Central Composite Design Scheme Research Articles

Thermodynamic modeling and performance optimization of nanofluid-based photovoltaic/thermal system using central composite design scheme of response surface methodology

This study develops and validates a programming code to demonstrate an iterative resolution analytical thermodynamic modeling method for nanofluid-based photovoltaic/thermal (PV/T) systems. The experimental validation of the model is conducted by constructing and testing a novel PV/T collector that incorporates a flow channel with a double-loop rectangular spiral design. Four different operating independent factors, including solar irradiation (G = 300–900 W/m2), ambient temperature as per climate condition of Jalandhar city of India in July (Ta = 283.15–313.15 K), the CuO-water nanofluid concentration (φ = 0.02–0.08%) and mass flow rate of nanofluid (ṁnf = 201–241 kg/h) are used for thermodynamic performance prediction. Mathematical correlations are developed for each of the dependent response factors, including energetic thermal power output, energetic electrical power output, exergetic thermal power output, and entropy generation. Correlations are based on operating independent factors and their interaction on proposed system performance. Different single and multiple optimization approaches aim to predict optimal dependent and independent factor values. The regression model proposed in this study recommends choosing G = 855.353 W/m2, Ta = 313.148 K, φ = 0.08%, and ṁnf = 201 kg/h in order to optimize the energetic and exergetic electrical and thermal power output while minimizing entropy generation.

Probabilistic Analysis of Shallow Foundations on c-φ Soils Using 2nd Order Response Surface Methods

The HL-Reliability Index is utilized to investigate the applicability of several linear and nonlinear response surface models based on design experiments techniques to evaluate the safety under random loading, against bearing capacity failure of shallow foundations resting on c-φ soils with multivariate correlated variables. The reliability results obtained using FORM/SORM coupled with these models, are checked by Monte Carlo simulation method. It is demonstrated that the application of these models significantly reduces the execution time and memory requirements, with the central composite design scheme being the most accurate. It is also concluded, that consideration of correlation, significantly affects the reliability index for large values of soil friction angle uncertainty. The reliability index is found to be highly sensitive to uncertainties of soil friction angle more than the cohesion and the loading which have approximately the same influence, especially for the case of lognormally distributed variables. In addition, the probabilistic results show that reliability index decreases substantially with the increase of the applied pressure, and that there is significant difference between the reliability indices values computed, based on the assumption of normal distribution as compared to lognormal distribution, especially for the lower ranges of applied loading.

Experiment and Research on Cutting Mechanical Properties of Little Cabbage

To reduce the cutting force and cutting power consumption during harvest, the cutting mechanical properties of the root of little cabbage were studied. The cutting experiment was carried out using a texture analyzer, and the influence of the individual factors, the cutting bevel angle, the sliding angle, and the cutting gap on the maximum cutting stress and specific cutting energy were studied, respectively. On the basis of single factor experiments, multi-factor experiments were carried out using the central composite design scheme of the response surface method (RSM), and finally, the cutting parameters were optimized. The single factor test results showed that the maximum cutting stress and specific cutting energy first decreased and then increased with the increase in the cutting bevel angle, decreased with the increase in the sliding angle, and first dropped and then went up with the increase in the cutting gap. Response surface test results showed that the order of significance of factors affecting the maximum cutting stress of the root were the oblique angle, sliding angle, and cutting gap in sequence, and the order of the significance of factors affecting the specific cutting energy are cutting gap, oblique angle, and sliding angle. The interaction between the sliding angle and the cutting gap had a significant impact on the maximum cutting stress, and the interaction between the oblique angle and the cutting gap had a significant impact on the cutting energy. The optimal parameter combination is as follows: oblique angle of 9.1°, sliding angle of 30°, and cutting gap of 1.3 mm. At this time, the predicted maximum cutting stress was 7.43 × 104 Pa, and the specific cutting energy was 0.28 mJ mm−2. Finally, a verification experiment was carried out, and the errors of the predicted and measured values of cutting under the optimal parameter combination were 6.9% and 10.8%, respectively, showing that the cutting parameter optimization results were reliable. This research can provide data support for the design and improvement in the cutting device of the little cabbage combine harvester.

Numerical Modelling and Multi Objective Optimization Analysis of Heavy Vehicle Chassis

The primary supporting structure of an automobile and its other vital systems is the chassis. The chassis structure is required to bear high shock, stresses, and vibration, and therefore it should possess adequate strength. The objective of current research is to analyze a heavy motor vehicle chassis using numerical and experimental methods. The CAD design and FE analysis is conducted using the ANSYS software. The design of the chassis is then optimized using Taguchi design of Experiments (DOE); the optimization techniques used are the central composite design (CCD) scheme and optimal space filling (OSF) design. Thereafter, sensitivity plots and response surface plots are generated. These plots allow us to determine the critical range of optimized chassis geometry values. The optimization results obtained from the CCD design scheme show that cross member 1 has a higher effect on the equivalent stresses as compared to cross members 2 and 3. The chassis mass reduction obtained from the CCD scheme is approximately 5.3%. The optimization results obtained from the OSF scheme shows that cross member 2 has a higher effect on equivalent stress as compared to cross members 1 and 3. The chassis mass reduction obtained from optimal space filling design scheme is approximately 4.35%.

Effect of Surface Tension, Foaming Stabilizer, and Graphene Oxide on the Properties of Foamed Paste.

Foamed paste has attracted much attention because of its excellent thermal insulation performance and diverse applications in infrastructure projects. However, there are still some shortcomings hindering the further application of foamed paste, such as the low mechanical strength and the lack of effective methods to evaluate the properties of foaming bubbles. In this study, surface tension was used as the key parameter to characterize the properties of bubbles. A novel nanomaterial, graphene oxide was employed to enhance the mechanical strength of foamed paste, which was also effective in decreasing the surface tension of aqueous solution. A central composite design scheme was employed to evaluate the influence of three selected factors, surface tension, Sodium Phosphate/foaming reagents mass ratio, and graphene oxide/binder mass ratio, on the engineering properties of foamed paste. Additionally, mercury intrusion porosimetry and scanning electron microscope were employed to elucidate the structure of pores, X-ray diffraction and thermogravimetric analysis were employed to further analyze the hydration products at the microscopic scale. This study reveals that surface tension holds great potential in predicting the engineering properties or performances of foamed paste, and a new mechanism may be developed for explaining the influence of graphene oxide on the pore structure of cementitious materials by evaluating the surface tension of pore solution.

Optical analysis of T-shaped stiffened plate under compressive loading using central composite design scheme

The buckling and post-buckling strength of stiffened panels subjected to compressive loads largely depends upon type and dimensions of stiffeners used. The current research investigates the use of T shaped stiffener in vertical configuration in rectangular plate with square opening for improving strength and buckling characteristics. The static structural analysis is conducted using ANSYS FEA software and dimensions of T shaped stiffeners are optimized using Taguchi response surface optimization. The design points are generated using CCD (Central Composite Design) scheme of response surface method and corresponding responses of optimization variables are captured in 3D plots. The sensitivity chart is generated to determine the effect of optimization variables on parameters of interest which are stress, strain, deformation, buckling load and safety factor. The optimization technique has successfully provided set of values for different parameters for which buckling and stresses are minimum and maximum.

Experimental assessment of a small scale hybrid liquid desiccant dehumidification incorporated vapor compression refrigeration system: An energy saving approach

This work investigates a small-scale hybrid experimental setup developed combining the two technologies of liquid desiccant dehumidification and vapour compression refrigeration. A hybrid system of 5 kW capacity is designed and developed for energy saving analysis. The experiments are designed with central-composite design scheme using three variables namely air mass flow rate, desiccant inlet temperature, and desiccant inlet concentration. Three responses namely specific humidity change in the dehumidifier, dehumidifier heat load and hybrid system performance coefficient are considered for the investigation. The regression correlations for all three responses are developed and presented. Further, the performance comparison of the hybrid system with the standalone vapour compression refrigeration unit is also carried out. The comparative results reveal that the maximum improvement of 27.54% is observed in the coefficient of performance at which 54.93% of the total latent heat load is being covered by the dehumidifier. Finally, the energy saving analysis reveals that the hybrid system is having payback duration of 4 years compared to the standalone vapour compression refrigeration system of same cooling capacity.

MEDIUM OPTIMIZATION FOR PROTEASE PRODUCTION VIA MODERATELY HALOTOLERANT VIRGIBACILLUS PANTOTHENTICUS USING RESPONSE SURFACE METHODOLOGY

Virgibacillus pantothenticus is an industrially promising, yet scarcely studied, moderately halotolerant microorganism (up to 10% NaCl) with high activity protease production potential. Following Response Surface Methodology, we employed a Central Composite Design for the experiments and constructed a second order polynomial model to represent the resulting data. For medium optimization for protease production we optimized the resulting model. 32 experiments (following the central composite design scheme) where, carbon (glucose), nitrogen (ammonium sulfate), potassium (potassium phosphate monobasic) and magnesium (magnesium sulfate) sources were studied in the media. Bacterial growth, residual glucose and protease activities were determined at the 48th hour of each experiment. The model was optimized and the concentrations were found for each parameter. Under the optimum conditions, the predicted protease activity is also experimentally verified and the model prediction was in very good agreement with experimental results. The interactions between medium components and their effect on cell growth and protease production are also sought. This work reports the improvements on protease production of a potentially interesting industrial host, Virgibacillus pantothenticus.

Crystal violet adsorption on industrial waste (hog fuel ash): equilibrium kinetics with process optimization by response surface modeling

The adsorptive removal of crystal violet from aqueous solution utilizing hog fuel ash, an industrial solid waste, available abundantly is reported in this article. The adsorbent is characterized by various physicochemical methods. Batch experiments are performed as functions of different process variables. The maximum removal (99.99%) was observed at equilibrium time (90 min). Results follow Freundlich isotherm (among five isotherms) and pseudo-second-order kinetics (among four kinetic models). The observed adsorption capacity of 17.002 mg/g is higher than many other reported waste materials. A three-factor full factorial central composite design scheme is adopted for optimizing different process variables and their interactions. The maximum removal predicted by response surface modeling is 99.99%, while corresponding experimental value is 99.13 ± 0.8895% (mean ± standard deviation of five replicates). The removal improves in the presence of NaCl (by 5%) and at higher temperature. Results on the effect of temperature favor spontaneity of adsorption and physisorption that follows from isotherm studies. The temperature effect is investigated exploiting the seasonal variation that does not seem to have been reported before and is the novelty of the present study. The advantages of the present investigation are the use of the adsorbent without pre-treatment, final pH falling well within the safe discharge limit and increased removal in the presence of NaCl. This study could be extended for gainful utilization of the industrial solid waste for similar application.

Effect of Powder Concentration in EDM Process with Powder-Mixed Dielectric (PMD-EDM)

Ti–6Al–4V is widely used in the aerospace, automobile, and biomedical fields, but is a difficult to machine material. Electrical discharge machining (EDM) is regarded as one of the most effective approaches to machining Ti–6Al–4V alloy, since it is a noncontact electro-thermal machining method, and it is independent from the mechanical properties of the processed material. In electro discharge machining (EDM), dielectric plays an important role during machining operation. The machining characteristics are greatly influenced by the nature of dielectric used during EDM machining. In present paper silicon powder suspended kerosene as dielectric is used to explore the influence of these dielectrics on the performance criteria such as material removal rate (MRR), tool wear rate (TWR) and surface roughness (Ra) during machining of titanium alloy (Ti-6Al-4V). Peak current, pulse on time, pulse off time and concentration of powders added into dielectric fluid of EDM were chosen as process parameters to study the PMEDM performance in terms of MRR, TWR and Ra. The experiments were carried out in planning mode on a specially designed experimental set up developed in laboratory. Response surface methodology, employing a face-centered central composite design scheme has been used to plan and analyze the experiments.

Modelling and optimisation of the process parameters in ultrasonic-assisted wire electrical discharge turning

In this article, an attempt to model and optimise the process parameters in ultrasonic-assisted wire electrical discharge turning has been proposed. In this process, ultrasonic vibration, which changes the normal machining conditions in conventional wire electrical discharge turning, is introduced. Response surface methodology, employing a face-centred central composite design scheme, was chosen to design and analyse the experiments. The power, time-off, rotational speed and the ultrasonic vibration amplitude of the wire were selected to assess the process performance in terms of material removal rate (MRR), surface roughness (Ra) and roundness. Suitable mathematical models for the response outputs were obtained using the analysis of variance technique, in which significant terms were chosen according to 95% of confidence interval. In order to find a simultaneous set of optimal input parameters yielding the highest achievable MRR along with the lowest possible Ra and roundness within the process input domain, a multi-objective optimisation technique based on the use of desirability function concept was applied to the response regression equations. Finally, the obtained predicted optimal results were verified experimentally. It was shown that the error values are all less than 7%, confirming the feasibility and effectiveness of the adopted approach.

Statistical Modeling and Optimization of Process Parameters in Electro-Discharge Machining of Cobalt-Bonded Tungsten Carbide Composite (WC/6%Co)

In this paper, attempts have been made to model and optimize process parameters in Electro-Discharge Machining (EDM) of tungsten carbide-cobalt composite (Iso grade: K10) using cylindrical copper tool electrodes in planing machining mode based on statistical techniques. Four independent input parameters, viz., discharge current (A: Amp), pulse-on time (B: μs), duty cycle (C: %), and gap voltage (D: Volt) were selected to assess the EDM process performance in terms of material removal rate (MRR: mm3/min), tool wear rate (TWR: mm3/min), and average surface roughness (Ra: μm). Response surface methodology (RSM), employing a rotatable central composite design scheme, has been used to plan and analyze the experiments. For each process response, a suitable second order regression equation was obtained applying analysis of variance (ANOVA) and student t-test procedure to check modeling goodness of fit and select proper forms of influentially significant process variables (main, two-way interaction, and pure quadratic terms) within 90% of confidence interval (p-value≤0.1) It has been mainly revealed that all the responses are affected by the rate and extent of discharge energy but in a controversial manner. The MRR increases by selecting both higher discharge current and duty cycle which means providing greater amounts of discharge energy inside gap region. The TWR can be diminished applying longer pulse on-times with lower current intensities while smoother work surfaces are attainable with small pulse durations while allotting relatively higher levels to discharge currents to assure more effective discharges as well as better plasma flushing efficiency. Having established the process response models, a multi-objective optimization technique based on the use of desirability function (DF) concept has been applied to the response regression equations to simultaneously find a set of optimal input parameters yielding the highest accessible MRR along with the lowest possible TWR and Ra within the process inputs domain. The obtained predicted optimal results were also verified experimentally and the values of confirmation errors were computed, all found to be satisfactory, being less than 10%. The outcomes of present research prove the feasibility and effectiveness of adopted approach as it can provide a useful platform to model and multi-criteria optimize MRR, Ra, and TWR during EDMing WC/6%Co material.

Butt autogenous laser welding of AA 2024 aluminium alloy thin sheets with a Yb:YAG disk laser

Higher productivity, lower distortion and better penetration are the main advantages provided by laser welding in comparison with conventional processes. A Trumpf TruDisk 2002 Yb:YAG disk laser is used in this work to increases productivity and quality. Aluminium alloys lead to many technological issues in laser welding, resulting in shallow penetration and defects. In particular, AA 2024 aluminium alloy in a thin sheet is investigated in this paper, being it is used extensively in the automotive and aerospace industries. Bead-on-plate and butt autogenous laser welding tests with continuous wave emission on 1.25 mm thick AA 2024 aluminium alloy sheets were examined morphologically and micro-structurally. The geometric and mechanical features of the welding bead were evaluated via a three-level experimental plan. In addition to the power and speed which are traditionally referred to, beam defocusing was considered as an additional governing factor in a central composite design scheme because it massively affects keyhole conditions. Softening in the fused zone is discussed via Vickers micro-hardness testing and magnesium loss through energy dispersive spectrometry. After properly performing the modelling and optimisation of the fused zone and the cross-section shape factor as the response variables, the laser welding conditions for thin sheets of AA 2024 aluminium alloy are suggested. X-ray and tensile tests were conducted on the specimens obtained with the recommended processing parameters to characterise the AA 2024 disk laser welded beads.

A dual response surface-desirability approach to process modeling and optimization of Al2O3 powder-mixed electrical discharge machining (PMEDM) parameters

This paper presents an effort to model and optimize the process parameters involved in powder-mixed electrical discharge machining (PMEDM). Aluminum oxide (Al2O3) fine abrasive powders with particle concentration and size of 2.5–2.8 g/L and 45–50 μm, respectively, were added into the kerosene dielectric liquid of a die-sinking electrical discharge machine. The experiments were carried out in planing mode on a specially designed experimental set up developed in laboratory. The CK45 heat-treated die steel and commercial copper was used as work piece and tool electrode materials, respectively. Response surface methodology, employing a face-centered central composite design scheme, has been used to plan and analyze the experiments. Based on the preliminary and screening tests as well as the working characteristics of selected EDM machine, discharge current (I), pulse-on time (Ton), and source voltage (V) were designated as the independent input variables to assess the process performance in terms of material removal rate (MRR) and surface roughness (Ra). Suitable mathematical models for the response outputs were obtained using the analysis of variance technique, in which significant terms (main effects, two factor interactions, and pure quadratic terms) were chosen according to their p values less than 0.05 (95 % of confidence interval). Having established the suitable regression equations, a search optimization procedure, based on the use of desirability functions, optimizes the process performance in each machining regime of finishing (Ra ≤ 3 μm), semifinishing (3 μm ≤ Ra ≤ 4.5 μm), and roughing (Ra ≥ 4.5 μm). The results are sets of optimum points which make the MRR as high as possible and keep the Ra and all machining parameters in their specified ranges simultaneously. Finally, the modeling and obtained optimization results were also discussed and verified experimentally. It was shown that the error between experimental and anticipated values at the optimal combination settings of input variables are all less than 11 %, confirming the feasibility and effectiveness of the adopted approach.

Burr Formation in Drilling Intersecting Holes with Machinable Austempered Ductile Iron (MADI™)

This paper presents an investigation of the burr formation for a new material, machinable austempered ductile iron (MADI™), while drilling intersecting holes in the presence of tool wear. A factorial design is used to evaluate the effects of drill point angle and helix angle as well as feed rate and cutting speed on the burr width and height at both curved and flat hole exit conditions. The result indicates the presence of a complex interrelationship among these four variables, particularly the interaction between helix and point angle and its influence on drill corner wear and, hence, burr geometry. Burrs are considerably larger at the flat exit condition. Further experiments were conducted in a central composite design scheme to develop second-order polynomial models of the burr width and height. The result suggests that burr width and height can be reduced by using larger helix and smaller point angles. The result further demonstrates that the somewhat unique work-hardening characteristic of MADI™ during machining can lead to smaller burrs when smaller chiploads are used, regardless of the drill helix and point angles.

Optimization of carotenoid production by Rhodotorula graminis DBVPG 7021 as a function of trace element concentration by means of response surface analysis

As the final step of a study aiming at the optimization of culture conditions for the production of carotenoids by red yeasts, a statistically-based experimental design has been applied to assess the influence of selected trace elements on carotenogenesis in Rhodotorula graminis DBVPG 7021. In particular, a central composite design scheme has been used to evaluate the influence of Fe 3+, Co 2+, Mn 2+, Al 2+ and Zn 2+ (within the range 0–50 ppm) on various responses, namely biomass (B), total carotenoid production (TC) and percentage of specific carotenoids (β-CAR, β-carotene; γ-CAR, γ-carotene; TN, torulene; TD, torularhodin) on total carotenoids. Second-order polynomial models were calculated and reduced equations were designed by neglecting non-significant ( P < 0.01) regression coefficients. Reduced equations were used to calculate the optimal concentration of trace elements in view of maximising the level of B, TC, β-CAR, γ-CAR, TN and TD. After optimization, average final values total carotenoids (TC = 803.2 μg/g DW) was about 370% of value observed as central point of the central composite design scheme. Under the same condition, average final values of other responses were: B = 5.40 g/L; β-CAR = 50.3%; γ-CAR = 15.4%; TN = 22.7%; TD = 11.6%. All above experimental data are in good agreement with calculated ones, thus confirming the reliability of the proposed empirical model in describing carotenoid production by R. graminis as a function of trace element concentrations.