Littérature scientifique sur le sujet « Densità di energia »

The density test for soil in the laboratory can be a mild density test (standard proctor) and a modified density test (modification proctor). Both types of compaction provide different levels of density. This paper aims to analyze the energy produced by both types of compaction. The results show that the compaction modification energy is greater than the standard compaction energy. These results are influenced by the number of layers and the difference of the mass of the pounder on both types of compactionKey words: compaction energy, standard proctor, modified proctor

Kebutuhan energi listrik menjadi isu penting yang dapat mendorong daya saing Indonesia di kancah perekonomian dunia. Saat ini, Indonesia masih menggunakan energi yang bersumber dari fosil. Energi fosil adalah energi yang tidak terbarukan sehingga akan habis pada suatu masa. Kemampuan Indonesia dalam menghasilkan energi listrik terbarukan merupakan solusi dari permasalahan tersebut. Salah satu sumber energi listrik terbarukan berasal dari Pembangkit Listrik Tenaga Bayu (PLTB). Penelitian ini bertujuan memetakan sumber energi PLTB di perairan Indonesia dengan menggunakan data dari satelit ASCAT. Penelitian ini dimulai dengan mengumpulkan data harian kecepatan bayu periode 01 Januari 2017 sampai dengan 31 Desember 2018. Data tersebut merupakan data pada ketinggian 10 m, dengan menggunakan model matematis data tersebut kemudian diolah agar didapatkan kecepatan bayu serta power density pada ketinggian 120 m. Langkah selanjutnya adalah pembuatan peta potensi PLTB di perairan Indonesia. Dari peta tersebut, diketahui bahwa perairan Indonesia di Samudera Hindia dan Laut Arafura memiliki potensi yang lebih baik dari pada perairan lainnya. Kecepatan bayu rata-rata pada ketinggian 120 m adalah 9,24 m/s, sedangkan rata-rata power density sebesar 955,64 W/m2. Jumlah turbin yang dapat dibangun di wilayah ZEE Indonesia adalah sebanyak 4.800.292 unit dengan jumlah tersebut maka dapat menghasilkan energi listrik sebesar 10.080 GW.

Arus Laut merupakan salah satu sumber energi terbarukan yang potensial untuk dikembangkan mengingat banyaknya pulau dan selat yang ada di Indonesia. Selat Sunda yang berada di antara Samudera Hindia dan Laut Jawa yang dipengaruhi oleh massa air dari Samudera Pasifik menjadi salah satu lokasi potensial. Tujuan dari penelitian ini adalah untuk mengetahui karakteristik arus laut beserta potensi energi arus laut yang dihasilkan. Penelitian ini menggunakan metode kuantitatif dan penentuan lokasi dengan metode sampling area. Pengolahan data dibagi menjadi tiga tahap yaitu analisa data arus dan pasang surut, pemodelan numerik dan perhitungan estimasi rapat daya. Hasil menunjukkan bahwa kecepatan arus maksimum sebesar 1.95 m/s. Daya terbesar dihasilkan pada saat kondisi surut menuju pasang yaitu sebesar 4.51 W/m2 di daerah antara Pulau Peucang dan Ujung Kulon. Ocean current is one of the potential renewable energy sources to be developed considering there are many islands and straits that exist in Indonesia. Sunda strait that located between Indian Ocean and Java Sea be affected water masses from Pacific Ocean to be one of potential location. The purpose of this study is to determine the characteristics of ocean currents and the potential of ocean current energy that can be generated. This study used a quantitative method and determination of the location with sampling area. Data Processing is divided into 3 major phases which is analysis for currents and tides, numerical modeling and calculation of power density estimation. The results showed that the maximum of ocean current velocity is 1.95 m/s. The biggest power density is generated during ebb to flood is 4.51 W/m2in the area between Peucang island and Ujung Kulon.

Latar Belakang : Kualitas diet rendah dikaitkan dengan konsumsi makanan berdensitas energi tinggi yang secara langsung berkontribusi dalam peningkatan asupan energi total dan berakibat pada peningkatan Indeks Massa Tubuh (IMT). Penelitian ini bertujuan untuk menganalisis hubungan antara densitas energi dan kualitas diet dengan IMT (Indek Massa Tubuh) pada remaja. Metode : Penelitian observasional dengan pendekatan cross sectional, bertempat di SMA N 9 Semarang dengan jumlah sampel 71 remaja usia 16-18 tahun yang dipilih dengan simple random sampling. Data yang dikumpulkan meliputi identitas sampel, Indeks Massa Tubuh (IMT), densitas energi, kualitas diet, dan aktisfitas fisik. IMT diperoleh dari perhitungan Z-score berdasarkan BMI/U, densitas energi menggunakan recall 3x24 jam, kualitas diet menggunakan formulir DQI-I (Diet Quality indexs International), dan aktifitas fisik menggunakan kuisioner IPAQ (International Physical Activity Questionnaire). Data dianalisis dengan uji rank spearman. Hasil : Konsumsi makanan berdensitas energi tinggi lebih banyak pada perempuan (32,4%) dibandingkan laki-laki (5,9%). Kualitas diet pada laki-laki 8,8% tergolong tinggi sedangkan pada perempuan 100% tergolong rendah. Gizi lebih (obesitas dan overweight) pada remaja sebesar 35,2% dan secara umum lebih tinggi pada perempuan 37,8% dibandingkan laki-laki 32,3%. Ada hubungan signifikan antara kualitas diet dengan densitas energi (r = -0,502; p=0,000). Ada hubungan signifikan antara densitas energi dengan IMT (r = 0,569; p=0,000). Namun, tidak terdapat hubungan antara aktifitas fisik dengan IMT (r = -0,194; p=0,106). Simpulan : Remaja yang mengkonsumsi lebih banyak makanan berdensitas energi rendah (buah dan sayur) kualitas dietnya lebih baik dan IMT nya lebih rendah daripada remaja yang mengkonsumsi makanan berdensitas energi tinggi (sumber lemak). Kualitas diet rendah berhubungan dengan tingginya konsumsi makanan berdensitas energi tinggi yang dapat berdampak pada peningkatan IMT.

Latar belakang: Prevalensi hipertensi obesitik terus meningkat dengan cepat khususnya pada remaja. Densitas energi makanan dan hereditas merupakan beberapa faktor risiko hipertensi obesitik. Tujuan dari penelitian ini adalah untuk mengetahui besarnya risiko faktor densitas energi makanan dan hereditas terhadap kejadian hipertensi obesitik pada remaja awal. Metode: Penelitian dilakukan di SMP Negeri 3, SMP Negeri 30, SMP Kesatrian 2, dan Madrasah Al-Khoiriyah. Desain penelitian case-control dengan jumlah subyek 72 yang terdiri dari 36 kasus dan 36 kontrol. Subyek yang dipilih adalah yang memenuhi kriteria inklusi. Data densitas energi makanan didapatkan dengan wawancara menggunakan food frequency questionnaire 1 bulan terakhir. Data hereditas diperoleh dari pengukuran orang tua kandung secara langsung. Pengukuran tinggi badan menggunakan microtoise, berat badan menggunakan timbangan digital, dan tekanan darah menggunakan sphygmomanometer. Hasil: Prevalensi hipertensi obesitas sebesar 7,5%. Ditemukan hubungan yang bermakna antara densitas energi (OR=5,8;CI=2,013–16,715;p=0,001) dan hereditas (OR=4,0;CI=1,518–11,000;p=0,004) dengan kejadian hipertensi obesitik pada remaja awal. Simpulan: Densitas energi makanan dan hereditas merupakan faktor risiko yang bermakna terhadap kejadian hipertensi obesitik pada remaja awal, dengan besar risiko 5,8 kali dan 4,0 kali.

Belum ada kajian yang komprehensif tentang sejauh mana potensi energi angin guna menjadi sumber energi listrik terbarukan di Kota Tarakan. Oleh karena itu, penelitian ini mengusulkan pengembangan aplikasi analisis potensi angin sebagai sumber energi listrik terbarukan di Kota Tarakan menggunakan estimasi parameter Weibull berbasis metode Power Density. Frekuensi kecepatan angin diubah ke dalam bentuk kurva distribusi Weibull berdasarkan parameter bentuk (k) dan skala (s). Kemudian kedua parameter ini dicari menggunakan formulasi Power Density berdasarkan perhitungan rata-rata kecepatan angin dan rata-rata kubik kecepatan angin. Hasil eksperimen aplikasi usulan terhadap 1000 sampel data primer kecepatan angin yang diambil selama 100 hari menunjukkan nilai k dan s adalah 1,32 dan 1,90, sedangkan hasil eksperimen terhadap 48 sampel data sekunder yang diambil per bulan dalam 4 tahun menunjukkan nilai k dan s adalah 2,55 dan 3,42. Kedua jenis data ini mengindikasikan bahwa Kota Tarakan memiliki variabilitas angin tinggi dan lebih banyak berhembus angin kecepatan rendah < 4 m/s. Selain itu, rata-rata potensi daya angin yang dapat diserap turbin skala sangat kecil (diameter 2 m) hanya 13,60 s/d 32,48 watt, sehingga energi angin memiliki potensi yang sangat kecil untuk diterapkan sebagai pembangkit energi listrik di Kota Tarakan.

Pemanas Air Tenaga Matahari (PATM) konvensional umumnya menggunakan air sebagai penyimpan energi termal. Pemakaian sensible heat storage (SHS) ini memiliki kekurangan, diantaranya adalah densitas energinya rendah. Di sisi lain, latent heat storage (LHS) mempunyai sifat khas yaitu densitas energinya tinggi karena melibatkan perubahan fasa dalam penyerapan atau pelepasan kalor. Material LHS sering disebut phase change material (PCM). Penggunaan PCM pada PATM menarik dilakukan untuk meningkatkan densitas energi sistem. Penelitian ini bertujuan untuk menyelidiki perilaku termal penggunaan paraffin wax di dalam tangki PATM jenis thermosyphon. Penelitian menggunakan kolektor matahari pelat datar dan tangki thermal energy storage (TES) yang dipasang secara horisontal di sisi atas kolektor. Di dalam tangki terdapat alat penukar kalor yang terdiri dari sekumpulan pipa kapsul dimana di dalamnya berisi paraffin wax. Air digunakan sebagai SHS dan heat transfer fluid (HTF). Termokopel dipasang di sisi HTF dan sisi PCM. Piranometer dan sensor temperatur udara luar diletakkan di dekat kolektor matahari. Pengambilan data dilakukan selama proses charging. Temperatur HTF, PCM dan intensitas radiasi matahari direkam setiap 30 detik. Data ini digunakan untuk mengetahui evolusi temperatur HTF dan PCM. Berdasarkan evolusi temperatur ini kemudian dianalisis perilaku termal PATM. Hasil dari penelitian ini adalah bahwa paraffin wax telah berfungsi sebagai penyimpan energi termal bersama air di dalam tangki PATM jenis thermosyphon. PCM memberi kontribusi yang cukup signifikan terhadap kapasitas penyimpanan energi sistem. Efisiensi kolektor lebih optimal karena PCM dapat mempertahankan stratifikasi termal sampai akhir charging. Adanya PCM mampu mengendalikan penurunan efisiensi pengumpulan energi saat intensitas radiasi matahari menurun. Alat penukar kalor yang digunakan cukup efektif yang ditandai dengan kecepatan pemanasan rata-rata antara HTF dan PCM yang tidak berbeda jauh.

Latar Belakang: Prevalensi sindrom metabolik pada remaja semakin meningkat karena peningkatan prevalensi obesitas pada remaja. Remaja lebih memilih mengkonsumsi makanan dengan densitas energi tinggi. Lingkar pinggang merupakan salah satu faktor risiko sindrom metabolik menunjukkan adanya inflamasi ringan. Kadar C-Reactive Protein (CRP) meningkat dengan adanya inflamasi. Densitas energi makanan dan lingkar pinggang merupakan faktor risiko peningkatan kadar CRP. Tujuan penelitian ini adalah untuk mengetahui besarnya risiko faktor densitas energi makanan dan lingkar pinggang terhadap peningkatan kadar CRP.Metode: Penelitian dilakukan di SMA Negeri 2 Semarang. Desain penelitian cross sectional dengan jumlah subyek 38. Data sindrom metabolik diperoleh dengan melakukan pengukuran antropometri, tekanan darah dan pemeriksaan lipid darah. Sindrom metabolik dinyatakan apabila memenuhi ≥3 kriteria sebagai berikut: trigliserid ≥110 mg/dl, HDL ≤40 mg/dl, glukosa darah puasa ≥110 mg/dl, tekanan darah dan atau lingkar pinggang ≥ persentil ke-90. Data densitas energi diperoleh dengan wawancara menggunakan food frequency questionaire.Hasil: Prevalensi obesitas sebesar 7,9%. Prevalensi sindrom metabolik pada remaja obesitas 15,2%. Ditemukan hubungan bermakna antara densitas energi (r: 0,506; p: 0,004)dengan lingkar pinggang. Tidak ada hubungan antara densitas energi (r: 0,240; p: 0,430) dan lingkar pinggang (r: 0,433; p: 0,139) dengan peningkatan kadar CRP.Simpulan: Dalam penelitian ini lingkar pinggang terbukti merupakan faktor risiko terhadap peningkatan kadar CRP. Densitas energi makanan tidak terbukti sebagai faktor risiko terhadap peningkatan kadar CRP.

I meccanismi di trasporto di energia nell’universo sono un argomento di fondamentale importanza per ricavare più informazioni possibili riguardo i corpi celesti in cui si origina l’energia. I principali meccanismi di trasporto presenti negli interni stellari sono tre: radiazione, convezione e conduzione (quest’ultimo generalmente trascurabile). Studiando il gradiente di temperatura si potrà comprendere quale meccanismo di trasporto domina sugli altri in una determinata regione stellare. Ad esempio, si possono fare distinzioni importanti tra stelle in base alla loro massa: infatti in stelle massicce è presente una struttura stellare dove nel nucleo dominano i moti convettivi e nell’involucro dominano quelli radiativi, mentre in stelle leggere accade il contrario. Nel principale capitolo del seguente elaborato vengono descritti in maniera sintetica ma esaustiva i tre meccanismi di trasporto appena citati, ricavando le equazioni del flusso di ogni meccanismo, soffermandosi sui criteri che rendono un meccanismo più efficiente di un altro, differenziando i casi di interno stellare ed atmosfera stellare e analizzando i fattori che causano i vari tipi di trasporto e alcune loro conseguenze. Nel capitolo finale viene studiato sinteticamente il trasporto d’energia tramite neutrini, analizzando il caso di neutrini prodotti dalle stelle e il caso di neutrini originati dai raggi cosmici che interagiscono con l’atmosfera terrestre. Questa trattazione è limitata per ovvi motivi di lunghezza dell’elaborato e complessità di alcuni argomenti, ma è una sintesi che racchiude le principali caratteristiche, concetti ed equazioni riguardo questo fondamentale argomento.

Sin dalla sua invenzione, la batteria agli ioni di litio ha dominato il mercato dei sistemi di accumulo elettrochimico, grazie alle sue eccezionali proprietà in termini di energia e densità di potenza. Tuttavia, il fatto che questa tecnologia sia indissolubilmente legata a risorse rare e disomogenee distribuite, per lo più litio e cobalto, rende indispensabile avere delle alternative, se non sostituirla completamente almeno per diversificare il mercato e ridurre la dipendenza dai suddetti risorse rare. Due esempi di tali alternative sono la batteria agli ioni di Na e il condensatore elettrochimico a doppio strato. Questi dispositivi hanno la possibilità di competere con i LIB in alcune situazioni, ma entrambi potrebbero trarre grandi benefici da un aumento della loro densità di energia. Inoltre, il monitoraggio dell'evoluzione delle loro prestazioni dovrebbe essere considerato una priorità al fine di ottenere informazioni più approfondite su come migliorarle in modo da renderle paragonabili alle LIB. La ricerca di dottorato qui descritta si è concentrata su due obiettivi principali: proporre modi per migliorare la densità di energia dei sistemi di accumulo (NIB e EDLC) e suggerire una nuova tecnica per monitorare tali dispositivi operando: la spettroscopia di impedenza elettrochimica dinamica. La fabbricazione di elettrodi ad alto potenziale è un modo per migliorare le capacità di accumulo di energia di una batteria agli ioni di Na. In questa tesi è stato sintetizzato Na3V2(PO4)2F3, un materiale attivo in grado di immagazzinare ioni sodio ad un potenziale medio di 3,8 V vs Na+/Na. Questo materiale è stato utilizzato per fabbricare elettrodi massicci autoportanti (carico di massa attiva: 25 mg cm-2), che si è rivelato un metodo molto interessante per migliorare la densità di energia. L'NVPF è stato anche testato come un vero catodo in una cella a ioni di sodio completa in modo da dimostrarne l'alto potenziale e i relativi problemi. Per migliorare le densità energetiche degli EDLC, sono state preparate e studiate soluzioni altamente concentrate di acetato di potassio in acqua dalla loro caratterizzazione fisico-chimica ed elettrochimica all'uso di quelle più concentrate (elettrolita acqua-in-sale) in EDLC simmetrici a base di carbonio. Tali soluzioni si sono rivelate in grado di aumentare sia la capacità che la massima differenza di potenziale raggiungibile tra i due elettrodi, risultando in densità di energia maggiori rispetto agli elettroliti convenzionali (es. soluzione 6M KOH in acqua). Infine, la spettroscopia di impedenza elettrochimica dinamica è stata valutata come metodo per studiare NIB ed EDLC durante il ciclo. Due sistemi, un EDLC acquoso e un materiale di inserimento per NIBs, sono stati analizzati con dEIS: una tecnica in grado di monitorare i cambiamenti temporali nella spettroscopia di impedenza elettrochimica mentre un dispositivo subisce un processo ciclico. Questo approccio si è rivelato fattibile sia per le tecniche potenziodinamiche che per quelle galvanostatiche, consentendo di sondare l'impedenza dei singoli elettrodi anche in condizioni sperimentali simili a quelle con cui opera un dispositivo reale.<br>Ever since its invention, the Li-ion battery has dominated the market of electrochemical storage systems, thanks to its outstanding properties in terms of energy and power density. However, the fact that this technology is inextricably linked to non-homogenously distributed and rare resources, mostly lithium and cobalt, makes it essential to have alternatives, if not to completely replace it at least to diversify the market and reduce the dependence on the aforementioned rare resources. Two examples of such alternatives are the Na-ion battery and the electrochemical double-layer capacitor. These devices have the chance to compete with LIBs in some situations but both of them could greatly benefit from an increase in their energy density. Also, monitoring the evolution of their performances should be considered a priority in order to get deeper insights on how to improve them so to make them comparable to LIBs. The doctoral research here described was focused on two main objectives: proposing ways to improve the energy density of storage systems (NIBs and EDLCs) and suggesting a new technique to monitor such devices operando: the dynamic electrochemical impedance spectroscopy. Fabricating high potential electrodes is a way to improve the energy storage capabilities of a Na-ion battery. In this thesis, Na3V2(PO4)2F3, an active material able to store sodium-ions at a mean potential as high as 3.8 V vs Na+/Na, was synthesised. This material was used to fabricate self-standing massive electrodes (active mass loading: 25 mg cm-2), which proved to be a very interesting method to improve the energy density. NVPF was also tested as an actual cathode in a full sodium-ion cell so to prove its high potential and relative issues. To improve EDLCs energy densities, highly concentrated solutions of potassium acetate in water were prepared and studied from their physicochemical and electrochemical characterization to the use of the highest concentrated ones (water-in-salt electrolyte) in symmetric carbon-based EDLCs. Such solutions proved to be able to increase both the capacitance and the maximum reachable potential difference between the two electrodes, resulting in higher energy densities compared to conventional electrolytes (e.g. 6M KOH solution in water). Finally, dynamic electrochemical impedance spectroscopy was evaluated as a method to study NIBs and EDLCs while cycling. Two systems, an aqueous EDLC and an insertion material for NIBs, were analysed with dEIS: a technique able to monitor the temporal changes in the electrochemical impedance spectroscopy while a device undergoes a cycling process. This approach proved to be doable for both potentiodynamic and galvanostatic techniques, allowing to probe the impedance of the single electrodes even in experimental conditions similar to those with which a real device operates.

Lo scopo dell'elaborato è quello di fornire una trattazione generale sul modello del Big Bang, sul modello cosmologico e sulla materia oscura. La cosmologia si occupa della struttura e dell'evoluzione del cosmo, cercando di risalirne alle origini e si è cominciata ad imporre come scienza grazie alle scoperte astronomiche del secolo scorso. Partendo dal concetto di redshift, i lavori di Edwin Hubble e Georges Lemaître sulle velocità di recessione delle galassie, hanno portato a parlare di espansione dell'universo. Tra le teorie circa l'origine dell'universo si è affermata quella del Big Bang, che è la più accreditata dai dati osservativi quali il problema dell’elio con la nucleosintesi primordiale, la scoperta della radiazione cosmica di fondo CMB e la teoria dell’inflazione. Nel corso degli ultimi anni il modello cosmologico è diventato sempre più complesso ed accurato anche alla base delle nuove scoperte. Nell'elaborato si mettono in evidenza i modelli cosmologici possibili dandone sia una trattazione geometrica con le equazioni di Newton, sia una qualitativa in termini di densità di materia ed e energia con le equazioni di Friedmann. Ci si concentra maggiormente sul modello cosmologico standard, quello attualmente adottato, per il quale i contributi principali sono quelli di un’energia e di una materia oscura che ad oggi rappresentano uno degli interrogativi più grandi legati al nostro universo. Alla materia oscura è dedicata la parte finale tramite un percorso storico con i calcoli legati alla sua ipotesi e il dettaglio della sua interazione gravitazionale con la materia ordinaria che ne ha confermato la presenza.

L'industria automobilistica è in anticipo rispetto all'aviazione per quanto riguarda l’applicazione del sistema di propulsione elettrico puro. Anche se esistono similitudini tra i due settori, differenze come intervalli di temperature operative, limiti di peso e requisiti di sicurezza rendono necessario lo studio in modo separato dello spazio di progettazione del sistema di propulsione. Gli strumenti di progettazione degli aeromobili tradizionali, non sono in grado di spiegare e modellare i significativi cambiamenti inerenti agli aeromobili progettati attorno ai sistemi di propulsione elettrica. I sistemi dipendenti dalla batteria, ad esempio, non hanno un significativo cambiamento di peso durante il volo, rendendo inutilizzabili le numerose routine di calcolo delle variazioni del peso dell'aeromobile a causa della riduzione della combustione del carburante. Lo scopo di questa tesi è di analizzare la possibilità di implementare un sistema di propulsione elettrica su un aereo leggero e discutere le questioni che dovrebbero essere ulteriormente modificate, se ce ne sono, affinché le sue prestazioni corrispondano il più fedelmente possibile al modello non modificato. Per poterlo fare, è stata condotta un'approfondita ricerca sullo stato attuale di sviluppo delle tecnologie utilizzate in questo tipo di applicazione, prestando particolare attenzione ai miglioramenti apportati negli ultimi anni vista la relativa novità di questa tecnologia di propulsione. Più precisamente si tratta di modificare o sostituire l’attuale sistema di propulsione convenzionale di un CESSNA 172K con un sistema propulsivo elettrico puro e di valutare i consumi energetici e le prestazioni di volo per una data missione.

In steel megastructures welding is a widely used and accepted joining technique. However, welds are geometrical discontinuities, resulting in severe local stress gradients, which strongly affect the fatigue strength of components. Advanced fatigue assessments are usually based on the local stress and strain state in the close neighborhood of such stress raisers. Despite this, current standards are lacking in giving a real guidance on how to perform a reliable fatigue assessment. Still, most of them do not refer to any local concept and lead to the nominal stress method. Even so, no recommendations exist on how to derive the nominal stress from a finite element (FE) model and it is left to the engineering assessment of a designer to establish which nominal stress is the right one. Within this framework, the present Ph.D. thesis, focused on making the fatigue assessment of large steel structures possible, is divided into ten chapters. Purposes of this thesis are both giving scientific contributions to advanced local approaches for fatigue assessment and developing a method fully compliant with current standards, in order to be employed in the industrial context. In the first chapter, a general introduction and the state of the art on fatigue design of welded structures are presented, with the aim to clarify the motivations of the present research work. In the second chapter, the adopted local approaches, namely the notch stress intensity factor (NSIF) based approach, the averaged strain energy density (SED) criterion and the peak stress method (PSM), are briefly introduced and described along with their theoretical frameworks. The third chapter deals with the fatigue behavior of large-scale welded cover plates, for which non uniform fatigue classification is highlighted at standards’ level. Through the application of the SED approach and adopting both bi-dimensional and three-dimensional FE models, parameters which mainly affect the fatigue strength are identified and alternatives to those provided by standards are proposed. Experimental data of four geometric variants are successfully summarized into a unique scatter band in terms of SED, regardless of the weld geometry. The suitability of the SED approach and of the related design curve to perform the fatigue assessment of welded cover plates is, therefore, not proven wrong. The fourth chapter is focused on the local SED numerical computation. Its principal drawback, consisting in the need of a specific control volume centered on a notch tip (i.e. at the weld toe and at the weld root in case of welded joints), within which the strain energy density has to be averaged, is overcome by using coarse meshes completely free-generated. The method and its limitations are formalized. For the sake of generality, some practical applications are given by using both Ansys® and Straus7® FE software. Robustness in terms of insensitivity to mesh pattern, mesh refinement and FE formulation are proven advantages of the method. The fifth chapter establishes a link between local stress fields, near weld toes and roots, and the nominal stress components evaluated at a proper distance from the weld. An analytical relationship between such distance and the loaded plate thickness is provided. A criterion to estimate SED values, both at the weld toe and at the weld root, as well as a posteriori the related NSIFs, as an explicit function of the nominal load components (membrane loads, shear loads and bending moments) is also presented. The proposed method is suitable for automation to perform the large number of fatigue assessments that a nowadays complex steel structure requires. However, the current lack of normative compliance of both SED and NSIF approaches can be a possible obstacle in industrial applications. That is why in the sixth chapter a method, scientifically and normatively compliant, to improve the classical nominal stress approach for welded structures, which is still the most widely accepted and recognized in standards, is proposed. The methodological problem of the nominal stress definition is overcome through an original, finite element based approach, which takes into account both membrane and bending effects. An experimental validation is presented and the implications in fatigue design of large steel structures are discussed. The seventh and eighth chapters present a finite element post-processor, developed to perform the almost automatic fatigue assessment of a large structure. The post-processor is compatible with Straus7® finite element solver and it is based on shell models to be suitable for large assemblies. Many of the findings of the present research work are automated: local SED and NSIF approaches are implemented, as well as the modified nominal stress and, finally, the classical nominal stress and hot spot stress approaches. A very good agreement between “manually” performed assessments, both through global and local approaches, and those rapidly performed by using the post-processor is found. Further good agreement is found between expected fatigue lives estimated through the local SED approach and those estimated through the modified nominal stress, in the presence of bending stresses. The ninth chapter deals with the rapid estimation of residual notch stress intensity factors (R-NSIFs), due to the welding process, by using the PSM and Sysweld® FE dedicated software. First, the calibration of the PSM in Sysweld® environment is presented; afterwards, practical applications of the PSM to evaluate the R-NSIFs are illustrated. Finally, the tenth chapter presents some overall concluding remarks, in order to discuss the main obtained results.<br>Nelle megastrutture in acciaio la saldatura è una tecnica di giunzione ampiamente utilizzata. Tuttavia, le saldature rappresentano delle discontinuità geometriche e introducono elevati gradienti tensionali locali che influiscono negativamente sulla resistenza a fatica dei componenti. Secondo la letteratura scientifica recente, le analisi di resistenza a fatica più avanzate si basano sugli stati di tensione o deformazione locali calcolati in prossimità dei punti singolari. Ciononostante, le normative vigenti mancano di fornire una guida reale su come eseguire tali stime della resistenza fatica: la maggior parte di esse non fa riferimento agli approcci locali e prevede l'impiego del metodo della tensione nominale. Tuttavia, non esistono raccomandazioni su come ottenere la tensione nominale mediante un modello agli elementi finiti ed è demandato alla capacità ingegneristica del progettista stabilire quale sia quella adeguata. In questo contesto, la presente tesi di dottorato, focalizzata sul rendere possibile la stima della resistenza a fatica delle grandi strutture in acciaio, è divisa in dieci capitoli. Scopo della tesi è sia fornire un contributo scientifico ad alcuni tra i più avanzati approcci locali per la stima della resistenza fatica, che sviluppare un metodo pienamente conforme alle normative vigenti, al fine di poter essere impiegato nel contesto industriale. Il primo capitolo rappresenta l'introduzione generale sul tema trattato, lo stato dell'arte in materia di progettazione a fatica delle strutture saldate e le motivazioni della presente ricerca. Nel secondo capitolo vengono introdotti gli approcci locali adottati e le loro basi teoriche: l'approccio basato sui fattori di intensificazione delle tensioni (NSIF), il criterio della densità di energia di deformazione (SED) e il metodo della tensione di picco (PSM). Il terzo capitolo riguarda la caratterizzazione a fatica dei coprigiunti saldati, tipicamente impiegati come rinforzo nelle travi da ponte, per i quali è stata evidenziata una non uniforme classificazione a fatica a livello normativo. Mediante l'impiego dell'approccio locale SED e adottando modelli agli elementi finiti sia bidimensionali che tridimensionali, sono stati isolati i parametri che influiscono sensibilmente la resistenza e proposte soluzioni ottimizzate rispetto a quelle fornite dalle normative. I dati sperimentali ottenuti testando a fatica quattro differenti soluzioni geometriche sono sintetizzati con successo in un'unica banda di dispersione in termini di SED, indipendentemente dalla geometria della saldatura. L'approccio locale SED e la relativa curva di progettazione si sono dimostrati quindi adatti a stimare la resistenza a fatica dei coprigiunti saldati in acciaio. Il quarto capitolo è incentrato sul calcolo numerico del SED. La principale criticità dell'approccio, rappresentata dalla necessità di uno specifico il volume di controllo localizzato all'apice di un intaglio strutturale (al piede e alla radice dei cordoni di saldatura, nel caso dei giunti saldati), entro il quale l'energia di deformazione deve essere calcolata e mediata, è superata mediante l'utilizzo di maglie di calcolo (mesh) rade e generate in maniera completamente automatica da un generico algoritmo di meshatura. La soluzione proposta e le relative limitazioni di applicabilità sono stati formalizzati. La robustezza in termini di insensibilità alla tipologia di mesh, alla sua raffinatezza e alla formulazione degli elementi finiti sono alcuni dei vantaggi provati. La generalità del metodo è dimostrata anche mediante alcune applicazioni pratiche con l'impiego di differenti software agli elementi finiti. Il quinto capitolo stabilisce un collegamento tra i campi di tensione locali, in prossimità del piede e della radice dei cordoni di saldatura, e le componenti di tensione nominale valutate ad una adeguata distanza dalla saldatura stessa. Nel capitolo viene fornita una relazione analitica tra tale distanza e lo spessore della piastra caricata; inoltre, viene presentato un criterio per stimare il valore del SED, sia al piede che alla radice dei cordoni di saldatura, e, a posteriori, i relativi NSIFs, come esplicita funzione delle componenti di tensione nominale (sollecitazione membranale, flessionale e tagliante). Tale metodo si presta all'automatizzazione e, quindi, a condurre l'enorme quantità di verifiche a fatica richieste per una complessa struttura saldata in acciaio. Tuttavia, l'attuale mancanza di conformità normativa degli approcci locali SED e NSIF rappresenta un possibile ostacolo nelle applicazioni industriali. Per questo motivo nel sesto capitolo viene proposto un metodo, conforme alle normative vigenti e alla letteratura scientifica, per modificare il classico approccio nominale, che tuttora è il metodo di riferimento ampiamente accettato e riconosciuto. Il problema metodologico della definizione di tensione nominale in un modello agli elementi finiti viene superato attraverso un approccio originale che tiene conto sia degli effetti membranali che di quelli di flessionali. Viene presentata una validazione sperimentale e vengono discusse le implicazioni nella progettazione a fatica delle grandi strutture in acciaio. I capitoli settimo e ottavo presentano un post-processore ad elementi finiti, sviluppato per automatizzare l'analisi della resistenza a fatica di una struttura di grandi dimensioni. Il post-processore è basato sul solutore ad elementi finiti Straus7® ed è compatibile con modelli di tipo shell per essere adatto ai grandi assiemi strutturali. Molte delle proposte illustrate nella presente tesi sono state quindi automatizzate: gli approcci locali SED e NSIF, il metodo della tensione nominale modificato e, infine, gli approcci classici basati sulla tensione nominale e di hot spot. È inoltre mostrato un ottimo accordo tra le analisi condotte "manualmente", sia attraverso approcci globali che locali, e quelle eseguite rapidamente utilizzando il post-processore, riscontrando generalmente un ottimo accordo tra la vita a fatica stimata mediante l'approccio locale SED e quella stimata attraverso il metodo della tensione nominale modificata. Il nono capitolo tratta la stima rapida dei fattori di intensificazione delle tensioni residue (R-NSIFs), conseguenti al processo di saldatura, utilizzando il PSM e il software agli elementi finiti dedicato Sysweld®. Innanzitutto, viene presentata la calibrazione del PSM in ambiente Sysweld®; quindi vengono illustrate alcune applicazioni pratiche. Infine, il decimo capitolo riporta alcune osservazioni conclusive di carattere generale e la discussione dei principali risultati ottenuti.

This research focuses on the stress analysis of periodic notches by using the strain energy density approach. Bolts, screws and rotary-shouldered connections, as examples of periodic notched components, play an important role in the performance of the machinery. The contents are related to two-dimensional (2D), as well as three-dimensional (3D) modeling of periodic notches both in the case of round and sharp notches. The analyses are based on the numerical modeling of periodic notches with linear elastic assumption of the material. The simple analytical expressions for the notch stress intensity factors (NSIFs) of periodic sharp notches, as well as theoretical stress concentration factors (SCFs) of periodic blunt notches are obtained. Using the strain energy density (SED) approach, the coarse mesh in the finite element models is used and compared with the results obtained from the fine meshing. In fact, using SED approach, the averaged strain energy in a control volume allows using the coarse meshes in order to determine the NSIFs and SCFs of notched components precisely. In the case of 3D analysis, the thickness effects with particular attention on coupling modes, which due to Poisson effect are automatically generated, are studied. These modes can have a significant effect on the structural integrity of mechanical components. In addition, two collaborative industry projects with: Officine Meccaniche Zanetti s.r.l. and Omera s.r.l. are successfully implemented.<br>Questa ricerca si concentra su "Analisi delle sollecitazioni di intagliati periodici utilizzando l'approccio di densità di energia di deformazione", si è occupato di problematiche relative alla modellazione bidimensionale e tridimensionale di intagli periodici raccordati e a spigolo vivo. Bulloni, viti e connessioni rotanti spalle, come esempi di componenti intagliati periodiche, svolgono un ruolo importante nelle performance delle macchine. L'attività ha coinvolto prevalentemente la modellazione numerica in campo elastico ed ha permesso di ottenere delle semplici espressioni per la stima dei fattori d’intensificazione delle tensioni (NSIFs) e dei fattori teorici di concentrazione delle tensioni (SCFs) in funzione di tutti i parametri geometrici considerati. Le analisi numeriche sono state effettuate in prima battuta con mesh fitte e successivamente con mesh molto rade. Nel secondo caso l’energia di deformazione mediata in un volume di controllo ha permesso di determinare con precisione i fattori tensionali di riferimento e alcune espressioni per l’applicazione diretta a problematiche simili. Nel caso tridimensionale sono stati studiati e analizzati gli effetti legati allo spessore con particolare riferimento ai modi accoppiati che vengono automaticamente generati per effetto Poisson e che possono incidere in modo rilevante sull’integrità strutturale di componenti meccanici. I risultati raggiunti sono stati applicati a casi aziendali con due collaborazioni tutt’ora in atto con Officine Meccaniche Zanetti e Omera formalizzate in progetti di ricerca in cui il dottorando è stato il principale protagonista.

Deliberately created or inadvertently induced, notches and defects unavoidably exist in engineering components. Then, fatigue strength assessments often need linear and nonlinear stresses and strains at the notch root or in the close neighbourhood of it. Whilst there is a large body of work on notch root stresses under tensile loading, in the previous literature there has been relatively little attention paid to torsional loading of prismatic shafts. Nevertheless, the engineering use of torque carrying shafts is extensive and they are susceptible to crack formation at notches and grooves under both static and cyclic conditions. In this work, a comprehensive evaluation of the components of the linear and non-linear stress fields ahead various kind of mode III loaded notches is presented. These expressions are also used to provide closed form solutions for some local parameters such as the averaged strain energy density and Rice J-integral. Finally an assessment of fatigue strength of welded joints subjected to multiaxial loading (combined Mode I and Mode III) as well as to complex three-dimensional welded joints based on the local energy is presented.<br>Variazioni geometriche, come fori e intagli, sono comunemente presenti nella maggior parte dei componenti meccanici. Tali discontinuità, causa di una perturbazione della distribuzione di tensione nominale, comportano un aumento locale delle tensioni e delle deformazioni. La conoscenza delle distribuzioni di tensione nelle adiacenze di tali variazioni geometriche è quindi di grande importanza nella valutazione della resistenza a fatica di componenti strutturali. Mentre in letteratura vi sono numerose soluzioni teoriche per componenti piani soggetti a trazione o flessione, relativamente pochi sono i contributi relativi a casi di torsione in travi prismatiche o assialsimmetriche. Tuttavia, gli alberi soggetti a coppia torcente rappresentano un caso di notevole interesse applicativo, essendo potenzialmente interessati da fenomeni di innesco e propagazione di cricche di fatica dovute a effetti di intaglio di diverso tipo. Il lavoro riporta delle soluzioni analitiche in forma chiusa per le distribuzioni di tensione generate da intagli circonferenziali in componenti assialsimmetrici soggetti a torsione, in condizioni lineari elastiche ed elastoplastiche. Tali soluzioni sono inoltre utilizzate per determinare delle espressioni in forma chiusa per alcuni parametri locali, quali la densità di energia di deformazione e il J-integral di Rice, e per discutere dal punto di vista teorico alcuni aspetti peculiari relativi all’effetto d’intaglio in presenza di sollecitazioni torsionali. Viene infine proposta una sintesi di un elevato numero di risultati sperimentali, tratti dalla letteratura, relativi a giunzioni saldate tridimensionali soggetti a fatica monoassiale (trazione o flessione) e multiassiale (Modo I e Modo III combinati) in termini di densità di energia di deformazione.

Fatigue life assessment is the key task of the design of mechanical components subjected to service loads for avoiding failure occurring in the form of incipient cracks which may cause damages to the entire mechanical system or even worse to people. The nowadays industrial applications increasingly require mechanical components having complex geometry subjected to complex loading conditions. Considering the guidelines of the fatigue design of welded joints as an example, the standards report several stress-based fatigue design curves each one related to the most common welded structural details under a given loading direction. For this reason, by adopting the nominal approach, if the welded detail is different from those reported in the standards, the choice of the proper design fatigue curve might not be done for certain. This dissertation deals with fatigue assessment of metallic material and components by adopting local energy-based parameter which can quantify the local damage due to stress gradient caused by notches as well as defects. More precisely, the extension of the applicability of three energy-based approaches to several factors that influence the fatigue strength of material and components in addition to those already covered is the aim of the present dissertation. The first energy-based method, the so-called Peak Stress Method deals with the fatigue assessment of welded joints by means of a numerical FE-oriented application of the Notch- Stress Intensity Factors (N-SIFs). The equivalent peak stress (the fatigue damage parameter used for assessing the fatigue strength of welded joints) can be obtained by invoking the averaged Strain Energy Density (SED) criterion. The second one deals with the fatigue characterization of metallic component by assuming the specific heat loss per cycles as a fatigue damage parameter which can be evaluated in a standard constant amplitude fatigue test by adopting an easy experimental technique based on temperature measurements of material surface. The third one deals with the fatigue characterization of metallic materials produced by additive manufacturing, one of the most attractive and studied technology nowadays. Since these materials are affected by the presence of irregular defects, energy-related fracture mechanics approaches seem to be the most suitable for fatigue life assessment. In the first chapter, the state of the art of energy-based methods for fatigue and fracture mechanics characterization are described along with their theoretical frameworks. In the second chapter, the theoretical framework for extending the applicability of Peak Stress Method to the fatigue strength assessment of welded joints subjected to multiaxial loading conditions has been presented. Then, several multiaxial fatigue data taken from the literature relevant to both aluminum and steel welded joints were analysed by using the PSM for validating the theoretical prediction. The equivalent peak stress has shown to correlate with good approximation about all the experimental data. The third chapter deals with the analysis of the thermal energy dissipated during fatigue tests on severely notched AISI 304L stainless steel specimens. For the first time, the specific heat loss per cycle (Q parameter) was evaluated experimentally on 4-mm-thick, hot-rolled AISI 304L stainless steel specimens, characterized by 3, 1 and 0.5 mm notch tip radii by means of a FLIR SC7600 infrared camera during fully reversed axial fatigue tests. The new fatigue test results were successfully included in the existing heat energy-based scatter band previously calibrated on plain and bluntly notched specimens. Finally, an analysis of the heat energy dissipated around the notch tip has been presented and discussed with the aim of proposing a semi-automatic procedure to evaluate the thermal energy dissipated distribution. The fourth and fifth chapters deal with the analysis of the thermal energy dissipation on both AISI 304L and C45 steels specimens subjected to multiaxial loads. The specific heat loss per cycle was measured during constant amplitude multiaxial fatigue tests adopting two different phase shift angles of the applied loads and two biaxiality ratios. All the fatigue test results on both materials are in good agreement with the relevant scatter band previously calibrated except for the out of phase multiaxial fatigue results relevant to the AISI 304L steel. These results seem to be justified by the strain-induced martensitic transformation in metastable austenitic stainless steel, significantly present in out of phase cyclic loading condition. In the sixth chapter, the influence of the defect on fatigue behaviour of maraging steel specimens has been investigated. Axial fatigue tests were carried out on three batches of AMed maraging steel specimens produced by two different AM systems. Furthermore, axial fatigue tests were carried out on wrought maraging steel specimens both in annealed and in aged condition. After failure, the √area of the killer defects was examined by SEM observations of the fracture surfaces. A stress intensity factor-based design curve for all the test series was obtained taking into account the short crack effect by means of the El-Haddad-Smith-Topper model. Due to the lack of expensive experimental data to determine the relevant material length parameter a0, a novel rapid method to approximately evaluate a0 has been proposed. In particular, it consists in matching El-Haddad-Smith-Topper model with Murakami’s expression of the threshold range of mechanically short cracks. The advantage of the adopted engineering approach is that only Vickers hardness of the material is necessary. Theoretically, this rapid method can be also adopted to estimate the size of the control volume of the averaged SED approach due to the analogy of the latter to the material length parameter a0. In the end, the stress intensity factor-based design curve was adopted to estimate the fatigue strength of sharp V-shaped notches characterized by a reduced notch opening angle.

L’infissione nel fondale marino di pali in acciaio di grandi dimensioni costituenti la sottostruttura delle turbine eoliche provoca la nascita e la propagazione di un campo di vibrazioni inquinanti. Tali vibrazioni, le quali possono raggiungere elevate distanze, se al di sopra di particolari soglie di intensità, possono causare danni temporanei o permanenti, di natura fisiologica o comportamentale, alle forme di vita acquatiche circostanti il sito di collocamento dell’elemento strutturale. Tuttavia, diverse soluzioni sono state ideate per ridurne gli effetti nocivi: una di queste è il sistema air-bubble curtain. Tramite questo elaborato, si procede, in un primo momento, allo studio ed all’approfondimento delle equazioni governanti il problema vibro-acustico unitamente all’interazione con il sistema di dissipazione. Successivamente, si sfrutta il software di calcolo COMSOL Multiphysics per la creazione dei modelli necessari allo studio delle caratteristiche del sistema dissipativo. L’indagine ha interessato i parametri di distanza dal palo di fondazione, spessore della cortina di bolle, frazione di volume d’aria nella miscela, numero degli strati attorno al palo e forma di modellazione. Si è così riscontrato che il fattore che incide maggiormente sull’attenuazione del segnale è la frazione di volume d’aria nella miscela acqua-aria (poco influiscono spessore ed il numero di strati). Tuttavia, un’adeguata distanza tra dispositivo e sorgente sonora garantisce un’efficace azione smorzante unitamente ad uno spazio di lavoro modesto. L’assunzione di una forma più prossima a quella reale lascia comunque dei dubbi relativamente ad una maggiore efficacia.

The present document summarized the aims and the results obtained by the candidate, during the Ph.D. programme. The research activity consisted in the investigation of the high temperature fatigue behaviour, considering the effect of the temperature combined with creep. After a preliminary analysis, the investigation of different notches reproducing the geometry of real components was considered a key topic in the present research activity. These geometries, indeed, are completely neglected in the past and recent literature, despite their important role played in industrial applications. Moreover, the interaction between creep and fatigue is still not well understood and the available design tools are not effective. Considering a topic so wide and complex, it was essential to approach and face the problems from different viewpoints strictly related one another: -from the experimental point of view: the aim was the characterization of the high temperature fatigue behavior of different innovative materials, considering a large number of notch geometries, in order to obtain a robust experimental set of new data; -from analytical/theoretical point of view: with the aim to develop and/or extend methods based on energy approaches to high temperature phenomena, to analyse the elastic-plastic behaviour of the material and try to give robust and reliable tool for the design against creep. For these reasons, high temperature fatigue tests have been conducted on Cu-Co-Be alloy, 40CrMoV13.9, Titanium grade 2, and a synthesis in terms of the strain energy density of high temperature fatigue data has been proposed successfully, for the first time. In addition, on the 40CrMoV13.9 steel, an investigation on the crack initiation from notches and on the influence of surface roughness at elevated temperature was accurately conducted. Because of the good results obtained with the SED approach, it was investigated the accuracy of the averaged SED considering a large bulk of high temperature fatigue data taken from literature. Notched components made of different C45 carbon steel at 250°C, Inconel 718 at 500°C and directionally solidified superalloy DZ125 at 850°C were considered. The control volume was derived for each material through the analytical relation within El Haddad-Smith-Topper parameter and the material characteristic length defined by the Theory of Critical Distances. SED based curves were obtained and allowed proving that the proposed approach can be a reliable design tool in practical applications when dealing with high temperature. Relating to the creep phenomenon, the author developed a useful numerical tool allowing assessing the stress relaxation and the strain evolution against time, at the tip of blunt V-notches. In detail, starting from Neuber’s rule extended to time-dependent problems and assuming Lazzarin-Tovo equations to describe the early elastic state of the system, a set of new differential equations to be solved numerically has been derived in order to predict the evolution of stresses and strains for a material obeying a Norton power law. The results have shown an excellent prediction of the stresses and strains evolution against time, with a maximum discrepancy within theoretical and finite element method prediction of 20%. Some preliminary analyses on the extension of SED under creeping conditions have been also reported. At the end, the contour J-Integral, developed for elastic-plastic problems, have been also considered for further applications to high temperature and creep. The results led to several international fruitful collaborations and solid bases for interesting future development of a unified SED approach of fatigue and creep<br>L’obiettivo del Dottorato di Ricerca era lo studio del comportamento a fatica di materiali metallici ad alta temperatura, indagando in modo particolare il fenomeno del creep, che diventa non trascurabile in determinate condizioni di carico e interagisce con la resistenza a fatica stessa. È stata ritenuta interessante soprattutto l’analisi di componenti in presenza di intagli e/o di geometrie complesse che rappresentassero in qualche modo la geometria di componenti effettivamente utilizzati nelle applicazioni industriali. Da un’iniziale e approfondita analisi bibliografica è emerso come in letteratura si trascurino la fatica ad alta temperatura ad alto numero di cicli e in particolar modo le applicazioni relative a componenti intagliati. Inoltre, l’interazione fra fatica e creep si presenta come un evento ancora poco chiaro e trattato con strumenti poco efficienti. Considerando fenomeni molto complessi e un tema così ampio, è stato indispensabile affrontare l’oggetto del presente dottorato di ricerca da diversi punti di vista ma strettamente interconnessi: -quello sperimentale: caratterizzando il comportamento a fatica ad alta temperatura di diversi materiali innovativi e multifunzionali d’interesse industriale, considerando varie geometrie d’intaglio, in modo tale da fornire un consistente numero di dati sperimentali di partenza; -quello analitico/teorico: cercando di sviluppare e/o estendere approcci energetici ad alta temperatura, analizzando il comportamento elasto-plastico, gli strumenti a disposizione e cercando, infine, di fornire strumenti efficaci per la progettazione in presenza di creep. Per queste ragioni, è stata condotta una campagna sperimentale al fine di caratterizzare il comportamento a fatica ad alta temperatura di geometrie intagliate di una lega Cu-Co-Be, 40CrMV13.9 a Titanio Grado 2. I dati sperimentali ottenuti sono stati sintetizzati in termini di Strain Energy Density, esteso per la prima volta all’alta temperatura. Sempre considerando l'acciaio 40CrMoV13.9, è stata condotta un’analisi sull’innesco di cricche a bordo foro, ad alta temperatura, valutando l’influenza della rugosità superficiale. Visti i positivi riscontri ottenuti con la sintesi in energia dei dati sperimentali, la potenzialità del metodo è stata ulteriormente verificata considerando nuovi materiali e geometrie presenti in letteratura. Sono state prese in esame prove a fatica condotte su un acciaio C45 a 250°C, Inconel 718 a 500°C e sulla superlega DZ125 a 850°C. I dati, originariamente sintetizzati attraverso la Teoria delle Distanze Critiche, sono stati ripresentati con successo in termini di densità di energia di deformazione mediata su un volume di controllo. Il raggio di controllo per ogni materiale è stato determinato attraverso la relazione che lega il raggio stesso con il parametro di El Haddad-Smith-Topper e la distanza critica caratteristica del materiale. Successivamente, il fenomeno del creep è stato accuratamente considerato. In dettaglio, è stato con successo fornito uno strumento numerico capace di prevedere il rilassamento delle tensioni e l’evoluzione delle deformazioni nel tempo, all’apice d’intagli a V raccordati. In dettaglio, partendo dall’estensione della regola di Neuber a problemi dipendenti dal tempo, e utilizzando le equazioni di Lazzarin-Tovo al fine di descrivere lo stato elastico iniziale del problema, è stato poi ricavato un set di equazioni differenziali da risolvere in modo iterativo/numerico al fine di valutare tensioni e deformazioni nel tempo, assumendo la legge di Norton per la rappresentazione del fenomeno del creep. Al fine di validare il metodo, i risultati ottenuti sono stati confrontati con quelli ricavati da accurate analisi agli elementi finiti, ottenendo un buon accordo. Tutte le tensioni sono state previste con errori trascurabili, mentre in alcuni e limitati casi, le deformazioni hanno mostrato un errore percentuale leggermente più elevato ma comunque inferiore al 20%. Sono state inoltre condotte delle analisi preliminari agli elementi finiti al fine di esplorare il comportamento del SED in presenza di creep, risultando tempo-variante ma tendente ad un valore di plateau. Infine, sono stati considerati approcci energetici alternativi utilizzati nella caratterizzazione dei fenomeni elasto-plastici che possono essere presenti alle alte temperature. In particolare, tra le varie metodologie presenti in letteratura, è stato considerato il J-Integral. L’attività lascia infine interessanti possibili sviluppi futuri di ricerca che possono portare a un approccio unificato, basato sul SED, per progettazione a fatica in presenza di creep e di forte interazione creep-fatica

AbstractGamma radiation detection finds many applications in different fields, including astrophysics, nuclear physics and medical diagnostics. Nowadays large Lanthanum Bromide crystals coupled to Photomultiplier Tubes (PMTs) represent the state of the art for gamma detection modules, in particular for spectroscopic measurements. Nevertheless, there is an interest in substituting photomultiplier tubes with solid state photodetectors like Silicon Photomultipliers (SiPMs), owing to the latter’s significant advantages. These include insensitivity to magnetic fields, low bias voltage, compactness, fast response and mechanical robustness. The aim of this thesis work, which was carried out within the context of the GAMMA project supported by IstitutoNazionale di FisicaNucleare (INFN), is the design, development and experimental characterization of a -ray spectrometer based on large Lanthanum Bromide scintillator crystals coupled with Silicon Photomultipliers. This detector specifications are compliant with nuclear physics experiments with energies ranging from 100 keV to 20 MeV, characterized by state-of-the-art energy resolution and imaging capability, in a compact, modular and robust structure. In order to perform the readout of large scintillator crystals, a matrix of 144 Silicon Photomultipliers was designed using NUV-HD SiPMs from Fondazione Bruno Kessler (FBK). These were chosen due to their high Photon Detection Efficiency in correspondence with the peak emission wavelength of the crystal, the high cell density and low Dark Count Rate.

From local mode stretching force constants and topological electron density analysis, computed at either the UM06/6-311G(d,p), UM06/SDD, or UM05-2X/6–31++G(d,p) level of theory, we elucidate on the nature/strength of the parallel π-stacking interactions (i.e. pancake bonding) of the 1,2-dithia-3,5-diazolyl dimer, 1,2-diselena-3,5-diazolyl dimer, 1,2-tellura-3,5-diazolyl dimer, phenalenyl dimer, 2,5,8-tri-methylphenalenyl dimer, and the 2,5,8-tri-t-butylphenalenyl dimer. We use local mode stretching force constants to derive an aromaticity delocalization index (AI) for the phenalenyl-based dimers and their monomers as to determine the effect of substitution and dimerization on aromaticity, as well as determining what bond property governs alterations in aromaticity. Our results reveal the strength of the C⋯C contacts and of the rings of the di-chalcodiazoyl dimers investigated decrease in parallel with decreasing chalcogen⋯chalcogen bond strength. Energy density values Hb suggest the S⋯S and Se⋯Se pancake bonds of 1,2-dithia-3,5-diazolyl dimer and the 1,2-diselena-3,5-diazolyl dimer are covalent in nature. We observe the pancake bonds, of all phenalenyl-based dimers investigated, to be electrostatic in nature. In contrast to their monomer counterparts, phenalenyl-based dimers increase in aromaticity primarily due to CC bond strengthening. For phenalenyl-based dimers we observed that the addition of bulky substituents steadily decreased the system aromaticity predominately due to CC bond weakening.

Heat transfer fluid (HTF) plays an important role in the efficiency and cost effectiveness of solar thermal collector. From several choices, Therminol VP-1 (eutectic mixture of diphenyl oxide and biphenyl) are successfully used as heat transfer fluid in the collector field of parabolic trough plants. This paper experimentally analyzes the buoyancy driven heat transfer performance of Therminol VP-1 in a square enclosure with uniformed heating from below and for a Rayleigh number up to 1.11×108. Thermophysical properties such as density, viscosity, and thermal conductivity of Therminol VP-1 were also measured experimentally. The results show that the density, viscosity, and thermal conductivity decrease with temperature within the measured temperature range 10–60°C. The obtained convective heat transfer coefficient was lower than the De-Ionized (DI) water, whereas the dimensionless Nusselt number was observed higher than DI water, which is because of the low thermal conductivity (approximately 25% of DI water) of Therminol VP-1.

The latest advances in power density and efficiency of internal combustion engines (ICEs), both diesel direct injection (DI) compression ignition (CI), and gasoline positive ignition (PI), DI and jet ignition (JI), ICEs, are transferrable to single fuel or dual fuel hydrogen engines (H2-ICEs). H2-ICEs have the potential to deliver peak efficiency about 50%, peak power efficiency above 46%, and cycle average efficiency above 35% when fitted to hybrid powertrains. The major hurdles to achieve these performances are the development of hydrogen injection system. Dual fuel DI diesel-hydrogen CI ICEs have the potentials to deliver extremely low emissions of the regulated pollutants, NOx, unburned hydrocarbons (HC), CO and particulate matter (PM), and CO2 emission. Hydrogen PI ICEs with DI and JI have the potentials to deliver extremely low emissions of the regulated pollutant NOx, practically zero emissions of regulated pollutant PM, and practically zero emission of CO2 (while a small amount of lubricating oil may end up in the combustion chamber, but this amount is negligible). The PI ICEs allow much higher power densities, being the combustion event controlled by the turbulent mixing rather than vaporization, mixing and diffusion times. Thus, combustion duration is about independent of the engine speed in PI ICEs but increasing with the engine speed in CI ICEs. While combustion of hydrogen only in a CI engine is still troublesome, needing added research and development, much simpler is the use of hydrogen and diesel in a dual fuel CI engine accepting the DI of both diesel and hydrogen. While the dual-fuel DI diesel-hydrogen CI ICEs are a workable short-term replacement of the traditional hydrocarbon fueled PI ICEs, as cryogenic H2-ICES may share infrastructure and fuel system technology with LNG-ICEs, the hydrogen PI ICEs with DI and JI are an even better environmentally-friendly proposal while offering better performances. Simulations are presented for a dual duel diesel-hydrogen engine featuring two injectors per cylinder, one for the diesel and one for the hydrogen. The coupling of a pilot/pre-injection of diesel with a main injector of hydrogen is straightforward. Mixed modes of combustion are possible injecting part of the hydrogen before, and a part after the diesel injection ignition. The engine has a super turbocharging, where the turbocharger shaft is connected to the crankshaft by gears and a continuously variable transmission. Steady-state maps are presented in detail. Even if this aspect is not investigated, thanks to the super turbocharging, the engine has excellent transient behaviors, in decelerations (energy recovery) as well as accelerations (no turbo-lag). Dual fuel CI ICEs have also the advantage of a hydrogen city driving delivering extremely low emissions of pollutants as well as CO2, and a diesel interstate and rural areas driving delivering still relatively low emissions of pollutants as well as CO2.

The systematic experiments were performed for buoyancy driven heat transfer of zinc oxide (ZnO)-water nanofluids with volume fraction 0.5%, 1%, and 2% in rectangular (50×50×75mm) cavity heated from below. In addition to determining the convective heat transfer coefficients, this study also included experimental determination of density, effective thermal conductivity, and rheological behavior of nanofluids. For all the properties and natural convection behavior De-Ionized (DI) water was used as the baseline data. The results show that density measurements agree well with predicted values by equation, thermal conductivity enhanced by ∼14% for 2 vol% nanofluids, and shear thinning behavior of nanofluids. The natural convection behavior shows degradation of heat transfer and degradation increases with the volume fraction of nanoparticles. Probable reasons of degradation are discussed in the paper.

In this paper, an innovative direct power generation technique from salinity gradient is proposed and demonstrated. The basis of this novel method encompasses forward osmosis (FO) and electrokinetic (EK) principles. Tapping the concentration difference between seawater and river fresh water, forward osmosis (FO) is utilized to allow for spontaneously transporting water across a semi-permeable membrane. The flow of water is then directed towards array of microchannels in the form of porous medium where power is produced from the electrokinetical streaming potential. Experimentally, NaCl solution and DI water were used to model as seawater and fresh river water, respectively. Both glass and polymer based porous media and commercial flat sheet FO membranes were employed herein. Results show power density could reach the order of 101W/m2. Having features of ease of fabrication, simple configuration and no mechanical moving parts, this method provides a feasible mean to harvest enormous energy from salinity gradient. Thus the proposed technique could contribute greatly to renewable energy and towards sustainable future.

Since the beginning of this century, Liquefied Natural Gas (LNG) has been attracting more and more attention as a cleaner energy alternative to other fossil fuels, mainly due to the possibility to transport it over longer distances than natural gas in pipelines and lower environmental impact than other liquid fuels. It is expected that this trend in the use of LNG will lead to steady increases in demand over the next few decades. At present, in the automotive sector, natural gas is employed as fuel in spark-ignited (SI) engines in the gas phase (CNG) adopting port-fuel injection system (PFI) in the intake manifold, with the main result of reducing CO2 emissions by up to 20%, compared with gasoline operation. However, SI engines which are operated in this manner suffer loss of peak torque and power due to a reduction in volumetric efficiency. Direct-Injection (DI) inside the cylinder can overcome this drawback by injecting CNG after intake valve closure. Another strategy could be the injection of natural gas in the liquid phase, both in PFI or DI mode. The injected fuel evaporation cools down the intake air; increasing the charge density with a substantial improvement in the engine volumetric efficiency and delivered power. However, at present, injection systems dedicated to cryogenic injection of natural gas are still in the prototype state. In the present study, the volumetric efficiency and performance of a turbocharged, LNG fuelled SI-ICE were numerically analysed both in the cases of DI and PFI modes and compared with the results of a conventional CNG system. Various fuel injection timings and injector position were analysed. The engine performance was evaluated by means of a one-dimensional model developed with the simulation program GT-Power, while the verification of the LNG-air mixture characteristics was carried out with the commercial code Aspen HYSIS. The numerical activity has shown that gaseous DI, before inlet valves closing, gives the worst result since methane, once injected into the cylinder, expands hindering the entry of air. On the other side, liquid PFI represents the best configuration to maximize the volumetric efficiency and therefore the engine power. All the technological issues related to a cryogenic liquid methane injection system were not taken into consideration in this study.

In this paper, the prototype of a circular Molten Carbonate Fuel Cell (MCFC) built in the laboratories of FN SpA Nuove Tecnologie e Servizi Avanzati is analyzed using a tridimensional computational fluid dynamic (CFD) model. The prototype is the result of FN and Politecnico di Torino activities developed for the Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA) within the framework of Ministry of Economic Development, MSE-ENEA. This model considers heat, mass and current transfer as well as chemical and electrochemical reactions. The results show that some inhomogeneous distributions in the reactants, causing non-optimal use of the reactant surfaces. An effective way to improve the distribution in current density consists in tracing tree shaped channels on the surface onto the distribution porous medium. In this paper Y shaped channels are adopted to improve the distribution of gas within the fuel cell and consequently to enhance the performance of the original design of the fuel cell. In addition, the configuration of the outlet of the anodic compartment is also investigated in order to further increase the performance of the fuel cell. The geometrical parameter identifying the topology of distribution channels are chosen accordingly to the constructal theory. The results show that significant improvements can be achieved. Power density is increased of about 6% when the tree-shaped channel is adopted. If a double anodic inlet is also considered the enhancement in the power density is of about 11% with respect to the initial configuration.

Cadangan minyak bumi dunia semakin lama semakin berkurang, sehingga perlu energi alternatif untuk menggantikan posisi minyak bumi, di antaranya adalah penggunaan biodiesel. Biodiesel dapat diproduksi dari berbagai macam minyak nabati, salah satunya minyak kelapa. Pembuatan biodiesel memerlukan katalis, katalis yang banyak dikembangkan saat ini adalah katalis heterogen CaO. CaO dapat diperoleh dari CaCO3 yang dikalsinasi. Salah satu sumber yang mengandung CaCO3 yang tinggi adalah cangkang telur bebek. Penelitian ini bertujuan untuk mengetahui pengaruh variasi suhu kalisnasi cangkang telur bebek pada 700, 800, 900 dan 1000℃ terhadap katalis CaO yang dihasilkan dan pengaruh terhadap pembentukan biodiesel menggunakan minyak kelapa. Pada penelitian ini kalsinasi cangkang telur bebek dilakukan selama 4 jam. Proses transesterifikasi dengan suhu reaksi 60℃ menggunakan metanol dan minyak kelapa dengan perbandingan mol 9:1 selama 4 jam. Kosentrasi katalis CaO yang digunakan yaitu 3,5%(b/b). Katalis diuji tingkat kristalinitas dengan analisis XRD. Metil ester dianalisa dengan GCMS, untuk standar kualitas biodiesel parameter yang diuji yaitu densitas, viskositas, angka setana, dan residu karbon. Pembentukan optimum CaO pada proses kalsinasi adalah pada suhu 900℃. Reaksi transesterifikasi yang dilakukan menghasilkan yield sebesar 92,12%. Biodiesel yang dihasilkan mempunyai nilai densitas 859 kg/m3 , viskositas kinematik 11,6 mm2 /s, angka setana 55,7 dan residu karbon 0,37%(b/b).

To reduce the dependency on fossil-based energy resources, the utilization of renewable fuels in unmodified diesel engines is gaining more emphasis from researchers in the recent years. The aim of the current study is to take part in the efforts being made to this regard by experimentally investigating a compression ignition engine fueled with different fuels ((diesel, diesel-biodiesel (B20), and diesel-biodiesel-butanol (BU20)) for their performance and emissions comparison. The experimental study was conducted in a water cooled single-cylinder direct injection (DI) diesel engine. It was operated at a constant engine operation speed of 1800 rpm and under varied engine load conditions. It is found that BU20 shows promising results in terms of performance and emissions characteristics as compared to using B20 and D100. Butanol addition to diesel-biodiesel blends is considered as an appropriate solution of higher density and viscosity the blend and thus for the sustainable usability of biodiesel. Maximum thermal efficiency improvement of 3.18% was observed at an engine load of 75%. The NOx emission was improved with BU20 as compared to the conventional diesel fuel (D100) at most of the engine loads. As an improvement on the engine performance and emissions is reported from the current study, the BU20 fuel blends can be used in similar engines with no further engine retrofitting. This blend can be a good environmental friendly fuel that can serve in the reduction of fossil-based diesel fuels. A further study on diesel engine tribology is required.

The purpose of this study is to examine the influence of biodiesel (BD) fuel properties on different characteristics of the engine and to compare with the baseline petroleum diesel (PD) fuel. This study consists of two parts, first one is biodiesel characterization and the second one is testing in the engine. Two BD fuels namely, the medium chain (C6–C24) coconut oil methyl ester (COME) and the long chain (C16–C18) sesame seed oil methyl ester (SSME) were selected. It is observed that, the physical and chemical properties such as viscosity, density, bulk modulus, calorific value, C/H ratio, and iodine value of SSME are higher than that of COME, while the cetane number, saturation% and oxygen% of the COME is higher than that of SSME. Experiments were conducted in a naturally aspirated, single cylinder, four-stroke, stationary, water cooled, constant rpm (1500), in-line (pump-high pressure tube-fuel injector) direct injection compression ignition (DI–CI) engine with COME, SSME (with and without preheating), and PD as fuels. The performance was evaluated in terms of fuel consumption (FC), brake specific energy consumption (BSEC), and thermal efficiency (BTE). Except for COME at full load, the BTE of the esters over all load ranges were less than that of PD fuel. Also, a significant improvement in BTE was observed, when the SSME is tested at PD’s viscosity by using preheating technique. At full load, the BSFC of COME and SSME are increased by 16.61% and 18.24% respectively. The minimum BSEC (at full load) of COME is decreased by 1.3% and while that of SSME is increased by 4.5%, as compared to that of PD fuel. The full load peak pressures for COME, SSME and PD fuel are 63.8 bar, 65.8 bar, and 62.9 bar respectively. The high peak pressures of the methyl esters are probably due to dynamic injection advance, caused by their higher bulk modulus. The net heat release rate (HRR) and cumulative heat release (CHR) were calculated from the acquired data. The results show that, at all loads there is a slight increase in peak HRR for COME and large increase in peak HRR for SSME against PD fuel. The higher values of peak HRR indicate better premixed combustion with the methyl esters. However, the peak HRR for preheated SSME (SSME_H) decreases due to late injection and faster evaporation of the fuel. It was observed that, at full load the nitric oxide (NO) emission of SSME is increased by 12.9%, while that of COME is decreased by 13.8% as compared to that of PD fuel. The smoke is increasing linearly with the fuels ‘C/H’ ratio regardless of their molecular structure. The HC emissions of both the esters are very low and are reduced by up to 73%, as compared PD. Also, there is a significant reduction in all exhaust emissions, and in particular the NO emission is observed with preheated SSME, due to change in premixed combustion phase.

There is a critical need for high-power mid-infrared diode lasers to be used in such military and commercial applications as IR countermeasures, IR illumination, and long-range chemical sensing. To date, the highest reported cw output power from a semiconductor diode emitting in the 3-5 μm spectral region has been 215 mW/facet. This was obtained from a 250-μm stripe at 80 K,1 and cw operation has never been observed in a III-V diode laser above 175 K.2 Although output powers exceeding 1 W are readily attainable from near-IR (λ ≈ 1 μm) lasers operating at or near ambient temperature, mid-IR emitters are inherently at a disadvantage due to the inverse scaling of the differential slope efficiency (dP/dI) with wavelength. That is, while the same current is required to inject one electron-hole pair as in a near-IR diode laser, the energy of the photon that results is 3-5 times smaller. A recent breakthrough has been the demonstration that this fundamental limitation may be circumvented by employing a cascade geometry. The unipolar quantum cascade laser (QCL) of Faist et al.,3 which achieves lasing due to optical intersubband transitions, can in principle emit as many photons for each injected electron as there are periods in the structure. However, high cw operating temperatures and large cw output powers have not yet been reported, in part because the threshold current density is inevitably rather large owing to a rapid nonradiative phonon relaxation of the population inversion.

Integrated Modification Methodology (IMM) has already been applied in established metropolitan contexts, such as Porto Maravilha in Rio de Janeiro, the neighbourhood of Shahrak-e Golestan in Tehran, and Block 39 in New Belgrade. When Unitec Institute of Technology’s Associate Professor of Urban Design Dushko Bogunovich came up with the idea of a comparative analysis of two sprawling metropolitan contexts – Auckland and Milan – he and Massimo Tadi, Director of the IMMdesignlab in Milan and Associate Professor at the School of Architectural Engineering at the Politecnico di Milano, decided to apply IMM to a sample area of low-density suburban Auckland. The project presented in this book was developed in a joint international design workshop organised by Politecnico di Milano, IMMdesignlab and Unitec Institute of Technology. The workshop was held at Politecnico di Milano, Polo Territoriale di Lecco (Italy), from 25–29 May 2015, and the team, comprising 14 international students from different design disciplines, was coordinated by Tadi and Bogunovich, assisted by engineers Hadi Mohammad Zadeh and Frederico Zaniol (IMMdesignlab). The outcomes of the workshop were then further developed by IMMdesignlab to demonstrate how, by adopting IMM, it is possible to retrofit, renovate and reactivate an inefficient and energy consuming neighbourhood into a more integrated and sustainable one.