Search

Imperfections in a rotor-bearing system may cause undesirable subcritical resonances occurring when the rotating speed of the rotor is a fraction of the natural frequency of the system. These resonances arise partly from rotor imperfections and partly from bearing imperfections. This study demonstrates that the subcritical twice-running-speed vibrations originating from bearing waviness may be investigated by combining a simplified rotor model with a detailed bearing model, using a finite element method. The rotor-bearing system under investigation is a roller test rig consisting of the tube roll of a paper machine supported by spherical roller bearings. The bearing waviness from the second to the fourth orders is emulated as accurately as possible in the finite element model. This is achieved by measuring the waviness of the real bearings and then incorporating the measurement results into a simulation model. The tube roll of the test rig is modeled as a symmetric tube, neglecting the effects of the uneven mass and stiffness distribution of the roll. The contact between the rotor and the bearings is described using nonlinear Hertzian contact theory. The subcritical responses of the system are studied by means of time integration, and the results are converted into the frequency domain using fast Fourier transformation. The results of the analysis are compared with the measurement results for the subcritical responses of the roll. The agreement between the simulation and experimental results of the studied system can be observed even though rotor imperfections are not considered.

Experiments comparing conventional and ultrasonic vibration assisted guillotine cutting of paper stacks have been performed on plain and aluminum coated label paper. It is shown that ultrasonic vibration assisted cutting reduces the cutting force for both paper species. Reduction of the cutting force allows the down holder force to be decreased and lowers the compression of the paper stack necessary to prevent pull-out of the top sheets of paper. Using a higher amplitude setting on the ultrasonic generator further decreases the cutting force for the paper stack. For three different cutting speeds, it is shown that ultrasonic vibration assisted cutting force reduction depends on the average speed of the tool for both paper species. A linear regression with present experimental data is done to obtain an equation for the relation between input generator power and resulting cutting force. Finally, the quality of the cutting edge is examined, quality parameters are defined, and according to these the cutting edge quality is assessed.

A modern paper machine is equipped with various finishing units e.g. calenders and coating units in order to produce better optical and printing properties. To accomplish these required properties paper is manipulated between two parallel mounted rolls. The contact area of these rolls is called a nip. The rolls are pressed together using hydraulic loading mechanism in order to achieve required pressure to paper web between the rolls. One of the most important nip unit driving parameter is linear load i.e. force per length. To compensate deflections, which are caused by line load and gravity, the rolls are crowned. In cases, where the total nip force surpass the gravity force of the roll the zero load condition exists. In the other words the roll floats freely and bearing clearances can place themselves arbitrary. To prevent misalignment due to bearing clearances and to achieve more accurate line load control a new closing procedure has been developed. The actual line load level is force-controlled while the approach maneuver of the roll is controlled using positioning sensors. Tampere University of Technology (TUT) has built up an experimental set-up to study both vibration phenomena and behavior of polymer roll cover material. This paper presents the equations and experimental results of a new nip closing procedure.

In this work, a semiactive electromagnetic vibration absorber has been developed based on a proposed electromagnetic stiffness adjustable spring model, which presents a new solution for adjusting stiffness in the field of vibration absorber devices. Simulation study on the electromagnetic spring has been performed to determine the structural parameter of the semiactive vibration absorber. An experimental rig is also built up to investigate its practical vibration control effectiveness. Firstly, the finite element model of the test bench is used to analyze its vibration characteristics. Then, the vibration reduction effect is predicted through the simulation analysis, from which the optimal control positions are found. Finally, the experimental studies are also conducted, and the results show that this semiactive electromagnetic vibration absorber has a frequency adjustment range from 21 Hz to 25 Hz, in which considerable vibration reduction from 5 dB to 10 dB can be achieved.

The objectives of this paper are to determine the structural and functional bending capacity, for an 18-3/4 inch 10 ksi Dry Completion Unit (DCU) external tieback connector (ETBC), utilizing more advanced analysis design verification procedures of API 17TR8 [1]. This requires the evaluation using a 3D nonlinear elastic-plastic finite element analysis (FEA). Although the design verification procedures of API 17TR8 [1] are written for high pressure high temperature (HPHT) equipment, this paper demonstrates the feasibility of applying it to lower pressure equipment which have more critical requirements for bending capacity vs. pressure capacity. The capacity results are compared between the existing linear elastic criteria of API 17G [2] and the requirements of API 17TR8 [1]. The application of this evaluation demonstrates that the analysis methodology for HPHT equipment can be applied to subsea tieback connectors to obtain maximum bending capacity of the connection.

High pressure testing and operation of industrial tools and equipment can be hazardous to personnel and property in the event of an accidental mechanical failure or release of contained pressure. Hazard barricades are commonly installed around equipment to protect nearby personnel or property from projectile impacts or overpressure. The ASME Standard PCC-2 “Repair of Pressure Equipment and Piping” allows the use of hazard barricades for this purpose when a safe standoff distance cannot be satisfied, but it currently provides minimal guidance for engineered design. Other references provide guidance for preventing projectile perforation of a barricade. While perforation prevention is a key component of shield design, properly anchoring a shield and inter-connecting the shield components will make the difference between an effective barricade application and a barrier that could potentially compound the consequences of an accidental failure. This paper investigates the importance of engineered structural connections and consideration of global structural response in the design of protective barricades. The structural models focus on impact loading of steel plates and bolted connections, and the results are directly compared to test results in terms of effective barrier response.

This paper discusses the design of a hardened enclosure for high pressure extreme temperature (HPET) pneumatic testing of seals. The seal test fixture is located within a blast-fragment barrier (BFB) in case of a failure of the test fixture. The BFB is located within a hardened test room since the BFB has a 1-in annulus air gap to allow for cabling access to the test fixture, through which shock and gas pressure can propagate out into the room. A 30.5in3 (0.51) volume charged with 15,000psi (1034bar) of compressed nitrogen under a temperature range of −50°F to 400°F was used to produce the worst-case energy release in the event of a catastrophic failure of the seal fixture. In order to assess the structural capacities of the BFB and test room, an equivalent axisymmetric computational fluid dynamics (CFD) model of the test fixture, BFB, and test room was used to estimate the fragment velocity and applied blast load time histories to the BFB and test room. The BFB was assessed using non-linear dynamic finite element analysis. All of the materials are modeled using a plasticity-based piecewise linear hardening constitutive model, with rate dependency and softening, fit to each material yield, tensile, and elongation limit. The seal fixture generated fragment interactions with the interior surfaces of the BFB model using slideline and pinball contact algorithms.

Detailed analysis of dissimilar metal welds (DMWs) is difficult and the accuracy of the results is often limited by the availability of materials data and knowledge of operating conditions. There are few design or assessment procedures that explicitly take account of the presence of DMWs under high temperature creep and fatigue conditions. One that does is the UK R5 procedure, which provides a simplified assessment approach based on laboratory testing and stress analysis supported by service experience. This paper briefly summarises the R5 approach. Then, more recent work on performance of DMWs operating at high temperature and issues for development of analysis methods is discussed.Copyright © 2016 by ASME

The rules for the design of high temperature reactor components in Section III, Division 5, Subsection HB, Subpart B (HBB) of the ASME Boiler and Pressure Vessel Code contain two options for evaluating the deformation-controlled design limits on strain accumulation and creep-fatigue: design by elastic analysis and design by inelastic analysis. Of these options design by inelastic analysis tends to be less overconservative and produce more efficient designs. However, the HBB currently does not provide approved material models for use with the inelastic analysis rules, limiting their widespread use. A nonmandatory appendix has been developed to provide general guidance on appropriate material models and provide reference material models suitable for use with the design by inelastic analysis approach. This paper describes a viscoplastic model for Alloy 617 suitable for use with the HBB rules proposed for incorporation into the new appendix. The model represents the high temperature creep, creep-fatigue, and tensile response of Alloy 617 and accurately accounts for rate sensitivity across a wide range of temperatures. The focus in developing the model was on capturing key features of material deformation required for accurately executing the HBB rules and on developing a relatively simple model form that can be implemented in commercial finite element analysis software. The paper validates the model against an extensive experimental database collected as part of the Alloy 617 Code qualification effort as well as against specialized experimental tests examining the effect of elastic follow up on stress relaxation and creep deformation in the material.

Bolted joints in gas turbines are used commonly to connect the parts of dissimilar materials to facilitate assembly, dis-assembly, and also to achieve modularity for advanced aero engines. In gas turbine engine, there are many rotating and stationary parts that are subjected to an extreme working environment. Bolted joints should have sufficient strength to support the mating parts such as safety critical fan/turbine discs, drums, and shaft assembly. Bolted joints are designed to avoid flange separation and slippage. This paper attempts to understand the challenges faced in designing a typical fan disc rotor plain flange type bolted assembly and structural integrity aspects under various thermo-mechanical operating loads. The understanding of stiffness of the bolt and joint members is necessary to evaluate the performance of the joint assembly. Based on literature, different approaches are used for estimating member stiffness to compare with finite element results. The effect of external loads such as thermo-mechanical loads on pretension behavior of bolted joint is studied with the help of standard commercial software platform ANSYS. Bolted joint preload loss has been assessed via the standard analytical method and validated with 3D finite element approach. This paper enables designer a quick understanding of rotor bolted joint behavior for finalization of gas turbine rotor layout, before going into complex and time consuming 3D finite element modelling and nonlinear stress analysis.

This paper predicts burst pressures of the steam generator tubes with multiple cracks using finite element (FE) damage analysis. Alloy 690(TT) tube (the outer diameter of 19.05 mm and the thickness of 1.07 mm) widely used in the nuclear power plant is considered in this study. Ductile failure at each element is predicted with the damage model known as ‘multi-axial fracture strain model’ as well as crack propagation is simulated by stress reduction technique in the FE analysis. Simplified ductile damage model for Alloy 690(TT) are determined using tube tensile test data and elastic-plastic FE analysis. FE damage analysis results are sensitive to the element size used in the crack propagation region. Using notched tube fracture test data, proper element size for Alloy 690(TT) is found. Single, collinear, parallel, non-aligned axial-cracks are considered in the simulations and the predicted burst pressures are compared with burst test data.Copyright © 2015 by ASME

Nowadays, nuclear power plant (NPP) has become one of the most important energy sources to generate electricity in the world. Steam generator (SG) is a heat exchanger included in primary system of NPP. Alloy 600 MA is widely used for SG tube material and this is well-known as weakness of stress corrosion cracking. In recent year, according to increase the number of long-term operation NPP, many axial surface flaws have been found on SG tube during an in-service inspection. Therefore, many researches have been carried out to maintain structural integrity of SG tube. Commonly, flaw shape needs to be idealized to calculate a burst pressure because detected flaw shape is complicated. In this paper, validation of EPRI’s weakest sub-crack model, one of the well-known flaw idealization rule, is conducted through finite element (FE) analysis. For this, three actual flaws are assumed and these are idealized by using four flaw shape idealization methods; semi-elliptical crack model, rectangular crack model, maximum length with effective depth crack model and weakest sub-crack model. Burst pressure of each model is calculated and compared with burst pressure of actual shape crack model. As a result, if actual flaw is idealized by weakest sub-crack model, it is expected that conservative and efficient structural integrity assessment will be possible.

With strong bearing capacity, good corrosion resistance, excellent wear resistance, light weight and easy transportation and installation, Plastic pipe reinforced by cross helically wound steel wires (PSP) is widely used in oil industry, coal chemical industry, slurry transportation engineering, and sea (river) bottom water projects. Due to the PSP at middle-high pressure, an effective and reliable method of connection between pipes is particularly important. Heat-fusion weld and electro-fusion weld are usually used in middle-high PSP connections, or adding steel plate reinforcement at present. The pipe welded-joint failure is the main failure mode at service stage, causing the damage of pipelines and fluid leakage. Ultrasonic phased array inspection, which is one of the non-destructive inspection methods, is mainly used in pipe welded-joints inspection. A higher attenuation coefficient of polyolefin materials and the interference of steel mesh skeleton among PSP can cause great impact to the ultrasonic inspection; It’s worse if a steel plate is added. In order to put forward a kind of method can better detect the connection joint, this paper examines a new method of ultrasonic phased array inspection in PSP welded-joints based on customized probe, focus law and scanning mode which overcomes the difficulties found in other usual non-destructive inspection measures.Copyright © 2015 by ASME

Methods to demonstrate break preclusion for pressure retaining components in nuclear power plants are summarized in the newly developed German safety standard KTA 3206, especially the requirements for the leak-before-break assessment of crack-like leaks. In this context numerical and simplified calculation methods for both the leak opening area and fluid flow rates of crack-like leaks were examined and validated on selected experiments. Second topic of the paper is an accident analysis for a postulated leak in form of a through-wall crack in the pressurizer surge line (SL) of a German PWR Konvoi type. The initial size of the leak as well as the changing size depending on system pressure and temperature during the postulated leak accident was calculated with a FEM analysis model of a cooling loop. The reduction of the leak area amounts in the examined transient to ca. 25 % after 1 h and leads also to an approximately 23 % smaller leak rate. These results depend on the assumed position of the leak and on the initial leak size. Therefore, the results of accident analyses due to postulated leaks can be influenced by the change of the leak size during the course of the accident.

This paper is related to fluid-structure interaction analysis of sodium cooled fast reactors core (Na-FBR). Sudden liquid evacuation between assemblies could lead to overall core movements (flowering and compaction) causing variations of core reactivity. The comprehension of the structure behavior during the evacuation could improve the knowledge about some SCRAMs for negative reactivity occurred in PHÉNIX reactor and could contribute on the study of the dynamic behavior of a FBR core. An experimental facility (PISE-2c) is designed composed by a Poly-methyl methacrylate hexagonal rods (2D-plan similitude with PHÉNIX assembly) with a very thin gap between assemblies. Another experimental device (PISE-1a) is designed and composed by a single hexagonal rod for testing the dynamic characteristics. Different experiments are envisaged: free vibrations and oscillations during water injection. A phenomenological analysis is reported showing the flow behavior in the gap and the structure response. Also computational simulations are presented in this paper. An efficient numerical method is used to solve Navier-Stokes equations coupled with structure dynamic equation. The numerical method is verified by the comparison of analytic models and experiments.

Current nondestructive examination (NDE) technology detection capabilities limit our ability to detect stress corrosion cracking (SCC) damage until it has progressed significantly. This work describes the continued development of an in-situ monitoring technique to detect and characterize mechanical damage caused by SCC, allowing the detection of the incipient stages of damage to components/piping. The application of this study is to prevent failures in the primary cooling loop piping in nuclear plants. The main benefit to the industry will be improved safety and component lifetime assessment with fewer inspections. The technique utilizes high resolution fiber optic strain gages mounted on the pipe outside diameter (OD). This technique has successfully detected changes in the residual stress profile caused by a crack propagating from the pipe inside diameter (ID). The gages have a resolution of less than 1 με. It has been shown experimentally for different crack geometries that the gages can readily detect the changes of approximately 10 to 60 με caused on the OD of the pipe due to crack initiation on the ID. This paper focuses on the latest in the development of the technology. Details of the previous work in this effort may be found in [1–3]. A short summary is provided in this paper. The main recent development was the full scale accelerated SCC cracking in boiling magnesium chloride (MgCl2) experiment. In conjunction with experimentation, both 2D and 3D finite element (FEA) models with thermal and mechanical analyses have been developed to simulate the changes in residual stresses in a welded pipe section as a SCC crack progresses.

The use of High Density Polyethylene (HDPE) is growing rapidly due to its corrosion resistance characteristics and ease of construction when compared to metal piping systems. As a result of its widespread use, a method of inspecting the piping joints is becoming essential to ensure safe, sound piping systems. This is particularly true for butt fusion joints, which can contain micro-structural defects that impact long term integrity of the piping system. These defects have proven to be difficult to detect using traditional means of inspection, such as ultrasound, because these micro-structural defects do not result in an acoustic reflector or impedance difference. This paper presents the results of a rigorous validation program for a microwave non-destructive inspection technique for HDPE butt fusions. The program includes inspection of a cross section of defect types that comprise geometric type defects, such as back and side drilled holes, and butt fusion inclusions. It also includes defects of types commonly found in field applications, such as grass, oil, fine particulate and other contaminants and procedural deviations, such as low and high pressure and longer than typical dwell times (wait time between heating the pipe ends and fusing them). The success of the microwave inspection protocol and equipment in detecting the many types of defects that comprise the set of samples has been reduced to Probabilities of Detection (POD) and Probabilities of False Alarm (POFA). These statistics have been calculated in a traditional fashion and are presented in this paper.

Since 1982 the nuclear industry has employed weld overlay repairs to address intergranular stress corrosion cracking (IGSCC) in boiling water reactors (BWR) and primary water stress corrosion cracking (PWSCC) in pressurized water reactors (PWR). The American Society of Mechanical Engineers (ASME) has created several documents to provide rules and guidelines for weld overlay repair of nuclear components that have experienced stress corrosion cracking (SCC). These documents include ASME Code Case N-504-4 and ASME Section XI, Nonmandatory Appendix Q which specifically address weld overlay repair of stainless steel components. Recently, stainless steel components that have experienced thermal fatigue cracking at the inner diameter surfaces have been repaired with structural weld overlays (SWOL) using the methodology of Code Cases N-504-4 and N-740-2. The SWOL is a good choice for repair of thermal fatigue cracks in piping because it provides structural reinforcement to the affected location and places the inside diameter (ID) surface into compression preventing, or significantly reducing, further flaw growth. However, the rules of Case N-504-4 and N-740 were not specifically written to address thermal fatigue cracking as the primary cause and may not adequately address design, analysis and examination requirements when thermal fatigue is the active mechanism because it is very different in nature than SCC. For example, SCC is driven by a combination of environment, steady state operating stresses, residual stresses from welding and fabrication processes, and operating temperature, whereas thermal fatigue is driven by thermal stress cycles resulting from fluid thermal cycling or stratification. The source of the thermal events that result in cracking may not be as well understood or predictable as SCC degradation. In addition, weld overlays applied to address SCC are constructed of SCC resistant material but are not resistant to thermal fatigue. Therefore, ASME Section XI recognized that alternative rules were needed for repair of piping damaged by thermal fatigue. This paper provides a technical basis for weld overlay repair of components that have experienced thermal fatigue cracking. It addresses design, analysis and examination requirements considering the nature of thermal fatigue in nuclear piping systems. The Code Case was originally drafted based on the industry accepted rules of Case N-504-4 and Appendix Q but includes appropriate modifications needed to address thermal fatigue cracking. These modifications include removing restrictions such as the delta ferrite limit for PWRs that is only applicable to address SCC in BWR environments, and enhancements to the examination requirements to ensure that the repaired location is adequately monitored throughout the remaining service life of the plant. The purpose of this paper is to document the technical basis for Code Case N-894, which is currently still under development by ASME Section XI.

The European Project INCEFA-PLUS (INcreasing Safety in NPPs by Covering gaps in Environmental Fatigue Assessment) characterizes environmentally assisted fatigue of stainless steels in light water reactor environments. The project includes a major test programme during which more than 200 fatigue tests have been carried out in different laboratories across Europe. The test campaign was structured in three successive phases with slightly different foci. All testing programmes were optimized by means of the Design of Experiment method. The majority of the tests were carried out on a single batch of 304L which were complemented by tests on different batches of 304L and on X6 CrNiTi 18 10, a Ti stabilized steel used in VVERs. The influences of mean strain, surface roughness and hold time on fatigue life in air and water environment at a given environmental fatigue correction factor Fen were investigated. Besides the main test campaign, additional activities on the effects of mean stress, testing at reduced Fen, and different applications of hold time as well as biaxial fatigue tests have been carried out. The paper is part of a special session for the dissemination of the project results. It summarizes the tests performed during the project and provides the basis for the project conclusions in a different paper in the same session.

This paper reports the results of experiments and finite element simulations on the structural response of piping systems to internal detonation loading. Specifically, the work described in this paper focuses on the forces that are produced at tee-junctions that lead to axial and bending structural responses of the piping system. Detonation experiments were conducted in a 2-in. (50 mm) diameter schedule 40 piping system that was fabricated using 304 stainless steel and welded to ASME B31.3 standards. The 4.1 m (162-in.) long piping system included one tee and was supported using custom brackets and cantilever beams fastened to steel plates that were bolted to the laboratory walls. Nearly-ideal detonations were used in a 30/70 H2-N2O mixture at 1 atm initial pressure and 300 K. Pressure and hoop, axial, and support strains were measured using a high-speed (1 MHz) digital data acquisition system and calibrated signal conditioners. It was concluded that detonations propagate through the run of a 90° tee with relatively little disturbance in either direction. The detonation load increases by approximately a factor of 2 when the detonation enters through the branch. The deflections of the cantilever beam supports and the hoop and axial pipe strains could be adequately predicted by finite element simulations. The support loads are adequately predicted as long as the supports are constrained to the piping. This paper shows that with relatively simple models, quantitative predictions of tee forces can be made for the purposes of design or safety analysis of piping systems subject to internal detonations.

An in-core transmutation analysis and evaluation code, named CATE, considering in-core fine flux calculation and fine depletion process, is verified and validated in the present paper. Verification and Validation of implementations for the OECD/NEA PWR cell benchmark for actinides transmutation, IAEA PWR benchmark and infinite homogenized plate problem to confirm reliability and numerical accuracy for the code have been performed in presented paper. The numerical performance of the code system is demonstrated in the analyses of the in-core fuel management calculation. It is found that the present code system gives stability in prediction of critical concentration of boric solution and radial power distribution. Based on the verifications and validations, a preliminary LLFP transmutation pattern is calculated. Numerical results indicate that CATE can be used not only for the fuel management calculation, but also for in-core transmutation evaluation of PWR.Copyright © 2012 by ASME

The Atucha II nuclear power plant is a pressurized heavy water reactor being constructed in Argentina. Nuclear power plants must be designed to maintain their integrity and performance of safety functions for a bounding set of normal operational events as well as abnormal events that might occur during the lifetime of the plant. Seismic fracture mechanics evaluations for the Atucha II plant showed that even with a seismic event with the amplitudes corresponding to an event with a probability of 10−6 per year, that a double-ended guillotine break (DEGB) was pragmatically impossible due to the incredibly high leakage rates and total loss of make-up water inventory. The critical circumferential through-wall flaw size for this case is 94-percent of the circumference. These analyses are performed by placing cracked-pipe-elements into a complete model of the primary cooling system including the reactor pressure vessel, pumps, and steam generators as summarized in the paper. This paper summarizes these results and further shows how much higher the applied accelerations would have to be to cause a DEGB for an initial circumferential through-wall crack that was 33 percent (about 120°) around the circumference. This flaw length would also be easily detected by leakage and loss of make-up water inventory. These analyses showed that the applied seismic peak-ground accelerations had to exceed 25 g’s for the case of this through-wall-crack to become a DEGB during a single seismic loading event. This is a factor of 80 times higher than the 10−6 seismic event accelerations, or 240 times higher than the SSE accelerations. This suggests there is a huge safety margin for beyond design basis seismic events and Atucha II plant rupture is pragmatically impossible. These surprising results are discussed and could be potentially applicable to other nuclear power plants as well.

Twenty-two years ago, adaptive munitions using piezoelectric actuators were conceived. The Barrel-Launched Adaptive Munition (BLAM) program used piezoelectric elements to articulate a 10 deg. half-angle conical section on the nose of a 73 mm caliber supersonic wind tunnel model. The test article was designed to pivot the forward portion of the round about the aerodynamic center (which was collocated with the forward section center of gravity). While effective in trim articulation, the majority of actuator power was expended resisting nose inertia rather than manipulating air loads. Adaptive actuators for guided munitions have progressed greatly since that time. In 2001, major advances canard articulation for guided bullets were achieved. These were followed by the Shipborne Countermeasure Range-Extended Adaptive Munition (SCREAM) program. While the piezoelectric effectors designed for these historic programs would allow for respectable deflections, the invention of post-buckled piezoelectric (PBP) actuation would dramatically boost total deflection levels while maintaining full blocked force capabilities. These PBP actuators would be used in a variety of flight control mechanisms for different classes of UAVs. In addition to these applications, the high bandwidth of piezoelectric actuators are particularly well suited to guided munitions. This paper describes the structural mechanics and dynamics of the PBP-class actuator as integrated in guided munitions. As a critical element in ultra-high bandwidth flight control actuation, PBP actuators have been shown to possess pseudo-corner frequencies in excess of 1 kHz. Additionally, PBP actuators have been integrated into tight packing volumes in guided cannon shells while demonstrating setback acceleration tolerances of tens of thousands of g’s. Previous work illustrates several different actuation configurations as well as integration methods with canards and fins. This study links the structural mechanics of previous authors with aeromechanics to arrive at performance predictions in aerial combat. The paper lays out a guided aerial round based on the PBP concept, then uses circular error probable (CEP) predictions in a standard atmosphere quantify the required deflections for engagement of a variety of targets. The results show one order of magnitude fewer rounds being expended per kill in direct air-to-air engagements with peer aircraft. The paper shows that PBP-class actuators could be used for defensive engagements as well with the engagement of oncoming hostile missiles. The paper concludes with prediction of engagement improvements for modern aircraft like the F-35 with 25 mm rounds as well as aircraft like the F-15 with 20 mm guided ammunition.

Codified fitness for service methods such as API 579 or BS 7910 require consideration of residual stresses in fracture assessments, and guidance is given for upper bound residual stress distributions in common weld geometries. However, these distributions are not appropriate for some welding processes currently or historically used in the manufacture of linepipe, such as high frequency induction welding or flash butt welding. In addition, some linepipe manufacturing routes generate large plastic strains which result in high residual forming stresses, or mechanically relax residual stresses generated in earlier stages of production. This paper first reviews the code recommendations for the effects of plastic strains and stresses from high level pressure testing on residuals stresses. The paper then briefly describes the major methods of producing carbon steel linepipe and provides recommended residual stress levels for the seam weld and parent material of linepipe using the code recommendations. These are based on assumed uniform residual stresses combined with mechanical stress relaxation due to manufacturing steps such as cold expansion and hydrostatic testing. The recommendations are compared with measured residual stress levels from the open literature. Proposals are given for reduced residual stress levels when assessing axial cracks in carbon steel linepipe.

At the core of electrified railroad design is the Pantograph and Overhead Contact System (OCS). The design of the OCS has been essentially unchanged for nearly 100 years. The pantograph has undergone structural changes in the last 50 years but it still functions the same way it did over 100 years ago. The technology has proven to be incredibly successful and reliable. However the relationship between the pantograph and the OCS has practical limitations that have become evident in recent times, as trains achieve ever faster operating speeds. Currently the world’s high sped trains all tend to have cruising speeds of about 220 MPH. This circumstance has been referred to in one paper as the Pantograph Barrier. (See Ref #1). The evident limitations on the cruising speeds of electric locomotives comes from several causes. Among these are the maintenance condition of the rails; the radius of curves; the use of roadbed super-elevation; and the presence of freight or commuter trains. But arguably the most pervasive limitation is the behavior of the OCS at higher speeds. History demonstrates the inevitable progress to ever faster rail speeds and the need for ever increasing traction power capacity. This paper will explore the evolution of the pantograph and OCS configuration as a means to identify the limitations that are endemic in the design. It proposes a list of design criteria that must guide the further evolution of the relationship between the OCS and the Pantograph. Further, it proposes a new configuration for the OCS and the Pantograph that may form the basis for the further evolution of the electric locomotives.

The paper presents the conceptual and functional design of a novel machine used to create chamfers on wooden beams and called RCT. The authors show, in this paper, the technical problem and the technical specifications used to design a machine to solve the problem. The novelty of the patented invention is based on its originality and usefulness. All claims of the invention are underlined by the novelty and innovation. In this paper, the steps performed to design the proposed machine are discussed in details. The chamfering process is performed using disc saws and the machine is moved on the wooden beam using rubber wheels. This machine uses four disk saws to create chamfers on wooden beams. The particularity of this machine is the possibility to use two or four disk saws for chamfering two or four edges. The market’s needs allow us to design a novel machine with original motion and manufacturing process giving a big impact to creativity and innovation in design for manufacturing.

Wing selection plays a crucial role for race cars as it generates the most downforce. This is essential to maintain traction which leads to faster lap timings, and maintain efficiency in the performance of the race car. In this paper, the numerical simulation of a Formula SAE (FSAE) Car is performed. The FSAE car is restricted by regulations in terms of the geometry of the front and rear wing configuration. Hence, it becomes necessary to optimize the selection of airfoils in order to get the best out of the wing configuration. It is also essential to observe the tradeoff between the downforce generated and the drag produced in a racecar for optimal performance. This serves as the primary motivation of this research paper. The focus is on Benzing airfoils, which show considerably better performance in terms of downforce production in a race car than conventional airfoils. The wing configuration utilized in this research paper consists of a single mainplane and two flaps.. The freestream velocity of the flow is in the range of 0–60mph (0–26m/s). The 122 series of Benzing airfoils is utilized for the mainplane and the 153 series of Benzing airfoils is utilized for the flaps for manufacturing reasons. Nine different combinations of Benzing airfoils were utilized wherein it was noticed that an appropriate selection of the airfoils for the mainplane and flaps with a fixed angle of attack difference, leads to a 12–15% increase in downforce amongst the Benzing airfoils itself. Similarly, it was also observed that an optimal configuration would lead to a 12–15% decrease in drag in comparison too poor performing airfoil. The Be 153-055 airfoil acts as an excellent flap within the limits of computational error. Data from an on-track test is used in order to verify the approach utilized in this paper in order to validate if the approach used in this paper would be feasible. It is observed that the Benzing airfoil does improve the average cornering speed of the car by around 10% in comparison to the previous configuration of S1223 airfoil as the main plane and the goe 477 airfoil as the flap.

Environmentally assisted fatigue of nuclear plant materials in the Pressurised Water Reactor (PWR) coolant environment is a phenomenon that has been extensively studied over the past 30 years. Methods for accounting for the PWR environment in an ASME III fatigue assessment are presented in NUREG/CR-6909. The deleterious effect of environment is described through a Fen factor dependent upon strain rate, temperature and the dissolved oxygen content of the water. The formulae which describe the Fen are based upon correlations observed in test data predominantly from tests conducted with constant temperature and strain rate (triangular or sawtooth loading). Actual loading histories encountered during service are far more complex, with both strain rate and temperature, and therefore Fen, varying through the cycle. NUREG/CR-6909 recommends a modified rate approach method for accounting for this, whereby the load cycle is broken up into a number of strain increments and then integrated to give the Fen for the cycle. There is a substantial and growing body of data for conditions in which the strain rate or temperature or both changes. The NUREG/CR-6909 modified rate approach does not generally perform well in describing the deleterious effect of environment in these complex conditions. In particular, the modified rate approach does not predict a difference in life when the temperature is varied in-phase or out-of-phase with the strain waveform, or when the slow portion of the strain rate is moved from the top to the bottom of the waveform. This paper presents new data from strain-controlled fatigue endurance testing of two casts of 304L with complex waveforms and temperature cycling. The paper then presents and compares a number of models for integrating the Fen through the cycle, including methods which weight Fen increments depending on position in the strain cycle. It is concluded that greater weighting on the environmental effect in the top of the cycle is necessary to describe the differences in life observed. This is further validated by a review of test data in the wider literature. An improved method is presented to account for the effects of the PWR environment on fatigue lives of austenitic stainless steel materials, which has similarities to the “Weighted K Rate” method previously presented by Rolls-Royce, PVP2016-63497, for environmentally assisted fatigue crack growth.

Modern petrochemical and chemical facilities consist of a significant number of pressure vessels. Adequate design of pressure vessels and their foundations have a significant impact on the safety and economics of such facilities. The design of pressure envelope components is well developed and specified in pressure vessel codes. A more less developed but significant aspect of the design of pressure vessels is the design of the vessel support and foundation. To adequately design the vessel support/foundation, engineers shall consider all the applicable loads on the vessel from attached piping and determine whether these loads could potentially entirely translate to the vessel base support/foundation. While methodology to determine these piping loads is well developed in literature and codes, there is a lack of guidance on how to determine the effect of these piping loads on the base support/foundation loading. This paper is a continuation of the paper presented at the PVP2016 conference (63694 “Effects of Piping Loads on Vessel Supports and foundation” [1]), where the effect of piping loads on a vessel support/foundation was discussed. The paper demonstrated that when flexibility was introduced into a simple piping system, the loads transferred to the foundation/supports were reduced. This paper expands the study by evaluating piping loads from a more complex piping system attached to a tall vessel. To observe the differences, two different vessel heights and three different shell thicknesses are evaluated. The effect of piping loads (loading at the base) is calculated when the vessel and the nozzles are considered rigid and when flexibilities are introduced into the system. The more flexibility is introduced into the system, the more reduction in base loads is observed.

During the 2012 outage at Doel 3 and Tihange 2 Nuclear Power Plants, a large number of quasi-laminar indications were detected, mainly in the lower and upper core shells of the Reactor Pressure Vessels (RPVs). The observed indications could subsequently be attributed to hydrogen flaking induced during the component manufacturing process. As a consequence, both units remained core unloaded pending the elaboration of an extensive evaluation demonstrating that they can be safely operated. The Structural Integrity Assessment of the RPVs, through the Flaw Acceptability Assessment, aimed at demonstrating that the identified indications do not jeopardize the integrity of the reactor vessel in all operating modes, transients and accident conditions. This demonstration has been done on the basis of a specific methodology inspired by the ASME B&PV Code Section XI procedure but adapted to the nature and the number of indications found in the Doel 3 and Tihange 2 RPVs. As requested by Article IWB-3610(d)(2) of ASME B&PV Code Section XI, one of the parts that have to be addressed through the Flaw Acceptability Assessment is the Primary Stress Re-Evaluation assuming local area reductions of the pressure retaining membrane i.e., of the core shells, due to presence of the flaws. This is performed using the limit analysis provided by Article NB-3228.1 of the ASME B&PV Code Section III. Results are compared to those using the plastic analysis of Article NB-3228.3. The acceptance criterion that needs to be verified is that the calculated collapse pressure should be more than 1.5 times the design pressure. The paper presents the 2D conservative approach developed in order to carry out this analysis dealing with large number and high density of flaws. Furthermore, the paper validates this 2D conservative methodology through detailed 3D XFEM elastic-plastic calculations.

Subsection NB, Section III of the ASME Code provides rules for the fatigue evaluation of nuclear pressure vessel and piping components. The stress analysis in ASME code evaluation is generally based on linear elastic analysis. Simplified rules using an elastic-plastic strain correction factor, Ke, are provided in Section III to account for plastic yielding when the primary plus secondary stress intensity range exceeds the 3Sm limit. While the simplified elastic-plastic analysis rules are easy to apply and do not require nonlinear analysis, the application of the Ke correction factor can produce extremely conservative results. This paper investigates different analytical methods that are available for simplified elastic-plastic analysis and proposes an alternative method that is not overly conservative (compared to the Code Ke) and offers a more realistic approach to simplified elastic-plastic analysis. The proposed methodology is applicable for both vessel (NB-3200), core support structures (NG-3200) and piping components (NB-3600) and does not require new finite element analysis. Information in existing ASME Code stress reports should be sufficient to determine the new Ke factor. The proposed methodology is applicable to structural materials including austenitic stainless steel and nickel based alloys, carbon steel and low alloy steel. Comparison of the proposed methodology with detailed elastic-plastic finite element analysis shows that the new Ke factors are conservative but offer relief from the excessive conservatism in the Code Ke values. This paper provides the technical basis for an ASME draft Code Case for Alternative Approaches for ASME Code Simplified Elastic-plastic Analysis being pursued through the Section III ASME Code Committees.

Aging coke drums and their connected overhead piping in delayed coking units experience fatigue cracks which most commonly occur at the skirt junction and high stress pipe welds. This paper presents 2-case studies of this new cost-effective repair methodology with fatigue resistant design upgrade. The first case study applies to coke drum weld build-up solid skirt crack repair and the second for overhead vapor line weld crack repair. This paper presents new field repair methodology which could also improve long term fatigue resistance. It also suggests optimizing the thermal operation & thermal gradients of coke drums for further reliability improvement. Based on FEA, successful field execution and our experience, these case studies demonstrate a long term improvement in reliability and fatigue life of the order of 2.5 to 3 or higher especially if combined with thermal operation optimization.

In a previous paper, it was demonstrated that a tight radius bend with uniform wall thickness equal to the pressure based thickness of the corresponding straight pipe does not meet the linear elastic criteria of NB-3221 Design Loadings. It was also demonstrated that the allowable wall thickness circumferential distribution of the ASME B&PV Code SEC XI Code Case N-597-2 achieves a uniform linear elastic stress intensity over the entire bend that meets the linear elastic criteria of NB-3221. As stated by the ASME B&PV Code under NB-3221, the provisions of NB-3228 may provide relief from certain of the linear elastic stress limits if plastic analysis techniques are applied. In this paper, the plastic collapse analysis approach of the COG FFSG is adopted to explore the relative safety margin when analyzing various Class 1 tight radius pipe bends’ configurations made of Carbon Steel SA-106 Grade B. In addition to the power law material model, three elastic plastic material models are constructed based on ASME B&PV Code Section II Part D material properties. The pressure-based thickness for the same size straight pipe is uniformly used in modelling the tight radius bends (no increased thickness on the intrados). It is demonstrated that the results from the ASME B&PV based flow stress model are marginal and that the ASME B&PV based bi-linear material model and the limit analysis results are not meeting the collapse pressure criterion. It is also demonstrated that the uniform pressure-based thickness along with the power law material model meets the requirements for the adopted plastic collapse pressure providing a considerable life extension.

The fatigue crack growth threshold is an important characteristic of crack growth assessment for the integrity of structural components. However, threshold values for austenitic stainless steels in air environment are not well provided in many fitness-for-service (FFS) codes, although extensive amount of fatigue crack growth tests data has been published. This paper focuses on fatigue crack growth threshold values for austenitic stainless steel in air environment at room and high temperatures. The paper introduces the current fatigue crack growth rates provided by the ASME (American Society of Mechanical Engineers) Code Section XI and summarizes the available test data of fatigue crack growth thresholds based on the literature survey. The paper then discusses the applicability of the existing fatigue crack growth thresholds for stainless steels and proposes a new relation as a function of the stress ratio for use by the ASME Code Section XI.

In the design of piping systems, there are many options for transitioning between HDPE and metallic piping. One common option is the use of flanged joints. As a result of the visco-elastic nature of HDPE, the use of HDPE-to-metallic flanged joints requires special design considerations. When HDPE-to-metallic flanged joints are used in ASME Class 3 systems, the design is further complicated by the requirements provided in the ASME B&PV Code, Section III for flanged joint analysis. This paper examines the differences between HDPE piping flanged joints and metallic piping flanged joints, including consideration of industry guidance and available industry testing results. The paper provides a proposed methodology for evaluating ASME Class 3 HDPE-to-metallic flanged joints and HDPE-to-HDPE flanged joints, including the determination of required bolt torque values and the determination of the maximum internal pressure that the joint can resist without experiencing leakage.

The cracking of CANOPY Seal Weld (CSW) of the Control Rod Drive Mechanism (CRDM) ever occurred and led to Boric acid solution leakage in nuclear power plant worldwide. The failure analysis on above failure CSW shows that stress corrosion crack (SCC) is main failure mode of CSW, and the crack usually originate from the weld root and grows along weld or HAZ under PWR service environment. The CSW structure parameter presented here are as following, the wall thickness is 2–3 mm, radius of curvature of cross-section is 6–12 mm, and the gyration radius is 50–100mm. In the latest year, CSW is required to implement surface examination (i.e. Visual Test or Penetration Test) during the plant outage. The flaw is that the CSW won’t be repaired till its failure is detected; therefore effective preventive maintenance can’t be performed. The specific inspection technology is developed for NDT volume testing method, aiming to detect the root crack occurred in weld and its adjacent base metal. This paper introduces the CSW structure, in-service inspection requirements, and technical solutions. The NDT technology corresponding UT, ET and CCTV was finally applied as applicable technical solution with automatic scanning devices to detect CSW crack. Ultrasonic inspection technology uses high-frequency water immersion focusing probes with frequency higher than 10MHz which is investigated to detect the defect in the weld root area. Meanwhile, Eddy current inspection technology is applied to detect the surface crack or subsurface crack with orthogonal difference array probes, which helps to distinguish false signals detected by UT in outer surface. Ultrasonic inspection technical solutions based on high-frequency water immersion focusing methods and the key technical parameters are discussed emphatically in this paper. By testing on blocks with characteristic artificial reflectors, characteristic rule of ultrasonic signals in different areas and sizing methods for crack is investigated respectively. It show that UT has higher detecting sensitivity for crack of where the height reaches 0.5mm and the length reaches 4mm, and sizing is accuracy and reliable for crack when the height over than 1 mm and the length over than 4mm. CSW is not incorporated in-service scope referring to ASME code or Chinese in-service code, and the acceptance criterion of weld flaw is also not found. So, the integrity shall be evaluated as far as CSW with flaw is concerned. Thus, the stress analysis and temperature field are carried out on the CSW mentioned above, and the structural integrity assessment is simultaneously performed based on ASME code. Finally, the acceptance criteria are recommended for both volumetric and planar flaw.

The prediction of aerodynamic damping is a key step towards high fidelity forced response calculations. Without the knowledge of absolute damping values, the resulting stresses from forced response calculations are often afflicted with large uncertainties. In addition, with the knowledge of the aerodynamic damping the aeroelastic contribution to mistuning can be considered. The first section of this paper compares two methods of one-way-coupled aerodynamic damping computations on an axial turbine. Those methods are: the aerodynamic influence coefficient, and the travelling wave mode method. Excellent agreement between the two methods is found with significant differences in required computational time. The average deviation between all methods for the transonic turbine is 4%. Additionally, the use of transient blade row methods with phase lagged periodic boundaries are investigated and the influence of periodic boundaries on the aerodynamic influence coefficients are assessed. A total of 23 out of 33 passages are needed to remove all influence from the periodic boundaries for the present configuration. The second part of the paper presents the aerodynamic damping calculations for a centrifugal compressor. Simulations are predominantly performed using the aerodynamic influence coefficient approach. The influence of the periodic boundaries and the recirculation channel is investigated. All simulations are performed on a modern turbocharger turbine and centrifugal compressor using ANSYS CFX V17.0 with an inhouse pre- and post-processing procedure at ABB Turbocharging. The comparison to experimental results concludes the paper.

The catcher bearing is a crucial part of the magnetic bearing system. It can support the rotor when the magnetic bearing is shut down or malfunctioning and limit the rotor’s position when large vibration occurs. The sleeve bearing has the advantages of a relatively large contact surface area, simple structure and an easily replaced surface. There are already many applications of the sleeve type catcher bearings in the industrial machinery supported by the magnetic bearings. Few papers though provide thorough investigations into the dynamic and thermal responses of the sleeve bearing in the role of a catcher bearing. This paper develops a coupled elastic deformation — heat transfer finite element (FEM) model of the sleeve bearing acting as a catcher bearing. The FEM model investigates the dynamic and thermal behavior when a flexible rotor drops onto the sleeve catcher bearing. The thermal load caused by the thermal expansion is also considered. The flexible rotor is composed of Timoshenko beam elements. A coulomb friction model is used to model the friction force between the rotor and the sleeve bearing surface. The contact force and 2-D temperature distribution of the sleeve bearing are obtained by numerical integration. To validate the FEM code developed by the author, firstly, both the mechanical and thermal static analysis results of the sleeve bearing model are compared with the results calculated by the commercial software, “SolidWorks Simulation”. Secondly, the transient analysis numerical results are compared with the rotor drop test results in reference 13. Additionally, this paper explores the influences of different surface lubrication conditions, different materials, such as stainless steel, bronze, and aluminum, on rotor-sleeve bearing’s dynamic and thermal behavior. This paper lays the foundation of the fatigue life calculation of the sleeve bearing and provides the guideline for the sleeve type catcher bearing design.

Composite fan blade ply lay-up design, which includes ply drop-off/shuffle design and stacking sequence design, makes fan blade structures different from traditional composite structures. It gives designers more freedom to construct high-quality fan blades. However, contemporary fan blade profiles are quite complex and twisted, and fan blade structures are quite different from regular composite structures such as composite laminates and composite wings. The ply drop-off design of a fan blade, especially for a fully 3D fan blade, is still an arduous task. To meet this challenge, this paper develops a ply lay-up way with the help of a software called Fibersim. The fully 3D fan blade is cut into ply pieces in Fibersim. As a result, an initial ply sequence is created and ply shuffle could revise it. Because of the complexity of ply shuffling, the ply shuffle table developed in this paper mainly refers to the design experience gained from simple plate-like laminate structures and some criterion. Besides, the impact of different ply orientation patterns on the reliability of composite fan blade is studied through static and modal numerical analysis. The results show that this ply lay-up idea is feasible for aero engine composite fan blade. Under the calculated rotating speeds, the ply stacking sequence 4 (i.e.[−45°/0°/+45°/0°] with the outer seven groups are [−45°/0°/−45°/0°]) shows the greatest margin of safety compared with other stacking sequences. Modal analysis shows that plies with different angles could have relatively big different impacts on blades vibration characteristics. The composite fan blade ply design route this paper presents has gain its initial success and the results in this paper might be used as basic references for composite blade initial structural design.

Several experimental apparatus have been designed in the past to evaluate the effectiveness of under-platform dampers. Most of these experimental setups allow to measure the overall damper efficiency in terms of reduction of vibration amplitude in turbine blades. The experimental data collected with these test rigs do not increase the knowledge about the damper dynamics and therefore the uncertainty on the damper behavior remains a big issue. In this paper a different approach to evaluate the damper-blade interaction has been put forward. A test rig has been purposely designed to accommodate a single blade and two under-platform dampers. One side of each damper is in contact with a ground support specifically designed to measure two independent forces on the damper. In this way both the normal and the tangential force components in the damper-blade contact can be inferred. Damper kinematics is rebuilt by using the relative displacement measured between damper and blade. This paper describes the concept behind the new approach, shows the details of the new test rig and discuss the blade frequency response from a new point of view.

Life6 software, developed by IFP Energies nouvelles, is the local model used by Technip to determine stresses in tensile armour layers of unbounded flexible risers. These stresses and their variations are then used to predict fatigue limits of the dynamically loaded risers. Life6 is based on periodic conditions to reduce the model length, with the assumption that all the tensile armour wires of a same layer share the same kinematics. This paper firstly presents recent improvements to obtain a better modeling of tensile armour wires kinematics, when the flexible riser loading includes external pressure. New models of the external sheath and the anti-buckling tapes have been developed and implemented in Life6. The results are successfully compared to a Finite Element periodic model. Applications to lateral buckling prediction of tensile armour layers are secondly presented in the paper. Indeed, in the design of flexible pipelines for offshore field developments, lateral buckling is one of the critical failure modes for the tensile armour wires, being associated with external pressure and flexible pipe cyclic bending. The latest developments made on the modeling of the external kernel of the flexible pipe allow to use Life6 as the basis of the enhancement of the lateral buckling engineering model used by Technip. It has been calibrated and validated against an extensive full scale test data base resulting in a physical, reliable and fast engineering model to predict lateral buckling mode. In accordance with standards, Technip methodology for flexible pipe lateral buckling determination ensures a robust and competitive design.

For merchant vessels full scale resistance is determined by extrapolating the towing tank tests using Hughes’ method. For blunt and simple shapes this approach might not be valid due to significant Reynolds dependency. In this paper a study is presented on two semi-submersible pontoon shapes and one drillship. The resistance for these hulls was calculated using URANSE simulations. Four different scales: 1:1, 1:10, 1:20 and 1:40 were investigated for all the different hull shapes. The goal of the study was to determine a form factor to use when scaling towing test results to full scale. However due to the simple shapes of the pontoons it was found that there was a significant Reynolds dependency at all the different scales. This Reynolds dependency had much more influence on the full scale resistance than a form factor. For the drillship no significant Reynolds dependency was found and applying ITTC 1978 method [1] with a form factor improved the accuracy of the resistance prediction compared to using the Froude method which is not using a form factor. The simple pontoon shapes used were based on a combination of boxes, cylinders and spheres. The cylindrical and spherical shapes have a Reynolds regime where a drag crisis occurs. For all the shapes the drag crisis regimes were right in the same Reynolds number range at which typical model tests would be performed. Therefore performing towing tests and making accurate full scale resistance predictions for these simple shapes is not straightforward. Applying the ITTC 1978 method does not provide the same level of accuracy as it does for merchant vessels. The paper identifies limitations involved in scaling towing test results for typical offshore hull shapes. Further possible solutions are proposed to improve the accuracy of the resistance predictions.

Subsea developments in seismically active areas present a number of engineering challenges. One such item, which is frequently underestimated, is design of jumpers to resist earthquake loading. Jumpers connect quite dissimilar pieces of subsea equipment, for example heavy manifolds on deep foundations, PLETs on mudmats and wellheads supported on slender well casings. If the structures connected have a different dynamic response (e.g. manifold, PLET and wellheads with different fundamental periods), the jumpers receive additional loads from the out of phase structure movements. Such “seismic coupling” is particularly an issue for high pressure high temperature (HPHT) fields, where stiff heavy jumpers are combined with large manifolds. This paper discusses possible approach to evaluate coupling, and provides practical advice for subsea designers. Specifically we address coupling from a point of view of the fundamental period of the connected structures and jumpers, making reference to results of dynamic modeling and codified experience from nuclear power plant design. Differentiation between cases which require fully coupled treatment, and those in which a more straightforward separation and analysis of the individual subsystems is very important to producing an efficient design in reasonable time frame. These aspects are illustrated using a case history from our project files. Coupled dynamic analysis of primary (supporting) and secondary (supported) systems may not be always feasible or desirable. The number of supported structures may be such that a coupled analysis may create computational difficulties. In addition to this, data regarding the secondary system may be not available at the time of the analysis of the primary system with the result that development of a coupled model would be not applicable. In cases where an attempt is made to develop complex coupled systems, sanity checks of such a system may be not an easy task. For these and other reasons, complete analysis of complex coupled systems is rarely performed. The objective of this paper is to explore the conditions under which an uncoupled analysis is justified and to give simplified indication to check the results of coupled models. The paper presents a case study of a manifold-jumper-PLET. The system is evaluated using a standard uncoupled approach in which seismic actions are computed for the manifold, jumper and PLET considered as separate structures. The resulting actions are compared to those from a “coupled analysis” in which the full system is analyzed. The standard uncoupled analysis is found to be unconservative in cases where the jumper’s natural period of vibration is similar to that of the manifold or PLET. This approach shows promise as a means of identifying cases where coupled analysis is required to correctly assess seismic forces.

Fatigue occurs in structures due to the stresses from cyclic environmental loads. Offshore environmental loads being highly cyclic and recurring in nature, fatigue analysis with high degree of accuracy is required for reliable and optimized design of offshore structures. The main aim of this paper is to automate the process of identification of fatigue critical tubular joints of an offshore jacket structure using deterministic fatigue analysis with emphasis on the Hot Spot Stress Range (HSSR), an important measure in estimating fatigue damage, calculated using three different approaches for each tubular joint. The first approach determines HSSR at the time of maximum base shear of the jacket, the second, by calculating the difference between maximum and minimum Hot Spot Stress (HSS) and the third, at all time-instants of the wave cycle. Thus fatigue damage and fatigue life of the tubular joints are estimated using the highest HSSR value and the joints with lower fatigue life are identified as fatigue sensitive joints. This ensures effective identification of critical tubular joints of the offshore jacket structure which needs detailed investigation or redesign for fatigue. The deterministic approach discussed in this paper is applicable to large jackets which contains more number of tubular joints where sophisticated fatigue assessment at the preliminary stage is computationally intensive and manual identification of fatigue critical joints is laborious.

Current methods for installation of offshore wind turbines are all sensitive to the weather conditions and the present cost level of offshore wind power is more than twice the cost of land-based units, increasing with water depth. This paper presents numerical simulations of a novel experimental gripper design to reduce the environmental effects applied to a catamaran type of vessel during wind turbine installation. In SFI MOVE project in NTNU Aalesund, our team proposed a novel wind turbine installation process. A new catamaran vessel will carry pre-assembled wind turbines to the installation location. Two new designed grippers on the deck will make a lifting operation to install the wind turbine onto the turbine foundation. Three prismatic grippers with several rolling contact points at the end are attached in an arc at the catamaran’s aft, designed to grasp the turbine foundation in order to make a connection between the two in the horizontal plane. This paper will only emphasize the contact responses between the turbine foundation and the three grippers during the wind turbine installation process. Numerical simulations are carried out using the virtual prototyping framework Vicosim which is developed by NTNU Aalesund. The simulation results show validation of a key part of the proposed new wind turbine installation idea.

Fatigue is the most common known problem of drill pipes, since the combination of make-ups performed to connect the pipes and all the external loads, together with the threaded geometry of the connections, will stimulate the appearance of high stress points, cracks and finally promoting considerable economic losses. When threaded connections are used to connect the casing string, the fatigue resistance of the connection will affect the whole integrity of the string, and thus, in most cases, it is lower as the casing body. Generally, fatigue is classified as low-cycle fatigue and multi- or high-cycle fatigue. For Oil Country Tubular Goods (OCTG), a typical high cycle fatigue is represented by drill pipe fatigue in deviated wells. Unlike drill pipe, the casing may be exposed both to low-cycle as well as to high-cycle fatigue. Low-cycle fatigue is a common type of failure when the applied loads induce high stresses in the metallic material. The number of cycles may vary from as low as 10 up to 100. High-cycle fatigue requires a large number of cycles to failure. In order to avoid catastrophic failures, high-cycle fatigue resistance is usually considered to be sufficient if the number of cycles is above 106. The oil business has focused excessively on testing drilling risers and drill pipes under fatigue loads, but when it comes to casing and tubing the experimental approach may require different solutions. Drilling with casing opened the intensive testing of casing connections against fatigue resistance. Moreover, recent papers have shown intensive work on redesigning connections to withstand fatigue. New applications like rotating while running require a rethinking of testing strategy of Casing and Tubing. The following paper focuses on answering the question whether we test enough. The first part compares existing testing facilities, followed by an intensive discussion about the true loads of a casing or tubing connection. Using public testing data, the second part of the paper tries to identify how far the results provided by various types of testing machines can be compared with each other. For example, we found that low cycle fatigue results may not fully reflect the predictions based on extrapolations of high cycle fatigue results.

The method of using residual curvature during pipeline installation, primarily for the purpose of lateral buckling control, has caught an increasing amount of attention over the past few years [1], [9]. The use of residual curvature sparked a particular interest after positive experiences from a 26 km long pipeline on Statoil’s Skuld project (2012) in the Norwegian Sea [7]. As such, a range of technical papers elaborating on the topic have recently been published [6], [7], [9]. Some of this work has identified some particularly novel applications for the residual curvature method including freespan mitigation to reduce the requirement for seabed intervention, allowing for direct pipeline tie-ins, use with s-lay installation and even for steel catenary risers [10], [11]. However, these applications are currently only identified and not yet proven successful in any published work. This technical paper focusses on validating the use of residual curvature for the purpose of lateral buckling control in subsea pipelines installed by reel-lay. The residual curvature method demonstrates high buckling reliability without the use of subsea structures or additional installation equipment, with a controlled buckle response and favourable operational bending moments [1]. The residual curvature method has been shown less sensitive to some design parameters than other lateral buckling control methods [6]. However, published work also show that high strains will develop for short residual curvature lengths, high pipe-seabed frictions and for certain levels of residual strains [6]. Previous research has predicted the behaviour of residual curvature as a means of controlling lateral buckling in a deterministic approach [6], [7], [9]. However, performing a lateral buckling design with a probabilistic approach can offer a more realistic design and demonstrate higher reliability. There is a range of research on probabilistic approaches for lateral buckling design of subsea pipelines, but there is little published work on the same approach for residual curvature in particular. For this reason, this paper suggests a method for determining the likelihood of buckling and the associated bending moments via structural reliability analysis (SRA). A numerical model combining Finite Element (FE) Analysis and a Monte Carlo simulation is applied. A similar approach has already been presented by others for a different lateral buckling control method, and involves forming a database of finite element solutions followed by multivariate interpolation for the stochastic variables [16]. The multivariate interpolation necessitates a permutation of the cases in an FE result database. In order to keep the simulation efficient, only a limited number of variables are treated as stochastic. The variables that are considered as stochastic are those that have been determined that the lateral buckling response due to residual curvature is sensitive to. The variations of the remaining parameters are also accounted for but in a simpler way. The suggested SRA is used to assess the reliability of a pipeline that resembles the Skuld pipeline. The proposed SRA validates that residual curvature is a reliable lateral buckling control method irrespective of great variations in the design parameters that cannot be quantified easily, such as target residual strain. The proposed SRA also serves as a cost attractive solution in the qualification testing, by potentially relieving the installation contractor from the expensive exercise of performing an additional straightening trial.

Hydroelastic response of Very Large Crude Carrier (VLCC), such as springing and whipping, is very important for the fatigue strength analysis. In the present paper, numerical simulation and model test are conducted simultaneously on the springing responses of a 350,000DWT VLCC. The numerical simulation results are obtained by combining 2-D strip method and 3-D Finite Element Method (FEM) in the frequency domain. Meanwhile, the segmented model tests are conducted in three conditions. Additionally, the experimental time histories of wave bending moments in regular and irregular waves are presented. In conclusion, the methods and results presented in this paper have shown that the springing would be much easier when the VLCC is in ballast condition or the full loading conditions with reduced stiffness. The springing response will happen, when the wave encounter frequency is near to the half and one third of the ship’s flexural natural frequency. The numerical method presented is available for springing response analysis quickly with acceptable accuracy.

The paper presents realistic horizontal wave drift force coefficients and low frequency damping coefficients for the Exwave semi-submersible under severe seastates. The analysis includes conditions with collinear waves and current. Model test data is used to identify the difference frequency wave exciting force coefficients based on a second order signal analysis technique. First, the slowly varying excitation is estimated from the relationship between the incoming wave and the low frequency motion using a linear oscillator. Then, the full quadratic transfer function (QTF) of the difference frequency wave exciting forces is defined from the relationship between the incoming waves and the second order force response. The process identifies also the linear low frequency damping. The paper presents results from cases selected from the EXWAVE JIP test matrix. The empirical wave drift coefficients are compared to potential flow predictions and to coefficients from a semi-empirical formula. The results show that the potential flow predictions largely underestimate the wave drift forces, especially at the low frequency range where severe seastates have most of the energy.