Phononic Crystals and elastic mechanical metamaterials have shown some unusual light and mechanical wave manipulating properties. These novel structure-type materials are also finding extensive use in energy harvesting as well as vibration control and attenuation. Phononic Crystals are mechanical metamaterials which are composites of two or more linear elastic materials of different mechanical properties, having vibration energy propagation inhibition over certain range of frequencies. These are called phonic band gaps, whose presence essentially signifies the reduction of flow of phonons in the form of elastic wave energy. Phononic crystals are generally constructed with some periodicity in geometry or boundary so that they are lightweight with a choice of tailoring their mechanical and dynamic properties. Some three dimensional recently developed phononic crystals with Acoustic Black Holes (ABH) also show flexural wave energy localisation inside a structure.
The present study concerns with the finding of wave energy localisation in an elliptic ABH engraved square periodic plate and the generation of locally resonant dispersion curves. Flexural band gaps are observed from the displacement component plots of the structure after simulation. The square periodic plate was next studied with extended external beam surfaces with added masses on the beams. The dispersion curves were plotted and the displacement component plots show torsional wave propagation modes. Now these two structures were combined to form a novel structure comprising of an elliptic ABH engraved square periodic plate with extended beams with masses on them. Coupled bending and torsional band gaps are seen in the structure. The displacement components show attenuation of vibration in torsion as well as flexure.
The numerical analysis was done using Comsol Multiphysics for all the three cases. The elliptic ABH plate is made of Structural Steel, for the torsion and coupled flexure-torsion cases, the plate and beams are made of Aluminium and the masses on the extended beams are made of structural steel. Floquet Theory was used for the Periodic Boundary Condition 1-D and the natural frequencies are found out for each type of unit cell. The frequencies are next swept along the reduced wave vector space to get the dispersion diagram for each unit cell, which show a complete band gap for the flexure case (around 2.5 kHz to 2.7 kHz) and the coupled flexure-torsion case (around 4 kHz to 4.4 kHz). These band gaps are mainly due to the local resonance feature of the unit cells, and was absent in the torsion unit cell. Next, a cantilver beam is constructed with each unit cell. A frequency domain analysis is performed in Comsol and the displacement, velocity and mean-square velocity transmissibility are next plotted in MATLAB for an input point at the mid-point of loaded edge and output point at the mid-point of periodic edge near the fixed edge. Beams are studied with 3, 5, 7 and 10 unit cells 

Coupled Flexural and Torsional Vibration Attenuation With Acoustic Black Hole Metamaterial

The design of a tip appendage for the passive control of tip leakage vortices in axial flow fans is investigated for the purpose of fan performance enhancement. The merging and subsequent bursting of the tip leakage vortex further downstream of the blade is associated with having a detrimental effect on fan performance characteristics. Periodic three-dimensional numerical computations are conducted using the open-source CFD library OpenFOAM and a newly implemented open-source meshing strategy.

Both steady and unsteady numerical computations are used to determine the effect of tip clearance on fan performance characteristics. An increase of 15.6 percent in total-to-static pressure rise and a 5.1 percentage point increase in total-to-static efficiency is found with a 66.6 percent reduction in tip clearance at the fan's design point flow rate. Normalized helicity contours are used in the visualization and quantification of the flow near the blade tip. The findings show a reduction in the relative tip leakage flow velocity through the tip gap and a reduction in the tip leakage vortex exit trajectory angle along the blade's chord with a reduction in tip clearance. This paper reports on numerical investigations that were performed on these two flow characteristics with the aim to control them through the implementation of a tip appendage design.

An average reduction of up to 6.8 percent in the tip leakage flow velocity through the tip gap is achieved through the introduction of three constant thickness end-plate designs. Comparing the pressure side constant thickness end-plate design to the fan datum, an increase in the fan's total-to-static pressure rise at lower than design point flow rates is achieved with an increase in the fan's peak efficiency plateau towards the rotor stall margin. However, none of the constant thickness end-plate designs are able to improve the fan's performance characteristics at its design point flow rate.

A novel trailing edge end-plate concept is introduced through modification of the downstream section of the blade tip. The trailing edge end-plate design is found to exhibit control of the tip leakage vortex exit trajectory angle while shifting the blade's peak loading distribution further downstream towards the blade's trailing edge. The introduction of the trailing edge end-plate design is found to increase the datum fan's performance characteristics across the entire evaluated stable operating range, with an indicated increase of 9.7 percent in total-to-static pressure rise and a 1.3 percentage point increase in total-to-static efficiency at the fan's design point flow rate.


Design of a Tip Appendage for the Control of Tip Leakage Vortices in Axial Flow Fans

Nowadays the use of numerical simulations for predicting the performance of turbomachinery is widely accepted and used, also to predict very complex phenomena such as particle/droplet erosion or deposition that occur in several turbomachinery. For instance, some induced draft fans for industrial applications elaborate particle laden flows resulting in a large erosion of the blades and then performance loss. The possibility of predicting such a process would improve the sizing and maintenance scheduling processes. However, particle erosion simulations are usually limited to a fraction of seconds because of computational costs, and from these simulations it is hard to extract some reliable predictions. A main reason is that the relative flow field varies depending on the operating conditions referred to the machine and to the installation environment, therefore, a single numerical experiment cannot include all real-life situation. In some previous publications we developed an algorithm to perform long time predictions, also considering the variations in blade geometry with time. Here, we present a method to obtain, given a fan blade section, its relative velocity triangle and the particle concentration, the time specific erosion damage pattern per unit of span. The resulting pattern is given by an artificial neural network (ANN) trained on a dense dataset of numerical simulations, based on the modelling developed and used by the authors in the last decade.

The synopsis of the method is basically the following. Create a large database of erosion patterns for a specific airfoil, considering as aerodynamic features, the relative angle of attack, the relative flow velocity and Reynolds number, and as particle flow features, the diameter, concentration, hardness and density. Each pattern is obtained simulating the particle erosion on a blade strip, in the condition defined by a specific set of the features defined above. Once the dataset is complete, an ANN is trained to solve the regression problem and estimate the specific erosion damage pattern for any set of features in the dataset bounds.


Integration of Computational Fluid-Particle Dynamics Techniques for the Instantaneous Estimation of Particle Erosion Damage on Axial Fan Blade Sections

Hydrodynamic Optimization of a Containership

Yanxin Feng, Ould el Moctar, Thomas E. Schellin

University of Duisburg-Essen, Duisburg, Germany

Abstract

The paper describes the process of generating a parametric hull for a containership using the open-source software Dakota. The hull is defined by a set of design variables. The selection of these variables is described and their influence on the resistance is analyzed and discussed in detail. Computations of the flow around the hull are based on a nonlinear potential flow boundary element method, which was validated against model scale experimental results. The multi-objective optimization algorithm Surrogate Based Global Optimization (SBGO) was used to reduce the computational effort. The hydrodynamic ship resistance was defined as the objective function. Compared with the original hull, the wave resistance of the optimal hull reduces remarkably in the calculated Froude number range.

Keywords: parametric hull; wave resistance; optimization; containership

Reference:

Moctar, O. E., Shigunov, V., & Zorn, T. 2012. “Duisburg Test Case: Post-Panamax container ship for benchmarking.” *Ship Technology Research* 59 (3): 50-64.

Harries, Stefan. 1998. *Parametric design and hydrodynamic optimization of ship hull forms.* Berlin: Institut fur Schiffs-und Meerestechnik, Technische Universitat Berlin.

Brizzolara, S., Vernengo, G., Pasquinucci, C., & Harries, S. 2015. “Significance of parametric hull form definition on hydrodynamic performance optimization.” *Proceedings of the MARINE.*


Hydrodynamic Optimization of a Containership

Turbine and compressor systems composed of many sub-systems, of which blade-disc assembly forms an important subsystem. All the blade-disc assemblies are designed to have uniform response at high speed rotation. The rotating parts of the system hold cyclic symmetry to provide a single period response or tuned response. On the other hand, the cyclic symmetry significantly simplifies vibration analyses. Non-uniformity in material properties, manufacturing tolerances and wear and tear during operation destroy the cyclic symmetry leading to loss in periodicity. The turbine system then develops non-uniform multi-frequency response. These are known as mistuned turbine system. A mistuned system suffers from localization in modes, subsequently concentration of vibration energy to a few blade-disc assembly. These assemblies undergo huge strain and stress due to high speed rotation. Furthermore, rotation causes centrifugal stiffening and gyroscopic effects. Considering all these parameters and complexities in the mathematical model, finding close form analytical solution is a tedious process. Hence, numerical analysis is carried out using finite element approximation which requires very fine mesh and is computationally exhaustive. Therefore, it is important to find a way to analyse the dynamics of rotating bladed disc systems at the design level with less computational complexities.

Under mistuning, physical parameters of the system vary neither uniformly nor deterministically. Therefore, deterministic analysis will not be able to capture the system response appropriately. This study focusses on probabilistic modelling of the bladed disc system parameters and calculate numerically the distributions of the response quantities of the system. Stochastic finite element model of the system consisting of all the assemblies and the hub is developed and reported. The spatial inhomogeneity of mistuned structures is modelled as non-Gaussian random field. Experimentally, coordinate measurement machine (CMM) is used to get the random geometry of the bladed disk structure. In this analysis, a synthetic data is generated which represent the CMM data. Further, Rosenblatt transformation is implemented to each component of the data set to get the polynomial chaos framework of the system parameters. Since, the random field of the system parameter is approximated as correlated random variables, Spearman’s rank correlation coefficient is used on this manuscript to obtain that correlation among the random parameters across the whole domain. The approximated probability density function through the aforementioned methodology is compared with the target probability density function of the parameter using Kullback – Liebler (KL) entropy.  Also, the same KL entropy is used as a metric to check the convergence of polynomial chaos terms in the expansion. Next, the proposed polynomial chaos method is integrated with commercial finite element software to quantify the propagation of r

Stochastic Modelling and Analysis of Rotating Bladed Discs

In the current fast-paced and global context of design within organizations and enterprises, there is significant interest in integrating design approaches and methodologies across fields and industry sectors.  Such an integration will provide a synthesis of design intent across user and stakeholder desirability, viability, feasibility, sustainability, and inclusivity.  At the heart of this integration is the merging of design thinking and systems thinking (including systems engineering) processes.  In this presentation, we provide a reflective case study of a ten month project between a large public organization, professional designers, and a university research center, focusing on the integration of design thinking and systems thinking.  The project is cast in light of our broader efforts to develop Design Innovation (DI) within organizations, concentrating on people, process, methods, principles, and mind sets (Camburn, et al., 2017; Sng, et al., 2017).

 

The reflective case study in this presentation entails the postscriptive analysis of a large infrastructure project in the transportation domain.  This project, as the design of a large, complex system, included over 25 personnel (architectures, engineers and designers) from the public organization, and over 20 professional designers and researchers.  The key outcomes from this collaborative project were two-fold: (1) teaching DI, inclusive of design thinking and systems thinking processes, to an in-house design (IHD) team from the organization, to create a shift in problem solving mindsets and approaches, and (2) actively applying DI process, methods, and principles in this context to the infrastructure design case. For the second outcome, we applied DI to two areas during the conceptual design stage: (a) choosing an appropriate infrastructure site, and (b) designing an innovative and optimized layout for key spatial components of the infrastructure.  The organization’s inclusive in-house design (IHD) team of architects, engineers, and designers explored design in different perspectives to expand beyond their own field of knowledge, with the objectives of developing innovation mindsets, a new paradigm for problem solving, and better solutions for projects undertaken by the organization through the practice of the Design Innovation methods, principles and mindsets.

 

The collaboration had three major phases. First, we engaged in a three-day DI sprint to start the project. This was to ensure that all team members were exposed to the full DI process and important methods, principles and mind sets. Second, we applied DI to choosing the infrastructure site location, as this was the first challenge/opportunity that presented itself during the collaboration. Third, we applied DI to the infrastructure spatial design with emphasis on optimizing layouts, while considering operations and maintenance needs. The project concluded with the team developing Design Innovation driven concepts and testing 

Design Innovation in Complex Systems Design: Integrating Design Thinking and Systems Thinking

Cycle-to-cycle variation (CCV) of in-cylinder flow strongly affects the performance and efficiency of SIDI engines. In order to achieve a precise flow control inside the engine, the underlying dynamic features of flow field CCV must be thoroughly investigated. In this work, large-eddy simulations (LES) with 50 consecutive cycles are employed for high fidelity numerical realizations of engine flow under motoring condition. To supplement the numerical analysis, time-resolved particle image velocimetry (PIV) measurements are also conducted in several cutting planes. Although the velocity root mean square (RMS) is calculated to quantify the cyclic variation intensity of simulation and experiment results, some important dynamic characteristics cannot be observed directly from velocity data. Therefore, dynamic mode decompositions (DMD), which is a widely used modal decomposition algorithm on fluid study, is used to decompose flow fields into modes with specific frequencies and provide growth rates of corresponding flow structures. This spectral information of in-cylinder flow field is ponderable for uncovering dynamic features of engine CCV. In this study, DMD algorithm is applied on both LES and PIV datasets. The frequency and growth rate differences are employed to elucidate the CCV feature deviations captured by LES and PIV. This research provides a guideline for extracting engine flow field cyclic variability feature using DMD algorithm. Based on the discussion for spectral features and potential sources of flow field variation, the capability of LES to capture CCV features is evaluated.  
 


Dynamic Mode Decomposition for Extracting Cycle-to-Cycle Variation of SIDI Engine In-Cylinder Flow Under Motoring Condition

The most common method of characterizing the printability and material properties of a food ink for 3D printed foods composed of a novel mixture of two or more food materials is the trial-and-error method. Trail-and-error design is inefficient, both in terms of time requirements and wasted materials.  The use of a design tool to predict the nutritional information of a printed construct, its rheological properties, and manufacturing properties is necessary to aid designers during the preparation of novel food mixtures.  The tool may allow for varying food concentrations and shape design while outputting information helpful for users to determine printability and finetune nutritional content of 3D printed foods. Our research ventures into the creation of this design tool along with the library of food inks required for its extended use.

Our methodology for reliably printing foods informs the development of the design tool and beings with mixing food ingredients to form a novel food ink that is tested by printing and assessing its print quality based on its rheological measurements. The method consists of first printing basic designs with biomaterials known to print consistently. Chocolate, Marzipan, and Potatoes are commonly used for 3D printing food applications. Hence, the rheological properties (complex modulus and mechanical loss tangent) are tested for these commonly used materials as a baseline reference for what rheological properties are required for the food ink to have proper extrudability. Compared to a novel pumpkin biomaterial for 3D food printing (Figure 1A), it is found the pumpkin has a higher complex modulus and lower mechanical loss tangent than all other biomaterials, therefore motivating the addition of rheological agents to reach more favorable properties. Varied concentrations of corn starch and guar gum are added to the pumpkin; Addition of guar gum to pumpkin leads to the rheological properties of the mixture to be closer to the properties of the more commonly used food printing materials. (Figure 1B). These formulations of pumpkin are printed, and a 4% inclusion of guar gum provides the most consistent prints. A complex 3D object is prototyped with the 4% guar gum pumpkin material, therefore demonstrating the merits in using rheological properties to inform printability of novel food biomaterials. Using the data obtained from the experiments, our aim is to create a design tool that would help predict the printability of a novel composition of the food ink being used to print constructs while also outputting nutritional information relevant for personalized health.

The design tool requires the input of the type of material present in the food ink, percentage constituents of the food ink, along with the details of the shape that is printed using the food ink. It uses linear interpolation between rheological data obtained from experiments to calculate the rheological properties of the food mixture of varying concentrations.

Design Tool for Predicting Printability and Nutrition of Novel Food Inks Using Rheological Property Measurements

Composite materials are the advanced materials which are widely used in manufacturing industries. The most commonly used composite materials are metal matrix composites. Due to the presence of abrasive reinforcing particles, traditional machining of these causes severe tool wear and hence reduces the life of cutting tool. Wire electrical discharge machining (WEDM) is quite successful for machining of metal matrix composites. Wire Electrical Discharge machining is a specialized thermal machining process capable of accurately machining parts of hard materials with complex shapes. The selection of process parameters in WEDM to obtain greater accuracy or cutting efficiency is still not fully solved due to the complicated stochastic process mechanisms with the most recent CNC wire cut EDM. One of the main research fields in WEDM is related to the improvement of the process productivity by avoiding wire breakage. The different factors viz., decrease in flushing pressure, inefficient removal of erosion debris and some other types of stochastic phenomena that occur during the machining process can lead to the breakage of wire electrode. In such cases, the wire has to be looped again by stopping the machining process, which leads to an undesired time waste. Before wire breaks, wire breakage has to be predict by diagnosing in advance low quality cutting regimes in order to perform an on line readjustment of the machine parameters. Worn electrode state dramatically affects the texture of the machined surface. Wire electrical discharge machining has been found to be a promising machining technique for obtaining desired dimensional accuracy and surface finish on hard and tough materials. Wire electrodes used in WEDM are the core of the system. WEDM is extensively used in machining of conductive material. In this study the effect of different wire electrode materials on dimensional accuracy and surface finish for wire electrical discharge machining of metal matrix composite material were investigated. The experiments were conducted under the following process parameters viz., pulse on-time, pulse off-time, current and wire feed speed. For the experiment the aluminium 6061 alloy with 0%, 5%, and 10 % of silicon carbide (SiC) reinforcement material was used. To conduct the experiment CNC wire EDM machine with two different wires viz., molybdenum and brass wire was used. L9 Taguchi orthogonal array technique was used to design the experiment. Experimental results indicate that for better surface finish and dimensional accuracy of Al6061 alloy, the brass wire is more suitable. Good surface finish and dimensional accuracy can be obtained with molybdenum wire in Al-SiC composite material. Increasing percentage of silicon carbide in aluminium 6061 alloy increases the variation in surface finish and dimensional accuracy. Wire wear rate of both brass and molybdenum wire is increased with increase in percentage of silicon carbide.


Effect of Wire Electrode Materials on Performance Characteristics for Wire Electrical Discharge Machining of Metal Matrix Composite Material

Thermo-acoustic systems are being considered as a potential sustainable solution for electricity generation where the sound waves can be used for electricity generation through a linear alternator. Thermo-acoustic is actually a field of science that is concern with the interaction between thermal energy (heat) and acoustic energy (sound) with the purpose of inducing cooling or generate electricity. Recently, there have been a significant increase in the development of thermo-acoustic refrigerators as well as thermo-acoustic generators with limited to no moving parts involved. Travelling wave devices have exhibited promising results with respect to their performance whilst working at very lower temperatures. This work describes the construction of a two-stage travelling-wave thermo-acoustic generator. In addition, an experimental investigation into the effect of the heat source on the potential of the device for electricity generation has been conducted in order to evaluate the device performance. The effect of the geometric configurations of the thermo-acoustic engines is examined for series and parallel arrangement. The prototype consists of two thermo-acoustic engine connected through Polyvinyl chloride (PVC) pipes forming a loop for the waves to travel through. A commercial loudspeaker was used as linear alternator in order to assess the potential for sound-to-electricity conversion of the system. Each engine consists of the regenerator, a cold heat exchanger and a hot heat exchanger. The magnitude of the sound generated by the engines, the onset time and the magnitude of electricity generated by the linear alternator have been considered as performance indicators for the device developed. Clear trends showing the effect of inputs parameters on device performance have been presented. The prototype was developed and thenceforth evaluated. It proved to perform better with the parallel configuration, and achieved a faster onset time than with series configuration. A minimum onset time of 3.15 minutes to produce a sound was recorded. The average minimum/maximum amount of heat that has produced a sound was 340/635^o^C corresponding to sound of 114.1/126.4 dB and a voltage of 387/486 mV respectively. Although the efficiency of the sound-to-electricity conversion was low, this work proves the viability of thermo-acoustic as the alternative solution for electricity generation. Research attention can be invested more on geometric arrangements and configurations of the multistage thermoacoustic devices i.e. the use of a suitable sound-to-electricity convertor, the best location for the alternator as well as whether single or multiple alternators produces better results. This paper provides clarity on the potential for thermo-acoustic system for sound-to-electricity conversion.


Construction and Performance Analysis of a Two-Stage Travellng-Wave Thermo-Acoustic Generator

Abstract:

Utilizing nanofluid in heat exchanger is extensively interested in petrochemical and power plant industries due to the durability provided to the exchanger long-life operation.   In the present research, an experimental investigation is carried out to study the influence of copper and aluminum oxide nanofluids on the performance of shell and tube type heat exchanger. Comparsion with theoretical outcome is also conducted.  Implementation of the experiments was performed using counter-flow double-pipe heat exchanger. The heat exchanger consists of 21 tubes through which the hot fluid flows. The 7 thermocouples are positioned along the hot and cold circuits so as to facilitate the measurement of temperatures at the inlet, exit and intermediate points of the exchanger. pure water is heated by means of an electric heating element to a specified temperature and is then pumped into the tubes of the heat exchanger unit. The second fluid (the nanofluid), stored in the cold fluid tank, is pumped into the heat exchanger unit by means of another impeller pump. The nanofluid flows in the annular space around the tubes. Although parallel and counter flow configurations can easily be established by making use of the four ball valves placed along the cold circuit, only counter flow configuration was setup for operation in the present study. Various volume fractions ranging from 0.26% - 0.83% were tested to assess the morphology of nanoparticle and volume fraction on the exchanger efficiency. It was observed that the volume fraction of nanofluid has a direct relationship to the heat exchanger effectiveness. As the volume fraction was increased, the effectiveness was found to increase by 7% and 10% for Al~2~O~3~ and Cu nanofluids, respectively.  Further, the effect of mass flow rate of cold-side nanofluid was investigated. The Reynolds number for the cold nanofluid was varied in the range 7000 - 15000. It was observed that the mass flow rate of cold nanofluid has a direct relationship with the Nusselt number. A significant enhancement in Nusselt number by 13% and 23% was observed for Al~2~O~3~ and Cu nanofluids, respectively. The effect of varying inlet temperature of hot fluid was also investigated.  Results indicate an enhancement in performance for higher inlet temperatures of hot fluid. Moreover, the heat leak from the shell side to the ambience was estimated for each case. Al~2~O~3~ nanofluid was observed to have greater heat leak in comparison to Cu nanofluid.


Evaluating the Influence of Nanofluid Type and Volume Fraction on the Performance of Heat Exchanger

In this paper we want to present an unsteady simulation of a full rotor of an axial fan with low pressure and high flow rate, developed during the MinWaterCSP EU project, specifically designed and optimized for Concentrating Solar Power (CSP) plants with the aim of reducing water consumption at the condenser stage. An earlier version of the fan, referred as M-Fan, was initially developed to serve the hybrid cooling system, to boost the overall heat transfer performance with dry cooling. In this work, we will evaluate the performance of a redesigned and scaled version of the fan, referred as T-Fan, by performing a Computational Fluid Dynamics (CFD) analysis of the unsteady flow. The T-Fan was designed and optimized to reduce noise emissions and improve efficiency with respect to the M-Fan. We perform the simulation using a in-house built C++ parallel software for CFD analysis using Finite Elements (FE). We model the flow dynamics using the Residual Based Variational MultiScale method (RB-VMS) to obtain a stabilized solution of the Navier-Stokes equation using a Finite Elements (FE) discretization.

We will discuss the simulation results of the RB-VMS model by comparing our the RB-VMS simulation of the T-Fan with LES and experimental results on the same fan.


Unsteady Flow Simulation of an Axial Fan for Dry Cooling in a CSP Plant Using the Variational Multiscale Method

This study investigates the influence of various inducer configurations on the single-phase and two-phase flow behavior. Three pitch values (*P* = 0.151, 0.251, and 0.351 m), as well as three different number of blades (N = 2, 3, and 4 blades), were studied, leading to a total of 9 different inducer geometries. The main objective of the present study is to analyze and compare the corresponding performances and the mixing behavior when pumping a gas/liquid mixture. For this purpose, 3D steady-state simulations using the Moving Reference Frame approach were applied for single-phase flows, while a transient setup using a moving-mesh approach was employed for two-phase simulations. Turbulence was modeled by the Reynolds Stress Model, whereas the standard Volume of Fluid method was applied to model air-water interactions. The results show that an increase in the number of blades leads to a high drop in performance at overload (high-flow) conditions and only a slight performance enhancement at part-load (low-flow) conditions. Additionally, the effective range in which the inducer efficiency is high becomes narrower for a higher number of blades. Concerning now the inducer pitch, at part-load conditions, a lower pitch is slightly beneficial to smoothly suck the flow and damp low-flow vortices. On the contrary, employing a high pitch at these conditions results in intensified flow vortices, reducing the performance. Furthermore, the blade pitch strongly impacts the performance at optimal and overload conditions, where a lower pitch causes flow blockage, leading to significant performance deterioration. Generally, it is found that the inducer configuration affects the performance much more at overload compared to part-load conditions. Concerning two-phase flows, the highest pitch provides the best mixing since the inducer is able to effectively churn the two phases, as compared to low-pitch inducers. Similarly, an increase in the number of blades amplifies the turbulence between the two phases, thus improving mixing. Overall, higher pitches and low to moderate number of blades are favorable to ensure high performance over a wide range of flow conditions and to improve pumping of two-phase flows.


Influence of Blade Pitch and Number of Blades of a Pump Inducer on Single and Two-Phase Flow Performance

This paper describes an investigation into the off-design performance comparison of single and two-shaft gas turbine engines. A question that has been asked for a long time in which gas turbine delivers a better thermal efficiency at part load. The authors, notwithstanding their intensive searches, were unable to find a comprehensive answer to this question. A detailed investigation was carried out using a state of the art performance evaluation method and the answer was found to be: It depends!

 

In this work, the performance of two engine configurations is assessed. In the first one, the single shaft gas turbine operates at constant shaft rotational speed. Thus, the shape of the rotational speed line will have an important influence on the performance of the engine. To explore the implications of the shape of the speed line, two single shaft cases are examined. The first case is when the speed line is curved and as the compressor pressure ratio falls, the non-dimensional mass flow increases. The second case is when the speed line is vertical and as the compressor pressure ratio falls, the non-dimensional mass flow remains constant.

 

In the second configuration, one shaft couples a compressor and a turbine (often called the gas generator shaft). The second shaft couples the power turbine to the driven equipment. The two shafts can be controlled to operate at different rotational speeds and also varying relationships between the rotational speeds. The part-load operation is characterised by a reduction in the gas generator rotational speed.

 

The tool, which was used in this study, is a 0-D whole engine simulation tool, named Turbomatch. It was developed at Cranfield and it is based on mass and energy balance, carried out through an iterative method, which is based on component maps. These generic, experimentally derived maps are scaled to match the design point of a particular engine before an off-design calculation is performed. The code has been validated against experimental data, it has been used extensively for academic purposes and the research activities taken place at Cranfield University.

 

For an ideal cycle, the single shaft engine was found to be a clear winner in terms of part-load thermal efficiency. However, this picture changed when realistic component maps were utilised. The basic cycle and the shape of component maps had a profound influence on the outcome.

 

The authors explored the influence of speed line shapes, levels of component efficiencies and the variation of these component efficiencies within the operating range. This paper describes how each one of these factors, individually, influences the outcome.


Off-Design Performance Comparison Between Single and Two-Shaft Engines: Part 1 \u2014 Fixed Geometry

In modern aviation business, the high bypass ratio turbofan engine is the main power plant of the aircraft. The fan of a high bypass ratio turbo fan engine produces up to 80% of the total thrust of the engine. The aerodynamic performance of low pressure turbine, which drives the fan, plays an important role in the economic benefits of engine. As the diameter of the fan increases, the problem of rotating speed mismatch between the fan and the low pressure turbine becomes more and more severe. The GTF (geared turbofan) engine is a good solution to the problem and has been proved by the Pratt & Whitney Company. For the GTF low pressure turbine, profile losses may account for most of the total losses like traditional LPTs, and these are mainly controlled by the separation, transition, and reattachment of the flow in the suction side of the airfoils. But unlike the traditional LPTs, the GTF LPT works in a higher Mach number environment. The traditional LPTs usually operate at Mach numbers in the range 0.4-0.7 while the GTF LPT could operate at a transonic environment. Generally, the GTF LPT works in a high Mach number and low Reynolds number environment.

In present study, a high-lift low pressure turbine cascade designed for GTF engine work environment is numerically investigated. The LES (large eddy simulation) method is used to investigate the influence of Mach number on the development of boundary layer of suction surface in low Reynolds number. Three different isentropic exit Mach numbers, which are 0.14，0.87 and 1.17 respectively, are simulated while the Reynolds number is kept the same value of 1×10^5^, where the Reynolds number is based on the axial chord length of the blade and the exit flow velocity. The condition of exit Mach number of 0.87 and the Reynolds number of 1×10^5^ is at the design point of the turbine. The turbine profile is designed with the after loaded method.

The simulated results show that the development of boundary on the blade suction surface is strongly affected by the Mach number. It is found that the total pressure loss of the turbine cascade is the lowest at the operating condition of the lowest isentropic exit Mach number of 0.14, while the total pressure loss of turbine cascade is the largest at design point condition with exit Mach number of 0.87. At the transonic condition of exit Mach number of 1.17, despite the existence of shock wave, the total pressure of turbine cascade reduced some compared with that at the design point condition.

It is found that the separation, transition, and reattachment process exist in the boundary layer on the suction surface of turbine cascade which is similar as that on traditional low pressure turbine cascade. The separation point is located at about 89% axial chord length and the reattachment point is located at just before the trailing edge. While the turbine cascade works at the condition with the Mach number of 0.87, the boundary layer on suction surface kept laminar and sepa

The Influence of Mach Number on the Boundary Layer Development of High-Lift Low Pressure Turbine in Low Reynolds Number

Logging while drilling (LWD) is a rapidly developing in-situ measurement technique due to its advantages of saving time and cost, less mud invasion during measurements, and the application in deviated or horizontal wells. Unlike the measurements in a vertical well, the LWD tools are inevitably off-centered in deviated or horizontal boreholes due to gravity. In this study, we investigate the wave propagation of unipole acoustic LWD with eccentric tools. The unipole transducer in a fluid-filled borehole can be characterized as a single point source deviated from the symmetric axis. The signals of unipole transmitters with arbitrary azimuths can approximately be equivalent to a linear combination of monopole, dipole, and quadrupole sources. According to analyses of the wave separation, it is concluded that the dipole components are dominant in the full wave arrays of unipole tools. The formulation of responses at the opposite azimuth with respect to a unipole transmitter reveals that the unipole data by this gathering mode would have less sensitivity to the tool positions. Numerical simulations by 3D finite difference further confirm this. For conventional multipole LWD including dipole and quadrupole logging, it is quite hard to evaluate the true shear velocity of the formation once the tool is highly off-centered in the borehole. For the unipole data gathered at the opposite azimuth to the source, however, the signal properties are very stable, with little dependence on either the tool eccentricity or the source orientation in horizontal wells. Both the fast and the slow shear velocities of an anisotropic formation can therefore be measured with good accuracy according to inversion tests in this study. Numerical examples further show it is feasible to evaluate the formation shear anisotropy by the unipole data during the tool rotating.


Unipole Sonic Logging While Drilling With Eccentric Tools and Anisotropy Evaluations

*The recent development in technology has made bio-based plastics an increasingly attractive alternative to petroleum-based plastics to tackle plastic pollution. However, currently, bio-based plastics have not been widely adopted in the design and manufacturing of new products. To advocate the use of bio-based plastics, this paper proposes two visualization-based tools to educate designers and engineers about the availabilities and the properties of different bio-based plastics. After analyzing the literature on visual tools for sustainable design and material selection, two new prototype tools for screening bio-plastic alternatives are designed with the advice and support of the engineers of a major U.S. manufacturer of agricultural equipment. Surveys and focus groups with the manufacturer's engineers are conducted to improve the tools, and a first case study is completed to examine their usefulness.*


Switching From Petroleum- to Bio-Based Plastics: Visualization Tools to Screen Sustainable Material Alternatives During the Design Process

The analysis and estimation for  rare events with extremely small probabilities under the acceptable computational cost are challenging in many engineering applications, especially for high dimensional problems. Those small probabilities of the engineering system often lead to the decline in the estimation accuracy and efficiency that recognizes the importance of the robust estimation of the probability with narrow bounds in rare events. Generally, confidence intervals of the estimator are established based on the central limit theorem. One of the main obstacles is that the widely used Monte Carlo method requires a huge number of samples to derive reasonably narrow confidence interval which is computationally expensive. This paper, therefore, proposes a powerful probability analysis approach that can estimate the probability of rare events in high dimensional systems efficiently and provide narrow bounds for estimations simultaneously. The asymptotic behaviors of the proposed estimator is proved theoretically without strong assumptions. Based on that, an asymptotic confidence interval is established for the proposed estimator. This study offers some important insights into the robust estimation of rare events. The efficiency of the developed technique for rare events estimation with confidence intervals is assessed with several engineering design examples. Our numerical experiments demonstrate that narrow bounds are built efficiently with probability estimations, and the real probability results are always located within the proposed estimation bounds, which indicates that the proposed approach can improve both efficiency and accuracy of the rare events estimation


Sequential Sampling Based Reliability Analysis for High Dimensional Rare Events With Confidence Intervals

Motion Decay Simulations of a Moored Wave Energy Converter

Changqing Jiang^1^, Ould el Moctar^1^, Guilherme Moura Paredes^2^, Thomas E. Schellin^1^

^1)^ University of Duisburg-Essen, Duisburg, Germany

^2)^Aalborg University, Aalborg, Denmark

Abstract

Significant cost reductions are required for marine renewable energy to become competitive. Aside from the deployment of arrays, one key area that has been identified as having potential for cost reductions is the mooring system \[1\]. A clear challenge therefore exists to design mooring systems which can satisfy their primary role of station keeping while being affordable and durable. This paper presents the effects of different mooring configurations on the motion behavior of a buoy type wave energy convertor (WEC), considering nonlinear mooring-induced fluid-structure interactions, such as the associated viscous effects. To simulate motion decay, we adopted an overset mesh method that coupled a dynamic mooring model with the viscous flow solver OpenFOAM \[2\]. We analyzed a floating WEC moored with three different mooring configurations (catenary, catenary with buoys, and catenary with buoys and clump weights) and validated our predictions against experimental measurements \[3\]. Of interest were not only the influence of environmentally-induced loads on the mooring systems and their components, but also the type of soil of the seabed and the associated seabed footprint, as these aspects affect the desired spacing between devices. Moreover, we demonstrated that our dynamic mooring model coupled with the viscous flow solver was capable of simulating the behavior of the moored WEC.

REFERENCES

\[1\] Hall, M.T.J., 2013. Mooring line modeling and design optimization of floating offshore wind turbines. PhD thesis, Technical University Delft, Delft, 2009.

\[2\] Jiang, C., el Moctar, O. and Schellin, T.E., 2019. Prediction of hydrodynamic damping of moored offshore structures using CFD. Proc. 38th Int. Conf. on Ocean, Offshore and Arctic Engg., OMAE 2019-95935, Glasgow, Scotland, June 2019.

\[3\] Paredes, G.M., Palm, J., Eskilsson, C., Bergdahl, L. and Taveira-Pinto, F., 2016. Experimental investigation of mooring configurations for wave energy converters. Int. Journal of Marine Energy, Vol. 15, pp.56-67.


Motion Decay Simulations of a Moored Wave Energy Converter

The air gap response is crucial for the safe design and operation of large-volume floating offshore systems such as semi-submersible or tension leg units. Calculating air gap of semi-submersible unit, considering the wave-free surface elevation and the motions of the floating vessel, is a complex task. A series of theoretical and numerical researches on air gap had been performed, but even second-order analysis is difficult to have an accurate description of that. Therefore, air gap response still relies heavily on experimental analysis.

This paper attempts to describe the wave run-up characteristics along columns and the effects of the mooring system, especially the length of mooring lines, on airgap response of semi-submersible unit based on model tests.

The scale model of the semi-submersible unit is supported by a symmetric mooring system composed of 8 mooring lines. A set of model tests by adjusting the length of the mooring system, considering the combined action of wind, wave and current loadings in 3 directions, were conducted in the State Key Laboratory of Ocean Engineering basin at Shanghai Jiao Tong University. Air gap combined wave run-up characteristics in the vicinity of columns at a total of 15 locations on the deck were evaluated under oblique wave status.

The results indicate that the mooring system plays an important role in air gap response of semi-submersible unit. Meaningful conclusions are drawn in this paper, which is helpful in air gap and mooring system design of semi-submersible unit.


Experimental Study on the Effects of Mooring System on Air Gap Response of Semi-Submersible platform

Pumped Thermal Electricity Storage (PTES) is a grid-scale energy storage device. During charge, grid electricity is used to drive a heat pump which creates hot and cold storage. Electricity is thereby stored in a thermal potential. The storage is discharged by reversing the cycle and operating a heat engine between the two stores. Compared to other bulk thermo-mechanical storage technologies, PTES is not geographically restricted, can achieve reasonably high round-trip efficiencies, energy and power densities, and can use cheap, abundant, non-toxic materials as the storage media.

A variety of PTES concepts exist, which may use Joule-Brayton cycles, steam Rankine cycles, or supercritical/transcritical CO~2~ cycles, for example. Similarly, a variety of storage materials may be used, such as molten salts, thermal oils, glycols, packed beds of pebbles, or concrete.

In this presentation, a thermo-economic tool for the analysis of PTES systems will be described. This model includes detailed technical models of the main system components, such as compression and expansion machinery, heat exchangers, storage tanks, and packed beds. The system economics (such as total capital cost and levelized cost of storage) are evaluated using a variety of component cost models, and this approach enables the uncertainty to be quantified.

Techno-economic results will be presented for several PTES concepts, including a recuperated Joule-Brayton cycle with two-tank liquid storage, a Joule-Brayton cycle with packed-bed thermal storage, and a supercritical-CO~2~ cycle. The tool allows the performance and cost of these various systems to be fairly compared to one another, and informs the future development of these energy storage devices.


Techno-Economic Modelling of Pumped Thermal Electricity Storage

Natural convection has a great its importance in several practical applications. In particular, the configuration of two horizontal parallel walls, with heated upper plate and open cavities, gets considerable attention in many thermal engineering applications, such as cooling of electronic components and devices, chemical vapor deposition systems and solar energy systems. The flow motion is strongly affected by the location of the heated surface, positioned on the upper or the lower wall of the horizontal channel. The main flow in natural convection is caused by the low heat exchanged between flow and walls, and one of the techniques to enhance the heat transfer is expanding the exchange surfaces. Porous media provided with high thermal conductivity, like metal foams, are an adequate method of heat transfer enhancement due to their large surface area to volume ratio and to intense mixing of the flow. In this work, a numerical investigation on two-dimensional steady state natural convection in a horizontal channel partially filled with a porous medium and heated at uniform heat flux from above is carried out. The lower plate is adiabatic. The porous medium is modeled using the Brinkman–Forchheimer-extended Darcy model and the local thermal equilibrium (LTE) hypothesis is assumed. The structure of the porous medium is homogenous and isotropic, the thermophysical properties of the air and the porous medium are temperature independent and the fluid flow is laminar and incompressible. The governing equations in the two-dimensional model is realized and solved by means of the ANSYS-FLUENT code. The computational domain is made up of the principal channel and two lateral extended reservoirs at the open vertical sections. The channel has dimensions L equal to 400 mm and the distance between the two horizontal plates, b, is equal to 40 mm. The two external reservoirs allow to simulate the external ambient and to assign at the boundary of the reservoirs a velocity equal to zero and the ambient temperature. Furthermore, a porous plate is considered near the upper heated plate and it has a thickness equal to 20 mm whereas the length and the width are the same of the channel. The aluminum foam has 10, 20 and 40 PPI and its porosity ranges from 0.89 and 0.97. Rayleigh number values are examined, from 10 to 1000. The main aim of the present study is to analyze the effect of pores per inch and porosity. The numerical simulations are performed with working fluid air. Different values of assigned wall temperatures are considered. Results are presented in terms of velocity and temperature fields, and both temperature and velocity profiles at different significant sections are shown, to obtain a description of the natural convection inside the open-ended cavity. Finally, Average Nusselt number values are evaluated.


Study on Natural Convection in Horizontal Parallel Plate Channels Heated on Upper Wall and Partially Filled With Metal Foam

A new design of an intercept valve assembly of the intermediate-pressure turbine part of greater power output is investigated in terms of pressure losses and flow fluctuations by using measurement on an experimental valve model. In addition, numerical simulations are used to further clarify measured phenomena. For such valve assemblies, it is important to exactly predict pressure losses and avoid danger of vibrations, which are caused by undesirable flow fluctuations, in order to guarantee valve´s efficiency and operational reliability. For this type of valve, it is especially important for turbine operations in partial loads (off-design conditions). Measurements were carried out in the Aerodynamic laboratory of the Institute of Thermomechanics of the Czech Academy of Sciences (IT) in a modular aerodynamic tunnel. Numerical simulations were carried out in the Doosan Skoda Power Company (DSP) by using a package of ANSYS software tools. The experimental valve model is a scaled model of a real valve assembly. It consists of an inlet pipeline, a stop valve and a control valve including its diffuser and outlet pipeline. Measured regimes were defined by a mass flow rate and a control valve lift which can be precisely changed. In order to investigate pressure loses, total and static pressures at valve characteristic locations were measured by using Prandtl probes and wall static pressure taps. In order to measure pressure fluctuations, Kulite fast response pressure transducers were used. They were situated near the valve throat where the flow fluctuations, which are strongly related to a flow separation, are the most visible and influential. Measurement results are compared with numerical results and locations with a flow separation were found. In order to reduce this phenomenon, different valve seat angles were also tested. As a result, a valve design could be optimized and, for a pressure loss prediction, a pressure loss model for this new intercept valve assembly could be created. Therefore, pressure losses in similar valve assemblies can be predicted with required accuracy for each new turbine where modern intercept valves are used. This helps to increase steam turbine efficiency and reduce fuel consumption. Based on pressure fluctuations results, operating conditions at which dangerous flow instabilities occur were identified. It was concluded that there is an operating condition border where the flow field starts to be unstable. As a result, the areas of safe and dangerous operating conditions can be predicted so that the operational reliability of the valve can be guaranteed.


Investigation of Pressure Losses and Flow Fluctuations in an Intercept Valve Assembly of an Intermediate-Pressure Turbine Part

In the near future, the world’s transportation system should be powered by less-pollutant or completely non-pollutant energy sources. The rationale behind these systems is the protection of the planet and all forms of lives. The transportation sector produces 15 to 20 % of greenhouse gas emissions. Many renewable energy sources are being explored for the transportation sector. But the technologies are less popular because of their infancy stages, as well as the cost associated with their use. Solar energy, compressed air, hydrogen, electric battery etc. are few examples of the clean and renewable energy sources which are prominent for powering the transportation of the future. Compressed air is one of the plausible solutions to solving the energy problem, considering the fact that air is readily available. But the problem in the usage of the compressed air energy has been the storage system. In this paper, the performance of two distinct compressed air reservoirs for energy storage in small scale systems was investigated. Physical experiments were conducted, and simulations were performed. The analysis performed in this work was focusing on the results trends. Two air compressors were utilized for the experiment and they were both of reciprocating type. The first air compressor was driven by an internal combustion engine (ICE) and the second was driven by an electric motor. The decision regarding which results to consider was made based on the data collected. The experimental results were used to provide a frame of reference for the computer (MATLAB) simulation. Additionnaly, the performance of the dynamic reservoir was analysed for three spring stiffnesses. In summary, this study shows that the maximum pressure that can be stored in any dynamic reservoir depends largely on the capacity of the compressor. The quick rise in pressure during the charging process and the quicker exit during the discharging period clearly indicated that something unusual took place. It appears that the spring has a beneficial impact on the working of compressed air reservoir. The piston and the spring represent the heart of the dynamic reservoir. During charging they convert the pressure to force and the force to strain energy respectively. During discharge, they reverse the charging process by converting the strain energy to force and the force to pressure. Thus, ensuring a consistent performance of the dynamic reservoir. The dynamic reservoir offers the capacity to store a high quantity of compressed air in a relatively small volume. It offers a better mass flow rate during discharge, because the spring pushes the gas out of the reservoir, making a steady flow possible. The rapid pressure rise inside the dynamic reservoir and the constant pressure supply during discharge will improve the performance of compressed air powered applications and will help those to become more reliable.


Development and Performance Evaluation of a Dynamic Compressed Air Energy Storage System

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