Preliminary Design Criteria Research Articles

A Numerical Study on the Influence of Transverse Grooves on the Aerodynamic Performance of Micro Air Vehicles Airfoils

Micro Air Vehicles (MAVs) airfoils usually operate at low Reynolds number conditions, where viscous drag will consume a large amount of propulsion power. Due to the small dimensions, many drag reduction methods have failed, resulting in limited current research. To develop an effective method of reducing viscous drag, transverse grooves were placed on the surface of MAVs airfoils in this study, and a numerical investigation was implemented to uncover the corresponding flow control law as well as the mechanism. Research has shown that transverse grooves have an impact on the drag and lift of airfoils. For drag, properly sized transverse grooves have the effect of reducing drag, but under high adverse pressure gradients or when the continuous arrangement of grooves is excessive, the optimal drag reduction effect achieved by the grooves is weakened, and even the drag increases due to the significant increase in pressure difference. In severe cases, it may also cause strong flow separation, which is not conducive to MAV flight. For lift, the boundary vortex in the groove has the ability to reduce the static pressure near the groove. However, high adverse pressure gradients or too many grooves will thicken the boundary layer and increase the blockage effect, resulting in a large static pressure on the grooved side of the airfoil (with an increase in drag). From the perspective of circulation, the static pressure changes on the suction and pressure surfaces have opposite effects on lift. Considering the comprehensive aerodynamic performance of the airfoil, we designed a high lift-to-drag ratio airfoil with grooves, which increased the lift-to-drag ratio by 33.747% compared to the smooth airfoil. Based on the conclusions, we proposed preliminary design criteria for grooved airfoils, providing guidance for subsequent research and applications.

Reduction of feedback pressure perturbation for rotating detonation combustors

The transient pressure propagation induced by the unsteady but stable rotating detonation combustor can lead to degradation of the compressor performance and stability. In this study, the propagation characteristics of feedback pressure perturbation are firstly investigated based on numerical simulations of internal flows. Then a form of isolator configuration, which is a cylinder with several rows of wedge obstacles on the inner wall, is constructed aiming at weakening the pressure perturbation. Furthermore, a preliminary optimization design criterion of the isolator is proposed based on balance between the feedback pressure reduction and total pressure recovery. The results show that, the feedback pressure perturbation mainly propagates upstream along the axial and circumferential direction against the outer wall of the flow channel. Meanwhile, the peak pressure slowly decays during the propagation of the pressure perturbation along the axial direction, and the feedback pressure perturbation rotates in the same direction as the detonation wave with a phase lag in the circumferential direction. The isolator with a series of wedge obstacles on the inner wall can accelerate the decay of the feedback pressure perturbation. Increasing the number of obstacles, the dimensionless height, width and spacing have a positive impact on the reduction of the pressure perturbation, while the effect of increasing the inclination angle is just opposite. Meanwhile, an expanded channel for the isolator is more beneficial for reducing the feedback pressure perturbation.

VPP Coupling High-Fidelity Analyses and Analytical Formulations for Multihulls Sails and Appendages Optimization

A procedure for the optimization of a catamaran’s sail plan able to provide a preliminary optimal appendages configuration is described. The method integrates a sail parametric CAD model, an automatic computational domain generator and a Velocity Prediction Program (VPP) based on a combination of sail RANS computations and analytical models. The sailing speed and course angle are obtained, with an iterative process, solving the forces and moment equilibrium system of equations. Analytical formulations for the hull forces were developed and tuned against a matrix of CFD solutions. The appendages aerodynamic polars are estimated by applying preliminary design criteria from aerospace literature. The procedure permits us to find the combination of appendages configuration, rudders setting, sail planform, shape and trim that maximise the VMG (Velocity Made Good). Two versions of the sail analysis module were implemented: one adopting commercial software and one based on the use of only Open-Source codes. The solutions of the two modules were compared to evaluate advantages and limitations of the two approaches.

Producing geothermal energy with a deep borehole heat exchanger: Exergy optimization of different applications and preliminary design criteria

This paper aims at proposing fast and plain design tools to evaluate the best energy application for deep borehole heat exchangers, exploiting geothermal resources. Exergy efficiency has been chosen as a performance index. Five possible utilization solutions have been analyzed: district heating, adsorption cooling, ORC power production, a thermal cascade system, and combined heat and power configuration. An extensive sensitivity analysis on source characteristics and well geometry has been performed to find the design criteria that ensure the maximum exergy performance. Results show that configurations involving district heating are recommended for exclusive power production. If optimized, district heating exergy efficiency can reach values in the range 40%–50% when a geothermal source at the well bottom is lower than 300 °C. For higher values, the combined heat and power production is a preferable choice, reaching an exergy efficiency of up to 60%. Design charts are also provided to read first-attempt values of the well operative temperatures and flow rate to maximize exergy efficiency for each utilization layouts.

Preliminary design criteria of prestressed concrete structures

Preliminary design criteria of prestressed concrete structures

A conceptual method to assess ship-helicopter dynamic interface

The combined operation of a ship and a helicopter is ubiquitous in every naval organization. The operation of a ship in combination with the landing and take-off operations of a helicopter results in a very complex flow phenomenon. This is due to the presence of ship airwakes, strong velocity gradients and widely varying turbulence length scales. An accurate assessment of the resultant flow phenomena is an outstanding challenge for naval architects as well as researchers. A conceptual method to gain insight into the combined ship-helo flow phenomena over a helodeck is presented. The prime objective of this work is to develop an economical design tool employing both experimental as well as computational techniques to simulate the ship-helicopter coupled environment regime at early design stages reasonably well so as to ease the burden of expensive and risky sea trials. For this purpose, a simplified dynamic interface (SDI) model is proposed to investigate the coupled effects of ship airwake and helicopter rotor downwash. The paper reports a parametric analysis to study the coupled ship-helo airwake behaviour and its impact on helicopter fuselage over the ship helodeck for different ship speed regimes by the proposed SDI model. Further, an attempt has been made to set up preliminary design criteria to grade the ship-helicopter interface for ensuring minimum standards of safe helo operations. Finally, we discuss the impact of the coupled flow dynamics in terms of induced fuselage drag, cross-flow characteristics, rotor plane wake and velocity gradients existing over the helodeck region and evaluate the proposed design criteria.

Selected Properties of Input Stock Material for the Production of Thin-Walled Cylindrical Products by Cold Flow Forming

This paper presents test results for the steel grade 15HGMV metallurgical purity, microstructure, method of production and effect on the mechanical performance of the input stock material for calibre 227 mm missile motor casings manufactured by cold flow forming. The reference product for the determination of preliminary design criteria of missile casings of the higher calibre were calibre 122 mm missiles manufactured in Poland. The final mechanical properties of the casings are a cumulative effect of quenching and tempering and strain hardening during cold flow forming. The research and industrial practice carried out so far have demonstrated that the production process of a Feniks missile (with a 1.5 mm thick casing wall) requires steel grades of extremely high purity. This steel grade is manufactured by VAD (Vacuum Arc Degassing) melting, followed by ESR (ElectroSlag Remelting) or, alternatively by melting and casting in vacuum oven. The content of hard and non-deformable non-metallic inclusions such as oxides is critical to the success of cold flow forming. The cal. 227 mm missile casings feature walls approximately 2.5 mm thick and produced by cold flow forming from a quenched and tempered intermediate product. New material specifications should be developed for this reason to enable correct cold flow forming and contribute to a significant improvement in the cost efficiency of manufacturing. The investigations covered herein were guided by an assumption that the thicker wall sections might make the material specifications applicable to lower-calibre missiles to restrictive and obsolete about cal. 227 missiles. After initial laboratory tests, this hypothesis will be verified in industrial experiments on the production of prototype missile casings from input stock materials varying in metallurgical purity.

Preliminary design criteria of Stirling engines taking into account real gas effects

This article deals with the main geometric parameters, operating variables and experimental results of engines with different size and characteristics, as well as simulation predictions at operating conditions for which the working fluid may evidence real gas effects. The concept of dimensionless quasi-static indicated work, introduced previously, is computed assuming both ideal and real gas models. Both values are compared with the Schmidt's model prediction, to evaluate separately how the mechanism simplification and the equation of state affect. The influence of physical gas properties are also analysed regarding the gas circuit performance and mechanical efficiency. Pending of experimental corroboration, some simulations show the possibility of obtaining interesting operating conditions under real gas effects.Semi-empirical equations and experimental correlations are proposed as preliminary design criteria. The ratio between the dimensionless values of the maximum indicated power (a sort of ‘indicated’ Beale number) and the quasi-static indicated work is analysed. The procedure to estimate the maximum indicated power is completed by analysing the characteristic Mach number (dimensionless rotation frequency). Analogous procedure is applied for the maximum brake power and corresponding engine speed. Use of dimensionless variables facilitates the generalization of analyses by means of dynamic similarity criteria.

Distributed Structural Monitoring for a Smart City in a Seismic Area

The concept of Smart City (SC) has been introduced to categorize the vast area of activities to enhance the life quality of citizen, which are characterised by a pervasive use of Information and Communication Technologies (ICT), to help cities, with various urban domains, making better use of their resources. Monitoring the structural behaviour of strategic buildings and monuments may be desirable for citizens, which have recently experienced a destructive earthquake in their own town, such as the case of L’Aquila. The paper deals with the design of a distributed structural monitoring network for a selected set of strategic structures belonging to the city of L’Aquila. Preliminary design criteria are discussed on the basis of previous authors’ experiences in this context. Specific attention has been dedicated to analyse the expected acceleration response measurements induced by small seismic excitations for the general purpose of monitoring.

Analysis of Influence of Structures and Strength about Corrugated Radius of Metallic Sealing Ring

In order to make the design criteria of metallic sealing rings, and improve the mechanical properties of metallic sealing rings used in aviation engine, using finite element analyzing the stress distribution of three corrugated sealing rings with different corrugated radius. Finally get a preliminary design criterion of metallic sealing rings of aero engine

Preliminary design and fast prototyping of an Autonomous Underwater Vehicle propulsion system

The Mechatronics and Dynamic Modelling Laboratory of the Department of Industrial Engineering, University of Florence, as a partner of THESAURUS (Italian acronym for ‘TecnicHe per l’Esplorazione Sottomarina Archeologica mediante l’Utilizzo di Robot aUtonomi in Sciami’) project, has developed an innovative low-cost, multirole autonomous underwater vehicle, called Tifone. This article deals with the adopted methodologies for the autonomous underwater vehicle design: in particular, the main focus of this study is related to its propulsion system. According to the expected performances and requirements of THESAURUS project, the vehicle has to maintain good autonomy and efficiency (typical features of an autonomous underwater vehicle), with high manoeuvrability and hovering capabilities, which are more common of remotely operated vehicles. Moreover, cooperative underwater exploration and surveillance involve the use of a swarm of vehicles. In particular, the optimization of costs versus benefits is achieved through the design of a fleet of three multirole vehicles. Each autonomous underwater vehicle has five controlled degrees of freedom, thanks to four thrusters and two propellers: in this article, the preliminary design criteria concerning the vehicle and the design and testing of its actuation system are described.

Providing Simulated Online and Mobile Learning Experiences in a Prison Education Setting

This article reports on the preliminary findings, design criteria and lessons learned while developing and piloting an alternative to traditional print-based education delivery within a prison environment. PLEIADES (Portable Learning Environments for Incarcerated Distance Education Students), was designed to provide incarcerated students with access to internet-independent secure digital and mobile technologies. An internet-independent version of Moodle was developed to complement course readings deployed on eReaders. The aim of the project was to increase access to and participation in higher education courses that are increasingly offered exclusively online. The article begins with an overview of the current provision of education within prison environments and introduces the rationale for commencing the project. The research findings of the project trial are discussed and the paper concludes with the lessons learned and implications for further research, development and implementation.

Wave-power absorption from a finite array of oscillating wave surge converters

Semi-analytical and fully numerical modelling is developed in the framework of the inviscid potential flow theory to investigate the dynamics of a wave farm made by flap-type wave energy converters in the nearshore. The hydrodynamic parameters and the efficiency of the system in typical layouts are calculated with both models. Good agreement is shown between the two approaches. Parametric analysis undertaken with the semi-analytical model allows to identify a near-resonant phenomenon which is responsible for increasing the absorbed power by the single elements of the array. Such result could be used as a preliminary design criterion. The numerical model is then applied to analyse a configuration of practical engineering interest, i.e. an array of two staggered converters. The dynamics arising in this more complex system is explained, showing that non-symmetric layouts can be less effective.

Acid leaching of uranium from a low-grade Indian uranium ore deposit

This paper discusses the leaching behavior of uranium from a low-grade unconformity-related uranium ore occurring in the northwestern part of the Kadapa basin in southern India. This is the major unconformity-related deposit located in India. The U3O8 assay of the ore is about 0.06%. The chief uranium-bearing phase is uraninite, and the ore also has a minor quantity of coffinite. The carbonaceous matter, as well as the porous titanium phases occurring in the ore, is also radioactive. The major gangue mineral is quartz, followed by minor quantities of sericite, chert, chlorite and feldspar. Detailed parametric variation studies were carried out on the ore to optimize conditions for sulfuric acid leaching of uranium values. Based on the laboratory results, preliminary design criteria were developed for process engineering. About 82% of uranium values were leached under conventional atmospheric leaching conditions. Uranium values present in the carbonaceous matter and the other refractory phases were solubilized only after roasting the leach residue. This process improved the overall leach recovery to about 89%.

Optimization design and exergy analysis of organic rankine cycle in ocean thermal energy conversion

Performance analytical function and exergy efficiency of organic rankine cycle (ORC) in ocean thermal energy conversion (OTEC) are derived and optimized in this paper. Firstly, the state function corresponding to every point in ORC and depending strongly on the temperature of the evaporator and condenser is successfully achieved, where the suitable working fluids include, but not limited to, ammonia, r134a, etc. And then the system net power output function is achieved based on the characteristics of the ORC, which is mainly decided by the warm seawater temperature, warm seawater mass flow rate, evaporator temperature, condenser temperature, etc. After that, a further optimization is carried out to maximize the net power output of ORC. Results show that ammonia is a good choice for ORC utilized in OTEC from net power output viewpoint. In addition, thermal efficiency and exergy efficiency at maximum net power output are also given as reference. Finally, the preliminary design criteria of ORC in OTEC illustrates that the design of the ORC in a certain scale should choose its corresponding reasonable heat exchanger since it is a choke point for the larger maximum net power output.

Seismic performance of buildings with thin RC bearing walls

In Latin America there is an urgent need for housing; thus, during the last few years a relevant number of mid-height buildings (usually, up to five stories) with thin RC shear–walls have been constructed for low-cost dwellings in Bolivia, Colombia, Ecuador, Mexico, Peru, Venezuela, and other countries located in seismic-prone regions. These walls are 10 cm thick and their reinforcement consists mainly of a single layer of welded wire mesh. This construction technology offers two main advantages: economy and rapidity of construction. These buildings do not fulfill the international seismic codes but some national regulations are less demanding, not preventing the use of thin bearing walls. These buildings might be vulnerable to earthquakes because of their low ductility, the insufficiency of the experimental information, the absence of observed damages and, in some cases, poor construction quality. This work describes the initial steps of a wider research aiming at providing reliable seismic design guidelines for thin-wall buildings; the initial objectives are analyzing the seismic performance of these buildings, proposing preliminary design criteria and identifying further research needs. This research focuses on buildings located in Peru, being representative of the situations in the other countries. The vulnerability is numerically evaluated by push-over and nonlinear time history analyses; the structural parameters are obtained from available testing information. The obtained results show that the seismic strength of the analyzed buildings is insufficient; however, minor changes in the structural design might improve significantly their seismic performance. Cheap and easy-to-implement design recommendations are issued.

Stepped Spillway with Hydraulic Jumps: Application of a Numerical Model to a Scale Model of a Conceptual Prototype

Hydraulic jumps on the steps of a stepped spillway were investigated analytically, physically, and numerically. Using classic hydraulic formulae, a conceptual prototype was designed. A large scale model was adapted and an experimental study was conducted to examine similarity of hydraulic jumps on each step, minimizing hydraulic jump length and maximizing discharge per unit width. A numerical model based on the 2D Reynolds averaged equations, where the free-surface is represented using a refined volume-of-fluid algorithm, the internal obstacles are described by means of the fractional area-volume obstacle representation method, and the turbulence is represented by a specially developed RNG (Renormalization Group) k-e closure model was used for evaluating velocities and pressures, and for characterizing hydrodynamic forces on the baffles and sills. Preliminary design criteria are proposed for stepped spillways with hydraulic jump formation of simple shapes and adequate relations of critical depth/step heig...

Experimental Study On Response Sensitivity Of Smoke Detectors In High Flow Velocity

The objective of this work was to investigate preliminary design criteria of automatic fire alarm systems for some places with high flow velocity, e.g., exits of large underground car parks, the air outlets of large air conditioner etc. In addition, another main motivation of this research is to evaluate the appropriateness of Chinese standard which states that photoelectrics should be used in high flow locations. Two corresponding series of experiments were designed to analyze the response sensitivity of photoelectric and ionization smoke detectors under the conditions of different flow velocities in the Fire Emulator/Detector Evaluator (FE/DE), using smoldering cottons as the smoke source. The combining analysis of results of the two series of experiments indicated that generally speaking, ionization smoke detectors showed better response sensitivity than photoelectric smoke detectors in environments with high flow velocity. Preliminary analysis suggested that the influence of flow velocity on size distribution of the smoke particles generated is the main reason for the results.

Recycling for all: preliminary criteria for the design of disability-friendly receptacles.

The design of current waste bins, paper and bottle banks presents barriers for disabled and elderly persons, as pointed out by several Danish studies. In drawing up design criteria for the development of receptacles to be usable by persons with disabilities and senior citizens it is essential to be aware of the problems caused by different types of disability as well as old age. On the basis of general user requirements, preliminary criteria for the design of disability-friendly receptacles are proposed. In collaboration with a collecting agent, current receptacles modified in accordance to the preliminary design criteria will be tested in pilot studies in three selected housing estates in the municipalities of Frederiksberg and Copenhagen. It is the authors' hope that the testing of the modified receptacles will result in achieving more efficient source separation not only for disabled and elderly persons, but for all user groups.

Defining the Interface for a Snowplow Lane Tracking Device Using a Systems-Based Approach

This paper summarizes a systems-based approach to the design of an operator interface for a “Magnetic Lateral Guidance and Warning System” for snowplow operations. The premise behind this interface is that providing continuous and accurate lane position information to complement existing roadway cues may increase driver situation awareness, and potentially reduce crash involvement. An extensive survey returned by over 1000 snowplow operators from Minnesota and Iowa identified operational issues critical to low-visibility operations. Survey findings and ride-along interviews supported an Operator Function Model - Cognitive Task Analysis (OFM-COG). The OFM-COG describes operational constraints and links them to the cognitive limits of drivers in order to identify critical functionality and preliminary design criteria. Findings suggest that the interface be designed as an “aid,‘ rather than as a “primary’ display, to complement existing roadway cues. The visual display should be augmented with haptic cues such as directional seat vibration and peripheral visual, and all alarms should have adjustable thresholds. A prototype user interface is presented.