Browsing by Author "Yang, Liang"
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Item Open Access Closed-form dynamic stiffness formulation for modal and dynamic response analysis of pile group foundations(Elsevier, 2023-04-24) Liu, Xiang; Zhao, Yaxing; Lu, Tao; Xu, Hao; Yang, LiangA closed-form dynamic stiffness (DS) formulation is proposed for pile group foundations. This model consists of a rigid cap and an arbitrary number of flexible piles. The rigid cap, connecting to all piles, is modeled as a rigid body resting on an elastic foundation. For each pile, a longitudinal soil–pile model and a preloaded Timoshenko beam on viscoelastic Pasternak foundation are adopted to describe the longitudinal and transverse vibration, respectively. The piles can be either friction piles or end-bearing piles, and pile sections surrounded by different soil layers can be easily modeled by the assembly of pile elements with different parameters. The proposed DS formulations essentially use very few degrees of freedom to, nevertheless, describe the broadband dynamic behaviors of complex pile group foundations in a highly accurate manner. The DS formulation is then used for modal and dynamic response analysis. For modal analysis, the Wittrick–Williams algorithm is applied, with the key issue count problems resolved. The proposed method is verified against some existing results. This research provides an exact and highly efficient modal and response analysis tool for pile group foundations, which can be used for the dynamic analysis of pile foundations subjected to earthquake or traffic excitations.Item Open Access Effects of eigen and actual frequencies of soft elastic surfaces on droplet rebound from stationary flexible feather vanes(Royal Society of Chemistry, 2020-05-05) Zhang, Chengchun; Wu, Zhengyang; Shen, Chun; Zheng, Yihua; Yang, Liang; Liu, Yan; Ren, LuquanThe aim of this paper is to investigate the effect of eigenfrequency and the actual frequency of the elastic surface for the droplet rebound. The elastic surface used in this study is the stationary flexible feather vanes. A fluid-structure interaction (FSI) numerical model is proposed to predict the phenomenon, and later is validated by the experimental that the droplets impact the stationary flexible feather vanes. The effect of mass and stiffness of the surface is analysed. First, the suitable combination of mass and stiffness of the surface will enhance the drop rebound. Second, a small mass system with higher eigenfrequency will decrease the minimum contact time. In the last, the actual frequencies of the elastic surface, approximate at 75 Hz, can accelerate the drop rebound for all cases.Item Open Access Experimental investigation of wave induced flapping foil for marine propulsion: heave and pitch stiffness effect(AIP, 2024-04-15) Wang, Junxian; Xing, Jingru; Siddiqui, M. Salman; Stawiarska, Adriana; Yang, LiangThe submerged hydrofoil has the capability to harness wave energy and convert it into thrust to work with the ship's power system. The current series of experiments investigated the interaction of a passive submerged hydrofoil with regular waves through a comparison of the generated horizontal forces. Springs provide the restoring force for the hydrofoil's heave/pitch motion, corresponding to heave spring and pitch spring. Maintaining a constant heave spring stiffness (490 N/m), subsequent statistical analysis summarized the force trends at different pitch stiffnesses (16–300 N/m) and suggested an optimal pitch spring stiffness in regular waves. A pulse-shaped force signal was observed and explained as a result of low pitch stiffness. Experiments with different spring setups revealed that the heave spring contributes to the harmonic force generated by the fully passive foil. Additionally, by varying wave conditions with limited wave amplitudes and frequencies, tests reproduced the variation of force signals over time and assessed their dependence on wave parameters.Item Open Access Experimental study of dynamic response of passive flapping hydrofoil in regular wave(American Institute of Physics (AIP), 2023-07-26) Wang, Junxian; Santhosh, Sabin; Colomés, Oriol; Capaldo, Matteo; Yang, LiangThe hydrofoil harnesses wave energy and converts it into thrust. In this paper, we present the results of the first experimental study investigating the dynamic behavior of a fully passive foil with spring-loaded pitch and heave in regular waves. Our study shows that the real-time load signal is multi-harmonic with strong superposition, directly proving the robust energy harvesting performance due to the restoring springs. By interpreting the hydrofoil's pose and path from an image sequence captured underwater, we conclude the dynamic evolution of the fully passive hydrofoil interacting with regular waves. The hydrofoil's dynamics exhibit asymmetric surge, pitch, and heave in a motion cycle. Furthermore, we employ a pixel capturing algorithm with self-correction utility to quantify the hydrofoil's forward displacement from the image sequence of the moving carriage. These findings provide valuable insight into the performance and potential of hydrofoils for marine propulsion.Item Open Access An explicit stabilised finite element method for Navier-Stokes-Brinkman equations(Elsevier, 2022-02-10) Nillama, Loic Balazi Atchy; Yang, Jianhui; Yang, LiangWe present an explicit stabilised finite element method for solving Navier-Stokes-Brinkman equations. The proposed algorithm has several advantages. First, the lower equal-order finite element space for velocity and pressure is ideal for presenting the pixel images. Stabilised finite element allows the continuity of both tangential and normal velocities at the interface between regions of different micro-permeability or at the interface free/porous domain. Second, the algorithm is fully explicit and versatile for describing complex boundary conditions. Third, the fully explicit matrix–free finite element implementation is ideal for parallelism on high-performance computers. In the last, the implicit treatment of Darcy term allowed larger time stepping and a stable computation, even if the velocity varies for several orders of magnitude in the micro-porous regions (Darcy regime). The stabilisation parameter, that may affect the velocity field, has been discussed and an optimal parameter was chosen based on the numerical examples. Velocity stability at interface between different micro-permeability has been also studied with mesh refinement. We analysed the influence of the micro-permeability field on the regime of the flow (Stokes flow, Darcy flow or a transitional regime). These benchmark tests provide guidelines for choosing the resolution of the grayscale image and its segmentation. We applied the method on real Berea Sandstone micro-CT images, and proceeded the three-phases segmentation. We studied the influence of the micro-porosity field, using the well-known Kozeny-Carman relation to derive the micro-permeability field from the micro-porosity field, on the effective permeability computed. Our analysis shows that a small fraction of micro-porosity in the rock has a significant influence on the effective permeability computed.Item Open Access Improved estimates of 222 nm far-UVC susceptibility for aerosolized human coronavirus via a validated high-fidelity coupled radiation-CFD code(Nature Publishing Group, 2021-10-07) Buchan, Andrew G.; Yang, Liang; Welch, David; Brenner, David J.; Atkinson, Kirk D.Transmission of SARS-CoV-2 by aerosols has played a significant role in the rapid spread of COVID-19 across the globe. Indoor environments with inadequate ventilation pose a serious infection risk. Whilst vaccines suppress transmission, they are not 100% effective and the risk from variants and new viruses always remains. Consequently, many efforts have focused on ways to disinfect air. One such method involves use of minimally hazardous 222 nm far-UVC light. Whilst a small number of controlled experimental studies have been conducted, determining the efficacy of this approach is difficult because chamber or room geometry, and the air flow within them, influences both far-UVC illumination and aerosol dwell times. Fortunately, computational multiphysics modelling allows the inadequacy of dose-averaged assessment of viral inactivation to be overcome in these complex situations. This article presents the first validation of the WYVERN radiation-CFD code for far-UVC air-disinfection against survival fraction measurements, and the first measurement-informed modelling approach to estimating far-UVC susceptibility of viruses in air. As well as demonstrating the reliability of the code, at circa 70% higher, our findings indicate that aerosolized human coronaviruses are significantly more susceptible to far-UVC than previously thought.Item Open Access Inactivation rates for airborne human coronavirus by low doses of 222nm far-UVC radiation(MDPI, 2022-03-25) Welch, David; Buonanno, Manuela; Buchan, Andrew G.; Yang, Liang; Atkinson, Kirk D.; Shuryak, Igor; Brenner, David J.Recent research using UV radiation with wavelengths in the 200–235 nm range, often referred to as far-UVC, suggests that the minimal health hazard associated with these wavelengths will allow direct use of far-UVC radiation within occupied indoor spaces to provide continuous disinfection. Earlier experimental studies estimated the susceptibility of airborne human coronavirus OC43 exposed to 222-nm radiation based on fitting an exponential dose–response curve to the data. The current study extends the results to a wider range of doses of 222 nm far-UVC radiation and uses a computational model coupling radiation transport and computational fluid dynamics to improve dosimetry estimates. The new results suggest that the inactivation of human coronavirus OC43 within our exposure system is better described using a bi-exponential dose–response relation, and the estimated susceptibility constant at low doses—the relevant parameter for realistic low dose rate exposures—was 12.4 ± 0.4 cm2/mJ, which described the behavior of 99.7% ± 0.05% of the virus population. This new estimate is more than double the earlier susceptibility constant estimates that were based on a single-exponential dose response. These new results offer further evidence as to the efficacy of far-UVC to inactivate airborne pathogens.Item Open Access A non-linear non-intrusive reduced order model of fluid flow by Auto-Encoder and self-attention deep learning methods(Wiley, 2023-04-03) Fu, Rui; Xiao, Dunhui; Navon, I. M.; Fang, F.; Yang, Liang; Wang, Chengyuan; Cheng, SiboThis paper presents a new nonlinear non-intrusive reduced-order model (NL-NIROM) that outperforms traditional proper orthogonal decomposition (POD)-based reduced order model (ROM). This improvement is achieved through the use of auto-encoder (AE) and self-attention based deep learning methods. The novelty of this work is that it uses stacked auto-encoder (SAE) network to project the original high-dimensional dynamical systems onto a low dimensional nonlinear subspace and predict fluid dynamics using an self-attention based deep learning method. This paper introduces a new model reduction neural network architecture for fluid flow problem, as well as, a linear non-intrusive reduced order model (L-NIROM) based on POD and self-attention mechanism. In the NL-NIROM, the SAE network compresses high-dimensional physical information into several much smaller sized representations in a reduced latent space. These representations are expressed by a number of codes in the middle layer of SAE neural network. Then, those codes at different time levels are trained to construct a set of hyper-surfaces using self-attention based deep learning methods. The inputs of the self-attention based network are previous time levels' codes and the outputs of the network are current time levels' codes. The codes at current time level are then projected back to the original full space by the decoder layers in the SAE network. The capability of the new model, NL-NIROM, is demonstrated through two test cases: flow past a cylinder, and a lock exchange. The results show that the NL-NIROM is more accurate than the popular model reduction method namely POD based L-NIROM.Item Open Access Non-wet kingfisher flying in the rain: the tumble of droplets on moving oriented anisotropic superhydrophobic substrates(American Chemical Society, 2020-07-08) Zheng, Yihua; Zhang, Chengchun; Wang, Jing; Yang, Liang; Shen, Chun; Han, Zhiwu; Liu, YanExtensive studies of antiwetting have been restricted to stationary substrates, while dewetting mechanisms on moving interfaces are still poorly understood. Due to the hydrophobic and anisotropic surface characteristics of kingfishers, they are able to easily change flight direction even under high-intensity precipitation. The present study aims to mechanistically analyze how the synergy of interfacial movement, anisotropy, and superhydrophobicity affects rapid dehydration. We have designed a droplet-conveyor system to simulate the bouncing of droplets on moving anisotropic superhydrophobic targets and performed simulations via the lattice Boltzmann algorithm. The moving interface can induce a directional tumbling behavior of the droplet and effectively avoid continuous wetting in the same region. We found that droplet tumbling is essentially caused by transformed depinning velocity vectors at the interface downstream. Also, the hang time of a tumbling droplet is positively related to the angle between the motion vector and the texture. The oriented anisotropic motion facilitates the tumbling of droplets and decreases their hang time by up to 23% as compared to that on a stationary inclined superhydrophobic surface. Similar interfacial process dehydration also occurs on a nonwet kingfisher flying in the rain, and we believe that these findings provide valuable new insights for high-efficiency water repellency of surfacesItem Open Access A novel approach to optimising well trajectory in heterogeneous reservoirs based on the fast-marching method(Elsevier, 2021-02-07) Lyu, Zehao; Lei, Qinghua; Yang, Liang; Heaney, Claire; Song, Xianzhi; Salinas, Pablo; Jackson, Matthew; Li, Gensheng; Pain, ChristopherTo achieve efficient recovery of subsurface energy resources, a suitable trajectory needs to be identified for the production well. In this study, a new approach is presented for automated identification of optimum well trajectories in heterogeneous oil/gas reservoirs. The optimisation procedures are as follows. First, a productivity potential map is generated based on the site characterisation data of a reservoir (when available). Second, based on the fast-marching method, well paths are generated from a number of entrance positions to a number of exit points at opposite sides of the reservoir. The well trajectory is also locally constrained by a prescribed maximum curvature to ensure that the well trajectory is drillable. Finally, the optimum well trajectory is selected from all the candidate paths based on the calculation of a benefit-to-cost ratio. If required, a straight directional well path, may also be derived through a linear approximation to the optimised non-linear trajectory by least squares analysis. Model performance has been demonstrated in both 2D and 3D. In the 2D example, the benefit-to-cost ratio of the optimised well is much higher than that of a straight well; in the 3D example, laterals of various curvatures are generated. The applicability of the method is tested by exploring different reservoir heterogeneities and curvature constraints. This approach can be applied to determine the entrance/exit positions and the well path for subsurface energy system development, which is useful for field applications.Item Open Access Numerical modelling of new flap-gate type breakwater in regular and solitary waves using one-fluid formulation(Elsevier, 2021-10-20) Chen, Songgui; Xing, Jingru; Yang, Liang; Zhang, Huaqing; Luan, Yingni; Chen, Hanbao; Liu, HaiyuanBreakwater is commonly used infrastructure for protecting coastal zones from waves and tsunamis. Computational modelling is frequently employed for prediction and validation of the breakwater design. Potential flow based models may not be ideal for such applications due to large energy dissipation. We apply the Computational Fluid Dynamics (CFD) to study the waves and breakwater interaction problem. In this work, we benchmark the performance of a new type of flap-gate breakwater in regular waves (airy wave theory and second order Stokes wave theory), where the multiphase Navier–Stokes equations are solved and the structure of breakwater is considered as one phase of fluid within the ‘one-fluid’ framework. In this way, the computational costs will be reduced to the same level as the numerical wave tank alone. We conduct a grid refinement study and compare results to experiments to investigate accuracy. The result shows a good agreement with the experimental data. Further, we use the validated model for sensitivity studies for different settings of flap-gate, and the solitary waves paradigm for tsunamis. The proposed novel numerical tool allows us to study large parametric spaces, impact of breaking waves, load and pressure producing process and interaction time.Item Open Access Numerical simulation of stabilisation of floating wind with submerged hydrofoil(IOP Publishing, 2024-06-10) Wang, Junxian; Yang, Liang; Xing, Jingru; Yang, JianhuiThis research focuses on the optimal design and method of attaching a submerged hydrofoil to an offshore platform to enhance stabilisation. The flapping hydrofoil, exhibiting a hybrid motion combining heave and pitch, is engineered to convert incoming wave energy. It generates a distinctive wake that effectively counteracts incoming waves, thereby reducing wave impact. In this study, a NACA0030-type hydrofoil was strategically positioned between two columns of the platform model. Comprehensive analyses were conducted to evaluate the free-floating platform's response to regular waves, with a focus on the attached hydrofoil. The results indicate that the hydrofoil significantly reduces the surge motion and drifting speed of the platform, affirming its effectiveness in enhancing stabilisation.Item Open Access Predicting airborne coronavirus inactivation by far-UVC in populated rooms using a high-fidelity coupled radiation-CFD model(Nature Research (part of Springer Nature), 2020-11-12) Buchan, Andrew G.; Yang, Liang; Atkinson, Kirk D.There are increased risks of contracting COVID-19 in hospitals and long-term care facilities, particularly for vulnerable groups. In these environments aerosolised coronavirus released through breathing increases the chance of spreading the disease. To reduce aerosol transmissions, the use of low dose far-UVC lighting to disinfect in-room air has been proposed. Unlike typical UVC, which has been used to kill microorganisms for decades but is carcinogenic and cataractogenic, recent evidence has shown that far-UVC is safe to use around humans. A high-fidelity, fully-coupled radiation transport and fluid dynamics model has been developed to quantify disinfection rates within a typical ventilated room. The model shows that disinfection rates are increased by a further 50-85% when using far-UVC within currently recommended exposure levels compared to the room’s ventilation alone. With these magnitudes of reduction, far-UVC lighting could be employed to mitigate SARS-CoV-2 transmission before the onset of future waves, or the start of winter when risks of infection are higher. This is particularly significant in poorly-ventilated spaces where other means of reduction are not practical, in addition social distancing can be reduced without increasing the riskItem Open Access Qualitative investigation of wake composition in offshore wind turbines: a combined computational and statistical analysis of inner and outer blade sections(EDP Sciences, 2024-02-06) Siddiqui, M. Salman; Badar, Abdul Waheed; Yang, Liang; Saeed, Muhammed; Keprate, ArvindHigh-fidelity numerical simulations are used to thoroughly analyze the evolution of the wake behind a megawatt-scale offshore wind turbine. The wake features are classified in terms of wake dynamics composition and the associated turbulence characteristics originating from the inner and outer sections of the blades. Understanding the wake is essential for developing compact layouts for future wind farms. We employed a transient Sliding Mesh Interface (SMI) technique to analyze the fully dynamic wake evolution of the offshore NREL 5MW full turbine. Our high-fidelity results have been validated against previously published results in the literature. We thoroughly investigated the dominant structures of the wake using Proper Orthogonal Decomposition (POD) techniques, which we applied to transient simulations of fully developed flows after five wind turbine revolutions over the snapshot data. Our findings show that the inner section of the blades, which is composed of airfoils with larger cross-sections, is responsible for the dominant components of the wake, while the contribution of the wake from the outer section of the blade is significantly lower. Therefore, designing more aerodynamic sections for the blade’s inner section can help reduce the dominant wake components and thus decrease the inter-turbine distance in future wind farms.Item Open Access Rapid prototyping of image contrast enhancement hardware accelerator on FPGAs using high-level synthesis tools(ScopeMed, 2023-09-30) Bilal, Muhammad; Harasani, Wail Ismael; Yang, LiangRapid prototyping tools have become essential in the race to market. In this work, we have explored employing rapid prototyping approach to develop an intellectual property core for real-time contrast enhancement which is a commonly employed image processing task. Specifically, the task involves real-time contrast enhancement of video frames, which is used to repair washed out (overexposed) or darkened (underexposed) appearance. Such scenario is frequently encountered in video footage captured underwater. Since the imaging conditions are not known a priori, the lower and upper limits of the dynamic range of acquired luminance values need to be adaptively determined and mapped to the full range permitted by the allocated bitwidth so that the processed image has a high-contrast appearance. This paper describes a hardware implementation of this operation using contrast stretching algorithm with the help of Simulink high-level synthesis tool using rapid prototyping paradigm. The developed model can be directly used as a drop-in module in larger computer vision systems to enhance Simulink computer vision toolbox capabilities, which does not support this operation for direct FPGA implementation yet. The synthesized core consumes less than 1% of total FPGA slice logic resources while dissipating only 7 mW dynamic power. To this end, look-up table has been employed to implement the division operator which otherwise requires exorbitantly large number of logic resources. Moreover, an online algorithm has been proposed which avoids multiple memory accesses. The hardware module has been tested in a real-time video processing scenario at 100 MHz clock rate and depicts functional accuracy at par with the software while consuming lower logic resources than competitive designs. These results demonstrate that the appropriate use of modern rapid prototyping tools can be highly effective in reducing the development time without compromising the functional accuracy and resource utilization.Item Open Access Taichi-LBM3D: a single phase and multiphase lattice Boltzmann solver on cross-platform multi-core CPU/GPUs(MDPI, 2022-08-08) Yang, Jianhui; Xu, Yi; Yang, LiangThe success of the lattice Boltzmann method requires efficient parallel programming and computing power. Here, we present a new lattice Boltzmann solver implemented in Taichi programming language, named Taichi-LBM3D. It can be employed on cross-platform shared-memory many-core CPUs or massively parallel GPUs (OpenGL and CUDA). Taichi-LBM3D includes the single- and two-phase porous medium flow simulation with a D3Q19 lattice model, Multi-Relaxation-Time (MRT) collision scheme and sparse data storage. It is open source, intuitive to understand, and easily extensible for scientists and researchers.Item Open Access A three-phase interpenetrating continua approach for wave and porous structure interaction(Emerald, 2020-05-14) Yang, Liang; Buchan, Andrew; Pavlidis, Dimitrios; Jones, Alan; Smith, Paul; Sakai, Mikio; Pain, ChristopherA three phase interpenetrating continua model for the numerical simulation of water waves and porous structure interaction is proposed in this work. In contrast with one-fluid formulation/multi-component methods, each phase has its own characteristics, density, velocity, etc and each point is occupied by all phases, this model requires additional closure laws to describe the interfacial momentum exchange, e.g., via the Ergun's equation. First, the porous structure is modelled as a phase of continua with a penalty force adding on the momentum equation, so the conservation of mass is guaranteed without source terms. Second, the adaptive unstructured mesh modelling with P1DG-P1 elements is employed here to decrease the total number of degree of freedom maintaining the same order of accuracy. Several benchmark problems are used to validate the model, which includes the darcy flow, classical collapse of water column and water column with a porous structure.Item Open Access Towards an integrative framework for digital twins in wind power(IEEE, 2024-02-01) Siddiqui, M. Salman; Keprate, Arvind; Yang, Liang; Malmedal, TirilThe present global climate crisis necessitates urgent integration of sustainable and renewable energy resources, coupled with digital technology. Renewable energy stands out as a viable solution, and among the various renewable energy sources, wind power is believed to play a crucial role in this transition. In the era of industrial digitalization, implementing smart monitoring and operation becomes a vital step toward optimizing resource utilization. Consequently, the application of Digital Twins (DT) emerges as a promising approach to enhance power output in the wind energy sector. DTs for energy systems encompass multiple areas of study, such as smart monitoring, big data technology, and advanced physical modeling. While several frameworks exist for structuring DTs, few standardized methods have been established based on the experience gained. To address this gap, the present research proposes an integrative development framework for DTs, tailored explicitly to the aerodynamics of wind turbines, to ensure their successful operation throughout the entire lifecycle, from aggregation to performing actions. A seven-step framework is presented, which identifies the potential components and methods required to create a fully developed DT.Item Open Access Water entry of slender segmented projectile connected by spring(Elsevier, 2020-09-16) Wu, Zhengyang; Zhang, Chengchun; Wang, Jing; Shen, Chun; Yang, Liang; Ren, LuquanAn object that enters the water experiences a large impact acceleration at the initial stage of water entry, which can cause structural damage to objects that are dropped or launched into the water. To reduce the peak impact acceleration, a spring-connected segmented projectile with compressible nose was designed. Through inertial measurement unit and high-speed camera, the influence of the nose compressibility on the initial impact acceleration was qualitatively investigated. The experimental results demonstrate that the introduction of a spring between the nose and the main body of the projectile can significantly suppresses the peak acceleration during the early stage of impact (0–50 ms). Furthermore, the maximum impact acceleration experienced by the main body is only related to the maximum compression of the nose without considering the spring stiffness. In addition, using the spring exerts a slight effect on the non-dimensional pinch-off times of the cavity but increases the initial velocity required for the occurrence of cavity pinch-off events on the side of the main bodyItem Open Access Wave devouring propulsion: an overview of flapping foil propulsion technology(Elsevier, 2023-07-29) Xing, Jingru; Yang, LiangA comprehensive review of flapping foils for Wave Devouring Propulsion (WDP) is presented. The flapping foil can effectively utilize wave energy and generate thrust. The development of WDP is discussed, followed by an introduction to the geometry, modes of motion, and operating principles. These research studies are classified as theoretical, experimental, and numerical and are provided in detail. They demonstrate that marine equipment with a flapping foil system can achieve high energy conversion efficiency and low resistance. Several prototypes of the combination of WDP with human-crewed and uncrewed vessels have been shown, including the latest initial concept models and company products. There is a huge prospect for self-driven, pollution-free propulsion of marine devices, and this paper suggests several future studies.