonskog bazena te njihovih varijabilnosti. Simulacije su verificirane pomoću in situ hidroloških podataka prikupljenih na više klimatoloških postaja u razdoblju 1960. -2012., te pomoću podataka razine mora dobivenih altimetrijskim mjerenjima. Simulacije spregnutih modela su pokazale bolju sposobnost reprodukcije stvaranja guste vode u Jadranu, s nižim zabilježenim odstupanjima temperature i saliniteta, varijabilnosti te promjena vezane uz BiOS: promjena u cirkulaciji sjevernog Jonskog mora i povezanu dekadsku varijabilnost termohalinih svojstava Jadrana. Simulacije nespregnutih modela koji imaju višu vertikalnu rezoluciju oceanskog modela pokazuju bolju sposobnost reproduciranja svojstava i dinamike Levantinske intermedijarne vode. Upotreba veće rezolucije atmosferskog i oceanskog modela je rezultirala realističnijim prostornim obilježjima procesa stvaranja guste vode u kompleksnom području sjevernog Jadrana. Utjecaj riječnih forsiranja na termohalina svojstva jadransko-jonskog sustava nije izražen. Uključivanje trenda aerosola je poboljšalo reprodukciju promjene u cirkulaciji sjevernog Jonskog mora. Simulacije spregnutih modela u načelu imaju bolju sposobnost reprodukcije stvaranja duboke vode u Jadranu te BiOS-a i svojstava jadransko-jonskog sustava. Stoga je i analizirana simulacija buduće klime Jadrana pomoću potpuno spregnutog atmosfersko-morskog modela NEMOMED za Sredozemlje, pri čemu su pretpostavljena tri uobičajena scenarija emisije stakleničkih plinova (RCP2.6, RCP4.5 i RCP8.5). Projekcije za sva tri scenarija pokazuju porast površinske temperature i saliniteta u Jadranu i jačanje mehanizma BiOS-a do kraja 21. stoljeća, posebice izraženo u scenariju RCP8.5.Wintertime cooling on the shelf and deep convection process, common for the Adriatic Sea, are recognized as major drivers of the Adriatic-Ionian thermohaline circulation (Orlić et al., 2006). To observe, simulate and understand climate-scale variability of the thermohaline circulation and its drivers is still very challenging. Because of geographical position of the Adriatic Sea and the surrounding topography, the bursts of cold and dry Bora wind blowing over the basin (Grisogono and Belušić, 2009) are responsible for the Dense Water Formation (DWF) processes, in particular for: -Very cold and dense Northern Adriatic Dense Water (NAdDW) generated at shallow northern Adriatic shelf. After its formation, NAdDW is advected towards southeast inform of a bottom density current that travels along the western shelf and fills the deepest parts of the Adriatic (Jabuka Pit and South Adriatic Pit). - Adriatic Deep Water (ADW) that is formed through deep convection inside the South Adriatic cyclonic gyre. Joined with NAdDW, through Otranto Strait, ADW flows towards the Ionian Sea, where it fills the deepest layers of the Eastern Mediterranean (Zore-Armanda, 1963; Schlitzer et al., 1991; Artegiani et al., 1997a; Vilibić et al., 2004). Adriatic deep water masses are important for several reasons. As mentioned, they contribute to the Eastern Mediterranean circulation sustainability (Roether and Schlitzer, 1991; Manca et al., 2002) and refresh the deep layers of that area by bringing oxygenized waters (Malanotte-Rizzolii Robinson, 1988). They drive the thermohaline circulation of the Adriatic-Ionian basin (Orlić et al., 2006; Vilibić et al., 2013), and influence observed decadal oscillation of the northern Ionian Sea circulation (Borzelli et al., 2009), which in turn affects the dynamics of entire middle and eastern Mediterranean, especially of the Adriatic Sea (Gačić et al., 2010). The feedback mechanism between the Adriatic DWF and the circulation patterns of northern Ionian is called The Adriatic-Ionian Bimodal Oscillating System (BiOS), and is recognized as the main feature that drives the decadal variability of the Adriatic thermohaline properties (Mihanović et al., 2015). In this PhD research regional climate modelling approach is used to study thermohaline properties and variability of the Adriatic Sea. The research includes qualitative and quantitative analysis of the Adriatic thermohaline circulation and its variability, focusing on the processes of the DWF and the BiOS. Past experiences in modelling studies suggest the important issues to be implemented in order to properly reproduce the Adriatic-Ionian ocean processes, such as the DWF and the BiOS: -proper introduction of topography and bathymetry (Hendershot and Rizzoli, 1976), -high spatial and temporal resolution of the ocean (Pinardi et al., 1996) and atmospheric (Bergamasco et al., 1999; Beg-Paklar et al., 2001) components of a model, -proper introduction of buoyancy fluxes (Vested et al., 1998; Raicich et al., 2013) and river discharges (Janeković et al., 2014), and -appropriate boundary conditions (Mantziafou and Lascaratos 2004, 2008; Oddo and Guarnieri, 2011). However, all these researches were conducted with short-term numerical simulations, for which their results were limited only to the evaluation of the Adriatic-Ionian ocean processes on shorter timescales (up to 10 years). In order to quantify long-term changes of oceanographic properties related to the Adriatic-Ionian thermohaline circulation, and to test the performance of climate models with different setup in the basin (following previous suggestions), seven different regional hindcast simulations based on various configurations of NEMO–Mediterranean versions covering ERA-Interim period (1980-2012) were tested. This work is also testing the performance of coupled vs. non-coupled modelling approach. The chosen simulations of regional climate models are produced within the framework of the Med-CORDEX initiative (www.medcordex.eu), and are differing in their vertical and horizontal resolution, freshwater load, surface heat fluxes, air-sea interaction, and inclusion or not of the aerosol trend. The objective of this research is to evaluate the reliability of regional climate models for the Mediterranean region to reproduce the Adriatic-Ionian ocean dynamics, through their validation on in situ observations, and through detailed assessment of both Adriatic DWF processes and the BiOS, as well as their multi-decadal variability. The goal is to find the optimal model which will be the most reliable for quantification of Adriatic-Ionian thermohaline circulation in the future. Performance of all seven simulations is evaluated on the long-term in situ data collected over three northern Adriatic transects, along the Palagruža Sill transect, at Jabuka Pit and at South Adriatic Pit, as well as on the altimetry satellite observations. Detailed description of the Adriatic-Ionian thermohaline properties and dynamics is provided in Section 1. Section 2 covers the description of all used simulations, in situ and altimetry obtained data, and details of the performed analysis. A performance analysis of the NEMOMED8 ocean regional circulation model is given in Section 3. The analysis was undertaken for the Adriatic Sea during the period of 1961–2012, focusing on two mechanisms: the DWF and the BiOS, which drive interannual and decadal variability in the basin. The model was verified on sea surface temperature, sea surface height and long-termhydrographic in situ observations from several key areas. NEMOMED8 simulation qualitatively reproduces basin-scale processes, in particular: -thermohaline-driven cyclonic circulation and freshwater surface outflow along the western Adriatic coast, -dense water dynamics, and -the inflow of Ionian and Levantine waters to the Adriatic. However, positive temperature and salinity biases are reported; the latter particularly large along the eastern part of the basin, presumably because of the inappropriate introduction of eastern Adriatic rivers into the model. The highest positive temperature biases in the vertical direction were found in dense water collectors in the Adriatic, i.e. Jabuka Pit and South Adriatic Pit, indicating either inappropriate quantification of DWF processes or temperature overestimation of modelled dense water, especially of NAdDW. Moreover, much reduced model domain compared to the real bathymetry, which does not include entire coastal area of the northern Adriatic where the largest heat losses are found, i.e. the part of the Kvarner Bay (Janeković et al., 2014), also led to an underestimation of the cumulative surface heat losses during wintertime cold outbreaks, and therefore to the under representation of the NAdDW formation. As a consequence, the simulated NAdDW is of lower volume when it comes to the deep layers of South Adriatic Pit. Thus, an over estimation in vertical mixing of water column during deep convection process has been documented by the NEMOMED8 model. The DWF rates are qualitatively well reproduced by the model, being larger when preconditioned by higher basin-wide salinities. The decadal variability in the thermohaline properties is reproduced better than interannual variability, which is considerably underestimated. However, a key process that drives the Adriatic decadal variability, the BiOS, is not properly reproduced, in particular current reversals and outreach of the Northern Ionian gyre. The only appearance of anticyclonic circulation simulated by the NEMOMED8in the northern Ionian Sea was found only during the Eastern Mediterranean Transient. Next, performance analysis of seven regional ocean configurations based on NEMO has been carried out for the Adriatic Sea over a common period (1980-2012). The goal of the study was to test the model performances with different settings, particulary when it comes to reproduction of the Adriatic-Ionian thermohaline properties and variability. The analysis is given in Section 4. Simulations differ in resolution, model physics, atmospheric forcing (forced vs. coupled models) and river discharges imposed within the Adriatic Sea. Models have been evaluated on the long-term temperature and salinity measurements in all of the Adriatic sub-basins, in particular within dense water collectors (Jabuka Pit and South Adriatic Pit) and dense water formation sites (northern and southern Adriatic). Adriatic-wide salinity values are mostly linked to the proper introduction of the overall water budget, rather than to the local river forcing. Forced models mostly overestimate temperature and salinity values. On average, coupled models better reproduce the thermohaline properties and processes, in particular the BiOS reversals and its decadal variability. Wintertime heat losses are playing major role in defining the ADW transport rates in coupled models, while preconditioning in salinity is the most important factor in forced models. Further on, increase of resolution of the atmospheric forcing results in more realistic ocean dynamics, including the DWF in the complex coastal northern Adriatic. However, all models have large positive temperature biases at the dense water collector sites, indicating overall underrepresentation of the Adriatic DWF. Consequently, mixed-layer depth in the southern Adriatic is overestimated, reaching the bottom during some years and in some models. Ocean model resolution and river forcing seem to play a second-order role in defining the overall Adriatic-Ionian thermohaline properties, while inclusion of aerosol trend only slightly modified the reproduction of the BiOS. Lastly, a preliminary analysis of future projections which contain the very first attempt to quantify the processes of the DWF and the BiOSin the future climate, is described in Section 5. This also applies to the evolution of surface temperatures and salinities. The NEMOMED8 simulations were forced by three future scenarios of Representative Concentration Pathways (RCP, IPCC, 2013): RCP2.6, RCP4.5 and RCP8.5. The analysis is performed for the three future periods: near (2011-2040), middle (2041-2070), and far future (2071-2100), with respect to the last 30 years of the referent period simulated in historical simulation (1976 -2005). No significant trends in all analyzed parameters were found in control simulation covering the period 1950-2100. Towards the end of 21st century, under all three scenarios, gradual increase in basin-wide sea surface temperature (SST) was found, of which RCP8.5 is resulting with highest SST at the end of the 21st century, about 2.7 oC on average. All scenarios result also in an increased sea surface salinity (SSS), more pronounced at the coastal parts of the Adriatic, with highest increase found in RCP8.5. All three scenarios show a decrease in maximum mixed layer depth (MLD), suggesting a weakening of deep convection processes by the end of the 21stcentury. As for the analysis of the BiOS related processes, all scenarios are projecting an increase in intensity of the positive BiOS index (anticyclonic circulation in northern Ionian Sea), which favors the advection of less saline water masses coming from the Western Mediterranean to the Adriatic. The strengthening of the both positive and negative BiOS regimes is only projected with RCP8.5 scenario, more pronounced in the anticyclonic phase

    Razvoj i implementacija termo-mehaničkog konstitutivnog modela za numeričku analizu ponašanja materijala sa svojstvom pamćenja oblika

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    Shape memory alloys (SMA) have wider and more frequent application in cases when it is useful to employ their advantages through specific behavior (pseudoelasticity and shape memory effect) in various conditions. As a side effect due to the high thermosensitivity, strong thermomechanical coupling occurs what increases the need for simulation of complex thermomechanical response in realistic problems. The complex stress states and deformation range impose the requirements for accurate analysis of large strain problems. The presented requirements are solved in several steps: (1) Phenomenological constitutive SMA model (Lagoudas) has been reformulated by derivation of variables to depend on effective values of stress and strain and martensitic volume fraction. Gibbs free energy is reduced to scalar form what provides stress integration in the direction of deviatoric stress for forward transformation or total transformation strain for the reverse transformation. (2) Simulation of SMA thermomechanical behavior is realized using partitioned approach by coupling of programs for structural analysis - PAK-S and heat transfer PAK-T. Dissipative energy of martensitic phase transformation imposes change of the material temperature as an internal heat source. As a communication interface between the PAK-S and PAK-T, Component Template Library (CTL) is used. (3) Extension to the large strain problems is based on multiplicative decomposition of the deformation gradient to decompose deformation on elastic and inelastic part. Using the energy conjugated stress and strain measures, easy extension of the algorithm for small strain is provided to solve complex stress states for large strains. (4) Experimental investigation of TiNi SMA samples under various loading rates is used for verification of thermo-mechanical coupling. Numerical simulation of initiation, development and saturation of the martensitic phase transformation under various loading rates is compared to experimental results to show qualitative and quantitative accuracy of such approach. Extension to large strain problems is realized using the logarithmic strain. Simulation of the chosen examples from literature, the functionality and accuracy of the presented approach is verified

    Experimental and FE Modeling Investigation of Spot Welded Thin Steel Sheets

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    The spot welded thin steel sheets specimens are experimentally and numerically examined in this paper. The two specimens are joined using Resistance Spot Welding (RSW) method. The spot-welded joints consist of three zones with different material properties. Change of material properties during the welding process is caused by mechanical and thermal loading. The mechanical properties of thin steel sheets are determined by several tension tests. The specimens are cut in three different directions regarding a rolling direction of the basic material plate. Shear resistance of the spot welded joints is experimentally examined on the universal testing machine by displacement-controlled tensile loading tests. The numerical analysis is performed by large-strain plasticity theory implemented into a Finite Element Method based software. Comparison of the Finite Element (FE) modeling and experimental results verifies the proposed stress integration algorithm and modeling technique as powerful tools for prediction of the spot-welded joint behavior

    Kvalitet života bolesnika s venskim ulkusima

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    Introduction. Chronic venous disease has been shown to have a significant impact on patients' quality of life (QoL). Objective. The aim of this study was to estimate the impact of chronic venous insufficiency (CVI) on QoL in patients with terminal stages of HVI, classified according to the CEAP clinical classification into classes C5 (healed ulcers) and C6 (active ulcers), on admission and after applied therapy. Methods. A cross-sectional study performed between October 2007 and June 2008 in a Belgrade outpatient clinic involved a total of 82 patients with venous ulcers (38 C5 and 44 C6) examined at the beginning of therapy. Of these, 14 C5 and 15 C6 patients in remission were re-examined after therapy from November 2007 to January 2010. QoL was assessed using a standard short-form (SF-36) questionnaire, and additionally by a brief CVD questionnaire specific for chronic venous disease. Results. At the beginning of therapy the SF-36 scores showed significant (p lt 0.05) reductions in all QoL domains of C5 and C6 patients regarding physical, general health, and vitality in C5 and C6 patients. After therapy QoL was significantly improved in both classes of patients, but remained unchanged in the domain of emotional functioning suggesting the patients' fear and worry of HVI progression. Conclusion. In patients with terminal stages of CVI QoL was decreased at the beginning of therapy, but with the remission of the disease and ulcer healing it was significantly improved. This indicates the significance of prevention and timely treatment, and the need for patients' education about the chronic nature of the disease.Uvod. Istraživanja vršena poslednjih decenija pokazuju da hronično oboljenje vena i hronična venska insuficijencija (HVI) nepovoljno utiču na kvalitet života bolesnika. Cilj rada. Cilj studije bio je da se utvrdi uticaj HVI na kvalitet života bolesnika u terminalnoj fazi HVI, svrstanih prema klasifikaciji CEAP u klasu 5 (zarasli ulkusi) i klasu 6 (aktivni ulkusi), na prijemu i posle primenjene terapije. Metode rada. Istraživanje je izvedeno u dve faze. Prva faza je dizajnirana kao studija preseka u kojoj su od oktobra 2007. do juna 2008. godine ispitana 82 bolesnika s venskim ulkusima (38 je pripadalo klasi 5, a 44 ispitanika su pripadala klasi 6). U drugoj fazi, izvedenoj od novembra 2009. do januara 2010. godine, 14 ispitanika klase 5 i 15 bolesnika klase 6 iz prve faze ispitano je nakon primenjene terapije, u periodu remisije HVI. Kvalitet života je ocenjen primenom standardnog upitnika SF-36 i originalnog upitnika specifičnog za hronično oboljenje vena. Rezultati. Svi ispitanici su na početku lečenja imali značajno slabiji kvalitet života u domenima onesposobljenosti zbog fizičkog zdravlja, opšteg zdravlja i vitalnosti. Nakon primenjene terapije, njihov kvalitet života se značajno poboljšao u svim domenima zdravlja, ali je ostao nepromenjen u domenu emotivnog funkcionisanja. Nepromenljivost ovoga domena u obe klase bolesnika ukazuje na njihovu zabrinutost i strah od napredovanja oboljenja. Zaključak. Kvalitet života bolesnika u terminalnim fazama HVI je smanjen na početku lečenja, ali se s remisijom bolesti i zarastanjem ulkusa značajno poboljšava. Ovo ukazuje na značaj edukacije bolesnika o hroničnoj prirodi oboljenja i potrebi za prevencijom i blagovremenim lečenjem
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