Transient Loading Research Articles

Probabilistic study on non-stationary extreme response of transmission tower under moving downburst impact

Localized severe non-synoptic winds, such as downbursts and tornadoes, cause frequent structural failures of the electric transmission lines worldwide. This paper aims to develop an analytical approach to evaluate the extreme non-stationary dynamic response of transmission towers under downbursts in frequency domain. First, the empirical models of time-varying mean wind and non-stationary fluctuating wind of moving downbursts are introduced to deduce the transient wind loads on transmission towers in time domain. The closed-form frequency domain solutions of non-stationary fluctuating downburst wind-induced response of transmission towers are derived based on the pseudo excitation method. Furthermore, through the up-crossing extreme value theory, the probability distribution of the non-stationary extreme response is studied. Finally, the peak factors of the non-stationary and the equivalent stationary theoretical methods are compared based on the proposed equivalent stationary extreme value distribution for engineering application. The proposed theoretical framework is validated by stochastic sampling simulation and finite element analysis. It is found that the proposed theoretical framework can accurately assess the extreme value responses of transmission towers under non-stationary moving downbursts.

AUTOMATION OF MEASUREMENTS OF ENGINE HEAT CONSUMPTION IN THE LUBRICATION AND COOLING SYSTEMS

The paper presents the results of an intermediate stage of the study of heat transfer processes in high-speed diesel engines of the automotive tractor type at transient load discharge-load-injection modes, which are characteristic of this type of diesel engines. In such modes, as evidenced by the results of calculations of the thermal stress state of combustion chamber parts, in particular pistons, exhaust valves of the gas distribution mechanism, significant tensile and compressive stresses are observed compared to operation at steady-state conditions. This is the reason for the occurrence of defects in the form of cracks on the heat exchange surfaces of these parts, which limits the service life of automotive tractor engines. For a more detailed study of transient processes, as the main approach, it is proposed to use the well-known method of heat balance tests of a high-speed diesel engine, but with the involvement of automated processing of measurement results in digital form at steady-state and transient modes. It is proposed to focus on heat consumption, which is a component of the heat balance in the lubrication and cooling system. Without the use of automated information processing directly at the time of transient load shedding and load shedding, it is impossible to obtain such information on cooling and lubrication systems. Recording of transient heat transfer processes makes it possible to track the influence of engine operating parameters, the dynamics of the transient process depending on its duration, the initial and final steady-state modes between which the transition is being studied. In general, this way, it is possible to assess the adaptability of cooling and lubrication systems to heat dissipation during sudden changes in load, to avoid, or at least limit, the growth of thermal stresses. The publication presents a possible variant of the schematic solution of such a system for automated processing of the results of heat balance tests with the maximum use of equipment that is mass-produced and has already been used previously in heat balance tests.

Dynamic Topology Optimization with Multiple Materials Based on Impedance Mismatching of Wave

Topology optimization with multiple materials studies were commonly adopted to address the issues of complex structures and dynamic loading cases. However, the perturbation excited from the transient load will be propagated and change the local stress level in the structure. Therefore, it is indispensable to consider impedance mismatching of waves at the interfaces of multi-materials layers in the optimization model. In this work, the wave impedance will be regarded as constraint conditions and assessment indicators in the optimization design. Firstly, a multi-material interpolation model using SIMP models is established based on the variable density method. Secondly, the optimization process is applied by combining using Newmark-[Formula: see text] method which is used to solve the dynamic response, an adjoint variable method for sensitivity study, and an optimization criterion method employed to update the design variables. Finally, the simulation examples are used to analyze the influence of impedance mismatching and volume fraction for multilayer dielectric on response. The results indicate that the position and content of the Polymethyl Methacrylate (PMMA) plays a key role in reducing vibration and buffering action.

Numerical simulation of deuterium retention in tungsten under ELM-like conditions

Retention of hydrogen isotopes (HI) in plasma-facing components (PFCs) is a crucial process influencing the operation of a fusion device. The dynamics of HI retention is mainly determined by irradiation conditions of PFCs. These conditions can change due to the onset of fast transient events, such as edge-localised modes (ELMs). The development of ELMs results in repetitive short-term plasma bursts on PFCs, affecting the exposure regime. In this work, the effect of ELM-like loads on the fuel retention is numerically analysed using a one-dimensional diffusion model, implemented in the FESTIM code. As a representative simulation case, the deuterium (D) retention in tungsten (W) is considered with the geometry and inter-ELM exposure conditions relevant for large fusion devices. Temporal dependencies of heat and particle fluxes during intra-ELM stages are accounted for by applying the free-streaming model for an ELM filament transport. The simulations were conducted for three inter-ELM exposure regimes with various properties of transient loads, D trapping sites, and D recombination rates. Compared to the ELM-free irradiation, the onset of transients is shown to mainly reduce the D retention rate because of significant material heating induced by the arrival of energetic ELMy particles. This relative difference can decrease if the material is characterised by strong trapping sites or limited desorption from a surface. The findings also demonstrate that additional heating during transients provides conditions for a faster D migration into the bulk. In addition, we discuss the possibility of using ELM-average loads to obtain quick assessments of the D content. The approach is shown to be applicable for the case of small ELMs and is used to derive the analytical expressions for the D distribution in W within the steady-state approximation.

Development and investigation for rigid-flexible coupling dynamic performances of the morphing wing with clearance joints

Morphing wings have enjoyed much research interest due to their advantages in improving aircraft adaptability to various service environments. A single drive and continuous variable bending morphing mechanism with multiple configurations is proposed. The morphing wing designed based on this mechanism can have the advantages of lightweight, multiple configurations and smooth morphing shapes. Transient aerodynamic loads will destroy the dynamic performance of the wing during the multi-mode morphing process. Therefore, it is crucial to analyze the vibration characteristics for the reliability of the morphing wing. However, it is difficult to obtain its dynamic model and solution because of the complex configuration and the multi-mode morphing. In this paper, a mathematical model for the multi-mode morphing of the morphing mechanism based on lockable joints is described using the constraint equation firstly. Then, a rigid-flexible coupling dynamic model of the morphing wing with clearance joints is established. Finally, the influence of the infective joint and the flexible link on the vibration properties of the morphing wing is analyzed in detail. Moreover, differences in the dynamic parameters between rapid and regular actuation are discussed. The results obtained in this paper have an important engineering value for the design and manufacture of the morphing wing.

Progressive collapse resistance of self-resilient composite frames under fire conditions

Self-resilient composite frames exhibit robust resistance to progressive collapse and excellent seismic performance. However, their behavior under fire conditions is inadequately explored. This study investigates the collapse resistance mechanisms and response of self-resilient composite frame substructures (SRCFS) under fire-induced progressive collapse. A three-dimensional finite element model was developed, incorporating temperature-dependent thermal and mechanical properties of concrete and steel. Sequentially coupled thermal-mechanical analysis was conducted using the ABAQUS/Explicit solver in a quasi-static manner. Existing experimental data at both ambient and high temperatures were used to validate the proposed model. The study analyzed the contributions of steel beams and strands to vertical resistance, examining their impact on the collapse-resistance mechanism through a constant load-heating transient loading scheme. Structural responses under ambient and fire conditions were compared, focusing on different damage mechanisms. The effects of initial prestressing of strands, angle gauge length, angle thickness, and various heating curves on collapse resistance were evaluated. Findings suggest that the ISO-834 standard's failure criterion is overly conservative for SRCFS, as it neglects the enhanced load-carrying capacity provided by tensile catenary action. This mechanism offers additional escape time, enhancing personnel safety. The study identifies factors influencing the performance of SRCFS against progressive collapse under fire and proposes design recommendations.

Prediction of rotation of a shrink-fitted cup of a tapered roller bearing under transient thermal loading

Modeling of tapered roller bearing, running torque and effect of the environment are often studied separately. However, bearing environment can have a significant impact on the behavior of the assembly and bearing performances. In some tapered roller bearing mountings, it is usual to shrink fit the cup of the bearing into its housing. Consequently, high transient thermal loads can lead to a decrease in clamping when the cup and its housing do not have the same thermal expansion coefficients. Under these conditions, the cup may start to rotate in the housing due to the torque transmitted by the bearing. Rotation of the outer ring could strongly affect the bearing performance. This study aims at predicting the risk of cup rotation.

Assessment of transient thermal stresses in gasketed plate heat exchangers

Thermal and mechanical stresses in stainless steel 316 L plates of gasketed plate heat exchangers (GPHEs) have been assessed with the aid of experiments. Stresses were indirectly determined with the aid of extensometers in critical plate areas. To the best of our knowledge, no experimental analysis of transient thermal loads on GPHE plates has been reported before. Experiments occurred with sudden and gradual heating processes with the aid of strain gauges. The former process implies that hot fluid enters the GPHE branch with the final target temperature, while the latter indicates that the hot fluid is progressively heated to the target temperature. Furthermore, combined mechanical and thermal stresses resulting from in-phase and out-of-phase loads are assessed in single and double operating conditions. Experiments were carried out with two plate thicknesses (0.5 and 0.7 mm). Stresses as obtained from experiments were compared to those provided by models containing simplified geometries and boundary conditions. Mechanical stresses promoted by the pressure difference between GPHE branches mostly affected the distribution area in single configuration. Thermal stresses at the porthole were higher than the ones found at the distribution zones, particularly for thicker plates. Besides, thermal stresses increased in double operation. Sudden heating processes with the system at rest promoted thermal peaking stress in a timescale of seconds, while the timescale to reach peak values by gradually heating the hot fluid is in the order of minutes. The most critical condition would be achieved at the porthole with in-phase loads and in double operation for the given settings.

Thermal shock protection with scalable heat-absorbing aerogels

Improving thermal insulation is vital for addressing thermal protection and energy efficiency challenges. Though silica aerogel has a record-low thermal conductivity at ambient pressure, its high production cost, due to its nanoscale porous structure, has hindered its widespread use. In this study, we introduce a cost-effective and mild method that enhances insulation by incorporating phase change materials (PCMs) into a micron-porous framework. With a thermal conductivity at 0.041 W m−1K−1 on par with conventional insulation materials, this PCMs aerogel presents additional advantages for thermal protection from transient high-temperature loads by effectively delaying heat propagation through heat absorption. Moreover, the PCMs aerogel remains stable under cyclic deformation and heating up to 300 °C and is self-extinguishing in the presence of fire. Our approach offers a promising alternative for affordable insulation materials with potential wide applications in thermal protection and energy conservation areas.

Evolution of pre-damaged ITER grade plasma facing components under WEST plasma exposure: smoothing and tungsten sources

The evaluation of the impact of plasma-facing units (PFUs) damage on subsequent plasma operation is an important issue for ITER. This is one of the topic addressed by the operation of dedicated PFUs in WEST. From the start of WEST in 2017, few ITER grade divertor PFUs were tested in the lower divertor for short plasma exposure (experimental campaigns C1–C5). A PFU is an assembly of tungsten blocks on CuCrZr tube via pure copper interlayer. Since 2022, WEST operates with a lower divertor fully equipped with ITER grade PFUs (experimental campaign C6–C7) with long duration plasma exposure capabilities. To test the ageing of the ITER-grade PFUs on an accelerated basis, well controlled damage was implemented on purpose with electron beam loading on the plasma facing surface of two different PFUs (pre-damage#1 and #2 featuring different level of damage). Damage tackled in this study is induced by the loading with numerous transient heat loading events to mimic the ELM impact on the ITER grade PFU. This paper presents the damage before and after WEST plasma exposure and shows the tungsten sources and temperature of the block measured during the operation. On damaged area, surface roughening is heterogeneous. With WEST campaigns (C3, C4 and C7) respectively ended in (2018, 2019 and 2023) a global smoothing of the pre-damaged surfaces, in particular those located in the high loaded erosion area, is observed. No evolution of the crack is observed in the electron beam loaded area, while new cracking are observed on non pre-damaged area on the tungsten top surfaces in highly loaded areas (outer strike point) after significant plasma duration and cumulated energy (first observation in C4 and tends to be confirmed with preliminary observations after the C7 campaign). Smoothing is less pronounced after the 2018 campaign, which may be due to the related short plasma duration. The surface smoothing of blocks also depends on their poloidal position. For PFU which has no shaping, toroidal positioning within a block has no influence on the surface smoothing. After 2019 and 2023 campaigns, equivalent relative smoothing is obtained (between 19 and 32%). For the explored plasma conditions, damage has no influence on the maximum brightness of W.

Study on Correlation between Impact-Resistance Performance and Microbial Characteristics by MPSR and SBR under Transient Organic Load Shock

Study on Correlation between Impact-Resistance Performance and Microbial Characteristics by MPSR and SBR under Transient Organic Load Shock

Transient surface pressure of a rectangular cylinder subjected to downburst-like winds

Thunderstorm downbursts are transient in nature and have been responsible for a variety of structural damages in recent years. Currently, the researchers have done several works on the characteristics of downburst wind speed. Nonetheless, rare attention has been placed on the structural aerodynamics characteristics subjected to downburst winds. Based on this, an experimental investigation is performed to reproduce downburst-like winds physically and to study the transient surface pressures (SPs) on a 5:1 rectangular cylinder (RC). The experiment is conducted within a multiple-fan active control wind tunnel (MFACWT) and mainly focuses on simulating the transient characteristics of downburst-like flow, including time-varying mean (TVM) wind speed and nonstationary wind fluctuation. The resulting SPs are measured to understand the influence of transient wind on the aerodynamic behavior of bluff bodies. The spatiotemporal characteristics of the SPs are analyzed using wavelet transform and Priestley's classic spectral theory. The results indicate that the transient nature of the downburst-like flow can be physically reproduced by a MFACWT. The instantaneous pressures of a RC are illustrated by both the turbulence parameters of the transient flow and the flow-separation characteristics. The pressure coefficients normalized by the TVM of the downburst-like winds remain constant, which provides a more appropriate way to estimate the transient gust loading in a quasi-steady manner. Interestingly, the phenomenon of the time-varying phase shift and time-varying correlation of chordwise SPs is observed when the turbulent velocity changes dramatically. In addition, the normalized surface pressure can be regarded as a stationary stochastic process, which provides a significant basis for further establishing the theoretical model of nonstationary gust-loading.

Thermomechanical conversion of CoCrNi medium entropy alloy subjected to transient reverse loading

Heat dissipation of CoCrNi alloy is investigated under fast reverse loading. The Taylor-Quinney coefficient (TQC) decreases during the initial strain hardening, while the subsequent kinematic hardening is associated with gradually constant TQC of about 50 %, indicating the cyclic plastic work equally divided into heat and cold work stored in CoCrNi.

A simple hydrodynamic model for clay

Laboratory description of clay normally distinguishes the scale of atoms from the scale of clay particles and aggregates. Contemporary constitutive models for clay tend to ignore this scale separation, and rather focus on phenomenology. By considering scale separation, this paper introduces a robust physics-based phenomenological constitutive model for clay that qualitatively captures their broad spectrum of rate-dependent mechanical features. The model is derived using the thoroughly rigorous hydrodynamic procedure. While some imagine that by considering rigour and physics, their models would get complicated, the resulting set of equations reveal a surprising degree of simplicity. The derivation strongly benefits from the principle of two-stage irreversibility, which describes energy flow within the material from the continuum scale down to the atomistic micro-scale, through the meso-scale of clay aggregates. While thermal and meso-related temperatures capture atomistic and clay aggregate fluctuating motions, a sink term from the latter to the former underpins the direction of the energy flow. The model’s standout feature is in pinpointing new transport coefficients that drive both volumetric and shear plastic flows in a thermodynamically coupled manner. A novel scheme is then proposed to calibrate these coefficients from conventional steady-state observations. Thanks to the formulation the model shows a remarkable level of predictiveness, despite being relatively simple mathematically. In particular, the model readily explains the broad spectrum of rate-dependent phenomena during transient loading, along with creep and relaxation processes. Given the generality of hydrodynamics, it is anticipated that the new model could be expanded to capture fluid-solid transitions between liquid-like soft mud and plastic-like stiff clay responses, contingent on water content variations.

Best-estimate water hammer simulations to avoid the calculation of unrealistically high loads or unphysical pressure and force peaks

For safety-related systems fluid loads due to fluid transients have to be quantified for subsequent structural analyses to ensure their integrity or function, as required. Usually transient fluid loads in pipe systems are determined with one-dimensional water hammer software. For single-phase liquid flow, the method of characteristics (MOC) is often used that gives in this case appropriate results. For the consideration of local vapor bubbles, the MOC is combined with the discrete vapor cavity model (DVC). The DVC model may generate unrealistic pressure spikes due to the calculation of the collapse of multi-cavities in scenarios, where only one vapor bubble should actually occur. The application of a two-phase code may improve the calculation results. One requirement for the latter codes is the ability to calculate the propagation of steep gradients without suffering from numerical diffusion to exclude the underestimation of fluid loads. This is commonly attained by applying higher-order numerical schemes. However, the application of a numerical method of pure 2nd order leads to the calculation of unphysical oscillations at steep gradients causing severe problems during the solution. To exclude this, numerical methods with flux limiters can be used. With their application, the calculation of unrealistically high loads due to numerical deficiencies can be minimized. In addition, the consideration of further physical effects, that lead to the reduction of loads during transient flow processes, allows for a more realistic calculation of the loads. These are unsteady friction, widening of the pipe caused by pressure increase, fluid-structure interaction at junctions and due to friction, degassing of gas that is initially dissolved physically in a liquid and thermodynamic non-equilibrium during vapor bubble collapse. The in-house code DYVRO applies a second-order accurate scheme with flux limiters based on the Godunov method and can account for the above-described physical phenomena. It is shown by comparison of calculation results obtained by DYVRO with experimental data from literature that with modeling of these physical effects the loads can be calculated more realistically. Generally, these loads are lower than the results calculated by simplified models, which do not account for these effects. Considering that these loads are applied in subsequent structural analyses, cost-intensive oversizing of pipes and their supports can be avoided, by ensuring the necessary safety.

Effects of control strategies of the electric supercharger on transient processes of a turbocharged diesel engine

The electric superchargers driven by a high-speed motor instead of exhaust gas to operate the compressor have excellent transient characteristics and can effectively reduce the turbo lag of diesel engines. To develop an optimal control strategy for the electric superchargers, it is necessary to explore the combined effects of the electric supercharger and turbocharger under transient processes. Therefore, this study investigated the influence of different intervention speed and time of the electric supercharger on the transient performances of a turbocharged diesel engine. The combined effects of the electric supercharger and turbocharger were analyzed to optimize control strategy through simulations. Effects of the optimization in control strategies were tested through engine experiments. According to the results, the optimized control strategy (slope control strategy) was able to effectively balance transient responsiveness and stability since the rise time of intake pressure were reduced by 52.5 % compared to the base engine and the fluctuations in intake pressure and engine torque were significantly eliminated. Besides, the slope control strategy achieved the lowest PM and NOx emissions during the transient loading process.

A fully integrated charge pump with double-loop control and differentiator-based transient enhancer for neural stimulation applications

This paper proposes a fully integrated charge pump (CP) with a double-loop control and a differentiator-based transient enhancer (DTE) for high-voltage neural stimulation applications. The double-loop control includes a clock-supply-voltage (VCLK) modulation loop and a pulse-frequency modulation (PFM) loop. The VCLK modulation loop regulates the output voltage by adjusting VCLK while the PFM loop adjusts the operating frequency of the CP in accordance with the load current in order to improve power efficiency. The proposed CP combines the function of output voltage regulation and VCLK generation into a single unit, leading to significantly reduced circuit complexity. The proposed double-loop control is capable of dealing with different dc current requirements while the proposed DTE suppresses the undershoots and overshoots of the output voltage during load transients. The proposed CP has been simulated using a 0.18-μm triple-well CMOS process and occupies an area of 0.537 mm2. The post-layout simulation results show that it can provide a regulated 9-V output voltage from a 3.6-V input voltage with a peak power efficiency of 73.4 % at 2-mA load condition. The Monte-Carlo simulation demonstrates that the overshoot and undershoot of the output voltage are kept below 3 % when undergoing a 2-mA load transient.

Manufacturing trials of PFCs with low thermal conductivity features for limiters

In future demonstration fusion power plants, plasma facing components will face high steady state and ultra-high transient heat loads from the plasma. Introducing low thermal conductivity features to the component can reduce the peak temperatures seen by the coolant pipe during transient loads, but at the trade-off of a loss of steady-state performance. Producing low-conductivity tungsten by additive methods has been investigated elsewhere, so this trial investigates production through subtractive means i.e., conventional milling. This method preserves the original temperature limits and majority of the microstructure and is much higher Technology Readiness Level (TRL) so requires less development to reach series manufacture. In this trial, diamond drilling produced holes in monoblocks down to 0.6 mm and ligaments down to 0.7 mm, showing that this method is capable of producing small features in a controlled way. With the geometric design of lattice used in this trial, these samples achieved thermal conductivity reductions of 15% to 40%. One monoblock assembly was tested up to 1100 °C for 500 cycles in the Heating by Induction to Verify Extremes (HIVE) High Heat Flux test rig and showed no signs of ligament cracking or thermal degradation. Electromagnetic modelling has been validated against the experimental results, so future designs can be accurately modelled ahead of testing in HIVE.

Disturbance Observer-Based Feedback Linearized Controller for Grid-Forming Four-Leg VSI Supplying Unbalanced and Nonlinear Loads

This paper presents the design of a disturbance observer-based controller that regulates the output voltage of three-phase four-leg voltage source inverters (VSIs) deployed for grid-forming operation in Renewable Energy-based Distributed Generation (REDG) Systems. The primary objective of the controller is to provide a symmetric and sinusoidal voltage at the output of the VSI when supplying highly unbalanced and nonlinear loads. The controller employs the feedback linearization (FL) technique and incorporates a disturbance observer (DO) to address a range of disturbances that include oscillations resulting from unbalanced loads, harmonics generated by nonlinear loads, and non-oscillatory disturbances. Notably, the controller adopts a direct control scheme without the need for nested current control loops and does not use any transformation frames. Simulation studies and experimental investigations were conducted to assess the controller’s performance under various load conditions, including both linear and nonlinear types, as well as load transients. The findings demonstrate the controller’s capability to accurately track references while complying with the IEEE power quality standards for the tested conditions.

Optimization of Technical Calculation of Precast Wall Application for Kawo Secondary Canal Improvement in Sempor Irrigation Area, Kebumen, Central Java

This study aims to perform technical calculations using precast lining in the repair of secondary channels. The planning data used included a concrete grade of fc 18.68 MPa and a reinforcement grade of fy 500 MPa. The service condition analysis was carried out by taking into account the loading during the most critical condition, where the channel is empty and active soil pressure and external water pressure are the main loads. The fixed load calculation was the main focus, where the active earth pressure (PD) was calculated by considering the soil-specific gravity, soil shear angle, and soil coefficient. The calculation results show that the PD reaches 12.24 kN, which gives an idea of the load that the structure has to bear. Furthermore, the internal force analysis provides a deeper understanding of the moments occurring at specific points in the structure. For example, the maximum negative moment at point A was calculated by considering the moments due to fixed load and transient load, which reached 12.73 kNm. This research contributes to improving efficiency and safety in the application of precast lining for secondary channel improvement.