1 前言
近几年来,对新建船舶的振动水平进行约定几乎成了一个习惯的做法。在新建船舶的规格书中,对船舶在营运过程中的振动极限值往往作了规定,船厂必须确保建成的船舶最终的振动水平达到约定的数值,否则的话,就必须采取相应的措施去减少振动水平。
在设计阶段,船厂必须对船舶的振动水平进行适当的分析、评估和计算。在对船东进行承诺新造船的振动水平时,船厂需要结合船型特点、主机特性、结构形式等因素进行综合考虑。
一般来讲,在规格书中进行振动水平的约定主要是考虑到以下几个方面的因素:
① 振动对船上人员舒适性的影响;
② 振动对船体结构寿命的影响;
③ 振动对主机和其他船上设备工作环境的影响。
在下面将对上述振动危害的因素进行阐述,其中振动水平涉及到的特征参数有以位移、速度、加速度和应力等表达的,有以
单幅峰值表达的,也有以均方根值(r.m,S,又称为有效值)来表达的。
5 振动水平在规格书约定描述中的案例
最后,下面给出一般船舶规格书里面对于振动要求的典型描述,以供参考。
英文:
VIBRATION AND N0SIE C0NTR0L
Special attention should be paid in the design and construction to limit the Vibration and noise levels within the ship to those generally accepted,and which will not give rise to discomfort and annoyance to the crew.not cause damage to the main propulsion system nor cause damage or m alfunction of other shipboard machinery and equipment.
(1) Vibration
Reference is m ade to International Standard ISO 6594: “Guidelines for the overall evaluation of vibration in merchant ships”
Measurements carried out in relevant loading conditions shall demonstrate that the fo llowing vibration levels are met:
. In accom modation and localities where people are exposed to vibration fo r a prolonged period of time, such as wheel house,radio room,control room s and offices,the vibration level shall be below 6 mm/s for
frequencies above 5 Hz.
For areas designed as working areas where no special comfo rt iS required,such as workshops, galley, stores, engine room platform s etc.,the vibration shall be blow 8 mm/s fo r frequencies above 5 Hz.
(2) Vibration limits for machinery andequipm ent
Special attention shall also be taken to avoid that machinery and equipm ent will have local vibrations causing risk for malfunction or dam ages when the ship is in service.The vibration levels of machinery。equipment,radars,structure etc.shall be in accordance with the recom mended limits given in DNV Report No.95-042 1 “ DNV Guidelines for Vibration Evaluation”.