Design Method of Engine Room Equipment Layout Based on Improved Fuzzy Comprehensive Evaluation

Engine room is the place where marine power equipments, pipelines and other equipments are arranged centrally. In order to optimize the design process of engine room equipment layout, this paper proposes a method for the optimization design of engine room layout baesd on improved fuzzy comprehensive evaluation. By constructing the personnel activity space model and equipment space model, formulating the engine room environment constraint conditions dominated by personnel experience factors and obtaining the feasible scheme of engine room equipment layout. By designing the evaluation model of equipment layout plan in the engine room, formulating the evaluation method dominated by fuzzy comprehensive evaluation algorithm and obtaining the optimal layout scheme. Based on fuzzy comprehensive evaluation method, the improved method directly retains the influence of the design experience factors of personnel, which can make engine room equipment layout and pipelines more in line with engineering requirements, as well as provide better equipment accessibility and personnel accessibility.


Introduction
Nowadays, the research on ship engine room layout is developing towards intellectualization [1]. Lee K H adopted artificial intelligence technology to optimize the layout of ship engine room [2]. Jin Hyung developed the unit generation method to automatically process the piping design of ship engine room [3]. Zhang used the genetic algorithm to optimize the layout of key equipments and carried out the 3D layout of engine room [4]. Various literatures mainly focus on the intelligent ship layout algorithm. They would like to use the algorithm model and 3D modeling to optimize the layout of the equipments in the ship's living room or the pipelines in engine room. However, excessive reliance on algorithms will weaken the designer's experience factor. At the same time, some valuable intelligent layout models only consider the living room, whose environment is greatly different from engine room. Therefore, it is necessary to redesign the layout model for the engine room environment.
In order to overcome these shortcomings, this paper designs a fuzzy comprehensive evaluation method. Compared with the algorithm-oriented design idea, this method takes the engine room environment constraint condition as the evaluation index before the algorithm evaluation, and directly exerts the influence of design experience factors on the scheme, so that the engine room equipment layout scheme is more in line with the actual needs. Compared with other evaluation index models, the evaluation index model developed by the invention focuses on the special environment of the engine room, making the algorithm more fit the requirements of engine room equipment layout, and has certain pertinence.

Design of engine room environmental constraint condition
Engine room environmental constraint condition refers to the state conditions that must or should be satisfied during equipment layout, including equipment level, location space, space model type and restrict indexes. On the basis of analyzing personnel activity space model, building equipment space model by the design experience of personnel, and determining the constraint conditions of engine room environment to obtain feasible layout schemes.

Personnel activity space model
Considering the personnel channel requirements and setting personnel attributes. Setting the standard figure of male is 1.78m, the shoulder width is about 440mm, the side width is about 210mm, and the arm length plus hand length are 680mm.
In terms of height, the main equipment layout area in engine room is between the steel plate and the upper deck. It is set that the minimum height for personnel to keep walking upright is 1.8m and the range of 0 ~1.8m from the steel plate is regarded as the personnel activity space. If the height of a certain area is lower than 1.8m, people need to bend down. If the height is lower than 1.6m, people need to squat down.
In terms of width, we take a shoulder width of 660mm as the minimum width of main evacuation passageway, and take a side width plus arm length of 680mm as the minimum width of maintainable space.
In addition, defining the main pipeline space area as the space above the height of 1.8m from the steel plate, which only affects the equipment layout. The restricted pipeline space is defined as the range of 1.6~1.8m height from the steel plate, which has an impact on equipment layouts and personnel activities.
The dimension table of personnel activity space model is shown in  [5] is an envelope of equipment model, which is created according to the inherent properties of the device model.
(2) Pipe coverage space: Defining the unit space of pipeline and its vertical downward space area as pipeline coverage space, where is not recommended to place equipments in order to avoid putting influence on personnel passage and maintenance work.
(3) Free space: Equipment accessibility refers to the state in which the maintenance personnel can see the equipment and carry out maintenance operation during maintenance [6]. The space which is set aside for equipment maintenance in the initial design stage is called free space, which expresses the maintenance operation space. The modeling process of free space is as follows: Analyzing the accessibility requirements of equipment, determing the size of space allowance, and assigning scope "base" to the equipment unit space. The "base" represents the size of the surrounding operating space, which is called free space allowance. There will be superimposed areas in the free space. The superimposed area is also regarded as a free space that satisfies the conditions and does not constitute interference with each other.
(4) Channel space The space which is set aside for personnel activities in the initial design stage is called channel space, which expresses the main activity area and evacuation area. The channel space in engine room is mainly arranged around the main engines, gear boxs, pedals, generator sets and main switchboards, as well as in front of escape doors and escape straight ladder passages.
The process of channel space modeling is the same as free space modeling. Defining minimum width of main evacuation passageway of 660mm as channel space allowance. The overlapping channel space also satisfies the conditions and does not constitute interference with each other.

Engine room environment constraint conditions
Using personnel activity space model and equipment space model. Then according to three principles of "First master, then auxiliary. First large, then small. First heavy, then light" to grade engine room equipments [7]. Building the engine room environment constraint conditions table as shown in table 2: Table 2. As far as possible layout in the free space, the main channel and pipe space outside

Design of fuzzy comprehensive evaluation method for engine room equipment layout
Using fuzzy mathematics theory and statistics principle to evaluate the comprehensive of engine room layout. Under the expert evaluation foundation, using the linear weighted method to assign rating labels for each objective function of multi-objective optimization problem. Then, multipling rating labels and weight coefficient of this objective function to get fuzzy comprehensive evaluation value so as to transform the multi-objective problem into a single-objective problem. Now the optimal solution of single objective problem is an effective solution of multi-objective optimization problem.
Where m i is the weight of equipment i. y i is the horizontal coordinate of center of mass of equipment i, and n is the total number of equipments.
(2) The interference distance f 1 is the largest For the sake of operational safety, a certain distance should be kept between equipments in engine room. The larger the interference distance f 1 between equipment, the better. 1 1, 1 Where q is the total number of equipments requiring interference distance. X i and X j are the location parameters of equipments requiring interference distance.
(3) The effective space utilization rate E is the largest Increasing the effective space utilization rate E of engine room can facilitate the personnel maintenance activities in engine room. Since the equipments cannot be reduced, the larger the effective space utilization rate E is, the better it will be for the work. corners (invalid space) that cannot be utilized. i is the equipment number. The value of E is between 0 and 1, and the larger the value is, the higher the effective space utilization is [8].
(4) The effective pipeline coverage space area S 1 is the minimum

Establish weight coefficient evaluation index
Constructing pairwise comparison matrix of factors u 1 , u 2 ..., u n from factor set U a and sub-factor set U b to obtaine the importance index weight matrix [9]. Then, solving the characteristic roots respectively, and obtained the relative weightω i of each index under a single criterion after normalization. Assuming the weight of factor i in U a be a i  , then the U a weighted set is [10] Where i represents the sub-factor set under the i U a , and m is the total number of evaluation indexes of sub-factor set.

Design fuzzy comprehensive evaluation set
Due to the nature of evaluation indexes and the units of measurements are different, there is often a lack of correlation between indexes. In order to avoid evaluation failure, establishing a expert team and providing effective evaluation set. Each evaluator makes an evaluation conclusion for each factor (that is, for a certain element in the evaluation set), and then calculates the percentage of various evaluation conclusions to obtain the membership degree S i . Membership degree S i constitute a single factor evaluation set r: Where m represents the total number of evaluation results. single factor evaluation set r i constitute a single factor evaluation matrix R i : Where n is the total number of evaluation indexes of a sub-factor set. The sub-factor weighted set B i is introduced to calculate the first-level fuzzy comprehensive evaluation set C i of factors i: Where C i is the fuzzy comprehensive evaluation of factor set i [11] [12]. The larger the C i value is, the better the effect of factor set i is.
Where   i C is the second-level single factor evaluation matrix. D represents the evaluation value of target layer, namely the scheme evaluation value. The larger the value of D, the better the effect of the scheme.

Method of equipment layout in engine room
Combined with personnel design experience factors and fuzzy comprehensive evaluation algorithm to guide the layout of equipment in engine room, constructing a method flow of equipment layout in engine room as is shown in figure 2:  (2) Verifing the engine room environmental constraint conditions of each scheme from grade 1 to n, and obtaining the feasible layout scheme which meets the conditions. If n=1, only verifing the engine room environmental constraint conditions of current level. (3) Using the fuzzy comprehensive evaluation algorithm to evaluate the feasible layout scheme, and obtaining the second-level comprehensive evaluation set D. Retaining the best scheme, namely the scheme with the maximum D.
(4) Cycling (1) and (3) until n= N ( the toatal number of quipement levels) , and end the cycle. At this time, all equipments are arranged, and the scheme with the maximum D value is retained, that is, the best scheme.
For example, when level-1 equipments satisfy constraint conditions, we design multiple feasible schemes. Checking the space constraint conditions of a scheme, the effect as shown in figure 3 can be obtained: Obtaining the optimal target layer evaluation value D under scheme A is 0.79. Compared with the optimal target layer evaluation value D under scheme B is 0.81. Selecting the evaluation value of 0.81 to retain the optimal scheme B.

Conclusion
Aiming at the problem of engine room equipment layout, this paper puts forward a method of engine room equipment layout optimization design with more engineering practice value. This method considers the influence factors of personnel experience and puts forward the preliminary equipment layout scheme according to the engine room environmental constraint conditions. Then through the fuzzy comprehensive evaluation indexes to accomplish the algorithm level of the pros and cons of scheme comparison to obtain the optimal scheme. This method increases the influence of human decision on the basis of algorithm evaluation, conforms to the design specification and avoids