183 research outputs found
Experimental and numerical investigation of the dynamics of a coalesced oscillating bubble near a free surface
Understanding the dynamics of oscillating bubbles beneath a free surface is crucial to many practical applications including airgun-bubble clusters, underwater explosions, etc. In this paper, an experimental and numerical study of the dynamic behaviors of a coalesced bubble near a free surface is conducted, which shows quite different physical features from single bubble dynamics. Firstly, two similar sized underwater discharge bubbles are generated simultaneously beneath a free surface and their complex interactions are experimentally studied with high-speed photography imaging. A strong interaction between two bubbles and the subsequent coalescence are observed when the initial distance between two bubbles is smaller than the maximum equivalent bubble radius. Secondly, both axisymmetric and three-dimensional (3D) boundary integral models are used to simulate the pre-coalescence and post-coalescence of two bubbles. The results obtained by the two models agree well in axisymmetric conditions. The essential physical phenomena in representative experiments are well reproduced by the present 3D model. The pressure field is calculated by the auxiliary function method, which helps to reveal the underlying mechanisms of bubble collapse patterns and jetting behaviors. A parametric study reveals the dependence of the coalesced bubble dynamics and free surface motion on the governing dimensionless quantities
Flow around an oscillating circular disk at low to moderate Reynolds numbers
Direct numerical simulations of the flow induced by a circular disk oscillating sinusoidally along its axis are performed. The aspect ratio of the disk is 10. The Reynolds number , based on the maximum speed and the diameter of the disk, is in the range of . The Keulegan-Carpenter number is in the range of . Five flow regimes are observed in the considered-space: (I) axisymmetric flow (AS), (II) planar symmetric flow in the low-region (PSL), (III) azimuthally rotating flow in the low-region (ARL), (IV) planar symmetric flow in the high-region (PSH) and (V) azimuthally rotating flow in the high-region (ARH). The critical boundaries between different flow regimes are identified based on the evolutions of the magnitude and direction of transverse force acting on the disk. For the non-axisymmetric flow regimes, the flow is one-sided with respect to the axis of the disk and is associated with a non-zero mean value of the transverse force acting on the disk
C2G2: Controllable Co-speech Gesture Generation with Latent Diffusion Model
Co-speech gesture generation is crucial for automatic digital avatar
animation. However, existing methods suffer from issues such as unstable
training and temporal inconsistency, particularly in generating high-fidelity
and comprehensive gestures. Additionally, these methods lack effective control
over speaker identity and temporal editing of the generated gestures. Focusing
on capturing temporal latent information and applying practical controlling, we
propose a Controllable Co-speech Gesture Generation framework, named C2G2.
Specifically, we propose a two-stage temporal dependency enhancement strategy
motivated by latent diffusion models. We further introduce two key features to
C2G2, namely a speaker-specific decoder to generate speaker-related real-length
skeletons and a repainting strategy for flexible gesture generation/editing.
Extensive experiments on benchmark gesture datasets verify the effectiveness of
our proposed C2G2 compared with several state-of-the-art baselines. The link of
the project demo page can be found at https://c2g2-gesture.github.io/c2_gestureComment: 12 pages, 6 figures, 7 table
Distributional Drift Adaptation with Temporal Conditional Variational Autoencoder for Multivariate Time Series Forecasting
Due to the nonstationary nature, the distribution of real-world multivariate
time series (MTS) changes over time, which is known as distribution drift. Most
existing MTS forecasting models greatly suffer from distribution drift and
degrade the forecasting performance over time. Existing methods address
distribution drift via adapting to the latest arrived data or self-correcting
per the meta knowledge derived from future data. Despite their great success in
MTS forecasting, these methods hardly capture the intrinsic distribution
changes, especially from a distributional perspective. Accordingly, we propose
a novel framework temporal conditional variational autoencoder (TCVAE) to model
the dynamic distributional dependencies over time between historical
observations and future data in MTSs and infer the dependencies as a temporal
conditional distribution to leverage latent variables. Specifically, a novel
temporal Hawkes attention mechanism represents temporal factors subsequently
fed into feed-forward networks to estimate the prior Gaussian distribution of
latent variables. The representation of temporal factors further dynamically
adjusts the structures of Transformer-based encoder and decoder to distribution
changes by leveraging a gated attention mechanism. Moreover, we introduce
conditional continuous normalization flow to transform the prior Gaussian to a
complex and form-free distribution to facilitate flexible inference of the
temporal conditional distribution. Extensive experiments conducted on six
real-world MTS datasets demonstrate the TCVAE's superior robustness and
effectiveness over the state-of-the-art MTS forecasting baselines. We further
illustrate the TCVAE applicability through multifaceted case studies and
visualization in real-world scenarios.Comment: 13 pages, 6 figures, submitted to IEEE Transactions on Neural
Networks and Learning Systems (TNNLS
Graph Contrastive Learning with Multi-Objective for Personalized Product Retrieval in Taobao Search
In e-commerce search, personalized retrieval is a crucial technique for
improving user shopping experience. Recent works in this domain have achieved
significant improvements by the representation learning paradigm, e.g.,
embedding-based retrieval (EBR) and collaborative filtering (CF). EBR methods
do not sufficiently exploit the useful collaborative signal and are difficult
to learn the representations of long-tail item well. Graph-based CF methods
improve personalization by modeling collaborative signal within the user click
graph. However, existing Graph-based methods ignore user's multiple behaviours,
such as click/purchase and the relevance constraint between user behaviours and
items.In this paper, we propose a Graph Contrastive Learning with
Multi-Objective (GCL-MO) collaborative filtering model, which solves the
problems of weak relevance and incomplete personalization in e-commerce search.
Specifically, GCL-MO builds a homogeneous graph of items and then optimizes a
multi-objective function of personalization and relevance. Moreover, we propose
a modified contrastive loss for multi-objectives graph learning, which avoids
the mutual suppression among positive samples and thus improves the
generalization and robustness of long-tail item representations. These learned
item embeddings are then used for personalized retrieval by constructing an
efficient offline-to-online inverted table. GCL-MO outperforms the online
collaborative filtering baseline in both offline/online experimental metrics
and shows a significant improvement in the online A/B testing of Taobao search
Seismic velocity structure of the crust and uppermost mantle beneath the Tien Shan and its adjacent areas
The Tien Shan and its adjacent areas have been a prime place to understand the process of continental collision, the mechanism of mountain building and the interaction of tectonic blocks. In this study, we collect seismic data recorded by 74 broad-band stations from the China Provincial Digital Seismic Networks and the Regional Kyrgyzstan and Kazakhstan Networks between January, 2007 and September, 2009. A joint inversion technique that combines three types of datasets (receiver functions, phase velocities of Rayleigh wave measured from both ambient noise and teleseismic earthquake data) is applied to image the crustal and upper mantle structure beneath the Tien Shan and its adjacent areas. The average crustal thickness in the study area is about 50 km, however, the Moho depth extends to ∼70 km beneath the Kyrgyz Platform near the southwestern Tien Shan. Our velocity models show a good correlation with subsurface geological features at shallow depths: low velocities are predominantly observed beneath the basins due to thick sedimentary layer, whereas high velocities are mainly distributed beneath the mountain ranges due to crystalline basement rocks. In the upper mantle a low velocity zone is obviously observed beneath the western Tien Shan. Both the crust thickness and S wave velocity structure of the Tien Shan and its adjacent regions display obvious horizontal and vertical heterogeneities from west to east, which suggests that the far-field effects of the collision between Eurasian plate and Indian plate plays an important role in the tectonic activity of the Tien Shan. The apparent velocity heterogeneities beneath the northern Tarim Basin may indicate that the Tarim Basin may have been eroded and damaged by upwelling hot materials from the upper mantle
A novel conceptual design of modularised offshore green hydrogen system
As a signatory to the Paris Agreement, the UK is committed to contribute efforts to prevent global temperature increase. The UK set its policies and proposals to meet zero net strategy by 2050. Offshore green hydrogen is one promising approach to transfer offshore wind energy to onshore demand areas due to its clean and high-power density. The UK is accelerating towards offshore green hydrogen and has made the price of green hydrogen competitive in the marketplace. The bottleneck of offshore green hydrogen system (OGHS) is the cost of scaling up hydrogen production in the current stage. Innovate designs of hydrogen production system may bring breakthrough to the cost when scaling up the OGHS. This study proposed a centralised OGHS which integrates with modularised production, storage, and offloading units using electricity coming from offshore wind farms. The paper offers an overview of the current situation and development of hydrogen platform and offshore wind farm for supporting the design of offshore platform as well as highlights the key features of technologies used by the different components of the OGHS, through a thorough literature review, including state-of-the-art technical reports and journal papers. A conceptual design of the proposed modularised OGHS is illustrated with a recommendation of site selection. Equipment layout of the OGHS distributed on a floating supporting structure is designed based on a case study of a 200-MW floating wind farm. Stability of the OGHS floating platform is analysed to verify safety of the in the case study, and linear hydrodynamics analysis is simulated based on linear potential theory
Peridynamic analysis of fragmentation of ice plate under explosive loading with thermal effects
Along with the development in arctic region, the icebreaking technologies are gradually becoming the focus. As one of the most powerful and effective way to breaking ice, especially in the ability to solve ice jams, the study of the behaviour of the sea and river ice under dynamic loads is an urgent subject of scientific research and it attracts extensive attention. In addition, the temperature change in the process of ice failure cannot be neglected since that temperature plays an important role in the mechanical properties of the ice. In this study, a fully coupled thermoelastic ordinary state-based Peridynamic model is employed to investigate fragmentation of ice cover subjected to an underwater explosion. Both the deformation effect on the thermal effects and the thermal effects on deformation are taken into consideration. The pressure shocks generated by the underwater explosion are applied to the bottom surface of the ice cover for non-uniform load distributions. Crack propagation paths are investigated, the damage is predicted and compared with existing experimental results. The corresponding temperature distributions are also examined. Furthermore, the ice failure mode in both the top surface and the bottom surface of the ice sheet is investigated
The level effect and volatility effect of uncertainty shocks in China
Previous studies have assumed that the volatility of exogenous
shocks is constant, which can only measure the level effects of
uncertain shocks. This article introduces the time-varying volatility
model into a Dynamic Stochastic General Equilibrium (D.S.G.E.)
model and uses the third-order perturbation method to identify
and decompose the level and volatility effects of uncertainty
shocks. Based on the results of empirical research in China, the
effect of volatility shocks is different from that of level shocks: the
effect of level shocks is direct and positive, and its impact is
larger, while the effect of volatility shocks is indirect and negative,
and its impact is smaller. This article also finds that the impact of
uncertainty shocks will lead to economic stagnation, inflation, and
the stagflation effect
A three-dimensional modeling for coalescence of multiple cavitation bubbles near a rigid wall
The Boundary Integral Method (BIM) has been widely and successfully applied to cavitation bubble dynamics; however, the physical complexities involved in the coalescence of multiple bubbles are still challenging for numerical modeling. In this study, an improved three-dimensional (3D) BIM model is developed to simulate the coalescence of multiple cavitation bubbles near a rigid wall, including an extreme situation when cavitation bubbles are in contact with the rigid wall. As the first highlight of the present model, a universal topological treatment for arbitrary coalescence is proposed for 3D cases, combined with a density potential method and an adaptive remesh scheme to maintain a stable and high-accuracy calculation. Modeling for the multiple bubbles attached to the rigid boundary is the second challenging task of the present study. The effects of the rigid wall are modeled using the method of image; thus, the boundary value problem is transformed to the coalescence of real bubbles and their images across the boundary. Additionally, the numerical difficulties associated with the splitting of a toroidal bubble and self-coalescence due to the self-film-thinning process of a coalesced bubble are successfully overcome. The present 3D model is verified through convergence studies and further validated by the purposely conducted experiments. Finally, representative simulations are carried out to elucidate the main features of a coalesced bubble near a rigid boundary and the flow fields are provided to reveal the underlying physical mechanisms
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