Set Of Design Parameters Research Articles

Deriving invariant checkers for critical infrastructure using axiomatic design principles

Cyber-physical systems (CPSs) in critical infrastructure face serious threats of attack, motivating research into a wide variety of defence mechanisms such as those that monitor for violations of invariants, i.e. logical properties over sensor and actuator states that should always be true. Many approaches for identifying invariants attempt to do so automatically, typically using data logs, but these can miss valid system properties if relevant behaviours are not well-represented in the data. Furthermore, as the CPS is already built, resolving any design flaws or weak points identified through this process is costly. In this paper, we propose a systematic method for deriving invariants from an analysis of a CPS design, based on principles of the axiomatic design methodology from design science. Our method iteratively decomposes a high-level CPS design to identify sets of dependent design parameters (i.e. sensors and actuators), allowing for invariants and invariant checkers to be derived in parallel to the implementation of the system. We apply our method to the designs of two CPS testbeds, SWaT and WADI, deriving a suite of invariant checkers that are able to detect a variety of single- and multi-stage attacks without any false positives. Finally, we reflect on the strengths and weaknesses of our approach, how it can be complemented by other defence mechanisms, and how it could help engineers to identify and resolve weak points in a design before the controllers of a CPS are implemented.

Optimal Design Parameters for a Phased-Array-Based Ultrasonic Polar Scan.

In the context of designing a next-generation ultrasonic polar scan (UPS) measurement system for viscoelastic material characterization, a novel approach is proposed, which draws on a set of cylindrically focused emitters in conjunction with a circular phased array (C-PA) receiver in order to create a portable measurement system while improving the data quality and ease the data interpretation. To explore the potential of the new approach and determine its optimal design parameters, a 3-D analytical model is presented to numerically simulate UPS experiments with the proposed system. Furthermore, a postprocessing procedure is worked out to treat the acquired raw data with the aim to deal with the integrating effect of finite size transducers and directly reconstruct the angle-dependent plane wave reflection coefficients of the sample under study. As the accuracy of the reconstruction heavily depends on various design parameters, a parameter study focusing on the influence of three main experimental parameters is performed to guide the optimal design. For each of these parameter studies, the UPS simulation results have been inverted, and the errors on the estimated C-tensor parameters have been deduced. First, it is shown that, for a given frequency, the radius of the C-PA must be large enough to capture both the specular and nonspecular reflected field, which is crucial to assure a correct reconstruction of the plane wave characteristics and find proper estimates of the C-tensor parameters. Second, the impact of the emitter and receiver lengths on the quality of the reconstruction and the C-tensor parameters has been investigated, yielding superior results upon increasing either of them. Finally, a dedicated study of the pitch of the C-PA elements and the angular range of the cylindrically focused emitters shows that aliasing effects disturb the results if the pitch is too large. However, this effect can somewhat be mitigated by employing multiple emitters with a restricted angular range. Using the knowledge of the abovementioned parameter studies, a simulated UPS experiment using a proper set of design parameters is performed for a cross-ply carbon epoxy laminate. The postprocessed reconstruction based on these data shows an excellent agreement with the theoretical plane wave results.

Thermal performance of reused shipping containers as building components

The era of disruption occurred influenced by innovations that emerged according to the needs and developments of the times. This occurs in various sectors, including the construction industry sector. One of the growing innovations in the construction industry sector is the reuse of shipping containers (SC) into buildings with various functions. The trend of reusing SC as buildings is quite significant. Several sectors have used a lot of SC as buildings, including: Offices, educational, commercial and residential. However, the reuse of SC as a building has several weaknesses, one of which is the thermal aspect. The structure of the container, which is generally composed of steel, should be considered in achieving indoor thermal comfort. The case study of the paper was SC buildings at Institut Teknologi Sains Bandung (ITSB). The aims of this study were to determine the contribution of design parameters of SC to indoor thermal comfort and its effect on energy efficiency. The method was model simulation on the thermal aspect using Sefaira software. The results showed that setting of design parameters considerably contributed to thermal comfort and energy efficiency.

Parametric study on mass minimization of radial network arch pedestrian bridges

This article deals with the optimization of radial network arch bridges for pedestrian traffic. This is a challenging optimization problem that involves determining certain topological parameters, as well as shape configurations and all sizing parameters of structural members, in order to seek minimum mass. An optimal bridge scheme was sought tuning a large set of design parameters of diverse character: the type of hanger arrangement, the number of hangers, their inclination and spread angles, the alteration of these angles, the arch rise, etc. Mathematically, the optimization of the bridge scheme is a mixed-integer constrained global optimization problem solved employing a stochastic evolutionary algorithm. Plane light-deck bridges of 60 m span were optimized using the proposed optimization technique. Decisive design parameters and their promising ranges were revealed. In addition, the influence of some simplified effects was shown: using constant spread and inclination angles, limiting the diameters of the hangers to a given value, etc. The results show that the available design recommendations for automotive and railway network arch bridges are not fully applicable to similarly designed pedestrian bridges.

Hierarchical Nano/Micro-Structured Surfaces With High Surface Area/Volume Ratios

Abstract Recently, many studies have investigated additive manufacturing (AM) of hierarchical surfaces with high surface area/volume (SA/V) ratios, and their performance has been characterized for applications in next-generation functional devices. Despite recent advances, it remains challenging to design and manufacture high SA/V ratio structures with desired functionalities. In this study, we established the complex correlations among the SA/V ratio, surface structure geometry, functionality, and manufacturability in the two-photon polymerization (TPP) process. Inspired by numerous natural structures, we proposed a 3-level hierarchical structure design along with the mathematical modeling of the SA/V ratio. Geometric and manufacturing constraints were modeled to create well-defined three-dimensional hierarchically structured surfaces with a high accuracy. A process flowchart was developed to design the proposed surface structures to achieve the target functionality, SA/V ratio, and geometric accuracy. Surfaces with varied SA/V ratios and hierarchy levels were designed and printed. The wettability and antireflection properties of the fabricated surfaces were characterized. It was observed that the wetting and antireflection properties of the 3-level design could be easily tailored by adjusting the design parameter settings and hierarchy levels. Furthermore, the proposed surface structure could change a naturally hydrophilic surface to near-superhydrophobic. Geometrical light trapping effects were enabled and the antireflection property could be significantly enhanced (> 80% less reflection) by the proposed hierarchical surface structures. Experimental results implied the great potential of the proposed surface structures for various applications such as microfluidics, optics, energy, and interfaces.

Estimation of stigmatized population total: A new additive quantitative randomized response model

In this article, we propose a new randomized response model to estimate the population total of a sensitive variable of quantitative nature. The objective is achieved by introducing additive scrambling mechanism when sample is drawn through probability proportional to size sampling scheme. The performance evaluation of the proposed model is carried with respect to notable model of Odumade and Singh (2010). To maintain the generality, we consider variety of settings of design parameters. Furthermore, log-log model approach is employed to assess the predictive effects of design parameters over the percentage relative efficiency of the proposed scheme. The gain of using proposed method over contemporary model is documented throughout the article.

Optimal design of preform shape based on EFA-FEM-GA integrated methodology

Preform shape design for complex forging is an important and intractable aspect in the design of forging process. This paper presents an integrated methodology based on elliptic Fourier analysis (EFA), finite element method (FEM) and genetic algorithms (GA) to determine optimal preform shape. Firstly, an elliptic Fourier analysis, which has the advantages of wide versatility and short design cycle, is adopted as the transformation rule for the first time in this paper. The similarity between elliptic Fourier analysis and plastic forming process is demonstrated theoretically. Meanwhile, the main steps for using elliptic Fourier analysis module to design preform shape are introduced: two-dimensional slice, elliptic Fourier analysis and three-dimensional reconstruction. The preform shapes generated by elliptic Fourier analysis module can be simulated directly in finite element method module. Next, in order to control the deformation amount and material distribution of preform, two sets of design parameters, i.e., shape factor and triaxial scaling factors, are employed to control the preform shape before entering the finite element method module simulation. Then, these design parameters are optimized using the genetic algorithm module. Finally, taking a heavy forging with complex shapes as an example, its optimized design scheme is carried out in real forging production. The results show that the forging is produced without problems of crack, folds, underfilling and unreasonable flash distribution, which validates the effectiveness of the presented methodology. Furthermore, this integrated methodology could be extended to other complex forgings.

A Configurable Architecture for Two Degree-of-Freedom Variable Stiffness Actuators to Match the Compliant Behavior of Human Joints.

Living beings modulate the impedance of their joints to interact proficiently, robustly, and safely with the environment. These observations inspired the design of soft articulated robots with the development of Variable Impedance and Variable Stiffness Actuators. However, designing them remains a challenging task due to their mechanical complexity, encumbrance, and weight, but also due to the different specifications that the wide range of applications requires. For instance, as prostheses or parts of humanoid systems, there is currently a need for multi-degree-of-freedom joints that have abilities similar to those of human articulations. Toward this goal, we propose a new compact and configurable design for a two-degree-of-freedom variable stiffness joint that can match the passive behavior of a human wrist and ankle. Using only three motors, this joint can control its equilibrium orientation around two perpendicular axes and its overall stiffness as a one-dimensional parameter, like the co-contraction of human muscles. The kinematic architecture builds upon a state-of-the-art rigid parallel mechanism with the addition of nonlinear elastic elements to allow the control of the stiffness. The mechanical parameters of the proposed system can be optimized to match desired passive compliant behaviors and to fit various applications (e.g., prosthetic wrists or ankles, artificial wrists, etc.). After describing the joint structure, we detail the kinetostatic analysis to derive the compliant behavior as a function of the design parameters and to prove the variable stiffness ability of the system. Besides, we provide sets of design parameters to match the passive compliance of either a human wrist or ankle. Moreover, to show the versatility of the proposed joint architecture and as guidelines for the future designer, we describe the influence of the main design parameters on the system stiffness characteristic and show the potential of the design for more complex applications.

AC Current Ripple in Three-Phase Four-Leg PWM Converters with Neutral Line Inductor

This paper presents a comprehensive study of peak-to-peak and root-mean-square (RMS) values of AC current ripples with balanced and unbalanced fundamental currents in a generic case of three-phase four-leg converters with uncoupled AC interface inductors present in all three phases and in neutral. The AC current ripple characteristics were determined for both phase and neutral currents, considering the sinusoidal pulse-width modulation (SPWM) method. The derived expressions are simple, effective, and ready for accurate AC current ripple calculations in three- or four-leg converters. This is particularly handy in the converter design process, since there is no need for heavy numerical simulations to determine an optimal set of design parameters, such as switching frequency and line inductances, based on the grid code or load restrictions in terms of AC current ripple. Particular attention has been paid to the performance comparison between the conventional three-phase three-leg converter and its four-leg counterpart, with distinct line inductance values in the neutral wire. In addition to that, a design example was performed to demonstrate the power of the derived equations. Numerical simulations and extensive experimental tests were thoroughly verified the analytical developments.

The development of microwave installations for separating the fluff from skins of rabbits in the agricultural enterprises of low power

The article is devoted to the development of technology and technical means designed to weaken the retention force of hair in the dermis of rabbit skins due to selective dielectric heating of hair bulbs under the influence of an ultra-high frequency electromagnetic field (UHFEMF). Microwave technologies and more than 20 installations with UHFEMF sources and non-traditional resonators have been developed that provide continuous collection of fluff from rabbit skins. Resonators have been tested that ensure the separation of downy raw materials from the skin of rabbit skins in a continuous mode when implementing a set of reasonable design and technological parameters. Novelty of technical solutions of developed technologies and microwave installations with non-traditional resonators, such as: cylindrical (2655770, 2651594, 2680543, 2682890); semi-cylindrical (2018101622, 2703918); toroidal (2674605, 2699709); coaxial (2655748, 2651593); biconic (2715341, 2018117136) proved by patents of the Russian Federation. A technical specification has been developed for creating a radio-hermetic microwave installation with low-power magnetrons and a biconic resonator, which ensures the separation of down raw materials from rabbit skins in a continuous mode at low operating costs.

Integration of Design Data into a Design Solution and their Modification in Problems of Geometrical Modelling

This article considers an approach to achieving modifiability of design solutions in the form of digital 3D parts and assembly units in CAD systems. This approach is based on a modular principle, according to which a design solution is represented by a system of 3D macro-objects. Such macro-objects are typical of a given subject area, have semantic content and are described by a set of design parameters. The variability of selected parameters forms a class of design solutions, which, although differing in terms of geometry and structure, have common structural and functional specific features. The main advantage of the proposed approach consists in the provision of the semantic integrity of a design solution during its modification and reuse.

Energy analysis of the performance of a hybrid solar still composed of a parabolic concentrator with PV generator

In this study, a hybrid system with the addition of a greenhouse solar still is proposed to improve the efficiency, performance, and productivity of solar still. The energy analysis is performed with the help of a computer program using a set of typical design and operating parameters. The result showed that the hybrid still coupled with a PCC (parabolic cylindrical concentrator) can produce 110 l/m2 per day. The temperatures of the basin and water of the hybrid still with PCC are 140 and 100 °C, respectively. The causes are the several sources of temperatures are added together in a single system. The obtained values of efficiency, production, and performance are 160%, 100 l/m2, and 2, respectively. The results show also that the temperature and production in the month of January are 70 °C and 50 l/m2 per day, respectively, despite the negative influence of meteorological parameters. The performance of the suggested hybrid still is found to be higher than that of the single still without a concentrator.

Design optimization of a novel screw conveyor based system to scoop oil sludge from floor of storage tanks

• Novel screw conveyor system for online sludge scooping from the oil storage tank floor without having to empty it. • Mathematical model results approximated the optimal set of screw design parameters for optimum scooping sludge volume. • In the CFD package, rheological material behavior is simulated to visualize the flow of particles in different screw designs. • Experimentally quantified the maximum amount of sludge scooped at a given speed for a certain range of radius and pitch ratio. This paper presents the design optimization and testing of a novel screw conveyor based system to scoop crude oil sludge from the floor of oil storage tanks. This proposed new system consists of a screw conveyor mounted on a ‘C’ shaped casing with a bearing on both sides driven by a waterproof motor through a worm drive. A novel mathematical model is developed to help the design of a screw conveyor for a maximum amount of sludge scooping per turn, and numerical simulations are performed using computational fluid dynamics to visualize the flow of material particles in various possible designs of the system. The proposed mechanism was 3D printed, and laboratory tests were conducted to quantify the amount of sludge removal by the different designs of the screw. Optimized design of a mechanism screw with a radius ratio of 0.40 and a pitch ratio of 0.15 scoops up to a maximum of 5.88 kg hr of material at 110 rev min .

Simulation study of rate limiting factors of Li-ion batteries using experimental functions of electronic and ionic resistances

The balance between the electronic and ionic resistances in electrodes is an important factor that governs the rate performance of Li-ion batteries. However, most battery simulation models reported to date use impractical formulas. We therefore conducted a simulation study using the Newman model under the constraint condition of constant energy density (250 Wh/kg), using the experimental functions of electronic and ionic resistances depending on the electrode structure. In addition to obtaining a battery design guideline that provides the best rate performance, we considered the rate-limiting factors. Using the conductive carbon weight ratio and the porosity and thickness of the positive electrode as the design parameters, we carried out a parametric study of the discharge properties. The batteries comprising a thin, low-porosity positive electrode exhibited better rate performances than those with a thick positive electrode of higher porosity for the design parameter sets with the same designed specific energy. Furthermore, the results revealed that the dependence on the electrode thickness of the diffusion-limiting behavior and thus, of the discharge rate performance was determined by the diffusivity of both the positive and negative electrodes.

A new formulation of Economic Model Predictive Control without terminal constraint

In this paper, it is shown that a simple formulation of Economic Model Predictive Control can be used which possesses two features that are generally viewed as mutually exclusive, namely, a rather short prediction horizon (reachability-compatible) on one side, and the absence of final constraint on the other side. Practical stability at an arbitrarily small neighborhood of the optimal unknown steady-state pair is shown when some design parameters increase. It is also shown that when the system is originated from the time discretization of a continuous-time dynamics, the size of the terminal region can be reduced by decreasing the sampling period for the same design parameter setting. A commonly used example is given to illustrate the results.

Adaptive Transmit Waveform Design Using Multitone Sinusoidal Frequency Modulation

This paper presents an adaptive waveform design method using Multi-Tone Sinusoidal Frequency Modulation (MTSFM). The MTSFM waveform's modulation function is represented as a finite Fourier series expansion. The Fourier coefficients are utilized as a discrete set of design parameters that may be modified to adapt the waveform's properties. The MTSFM's design parameters are adjusted to shape the spectrum, Auto-Correlation Function (ACF), and Ambiguity Function (AF) shapes of the waveform. The MTSFM waveform model naturally possesses the constant envelope and spectrally compact waveforms that make it well suited for transmission on practical radar/sonar transmitters which utilize high power amplifiers. The MTSFM has an exact mathematical definition for its time-series using Generalized Bessel Functions which allow for deriving closed-form analytical expressions for its spectrum, AF, and ACF. These expressions allow for establishing well-defined optimization problems that finely tune the MTSFM's properties. This adaptive waveform design model is demonstrated by optimizing MTSFM waveforms that initially possess a "thumbtack-like" AF shape. The resulting optimized designs possess substantially improved sidelobe levels over specified regions in the range-Doppler plane without increasing the Time-Bandwidth Product (TBP) that the initialized waveforms possessed. Simulations additionally demonstrate that the optimized thumbtack-like MTSFM waveforms are competitive with thumbtack-like phase-coded waveforms derived from design algorithms available in the published literature.

Analysis and Characterization of Normally-Off Gallium Nitride High Electron Mobility Transistors

High electron mobility transistor (HEMT) based on gallium nitride (GaN) is one of the most promising candidates for the future generation of high frequencies and high-power electronic applications. This research work aims at designing and characterization of enhancement-mode or normally-off GaN HEMT. The impact of variations in gate length, mole concentration, barrier variations and other important design parameters on the performance of normally-off GaN HEMT is thoroughly investigated. An increase in the gate length causes a decrease in the drain current and transconductance, while an increase in drain current and transconductance can be achieved by increasing the concentration of aluminium (Al). For Al mole fractions of 23%, 25%, and 27%, within Al gallium nitride (AlGaN) barrier, the GaN HEMT devices provide a maximum drain current of 347, 408 and 474 mA/μm and a transconductance of 19, 20.2, 21.5 mS/μm, respectively. Whereas, for Al mole fraction of 10% and 15%, within AlGaN buffer, these devices are observed to provide a drain current of 329 and 283 mA/μm, respectively. Furthermore, for a gate length of 2.4, 3.4, and 4.4 μm, the device is observed to exhibit a maximum drain current of 272, 235, and 221 mA/μm and the transconductance of 16.2, 14, and 12.3 mS/μm, respectively. It is established that a maximum drain current of 997 mA/μm can be achieved with an Al concentration of 23%, and the device exhibits a steady drain current with enhanced transconductance. These observations demonstrate tremendous potential for two-dimensional electron gas (2DEG) for securing of the normally-off mode operation. A suitable setting of gate length and other design parameters is critical in preserving the normally-off mode operation while also enhancing the critical performance parameters at the same time. Due to the normally-on depletion-mode nature of GaN HEMT, it is usually not considered as suitable for high power levels, frequencies, and temperature. In such settings, a negative bias is required to enter the blocking condition; however, in the before-mentioned normally-off devices, the negative bias can be avoided and the channel can be depleted without applying a negative bias.

Optimization of a shell and tube heat exchanger with staggered baffles using Taguchi method

In this work, Taguchi method is applied on the numerical simulation results of a shell and tube heat exchanger with staggered baffles (STHX-ST) for the purpose of optimizing its design parameters corresponding to maximum heat transfer rate and minimum pressure drop. An STHX-ST integrates the characteristics of a shell and tube heat exchanger with segmental baffles as well as helical baffles. The baffles in these heat exchangers are oriented in such a way that a constant clockwise or counter clockwise angle is maintained between the adjacent baffles. The analysis of the shell side of these heat exchangers in this work is carried out using computational fluid dynamics (CFD) by varying its design parameters. The rate of heat transfer obtained and total pressure drop across the shell side of the heat exchanger is calculated using CFD. A set of experiments are designed as an orthogonal array as per Taguchi method through combinations of design parameters such as shell inside diameter, tube outside diameter, baffle cut, baffle spacing and baffle orientation angle. CFD Simulations are carried out on each parameter combination in this array. Finally signal to noise ratio analysis is conducted on this array and two set of optimum design parameters corresponding to maximum heat transfer and minimum pressure drop is obtained. The optimum combination of variables for maximum heat transfer yields a maximum heat transfer rate of 141252 W and the optimum parameter combination for minimum pressure drop yields a minimum pressure drop of 58352.6 Pa.

Optimisation of friction stir welding parameters using combined Taguchi L9 and genetic algorithm

'Friction stir welding' (FSW) is an eco-friendly, energy-efficient solid-state welding procedure invented for high strength alloys as well as materials that are otherwise difficult for welding through the traditional fusion welding methods. This research paper elaborates on a hybrid Taguchi-genetic algorithm that optimises the FSW process parameters to yield favourable electrical conductivity of aluminium alloy AA1350. The optimisation parameters considered are travel speed, rotational speed and tool tilt angle. First, the Taguchi method is applied to reduce the number of design experiments and find the optimal set for quality parameters of the system. Subsequently, the genetic algorithm is employed to search for the optimum set of design parameters by using Taguchi solution as the initial population. The results obtained by the proposed method were compared to the outcomes of the conventional Taguchi L9 method and the simple genetic algorithm. The best performance was obtained by the proposed method in 51 iterations, whereas simple genetic algorithm used 182 iterations for the same.

Optimisation of friction stir welding parameters using combined Taguchi L9 and genetic algorithm

'Friction stir welding' (FSW) is an eco-friendly, energy-efficient solid-state welding procedure invented for high strength alloys as well as materials that are otherwise difficult for welding through the traditional fusion welding methods. This research paper elaborates on a hybrid Taguchi-genetic algorithm that optimises the FSW process parameters to yield favourable electrical conductivity of aluminium alloy AA1350. The optimisation parameters considered are travel speed, rotational speed and tool tilt angle. First, the Taguchi method is applied to reduce the number of design experiments and find the optimal set for quality parameters of the system. Subsequently, the genetic algorithm is employed to search for the optimum set of design parameters by using Taguchi solution as the initial population. The results obtained by the proposed method were compared to the outcomes of the conventional Taguchi L9 method and the simple genetic algorithm. The best performance was obtained by the proposed method in 51 iterations, whereas simple genetic algorithm used 182 iterations for the same.