URANS Computations of Cavitating Flow around a 2-D Wedge by Compressible Two-Phase Flow Solver

This paper deals with the computation of unsteady cavitating flow around a twodimensional wedge by using Unsteady Reynolds Averaged Navier-Stokes (URANS) flow solver. Because of accuracy deterioration problem due to excessive numerical dissipations for low Mach number unsteady flow, properly scaled RoeM and AUSMPW+ numerical flux schemes are used to accurately compute unsteady cavitating flow. Fast Fourier Transform (FFT) analysis results of experiments and computations are compared to show similar dominant frequencies of shedding vortices. Shedding pattern and location of vortices are also compared to show similar behavior of each flow result.OAIID:RECH_ACHV_DSTSH_NO:A201606327RECH_ACHV_FG:RR00200003ADJUST_YN:EMP_ID:A001138CITE_RATE:FILENAME:M2J.1.AS733_1588F1.pdfDEPT_NM:기계항공공학부EMAIL:[email protected]_YN:FILEURL:https://srnd.snu.ac.kr/eXrepEIR/fws/file/d3e93894-8ef1-4bce-9dfe-e2c270ced9d8/linkCONFIRM:

Improving Visual Recognition with Hyperbolical Visual Hierarchy Mapping

Visual scenes are naturally organized in a hierarchy, where a coarse semantic is recursively comprised of several fine details. Exploring such a visual hierarchy is crucial to recognize the complex relations of visual elements, leading to a comprehensive scene understanding. In this paper, we propose a Visual Hierarchy Mapper (Hi-Mapper), a novel approach for enhancing the structured understanding of the pre-trained Deep Neural Networks (DNNs). Hi-Mapper investigates the hierarchical organization of the visual scene by 1) pre-defining a hierarchy tree through the encapsulation of probability densities; and 2) learning the hierarchical relations in hyperbolic space with a novel hierarchical contrastive loss. The pre-defined hierarchy tree recursively interacts with the visual features of the pre-trained DNNs through hierarchy decomposition and encoding procedures, thereby effectively identifying the visual hierarchy and enhancing the recognition of an entire scene. Extensive experiments demonstrate that Hi-Mapper significantly enhances the representation capability of DNNs, leading to an improved performance on various tasks, including image classification and dense prediction tasks.Comment: This paper is accepted to CVPR 2024. The supplementary material is included. The code is available at \url{https://github.com/kwonjunn01/Hi-Mapper

Layer-wise Auto-Weighting for Non-Stationary Test-Time Adaptation

Given the inevitability of domain shifts during inference in real-world applications, test-time adaptation (TTA) is essential for model adaptation after deployment. However, the real-world scenario of continuously changing target distributions presents challenges including catastrophic forgetting and error accumulation. Existing TTA methods for non-stationary domain shifts, while effective, incur excessive computational load, making them impractical for on-device settings. In this paper, we introduce a layer-wise auto-weighting algorithm for continual and gradual TTA that autonomously identifies layers for preservation or concentrated adaptation. By leveraging the Fisher Information Matrix (FIM), we first design the learning weight to selectively focus on layers associated with log-likelihood changes while preserving unrelated ones. Then, we further propose an exponential min-max scaler to make certain layers nearly frozen while mitigating outliers. This minimizes forgetting and error accumulation, leading to efficient adaptation to non-stationary target distribution. Experiments on CIFAR-10C, CIFAR-100C, and ImageNet-C show our method outperforms conventional continual and gradual TTA approaches while significantly reducing computational load, highlighting the importance of FIM-based learning weight in adapting to continuously or gradually shifting target domains.Comment: WACV 202

Multistep assembly of DNA condensation clusters by SMC

SMC (structural maintenance of chromosomes) family members play essential roles in chromosome condensation, sister chromatid cohesion and DNA repair. It remains unclear how SMCs structure chromosomes and how their mechanochemical cycle regulates their interactions with DNA. Here we used single-molecule fluorescence microscopy to visualize how Bacillus subtilis SMC (BsSMC) interacts with flow-stretched DNAs. We report that BsSMC can slide on DNA, switching between static binding and diffusion. At higher concentrations, BsSMCs form clusters that condense DNA in a weakly ATP-dependent manner. ATP increases the apparent cooperativity of DNA condensation, demonstrating that BsSMC can interact cooperatively through their ATPase head domains. Consistent with these results, ATPase mutants compact DNA more slowly than wild-type BsSMC in the presence of ATP. Our results suggest that transiently static BsSMC molecules can nucleate the formation of clusters that act to locally condense the chromosome while forming long-range DNA bridges

Knowing Where to Focus: Event-aware Transformer for Video Grounding

Recent DETR-based video grounding models have made the model directly predict moment timestamps without any hand-crafted components, such as a pre-defined proposal or non-maximum suppression, by learning moment queries. However, their input-agnostic moment queries inevitably overlook an intrinsic temporal structure of a video, providing limited positional information. In this paper, we formulate an event-aware dynamic moment query to enable the model to take the input-specific content and positional information of the video into account. To this end, we present two levels of reasoning: 1) Event reasoning that captures distinctive event units constituting a given video using a slot attention mechanism; and 2) moment reasoning that fuses the moment queries with a given sentence through a gated fusion transformer layer and learns interactions between the moment queries and video-sentence representations to predict moment timestamps. Extensive experiments demonstrate the effectiveness and efficiency of the event-aware dynamic moment queries, outperforming state-of-the-art approaches on several video grounding benchmarks.Comment: ICCV 2023. Code is available at https://github.com/jinhyunj/EaT

Computations of Cryogenic Cavitating Flows around Turbopump Inducer

This paper deals with the numerical computations of cryogenic cavitating flows around turbopump inducer in liquid rocket. The baseline numerical fluxes for the computations of all-speed two-phase flows (two-phase RoeM and AUSMPW+ schemes) are extended for treating general equation of states, and improved preconditioning techniques are developed for robust and efficient computations in low-speed region. As a validation step for such progress, cryogenic cavitating flows around hydrofoil and ogive are computed. Finally, numerical simulations of three-dimensional KARI turbopump inducer are carried out under various flow conditions with water and cryogenic fluids, and the difference in inducer flow physics depending on the working fluids are examined.OAIID:oai:osos.snu.ac.kr:snu2014-01/104/0000004648/19SEQ:19PERF_CD:SNU2014-01EVAL_ITEM_CD:104USER_ID:0000004648ADJUST_YN:NEMP_ID:A001138DEPT_CD:446CITE_RATE:0FILENAME:김종암_국제학술대회_20140717_김형준.pdfDEPT_NM:기계항공공학부CONFIRM:

Computations of all-speed cryogenic cavitating flows in turbopump inducer

The present paper deals with a numerical method for all-speed cryogenic cavitating flows in turbopump inducer. Recently, we have developed an accurate and efficient baseline numerical scheme for the computations of all-speed two-phase flows. By extending such progress, we conduct some modification of preconditioning technique and propose an accurate and efficient numerical method to deal with the computations of cryogenic two-phase flows. To verify pressure and temperature depression effect in cryogenic cavitation, we carry out numerical simulations of cryogenic cavitation flows around hydrofoil. Compared with Hords experimental data, computed results are turned out to be quite satisfactory. Finally, numerical simulations of KARI turbopump inducer are carried out under various flow conditions with water and cryogenic fluids, and we examine the differences in inducer flow physics depending on the working fluids.The authors appreciate the financial supports provided by NSL (National Space Laboratory) program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology (GRANT 20120009099).OAIID:oai:osos.snu.ac.kr:snu2012-01/104/0000004648/39SEQ:39PERF_CD:SNU2012-01EVAL_ITEM_CD:104USER_ID:0000004648ADJUST_YN:NEMP_ID:A001138DEPT_CD:446CITE_RATE:0FILENAME:COMPUTATIONS_OF_ALL-SPEED_CRYOGENIC_CAVITATING_FLOWS_IN_TURBOPUMP_INDUCER.pdfDEPT_NM:기계항공공학부EMAIL:[email protected]:

Numerical Investigation on Effects of Sub-cooling Methods on Performance of Multi-split Variable Refrigerant Flow Systems with Bypass and Vapor Injection Techniques

The pipeline connected between outdoor units and indoor units is lengthened in the VRF systems because the VRF systems are generally used in light commercial buildings. Therefore, a sub-cooler is installed in the VRF systems to avoid flash gas caused by pressure drop and heat transfer in the liquid pipeline. Usually, the liquid refrigerant in the pipeline can be cooled by bypass and refrigerant injection techniques with an internal heat exchanger (IHX) and electric expansion valve (EEV). In this study, the performance of the VRF systems using bypass and refrigerant injection cycles are compared by numerical method. The simulation for multi-split VRF is developed with considering application of vapor injection and bypass cycle and validated with experimental data. The bypass and refrigerant injection have improvement potential for cooling capacity by 3.11% and 15.5%, respectively due to increasing enthalpy difference in evaporators. The vapor injection technique has more improvement potential of performance than bypass technique. Subcooling degree at inlet of EEV is above 10°C degree in two systems, which can avoid flash gas generation

Efficient and accurate computations of all-speed cryogenic two-phase flows around turbopump inducer

The present paper deals with a numerical method for all-speed cryogenic cavitating flows in turbopump inducer. Recently, we have developed an accurate and efficient baseline numerical scheme for the computations of all-speed two-phase flows. By extending such progress, we conduct some modification of preconditioning technique and propose an accurate and efficient numerical method to deal with the computations of cryogenic two-phase flows. To verify pressure and temperature depression effect in cryogenic cavitation, we carry out numerical simulations of cryogenic cavitation flows around hydrofoil. Compared with Hords experimental data, computed results are turned out to be quite satisfactory. Finally, numerical simulations of KARI turbopump inducer are carried out under various flow conditions with water and cryogenic fluids, and we examine the differences in inducer flow physics depending on the working fluids.The authors appreciate the financial supports provided by NSL (National Space Laboratory) program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology (GRANT 20120009099).OAIID:oai:osos.snu.ac.kr:snu2013-01/104/0000004648/24SEQ:24PERF_CD:SNU2013-01EVAL_ITEM_CD:104USER_ID:0000004648ADJUST_YN:NEMP_ID:A001138DEPT_CD:446CITE_RATE:0FILENAME:hj_kim.pdfDEPT_NM:기계항공공학부EMAIL:[email protected]: