Thermal Expansion Loads Research Articles

Study on the cantilever ratio optimization of high-temperature molten salt pump for molten salt reactor based on structural integrity

The high-temperature molten salt pump is the core equipment in the small modular molten salt reactor with media temperatures up to 700 °C. The cantilever ratio of the molten salt pump is usually large. Excessively large cantilever ratios cause increased deformations and rotational amplitudes at the impeller, thus affecting the operational stability of the main pump; small cantilever ratios cause heavy temperature gradients, thus affecting the structural integrity evaluation. This paper used numerical simulation methods to calculate and analyze the temperature field, stress, and structural integrity, optimized the pump shaft cantilever length of the original scheme based on structural integrity using the dichotomy method, and analyzed the rotor dynamics of the optimization results. The results of this study show that the thermal expansion load caused by the temperature difference has a significant mechanical effect on the structure; the first-order critical speed of the rotor system of the optimized schemes has been improved, and the amplitude of the unbalanced response has been significantly reduced, which not only improves the operational stability of the rotor, also contributes to the compact design of the main pump of a small modular molten salt reactor.

Fire performance of gypsum-sheathed cold-formed steel walls with rectangular section studs

This study conducted axial compression experiment of one full-scale CFS wall at ambient temperature and four full-scale fire experiments of CFS walls with two initial load ratios of 0.27 and 0.85. Specimens were sheathed with double layers of gypsum plasterboard, rock wool was the cavity insulation and the wall studs had rectangular cross sections. A finite element model was used to optimize the arrangement of rock wool cavity insulation for the CFS walls. The results showed that the failure mode changed from local buckling of the hot flange under a load ratio of 0.27 to local buckling of the whole stud section under a load ratio of 0.85. The fire resistance time of the specimen without rock wool insulation in the stud cavity was 7 min longer than that of the specimen with rock wool insulation. This was attributed to the thermal radiation effect of the stud cavities, which delayed the increase in hot flange temperature and improved the fire resistance time of the CFS walls. Thus, for CFS walls with rock wool-insulated cavities, the stud cavity configuration was more reasonable without than with rock wool insulation. When the axial thermal expansion load was considered, the load on the wall studs increased by a maximum of 43.3 kN per stud. In addition, for CFS walls with low load ratios of 0.27, the wall studs near the face-layer board joints tended to buckle first.

Application of CFRP Wrap for Reinforcing Undamaged Thin-Walled Pipe Bends under Thermal Expansion Loads

Application of CFRP Wrap for Reinforcing Undamaged Thin-Walled Pipe Bends under Thermal Expansion Loads

Fire performance of superabsorbent polymers protecting cold-formed steel walls with high load ratios

Superabsorbent polymers (SAPs) have great potential in the fire protection of steel structures due to their high absorbency and water-holding capacity. In this paper, SAP is applied to the full-scale cold-formed steel (CFS) wall studs to investigation the fire performance of the CFS walls. An axial compression experiment of CFS wall specimen at ambient temperature and three experiments at elevated temperature were conducted. Meanwhile, considering the effect of thermal expansion load, the actual load of CFS walls may increase significantly under fire condition. Hence, the load ratio of the specimens was 0.85 in the fire experiments. The specimens use an autoclaved lightweight concrete (ALC) board and calcium-silicate (CS) board as the face and base layers of sheathings, respectively. The effect of SAP insulation material, high load ratios and thermal expansion load on the fire resistance of walls are discussed. The results indicate that SAP insulation materials can improve the structural and insulation performance of CFS walls under fire exposure. This is because the dehydration and heat absorption process of the SAP insulation material removes the heat inside the wall cavity, maintaining the maximum temperature of the wall studs below 140 °C. Hence, the fire resistance time (FRT) is extended by 41 min after using the SAP insulation material. In addition, neither a high load ratio nor SAP insulation material changes the failure mode of the wall studs. For the present specimens at ambient and elevated temperature, local buckling was identified on the whole section of stud ends. However, the SAP insulation material will change the fire-induced failure position of wall studs. Specimen W3 with SAP insulation material fails at the top of the studs. Furthermore, a thermal expansion load will significantly speed up the fire-induced structural failure of CFS walls with a high load ratio. The FRT of specimen W4 decreases by 79 min after considering the effect of thermal expansion load.

A two-dimensional ordinary state-based peridynamic model for elastic and fracture analysis

A framework of the two-dimensional (2D) ordinary state-based peridynamic model is established for quantitative elastic and fracture analysis, in which the peridynamic force state considering the thermomechanical loading (elastic model), bond failure criteria, and numerical implementation method are presented. The critical time step for explicit time integration in the state-based peridynamics is given. Then, a plate under combined tensile and thermal expansion loads and a compact tension (CT) test specimen are analyzed using the present 2D peridynamic model, and the results are compared well with the available analytical and finite element modeling solutions. The present 2D peridynamic model can quantitatively capture the elastic and fracture behavior of 2D problems.

Topology design of binary structures subjected to design-dependent thermal expansion and fluid pressure loads

The future perspective of using topology optimization to solve challenging design-dependent physics problems motivates the creation of methods with clear structural boundaries and well-defined volume. This paper develops the topology optimization of binary structures (TOBS) method to include design-dependent fluid pressure and constant thermal expansion loads. Topology design in thermoelastic and fluid pressure problems have been only handled separately up to date. To the authors’ best knowledge, this is the first work to consider both type of loads simultaneously within a structural topology optimization framework. The TOBS method uses discrete design variables, sensitivity filtering, and formal mathematical programming (integer linear optimization) to achieve convergent and mesh-independent solutions. The discrete nature of the method presents attractive features when dealing with design-dependent body and surface loads. In this paper, we use the structural mean compliance and volume as functions for optimization. The sensitivity analysis is carried out using the adjoint and semi-analytical methods. Numerous examples are shown to design novel structural designs which perform well under the applied fluid pressure and thermal loads. The observed computational times signify the practicability of integer programming for structural optimization problems.

Design of Architected Materials for Thermoelastic Macrostructures Using Level Set Method

A level set topology optimization method is introduced and used to design periodic architected materials optimized for the maximum macrostructural stiffness considering thermoelasticity. The design variables are defined at the microscopic scale and updated by minimizing the total structural compliance induced by mechanical and thermal expansion loads at the macroscopic scale. The two scales are coupled by the effective elasticity tensor calculated through the homogenization theory. A decomposition method is constructed to formulate several subproblems from the original optimization problem, enabling the efficient solution of this otherwise computationally expensive problem, especially when the number of material subdomains is large. The proposed method is demonstrated through several numerical examples. It is shown that the macrostructural geometry and boundary conditions have a significant impact on the optimized material designs when thermoelastic effects are considered. Porous material with well-designed microstructure is preferred over solid material when the thermal load is nonzero. Moreover, when a larger number of material microstructures is allowed in optimization, the overall performance is improved due to the expanded design space.

高速炉配管のLBB評価におけるスクリーニングルール

Since the piping of fast reactor is used at low internal pressure and its material has high ductility, LBB is easily satisfied in general. Especially when the internal pressure is low and thermal expansion reaction force is small, both crack driving force and fracture load are small, then it is easily imagined that LBB might be easily satisfied. However, the crack opening displacement and leak rate dynamically evaluated are small in such conditions. For this reason, the contradiction occurs that LBB evaluation is not satisfied despite the crack driving force and the fracture load are small. To eliminate such inconsistencies, screening rules to determine the necessity of a detailed LBB evaluation were proposed. According to the rules, the detailed LBB evaluation can be omitted for the cases of low internal pressure and small thermal expansion load as the fracture of pipes do not occur. Based on the piping design of the constructed fast reactor plant, the applicability of the proposed screening rules was examined.

Stress analysis of the subsea dynamic riser baseprocess piping

Thesubsea dynamic riser base (SDRB) is an important piece of equipment for the floating production platform mooring system. One end is connected to the rigid pipeline, carrying a rigid pipeline thermal expansion load and the other end is connected to a flexible riser, carrying the dynamic load of the flexible riser, so its function is a transition connection between the flexible riser and the rigid pipeline which fixes the flexible riser on the seabed. On the other hand, as a typical subsea product, the design will satisfy the requirements of the standards for subsea products. By studying the stress analysisphilosophy of the topside piping and subsea pipeline, a physical model and procedure for piping stress analysis of the SDRB have been established. The conditions of the adverse design load have been considered, and a combination of the static load from the rigid pipeline and the dynamic load flexibility has also been optimized. And a comparative analysis between the AMSE, DNV and API standards for piping stress with the checking rules has been done. Because the SDRB belongs to the subsea pipeline terminal product, the use of DNV standards to check its process piping stress is recommended. Finally, the process piping stress of the SDRB has been calculated, and the results show that the jacket pipe and the carrier pipe stress of the SDRB process piping satisfy the DNV standards as a whole.The bulkhead cannot be accurately simulated by the AutoPIPE software which uses the FEA software ANSYS in the detailed analysis, but the checking results will still meet the requirements of the DNV standards.

The TransAlta High-Energy Piping Program—A Five-Year History

In 1995, the High-Energy Piping Strategic Management Plan (HEPSMP) was initiated at TransAlta Utilities Corporation (TAU) for the three generating facilities. At that time, it was recognized that several of the piping systems were exhibiting signs of creep relaxation, with some hangers bottomed or topped out online and/or offline. Previous hanger adjustment attempts were not always adequate. The program workscope included: 1) hot and cold piping system walkdowns, 2) selection of high-priority girth weld inspection locations, 3) examination of critical weldments, 4) weld repairs where necessary, 5) adjustments or modifications of malfunctioning steam line hangers, and 6) recommended work for future scheduled outages. Prior to 1996, examination locations were limited to the traditional locations of the terminal points at the boiler and turbine, with reexaminations occurring at arbitrary intervals. Since the terminal points are not necessarily the most highly stressed welds causing service-related creep damage, service damage may not occur first at the pre-1996 examined locations. There was a need to maximize the safety and integrity of these lines by ensuring that the highest risk welds were identified and given the highest priority for examination. An engineering consulting company was selected to prioritize the highest risk weldments for each piping system. This risk-based methodology included the prediction and evaluation of actual sustained loads, thermal expansion loads, operating loads, multiaxial stresses, creep relaxation, and cumulative creep life exhaustion. The technical process included detailed piping system walkdowns and application of advanced analytical techniques to predict and rank creep/fatigue damage for each piping system. TAU has concluded that the program has met its objective of successfully prioritizing inspection locations. The approach has also resulted in reducing the scope and cost of reexaminations. Phases 1 and 2 evaluations and examinations have been completed for all units. Results of some of the important aspects of this program are provided as case history studies.

Parametric equations for maximum stresses in cylindrical vessels subjected to thermal expansion loading

This paper derives a set of parametric equations for finding the maximum stresses developed in a cylindrical vessel which is supported by two saddles firmly secured to the foundation and subjected to thermal expansion loading. Three types of stresses are considered: maximum stress intensity, maximum circumferential stress and maximum axial stress. The maximum stresses in the vessel are found to be governed by the height and width of the saddle, the spacing between the two supports and the relative structural rigidity between the support and the vessel. This paper is an extension of the work reported by Tooth et al. (1996) [1]. Using a least square curve fitting procedure, parametric equations for the maximum stresses developed in the vessel have been established. Raw data used for the curve fitting were obtained from a comprehensive finite element study which covers a wide range of key dimensions. A total of 900 finite element runs have been performed. The derived parametric equations are subsequently validated against the raw data and their error bounds are established. In all cases the maximum errors are found to be within 20%. The established parametric equations can be used directly in design calculations. The curve fitting procedure outlined in this paper has wide application for any set of generated or measured data.