本文選題：物理試驗(yàn)　切入點(diǎn)：流體共振　出處：《大連理工大學(xué)》2014年碩士論文

【摘要】：海上多浮體結(jié)構(gòu)間往往存在相對于結(jié)構(gòu)自身尺寸很小的窄縫。在特定頻率的波浪作用下,這些窄縫內(nèi)會出現(xiàn)流體大幅度振蕩現(xiàn)象,稱為窄縫流體共振。此時(shí),結(jié)構(gòu)物所受波浪力將顯著增大,嚴(yán)重威脅工程安全作業(yè)。為了深入了解和認(rèn)識窄縫流體共振的物理特性和作用機(jī)制,本文通過物理試驗(yàn)和數(shù)值分析方法對該問題開展研究。 傳統(tǒng)的勢流模型因無法考慮流動(dòng)中的機(jī)械能耗散,所以會嚴(yán)重高估窄縫內(nèi)流體的共振波高。粘性流模型能夠給出較可靠的模擬結(jié)果,但非常耗時(shí)。在勢流理論框架內(nèi),通過引入合適的人工阻尼項(xiàng),修改自由表面邊界條件或邊界匹配條件,可得到較可靠的共振幅值的預(yù)測結(jié)果,然而經(jīng)驗(yàn)性的人工阻尼系數(shù)需要結(jié)合試驗(yàn)結(jié)果或CFD結(jié)果進(jìn)行率定。本文通過二維水槽物理試驗(yàn),對存在窄縫的箱體-箱體結(jié)構(gòu)以及方箱-直墻結(jié)構(gòu),在正向線性入射波作用下的流體共振特性,以及窄縫流體共振中,入射波波高和結(jié)構(gòu)尖角引起的渦流對機(jī)械能耗散的影響作用開展了研究。 在雙箱窄縫流體共振試驗(yàn)中,通過設(shè)置具有不同半徑的圓角底角的箱體,觀測對應(yīng)的窄縫內(nèi)流體共振特性的變化規(guī)律。試驗(yàn)結(jié)果表明,首先,窄縫內(nèi)流體共振波高隨入射波波高的增大呈冪函數(shù)趨勢增大,這體現(xiàn)了入射波波高對水體流動(dòng)過程中的機(jī)械能耗散的影響作用。而共振波高與入射波波高之間的依賴關(guān)系,與模型的幾何參數(shù)及設(shè)置相關(guān)。其次,當(dāng)箱體的底角形狀由直角變?yōu)榫哂休^小半徑的圓角后,窄縫內(nèi)流體共振頻率變化很小,而共振波高則顯著增大,這意味著由方箱尖角引起的渦流對機(jī)械能耗散的影響十分重要。而隨著圓角半徑增大,窄縫內(nèi)流體的共振頻率不斷增大,共振波高則逐漸減小,但仍明顯高于箱體底角為直角的情況,這反映了結(jié)構(gòu)尖角對窄縫流體共振過程中的機(jī)械能耗散的影響機(jī)制。而窄縫流體共振頻率的變化則與窄縫內(nèi)流體質(zhì)量的變化有關(guān),隨著箱體底角半徑的增大,窄縫內(nèi)參與垂向振蕩的流體質(zhì)量減小,對應(yīng)的共振頻率因此增大。此外,隨著箱體底角形狀的變化,窄縫內(nèi)流體共振波高與入射波波高之間的依賴關(guān)系也隨之改變。 本文在方箱-直墻系統(tǒng)窄縫流體共振試驗(yàn)中,分別研究了不同的方箱吃水深度、窄縫間隙以及入射波頻率和波高的影響作用,為數(shù)值模型的驗(yàn)證和人工阻尼(力)系數(shù)的率定提供了依據(jù)。此外,通過分析水動(dòng)力系數(shù)隨入射波頻率、波高的變化規(guī)律,對水體流動(dòng)過程中的機(jī)械能耗散進(jìn)行了研究。試驗(yàn)結(jié)果表明,方箱與直墻間窄縫內(nèi)共振波高可達(dá)到入射波波高的7倍以上；直墻-方箱系統(tǒng)的反射系數(shù)對方箱吃水深度、窄縫寬度和入射波波高存在復(fù)雜的非線性依賴關(guān)系,這體現(xiàn)了共振響應(yīng)過程中的機(jī)械能損耗機(jī)制。 在數(shù)值研究方面,本文在勢流理論框架內(nèi)建立控制方程,通過引入人工阻尼改善共振波高的預(yù)測精度,分別采用匹配特征函數(shù)展開法和邊界元法求解方法分別建立了半解析模型和邊界元模型。首先,根據(jù)物理試驗(yàn)結(jié)果對數(shù)值模型的阻尼(力)系數(shù)進(jìn)行率定。然后,采用數(shù)值分析方法對窄縫流體共振特性與結(jié)構(gòu)幾何參數(shù)間的依賴關(guān)系進(jìn)行了分析,并對結(jié)構(gòu)所受波浪力進(jìn)行了研究。數(shù)值結(jié)果表明,雙箱(圓角底角)間窄縫流體共振中,雙箱所受水平方向波浪力可達(dá)2.5倍pgha,其中ρ為流體密度,g為重力加速度,h為水深,a為入射波波幅。方箱-直墻間窄縫內(nèi)流體共振中,方箱吃水深度、窄縫寬度及方箱寬度的增大,均會導(dǎo)致窄縫內(nèi)水體共振頻率單調(diào)減小。在共振頻率附近,方箱及直墻所受水平方向波浪力可達(dá)4倍pgha,且隨著方箱吃水深度的增大而逐漸增大。
[Abstract]:The multi body floating structure often exist with respect to narrow their very small size. In the wave of specific frequency, the narrow gap in large amplitude oscillation will appear fluid, called narrow fluid structure resonance. At this time, the wave pressure will significantly increase, Yan Zhongwei threatened the safe operation in order to project. A deeper understanding of the physical characteristics and mechanism of narrow resonance fluid, this paper carried out research on this problem through physical experiments and numerical analysis method.
The traditional potential flow model cannot consider the flow of mechanical energy dissipation, so it will seriously overestimate the height of fluid in narrow resonance. Simulation results are given to a reliable viscous flow model, but is very time-consuming. In potential theory, by introducing a suitable artificial damping, modify the free surface boundary condition or boundary the matching condition, the predicted results can be more reliable than the resonance amplitude, however artificial damping coefficient requires a combination of empirical test results or CFD results were calibrated. Through 2D physical test, the structure of box - slot structure of box and box - straight wall, fluid in the role of positive linear resonance characteristics of incident wave the narrow and fluid resonance, wave structure and high angle caused by the eddy current research on effect of mechanical energy dissipation.
In the double slit fluid resonance test box, box by setting with different radii of the rounded corners, variation of the observations corresponding to narrow the fluid in the resonance characteristics. The experiment results show that, firstly, the fluid in the narrow resonance wave with wave height increases exponentially increasing trend, which reflects the incident wave high impact on water flow in the process of mechanical energy dissipation effect. And the resonance between wave height and incident wave height dependence associated with the geometric parameters and the set model. Secondly, when the box bottom shape by angle varying with smaller radius fillet, narrow fluid in the resonance frequency change is very small, and the resonance wave height increases obviously, which means that the important influence of eddy current by square box on the cusp of mechanical energy dissipation. As the radius increases, increasing the resonance frequency of the fluid in the narrow resonance wave. Then gradually decreased, but still higher than the bottom of a rectangular box, which reflects the structure of narrow angle influence mechanism of fluid resonance in the process of mechanical energy dissipation. And narrow resonance frequency changes of fluid changes and narrow fluid quality, with the increase of the radius of the bottom of the box body angle, narrow in the vertical mass of fluid oscillation decreases, thus increasing the corresponding resonance frequencies. In addition, with the change of the shape of the box bottom, the dependence between the fluid in the narrow resonance wave height and wave height change.
In this paper, square box - straight wall system narrow fluid resonance test, were studied in different depth box, narrow gap and the influence of the frequency of the incident wave and wave function verification for the numerical model and artificial damping coefficient (force) was provided. In addition, through the analysis of water power the coefficient of variation with the incident wave frequency, wave height, the water flow in the process of mechanical energy dissipation are studied. The experimental results show that the square box and the straight wall between the narrow resonance wave high Gao can reach more than 7 times; the reflection coefficient of square box box system of straight wall - depth, narrow the width and the incident wave height are complex nonlinear dependence, which reflects the resonance response process of the mechanical energy loss mechanism.
In the numerical study, the theoretical framework established within the control equation in potential flow, improve the prediction accuracy of resonance wave by introducing artificial damping, respectively using a semi analytical model and boundary element model is established and the matched eigenfunction expansion method and boundary element method respectively. First, according to the physical test results of the numerical model (damping force) coefficient was set. Then, analyzes the narrow dependence of fluid resonance characteristic and structure of geometric parameters between using the numerical analysis method, and the structure of the wave force are studied. The numerical results show that the double box (rounded corner) between the narrow resonance fluid in the horizontal double box the direction of the wave is 2.5 times pgha, where p for fluid density, G for the acceleration of gravity, H depth, a wave amplitude. The square box - straight wall slot between the fluid in the resonance, square box depth, narrow width and square box The increase of width, which leads to narrow gap in water resonance frequency decreases monotonically. Near the resonance frequency, the square box and straight wall under horizontal direction of the wave is 4 times of pgha, and with the increasing of square box draft and increased gradually.

【學(xué)位授予單位】：大連理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：U661.1;O353

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