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Research Article
Investigation of the Surface Produced by Shape Adaptive Polishing
Issue:
Volume 12, Issue 1, February 2024
Pages:
1-7
Received:
11 May 2023
Accepted:
29 May 2023
Published:
8 January 2024
Abstract: Ultra-precision machining (UPM), is renowned for manufacturing products with high precision and surface quality has found diverse application in the optics, automobile, medical instruments, and aerospace industries. Shape adaptive bonnet polishing (SABP), which uses a flexible, non-rigid bonnet tool can be used an alternative ultra-precision polishing method for polishing of complex and delicate microstructures. This paper aims at the investigation on the surface roughness produced by SABP by experimental and analytical model as well as scrutinizing the effects of polishing time and tool offset on tool imprints and surface roughness within the SABP process. Notably, our analytical model highlights the significant influence of polishing time over offset distance for enhancing surface quality, due to its capacity to generate a tool influence curve with a high radius of curvature. The elongation of polishing time leads to a deeper and more flattened tool influence curve, thus resulting in an improved surface quality, a conclusion further affirmed by our experimental outcomes. The utilization of SABP has demonstrated a capacity to enhance workpiece surface quality tenfold, yielding a smooth and uniformly polished surface with surface roughness of 0.008μm. In light of these results, to enhance surface quality further, the study advocates for the prioritization of extending polishing time over altering tool offset in ultra-precision machining.
Abstract: Ultra-precision machining (UPM), is renowned for manufacturing products with high precision and surface quality has found diverse application in the optics, automobile, medical instruments, and aerospace industries. Shape adaptive bonnet polishing (SABP), which uses a flexible, non-rigid bonnet tool can be used an alternative ultra-precision polish...
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Research Article
Mechanical Properties of Spherical Deep-Sea Pressure Structures by Integral Hydrobulge Forming with Triangular Patch Polyhedrons
Yang Jing,
Chenghai Kong,
Jingchao Guan*,
Wei Zhao,
Xilu Zhao
Issue:
Volume 12, Issue 1, February 2024
Pages:
8-17
Received:
14 December 2023
Accepted:
2 January 2024
Published:
23 January 2024
Abstract: Manned pressure shells subjected to deep-sea pressure are designed with a spherical shell structure because they are subjected to perfectly symmetrical pressures. A spherical pressure shell has excellent mechanical properties against deep-sea pressure; therefore, it has the advantage of relatively good buckling properties. However, there are high demands on the processing accuracy of spherical pressure shells, such as thickness distribution and roundness. Even when a small asymmetrical element is present, the buckling characteristics under deep-sea pressure are significantly reduced. In this paper, we propose a new type of spherical pressure shell composed of multiple triangular-plate parts and an integral hydrobulging forming (IHBF) method to process it. Specifically, multiple triangular metal plate parts were prepared and welded along the right side to form a preformed box. A spherical pressure shell was plastically formed by applying water pressure to the interior of the preformed box, causing it to expand outward. For verification, an actual molding experiment was conducted using a spherical pressure shell with a design radius of 250 mm as the research object. The measurement of the outer surface shape of the formed spherical pressure shell showed that the radius value of the spherical pressure shell was 246.52 mm, the error from the design radius was 1.39%, the roundness of the spherical surface was 3.81 mm, and the maximum reduction rate of the plate thickness was 3.2%. Therefore, the processing quality of the proposed IHBF method was confirmed to be high. Buckling analysis was performed by applying a uniformly distributed external pressure to simulate the deep-sea pressure. Compared with the conventional spherical shell structure, the crushing/buckling load of the spherical pressure shell processed by the IHBF method proposed herein is affected by work hardening owing to plastic forming, local defects, and welding line. The effect of the size is relatively small.
Abstract: Manned pressure shells subjected to deep-sea pressure are designed with a spherical shell structure because they are subjected to perfectly symmetrical pressures. A spherical pressure shell has excellent mechanical properties against deep-sea pressure; therefore, it has the advantage of relatively good buckling properties. However, there are high d...
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Research/Technical Note
Design of Multi-Input Multi-Output Non-linear Model Predictive Control for Main Steam Temperature of Super Critical Boiler
Sumanta Basu*,
Sushil Cherian,
Jisna Johnson
Issue:
Volume 12, Issue 1, February 2024
Pages:
18-31
Received:
6 January 2024
Accepted:
1 February 2024
Published:
21 February 2024
Abstract: Flexible operation of coal-fired power plants is becoming increasingly necessary for successful integration of large-scale renewable power generation into the power grid. The maximum ramp rate and the number of load cycles are generally limited by the thermal stress experienced by the boiler pressure parts, turbine metallurgy and creep and fatigue of critical thick-walled components Main steam temperature is a critical operating parameter that must be controlled within acceptable limits for safe operation. Main steam temperature deviation beyond acceptable limit has impact on boiler pressure parts and turbine material of construction due to creep and fatigue effect. Base load operating units do not require steep ramp rate and hence recommended ramping rates are kept low within the safe operating zone in comparison to the flexible operation of the units with wide range load change width. Thermal stresses are caused by the temperature changes inside the thick-walled components and turbine steam admission parameters. Hence, the quality of main steam temperature control plays a vital role in flexible operation of the coal fired units. Conventional cascaded PID temperature control loop architecture performs well at steady state condition within a limited variation of load change at low ramp rate but it acts slowly and performs poorly at transient operating conditions of flexible operation of the boiler turbine with wide range load variation and load cycle with high ramp rate and remains far from rated conditions. In this paper, a Multi-Input Multi-Output (MIMO) Non-linear Model Predictive Control (MPC) design for regulation of the main steam temperature of a Once-Through supercritical Boiler is proposed. The controller is based on a non-linear dynamic model which incorporates dynamics of the variables of interest. It has the capability to operate effectively across a wide load range while maintaining main steam temperature within acceptable limits. A notable advancement in this design of MPC is the incorporation of coal flow demand and feedwater flow demand as additional control inputs alongside primary and secondary spray flows. In simulation test cases, the MPC controller demonstrates satisfactory performance and computational efficiency.
Abstract: Flexible operation of coal-fired power plants is becoming increasingly necessary for successful integration of large-scale renewable power generation into the power grid. The maximum ramp rate and the number of load cycles are generally limited by the thermal stress experienced by the boiler pressure parts, turbine metallurgy and creep and fatigue ...
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Research Article
Checking the Mechanisms of Internal Combustion Engines for the Presence of Parasitic Forces Using a New Methodology
Tursunbaev Bakhodir*,
Fayzullaev Khasan,
Tursunbaev Temur
Issue:
Volume 12, Issue 1, February 2024
Pages:
32-36
Received:
23 January 2024
Accepted:
5 February 2024
Published:
28 February 2024
Abstract: This article presents the results of a study of internal combustion engines equipped with a crank mechanism according to the efficiency criterion using a new method for determining the operating efficiency of machines and engines. The study revealed the presence of parasitic forces in internal combustion engines equipped with a crank mechanism. The occurrence of parasitic forces present in internal combustion engines and the law of their dependence on the movement of the piston have been studied. As well as the negative impact of parasitic forces on engine efficiency. This article presents the main results of the study. As a result of the research, it was revealed that when converting the thermal energy generated in the combustion chamber of internal combustion engines equipped with a crank mechanism into mechanical work, more than 30% of the energy of the pressure force is spent on parasitic forces. The influence of the mechanical friction force (friction of the plain bearings) with the crankshaft on the effective torque was also studied. Thus, the inefficiency of internal combustion engines equipped with a crank mechanism has been theoretically and practically proven. Finally, recommendations are given for eliminating parasitic forces when designing new internal combustion engines. It is proposed to equip new internal combustion engines with mechanisms without parasitic forces. Equipping internal combustion engines with a mechanism that does not contain parasitic forces (that is, equipping them with more efficient mechanisms) significantly increases the possibility of efficient use of the thermal energy of the fuel introduced into the combustion chamber in internal combustion engines. Consequently, this increases the engine efficiency by 130%. or more. For internal combustion engines, a new mechanism is recommended that eliminates the loss of force and allows the use of rolling bearings. This feature of the new mechanism makes it possible to increase the efficiency of internal combustion engines by another 4-6%. From previous studies it is known that the efficiency of a rolling bearing relative to a plain bearing is more than 2-3 times.
Abstract: This article presents the results of a study of internal combustion engines equipped with a crank mechanism according to the efficiency criterion using a new method for determining the operating efficiency of machines and engines. The study revealed the presence of parasitic forces in internal combustion engines equipped with a crank mechanism. The...
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