摘 要

In this study, the submerged abrasive water jet turning (AWJT) system was used for improving machinability of castamide material and process parameters have been investigated comprehensively. Optimum parameters were determined as to minimize the surface roughness and maximize the material removal rate in the submerged turning process of castamide. 3-level traverse speed (TS), abrasive flow rate (AFR) and spindle speed (SS) were taken as the input parameters, and the experimental design was made as a full factorial design. The effect ratios of the input parameters were analyzed statistically by ANOVA and graphical methods, and their interactions were examined by 3D surface images. Optimum test condition was determined by TOPSIS and VIKOR methods. Experimental results were compared with conventional abrasive water jet process. In addition, regression equations were obtained for the explanation of the experimental results mathematically to show the relationships between the variables. According to the experimental results, submerged AWJT increased the surface roughness of castamide material by 15% compared to conventional AWJT and decreased the metal removal rate by 5.22%. ANOVA results showed that the traverse speed is the most effective parameter on the machinability of castamide. Traverse speed was found to be 83.11% effective on surface roughness and 85.56% on material removal rate. According to TOPSIS and VIKOR optimization results, 40 mm/min TS, 310 g /min AFR and 300 rpm SS values were determined as the optimum test conditions.

The purpose of this study is to experimentally investigate thermal performance of Two Phase Closed Thermosyphon (TPCT) using nanofluid containing CuO nanoparticles at a mass concentration of 1% and 2% wt. For this purpose, an experimental setup was designed and manufactured which contains a copper pipe, 100 cm in length and 18 mm in the inner diameter. TPCT consists of three sections: the evaporator section (40 cm), adiabatic section (20 cm) and condenser section (40 cm). The evaporator section was wrapped with electrical spiral heater to apply heat, and whole section of TPCT was insulated. A cooling water circuit was used to remove the heat from condenser section. The temperatures were measured on the TPCT surface and cooling water inlet and outlet. The inclination angle of the TPCT was fixed at 90°. The effects of various parameters such as heat load (ranging from 200 to 800 W), cooling water flow rate (ranging from 18 to 54 l/h) and type of working fluid on the thermal performance of TPCT were examined. The results were plotted graphically and discussed in detail. As a result, the performance enhancement was established by using CuO/water nanofluids instead of pure water in TPCT. Approximately 10% and 18.5% enhancement were found when 1% CuO/water and 2% CuO/water nanofluids were used, respectively. In addition, TPCT thermal resistance was reduced averagely 25% and 35% with the use of 1%CuO/water and 2%CuO/water working fluids, compared to the base fluid pure water.

摘 要

A monitoring mechanism is vital for detecting malicious attacks against cyber systems. Detecting denial of service (DOS) and distributed DOS (DDOS) is one of the most important security challenges facing network technologies. This paper introduces a reliable detection mechanism based on the continuous ranked probability score (CRPS) statistical metric and exponentially smoothing (ES) scheme for enabling efficient detection of DOS and DDOS attacks. In this regard, the CRPS is used to quantify the dissimilarity between a new observation and the distribution of normal traffic. The ES scheme, which is sensitive in detecting small changes, is applied to CRPS measurements for anomaly detection. Moreover, in CRPS-ES approach, a nonparametric decision threshold computed via kernel density estimation is used to suitably detect anomalies. Tests on three publically available datasets proclaim the efficiency of the proposed mechanism in detecting cyber-attacks.

摘 要

摘 要