The labyrinth seal in turbomachinery is a key element that restricts leakage flow among rotor-stator clearances from high-pressure regions to low-pressure regions. The fluid-induced forces on the rotor from seals duri...The labyrinth seal in turbomachinery is a key element that restricts leakage flow among rotor-stator clearances from high-pressure regions to low-pressure regions. The fluid-induced forces on the rotor from seals during machine operation must be accurately quantified to predict their dynamic behavior effectively. To understand the fluid-induced force characteristics of the labyrinth seal more fully, the effects of four types of pre-swirls on the leakage, flow field, and fluid-induced force of a rotary straight-through labyrinth gas seal (RSTLGS) were numerically investigated using the proposed steady computational fluid dynamics (CFD) method based on the three-dimensional models of the RSTLGS. The leakage, flow field, and fluid-induced force of the RSTLGS for six axial pre-swirl velocities, four radial preswirl angles, four circumferential positive pre-swirl angles, and four circumferential negative pre-swirl angles were computed under the same geometrical parameters and operational conditions. Mesh analysis ensures the accuracy of the present steady CFD method. The numerical results show that the four types of pre-swirls influence the leakage, flow field, and fluid-induced force of the RSTLGS. The axial pre-swirl velocity remarkably inhibits the fluid-induced force, and the circumferential positive pre-swirl angle and circumferential negative pre-swirl angle remarkably promote the fluid-induced force. The effects of the radial pre-swirl angle on the fluid-induced force are complicated, and the pressure forces and viscous forces show the maximum or minimum values at a specific radial pre-swirl angle. The pre-swirl has a negligible impact on the leakage. The four types of pre-swirls affect the leakage, flow field, and fluidinduced force of the RSTLGS to varying degrees. The pre-swirl is the influence factor affecting the leakage, flow field, and fluid-induced force of the RSTLGS. The conclusions will help to understand the fluid-induced force of labyrinth seals more fully, by providing helpful suggestions for engineering practices and a theoretical basis to analyze the fluid–structure interaction of the seal-rotor system in future research.展开更多
Cracked straight-through Brazilian disc(CSTBD) samples prepared using two rock materials were used for thermal treatment from room temperature to 700℃. Uniaxial splitting experiments were performed using an automatic...Cracked straight-through Brazilian disc(CSTBD) samples prepared using two rock materials were used for thermal treatment from room temperature to 700℃. Uniaxial splitting experiments were performed using an automatic electro-hydraulic servo press to study the evolution laws of physical and fracture properties of different deep rock materials under high-temperature geological conditions. The fracture characteristics were measured using an industrial camera and digital image correlation technology to analyze the effect of high temperature on fracture properties and failure modes of the CSTBD samples after different thermal treatments. The micro-damage properties of green sandstone and granite materials were obtained using a scanning electron microscope(SEM). The following conclusions were drawn from the test results:(1) With the increasing temperature, the fracture characteristics of green sandstone and granite change from brittle fracture to plasticity fracture, the longitudinal wave velocity of granite decreases sharply at 600℃, and the damage factor reaches 0.8748 at 700℃.(2) The fracture toughness of green sandstone and granite decreases with increasing temperature;however, the decreasing range of granite is larger than that of green sandstone.(3) As the temperature increases, the fracture morphologies of green sandstone and granite materials become rougher, whereas thermal damage cracks of granite and intergranular fractures inside sandstone as well as pores of sandstone increase.(4) The crack tip opening displacement and peak strain corresponding to peak load increase with the temperature.展开更多
社交推荐系统旨在探索社交网络用户社交标签背后的协同信息,为用户提供个性化推荐。然而,社交网络中大量的用户之间没有显式社交关系,但他们却共享相同的项目历史交互行为。以往研究者主观上期望通过复杂元路径挖掘用户间的高阶隐式社...社交推荐系统旨在探索社交网络用户社交标签背后的协同信息,为用户提供个性化推荐。然而,社交网络中大量的用户之间没有显式社交关系,但他们却共享相同的项目历史交互行为。以往研究者主观上期望通过复杂元路径挖掘用户间的高阶隐式社交特征,客观上却降低了模型的实用性。而且,高阶隐式社交特征中的噪声较大,根据特征拼接或深度学习的方式与显式社交特征融合后反而会降低模型的适应能力。近年来,生成式对抗网络(GAN)为数据增强提供了有力的支持,但其复杂的结构令模型收敛困难,导致其应用于社交推荐场景时使得模型整体效率不高。基于此,提出一种社交特征自适应融合的生成式对抗网络推荐模型AFS-GAN(generative adversarial networks recommender systems for adaptive fusion of social features)。首先,采用2个简单元路径分别提取用户的1阶显式社交特征和2阶隐式社交特征,以消除研究者主观判断的不利影响,提高模型的实用性;其次,设计自适应因子灵活地融合显示和隐式社交特征,充分体现用户社交行为的多样性,提升推荐的适应能力;最后,在生成器中采用直通Gumbel Softmax加速生成伪项目,在判别器中采用四元BPR(Bayesian personalized ranking)损失函数直接最大化判别损失,既简化了模型,又提升了其收敛速度,从而整体上提高了模型的效率。在4个基准推荐数据集上与8种目前较先进的社交推荐模型进行了广泛的比较,实验结果表明,所提方法在Precision,Recall,NDCG这3个指标表现卓越。展开更多
基金Supported by National Basic Research Program of China(973 Program,Grant No.2012CB026006)
文摘The labyrinth seal in turbomachinery is a key element that restricts leakage flow among rotor-stator clearances from high-pressure regions to low-pressure regions. The fluid-induced forces on the rotor from seals during machine operation must be accurately quantified to predict their dynamic behavior effectively. To understand the fluid-induced force characteristics of the labyrinth seal more fully, the effects of four types of pre-swirls on the leakage, flow field, and fluid-induced force of a rotary straight-through labyrinth gas seal (RSTLGS) were numerically investigated using the proposed steady computational fluid dynamics (CFD) method based on the three-dimensional models of the RSTLGS. The leakage, flow field, and fluid-induced force of the RSTLGS for six axial pre-swirl velocities, four radial preswirl angles, four circumferential positive pre-swirl angles, and four circumferential negative pre-swirl angles were computed under the same geometrical parameters and operational conditions. Mesh analysis ensures the accuracy of the present steady CFD method. The numerical results show that the four types of pre-swirls influence the leakage, flow field, and fluid-induced force of the RSTLGS. The axial pre-swirl velocity remarkably inhibits the fluid-induced force, and the circumferential positive pre-swirl angle and circumferential negative pre-swirl angle remarkably promote the fluid-induced force. The effects of the radial pre-swirl angle on the fluid-induced force are complicated, and the pressure forces and viscous forces show the maximum or minimum values at a specific radial pre-swirl angle. The pre-swirl has a negligible impact on the leakage. The four types of pre-swirls affect the leakage, flow field, and fluidinduced force of the RSTLGS to varying degrees. The pre-swirl is the influence factor affecting the leakage, flow field, and fluid-induced force of the RSTLGS. The conclusions will help to understand the fluid-induced force of labyrinth seals more fully, by providing helpful suggestions for engineering practices and a theoretical basis to analyze the fluid–structure interaction of the seal-rotor system in future research.
基金funding support from the Sichuan Science and Technology Program (Grant No. 2021YJ0511)the State Key Laboratory for Geo-Mechanics and Deep Underground Engineering,China University of Mining&Technology (Grant No.SKLGDUEK2111)the Key Laboratory of Rock Mechanics and Geohazards of Zhejiang Province (Grant No. ZJRMG-2020-01)。
文摘Cracked straight-through Brazilian disc(CSTBD) samples prepared using two rock materials were used for thermal treatment from room temperature to 700℃. Uniaxial splitting experiments were performed using an automatic electro-hydraulic servo press to study the evolution laws of physical and fracture properties of different deep rock materials under high-temperature geological conditions. The fracture characteristics were measured using an industrial camera and digital image correlation technology to analyze the effect of high temperature on fracture properties and failure modes of the CSTBD samples after different thermal treatments. The micro-damage properties of green sandstone and granite materials were obtained using a scanning electron microscope(SEM). The following conclusions were drawn from the test results:(1) With the increasing temperature, the fracture characteristics of green sandstone and granite change from brittle fracture to plasticity fracture, the longitudinal wave velocity of granite decreases sharply at 600℃, and the damage factor reaches 0.8748 at 700℃.(2) The fracture toughness of green sandstone and granite decreases with increasing temperature;however, the decreasing range of granite is larger than that of green sandstone.(3) As the temperature increases, the fracture morphologies of green sandstone and granite materials become rougher, whereas thermal damage cracks of granite and intergranular fractures inside sandstone as well as pores of sandstone increase.(4) The crack tip opening displacement and peak strain corresponding to peak load increase with the temperature.
文摘社交推荐系统旨在探索社交网络用户社交标签背后的协同信息,为用户提供个性化推荐。然而,社交网络中大量的用户之间没有显式社交关系,但他们却共享相同的项目历史交互行为。以往研究者主观上期望通过复杂元路径挖掘用户间的高阶隐式社交特征,客观上却降低了模型的实用性。而且,高阶隐式社交特征中的噪声较大,根据特征拼接或深度学习的方式与显式社交特征融合后反而会降低模型的适应能力。近年来,生成式对抗网络(GAN)为数据增强提供了有力的支持,但其复杂的结构令模型收敛困难,导致其应用于社交推荐场景时使得模型整体效率不高。基于此,提出一种社交特征自适应融合的生成式对抗网络推荐模型AFS-GAN(generative adversarial networks recommender systems for adaptive fusion of social features)。首先,采用2个简单元路径分别提取用户的1阶显式社交特征和2阶隐式社交特征,以消除研究者主观判断的不利影响,提高模型的实用性;其次,设计自适应因子灵活地融合显示和隐式社交特征,充分体现用户社交行为的多样性,提升推荐的适应能力;最后,在生成器中采用直通Gumbel Softmax加速生成伪项目,在判别器中采用四元BPR(Bayesian personalized ranking)损失函数直接最大化判别损失,既简化了模型,又提升了其收敛速度,从而整体上提高了模型的效率。在4个基准推荐数据集上与8种目前较先进的社交推荐模型进行了广泛的比较,实验结果表明,所提方法在Precision,Recall,NDCG这3个指标表现卓越。
