航向稳定性和回转性邱磊讲解课件.ppt

船舶操纵性与耐波性第2章 航向稳定性和回转性,邱磊qiu-,船舶操纵性与耐波性课件,船舶有哪些操纵方面的性能？,船舶操纵性与耐波性课件,固有动稳性(直线运动稳定性),船舶操纵性与耐波性课件,航向稳定性能(保向性),船舶操纵性与耐波性课件,初始转向性能与航行安全的关系,船舶操纵性与耐波性课件,回转性能与航行安全的关系,船舶操纵性与耐波性课件,停船操纵 - 停船性能,船舶操纵性与耐波性课件,第二章 航向稳定性和回转性,船舶操纵性与耐波性课件,第二章 航向稳定性和回转性,稳定性的概念：对处于定常运动状态的物体(或系统)，若受到极小的外界干扰作用而偏离原定常运动状态；当干扰去除后，经过一定的过渡过程，看是否具有回复到原定常运动状态的能力。若能回复，则称原运动状态是稳定的。,(a)直线运动稳定性,(b)方向稳定性,(c)位置稳定性,船舶操纵性与耐波性课件,Directionally unstable ships,An increasing number of new ships are directionally unstable under certain conditions of trim and are difficult to steer manuallySteady steering is only achieved by continually applying small short alternating helm actionsDespite its problems, directional instability does allow a ship to make tight turnsBut it is important that the pilot or master is familiar with the ships behaviour and plans an alter course to allow for this,船舶操纵性与耐波性课件,影响方向稳定性的因素(Factors affecting directional stability),Neither the centre of the hydrodynamic hull force, point A, nor the neutral steering point (N0) are fixed in position for a single vesselThe location of N0 depends uponthe centripetal force relative to the turning moment required for a given rate of turn and hullformThe position of A depends upon压力足以的位置取决于：the flow conditions around the immersed hullformits fore and aft distribution of surface areaSo, the main factors affecting the directional stability are影响方向稳定性的主要因素有:Trim 纵倾Hullform 船型ahead speed 前进速度,船舶操纵性与耐波性课件,How does trim affect the directional stability?,Both head and stern trim increase the ships moment of inertia 首倾和尾倾都增大了船舶的惯性矩So the required moment for a given rate of turn is increased by trim and the point N0 is moved further forwardMore important is that the trim also alters the fore and aft distribution of immersed hull surface and thus the position of A (see next page)更为重要的是纵倾也改变了首尾湿表面积的分布和压力中心A的位置,船舶操纵性与耐波性课件,Stern trim moves A further aft Point A is well aft of the N0-pointso the ship needs a large helm force to maintain the turn the ship will steady up quickly with midships helmThus, directional stability is increased,Head trim moves A further aheadPoint A is just aft of the N0-pointso only a small helm force is needed to maintain the turnbut the ship will be slow to steady up with midships helmThus, directional stability is decreased,船舶操纵性与耐波性课件,How does the hullform affect the directional stability?,Moderately high CB-hulls have a relatively large moment of inertia about the vertical axes so point N0 will tend to be further forward than for finer lined shipsVery full-bodied hulls: point A tends to be even further forward than N0 so these ships are likely to be directionally unstable at small rudder anglesThe swing of the ship can distort the boundary layer to the extent that flow is directed to the wrong side of the rudder and the rudder force is reversed,船舶操纵性与耐波性课件,How does the ships ahead speed affect directional stability?,Increasing a ships ahead speed for a given rudder angle will move the N0-point further aft, thus the directional stability is decreasedA reduction in speed thus tends to increase a ships directional stability for a given rudder angleBut if the ship is moving too slow there will be insufficient flow for the rudder to be effective and the ship has lost “steerage way”.,船舶操纵性与耐波性课件,The directional stability can be improved by using more “deadwood” at the stern 在船尾安装呆木analogous to the feathers on an arrow or dart!Examples of ways of increasing the deadwoodSkegs 尾鳍Fixed fins (submarine “stabilizers”) 稳定鳍Other stern appendages 其他附体,Ways of improving directional stability如何提高方向稳定性？,船舶操纵性与耐波性课件,第二章 航向稳定性和回转性,对稳定性概念的理解,船舶操纵性与耐波性课件,(2-1),小扰动方程,为对稳定性作定量分析，采用“运动稳定性理论”分析方法。设船舶初始运动状态：u1=const=U, v1=r1=0.扰动后引起的扰动运动参数：由于对初始状态是小扰动，故可采用线性操纵运动方程(1-25)式来描述。因不操舵， .将式(2-1)代入式(1-25)，,(1-25),船舶操纵性与耐波性课件,其中，第一式与后两式无关.第一式可重写为：,小扰动方程,即可求得小扰动方程：,(2-2),(2-3),第一式对应的特征方程为：,船舶操纵性与耐波性课件,小扰动方程,特征根为：故式(2-3)的解为： 总为负值，故对纵向速度扰动总具有稳定性。因此，船舶在水平面内的航向稳定性主要取决于方程(2-2)的后二式。,分母为正，分子为负。,(2-4),(2-5),(2-3),船舶操纵性与耐波性课件,二元一阶常系数微分方程组,(2-7),(2-8),(2-6),小扰动方程,船舶操纵性与耐波性课件,特征方程,特征根,角速度扰动方程(2-7)的解为:,(2-9),(2-10),(2-11),船舶操纵性与耐波性课件,航向稳定性分析,接下来我们进行航向稳定性分析,其根为：,于是有：,可见：,船舶操纵性与耐波性课件,航向稳定性分析,皆为负实部的必要条件是：,两根将皆为实数，且必有一个正根,船舶操纵性与耐波性课件,航向稳定性分析,皆为负实部的必要条件是：,船舶操纵性与耐波性课件,航向稳定性分析,可见，航向稳定性条件可归结为：,船舶操纵性与耐波性课件,水动力导数分析,较大的负值,不定符号的小量,图2-3,当具有横向加速度扰动时,船舶操纵性与耐波性课件,不定符号的小量,较大的负值,图2-4,当具有回转加速度扰动时,船舶操纵性与耐波性课件,受侧向扰动速度v作用时,较大的负值,不很大的负值,图2-5,船舶操纵性与耐波性课件,由角速度r引起的力和力矩,不定符号的小量,较大的负值,图2-6,船舶操纵性与耐波性课件,稳定性衡准数C,船舶操纵性与耐波性课件,稳定性衡准数C,船舶操纵性与耐波性课件,C0 船舶在水平面的运动具有直线稳定性；C0 不具有直线稳定性,转首稳定力臂（抗干扰力臂）,偏航力臂（或干扰力臂）,稳定性衡准数C,船舶操纵性与耐波性课件,图 2-7,转首稳定力臂,偏航力臂,船舶操纵性与耐波性课件,影响航向稳定性的因素,(1)为改善其航向稳定性，应使Nr、Yv二者的负值增加，从C的表达式可见，此二者之乘积的正值就越大，显然有利于改善稳定性。(2) Nv 对稳定性的影响较大。虽然Nv 是个符号不定的小量，但在C 表达式中是以Nv(Yr-mu1) 形式出现的，而括号内的值是个大量，以便Nv 值变化对C 值影响较大。对一般船舶Yv、Nr 皆为负值，Yr 是个不定符号的数，所以只要Nv 为正值，船舶就能保证航向稳定性。(3)若沿船纵向设置升力面(如鳍、舵等能产生升力的物体)，则将其加在首或尾部都能使Nr 的负值增加，但若加在首部会使Nv增加负值，而加在尾部会使Nv 变正，故升力面设置在尾部可使Nr负值增加的同时又使Nv 值变正，故对航向稳定性的贡献比设置在首部要大。,船舶操纵性与耐波性课件,与船体几何形状的关系：,增加船长可使Nr负值增加，增加船舶纵中剖面的侧面积可使Nr、Yv的负值增加，增加Nv的有效方法是，增加纵中剖面尾部侧面积，可采用增大呆木，安装尾鳍，使船产生尾倾，削去前踵等，如图2-8所示。,图2-8,船舶操纵性与耐波性课件,船舶操纵性与耐波性课件,船舶操纵性与耐波性课件,船舶操纵性与耐波性课件,水深变化对航向稳定性的影响,图2-9,由于浅水影响，可使在深水中不稳定的船，在浅水中成为稳定。在深水中稳定的船，到浅水中变得更稳定。但对某些肥大型船，存在某一危险水深，此时稳定性低于深水状态;随着水深进一步变浅，超过危险水深后，又会使稳定性好转。,船舶操纵性与耐波性课件,水深变化对航向稳定性的影响,水深变化将影响船舶的航向稳定性。由式(2-13) 可知，当Ir Iv 时，船舶具有航向稳定性。试验结果表明，对一般排水量船舶lv0 ，即位置力的压力中心总位于船中前，随水深变浅，lv 变化不大，而lr 的变化甚大，原因是随水深变浅，Yr 增加而引起，见图2-9。,图2-9,船舶操纵性与耐波性课件,开始操舵时，船舶重心的瞬时位置为回转运动的起始点，称之为执行操舵点。,回转圈的主要特征参数为：,1)反横距从船舶初始的直线航线至回转运动轨迹向反方向最大偏离处的距离为S1。,2)正横距从船舶初始直航线至船首转向90度时，船舶重心所在位置之间的距离为S2。该值越小，则回转性就越好。,船舶操纵性与耐波性课件,回转圈的主要特征参数为：,3)纵距从转舵开始时刻船舶重心G点所在的位置，至船首转向90度时船舶纵中剖面，沿原航行方向计量的距离S3。一般船舶纵距约为3、4倍船长。其值越大，表示船舶对初始时刻的操舵反应越迟钝，即应舵较慢。,船舶操纵性与耐波性课件,4)战术直径从船舶原来航线至船首转向180度时，船纵中剖面所在位置之间的距离DT。其值越小，则回转性越好。对一般普通船DT约为36倍船长，回转性较差者可达78倍船长。,回转圈的主要特征参数为：,船舶操纵性与耐波性课件,5)定常回转直径定常回转阶段船舶重心点圆形轨迹的直径D。一般D0.9DT。通常采用相对回转直径DL代表回转性优劣。通常认为回转性好的船，最小相对回转直径为3左右，回转性差的船约为10左右，大多数船在57的范围内。,回转圈的主要特征参数为：,船舶操纵性与耐波性课件,6）进程R自执行操舵点起至回转圈中心的纵向距离；R=S3-R；它表示船舶对舵作用的应答性，R越小则应答性越好，通常R/L数值约为l2。,回转圈的主要特征参数为：,船舶操纵性与耐波性课件,船舶回转过程中，在船上还存在一个横向速度分量为零的点，称为枢心点p，,由图可见，枢心点前后横向速度反向。一般在初始操舵瞬时，枢心处于船体之撞击中心，约在船舶重心前1/10船长处。以后随回转过程的发展，枢心点位置向船首移动，直至定常回转状态，枢心位置稳定在重心前1/61/3船长处。所以，当船舶回转时，若驾驶人员站在枢心点p上，则可看到一方面船以Vp速度平移，另一方面船上前后各点以角速度r绕p点旋转。这样在操纵时可清晰地观察船舶的运动情况。所以，在条件许可时，驾驶室的位置最好设在枢心附近。,船舶操纵性与耐波性课件,回转圈(Turning Circle),最小回转直径是度量船舶操纵性能的一个重要参数(The minimum turning diameter is one measure of a ships manoeuvring characteristics)影响最小回转直径的因素主要有(The minimum turning diameter varies with, for example):舵角、船速、船舶尺度、水深和纵倾,船舶操纵性与耐波性课件,影响最小回转直径的一些因素(Examples of factors effecting the minimum turning diameter),速度(Speed):舵角不变，船速增大，回转圈随之增大(With constant rudder angle, an increase in speed results in an increased turning circle)船速很低时由于舵效降低回转圈增大Very low speed (those approaching bare steerageway) also increases theturning circle because of reduced ruddereffect 船舶尺度(Vessel size):回转直径随着船舶尺度增大而增大(The turning diameter tends to increase with vessel size)水深(Water depth)：水深极浅的情况下，最小回转直径可能倍增(Minimum turning diameter may more than double in very shallow water)!Smaller right-handed screw vessels may show a bias in turning a tighter circle to port than to starboard, due to the transverse thrust effectthis effect is often negligible in larger ships,船舶操纵性与耐波性课件,PROPELLER FORCES,LONGITUDINAL THRUST,TRANSVERSE THRUST (SIDE FORCE OR PADDLEWHEEL FORCE),COUPLE (TWIST),STERN WALKS THE SAME DIRECTION PROPELLER TURNS,船舶操纵性与耐波性课件,Visualize the lower blades walking along the bottom.,Side Force,单桨(SINGLE PROPELLER),STERN WALK,船舶操纵性与耐波性课件,调距桨CONTROLLABLE PITCH PROPELLERS,STERN WALKS TO STBD,FFG,DD/CG/MCMDD/CG DEVELOP STERN WAY 0% PITCH AND WHEN TWISTING,DDG 51,船舶操纵性与耐波性课件,Turning circle - terminology,纵距(Advance)Distance gained toward the direction of the original course after the rudder is put over.正横距(Transfer)Distance gained perpendicular to the original course after the rudder is put over.反横距(Kick)Momentary movement, at the start of a turn, of the ships stern toward the side opposite to the direction of the turn定常回转直径(Final Diameter)Diameter of the ships turning circle战术直径(Tactical Diameter)Perpendicular distance between the path of the ship on original course and final course after a 180 turn,船舶操纵性与耐波性课件,枢心点(The pivot point),枢心点是船舶纵中线上的一个点，操舵后船舶绕通过该点的垂轴旋转 (A ships (dynamic) pivot point is a point in the centreline about which the ship turns when the rudder is put over)它是船舶纵中线上唯一的漂角为零的点船舶在稳定地直航时，不存在枢心点枢心点仅仅是因为船舶转向而存在的!正车前进：枢心点几乎总是位于距船首1/3船长处；倒车后退：枢心点位于船尾附近(A ships pivot point is nearly always located about one-third of the ships length from her bow when moving ahead, and at or near her stern when moving astern)船舶加速时，枢心点会向船舶运动的方向移动,船舶操纵性与耐波性课件,枢心点(PIVOT POINT),HEAD WAY, STEADY COURSE & SPEEDAHEAD BELL FROM DIW. LONG STEERING LEVER FROM PROPS/RUDDERSASTERN BELL FROM DIW. NO EFFECTIVE STEERING LEVER UNTIL SOME STERN WAY,船舶操纵性与耐波性课件,Ships Tactical Data Folder,# of Screws,# of Rudders,Length/Beam,Pivot Point,Turn Diagrams,Acceleration/Deceleration,Advance/Transfer,Navigational Draft,船舶操纵性与耐波性课件,枢心点 船体外漂(indication of the bodily outward drift),操船者利用枢心点的位置来判断操舵后船舶外漂究竟有多远(Ship handlers use the position of the pivot point to indicate how far the ship will drift bodily outward when the rudder is put over)知道在限制水域中转向操船的余裕空间(To know how much sea room that must be allowed for when making course changes in restricted waters)枢心点在重心之前，标示在产生非对称流和向心力过程中船舶重心外漂有多远(The pivot point is forward of the centre of gravity and indicates how far outwards the centre of gravity has drifted during the build up of the asymmetrical flow and centripetal force),船舶操纵性与耐波性课件,漂角和枢心点(Drift angles and dynamic pivot point),定常回转条件下漂角沿船舶纵中线是变化的：外漂，在船尾处达到最大，向船首部递减，在动枢心点处为零；然后是内漂，向船首逐渐增大(A ship in steady turn conditions develops outward drift angles along its centreline that is greatest at the stern, steadily decrease to zero at the dynamic pivot point, then turns inward and increases towards the bow)枢心点前移的结果是在船舶中部区域产生了一个净外漂角(The forward position of the pivot point produces a net outward drift angle at the centre of gravity in the midship region),船舶操纵性与耐波性课件,静枢心点(Static pivot point),静枢心点为船舶初始旋转围绕的点(The static pivot point is the point about which the ship starts to rotate).这时只有船尾的舵力使在水中静止不动的船舶开始旋转(At that time, there is a single force at the stern that acts on the rudder to swing a ship that is stopped in water)船舶仍然不动，舵力矩使船尾开始旋转起来(Thus, the ship is stationary, but helm is used to generate momentary swings of the stern by giving short bursts of ahead thrust against the rudder, for example when manoeuvring a ship alongside)当船舶绕静枢心点开始旋转时(When the ship starts to rotate about its static pivot point):横向速度增加时重心外移一定距离(its centre of gravity will move a certain distance outward as it increases its outward lateral velocity) 然后船舶绕另一个枢心点旋转(then the ship appears to rotate around another pivot point)这就是动枢心点(This is dynamic pivot point)!,船舶操纵性与耐波性课件,静枢心点的位置(Location of the static pivot point),静枢心点的位置取决于(The location of the static Pivot point depends on) 惯性矩(the moment of inertia)决定于船舶质量的分布(determined by the ships mass distribution)舵力臂(the rudder leverage)determined by the distance between the rudder and the centre gravity影响船舶惯性矩和舵力臂最重要的因素是方形系数The most important factor affecting the moment of inertia and the rudder leverage is the block coefficient (CB)纵倾对惯性矩和舵力臂也有影响(However, trim also affects the moment of inertia and the rudder leverage),船舶操纵性与耐波性课件,How does hull form affect the location of static pivot point?,方形系数大的船舶其惯性矩大，而舵力臂小(Ships with a high CB-value will have a high moment of inertia and a small rudder leverage)表明枢心点更靠近船首(means that the pivot point is moved closer to the bow)方形系数小的船舶其惯性矩小，而舵力臂大(Ships with a low CB-value will have a lower moment of inertia (more mass concentrated in the midship) and a larger rudder leverage)表明枢心点更靠近重心(means that the pivot point is moved closer to the centre of gravity),船舶操纵性与耐波性课件,纵倾对静枢心点位置的影响如何(How does trim affect the location of static pivot point)?,艉倾使得重心更靠近舵(A stern trim moves the centre of gravity closer to the rudder, which means that)惯性矩增大，因船首质量离重心越远(the moment of inertia is increased, since the mass in the bow becomes further away from the centre of gravity)舵力臂减小(the rudder leverage is decreased)艏倾使得静枢心点移向船首 (A stern trim thus moves the static pivot point forward, closer to the bow)艏倾使得重心移向船首(A head trim moves the centre of gravity closer to the bow)舵力臂增大(the rudder leverage is increased)惯性矩也增大(BUT the moment of inertia is also increased).艏倾使得静枢心点向船尾方向移动靠近重心(However a head trim tends to move the static pivot point aft, towards the centre of gravity),船舶操纵性与耐波性课件,纵倾对静枢心点位置的影响分析,船舶操纵性与耐波性课件,Criteria affecting the location of the pivot point,Moving the pivot point forwardsmall length to beam ratiotrimmed by the headdirectionally unstable shipthe wind force acts with the rudder force“high-lift rudders”The Pivot Point can be situated ahead of the vessel when one or more of the criteria moving the pivot point forward is combined with a high vessel speed,Moving the pivot point aftlarge length to beam ratiotrimmed by the sterndirectionally stable shipthe wind force counteracts the rudder forcethe turn is conducted in shallow water with a small under-keel clearance,船舶操纵性与耐波性课件,枢心点,PIER,PIER,PIER,DIW - BOTH TUGS EQUAL LEVERAGE,SLOW HEAD WAY- AFT TUG HAS MORE LEVERAGE,SLOW STERN WAY - FWD TUG HAS MORE LEVERAGE,船舶操纵性与耐波性课件,回转试验,船舶操纵性与耐波性课件,回转过程分析,1转舵阶段,分母第二项总比第一项绝对值小得多；分子第一项比第二项小得多，,船舶操纵性与耐波性课件,Cp表示转单位舵角后，在回转的初始阶段所能产生的回转角加速度。显然Cp是船舶开始回转得快慢的一种标志。Cp越大，则转舵后越能迅速进入回转运动。,近似认为，阶跃操舵后(指操舵速度很大的操舵)，初始阶段船舶的回转是等角加速运动的，首向角变化为：,(2-16),操右舵的情形(以向右舷回转为例),船舶操纵性与耐波性课件,由于边界层的存在，艉部产生的压差要小于艏部，故船体的水动力作用中心A通常在船舯和船舶重心G之前水动力产生了回转力矩，加速了船舶的回转角速率A的位置越靠前，回转速度越快，回转圈越小向心力FC是船体水动力和舵侧向力(升力) fL的合力.,船舶操纵性与耐波性课件,2过渡阶段(或渐变阶段),船舶操纵性与耐波性课件,3定常回转阶段,经过渡过程的发展变化，当作用于船体的力和力矩相平衡时,船舶就以定的侧向速度v和回转角速度r绕固定点作定常圆周运动。,(2-19),船舶操纵性与耐波性课件,定常回转阶段,当转过一舵角后，船舶各运动参数随时间的变化如图213所示,图2-13,船舶操纵性与耐波性课件,回转过程各阶段的特点,船舶操纵性与耐波性课件,(2-20),无因次形式为,(2-19),船舶操纵性与耐波性课件,对具有直线运动稳定性的船舶，“左舵左旋，右舵右旋”； 不具有稳定性的船舶，“右舵左旋，左舵右旋”反操现象,各水动力导数之值对定常回转运动的影响,船舶操纵性与耐波性课件,船舶操纵性与耐波性课件,船舶回转过程中，船体上承受的侧向力其作用点高度各不相同，于是形成对ox轴的倾侧力矩，这是产生回转过程横倾运动的根本原因。,船舶在水平面内作回转运动时，还会同时产生横摇、纵摇、升沉等运动，以及由于回转过程阻力的增加引起的速降。以上所述可理解为回转运动的耦合，其中以回转横倾与速降最为明显。,船舶操纵性与耐波性课件,船舶横摇运动方程,过渡阶段中，横倾角随时间的变化是振动的，体现出横摇特性。同时由于动力作用，最大的横倾角出现在过渡阶段，一般是稳定回转倾角的1.32.2倍左右。,回转过程中的横倾将会降低船舶的横稳性，需估算定常回转阶段的稳定横倾角。,船舶操纵性与耐波性课件,R0=2.6L; V0=0.7u1,回转对螺旋桨的影响,回转过程中舵力的阻力部分和船体阻力的增加部分在降低航速的同时，增大了螺旋桨的负荷船舶在全速前进时,满舵只能在紧急情况下使用a tight turn can overload the engine,船舶操纵性与耐波性课件,费尔索夫速降公式,回转过程速降,船舶操纵性与耐波性课件,回转速降估算,线性的操纵理论求不出回转过程的速降，需采用非线性方法确定。通常用近似方法估算。回转速降系数与相对回转直径之间的经验关系,船舶操纵性与耐波性课件,回转速降估算,费加耶夫斯基用下式估算回转速降,Thank You !,