The force of oblique incident wave on the breakwater with a partially perforated wall

Wave forces induced by the interaction between the oblique incident wave and the breakwater with a partially perforated front wall is investigated. The fluid domain is divided into two sub-domains and the eigen-function expansion method is applied to expanding velocity potentials in each domain. In the eigen-expansion of the velocity potential, evanescent waves are included. Numerical results of the present model are compared with other theories and a good agreement can be found between them. Experimental data have been compared with the present theoretical results. The effect of the traverse wall on wave forces has been discussed in detail. On the basis of the linear wave theory, it is shown that in the range Of engineering practice, the incident angle of wave has small influence on wave forces on the unit length of perforated caisson.

STUDY AND ANALYSIS OF CUTTING FORCES ON OBLIQUE CUTTING OF WOOD

Obilque cutting of wood is an important form of cutting wood. With the developing of woodworking industry, it is widely used in wood machinary processing such as planing, milling, sawing, drilling and so on. This paper takes oblique planing and helix milling of wood as examples. The influences of bevel angle and other factors on the cutting force have been shown. The changing rules of cutting forces have been summarized. On the basis of it, we especially carried out theoretical analysis on the changing rules of cutting forces and discussed the influence of the changing rules on practice.

Dynamic analysis of double-layer and pre-stressed multi-limb six-axis force sensor

In order to adapt to the specific task, the six-axis dynamic contact force between end-effectors of intelligent robots and working condition needs to be perceived. Therefore, the dynamic property of six-axis force sensor which is installed on the end-effectors of intelligent robots will have influence on the veracity of detection and judgment to working environment contact force by intelligent robots directly. In this paper, dynamic analysis to double-layer and pre-stressed multi-limb six-axis force sensor is conducted. First, the structure of the sensor is introduced, and the limb number is confirmed by introducing the related definitions of convex analysis. Then, based on vibration of multiple-degree-of-freedom system, a mechanical vibration simplified model of double-layer and pre-stressed multiple limb six-axis force sensor is set up. After that, movement differential equations of sensor and the response of analytical expression are deduced, and the movement differential equations is solved. Finally, taking the double-layer and pre-stressed seven limb six-axis force sensor as an example, numerical calculation and simulation of deriving result is conducted, which verify the correctness and feasibility of the theoretical analysis.

Study of Slope Reinforcement Force Based on FLAC

A slope will slide if the unbalanced force does not tend to zero when the stability of the slope is analyzed with the help of FLAC. Thus the ultimate reason of slope sliding is the unbalanced force determined by FLAC. The slope will remain stable if the unbalanced force is counterbalanced by a reinforcement force which is produced by a suitable reinforcement method. In this paper, the stability of the slope was analyzed by using FLAC, and the unbalanced force of the slope was obtained through the FISH function in FLAC. According to the equilibrium conditions, the relationship between the reinforcement force and unbalanced force was derived and accordingly the reinforcement force was determined. The reinforcement design was adopted by using pre-stressed anchor bars on the basis of the reinforcement force. An example is used to show that the effect of slope reinforcement based on the reinforcement force is safe and economical. The method doesn＇t need to suppose a sliding surface to obtain the reinforcement force, and it is also clear in physical meaning. So this method realized the organic unification of the stability analysis and the slope reinforcement.

Oblique and Multi-Directional Random Wave Loads on Vertical Breakwaters

Extensive 3-D model tests have been performed to study the effects of wave obliquity and multi-directionality on the wave loads acting on vertical breakwaters. The variation of horizontal and uplift forces acting on an unit length of a breakwater with wave direction, the longitudinal distribution of wave forces, as well as the longitudinal load reduction are analyzed. Some empirical formulae of the longitudinal distribution coefficient and the longitudinal load reduction factor are presented for practical use.

Scattering of Oblique Water Waves by Two Unequal Surface-Piercing Vertical Thin Plates with Stepped Bottom Topography

Based on linear water-wave theory, this study investigated the scattering of oblique incident water waves by two unequal surface-piercing thin vertical rigid plates with stepped bottom topography. By using the matched eigenfunction expansion method and a least square approach, the analytical solutions are sought for the established boundary value problem. The effects of the incidence angle, location of step, depth ratio of deep to shallow waters,and column width between two plates, on the reflection coefficients, the horizontal wave forces acting on the two plates, and the mean surface elevation between the two plates, are numerically examined under a variety of wave conditions. The results show that the existence of the stepped bottom between two plates considerably impacts the hydrodynamic performances of the present system. It is found that the effect of stepped bottom on the reflection coefficient of the present two-plate structure is evident only with waves of the low dimensionless frequency.Moreover, the influence of the step location on the hydrodynamic performance of the present two-plate structure is slight if the step is placed in between the two plates.

Wave Forces Acting on Vertical Walls

Regular and irregular wave forces acting on vertical walls are studied by a previously developed numerical model. The computed wave forces are compared with the available experimental data to verify the numerical model, and satisfactory agreements are obtained. The variation of wave forces with incident angles and the shape of simultaneous pressure distribution are investigated, and the comparisons between numerical results and Goda＇ s predictions are also carried out. It is concluded that the maximum wave forces acting on the unit length of vertical wall is often induced by the obliquely incident waves instead of normally incident waves, while Goda＇ s formula may be inapplicable for oblique wave incidence. The shape of simultaneous pressure distribution is not significantly influenced by incident angles, and it can be favorably predicted by Goda＇ s formula. When regular wave heights are taken as the same as irregular wave height H1%, the irregular wave forces Ph. 1% are slightly larger than regular wave forces in most cases.

A comparative crashworthiness analysis of multi-cell polygonal tubes under axial and oblique loads

In order to investigate the energy absorption characteristics of multi-cell polygonal tubes with different cross-sectional configurations,firstly,the theoretical formulae of the mean crushing force under axial load for four multi-cell polygonal tubes were derived by combining the Super Folding Element theory with Zhang’s research results.These formulae can be used to validate the numerical model and quickly evaluate the energy absorption ability of multi-cell polygonal tubes.Furthermore,a comparative study on the energy absorption performance of eight multi-cell polygonal tubes under axial and oblique loads was conducted.The results show that all tubes have a stable mixed deformation mode under axial load.The multi-cell decagon tube has better energy-absorption ability compared with other tubes.Whenθis less than 10°,all the tubes maintain a stable deformation mode,and the multi-cell decagon tube also has the biggest crushing force efficiency and specific energy absorption among these eight tubes;meanwhile compared with the results atθ=0°,the specific energy absorption of all tubes decreases by about 8%-21%,while the crushing force efficiency increases by 20%-56%.However,at large angles 20°and 30°,all of the tubes collapse in bending modes and lose their effectiveness at energy absorption.

NEW ANALYTICAL METHOD ON SPACE OBLIQUE SPRING

The kinematical characteristic analysis of a space oblique spring is carried out.It first points out that the vibration of a space oblique spring can be regarded as the composition of an oscillatory vibration and a straight linear vibration.The formulas are derived for the calculation of restoring force and damping force of the spring according to the idea above.

Computation of the Viscous Hydrodynamic Forces on a KVLCC2 Model Moving Obliquely in Shallow Water

The viscous hydrodynamic force and moment on ships moving obliquely in shallow water are important for ship navigation safety.In the paper,the viscous flow field around a KVLCC2 model moving obliquely in shallow water is simulated and the hydrodynamic drag,lateral force and yaw moment acting on the hull are obtained by a general purpose computational fluid dynamics(CFD) package FLUENT with shear-stress transport(SST) k—ωturbulence model.The numerical computation is performed at different drift angels and water depths.The numerical results are compared with experimental results,and a good agreement is demonstrated.

Effects of process parameters on periodic impact force exerting on cutting tool in ultrasonic vibration-assisted oblique turning

During ultrasonic vibration-assisted machining,the large impact force induced by tool-workpiece reengagement(TWR)is an important factor that affects tool chipping.However,mechanical analysis into process factors that affect the impact force and their influencing mechanisms are insufficient.Herein,a prediction model for the instantaneous cutting force during both TWR and the stable turning process,which depends on the process parameters and material properties,is firstly proposed based on the kinematic and dynamic analysis of ultrasonic vibration-assisted oblique turning(UVAOT).The results calculated using the developed cutting force model agree well with the experimental results presented in the literature.Next,the linear change law of the instantaneous cutting force with cutting time during the actual TWR is clarified using the proposed model.The effect of the UVAOT process parameters on the average impact force during the periodic TWR process is discussed,and the influence mechanism is analyzed from the perspective of mechanics.A positive linear correlation is discovered between the feed speed and average impact force.The ultrasonic amplitude and cutting speed do not significantly affect the average impact force of the new sharp cutting tools.These findings are consistent with the experimental observations of tool chipping and are applicable to select process parameters for reducing tool chipping during UVAOT.

多连杆式下斜刃横切剪剪切力数值分析

针对多连杆式下斜刃横切剪剪切力求解问题,采用有限单元法建立了数值求解模型。用装配后的实物进行了剪切实验,将数值解和实验解、文献解进行对比,三者结果之间比较吻合,验证了数值求解模型合理性。对不同带材厚度h、剪刃侧向间隙Δ、下剪刃斜度tanα、剪切液压缸伸出速度v及上下剪刃磨损量ω下的横切剪剪切力分布规律进行了归纳。分析结果表明,下剪刃磨损对剪切力的分布影响大于上剪刃的磨损,剪切厚度为6mm的带材的最佳剪刃侧向间隙Δ可取为(0.4±0.1)mm、下剪刃斜度tanα可取为1/25、剪切液压缸伸出速度可取为(300±50)mm/s。提出了横切剪在设计、选型、电气调试以及实际使用过程中的一些建议。

大口径锥头弹体高速倾斜入水偏转规律数值模拟

结合某大口径锥头弹体高速倾斜入水试验,采用任意拉格朗日-欧拉(arbitrary Lagrange-Euler,ALE)流固耦合方法对弹体倾斜入水偏转行为进行数值模拟,研究了弹体以500 m/s高速倾斜入水过程中不同受力模式、载荷变化特征以及弹体发生偏转的力学机理,分析了入水角度对弹体偏转规律的影响。结果表明:在俯仰力矩作用下,弹体均发生抬头方向偏转,且偏转速度呈现先增大后减小的趋势,偏转程度在不同入水角度范围内呈现不同的变化趋势。当入水角度小于15°时,弹体会发生“跳弹”现象;当入水角度为30°~60°时,弹体偏转趋势基本一致,均由初始倾斜状态逐渐转动至水平状态、竖直状态并最终以弹头入水反方向的“出水”姿态向水下运动;当入水角度为75°时,弹体转动至水平状态后,并未继续偏转至竖直状态,弹头以朝斜上方的姿态向水下运动;弹体的入水侵深随入水角度的增大而增大,且增大趋势近似满足指数函数关系。

面向临床应用的股骨颈斜向钻削机制研究

股骨颈骨折是股骨头以下至股骨基底部之间的骨折,在内固定治疗时存在不同角度的置钉需求。采用正交实验设计方案对各向异性股骨颈材料进行仿真实验和牛股骨钻削实验,旨在研究施加生理盐水条件下股骨颈斜向钻削基理。对采集的钻削轴向力和温度结果进行方差和响应面分析,并通过Design-Expert软件对实验结果进行寻优。研究结果表明:在研究范围内,钻削参数为n=1500r/min,f=40mm/min时,各角度轴向力最低;钻削角度超过20.9°时,进给速度为40mm/min的生理盐水流速存在局限性。

Possible obliquity-forced warmth in southern Asia during the last glacial stage

Orbital-scale global climatic changes during the late Quaternary are dominated by high-latitude influenced~100,000-year global ice-age cycles and monsoon influenced~23,000-year low-latitude hydroclimate variations.However,the shortage of highly-resolved land temperature records remains a limiting factor for achieving a comprehensive understanding of long-term low-latitude terrestrial climatic changes.Here,we report paired mean annual air temperature(MAAT)and monsoon intensity proxy records over the past 88,000 years from Lake Tengchongqinghai in southwestern China.While summer monsoon intensity follows the~23,000-year precession beat found also in previous studies,we identify previously unrecognized warm periods at 88,000-71,000 and 45,000-22,000 years ago,with 2-3℃amplitudes that are close to our recorded full glacial-interglacial range.Using advanced transient climate simulations and comparing with forcing factors,we find that these warm periods in our MAAT record probably depends on local annual mean insolation,which is controlled by Earth’s~41,000-year obliquity cycles and is anti-phased to annual mean insolation at high latitudes.The coincidence of our identified warm periods and intervals of high-frequent dated archaeological evidence highlights the importance of temperature on anatomically modern humans in Asia during the last glacial stage.

大跨度斜向井字梁结构设计分析与应用

基于实际工程中遇到的大跨度楼盖结构设计案例,通过不同的结构方案对比,选择了受力特性和经济效益更优的钢筋混凝土斜向井字梁方案,对斜向井字梁结构设计时遇到的问题进行了分析,提出了结构设计要点及后期施工中的注意事项,可供类似大跨度楼盖结构工程借鉴与参考。

腰椎斜扳手法所致“咔哒”声时推扳力的研究

目的:研究腰椎斜扳手法所致咔哒声响时推扳力的大小,为手法提供定量化依据。方法:使用压力检测系统,测量并记录向左右分别进行斜扳手法出现咔哒声响时作用在肩部和臀部的推扳力。结果:以出现咔哒声响作为腰椎斜扳手法成功的标志,此刻对左右肩部平均推扳力分别为12.552±1.715kg和12.748±1.645kg,对左右臀部平均推扳力分别为13.587±1.631kg和13.274±1.200kg。结论:向左右分别进行斜扳手法时,对左右肩部或臀部的平均推扳力无显著差异(P>0.05),但对臀部的推扳力大于对肩部的推扳力(P=0.016)。

基于斜角切削理论的立铣切削力预测研究

为了预测立铣加工的切削力,把立铣刀的切削刃离散为一系列无限小的斜角切削单元。对于每个微元斜角切削单元,应用斜角切削理论来建立切屑通过时剪切区的应力、应变、应变率和温度的控制方程。采用数值方法根据控制方程计算出流动应力,并根据斜角切削和铣削之间的力变换关系,把流动应力转化为铣削力。最后,对45钢进行了多组不同切削参数的立铣实验,仿真和实验的对比结果验证了所提出模型的有效性。该方法同样可以用于其他加工方式(如车削和钻削)的建模。

斜角切削的热力建模与仿真分析

提出了斜角切削热力模型。用等效平面方法把不等分剪切区的直角切削理论延伸并应用于斜角切削中,等效平面的方位由定义的等效平面角来确定。使用坐标变换法分析了斜角切削几何参数之间的关系。建立了剪切区剪切速度、剪应变、剪应力和温度分布的控制方程,在考虑了工件材料加工硬化和热软化影响的条件下,由材料的Johnson-Cook本构方程预测出了剪切区的流动应力。计算了一定加工条件下的切削力,计算结果与已有文献斜角切削实验数据具有较好的一致性,同时,试验表明所提出的斜角切削模型适合于立铣切削力的预测。

滚筒采煤机斜切进刀过程截齿受力分析

通过对鸡西矿务局小恒山煤矿滚筒采煤机斜切进刀过程中截齿受力分析 ,找出在使用滚筒采煤机时截齿损坏普遍存在的主要原因 。