航向稳定性和回转性邱磊讲解课件

1、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？1固有动稳性(也称直线运动稳定性)(Inherent dynamic stability, also called straight line stability)2方向稳定性或保向性(Course-keeping ability, also called directional stability)3初始转首性能(Initial turning/course-changing ability)4偏转抑制性能(Yaw checking ability)5回转性能(Turning abilit

2、y)-大舵角下6停船性能(Stopping ability)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1. 航向稳定性2. 船舶回转性3. 回转运动的耦合特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

3、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 shipsAn 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 h

4、elm 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

5、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 co

6、nditions 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 o

7、f 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

8、中心A的位置stern trimhead trim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 increasedHead trim moves A further aheadPoint A is just aft

9、 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 inert

10、ia 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

11、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 dec

12、reasedA 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

13、 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物体的运动状态是否稳定，不仅取决于物体的性质，也取决

14、于所考察的运动状态和运动参数 1需针对某运动状态，或某一运动参数来分析其稳定性 2具有位置稳定性的船舶必具有直线稳定性和方向稳定性；具有方向稳定性的船舶必具有直线稳定性 3按是否操舵，稳定性又分为自动(固有)稳定性(取决于 船体几何)和控制稳定性(取决于闭合回路) 4对于通常的水面舰船，若不操舵，不具备方向稳定性和位置稳定性，最多具有直线稳定性，也可能不具稳定性 5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

15、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-

16、7)的解为:(2-9)(2-10)速度v的小扰动方程的解为:(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

17、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；C 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

18、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

19、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

20、，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 characte

21、ristics)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

22、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 i

23、n 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 FORCESLONGITUDINAL THRUSTTRANSVERSE THRUST (SIDE FORCE OR PADDLEWHEEL

24、 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 PROPELLERSSTERN WALKS TO STBDFFGDD/CG/MCMDD/CG DEVELOP STERN WAY 0% PITCH AND WHEN TWISTING DDG 5

25、1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

26、 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

27、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

28、 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

29、 Data Folder # of Screws# of RuddersLength/BeamPivot PointTurn DiagramsAcceleration/DecelerationAdvance/TransferNavigational 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

30、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 gr

31、avity 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 greate

32、st 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 poin

33、t)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

34、 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

35、 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

36、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, tr

37、im 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

38、 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 o

39、f 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

40、 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 po

41、int 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stern trimhead trim船舶操纵性与耐波性课件Criteria affecting the location of the pivot pointMoving the pivot point forwardsmall length to beam ratiotrimmed by the headdirectionally unstable shipthe wind force acts with the rudder force“high-lift r

42、udders”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 speedMoving the pivot point aftlarge length to beam ratiotrimmed by the sterndirectionally stable shipthe wind force counteracts the rudder forcethe turn