Abstract This contribution deals with the efficient numerical modeling of tapped thread joints. Commercial FE packages provide different strategies to tackle the problem of modeling threaded joints, which is a recurrent one for the design engineer. Different modeling techniques are characterised by how the screw is modeled: either three-dimensional elements (thetra, hexa or wedge) or mono-dimensional elements (beam) can be used. In the case of three-dimensional approaches, the thread helix is seldom modeled: the actual geometry is often replaced by a plain cylinder and a suitable choice of contact settings between the screw and the “threaded” hole. In the case of road vehicles, due to the high number of threaded connections to be modeled, it is paramount to reach a trade-off between modeling accuracy and computational effort. This paper aims at comparing two modeling approaches, namely a three dimensional approach (baseline) and a mono-dimensional one (simplified model). Based on several criteria, such as equivalent stress on the screw shank, pressure distribution at the interface of the plates and in the underhead region, optimal contact settings for the simplified model are suggested. These settings allow replicating the results provided by the three-dimensional approach for given load case. The comparison is carried out on single lap, single screw joints, by the ANSYS R17 software. The methodology can be easily extended to other softwares or joint configurations.

Abstract Printed circuit heat exchangers (PCHEs) are used in a number of novel nuclear reactor designs. In order to use a PCHE as a primary coolant confinement unit in the United States, the stress and strain must be modeled under realistic service loads, and shown to remain within limits imposed by ASME standards. Due to the complex geometry and multi-length scale features, direct simulation of the stress and strain in a utility scale PCHE is not practical because of the large number of degrees of freedom. This work presents an algorithm to model damage to the core region of a PCHE using planar 2D formulation and realistic service loads. We compare how closely the results from three different planar formulations match the results of a corresponding 3D model. We also explore other ways of reducing the size of the numerical model required to accurately simulate the stress and strain in the core region of a PCHE. Finally, we perform strain-limits evaluation on a core region of a PCHE using fully temperature coupled, elastic perfectly plastic material properties, and realistic service loads, obtained from plant dynamics code of sodium cooled fast reactor coupled with a supercritical CO 2 Brayton cycle. For our analyses, we used CSIMSOFT Trelis: a commercial meshing software, Multi Object Oriented Solver Environment (MOOSE): an open source finite elements solver, and Paraview: an open source post processing tool. Our methodology is presented and discussed in sufficient detail so that the work can be reproduced by others.

Abstract Dents are one of the common integrity threats of long-distance transmission pipelines. The current CSA Z662 standard assesses dents based on the dent depth. However, the severity of dent features is a function of many factors. Most recently, numerical modeling via finite element analysis (FEA) has been utilized to assess dent severity, however the approach is computationally expensive. Recently, the authors’ research group developed a robust but much simplified analytical model to evaluate the strains in dented pipes based on the geometry of the deformed pipe. When the strain distribution predicted using the analytical model is benchmarked against the strains by nonlinear FEA they showed a good agreement with certain error. The procedure, however, predicts more conservative results in terms of the maximum equivalent plastic strain (PEEQ). In order to estimate the accuracy in the recently developed model, a series of nonlinear FEA pipe indentation simulations were conducted using the finite element analysis tool, ABAQUS and compared with the analytical prediction. This paper presents an application of a Bayesian machine learning method named Gaussian Process Regression (GPR) for the accuracy assessment of the developed analytical model for dent strain assessment, quantifying the error in comparison with the FEA in terms of the maximum PEEQ. The Gaussian Process (GP) model holds many advantages such as easy coding, prediction with probability interpretation, and self-adaptive acquisition of hyper-parameters. By varying the dent depth and the indenter radius, this paper provides a model that quantifies the error in the developed analytical model. The proposed model can be utilized to rapidly determine the severity of a dent along with the accuracy of the prediction. This analysis method can also serve as a reference for other analytical expressions.

Abstract This paper discusses our efforts to develop a robust branch fitting that can withstand AIV related to higher sound power levels than a standard contour fitting and accommodate FIV related vibration loads, without compromising project cost and schedule. Numerical simulation results and experimental test data are presented to substantiate our claims that a sweeplus ® performs much better than any other contoured branch fittings available in the market with respect to any AIV, AR and FIV related risks. The aerodynamically shaped new fitting can withstand higher sound power level (PWL) limits in AIV, has smoother curvature to reduce flow separation, vortex formation and shedding thereby lowering peak stress concentrations and avoiding AR and FIV related risk, has an extended fatigue life, while adhering to ASME B16.9 Code requirements.

Abstract The cover of a cylindrical explosion containment vessel would suffer an extremely intense impact because the shock wave and blast products would converge at the cover area. To reduce the impact of shock waves to the cover, cases with aluminum foam placed at the end of the vessel and in the interior of the cylindrical portion are studied by numerical simulation and experiment. The result shows that aluminum foam located at the end of the vessel can have a great effect on the protection of the cover because it can absorb the energy of the shock wave that has spread to the end of the vessel. Aluminum foam located in the interior of the cylindrical portion would have a negative effect on the protection of the cover because it would reduce the distance between the charge and the cylindrical portion, the effect of which is more significant than the effect of energy absorption. These results can contribute to the design of cylindrical explosion containment vessels.

Abstract Vortex Shedding at pipe junctions can create pressure pulsations and flow-induced vibrations. The flow through one pipe may result in a shear layer at the junction with a second pipe. Instabilities such as vortex shedding in the shear layer can then excite acoustic modes in the second pipe, especially when the flow in the secondary pipe is stagnant or weak. The effect is the excitation of a pipe organ mode, which under certain conditions, may result in unacceptable noise and/or vibration levels. Within the nuclear industry this phenomenon has been most frequently observed in boiling water reactors (BWRs), resulting in vortex-induced, main steam line associated stand pipe acoustic resonances. This phenomenon has not been typically observed in pressurized water reactors (PWRs), especially in primary coolant loops due to the lengths of pipe needed to support acoustic resonances in water systems relevant to driving lower order structural piping modes. However, if certain conditions exist, PWRs do contain large sections of piping which can be susceptible to such flow-induced adverse noise and vibration effects. This paper describes the evaluation and mitigation of structural vibrations due to a vortex-induced excitation of an acoustic mode of a large side branch pipe in a high-energy, water-filled, PWR piping system. Specifically, an acoustic resonance was observed and structurally significant resultant vibration levels were measured on a safety related piping system directly connected to a PWR primary reactor coolant system (RCS) between the reactor and a steam generator. A rapidly employed evaluation program was implemented, which included significant in-situ structural vibration measurements that informed a combination of acoustic, structural, and fluid-domain numerical modeling evaluations. These evaluations were performed in concert to provide both root cause insights and candidate mitigation strategies. Candidate mitigation strategies were then evaluated prior to inplant implementation via further modeling evaluations and a model-scale testing program. This paper describes the primary vibration characteristics of interest of the affected piping system, the data analyses and modeling methods used to successfully identify the vibro-acoustic phenomena, the developed mitigation strategies, and verification of the final mitigation strategy via model-scale with final demonstration occurring in the plant prior to fuel load.

Abstract This work presents a numerical model for a fully-flexible CANDU fuel bundle to predict the vibration response due to turbulence excitation. The model includes 37 fuel elements and two endplates. The contact between system components such as fuel-to-fuel and fuel-to-pressure tube is modeled using the single point contact method (SPC). A range of flow velocities was examined, and the associated impact forces and work rates were calculated. In addition, the stresses on the endplates due to vibration of the fuel elements were predicted.

Abstract The welding task focuses on development of advanced welding technologies for repair and maintenance of nuclear reactor structural components to safely and cost-effectively extend the service life of nuclear power reactors. This paper presents an integrated research and development effort by the Department of Energy Light Water Reactor Sustainability Program through the Oak Ridge National Laboratory (ORNL) and Electric Power Research Institute (EPRI) to develop a patent-pending technology, Auxiliary Beam Stress Improved Laser Welding Technique, that proactively manages the stresses during laser repair welding of highly irradiated reactor internals without helium induced cracking (HeIC). Finite element numerical simulations and in-situ temperature and strain experimental validation have been utilized to identify candidate welding conditions to achieve significant stress compression near the weld pool during cooling. Preliminary welding experiments were performed on irradiated stainless-steel plates (Type 304L). Post-weld characterization reveals that no macroscopic HeIC was observed.

Abstract Steel storage tanks are critical components of an industrial installation due to their high seismic vulnerability and containment of hazardous materials. Failure of a which, may lead to loss of containment (LOC) triggering domino effects such as explosion, environmental pollution, loss of functionality and disruption of business. Past earthquakes have demonstrated different type of failure modes in steel storage tanks. Although there are plenty of studies related to different failure modes like elephant foot buckling or tank uplifting, there are very few efforts on the sliding behavior of tank. Large displacements caused by the tank sliding can lead to pipe detachment and release of hazardous material which might cause damage propagation. Consequently, this damage state is very important for the Quantitative Seismic Risk Assessment of industrial plants. In order to enumerate the sliding displacement of unanchored steel storage tanks, a simplified numerical model realized with OpenSees platform is proposed. The friction model used in OpenSees is calibrated with the results obtained from ABAQUS FE model. Sliding response of tanks with different D/H ratio is analyzed using the simplified model. Fragility curves for the tank sliding damage state are analytically evaluated for different D/H ratio of the tank using the “cloud method”. Finally, a parametric study is conducted in order to comprehend the influence of different parameters on the sliding behavior such as friction coefficient, tank filling level and the influence of the vertical component of ground motions.

Abstract There are many high-rise buildings all over the world, especially urban areas. Their usage is diverse, such as offices and residences. Therefore, earthquake countermeasures for high-rise buildings are indispensable. It is known that a tuned mass damper (TMD), which is mainly installed for countermeasures against wind shaking, does not show sufficient damping effect when large earthquake occurs or when higher modes vibration is excited. In addition, when exceeding the drive limit of the TMD in resonance, the TMD may collide against the stopper and deteriorate the response of the building. There are some researches targeting building with TMD, and many of them aim at developing new devices. However, installing a new equipment instead of TMD requires a lot of cost and construction period. Therefore, in this research, an active device that can be attached to TMD is developed. Moreover, validity is examined by numerical simulation. In this paper, parameters of the passive elements are verified as a basic research of the proposed device.

Abstract The seismic vulnerability of aboveground steel storage tanks has been dramatically proved during the latest seismic events, which demonstrates the need for reliable numerical models for vulnerability and risk assessments of storage facilities. While for anchored aboveground tanks, simplified models are nowadays available and mostly used for the seismic vulnerability assessment, in the case of unanchored tanks, the scientific community is still working on numerical models capable of reliably predicting the nonlinearity due to uplift and sliding mechanisms. In this paper, a surrogate model based on a Kriging approach is proposed for a case study of an unanchored tank, whose calibration is performed on a three-dimensional finite element (3D FE) model using a reliable design of experiments (DOE) method. The verification of the 3D FE model is also done through a shaking table campaign. The outcomes show the effectiveness of the proposed model to build fragility curves at a low computational cost of the critical damage state of the tank, i.e., the plastic rotation of the shell-to-bottom joint.

In this paper, different techniques to test notched Small Punch (SPT) samples for the estimation of the fracture properties in aggressive environments are studied, based on the comparison of the micromechanisms at different rates. Pre-embrittled samples subsequently tested in air at conventional rates (0.01 and 0.002 mm/s) are compared to embrittled ones tested in environment at the same rates (0.01 and 0.002 mm/s) and at a very slow rate (5E−5 mm/s); a set of samples tested in environment under static loads that produce very slow rates complete the experimental results. To close the study, numerical simulations based on obtaining a punch rate that produces an equivalent CTOD growing rate in the edge of the notch to the one at the crack tip of a C(T) specimen for a given solicitation rate is carried out. As a conclusion, is recommended to test SPT notched specimens in environment at very slow rates, of arround E−6 mm/s, when characterizing in Hydrogen Embrittlement (HE) scenarios, in order to allow the interaction material-environment to govern the process.

During the 2012 outage of the Belgian nuclear power plants (NPP) Doel 3 and Tihange 2 non-destructive testing (NDT) measurements revealed a high quantity of indications in the upper and lower core shells of the reactor pressure vessels (RPV). A root cause analysis leads to the most likely hypothesis that the indications are hydrogen flakes in segregated zones of the RPV ferritic base material. The laminar and quasi-laminar orientation (0° – 15° inclination to the pressure retaining surface) of the hydrogen flakes, the interaction of several adjacent flakes and the mechanical loading conditions lead to a mixed-mode behavior at the crack tips. In the framework of an ongoing research project, experimental and numerical investigations are conducted with the aim to describe the failure behavior of such complex crack configurations. The experiments are carried out using two ferritic materials. One is a non-irradiated representative RPV steel (SA 508 Class 2) and the second material is a special lower bound melt of a modified 22NiMoCr3-7 steel (FKS test melt KS 07 C) containing hydrogen flakes. A material characterization is done for both materials including tensile specimens, notched round bars, shear-, torsion- and compact-tension-shear (CTS) - specimens to investigate different stress states. Furthermore, flat tensile specimens with eroded artificial crack fields are used to investigate the interaction between the cracks in different arranged crack fields. Numerical simulations are carried out with extended micromechanical based damage mechanics models. For the description of ductile failure an enhanced Rousselier model is used and an enhanced Beremin model to calculate the probability of cleavage fracture. To account the sensitivity for low stress triaxiality damage by shear loading, the Rousselier model was enhanced with a term to account for damage evolution by shear. The Beremin model will be enhanced with a term to account for different levels of triaxiality. For the numerical simulations in the transition region of ductile-to-brittle failure a coupled damage mechanics model (enhanced Rousselier and Beremin) will be used. In this paper, the current status of the ongoing research project and first results are presented.

The damage states in a storage tank subjected to seismic loading can induce loss of containment (LOC) with possible consequences (fire, explosion, etc..) both for the surrounding units and people. This aspect is particularly crucial for the Quantitative Risk Analysis (QRA) of industrial plants subjected to earthquakes. Classical QRA methodologies are based on standard LOC conditions whose frequency of occurrence is mainly related to technological accident rather than natural events and are thus useless. Therefore, it is evident the necessity of establishing new procedures for the evaluation of the frequencies of occurrence of LOC events in storage tanks when subjected to an earthquake. Consequently, in this work a simple procedure founded on a probabilistic linear regression-based model is proposed, which uses simplified numerical models typically adopted for the seismic response of above ground storage tanks. Based on a set of predetermined LOC events (e.g. damage in the pipes, damage in the nozzles, etc..), whose probabilistic relationship with the local response (stress level, etc..) derives from experimental tests, the probabilistic relationship of selected response parameters with the seismic intensity measure (IM) is established. As result, for each LOC event, the cloud analysis method is used to derive the related fragility curve.

Seismic responses from linear and nonlinear dynamic analyses of reinforced concrete (RC) shear walls are compared to see how the damping ratio and cracking behavior affect the dynamic response of the RC structures used in the nuclear power plant. The nonlinear dynamic analyses are conducted based on the numerical model which is developed to simulate the nonlinear hysteretic behavior of RC structures subjected to in-plane shear. Through comparison of the obtained numerical results with experimental data such as load-displacement relationships and response time-histories, the developed numerical model is validated. The acceleration response spectra from the nonlinear dynamic analysis results of selected RC shear wall and those from linear dynamic analysis with combinations of the damping ratio and concrete stiffness considerations according to the level of earthquake loads and the resultant stresses are addressed.

This paper presents a technical review of remaining strength assessment methods, major technical challenges and on-going progress for line pipes containing metal loss defects. A brief review is first given to burst prediction models for defect-free pipes, including the strength solutions and flow solutions of burst pressure and their experimental validations. Followed are more detailed review and evaluation of existing corrosion assessment methods, including three-generation models developed for low to high strength pipeline steels. Major challenges to improve the corrosion models are then discussed in regard to full-scale testing, numerical modeling, material failure criteria, constraint effects, and applications to real corrosion defects. Finally, on-going progress is presented for developing improved assessment models to predict more accurate remaining strength of corroded pipelines.

Distortion is a common problem in welded panel structures, historically techniques to mitigate this problem have been developed empirically. A usual approach involves defining an intermittent weld sequence, a process that is extremely difficult to optimize given the large number of possible combinations i.e. hundreds or even thousands for multi-pass welds. Typically, plans to control weld distortion are therefore largely intuitive with welding engineers relying on their experience combined with the results of a limited number of practical tests. However, with modern computing, welding engineers can now include all the physics of welding in a simulation allowing them to cheaply and efficiently optimize a welding sequence without the need for multiple physical samples. The final welding procedure is then physically qualified based on the simulation results. In this paper, the authors present their use of computer modeling to automate the implementation of welding patterns to minimize distortion in panel lines. We describe a signature technique based on the Joint Rigidity Method where a combinatorial algorithm optimizes the welding sequence based on the panel’s resistance to angular bending i.e. the welding sequence starts at the point in the panel with the highest rigidity and moves progressively toward the lowest rigidity thereby minimizing distortion. This enables the designer to carry out an optimization of this complex weld design without relying on empirical observations.

Bolted flange joints (BFJs) are widely used in the process industries, and there is a large proportion served in the high temperature environment. During the long term service at high temperature, the creep relaxation of each component of BFJ will cause the decline of the residual gasket stress, which will further affect the sealing effect. So, it is very important to make sure the change rule of the leakage rate of BFJ during the long term service at high temperature. Firstly, according to constructing the relationship between the leakage rate and the service time, the leakage rate calculation method of BFJ during the long term service at high temperature was proposed. Secondly, the stress distributions of the gasket during the long term service at high temperature, which was time-dependent, were calculated at the tightness level T2 and T3 by using the numerical simulation method. Finally, based on the time-dependent average gasket stress and maximum gasket stress, the change rule of the time-dependent leakage rate of BFJ during the long term service at high temperature was obtained. The research results will play an important role in mastering the attenuation rule of the leakage rate of BFJ and supporting the leakage rate control of BFJ during the long term service at high temperature.

Numerical simulations were performed on the damage behavior of carbon-fiber-wrapped composite cylinder subjected to impact by a flat-ended impactor. The simulation results were in agreement with the test in terms of both the damage morphology of the cylinder and the impact acceleration-time curve of the impactor. The relationship between the impact acceleration-time curve characteristics and the initiation and propagation process of the various damages was analyzed. The effects of the internal pressure on the damage morphology of the cylinder, the impact acceleration-time curve of the impactor, and the critical perforation energy of the cylinder wall were discussed. Change law of the residual burst pressure of the cylinder with different impact energies was obtained. The conclusions in this paper are helpful for the safety assessment of the composite cylinders subjected to impact by foreign objects.

In this work, the mechanical properties of two different adhesives compositions have been investigated both experimentally and numerically. The studied thermoplastic adhesives are Hot-Melt Adhesive (HMA). In particular, a pristine and a nanomodified adhesive with 10% in weight of iron oxide have been considered. The adhesives have been subjected to a series of single lap joint (SLJ) tests using adherends made of polypropylene copolymer. As it is well-known, the structural-mechanical behavior of adhesive joints is mostly influenced by the bonding process: thickness of adhesive as well as its application procedures and the surface preparation of adherends are among the most influencing factors. In addition, the mechanical behavior of SLJ test is particularly influenced by the correct alignment of adherends and applied load. These aspects have been investigated, analyzing the experimental results. Moreover, the experimental results have been used to develop a numerical model of the two adhesives. The numerical analysis has been carried out using the commercial software LS-DYNA. Transient nonlinear finite element analysis has been performed to simulate the mechanical behavior of the thermoplastic adhesives. In particular, the cohesive formulations of the elements have been taken into consideration after a careful literature review. In order to set-up and to validate the mechanical properties of the adhesives, the experimental SLJ tests have been simulated. The developed finite element models enable to investigate more complex joint structures where these types of adhesives are used, such as plastic piping systems and automotive applications. Further, the numerical models allow to investigate with higher accuracy and lower time different aspects such as manufacturing and non-linear effects.