【正文】 ic coefficient’.另外一個有用的系數(shù)就是所謂的“棱形系數(shù)”。The ship form could be imagined to have been cut from a prism of length equal to the length of the ship and of constant cross section of area equal to The immersed midship area. Thus船型可以想象為是從棱柱體中切割出來的，棱柱體長度等于船長且截面積等于船舯浸沒部分的面積的。因此Prismatic coefficient Cp=V/(Midship areaL)棱形系數(shù)Cp=V/（舯面積L）This particular coefficient has its use in dealing with resistance.處理船舶阻力時能用到這個特殊的系數(shù)。A coefficient which is used to express the fullness of the midship section is the midship area coefficient. If the midship section is imagined to be out out of a rtx:tangle of dimensions breadth draught then一個用來表示船舯剖面豐滿度的系數(shù)是中站面系數(shù)。若將船舯剖面想象為是從尺度等于船寬吃水的矩形中切割出來的，那么Midship area coefficient Cm=Midship area/(Bd)中站面系數(shù)Cm=舯面積/（Bd）The three coefficients so far discussed are related to one another sinceCB=V/(LBd)=[V/(Midship areaL) ][Midship area/(Bd)]CB=CpCm目前為止討論的這三種系數(shù)是相互關(guān)聯(lián)的，因為CB=V/（LBd）=[V/（舯面積L）][舯面積/（Bd）]CB=CpCmGenerally speaking, as the block coefficient bees finer the midship area coefficient bees finei, as does the prismatic coefficient.一般認為,方形系數(shù)越小，中站面系數(shù)也越小，棱形系數(shù)也一樣。The waterplane area of a ship, . the area enclosed by any particular waterline, can also be expressed in terms of a coefficient and the area of the circumsecting rectangle. Hence waterplane area coefficientCw=Waterplane area/(LB)船舶水線面面積，即被特殊水線包圍的面積，也能夠用一個系數(shù)和該面的外切矩形來表示。因此，水線面系數(shù)Cw=水線面面積/（LB） Chapter 2 Ship Rudiments（船舶基本原理）Lesson 7 Equilibrium and Stability（平衡性和穩(wěn)定性） Introduction（引言）In chapter 2 the condition for static equilibrium was defined in terms of the balance of forces and moments. 第二章中的靜力平衡狀態(tài)是以力和力矩的平衡來定義的From Newton’s laws of motion, it is seen that a body can be at rest or moving at constant speed only if the sum of all forces and moments acting on the body is equal to zero.從牛頓運動定律中可以知道，若作用于物體上的合外力和和外力矩等于零，那么物體將處于靜止或以恒定不變速度運動。The concept of stability is somewhat more plex. 穩(wěn)定性的概念某種程度上更復雜些。Here,one is concerned with whether or not a body will return to an initial state of static equilibrium when disturbed by an unbalanced force or moment. 其中一種情況與物體受到不平衡的力或力矩的干擾時是否能夠回復到初始靜力平衡狀態(tài)有關(guān)。While in the broader sense equilibrium refers to an overall balance of forces, which involves no acceleration or deceleration, static equilibrium is defined as follows:A body at rest is said to be in static ：處于靜止狀態(tài)的物體就出于靜力平衡。但廣義上的平衡指的是合力的平衡，與加速和減速無關(guān)。If this body is disturbed by an outside force and returns to its original position when the force is removed, it is said to be in stable equilibrium. An example of this condition is a round ball lying in an upward facing bowl,as in Figure (a). 若此物體受外力作用而當外力移除時又回到初始位置，那么就說物體處于穩(wěn)定平衡狀態(tài)。一個這種狀態(tài)的例子是，一個處于開口朝上的碗中的圓球，（a）所示。The ball will always return to its rest position when disturbed by an outside force.當受到外力作用時，圓球?qū)⒖偰芑氐届o止位置。Figure (b) illustrates the condition of neutral equilibrium.圖 （b）用 圖說明了中性平衡狀態(tài)。The ball lying on a flat horizontal plane will e to rest at any point on the plane if motion is started and then stopped by an outside force (including friction). 若球在水平面上運動，然后受到外力（包括摩擦力）作 用而靜止，那么球?qū)⑼Ｔ谒矫嫔系娜我馕恢?。Unstable equilibrium is illustrated in Figure (c) ,where a round ball is balanced on top of an inverted bowl. Any slight disturbance of the balanced position will result in the ball rolling off the （c）用圖說明了非穩(wěn)定平衡，圖中圓球在倒置的碗的頂部處于平衡狀態(tài)。平衡位置的任意細微的擾動將導致圓球從碗上滾落下來。 The Basis for Ship Equilibrium（船舶平衡原理）Consider a ship floating upright on the surface of motionless water. 假如一艘船平浮于靜止的水面上。In order to be at rest or tn equilibrium, there must be no unbalanced forces or moments acting on it. 為了使船靜止或出于平衡狀態(tài)，那么就一定沒有不平衡的力和力矩作用于船上。There are two forces that maintain this equilibrium：the force of gravity and the force of buoyancy. 有兩個維持這種平衡的力：重力和浮力。When the ship is at rest, these two forces are acting in the same vertical line,and in order for the ship to float m equilibrium, they must be exactly equal numberically as well as opposite in ，這兩個力作用在同一條豎直線上，而且，為了使船平浮于水面上，那么力就一定是大小相等方向相反。The force of gravity acts at a point or center of gravity where all of the weights of the ship may be said to be concentrated. 重力作用于一點，或者這樣說，重心是船舶全部重量集中的點。Gravity always acts vertically 。The force of buoyancy acts through the center of forces is considered to be acting. 通過力的中心的浮力被認為作用于力的中心This forces always acts vertically upward. 這個力的作用方向總是豎直向上。When the ship is heeled, the shape of the underwater body is changed, thus moving the position of the center of buoyancy.船舶橫傾時,水下部分的形狀發(fā)生變化，因此浮力中心的位置發(fā)生變化。Now, when the ship is heeled by an external inclining force and the center of buoyancy has been moved from the centerline plane of the ship, there will usually be a separation between the lines of action of the force of gravity and the force of buoyancy. 如果，船舶受到外界傾斜力作用發(fā)生橫傾，浮心偏離了船舶中線面時，重力與浮力作用線將發(fā)生了分離。This separation of lines of action of the two equal forces, which act in opposite directions, forms a couple whose magnitude is equal to the product of one of these forces(that is,displacement) and the distance separating them. 兩個作用于相反方向上的力的作用線的分離，形成 了一個力偶，其大小等于其中任意一個力（即，排水量）和兩個力作用線的間距的乘積。In Figure (a) , where this moment tends to restore the ship to the upright position, the moment is called a positive righting moment，and the perpendicular distance between the two lines of action is the righting arm (GZ).圖 （a）中，這個力矩試圖去使船回復至平浮位置，這種力矩稱為正扶正力矩，而且，兩個力的作用線間的距離稱為正扶力臂（GZ上橫線）。Suppose now that the center or gravity is moved upward to such a position that when the ship is heeled slightly,the buoyant force acts in a line through the center of ，浮力作用線通過重心。In the new position, there are no unbalanced forces, or in other words, the ship has a zero moment arm and a zero moment.在這個新位置，沒有不平衡力，或者說，船舶力臂和力矩都為零。the ship is in neutral equilibrium,with both the righting moment and the righting arm equal to ，其中正扶力矩和正扶力臂都等于零。If one moves the center of gravity still higher,as in Figure (c), the separation between the lines of action of the two forces as the ship is incline